U.S. patent application number 17/219345 was filed with the patent office on 2022-01-06 for process for converting c2-c5 hydrocarbons to gasoline and diesel fuel blendstocks.
This patent application is currently assigned to Swift Fuels, LLC. The applicant listed for this patent is Swift Fuels, LLC. Invention is credited to Chris D'Acosta, Jeffery Miller, Kurtis Sluss, Benjamin Wegenhart.
Application Number | 20220002214 17/219345 |
Document ID | / |
Family ID | |
Filed Date | 2022-01-06 |
United States Patent
Application |
20220002214 |
Kind Code |
A1 |
D'Acosta; Chris ; et
al. |
January 6, 2022 |
PROCESS FOR CONVERTING C2-C5 HYDROCARBONS TO GASOLINE AND DIESEL
FUEL BLENDSTOCKS
Abstract
A process for converting C2-5 alkanes to higher value C5-24
hydrocarbon fuels and blendstocks. The C2-5 alkanes are converted
to olefins by thermal olefination, without the use of a
dehydrogenation catalyst and without the use of steam. The product
olefins are fed to an oligomerization reactor containing a zeolite
catalyst to crack, oligomerize and cyclize the olens to the fuel
products which are then recovered. Optionally, hydrogen and methane
are removed from the product olefin stream prior to
oligomerization. Further optionally, C2-5 alkanes are removed from
the product olefin stream prior to oligomerization.
Inventors: |
D'Acosta; Chris; (West
Lafayette, IN) ; Miller; Jeffery; (Naperville,
IL) ; Sluss; Kurtis; (Carmel, IN) ; Wegenhart;
Benjamin; (West Lafayette, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Swift Fuels, LLC |
West Lafayette |
IN |
US |
|
|
Assignee: |
Swift Fuels, LLC
West Lafayette
IN
|
Appl. No.: |
17/219345 |
Filed: |
March 31, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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63002887 |
Mar 31, 2020 |
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63042305 |
Jun 22, 2020 |
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63060835 |
Aug 4, 2020 |
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63068457 |
Aug 21, 2020 |
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63091644 |
Oct 14, 2020 |
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International
Class: |
C07C 2/12 20060101
C07C002/12; C07C 5/327 20060101 C07C005/327 |
Claims
1. A method for converting C.sub.2-5 alkanes to a broad-range of
fuel products constituting higher-value C.sub.5-24 hydrocarbon
fuels or fuel blendstocks, comprising: passing a fresh, C.sub.2-5
alkane-rich feedstream through a thermal olefination reactor, the
fresh, C.sub.2-5 alkane-rich feedstream having any one or more of
the C.sub.2 to C.sub.5 alkanes and containing at least 90 wt %
C.sub.2-5 feed alkanes, the thermal olefination reactor operating
without a dehydrogenation catalyst and without steam, the
olefination reactor converting the C.sub.2-5 feed alkanes to
product olefins in an effluent olefination stream; passing at least
a portion of the effluent olefination stream to an oligomerization
reactor containing a zeolite catalyst and operating at a
temperature, pressure and space velocity to crack, oligomerize and
cyclize the product olefins to form an effluent oligomerization
stream comprising the fuel products, unconverted C.sub.2-4 alkanes
and methane; passing a recycle stream comprising unconverted
C.sub.2-4 alkanes and methane from the effluent oligomerization
stream back through the thermal olefination reactor, the
olefination reactor operating at a temperature, pressure and space
velocity to convert at least 80 wt % of the feed C.sub.2-5 alkanes
to product olefins in the effluent olefination stream; and
recovering the fuel products from the effluent oligomerization
stream.
Description
FIELD
[0001] The field of this invention is the low-cost production of
performance-grade gasoline and distillate fuel products from C2-C5
alkane-rich light hydrocarbon feedstreams. The field more
particularly relates to a specialized dry-heat "Thermal
Olefination" reaction converting C2-C5 alkanes to alkenes and
subsequently uses a controlled zeolite-catalytic reaction or
sequence of reactions to crack, oligomerize, dimerize, trimerize,
couple and/or cyclize the alkenes to form fuel formulations and
blendstocks. A particular application of the invention is in the
tailored derivation of performance-grade fuels and fuel blendstocks
from readily-available, lower-value, hydrocarbon streams.
BACKGROUND
[0002] While the total U.S. demand for gasoline is steady or in a
small level of decline, there is an increasing demand for premium
gasoline blendstocks to meet the needs of new, more efficient,
higher-compression spark-ignited automotive engines. There is also
an increasing demand of high-performance, ultra-low sulfur, diesel
fuel blendstocks with high cetane values and effective
cold-temperature flowability properties used in
compression-ignition diesel engines and gas turbine engines. These
demands exist while surplus light hydrocarbons are stranded in
certain markets without supply-chain options, despite being
available from midstream, refinery and petrochemical facilities for
transformation to fuel grade products.
[0003] According to the US Energy Information Administration (EIA),
sources of natural gas and gas liquids in the midstream industry
are abundant across the nation. See, for example, Table 1. The EIA
recently estimated that the total production of C2+ light
hydrocarbon gases (NGL's) on a global scale is 7.8 million barrels
per day. Note that the portrayal of NGL volumes in the US may
under-report rejected ethane sold with methane. Any separation of
natural gas from natural gas liquids, e.g. via de-methanization,
leaves an alkane-rich admixture of light hydrocarbon compounds,
typically C2-C5+ natural gas liquids (NGL's). These may undergo
further separations, e.g., de-ethanization, de-propanization,
de-butanization of gases and liquids. This invention particularly
targets any C2-C5 alkane rich source of NGL's (preferably NGL's
without ethane rejection), or similar industrial gases comprising
such light hydrocarbons, to transform alkane-rich feedstreams to
high-value fuel products, thereby avoiding the need for such C2,
C3, C4 separations.
TABLE-US-00001 TABLE 1 US GAS PLANT 2-YEAR AVG. PRODUCTION
(BBL/DAY) ETHANE 1,577,870 PROPANE 1,323,455 n-BUTANE 340,604
iso-BUTANE 370,782 PENTANES+ 478,112
[0004] The petrochemical industry, a major consumer of ethane and
propane, uses extremely complex, high-precision, and
capital-intensive methods to separate and purify chemical grade
compounds such as ethylene and propylene. For example, conversion
of propane to propylene, or ethane to ethylene, requires cryogenic
separation (-100.degree. C.) followed by ultrapure, dry,
non-contaminated hydrogeneration processing to eliminate very-close
boiling molecules (e.g., butadiene, propyne, acetylene) that can be
highly reactive to chemical processing and/or poison polymerization
catalysts. None of these are a concern for the process of this
invention.
SUMMARY
[0005] The invention comprises a process of thermal and chemical
reactions which provide a high-conversion of alkane-rich C2-C5
hydrocarbon feedstreams that contain ethane, propane, butanes, or
pentanes, or any admixture thereof, to performance-grade gasoline
and distillate fuel products, and aromatic hydrocarbons. The
process includes a specialized method of converting certain alkane
feeds to olefins by way of a low-cost, non-catalytic, dry-heat,
alkane-to-olefin reaction called "Thermal Olefination". The process
combines this Thermal Olefination reaction with subsequent
cracking, oligomerization, dimerizing, trimerizing coupling, and/or
cyclization reactions of olefins to fuel-grade products using
zeolite catalysts. In embodiments, the process includes variations
useful in the conversion of alkene-containing feedstreams.
[0006] The process can be arranged in appropriate sequences with
thermal and catalytic reactors operating in parallel or in series
and utilizing various recycling methods based upon feedstock
characteristics, operating conditions, and desired products.
[0007] The thermal and catalytic reactors utilize innovative
low-cost methods to minimize carbon build-up including the use of
specialized catalytic regeneration techniques. These techniques
reduce coking of the reactor and minimize deactivation of the
catalysts.
[0008] The liquid fuel products produced from the process can be
specifically targeted by operating conditions and catalyst choices
to yield any desired range of C.sub.4 to C.sub.12 gasoline
compounds (i.e., high octane paraffins, olefins and aromatics), or
to yield C.sub.9 to C.sub.16+ high-performance middle distillate
compounds (e.g., containing low-ppm sulfur, high cetane, low pour
point) for use in ultra-low-sulfur diesel fuel that achieve
pre-specified fuel performance targets.
[0009] The process also accommodates any alkene-containing C2-C5
light hydrocarbon feedstreams that contain ethene, propene, butenes
or pentenes, or any admixture thereof, which are convertible to
fuel blendstocks using the same thermal and catalytic process and
reactions albeit sequenced based upon the characteristics of the
collective feedstream constituents as outlined in this
invention.
[0010] Further objects and advantages will be apparent from the
description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic showing the process flow and system
components of the conversion method and system of the present
invention.
[0012] FIG. 2 is a graph showing yield versus conversion for
processing of pentane in accordance with the method of FIG. 1.
[0013] FIG. 3 is a more detailed flow diagram of an embodiment of
the Light Gas to Fuels Process (the "LG2F Process").
[0014] FIG. 4 is a simplified version of the flow diagram of FIG.
3, modified to include a Knockout Unit between the non-catalytic
Thermal Olefination reactor ("R1") and the zeolite-catalytic
reactor ("R2").
[0015] FIGS. 5A and 5B are graphs showing selectivity of product
distribution of aliphatics as a function of space velocity.
[0016] FIGS. 6A and 6B are graphs showing selectivity of product
distribution of aliphatics as a function of space velocity.
[0017] FIG. 7 is a graph showing mass percentages of hydrocarbons
for Average Jet A fuel.
[0018] FIG. 8 is a graph of mass percentages in a typical carbon
distribution for diesel fuel.
[0019] FIG. 9 is a flow diagram of an alternate embodiment of the
LG2F Process including a series of zeolite-catalytic R2
reactors.
[0020] FIG. 10 is a flow diagram of an alternate embodiment of the
LG2F Process including a combination with light gas feedstreams
from refining processes.
[0021] FIG. 11 is a flow diagram of an alternate embodiment of the
LG2F Process including direct alkene feed to the zeolite-catalytic
R2 reactor.
[0022] FIG. 12 is a graph showing a single pass yield of propene in
accordance with the flow diagram of FIG. 11.
[0023] FIG. 13 is a flow diagram showing optimal elimination of
benzene from gasoline blendstocks produced by methods herein.
[0024] FIG. 14 is a diagram showing construction elements typical
of single and dual reactors.
[0025] FIG. 15 is a diagram of a dewaxing process flow in
accordance with the present disclosure.
[0026] FIG. 16 is a flow diagram showing the process including four
alternatives for the entry of C2-C5 alkanes into the LG2F process
by way of alkane-rich feedstream options F1, F2, F3 and F4.
[0027] FIG. 17 is a flow diagram showing an embodiment of the
process in which an unprocessed wet gas feedstream comprises of
greater than 50% (wt.) methane is merged into the LG2F process at
feedstream F4.
[0028] FIG. 18 is a flow diagram showing an embodiment including
the use of the Methane Thermal Olefination process to transform the
methane molecules to alkanes or alkenes and entry of the converted
molecules into the LG2F process at feedstream F5, without methane
gas open-air combustion.
[0029] FIG. 19 is a diagram showing components of a novel reactor
design featuring a dual phase catalytic quench.
[0030] FIG. 20 is a flow diagram showing the LG2F process including
liquid recovery, H2 separation, and a recycle subsystem.
[0031] FIG. 21 is a flow diagram showing an embodiment tailored to
produce non-aromatic fuel compounds.
DESCRIPTION
[0032] For the purpose of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated herein and specific language will be used
to describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended. Any
processing alternatives, sequencing options, alterations and/or
further modifications in the described embodiments, and any further
applications of the principles of the invention as described herein
are contemplated as would normally occur to one skilled in the art
to which the invention relates. Embodiments of the invention are
shown in detail, but it will be apparent to those skilled in the
relevant art that some features that are not relevant to the
present invention may not be shown for the sake of clarity. All
percentages used herein are weight percentages, unless indicated
otherwise.
[0033] An aspect of this disclosure, referred to herein generally
as the Light Gas to Fuel Process, or "LG2F Process", converts
alkane-rich feedstreams of hydrocarbons comprising 2-5 carbons, or
any admixture of C.sub.2-5 hydrocarbon compounds, to selected
ranges of C.sub.4 to C.sub.16+ fuel grade hydrocarbons. The process
includes a non-catalytic dry-heat Thermal Olefination reaction
using R1, followed by an acid-catalyzed reaction using specific
zeolite catalysts in R2 (which may vary in different embodiments)
which chemically create a controlled series of cracking,
oligomerizing, dimerizing, trimerizing, coupling, and/or cyclizing
reactions. The process may be performed in a variety of sequences
using single or multi-bed reactors subject to the feedstream
characteristics, operating parameters and targeted products. As
used herein, the term LG2F Process includes all processes, and
corresponding systems, coming within the scope of the present
disclosure.
[0034] This invention utilizes a Thermal Olefination reactor
producing a series of complex high-temperature reactions that may
include non-catalytic dehydrogenation and cracking reactions to
upgrade any source of light hydrocarbon gas phase alkane-rich
compounds (i.e., in preferred embodiments >90% alkanes) to
produce an olefin-containing light gas effluent stream. These
lower-boiling olefin compounds are then transformed to produce a
spectrum of longer alkanes and/or alkenes and/or aromatics, by
using zeolite catalysts in a temperature and pressure controlled
catalytic reactor(s). This complete thermal and catalytic
transformation of light alkane-rich gases results in unique,
higher-valued longer-chain hydrocarbon streams which can be
condensed into liquid products including targeted high-octane
compounds for use as gasoline blendstocks or longer-chain,
high-cetane compounds for use as diesel blendstocks.
[0035] The LG2F Process is extremely efficient and does not require
complex multi-stage distillation or fractionation columns,
multi-stage cryogenic separation, or hydrogenation processing (such
as those typically used for purification in the base petrochemical
industry), while producing a diverse molecular spectrum across
selected C.sub.4 to C.sub.16+ blendstocks with targeted performance
characteristics ideal for transportation fuels with up to 60% less
capital investment.
[0036] The LG2F Process employs a Thermal Olefination technique to
avoid traditional catalytic dehydrogenation and/or the use of steam
cracking, while leveraging a light-gas recycle system to maximize
finished product yields of targeted high-performance fuel
products.
[0037] The LG2F reactor systems may utilize unique reactor and
catalytic regeneration/cleansing processes to eliminate the need
for steam cracking, boilers and in-line water separation processes.
An automated, in-line regeneration process allows operability of
the reactors to be extended preferably in excess of 10 years for R1
thermal activation and preferably in excess of -4 years for
efficient R2 catalyst activity levels including R2 and R2L).
[0038] The LG2F process can also convert de-methanized gas streams
and industrial alkane-rich off-gas compounds to liquid fuels, and
thereby minimize production losses attributed to low-value off-gas
compounds. The LG2F process can receive methane of any amount in
the alkane-rich feedstream, but since it is virtually inert, the
inclusion of methane in LG2F is commercially preferably at
equilibrium from 5% to 25% (wt) to serve both as a diluent and to
control heat management. In some aspects, C3+ or C4+ or C5+ gas
streams can be easily condensed and removed to increase the
concentration of C1/C2+ alkanes to feed the R1 reaction. Due to
market/location imbalances, compounds such as methane vs. NGL's, or
even various grades of gasoline or diesel, may have economic values
which vary, allowing location arbitrage introducing an additional
factor in assessing the optimal configuration of feed sources,
operating conditions, and market dynamics impacting targeted
product and byproduct portfolios. The availability of light
hydrocarbon feedstreams (e.g., whether alkane-rich or
alkene-containing) and the appropriate sequencing of the Thermal
Olefination and catalytic processes of this invention are tailored
to yield high-octane gasoline blendstocks or high cetane diesel
fuel blendstocks or aromatic hydrocarbons to meet specific
market-based, performance-based, and regulatory-driven fuel
specification requirements.
Overview
[0039] The present disclosure is based upon a unique and efficient
process for the conversion of C2+ light paraffins into
performance-grade fuel components suitable for the transportation
fuels market. Selected alkane-rich feeds undergo Thermal
Olefination reactions in a first reactor (R1), transforming the
light paraffin compounds to olefins. The olefins from the Thermal
Olefination reactions are then catalytically transformed via a
specified zeolite catalyst in a second reactor or sequence of
reactors (R2) into high-performance fuel-grade blendstock. This
combination of the specific Thermal Olefination and catalytic
conversion reactions is referred to herein as the LG2F Process.
This process converts light hydrocarbon gases into high-grade
transportation fuels and fuel blendstocks that span select ranges
of hydrocarbon compounds possessing targeted fuel compositions and
performance characteristics.
Industry Need
[0040] Due to the increased abundance of C2-C5 light hydrocarbons
and shale gas production on a global scale there is a surplus
supply and growing market dislocation of light hydrocarbons (also
known as NGL's) with limited pathways to petrochemical markets
(e.g. ethane crackers). Accordingly, there is growing interest in
converting and upgrading such lower value light hydrocarbons
(particularly the lighter ethane and ethane/propane mixtures) using
R1 Thermal Olefination with non-catalytic dry heat and R2 with
zeolites in the absence of steam, cryogenics and heavy
fractionation to produce selected higher-value C6-C24+ fuel range
components as performance-ready consumable fuel products leveraging
the existing transportation fuels supply chain. This requires that
fuel components be produced to match critical performance
specifications for gasoline, middle distillate and diesel fuels,
etc. such that they can be blended into existing supply chain
pathways.
Solution
[0041] The LG2F process provides an efficient,
low-capital-intensive technique to produce any number of
hydrocarbon fuels or fuels blendstocks in the gasoline and middle
distillate spectrum that are capable of meeting fuel performance
criteria set by the industry. This allows the fuels produced by
this invention to be compatible with fuels in the existing supply
chain and available for immediate blending primarily with
transportation fuels, or as petrochemical feedstocks or other
boutique blends with some added commercial value.
[0042] The basic LG2F Process is exemplified in FIG. 1. A C2-5
light gas alkane-rich feedstream is directed to Thermal Olefination
reactor (R1), wherein C2-5 Alkanes are converted into olefins.
Cracking, oligomerization and/or aromatic cyclization take place in
a second, catalytic conversion reactor (R2). Upon completion of the
catalytic process, the resulting hydrocarbon stream undergoes any
appropriate steps to liquify the products (e.g. cooling,
compressing, quenching, partially condensing, and flashing) for
liquid recovery of the fuel-grade blendstock product. Any
uncondensed gases and vapors not targeted for fuel grade products
are available for recycling. At this point, some portion of the
hydrogen and methane in the cooled light gases from the catalytic
reactor are separated from the C2+ gases for commercial reuse, and
the remaining collection of gases and vapors may be recycled to the
Thermal Olefination reactor.
[0043] Fuel-grade hydrocarbons, with selected ranges of C4-C12
blendstock for gasoline and C.sub.9-C.sub.24+ blendstock for diesel
fuel are recovered. As a result, select C.sub.2+ light alkanes are
transformed to any range of C.sub.4 to C.sub.16+ hydrocarbon
constituents for use in various transportation fuels, with methane
and hydrogen as byproducts. Another feature of the light gas
transformation is the creation of aromatic hydrocarbons which add
energy density and bring a higher-octane value to the gasoline
blendstock and contribute to thermal stability and cold-flow
properties for diesel fuels. Optionally, the aromatic hydrocarbons
are recoverable as low-cost petrochemical feedstock, e.g. for BTX
operations, as naphtha supply constraints gradually increase
pushing aromatic prices higher.
C2-5 Alkane Feedstreams
[0044] The Thermal Olefination reactor receives and processes
alkanes including 2-5 carbon atoms, namely, ethane, propane, butane
and/or pentane. As used herein, the term "C2-5 Alkane" is used to
refer to alkanes having specifically from 2 to 5 carbon atoms. The
term "Feedstream" refers to a reactor feed not including any
recycle component. The term "C2-5 Alkane Feedstream" refers to a
Feedstream comprising any single compound or admixture of C2-5
alkanes. For example, a typical C2-5 Alkane Feedstream may include
ethane, propane, n-butane, iso-butane and n-pentane. As described
hereafter, in a preferred aspect the C2-5 Alkane Feedstream is
sourced as an effluent stream from existing commercial operations.
It may have been the subject of pretreatments, and it may also be
formed from the combination of more than one feed source. Depending
upon the feedstock source, these light hydrocarbon feedstreams may
be treated to remove unwanted trace compounds that can otherwise
contaminate process streams or corrode equipment.
[0045] The LG2F Process specifically uses a C2-5 Alkane Feedstream
which is "alkane-rich", meaning that in a typical embodiment at
least 50% of the Feedstream comprises C2-5 Alkanes, and in the
preferred embodiment at least 90% of the Feedstream comprises C2-5
Alkanes. In another aspect, the alkane-rich, C2-5 Alkane Feedstream
includes at least 95%, and preferably at least 98%, C2-5 Alkanes.
The C2-C5 Alkane Feedstream in certain embodiments may then be
merged with LG2F recycled compounds, including up to about 25-40%
wt. inert compounds (e.g. methane, hydrogen, etc.) operating as
diluents or unreactive compounds, which once merged are fed into
the R1 Thermal Olefination Reactor.
[0046] In particular embodiments, the C2-5 Alkane component is a
specific subset of all C2-5 Alkanes. For example, certain
embodiments utilize a C2-5 Alkane Feedstream constituting a single
C2-5 Alkane, namely any one of ethane, propane, butane or pentane.
In a particular aspect, the LG2F Process uses ethane as the C2-5
Alkane Feedstream. In other embodiments, the C2-5 Alkane Feedstream
contains at least 90%, preferably at least 95%, and more preferably
at least 98% ethane. In an alternative embodiment, the C2-5 Alkane
Feedstream comprises 80-100% ethane and 0-20% propane. Ethane and
propane are less expensive alkanes and there is thus a greater
value in upgrading them to use in fuels. In another aspect, the
C2-5 Alkane Feedstream comprises at least 90% of a mixture of
ethane, propane and butane.
[0047] In particular embodiments, the upstream preparation of the
C2-C5 Alkane Feedstream for use in the LG2F process may come from
any appropriate raw gas feed, or stored, or processed C2-C5 light
gas streams or the prior demethanization of C2-C5 light gas
streams, or the deethanization of C2-C5 light gas streams, or the
depropanization of C2-C5 light gas streams, or the debutanization
of C2-C5 light gas streams, or any combination of related methods
known to those schooled in the art of C1-C5 light gas separation
technology. There may also be opportunities to modify the system
requirements between the LG2F process and any upstream C1-C5 Alkane
Feedstream gathering processes to manage the efficient co-usage of
compression horsepower, electricity, methane as fuel gas (or as
diluent), light-gas stripping/flashing, hot oil, instrument air,
heat exchangers, boiler feed water, chillers, distillation methods
(e.g. tray configurations, etc.), cooling or refrigeration
requirements, and other related matters between the interfacing
systems.
[0048] In one embodiment, a demethanizer tower is adjusted to
provide a slit stream comprised of >90% wt. ethane being thereby
separated from the C3+ light gas stream for use as a highly
concentrated ethane source for input to the R1 Thermal Olefination
process. The compression horsepower is adjusted to meet the needs
of the demethanizer and the LG2F front-end process. Upon
establishing an LG2F processing equilibrium, the fresh ethane
stream continues thereafter with the option to merge with an
existing LG2F recycle stream containing about 60%-80% unreacted C2+
alkanes and about 20-40% inert gases (e.g. methane, hydrogen). In a
similar embodiment, a slit-stream method is employed to provide a
>80% C2 ethane feed stream for use as a concentrated ethane
source for input to the R1 Thermal Olefination process. Upon
establishing a processing equilibrium, the fresh ethane stream
continues thereafter with the option to merge with a the LG2F
recycle stream containing additional C2+ unreacted alkanes and
inert gases. In another embodiment, an ethane pipeline is employed
comprising a >90% C2 ethane feed stream for use as a highly
concentrated ethane source for input to the R1 Thermal Olefination
process. Upon initiation of the LG2F process, an equilibrium is
formed whereby the fresh ethane stream continues thereafter with
the option to merge with a the LG2F recycle stream comprised of C2+
alkanes, methane and other inert gases. In another embodiment, an
ethane storage facility is employed comprising a >90% C2 ethane
feed stream for use as a highly concentrated ethane source for
input to the R1 Thermal Olefination process. Upon initiation of the
LG2F processing, an equilibrium is formed whereby the fresh ethane
stream continues thereafter with the option to merge with a the
LG2F recycle stream comprised of C2+ unreacted alkanes, methane and
other inert gases.
[0049] Similar embodiments can be expressed for the use across a
wide range of operational scenarios whereby any C2-C5 light gas
mixture comprising ethane, or ethane and propane (e.g. E/P mix), or
mixtures comprising ethane, propane, and butane, including higher
concentrations of >20% propane and/or high concentrations of
>20% butane. The proportionality of C2-C5 carbon molecules in
the feedstream directly impacts the R1 Thermal Olefination
processing temperature, which can be adjusted to compensate for the
degree of heat needed to thermodynamically crack the carbon bond in
the C2-C5 feedstream. A higher proportion of C2 ethane molecules in
the feedstream requires a higher R1 operating temperature (e.g.
typically 800-1050.degree. C. at <10 atm), whereas a higher
proportion of C3 propane molecules requires a milder R1 operating
temperature (e.g. 650-850.degree. C. at <10 atm), and a higher
proportion of C4 butane molecules requires an even milder R1
operating temperature (e.g. 550-850.degree. C. at <10 atm) in
the Thermal Olefination reactor.
[0050] The Thermal Olefination reaction can be designed to use any
combination of R1 reactors in any sequence operating at any
appropriate conditions to convert alkanes to alkenes. These
techniques are well known to those schooled in the art of
high-temperature reactor design. The Thermal Olefination reaction
does not employ or require the use of catalysts and is therefore
not described as a dehydrogenation (chemical) reaction. It is
instead a high-temperature thermal reaction operated without steam,
catalyst or toxic chemical additives (e.g. DMDS) with or without
the specially designed plating (anti-coking), carbon capture and
regeneration methods outlined herein.
Other Feedstream Constituents
[0051] The typical C2-5 Alkane Feedstream contains at least 50% to
90% by weight of C2-5 Alkanes. Therefore, in certain embodiments
the Feedstream includes other constituents. These other
constituents may, for example, include other hydrocarbons,
contaminants and inert materials.
[0052] The additional components may include other hydrocarbons.
Methane may be present in the Feed Stream, particularly depending
on the source. Methane is preferably kept to a low amount
(preferably less than 5-20%) as it is unreactive and therefore
unproductive in the LG2F Process. Controlled accumulations of
methane via recycle can be productive for dispersing consumed and
generated heat in the R1 and R2 reactors, respectively. In an
embodiment, methane gas may be used as a diluent to sustain heat
for the R1 Thermal Olefination reactor (an endothermic reaction).
In a related embodiment, methane gas may be used as a diluent to
disperse heat in the zeolite-catalytic R2 reactor (an exothermic
reaction). In another embodiment, it is possible to utilize a
membrane or other (non-distillation) gas separation unit prior to
the Thermal Olefination reaction to remove unproductive quantities
of methane from the feedstream for higher purity C2-C5 feedstreams.
Higher alkanes may be present and can be thermally cracked in the
LG2F Process, but they are also useful as gasoline constituents and
there is therefore limited value in including them in the Alkane
Feed Stream. Accordingly, in a similar embodiment, an option exists
to capture C6+ liquids from the C2-C5 feedstream in a liquid/vapor
flash drum prior to the Thermal Olefination reaction to minimize
cracking of these compounds. Light hydrocarbon feedstreams with
smaller quantities of alkenes and alkynes are to be avoided as they
lead to low yield (making benzene and methane), and they tend to
coke the R1 reactor. Note that LG2F alternatives exist to handle
feedstreams with larger quantities of alkenes via use of the R2
reaction. Furthermore, R2 converts alkenes at levels greater than
90-95%. Therefore, alkenes and alkynes preferably comprise less
than 5% of the R1 recycle feedstream, and more preferably less than
2%, of the C2-5 Alkane Feed Stream including once merged with the
R2 recycle stream.
[0053] FIG. 16 illustrates the flexibility of the LG2F process to
accommodate a wide range of light hydrocarbon feedstreams. The
chart identifies four main options F1, F2, F3 and F4 that
feedstreams comprised of C2-C5 alkanes may enter the LG2F
process.
[0054] Using feedstream option F1, the alkane-rich feedstream would
preferably be comprised of >80% (wt.) ethane prior to being
combined with the LG2F recycle loop. Using feedstream option F2,
the alkane-rich feedstream would preferably be comprised of >50%
C3+ alkanes at low pressure. Using feedstream option F3, the
alkane-rich feedstream would preferably be comprised of >50% C3+
alkanes at a pressure higher than the pressure level output from
compressor C. Feedstreams F2 and F3 will undergo the liquid
recovery process (quench and stabilization) of the C4+ compounds
with the further option to recycle these or use these in the liquid
product (depending upon the liquid product requirements). Using
feedstream option F4, the alkane-rich feedstream would preferably
be comprised of >20% (wt.) methane allowing some excess methane
to be separated for fuel or commercial use and some to pass through
recycle at equilibrium for use as diluent in the LG2F process. The
LG2F process can accommodate any single feedstream option or any
combination of alkane-rich feedstream options F1, F2, F3 or F4.
[0055] In the case where the available C2-C5 feedstream is
alkene-rich, the LG2F process can accommodate this by feeding the
C2+ alkene-rich feedstream directly into the R2 catalytic reaction
and bypassing the initial Thermal Olefination reaction, as
previously mentioned in this invention. It is also possible to
tailor a process using an alkene-rich feed comprised of C3+ or C4+
alkenes to isolate these compounds for direct entry into the quench
and stabilization process and then the resulting stream comprised
of C3+ alkenes can be recycled directly into the R2 catalytic
process (not depicted in Chart X1) to maximize the production of
fuel grade products from alkene feedstreams. The LG2F process can
accommodate these further alkene-rich alternatives, including those
comprised of >20% wt. methane (as depicted in stream F4 above)
which are then diverted to R2 oligomerization reaction, as long as
the alkene-rich feedstreams are appropriately isolated from the
alkane-rich feedstreams to be used in R1 Thermal Olefination.
[0056] In one embodiment, a C2-C5 alkane-rich feedstream preferably
comprised of >50% C3+ alkanes is merged with the effluent of the
R2 catalytic reactor (e.g. via F2 or F3) and processed by the
liquid recovery system to remove specified C4+ liquids and separate
light gases and then the C3 alkane-rich feedstream is returned via
the recycle loop, but without receiving ethane from the F1
feedstream, to reenter the LG2F process via the R1 reactor
configured for Propane Thermal Olefination. In another embodiment,
an C2-C5 alkene-rich feedstream preferably comprised of >50% C2+
alkenes (e.g. refinery FCC intermediates) is merged with the
recycling effluent of the R2 catalytic reactor (F2 or F3), then
processed by the liquid recovery system to remove specified liquids
and separate light gases and then returned via the recycle loop,
without receiving ethane from the F1 feedstream or utilizing any
Thermal Olefination, to directly enter the single or multi-step R2
catalytic oligomerization process to produce fuels. In another
embodiment, an alkane-rich feedstream comprised of >20% methane
enters the LG2F process by being merged with the recycling light
gas effluent of the LG2F liquid recovery system (shown as
feedstream F4), then together is processed by separating the H2 and
methane light gases without cryogenics or fractionation, and then
the light alkanes collectively are returned via the recycle loop
being merged with the F1 feedstream before they enter the LG2F
Thermal Olefination process. In this embodiment, surplus LG2F
methane can be utilized individually or in any combination as: a
diluent, industrial fuel gas, flare gas (C3+ removed), commercial
use, converted to LNG, stored or sequestered underground from the
atmosphere. In another embodiment, a C2-C5 alkane-rich feedstream
preferably comprised of >20% C3+ alkanes is merged with the
effluent of the R2 catalytic reactor (e.g. via F2 or F3) and
processed by the liquid recovery system to remove specified C4+
liquids and separate light gases and then the C3 alkane-rich
feedstream is returned using a high pressure module (e.g.
>100-400 psi) to condense and separate C3 alkanes from lighter
compounds and passing the C3 compounds into the C3 recycle loop,
but without receiving ethane from the F1 feedstream, to reenter the
LG2F process via the R1 reactor configured for Propane Thermal
Olefination. The propane Thermal Olefination process may benefit
from receiving a slit stream of methane gas from the light gas
separation process. A parallel flow stream is established for C2
and lighter alkanes (once separated from the C3's) to merge with
the ethane feedstream depicted as the F1 feedstream and then enters
the Ethane Thermal Olefination process. These parallel Thermal
Olefination processes (Ethane and Propane) are devised to optimize
the recovery of liquid products where the ratio of alkane-rich
feedstream for C2's vs. C3+ is less than 4:1 (wt. %).
[0057] The LG2F process can be utilized to extract C3+ compounds
known to emit black carbon upon combustion. Black carbon emissions
are often emitted into the atmosphere when C3+ hydrocarbons
comprised in wet natural gas feedstreams are combusted into the air
at the time of flaring or any form of open-air combustion. This
type of flaring may occur particularly where crude oil and
condensate liquid production is underway but there is an absence of
a natural gas supply chain. In one embodiment, shown in FIG. 17,
the LG2F process operates to dry methane gas by extracting C3 and
black carbon emissions. The unprocessed wet gas feedstream
comprised of >50% (wt.) methane is merged into the LG2F process
at feedstream F4, whereby the majority of the methane gas is
separated under pressure without cryogenics or fractionation (i.e.
"cleansed" of C3+ hydrocarbons) and if sufficient C2+ light alkanes
remain, they can be merged and fed into the Thermal Olefination
process. In the event the ratio of remaining C2 vs. C3 alkanes
(i.e. % weight once the methane is stripped away) is less than 4:1,
then a module is utilized to separate the C3+ hydrocarbons under
pressure (e.g. 100-400 psi) to condense and separate the C3 alkanes
from the lighter compounds and passing the C3 compounds into the C3
recycle loop, but without receiving ethane from the F1 feedstream,
to reenter the LG2F process via the R1 reactor configured for
Propane Thermal Olefination. The propane Thermal Olefination
process may benefit from receiving a slit stream of methane gas
from the light gas separation process. An optional parallel
flowstream can be established for C2 and lighter alkanes (once
separated from the C3's) to enter the Ethane Thermal Olefination
process. This parallel process can then be remerged before entering
the R2 catalytic oligomerization process. All liquid product
produced from the liquid recovery system can be utilized as
gasoline blendstock, gasoline fuel, product storage or comingled
with the crude oil or fuel supply chain for efficient
transportation. In this embodiment, surplus LG2F methane can be
utilized individually or in any combination as: a diluent,
industrial fuel gas, anti-coking flare gas (C3+ removed),
commercial use, converted to LNG, stored or sequestered underground
from the atmosphere.
[0058] A similar embodiment shown in FIG. 18 follows the same
pattern of methane gas entering at feedstream 4, however instead of
combusting or flaring the methane gas post-separation, the methane
is processed by the Methane Thermal Olefination (MTO) process, or
any equivalent methane activation process known to those schooled
in the art of such activation, to decouple and primarily transform
the methane molecules to alkanes or alkenes. The converted
molecules reenter the LG2F process at feedstream 5, after which
they are available for downstream utilization of either alkane-rich
feedstreams (for R1 processing) or alkene-rich feedstreams (for R2
processing) to produce the desired liquid products. This technique
allows for the full-scale elimination of wet-gas flaring and is a
major environmental benefit to remote oil field operations
throughout the world by 1) reducing emissions of un-combusted
methane, 2) lowering CO2 emissions by ceasing unnecessary gas
flaring, and 3) eliminating so-called "black carbon scarring" that
results from C3+ emissions and soot being deposited on the artic
snow and polar ice caps.
[0059] In practice, some field sources of the C2-5 Alkanes may
contain contaminants. In this setting, a contaminant may be any
component that adversely affects the LG2F Process or its system
components. For example, contaminants may include ammonia, hydrogen
sulfide, nitrogen, sulfur and/or water. Some source streams are not
scrubbed to reduce such contaminants. These contaminants could
poison later-used catalysts or cause accelerated corrosion to
downstream (e.g., refining or petrochemical) processing units.
[0060] Significant concentrations of these contaminants are
preferably removed in advance by conventional pre-treatments
including various scrubbing and catalytic methods. The C2-5 Alkane
Feedstream preferably contains less than 1%, and more preferably
less than 0.5% contaminants. However, pre-treatment is not
necessary when using clean light gas feedstocks, e.g., cracked
gases from reformate, as these light hydrocarbon streams are
treated upstream and contain ultra-low quantities of
contaminants.
[0061] Inert components (e.g., nitrogen, argon, helium) are by
definition non-reactive in the LG2F Process. However, it remains
preferable to keep the inert components in limited amounts prior to
being purged (e.g. via membrane) from the LG2F Process.
Accordingly, the C2-5 Alkane Feedstream (excluding methane)
preferably contains less than 5%, and more preferably less than 1%
inert materials.
[0062] A given C2-5 alkane-rich hydrocarbon source may be processed
as obtained, or it may be combined with other available light gas
streams for transformation to targeted gasoline or diesel-range
transportation fuel blendstocks. Blending streams from 2 or more
sources, or augmenting a source stream with one or more added
components, is one manner of directing the compositions of the
final products.
Example C2-5 Alkane Sources
[0063] There are many diverse sources of C2 to C5 light hydrocarbon
gas streams. Sources include NGL's, gas condensate, industrial fuel
gas, petroleum gases and liquified petroleum gases (LPG), which are
available across the oil, gas and petrochemical industry. Suitable
C2-5 Alkane sources are typically found in refineries, oil and gas
extraction facilities, gas processing plants, petrochemical plants,
and liquid petroleum gas (LPG) storage facilities. C2-5 Alkane
sources also include any light hydrocarbon gases output of
catalytic cracking or catalytic reforming, or streams exiting any
paraffin cracking unit. Additional examples include light
hydrocarbon gases from hydrotreating and hydrodesulfurization
units. These and other C2-5 sources are all eligible to be
thermally and catalytically converted to C.sub.5+ constituents to
maximize liquid volume yield of gasoline or diesel fuel
blendstocks.
[0064] Such streams are light gas compounds, typically containing
ethane, propane, butane, pentane or any mixtures thereof. Pentane
and butane/pentane mixtures may also be in liquid form at ambient
temperatures and pressures. Some sources may be an isolated stream
of virtually one compound (e.g. propane). Any combination of
suitable C2-5 alkane gas streams can be merged together to utilize
this transformative LG2F Process.
[0065] The LG2F Process thus provides enhanced utilization of
available plant effluents. For example, a cracked, long-chain
paraffin byproduct having between 3% and 14% hydrocarbon gases
upgrades from low-value industrial fuel uses to a higher-value
gasoline blendstock by the LG2F Process. Similar gas constituents
(predominately C2+ with hydrogen) from the outputs of catalytic
reformers create the opportunity for even larger liquid volume
yields of high-octane gasoline blendstocks using the LG2F Process.
Any such gas streams can be pretreated if necessary, and processed
individually or merged with any number of other available C2-C5
alkane-rich gas streams. For example, in one embodiment, a single
incoming or merged light gas feedstream stream may contain a sulfur
content in the form of H.sub.2S exceeding a desired fuel
specification of typically less than 10 ppm S. In this case, a
desulfurization membrane, molecular sieve, or similar separation or
molecular absorption technique can be utilized alone or in series
to reduce the sulfur content to the required fuel specification
levels without adding hazardous processes (e.g. requiring reaction
with HF or H.sub.2SO.sub.4 or other such toxic chemical reactions)
to the process solely to remove sulfur. Since sulfur does not react
in the LG2F process, this separation technique can be utilized at
any point upstream of the liquid recovery process, but preferably
upstream of the Thermal Olefination reactor to reduce any
likelihood of sulfur corrosion to the LG2F metallurgy. This
technique results in a closed-loop, fully integrated LG2F
production process that can provide high-quality ultra-low-sulfur
fuels and fuel blendstocks without high cost and resulting in low
corrosivity to equipment.
Thermal Olefination
[0066] Using an alkane-rich feedstream comprised of >90%
alkanes, the production of liquid fuels in one embodiment starts
with the alkanes being largely converted to olefins via a
dehydrogenation step. The LG2F Process uses a Thermal Olefination
reaction for this purpose.
[0067] Thermal Olefination utilizes endothermic reactions which
suitably occur, for example, in an isothermal reactor operating
with a constant supply of heat. The Thermal Olefination reactor
uses dry heat (>600.degree. C.) to convert the C2-5 Alkanes into
olefins having 2 or more carbons ("C2+"). The Thermal Olefination
reaction avoids the use of catalysts and steam, operating with a
very fast reaction time to minimize coking. Various light gas
compounds are produced as byproducts, depending on the alkane
feedstream but generally, the olefins formed from the Thermal
Olefination reaction have the same or fewer carbons than the alkane
reactant. For example, pentane may be cracked into olefins and
paraffins as illustrated by the following examples:
C.sub.5H.sub.12.fwdarw.C.sub.4H.sub.8 (olefin)+CH.sub.4
(paraffin)
C.sub.5H.sub.12.fwdarw.C.sub.3H.sub.6+C.sub.2H.sub.6
C.sub.5H.sub.12.fwdarw.C.sub.2H.sub.4+C.sub.3H.sub.8
C.sub.5H.sub.12.fwdarw.C.sub.5H.sub.10+H.sub.2
As another example, ethane may be cracked into ethene, with small
quantities of methane and hydrogen as light gas byproducts.
[0068] The results of the Thermal Olefination reactions therefore
depend largely upon the composition of the alkane-rich C2-5 Alkane
Feedstream. The intermediate product is a mix comprised of C2 to C5
olefins, along with a lesser amount of C1-5 alkanes and hydrogen as
byproducts. The conversion is selected to maximize gasoline or
diesel fuel yields. Methane byproduct may undergo separation (e.g.
via various known selective and/or reverse selective membrane
separation techniques) from the other light gases and can be
utilized as fuel or used as a temperature controlling diluent in
the reaction process.
[0069] In one embodiment, an alkane feedstream comprised of >90%
ethane is merged with a recycle stream containing a blend C1 to C5
of alkanes comprising up to 25% methane and up to about 1%
hydrogen. It is found that the inclusion of methane and hydrogen
acting as a diluent in the non-catalytic Thermal Olefination
reaction not only effectively controls the temperature of reaction
in the radiant and adiabatic sections of the reactor, but it also
increases the metallurgical longevity of the reactor tube. Unlike
LG2F, traditional steam crackers tend to experience corrosion due
to the presence of H20 and other chemical additives (e.g. DMDS)
which add processing cost and can compromise the metallurgy of the
reactor. Based upon our analysis of the reactor, the preferred
residence time of the Thermal Olefination reaction is <1 second.
The "new ethane" added to the merged feed stream from the recycled
portion of the R2 effluent produces a light olefin conversion of
more than 80% (wt) in a single pass yield, net of incremental
methane and hydrogen from the prior recycle stream. In addition,
olefin conversions of greater than 100% are possible because the R2
catalytic conversion created light alkanes which can be recycled to
the R1 thermal olefination reaction.
TABLE-US-00002 Single-Pass Yield of New + Recycled Feedstream
Comprising C1-C5 Alkanes R1 Residence Time (sec) 0.20 0.20 0.65
0.60 0.56 0.52 New Ethane (lbs/hr) 700 700 700 700 700 700 Merged
Flow Rate (lbs/hr) 1,574 1,574 1,574 1,666 1,757 1,849 FEED
Hydrogen % wt 0.73 0.73 0.73 0.69 0.65 0.62 Methane % wt 11.65
11.65 11.65 16.62 20.88 24.80 Ethane % wt 64.94 64.94 64.94 61.37
58.17 55.28 Propane % wt 6.84 6.84 6.84 6.47 6.13 5.82 Propylene %
wt 0.63 0.63 0.63 0.60 0.57 0.54 C4's % wt 12.82 12.82 12.82 12.11
11.48 10.91 C5's % wt 1.52 1.52 1.52 1.44 1.36 1.29 C6's % wt 0.87
0.87 0.87 0.70 0.76 0.74 YIELD Hydrogen % wt 2.57 2.55 2.90 2.77
2.66 2.55 Methane % wt 20.16 20.14 24.98 28.56 31.48 34.34 Ethylene
% wt 31.65 31.46 37.16 35.50 33.96 32.47 Propylene % wt 3.82 3.83
2.35 2.31 2.28 2.25 C4-Olefins % wt 2.32 2.33 2.19 2.07 1.95 1.85
Unconverted Ethane % wt 34.86 35.05 25.48 24.28 23.16 22.20
Unconverted C3+ % wt 4.62 4.64 4.94 4.51 4.51 4.34 Net Conversion-
Olefins/C2+ FEED % wt 43.1% 42.9% 47.6% 48.2% 48.7% 49.0% Net
Conversion-Olefins/% New Ethane % wt 97.0% 96.5% 107.0% 114.8%
122.2% 129.5%
[0070] In a second embodiment in a similar thermal reaction, an
alkane feedstream is comprised of >10% methane and <1%
hydrogen. In a third embodiment in a similar thermal reaction, an
alkane feedstream is comprised of >15% methane and <1%
hydrogen. In a fourth embodiment in a similar thermal reaction, an
alkane feedstream is comprised of >20% methane and <1%
hydrogen. In a fifth embodiment in a similar thermal reaction, an
alkane feedstream is comprised of >30% methane and <2%
hydrogen. In a sixth embodiment, the merged flow rate, either with
or without "new ethane", varies in such a way as to keep at least
50% wt. of C2-C5 alkanes present in the R1 Thermal Olefination
reaction to sustain a high net olefin conversion rate in a single
pass. The use of methane as an inert hydrocarbon diluent in these
embodiments also serves to reduce carbon dioxide emissions from the
process which in traditional steam crackers is caused by the
reaction of excess carbon and steam.
[0071] As used herein, the term Thermal Olefination refers to the
conversion of alkanes to olefins in relation to controllable
variables including the Feedstream composition, temperature,
pressure and space velocity. As used herein, Thermal Olefination
does not comprise the use of either catalytic or steam cracking.
The absence of any dehydrogenation catalyst avoids the high cost
and marginal value of managing such dehydrogenation catalysts. The
absence of steam in the LG2F Thermal Olefination process eliminates
the burden of handling water, steam and fractionation columns and
any water separation prior to the downstream R2 catalytic
reactor(s). Water is known to rapidly deactivate zeolite catalysts
which are utilized in the downstream R2 process. This invention
thus uses a low-cost, steam-free, non-catalytic dehydrogenation
technique targeting alkane-rich feedstreams.
[0072] The results of an exemplary, single-pass LG2F processing of
a C5 alkane (pentane) feedstock is shown in FIG. 2. This
demonstrates the dependence of the product mix on operating
parameters of the LG2F Process. That is, modification of the C2-5
Alkane Feedstream and/or of the operating conditions allows control
of the product mix. For example, it is apparent from FIG. 2 that
the production of ethene as compared to methane reached an optimal
point for product yield. It is also shown that going to 100%
conversion was disadvantageous in view of the increased production
of methane and the consequent reduction in ethene.
[0073] Light Olefin Concentration--The LG2F Process eliminates the
use of cryogenic and fractionation processes typical of traditional
techniques to process light gases to produce fuels, blendstocks and
base chemicals (e.g. BTX aromatics). In one embodiment, the Thermal
Olefination process can be isolated to produce a high proportion of
light olefins which may also carry unreacted C2-C4 alkanes. New
emerging techniques allow for the use of metal-organic frameworks
and similar techniques to achieve >90% separation of C2-C4
olefins from alkanes (e.g. using Cu(I) applied to MFU-4/at varying
concentrations, molecular sieves, membranes, etc.) without
cryogenics, liquification or distillation. This technique thereby
allows the unreacted C2-C4 alkane effluent from the Thermal
Olefination process to be separated and recycled to R1 while the
C2-C4 olefin effluent can be further concentrated or separated,
with or without a subsequent R2 oligomerization reaction. In one
further embodiment, the ethylene and/or propylene produced from
this isolated Thermal Olefination reaction can be used as
specialized petrochemical feedstocks as a precursor as for making
such materials as polyethylene and polypropylene.
[0074] Standalone Thermal Olefination--The capabilities of the
Thermal Olefination reaction without the use of catalysts, chemical
additives or steam provide a unique and novel method for producing
olefins from any C2-C5 alkane-rich streams of light hydrocarbons
including ethane-rich feedstreams. In one embodiment, the
traditional use of steam cracking of ethane can be replaced by the
Thermal Olefination process to produce ethylene from ethane without
the use of steam or chemical additives. In another embodiment, the
traditional methods of steam cracking of propane or the use of
propane dehydrogenation methods can be replaced by the Thermal
Olefination process to produce propylene from propane without the
use of steam, catalysts, or chemical additives. In another
embodiment, the traditional methods of catalytic dehydrogenation of
C3/C4 propane and butanes can be replaced by the non-catalytic
Thermal Olefination process to produce light olefins without the
use of steam, catalysts, or chemical additives. These traditional
processes must continue to utilize capital-intensive separation
methods including cryogenics and multiple fractionation steps to
separate close boiling compounds to achieve high-purity compounds
for petrochemical processing and certain alkylation methods.
However, the isolated process of converting, for example, ethane to
ethylene or propane to propylene or any combinations thereof are
simplified by the Thermal Olefination process. Computer simulations
and pilot scale production results indicate that ethylene and light
olefin yields are very similar to steam cracking yields, coking
levels are very low and runtimes average 60 to 90 days between
regeneration steps. The absence of steam and chemicals such as DMDS
brings the additional advantages of lowing costs, reducing CO2
emission levels, reducing the impact of corrosion on the metallurgy
of the reactor, and reducing the handling of hazardous
chemicals.
TABLE-US-00003 Ethane Thermal Olefination vs. Steam Cracking -
Single Pass High Ethylene Yield Thermal olefination performance was
evaluated at a 17 lb/hr pure ethane feed stream with 950.degree. C.
furnace set-point. Absorbed duty of the reaction is 800 W/lb with a
total net of 13.5 kW of absorbed duty. Thermal Olefination Steam
Cracking Pressure 15 PSIA 15 PSIA Ethane Partial Pressure 15 PSIA
7.5 PSIA Outlet Temperature 812.degree. C. 850.degree. C. Residence
Time 0.12 Sec 0.1 Sec Conversion Yield (w/w) 65.5% 67.4% Hydrogen
3.3.% 4.1.% Methane 3.8.% 5.0.% Ethylene 52.2% 52.8% C3 1.5.% 1.4.%
C4 2.3.% 1.9.% C5 0.3.% 0.4.% C6 1.3.% 0.9.% C7 0.2.% 0.1.%
TABLE-US-00004 Propane Thermal Olefination (Recyclable) - 1.sup.st
Pass Ethylene/Propylene Yield and Selectivity Propane Thermal
Olefination 1 2 3 4 5 6 7 8 9 Conditions: Heater SP, .degree. C.
665 690 690 700 700 700 710 710 715 Internal T 697 727 735 746 745
741 758 758 761 Tube Exterior T 696 720 723 732 732 733 743 743 747
Propane, mL/min 4 4 3 3 3 3 3 3 3 Pressure, psig 10 10 10 10 10 0 0
0 0 % Propane Conversion 22.6 35.6 48.7 47.4 53.1 44.8 52.0 54.0
57.1 Yield, Wt %: Methane 4.68 7.51 10.71 10.33 11.81 9.21 11.07
11.49 12.33 Ethylene 7.80 12.17 16.54 16.20 18.12 15.99 19.11 19.85
21.19 Ethane 1.25 2.19 3.39 3.18 3.74 1.86 2.24 2.34 2.53 Propylene
7.57 11.95 15.23 14.63 15.85 14.77 16.33 16.83 17.22 Propane 77.45
64.37 51.29 52.58 46.92 55.19 47.97 46.04 42.86 C2 + C3 Olefins
15.38 24.12 31.77 30.83 33.97 30.76 35.45 36.68 38.41 Selectivity
Methane 20.74 21.06 21.99 21.78 22.26 20.56 21.27 21.29 21.58
Ethylene 34.61 34.16 33.97 34.16 34.14 35.68 36.74 36.78 37.08
Ethane 5.55 6.15 6.97 6.71 7.04 4.14 4.3 4.34 4.42 Propylene 33.58
33.53 31.27 30.85 29.86 32.96 31.39 31.19 30.14 C2 + C3 Olefin
Selectivity 68.19 67.69 65.23 65.01 64 68.64 68.13 67.97 67.22
Propane Thermal Olefination 10 11 12 13 14 15 16 17 18 19
Conditions: Heater SP, .degree. C. 715 715 715 715 715 715 725 725
735 735 Internal T 760 758 761 762 760 761 768 768 785 786 Tube
Exterior T 747 747 747 747 746 746 758 758 768 768 Propane, mL/min
3 3 3.5 3.5 4 4 4 4 4 4 Pressure, psig 0 10 10 10 10 10 10 10 10 10
% Propane Conversion 55.2 65.5 63.2 71.1 67.5 67.6 74.5 78.3 85.1
87.8 Yield, Wt %: Methane 11.79 15.71 14.76 17.44 15.94 16.21 18.61
19.89 24.08 25.42 Ethylene 20.37 22.20 21.37 24.05 22.91 22.92
25.72 26.94 30.40 30.80 Ethane 2.38 5.24 4.83 5.76 5.23 5.31 5.96
6.38 7.23 7.48 Propylene 16.93 17.14 16.67 17.12 17.40 17.17 17.41
16.86 15.01 14.06 Propane 44.83 34.53 36.77 28.89 32.49 32.36 25.50
21.74 14.86 12.23 C2 + C3 Olefins 37.30 39.34 38.04 41.17 40.32
40.09 43.13 43.79 45.41 44.86 Selectivity Methane 21.37 24.00 23.35
24.53 23.61 23.96 24.98 25.41 28.28 28.96 Ethylene 36.92 33.90
33.80 33.82 33.94 33.89 34.52 34.42 35.70 35.10 Ethane 4.32 8.01
7.63 8.09 7.75 7.84 8.00 8.15 8.49 8.52 Propylene 30.68 26.18 26.36
24.08 25.78 25.39 23.37 21.54 17.63 16.02 C2 + C3 Olefin
Selectivity 67.60 60.09 60.16 57.90 59.72 59.27 57.89 55.95 53.33
51.12
[0075] In one embodiment, the Thermal Olefination reactor is
configured to convert a light gas comprised of >90% ethane and
propane into ethylene and propylene. As needed, critical feedstock
impurities (e.g. sulfur, arsenic, mercury, metals) are removed
prior to R1 processing. The R1 reactor system is configured as a
single pass process without recycle to generate the maximum C2+
olefin yield. The absence of steam, CO, CO2, and sulfur brings
significant processing advantages to this invention. The
availability of excess hydrogen without CO is an advantage to this
invention in the alkyne hydrogenation process. The Thermal
Olefination effluent, following a rapid quench process in the
transfer line exchanger, has the option to undergo membrane
separation of inert gases (e.g. methane, hydrogen) and/or any
alkane/alkene separation methods at ambient or moderate pressures
as a precursor for downstream processing. Upon passing this
optional separation phase, the (remaining) effluent enters a
higher-pressure gas phase cryogenic separation process whereby the
methane is separated from the effluent (demethanized) for recycle
or commercial use. Then at about 20-40.degree. C. and about 400-500
psi, the C2+ bottoms comprising close-boiling ethane and ethylene
are further separated (deethanized), and then together fed to an
alkyne hydrogenation process to improve alkane/alkene purity,
followed by a C2 fractionation unit to split the ethane from the
ethylene. Then taking the C3+ deethanized bottoms at about 150 to
300 psi, the close-boiling propane and propylene are separated
(depropanized) and then together catalytically hydrotreated to
remove alkynes, followed by a C3 fractionation unit to split the
propane from the propylene. The remaining C4+ bottoms of the
depropanizer may be further processed or used for LG2F fuel
blendstock. At this point, the separated methane (as needed for
diluent), ethane and propane streams can be recycled to the Thermal
Olefination process. Polymer grade ethylene may require further
handling and purification. Polymer grade propylene may require
further handling and purification.
[0076] In another embodiment, the Thermal Olefination reactor is
configured to process a light gas feedstream comprised of >50%
ethane or propane for conversion into ethylene and propylene. As
needed, critical feedstock impurities (e.g. sulfur, arsenic,
mercury, metals) are removed prior to R1 processing. The R1 reactor
system is configured as a recyclable process to generate the
maximum C2+ olefin yield. The absence of steam, CO, CO2, and sulfur
in the reaction brings low-cost processing advantages to this
invention. The availability of excess hydrogen without CO is an
advantage to this invention in the alkyne hydrogenation process.
The Thermal Olefination effluent, following a rapid quench process
in the transfer line exchanger, has the option to undergo membrane
separation of inert gases (e.g. methane, hydrogen) and/or any
alkane/alkene separation methods at ambient or moderate pressures
as a precursor for downstream processing. Upon passing this
optional separation phase, the (remaining) effluent enters a
higher-pressure cryogenic separation process whereby the methane is
separated from the effluent (demethanized) for recycle or
commercial use, then at about 20-40.degree. C. and about 350-500
psi the C2+ bottoms comprising close-boiling ethane and ethylene
are separated (deethanized), and then together fed to an alkyne
hydrogenation process to improve alkane/alkene purity, followed by
a C2 fractionation unit to split the ethane from the ethylene.
Taking the C3+ deethanized bottoms at about 150 to 300 psi which
include the close-boiling propane and propylene are then separated
(depropanized) and then together catalytically hydrotreated to
remove alkynes, followed by a C3 fractionation unit to split the
propane from the propylene. The remaining C4+ bottoms of the
depropanizer may be further processed or used for LG2F fuel
blendstocks. At this point, the separated methane (as needed for
diluent), ethane and propane streams may be recycled to the R1
Thermal Olefination process. Polymer grade ethylene
post-C2-fractionation may require further treating and
purification. Polymer grade propylene post-C3-fractionation may
require further treating and purification. Any residual C4+
materials are available as fuel grade blendstocks, for further
product separations or for continued LG2F processing.
[0077] These specialized Thermal Olefination methods outlined
herein that utilize techniques known to those schooled in the art
of Hydrogen, C1, C2, C3 and C4 gas-liquids separation methods and
the subsequent alkyne hydrogenation methods to increase
alkane/alkene yields (purity) and the final splitting of ethane
from ethylene and propane from propylene may be utilized in any
commercially viable manner to accommodate this process. Cold box
cryogenics and NGL fractionation technology including tray design
(e.g. valve and sieve, dual-flow, crossflow, baffle-deck, etc.) and
choice of random vs. structured packing materials are all critical
design choices. Novel techniques may include the use of
divided-wall distillation columns to separate C1 from C2 from C3
from C4 streams prior to the alkyne hydrogenation steps. Light
gases from any of the fractionation towers may be recycled to the
compression systems to offset demands for increased horsepower.
High pressure gas separation methods (i.e. C2 and C3 splitters)
include the configuration of condensers, reflex vessels, and
reboilers to adequately affect separation of close-boiling alkane
vs alkene hydrocarbons. Together these collective processes are
called the Thermal Olefination process for producing Base
Petrochemicals ("TOBP").
[0078] It is further understood that polymer grade ethylene from
the TOBP process is a major feedstock to the production a wide
range of petrochemical products including polyethylene (HDPE, LDPE,
LLDPE), alpha-olefins (via oligomerization), and various other
chemical products. Similarly, it is understood that polymer grade
propylene from the TOBP process is a major feedstock to the
production a wide range of petrochemical products including
polypropylene, propylene oxide, acrylonitrile, and various other
chemical products.
[0079] It is understood that any attempt to retrofit an ethane
steam cracker or propane steam cracker or naphtha cracker or
propane dehydrogenation unit or any similar thermal or catalytic
unit to crack or dehydrogenate hydrocarbons to function as a
Thermal Olefination reactor as described herein falls with the
scope of this invention. The removal of steam, chemical additives,
and/or catalytic techniques from these existing process devices in
order to employ the benefits of the Thermal Olefination process is
included in this invention. The Thermal Olefination process may
also utilize any heating technique known to those schooled in the
art, including gas-fired heat (comprised primarily of either
methane or hydrogen as btu sources), and/or the use of electrical
heating or resistance heating methods to deliver process heat in
the convection and/or radiant sections of the furnace, but without
any requirement to use catalysts or steam in the R1 reactor.
Furthermore, the incorporation of the various plating (anti-coking)
techniques and carbon capture methods and/or regeneration
techniques are also distinguishing features of the Thermal
Olefination process as identified in this invention. These factors
taken individually or together bring about a process
simplification, a reduction to CO and CO2, and a lower-cost
alternative to the global process industry seeking to create
valuable fuel products and petrochemicals from hydrocarbons.
[0080] The LG2F Process utilizes Thermal Olefination reactors
configured to dehydrogenate the C2-5 Alkanes to form olefins
without the requirement of any catalyst. The Thermal Olefination
reactor may be of conventional design, including as simple as a
tubular chamber, designed to withstand high continuous service
temperatures from as low as 450.degree. C. for cracking butanes to
greater than about 925.degree. C. for cracking ethane. To minimize
carbon build-up, a protective layer may be crafted onto the
internal surface area of the entire reactor via plating (e.g.
chemical plating, electroplating, or other thin film deposition
techniques,) to produce a superficial layer of aluminum that is
oxidized to alumina. Alumina has known chemical and heat resistive
properties up to 1700.degree. C. in the absence of high-temperature
steam and will thereby inhibit deposition of carbon onto the inner
tube surface by preventing chemical access to iron surface atoms.
This specialized aluminum/alumina coating thus increases the
process lifecycle by reducing coke accumulation.
[0081] Other high temperature metals (e.g. B, Ce, Cr, Co, Hf, Ho,
Ir, Mo, Nb, Re, Ta, and Ti), high temperature ceramics, or selected
metallic oxides are viable materials for thin-layer deposition on
the inner wall of any R1 reactor(s) for minimizing the effect of
coking. Formulations for the thin film deposition technique vary
but preferred embodiments include halide anions (activators)
selected from fluoride (F--), chloride (Cl--), bromide (Br--),
iodide (I--) and/or astatide (At--) to enhance the evaporation
process. Other non-halide activators may also be applied as known
by those schooled in the art of thin film deposition. The selected
metals and metal oxides or their alloys (non-oxides) or
combinations of these may be utilized for thin film deposition in
the preferred embodiments must have melting points >500.degree.
C. and boiling points >2000.degree. C. and may be applied using
halides with specialized evaporative or vaporized carrier-gas
bonding techniques to form a metallurgical aluminide surface.
TABLE-US-00005 High Temp Boiling Melting Metals Element Pt .degree.
C. Pt .degree. C. Aluminum Al 2,470 660 Aluminum Oxide
Al.sub.2O.sub.3 2,977 2,072 Boron B 3,927 2,076 Cerium Ce 3,443 795
Chromium Cr 2,672 1,907 Cobalt Co 2,870 1,495 Hafnium Hf 4,602
2,233 Holmium Ho 2,695 1,472 Iridium Ir 4,130 2,466 Molybdenum Mo
4,639 2,623 Niobium Nb 4,927 2,477 Rhenium Re 5,597 3,185 Tantalum
Ta 5,457 3,017 Titanium Ti 3,287 1,668
[0082] Other coke-resisting methods applied to the inner wall of
the R1 reactor(s) may include the use of acid-bath passivation
techniques. These methods outlined herein to minimize coking on the
inner wall of the reactor are all integral to the design of the
Thermal Olefination reactor.
[0083] In one embodiment, each Thermal Olefination (R1) reactor
tube is configured using a special interior plating technique via a
thermal evaporative thin film chemical deposition process whereby
aluminum oxide (alumina) is deposited onto the entire inner wall of
each reactor tube including the tubing and manifolds immediately
downstream of the reactor leading to an entrained-gaseous carbon
extraction device through which the effluent of the R1 reaction
passes. In a second embodiment, the reactor tubes are packed with a
powered formulation of metallic compounds comprising a
high-temperature metal (preferably aluminum), a halide (preferably
aluminum chloride) to activate the evaporation purposes and an
inert diluent (preferably aluminum oxide) which are then sealed
inside the tube and heated until the temperature exceeds the
evaporation point of the powdered mixture, typically between
500.degree. C. to 1500.degree. C., for a period of 0.5 to 4 hours
to form a thermo-chemical vapor followed by a diffusion bonding
period of up to 48 hours during which the chemicals oxidize and
uniformly diffuse across the sealed vessel creating a thin aluminum
oxide layer onto the inner walls of each sealed vessel, thereby
providing a non-reactive and non-corrosive sheath on the inner wall
of each reactor tube. The time of the diffusion process and the
chemical formula vary based upon the desired thickness of the
deposition required. Another group of embodiments uses variations
of this thin film deposition technique including chemical vapor
deposition with one or more high temperature metals, halides and
metal oxide compounds and/or any physical vapor deposition method
for adhering to the inner walls of the reactor and related vessels
via any appropriate high-temperature metallic oxide diffusion
coating technique. These high-temperature metallic reactor vessels
may use any appropriate form of physical vapor or chemical vapor
thin film deposition process to achieve the desired coating
thickness and anti-corrosion behavior typically ranging between as
thin as 1-10 nanometers up to a thickness of 100 micrometers on
their inner walls. This protective layer prevents the iron (Fe),
typically found as a component at >50% (m/m) in various grades
of carbon steel, stainless steel and iron- or nickel-based-alloy
reactor vessels, from chemically bonding with the carbonic
reactants from the dry-heat Thermal Olefination reaction which can
thereby form coke deposits on the walls of the reactor which could
then build-up and obstruct the high temperature gaseous hydrocarbon
flow through the reactor.
[0084] Our research shows that the aluminized coating of a 310
stainless steel reactor tube operating at temperatures from
600.degree. C. to 900.degree. C. with a continuous gas flow of
hydrocarbons in the absence of steam or harsh chemical additives
(e.g. dimethyl disulfide) was able to virtually eliminate the
effect of catalytic coking, operate with unobstructed gas flow and
thereby extend the life of the reactor vessel. Prior to any
thin-film aluminizing treatment, the inner reactor walls of a 310
stainless steel vessel became caked by the catalytic
iron-carbonization reaction that drew iron out of the stainless
steel vessel creating a coking hot-spot which accumulated multiple
layers of carbon within 120-hours of operation ultimately leading
to an obstruction in the gas flow. However, with the appropriate
thin-film deposition technique using alumina on the inner wall of
the entire reactor tube, there was no catalytic iron-carbonization
affect observed along the entirety of the vessel over long
operating periods and it was observed that the hydrocarbon gas flow
was not obstructed. The impact of eliminating catalytic coking in
this controlled experimental environment reduced the total amount
of carbonized coke produced from the Thermal Olefination reaction
by 80%. The residual 20% attributed to pyrolytic coking occurring
away from the reactor walls was then efficiently captured by
downstream carbon collectors for removal from the system--thereby
reducing the total coke formation from the entire Thermal
Olefination reactor system without any emissions of CO2.
[0085] The Thermal Olefination process can be applied with or
without any of the chemical plating methods described above, such
as the thermal evaporative deposition technique. However, the use
of alkane feed compounds comprised of >10% C3+ alkanes generally
tends to result in higher amounts of catalytic coking on the
reactor walls in the absence of any plating technology. Test
results of this invention have shown that the Thermal Olefination
conversion from alkanes to alkenes is increased by 20-50% using
alumina thin film deposition methods due to the significant
reduction of coking specifically caused by the high-temperature gas
stream coincidentally reacting to the inside metallurgy of the
reactor walls caused particularly by the thermal cracking of C3+
alkanes. In the chart below, lab-scale test runs 4, 5, and 7-10
indicate the higher yield of olefins resulting from the use of such
specialized plating techniques to shield the metallurgy on the
interior of the reactor tube from the hot gas stream. In testing of
this invention, the use of high-temperature materials for plating
the inside of the reactor tube reduced coincidental coking by up to
85%.
TABLE-US-00006 Thermal Olefination of Propane Run 1 Run 2 Run 3 Run
4 Run 5 Run 6 Run 7 Run 8 Run 9 Run 10 Test A = 316 Stainless Steel
Feed Heater SP, .degree. C. 665 700 700 700 715 715 715 715 735 735
Propane, mL/min 4 3 3 3 3 3 3.5 3.5 4 4 Pressure, psig 10 10 10 0 0
10 10 10 10 10 Yield Conversion (wt % Reacted) 13.3 40.8 42.2 31.3
41.5 50.7 45.9 48.7 52.7 51.9 Ethylene (wt %) 4.9 13.6 14.1 10.8
14.7 17 15.5 16.4 18.2 18.3 Propylene (wt %) 3.4 13.4 13.8 10.9
13.9 15.5 14.5 15.1 15.7 15.4 Olefin Yield (wt %) 8.3 27 27.9 21.7
28.6 32.5 30 31.5 33.9 33.7 Test B = Aluminized 310 Stainless Steel
Feed Heater SP, .degree. C. 665 700 700 700 715 715 715 715 735 735
Propane, mL/min 4 3 3 3 3 3 3.5 3.5 4 4 Pressure, psig 10 10 10 0 0
10 10 10 10 10 Yield Conversion (wt % Reacted) 22.6 47.4 53.1 44.8
55.2 65.5 63.2 71.1 85.1 87.8 Ethylene (wt %) 7.8 16.2 18.1 16 20.4
22.2 21.4 24.1 30.4 30.8 Propylene (wt %) 7.6 14.6 15.9 14.8 16.9
17.1 16.7 17.1 15 14.1 Olefin Yield (wt %) 15.4 30.8 34 30.8 37.3
39.3 38.1 41.2 45.4 44.9 Olefin Yield Improvement (TEST B vs A) 86%
14% 22% 42% 30% 21% 27% 31% 34% 33%
[0086] Chart: Impact of Aluminized SS Tubes in Thermal Olefination
Reactor Using Propane
[0087] In one embodiment, a high-temperature reactor is designed to
utilize a configuration of stainless steel reactor tubes
appropriately treated with plating methods such as aluminized thin
film deposition techniques so as to largely eliminate coincidental
catalytic coking of the walls of the tubes and related interfacing
areas contacting the alkane-rich feedstream with >20% C3+
alkanes during the Thermal Olefination reaction. This resulted on
average 30% higher olefin yields, fewer hot spots, less flow
obstructions, and longer processing times between regeneration
cycles for the reactor tubes. This C2-C5 alkane cracking technique
without steam or catalysts can be utilized in a specialized single
pass or recyclable process for producing a light gas effluent
comprising ethylene and propylene for downstream petrochemical
uses. Subsequent distillation may be utilized for tailoring
specialized products to feed downstream processes. This C2-C5
alkane cracking technique without steam or catalysts can also be
utilized in a single pass or recyclable process for producing an
alkene-rich feedstream for the LG2F R2 Oligomerization process.
[0088] One advantage of the Thermal Olefination C2-C5 alkane-rich
cracking technique without steam or catalysts used in this
invention is, when applied to high concentrations of propane, this
invention outperforms typical propane (catalytic) dehydrogenation
techniques found in industry. This is the result of eliminating the
complex catalytic regeneration processes often used in Propane
Dehydrogenation processes (e.g. licensed as CATOLIN or Oleflex)
which in many cases may require complex reactor designs supporting
catalytic regeneration methods within 10-30 minutes or within 8
hours, respectively. The Thermal Olefination process in this
invention as described only requires regeneration of the reactor
tubes about every 30 to 90 days depending upon the processing
configuration.
Olefination Operating Conditions
[0089] The Thermal Olefination reaction is performed at a
high-temperature, with no catalyst or steam utilized. The Thermal
Olefination reactor is preferably operated with dry heat at a
temperature above 600.degree. C., an internal pressure of 0-1500
psig, and a gas weight hourly space velocity of 30-1000 hr.sup.-1.
The Thermal Olefination process does not materially affect methane
in the Feedstream. The presence of steam as a byproduct of the R1
Thermal Olefination reaction with light hydrocarbons must be
avoided as it can be damaging to the subsequent R2 catalytic
reaction.
TABLE-US-00007 TABLE 2 Examples of R1 Thermal Olefination Reactions
Test Run # 018-1 018-3 118-1 118-2 118-3 118-4 218-1 218-2 218-3
Conditions Reactor T, .degree. C. 800 800 800 800 800 800 810 820
830 Ethane, sccm 1580 790 1185 1580 790 790 790 790 790 Pressure,
psig 30 18 19 19 14 0 0 0 0 % Conv 39.52 45.64 35.18 29.59 46.90
37.17 39.66 47.81 54.31 % Yield Methane 5.74 9.30 5.48 4.03 9.25
4.13 4.85 6.59 8.22 Ethene 28.02 33.53 27.56 23.71 34.77 31.48
33.16 39.14 43.69 Ethane 60.89 54.62 65.07 70.64 53.38 63.09 60.61
52.47 45.97 Propylene 1.69 1.21 0.89 0.71 1.22 0.60 0.61 0.81 0.92
Propane 0.22 0.14 0.18 0.24 0.12 0.16 0.15 0.11 0.11 Benzene 1.05
0.27 0.13 0.08 0.33 0.06 0.09 0.16 0.26 % Methane 14.51 20.37 15.57
13.63 19.73 11.10 12.23 13.79 15.13 Selectivity Ethene 70.92 73.46
78.35 80.14 74.14 84.69 83.63 81.87 80.44 Propylene 4.27 2.64 2.52
2.41 2.61 1.61 1.55 1.70 1.69 Propane 0.55 0.31 0.51 0.82 0.27 0.44
0.38 0.24 0.21
[0090] In one embodiment, the introduction of hydrogen (H2) into
the R1 feedstream as a diluent can be used to manage the effective
use of heat and reduce the potential of coking and carbon build-up
in the R1 reactor system. This hydrogen can be introduced from any
H2 byproduct recycled from any R2 rector and appropriately
separated to isolate H2 or it can originate from any alternative H2
sources. The continuous recycle of this H2 gas reduces unnecessary
or inefficient H2 consumption. For those skilled in the art of
membrane separation, low-cost H2 recovery methods using various
pressurized membrane diffusion methods are routinely available
without the use of cryogenic cooling. Other cost-effective methods
may also be employed in similar embodiments.
Reactor Regeneration--R1
[0091] The LG2F Thermal Olefination system may include an
integrated reactor regeneration and cleaning sequence (RRC).
Operability of the Thermal Olefination reactor(s) is dependent upon
reactor lifecycles and the resulting amount of thermal resistance
that may occur from carbon build-up on reactor walls. This RRC
sequence is performed to reduce or eliminate carbon buildup
(coking). Regeneration and cleaning of the reactor(s) operating at
high temperatures involves a unique series of steps, during which
the light hydrocarbon feedstream flow is paused, in order to
restore active levels of the reactor(s). Alternative reactor
designs (e.g. continuous regen designs) may also allow for a
continuous R1 reactor operation without any pause in operation Two
methods for regenerating and cleansing the Thermal Olefination
reactors are provided, which can be used with a single reactor, or
with multiple units operated in parallel or in series.
[0092] The Reactor Regeneration intentionally avoids the potential
for deleterious amounts of high-temperature steam impacting the
Thermal Olefination reactor and prevents water contaminants from
passing to the downstream zeolite-catalytic reactor(s). This is to
prevent permanent deactivation of the downstream zeolite catalyst
used in the R2 reactor(s). The removal of generated water (i.e. via
low-temperature burning of the hydrogen in carbon-coke) avoids the
detrimental effects of water gaining access to the zeolite catalyst
(via active site reduction and dealumination) used downstream in
the R2 reaction. Subsequently, the remaining carbon in the coke is
burned-off at higher temperatures forming CO2, which is not harmful
to the zeolite catalyst.
[0093] The Thermal Olefination process allows for the capture and
collection of residual carbon primarily caused by the pyrolytic
coking of the thermal reaction. Coke deposits are gathered and shed
by some combination of agitation and/or high temperature calcining
of the residual carbon deposits captured in the collector
device.
[0094] Traditionally, alkane dehydrogenation reactors have used
either catalytic or steam cracking methods. Steam or steam/air
methods were used to reduce or eliminate coking. However, such
methods require large capital investments to manage water, steam
boilers and water separation techniques. In the LG2F Processes,
regeneration is performed without the use of steam or steam/air
mixtures, making the overall LG2F System long-lived and cost
efficient. The absence of added water (e.g., by way of steam)
enhances operation of the LG2F System.
A. Low Temperature Hydrogen and High Temperature Carbon
Regeneration
[0095] One Reactor Regeneration sequence for regeneration of the
Thermal Olefination reactors requires two-steps. This sequence is
specifically designed to (1) safely react hydrogen with oxygen to
form water at low temperature (under such conditions that the
carbon in the reactor does not burn), and (2) then after burning
hydrogen, water is removed entirely from the system, before
conducting a high-temperature carbon/oxygen reaction to
cleanse/regenerate the reactor.
Step 1: Low Temperature Hydrogen Removal
[0096] The first step in the regeneration sequence is initiated by
flowing a low concentration of oxygen, e.g., in air, through the
Thermal Olefination reactor at a temperature where only hydrogen in
coke will burn. The oxygen comprises preferably no more than 21%
v/v, and more preferably no more that 5% v/v, and even more
preferably no more than 1% v/v. A diluent gas, such as nitrogen,
CO2 or argon, is used to decrease the concentration of combustible
oxygen for the water production phase. The reduced oxygen
concentration during regeneration allows for a lower temperature
flame front.
[0097] This oxygen-containing feed gas is heated in the Thermal
Olefination reactor until a flame front is observed in the reactor.
This flame front is strictly due to the combustion of hydrogen to
water at a lower temperature than that of combusting carbon. The
flame front travels through the reactor until no hydrogen is
present at the reactor outlet, and the hydrogen burndown process is
then complete. The generated water is collected as a liquid in a
condensing chamber or vented to the atmosphere, or recycled and
mixed in the air containing regeneration gases.
Step 2: High Temperature Carbon Removal in the Absence of
Hydrogen
[0098] The second step is a carbon combustion cleansing sequence
performed once the water has been appropriately purged from the
system. While an oxygenated gaseous stream is still being passed
through the R1 reactor system the temperature is increased from its
initial water removal step to a temperature at which a second flame
front is observed. This second flame front is largely devoid of
water as the first burndown sequence combusted preferably at least
90% of the hydrogen, more preferably at least 95%, and even more
preferably at least 99% of the hydrogen. The only combustion
product resulting from the second carbon combustion sequence is
therefore primarily due to the production of carbon dioxide, with
little to no carbon monoxide. This flame front is followed through
the R1 reactor until a flame front is no longer observed. Once the
flame front is no longer being produced, the reaction chamber of
the Thermal Olefination units is sufficiently devoid of coke.
[0099] This two-step sequence can be conducted at any level of
carbon build-up, but preferably not more than at 50% of the unit's
lifecycle, more preferably not more that 30% of the unit's life
cycle, and most preferably not more than 20% of the unit's
lifecycle. This 2-step sequence can be performed in-situ, offline
from the hydrocarbon flow, on an individual reactor operating in
parallel with other Thermal Olefination reactors, to assure a
continuous LG2F Process. In another embodiment, duplicate reactors
of the same type are used in parallel with different burndown time
rotations so at least one unit can be online continuously. The
procedure can be fully automated to allow the starting and stopping
of the regeneration sequence and the resumption of the hydrocarbon
feedstream to continue Thermal Olefination reaction.
B. Compressed Air
[0100] A second option for the Reactor Regeneration method involves
stopping the hydrocarbon feed before substantial coke formation
occurs, then introducing compressed air into the reactor zone at
0-50.degree. C. below the typical unit operating temperature. The
regeneration proceeds for a short time duration, which may be
limited by the effects of exothermic heat. This regeneration cycle
is preferably designed to limit exothermic heat, by using a
frequent regeneration cycle which keeps carbon build-up at low
levels. Within minutes, the carbon build-up is purged. The process
thereby emits CO.sub.2, H.sub.2O and excess air for venting to the
atmosphere.
[0101] While any regeneration cycle can be used, a higher frequency
regeneration cycle (e.g., 15 minutes every 1-15 days) allows for
minimal water partial pressure in the combusted products as carbon
and hydrogen become the limiting reactants, rather than oxygen. In
general, the frequency of the regeneration is dependent on the
feedstream quality which impacts the level and/or rate of coke
formation.
Pre-Processing Natural Gas Feedstream for R1
[0102] The Thermal Olefination process is highly flexible and may
function using any combination of feedstreams comprising any C2,
C3, C4 and/or C5 alkanes. In addition, the R1 feedstream may also
contain methane in any amount, which will be unreacted in the R1
and R2 processes, but which can serve as a diluent for thermal
control in both the R1 and the R2 reactions. Based upon our
research, the use of methane from 5%-35% (wt) in the R1 Thermal
Olefination reaction can be cost-effective to reduce the
undesirable cracking of C2+ alkanes into shorter-chain molecules
that would otherwise form surplus methane and carbon coke. This
intentional use of surplus methane represents a useful carbon
mitigation technique that increases the overall yield of C2+
alkenes per net consumption of C2+ alkanes processed. The following
example shows how in isolation the methane feed is increased up to
250% (from 183.4 to 458.6 lb/hr) resulting in a) an unexpected 12%
reduction of "new" methane production, and b) increased ethylene
and olefin production as a percent of converted ethane.
TABLE-US-00008 TABLE X Impact of Increased Methane on Net Olefin
Yield Base 1.5X 2X 2.5X Impact of Methane on R1 Reaction Methane
Methane Methane Methane IN TOTAL FEED (lb/hr) 1574 1666 1757 1849
Hydrogen Feed (lb/hr) 11.4 11.4 11.4 11.4 Methane Feed (lb/hr)
183.4 275.2 366.9 458.6 Ethane Feed (lb/hr) 1022.2 1022.2 1022.2
1022.2 C3+ Feed lb/hr (Propane, i-Butane, n-Butane) 356.9 356.9
356.9 356.9 -- Ethane Consumed = Feed - Avg Out (lb/hr) 558.5 549.6
545.5 540.0 OUT Unreacted Methane (lb/hr) 183.4 275.2 366.9 458.6
Unreacted Ethane Out (avg) (lb/hr) 463.7 472.6 476.7 482.2 New
Methane Produced (lb/hr) 209.8 200.6 192.2 184.7 Ethylene
Production (lb/hr) 584.9 591.4 596.7 600.4 Ethylene/Net Ethane
Consumed 105% 108% 109% 111% Olefin Production (lb/hr) 656.4 664.4
671.0 676.2 Olefins/Net Ethane Consumed 118% 121% 123% 125%
[0103] In addition, the increased use of methane reduces the
formation of carbon coke and thereby extends the operating horizon
of the R1 reactor. In one simulation model calculation, the
operational run length increased up to 25% (from 64 to 80 operating
days) between R1 regeneration cycles.
TABLE-US-00009 TABLE X Impact of Increased Methane on Carbon
Buildup/Regeneration Base 1.5X 2X 2.5X Impact of Methane on R1
Reaction Methane Methane Methane Methane COKE Coking Rate (mm/d)
0.35 0.31 0.29 0.27 Estimated Runlength (days) 64 70 74 80 #
Decokes/yr 5.5 5.1 4.8 4.5 Decoke Days Down/yr 11.1 10.1 9.6
8.9
[0104] It is important to note that methane's behavior with the
metallurgy of the R1 reactor is preferred vs steam cracking. Using
steam in the R1 reaction is undesirable due to a) its corrosive
impact to the metallurgy and b) its chemical reaction with C2+
alkanes results in excessive CO2 emissions which LG2F avoids by not
using steam in the reaction. The amount of methane to consider
merging into the R1 feedstream is driven by the ratio of C2+
compounds vs. methane, the tradeoff of capital vs. reduced and the
sizing of the LG2F process. Any excess quantities of methane can be
regulated during this pre-processing step and diverted at any point
(e.g. via slit-stream) to be reused elsewhere, thereby assuring the
ratio of the C2-C5 alkanes to methane is preferably >1.0:1.0 in
the fresh feedstream or merged recycle feedsteam before passing
this into the R1 Thermal Olefination reactor.
[0105] The availability of such C2+ alkane-rich feedstreams with or
without methane may depend upon local oil & gas processing
alternatives and ever-changing market economics. Accordingly, this
invention identifies a unique method to prepare a C2+ alkane-rich
feedstream for R1 processing by merging the two primary outputs of
a typical wet-gas demethanizer unit, but in a specialized design
called "C2Rich". This method calls for utilizing two
feedstream--all or any portion of a C1+ vaporous methane stream
(e.g. using the preprocessed "wet gas" or using the demethanized
"dry gas" comprised of methane and ethane) as the Vapor Feed, and
any demethanized C2+ alkane liquid stream (sometimes referred to as
y-grade product) as the Liquid Feed. Then the Vapor Feed and the
Liquid Feed are passed into a single-stage gas stripper operating
at a temperature and pressure to produce a) a heavier C1+ natural
gas effluent stream with a greater proportion of ethane (C2Rich
Tops) and b) a new comingled blend of heavier alkanes which now has
a reduced quantity of ethane (Bottoms). This C2Rich output stream
may also include methane in any amount from 0% up to 50% (wt.) of
this total newly comingled stream. (For those skilled in the art of
gas processing, there is no requirement that the C1+ vapor stream
or the C2+ liquid stream are produced from a demethanizer unit or
that they are even from the same gas-processing source. The goal is
to eliminate capital intensive cryogenic processing, refrigeration
and complex multi-stage fractionation steps.)
[0106] The C2Rich gas stripper passes the C1+ vapor phase natural
gases and C2+ condensable liquids past each other in a
counter-current fashion to intermingle and separate in order to a)
selectively capture residual ethane and increase its concentration
preferably >50% in the methane stream making it C2Rich, b)
removing some portion of the ethane in the liquid stream (known as
rejected ethane) leaving a heavier product stream by using the
mixed-phase action of the gas stripper, c) return any unused or
unneeded methane to the natural gas source or utilize for alternate
use, d) optionally knockout any condensed heavy liquids (e.g. C4+)
from the gas stripper liquid effluent for alternate commercial use.
The resulting C2Rich vapor stream from the gas stripping step is
then comprised of 0% to 50% (wt) methane and 50% to 100% (wt) C2+
alkane compounds for feed into the Thermal Olefination R1 reactor.
This method avoids the use of cryogenics or complex fractionation
to extract the desired ethane components needed for the C2+
feedstream to R1, thereby reducing capital investment. This method
is also more efficient than processing traditional "wet gas"
(pre-demethanizer which may contain only 5-20% C2+ hydrocarbons)
because the use of a controllable slit-stream of C1+ vapors allows
for efficient use of the methane gas stream during volatile market
conditions without having to handle the entire "wet gas" or "dry
gas" methane gas stream in the Thermal Olefination reaction. The
gas stripper provides a method to regulate an ever-changing volume
and composition of vapor and liquid phase feedstreams. The
preferred choice for R1 feedstream may be the "top" of the stripper
output as shown in case #2 or #3. This stripping method does not
use cryogenics or refrigeration or complex multi-stage
fractionation as these temperatures shown are a function solely of
evaporation.
TABLE-US-00010 TABLE X Gas Stripper Tailoring C2 + Methane for R1
Mass % Case 1 Case 2 Case 3 Feed Vap. C1 88% 93% 96% C2 12% 7% 4%
Liq. C2 10% 35% 61% C3+ 90% 65% 39% Strip Top C1 28% 20% 6% Out C2
23% 52% 76% Bot. C2 5% 16% 34% C3+ 86% 78% 57% Pressure (PSI) 425
400 400 Feed Temp (C.) 25 25 25 Top Temp (C.) 29 16 19 Bot Temp
(C.) -6 -25 -28 Vap Feed (Lb/hr) 800 400 138 Liq Feed (Lb/hr) 4800
2400 1650 Top Out (Lb/hr) 1661 1165 950 Bot Out (Lb/hr) 3939 1635
839 Total Top C2 (Lb/hr) 377 605 719
[0107] In a preferred embodiment, a C1+ natural gas steam
containing 85-95% methane and 5-15% ethane enters a gas stripping
reactor simultaneously with a y-grade or demethanized product
ranging from about 5-60% ethane plus heavier C3+ alkanes. The two
streams interact in the stripper at 400 psi and 25.degree. C. and
the resulting C1+ light gases (C2Rich Tops) from the light ends
have an increased ethane content and the resulting liquid effluent
exiting the bottom of the stripper has correspondingly decreased
its content of ethane. In addition, the C2Rich tops effluent has
been commingled with a variable portion of C1+ methane gas ranging
from 5% to about 35% (wt) from the natural gas stream using a
control valve to compensate for changing conditions for use in
LG2F. This methane serves as a diluent in the LG2F reaction
processes and to reduce metallurgical corrosion in R1. Using this
unique hydrocarbon recovery method maximizes the capture of
low-cost ethane for use in LG2F while avoiding the use of a
deethanizer and it avoids capital-intensive cryogenic processing,
refrigeration and complex fractionation methods which are typically
necessary in such gas processing operations. This C2Rich comingled
alkane blend is then passed into the R1 thermal olefination reactor
as described in this LG2F invention to produce a range of gasoline
grade and diesel grade fuel products. The C2+ heavier liquid stream
exiting the stripper (also called y-grade) now has a higher value
per gallon due to the reduction of the lighter ethane
molecules.
[0108] In another embodiment, the C1+ natural gas stream is a
desulfurized wet-gas stream containing >80% methane, and a
different C2+ light alkane stream (a y-grade stream, e.g. exiting a
demethanizer), are passed in a multi-cycle gas stripper process
augmented with a methane membrane unit. The methane and C2Rich
light gases extracted from the top of the stripper now have a
higher concentration of ethane (greater than methane) and are used
as low-cost feedstream to the R1 Thermal Olefination process. The
C2+ bottoms y-grade effluent is available for any alternate use,
albeit at a higher value per gallon due to the ethane extraction
process.
[0109] In another embodiment, a demethanizer is configured to add a
single or multi-stage gas stripper module that allows wet gas or
dry gas and any demethanized C2+ alkanes to converge and interact
so as to strip a controlled portion of C2 light hydrocarbons into
the C2Rich (tops) stream and a heaver y-grade effluent without the
additional of any cryogenic processes. The C2Rich light
hydrocarbons may contain any amount of methane but preferably from
0% up to 35% (wt), plus about 50%-90% ethane, and 0% up to about
15% propane of the C1+ light alkane stream. This C1+ stream then
passes to the R1 Thermal Olefination reaction for further LG2F
processing.
C2-5 Olefin Catalytic Processing
[0110] The Thermal Olefination results in a product stream which is
passed to a catalytic reactor in which the olefins are converted
into a broad spectrum of fuel grade hydrocarbons. The conversion
involves chemical reactions comprising cracking, oligomerization
and/or aromatic cyclization, and transforms the olefins without
affecting lighter (C.sub.2/C.sub.3) paraffins in the Feedstream. In
one sense, the catalytic conversion may be affected in any manner
known in the art to be effective in cracking, oligomerizing and/or
cyclizing C2-5 olefins. Particularly preferred catalytic processes
are disclosed herein.
[0111] As used herein, the term "Olefin Feedstream" refers to a
Feedstream comprising C2-5 olefins. The Olefin Feedstream may
comprise all or a portion of the product stream of the Thermal
Olefination reactor. For example, methane and hydrogen present in
the olefination product may be separated prior to passing the
stream to the catalytic reactor. Or alternatively, methane and
hydrogen may be fed into the catalytic process, serving to help
manage the isothermal reaction of the R2 reactor(s). Similarly,
C2-5 Alkanes present in the product stream, particularly ethane and
propane, may be separated out and recycled to the Thermal
Olefination reactor at any point in the LG2F process--either
combined with the C2-5 Alkane Feedstream, or separately. An Olefin
Feedstream derived from the product stream of the Thermal
Olefination reactor will contain C2-5 olefins.
[0112] In one aspect, the C2-5 Olefin Feedstream is input to the
catalytic reactor. As used herein, the term "catalytic reactor" is
used to refer to a reactor using a zeolite catalyst and operating
under controlled conditions so as to cause cracking, oligomerizing,
dimerizing, trimerizing and, in many conditions, cyclizing of the
feed olefins to form higher carbon alkanes, alkenes and aromatics
suitable for gas or diesel blending stocks. The use of zeolites as
a three-dimensional crystalline structure is the preferred catalyst
in all LG2F oligomerization reactions, but variations of the
zeolite support structures using metalloids and post-transition
metals may be used individually or in combinations in a given R2
reactor designed to maximize the commercial outcome of the LG2F
oligomerization process. In addition, the LG2F process may use a
multi-step oligomerization reaction sequence described herein for
producing longer-chain molecules by operating first at low pressure
(gas phase) and then condensing the effluent to a liquid for a
second high pressure reaction, coupled with the use of single or
multi-catalyst processing techniques offering a range of unique
combinations to produce many specialized high-performance fuel
grades, fuel blendstocks and base chemical feedstocks.
[0113] It will be appreciated that these reactions may occur in
various combinations and orders, with some molecules undergoing
several such reactions. Thus, reactions leading to the end products
may act on the olefins in the feed, or may act on the olefins after
they have already undergone one or more reactions. It is therefore
contemplated, and is to be understood, that reference to reactions
of the feed olefins refers generally to reaction of any molecule
that was originally fed to the catalytic reactor as a C2-5
olefin.
[0114] The catalytic reactor uses a zeolite catalyst and operates
above 200.degree. C., at 0-1500 psig, and a weight hourly space
velocity (WHSV) between 0.5 and 10 (preferably about 1). This
reactor produces multi-iterative, random-sequenced chemical
reactions to crack, oligomerize, and in many conditions, cyclize
the broad-spectrum of hydrocarbons comprising olefins and
olefin-derived compounds. The catalytic process can be caused to
produce any range of fuel grade products, including for example,
C.sub.5+ or C.sub.6+ or C.sub.7+ gasoline ranges (primarily
paraffins, olefins, and aromatics), or C.sub.9+ or C.sub.10+ or
C.sub.12+ ranges of light gas oil or middle distillate hydrocarbons
(for use primarily as diesel fuel blendstocks).
[0115] The chemical reactions in the catalytic reactor (R2)
comprise multi-iterative, building, degrading and sometimes
cyclizing of different molecular formations creating a portfolio of
hydrocarbons that can be selectively tailored to any specific
carbon range of products. The end products can be affected, for
example, based on the composition of the C2-5 Alkane Feedstream,
the configuration of a recycle loop, and various other operating
conditions of the overall LG2F Process. For example, operating
conditions (e.g., T, P, WHSV) are varied depending upon the desired
product--gasoline grade or middle distillate grade fuel
blendstocks.
Catalysts
[0116] The catalytic reactions disclosed herein utilize catalysts
in the R2 reactor(s) that crack, oligomerize, dimerize, trimerize
and in many conditions cyclize the olefin feedstream with high
efficiency. The catalysts used in the preferred embodiments of LG2F
Process generally contains a strongly acidic (non-metallic)
zeolite, with a high surface area support, for example,
alumina.
[0117] Over the past several decades, the oligomerization of
alkenes has involved the use of many types of catalysts to produce
fuels. Examples of such catalysts include: [0118] Heterogenous acid
catalysts (primarily zeolites; preferable ZSM-5) [0119]
Dealuminated acid catalysts (zeolites) in proton form to dimerize
olefins [0120] Heterogenous nickel catalysts (to dimerize light
olefins) [0121] Homogeneous nickel catalysts (to dimerize or to
produce long-chain linear oligomers) [0122] Bi-functional catalysts
using various metals (e.g. Co, Cu, Pt, Pd, Fe, Rh, Ir, Ru, Ta, Zn,
Ga, In, Al, K, etc.) incorporated into heterogenous acid catalysts
As anyone skilled in the art of catalysis knows that any of these
catalytic methods or combinations thereof could be used in the LG2F
oligomerization process under the proper temperature, pressure, and
space velocity to produce a viable fuel or fuel blendstocks. Hence
all these catalytic methods are hereby incorporated into this
invention. (Reference: Alkene Oligomerization, C. T. O'Connor, Dept
of Chemical Engineering, UCT, S. Africa, 1990; n-butene skeletal
isomerization to isobutylene--Ferrierite/ZSM-35, Wen-Qing Xu, et.
al. University of Connecticut, 1995; Conversion of n-Butane to
iso-Butene on Gallium/HZSM-5 catalysts, S. M. Gheno, et al., Dept
de Engenharia Quimica, Sao Paulo Brazil, 2001; U.S. Pat. Nos.
3,325,465, 6,852,901, 6,914,166)
[0123] In some selected embodiments, the addition of the metalloid
Boron (B), utilized with a ZSM-5 structure in a specialized
synthesis process, greatly increases the number of crystals
supported in the catalytic structure without limiting the pore
size. This Boron-enhanced non-metallic zeolite structure with Boron
>5 wt. % of the catalyst and Si/Al.gtoreq.500, herein called
"ZSM-5B", reduces activation and allows a more controlled
dimerization and trimerization of olefin compounds when processing
R1 effluent or any light olefin-containing feed stream,
particularly any stream comprised of C2 or C3 olefinic compounds.
Other experimental lab testing of ZSM-5 structures using >5%
Boron substituted alumina with metalloid germanium and non-metallic
phosphorus and found all three to be similar in their effectiveness
at dimerizing ethylene. The use of the ZSM-5B catalyst in such an
R2 reactor results in the intermediate production of effluent
comprised of C4+ or C6+ olefins as a precursor to further
downstream R2 catalytic conversions. The preferred embodiments of
utilizing the ZSM-5B catalyst were found when operating a first R2
catalytic reactor with the ZSM-5B catalyst operating at low
temperatures (about 250 to 400 C) and low pressures (about 0 to 300
psig) with limited reaction time thereby producing dimerized and
trimerized olefins. This reaction was then followed by a
high-pressure liquification step (via pump or compression) to
concentrate the intermediate olefin-containing feedstream, followed
by secondary R2 reaction using a non-metallic zeolite (with or
without the use of ZSM-5B) operating at any appropriate pressure
and temperature to produce a targeted range of longer-chain
hydrocarbons particularly useful in the production of middle
distillate fuel.
[0124] The initial production of the ZSM-5B catalyst outlined
herein was developed using the follow laboratory procedures: 1)
Ethylenediamine (80 mL) and Boric Acid (49.46 g) were added to
water (735.07 g) and stirred for 15 min, 2) Aluminum Nitrate
Nonahydrate (6.00 g) and Tetrapropylammonium Bromide (21.31 g) were
added to the mixture and stirred for 15 min., 3) Colloidal Silica
(Ludox HS-40, 601.8 g) was added and stirred for 30 min. before
transferring entire mixture to a 2-L autoclave with a Teflon cup.
The mixture continued stirring at ambient conditions as the
autoclave heated up, 4) The autoclave was set to heat at
175.degree. C. and left for 132 hours, 5) After cooling down, solid
products were recovered by decanting off the liquid. Solids were
washed, alternating between water and acetone, 3 times each. Solids
were recovered by decantation, 6) The wet solids were transferred
to glass containers and placed in a 70.degree. C. oven for 48 h.
The oven temperature was increased to 100.degree. C. for 24 h. Then
increased again to 120.degree. C. for 6 h, 7) Solids are calcined
at 580.degree. C. for 10 h to remove residual organics, 8) B-Al-MFI
are converted to NH4-form by ion-exchange using a 1.0 M Ammonium
Nitrate solution, then washed four times with water, 9) NH4-form
zeolites are converted to H-form by heating in air at 500.degree.
C. Subsequent versions of the catalyst were prepared and tested to
reduce activation, lower benzene content, lower total aromatic
content and other tailorable fuel attributes.
[0125] In traditional hydrothermal synthesis of zeolites, the
crystallite size is generally linked to the amount of aluminum
heteroatoms; lower amounts of Al results in larger crystallite
sizes. Large crystallite sizes are problematic for the LG2F R2
reaction for a variety of reasons such as diffusion issues and
increased residence time inside the crystal, which can result in
undesired secondary reactions and catalyst deactivation.
Incorporation of .gtoreq.5% wt. non-catalytic boron heteroatoms
during synthesis allows for independent control of crystallite
size. At various low Al concentrations as illustrated below,
increasing amounts of B yielded smaller crystallites. This allows
for the synthesis of zeolites with low active-site concentrations
(i.e. low Al) while avoiding the issues associated with large
crystallite sizes.
[0126] The derivation of the ZSM-5B catalyst is outlined below as
follows using a Si/B ratio of 2.5:1. All the variations of ZSM-5B
catalysts tested had a Boron weight .gtoreq.5% wt.
TABLE-US-00011 Si O.sub.2 = Silica (Silicone Dioxide) Si.sub.2.5 B
O.sub.7 = Zeolite w/Boron (no Al) Si.sub.2.5 B O.sub.7
Al.sub.0.XXXX = Zeolite w/Boron (with Alumina)
TABLE-US-00012 Alumina (wt %) per 2.5 units of Silica (Assuming
Si/B = 2.5) Si/Al = 200 Si/Al = 333 Si/Al = 500 Si/Al = 750 Si/Al =
1000 Si 2.5 Si 2.5 Si 2.5 Si 2.5 Si 2.5 Al 0.0125 Al 0.0075 Al
0.0050 Al 0.0033 Al 0.0025
TABLE-US-00013 Si B O Al Atomic Wt. 28.1 10.8 16 27 Si/Al Ratio
Si.sub.2.5 B O.sub.7 Al.sub.0.XXXX Total Wt. Boron (% wt) Si/Al =
200 70.25 10.8 112 0.3375 193.3875 5.585% Si/Al = 333 70.25 10.8
112 0.2027 193.2527 5.589% Si/Al = 500 70.25 10.8 112 0.1350
193.1850 5.590% Si/Al = 750 70.25 10.8 112 0.0900 193.1400 5.592%
Si/Al = 1000 70.25 10.8 112 0.0675 193.1175 5.592%
[0127] In one lab experiment of the Boron catalyst shown above, the
liquid product from reacting C3=(propylene) with the BCat
(Si/Al.apprxeq.500, Si/B.apprxeq.2.5) was run in a reactor. The
resulting data shows a liquid rich in C4, C5, C6 and C7 olefin
compounds, which has a density of 0.70 g/mL. This case demonstrates
the effectiveness of the dimerization and trimerization process
using Boron by slowing the activation process. The example here was
obtained at 40 psig, reactor temperature of 300.degree. C., and
propylene flow of 5 WHSV.
TABLE-US-00014 C3 = --> Dimers/Trimers R2 Dimerization Wt %
C1-C4 13.96 C5 19.47 C6 17.32 C6AR 0.10 C7 18.97 C7AR 0.69 C8 12.76
C8AR 1.66 C9 6.22 C9 AR 1.57 C10 2.85 C10 AR 0.96 C11 0.63 C11 AR
0.00 C12+/Unknown 2.85 100.00
[0128] In a follow-up experiment, taking the liquid effluent
produced above and reacting it over a regular ZSM-5 (80:1). This is
GC/MS data to get info on the heavier compounds and shows a lot of
heavier olefinic compounds--typical of diesel fuel. The attached
data shows the chromatogram for this product. Approximately 80% of
the product is C8 and up when using the C2-C5 recycle process. The
liquid product had a density of 0.75 g/ml. For this reaction, the
reactor pressure was 330 psig, a set point of 225.degree. C., and
flow at 3.5 WHSV. This product output is well within the range of
typical diesel fuel products.
TABLE-US-00015 R2 Oligomerization Reaction #2 (target Diesel) GCMS
Area % Recycle Options Two Fuel Products C3 0.19 Recycle R2-Low P
Recycle R2-Low P C4 1.65 Recycle R2-Low P Recycle R2-Low P C5 4.18
Recycle R2-High P Gasoline C6 6.04 Recycle R2-High P Gasoline C7
7.25 Recycle R2-High P Gasoline C8 10.64 Recycle R2-High P Gasoline
C9 8.95 Diesel Gasoline C10 7.91 Diesel Gasoline C11 7.57 Diesel
Diesel C12 7.86 Diesel Diesel C13 6.59 Diesel Diesel C14 7.08
Diesel Diesel C15 1.66 Diesel Diesel C16 6.08 Diesel Diesel C17
2.08 Diesel Diesel C18 4.37 Diesel Diesel C18+ 9.90 Diesel Diesel
100.00
[0129] In one embodiment, the olefin effluent from the first low
pressure R2 reactor processed using the ZSM-5B catalyst contains
dimerized C4+ olefins which are then further oligomerized in a high
pressure R2 reactor using a different combination of zeolite
catalysts. The effluent of the high-pressure reaction is split
between C5-C9 grade gasoline compounds and C10+ distillate grade
compounds with the C2-C4 residual being recycled. In another
embodiment, the C2-C8 portion of the high pressure R2 reactor
effluent is recycled back to the inlet of the high-pressure R2
reaction to create more long-chain compounds. In another
embodiment, the C2-C4 olefins from the effluent of the high
pressure R2 reaction are recycled back to the low pressure
gas-phase R2 reaction for re-dimerization, and the C5-C8 portion of
the high pressure effluent is recycled to the inlet of the high
pressure R2 oligomerization process to support the making of longer
chain molecules.
[0130] Additionally, in selected embodiments involving the
production of high aromatic compounds (e,g, pygas, toluene, LG2F
pseudo-reformate, BTX, etc.), there may be a weakly active metal as
outlined in earlier research, for example Pt, Pd, Re, Rh, Ir, or
Mo, which may be utilized in any R2 reactor, either staged within
the reactor downstream of a non-metallic zeolite catalyst or used
in some sequence as a standalone R2 reactor, to saturate cracked
olefins and/or hydrodealkylate cyclized aromatic compounds to
produce methyl-aromatics using the R2C9 process (invented by
inventor), which may be desirable in a specialized spectrum of
targeted fuels or base chemicals. If utilized, these catalyst
metals may be present as an oxide, metallic or alloy
nano-particles. The preferred metals are Pt, Re and Mo operating at
temperatures between 200-500 C at pressures from 0 to 1500 psig and
a space velocity from 0.1 to 10 hr.sup.-1. The metal loading can be
from 0.05 to about 10 wt. % as metal impregnated in the catalyst.
The metals are typically supported on a high surface area support
such as alumina, silica, and other refractory oxides. These oxides
provide high surface area, porosity and physical strength. The
oxide support also contains an acidic form of zeolite Y(FAU), beta
(BEA), mordenite (MOR), and ZSM-5 (MFI). The amount of zeolite may
be from 10% to 90% wt. of the finished catalyst.
[0131] The LG2F Process uses any catalyst or combination of
catalysts in the R2 reactor(s) which are functional to
substantially crack, oligomerize, dimerize, trimerize and under
some conditions cyclize the olefins in the feedstream. A catalyst
is functional to substantially crack, oligomerize, and/or cyclize
the olefins if it transforms at least 65%, preferably at least 80%,
and more preferably at least 95% of the olefins to fuel grade
compounds in a single-pass conversion. In selected embodiments, the
reactions are accomplished by a two-step R2 zeolite reaction
whereby C2+ olefins (e.g. ethene, propene) are initially dimerized
and trimerized in an abbreviated (rapid) low-severity reaction
using a ZSM-5B catalyst to limit the production of longer-chain
molecules and this effluent comprising any C4+ or C6+ olefins is
subsequently concentrated into a high-pressure liquid before
entering another R2 vapor-phase reaction with a zeolite catalyst
but at various temperatures and pressures that depend upon the
desired product slate. This second R2 reaction when used along with
a liquid/vapor flash drum and a recycle loop back to R1 can better
control the production of longer-chain molecules (generally
.gtoreq.C9 hydrocarbons) due to its thermodynamic stability (from
less exothermic activity) for more tailored fuel products
particularly in the middle distillate range.
[0132] In one embodiment, the catalytic reaction is performed using
a zeolite catalyst. The acidic sites in zeolite catalyze cracking
reactions more rapidly than other components. These reactions are
conducted without metal impregnation to eliminate the undesired
production of propane caused from hydrogen/metal reactions at
higher temperatures. In another embodiment, the zeolite catalyst is
used in the R2 reactor in combination with a metal impregnated
zeolite to specifically hydrogenate unreacted olefins at
temperatures below about 275 C to improve the targeted fuel
characteristics.
[0133] In one aspect, the processes use a zeolite catalyst having a
pore size of 2 to 8 Angstroms. Exemplary surface areas for the
catalyst are 400 to 800 m.sup.2/gram. Examples of the zeolite
catalysts include Si, Al and O, preferably with an Si:Al ratio of 3
to 560. Zeolite catalysts with properties outside of these
limitations may also be useful. The catalyst is preferably selected
to substantially catalyze the olefins while not significantly
affecting other components of value in the feed stream.
[0134] In embodiments, the catalyst is Zeolite ZSM-5, Zeolite Beta,
Zeolite-Y or Zeolite Mordenite. Zeolites are characterized in the
following ways: pore size--3 to 8 angstroms usually; pore
structure--many types; and chemical structure--combination of Si,
Al, and O. All have ammonium cations (except one version of
mordenite) prior to any impregnation and all have molar Si/Al
ratios of 3 to 560.
[0135] Zeolite Beta has the following properties: 2-7 angstroms
pore size, SiO2 to Al2O3 molar ratio (Si/Al) ranging from 10 to
150, intergrowth of polymorph A and B structures, and surface area
between 600 and 800 m.sup.2/gram.
[0136] Zeolite-Y has the following properties: averaging 7-8
angstroms pore size, SiO2 to Al2O3 molar ratio (Si/Al) greater than
3, and surface area between 600 and 1000 m2/gram.
[0137] Zeolite Mordenite has the following properties: 2-8
angstroms pore size, sodium and ammonium nominal cation forms,
Si/Al ratio of 10 to 30, and surface area between 400 and 600
m2/gram.
[0138] In a particular embodiment, the catalyst is Zeolite ZSM-5.
ZSM-5 has the following properties: 4-6 angstroms pore size,
pentasil geometry forming a 10-ring-hole configuration, Si/Al ratio
of 20 to 560, and surface area between 400 and 500 m.sup.2/gram.
The ZSM-5 is the preferred catalyst for its ability to support the
R2 transformation reaction to produce fuel grade gasoline and
diesel products. The smaller pore size of the ZSM-5 catalyst
results in far less undesired saturation, coking and deactivation.
This preferred reaction is conducted without metal impregnation.
However, in some specialized embodiments, a metal impregnated
zeolite used downstream of a non-metallic zeolite allows hydrogen
(e.g. R1-produced hydrogen) to add across olefinic compounds which
may produce a more desired result for some selected fuel
grades.
Zeolite Catalyst Example
[0139] In one embodiment, the proprietary acid-based ZSM-5 zeolite
catalyst specifically targets C.sub.2-rich hydrocarbon streams
(e.g., one embodiment: 80:1 silica on alumina ratio). The process
design may also have catalyst beds which favor C.sub.2 reactions
more than C.sub.3 reactions or C.sub.4 reactions, etc., resulting
in layers or sequences of oligomerization, dimerizing, trimerizing
and cracking reactions with different conditions to maximize the
yield and performance properties of the fuel products.
[0140] The R2 reactor design is tailored to mitigate the tendency
of the chemical reaction to generate a highly exothermic response
during the oligomerization process. The design considers the impact
of isothermal vs. adiabatic methods. In one embodiment, the R2
reactor design is tailored as an isothermal reaction with
intermittent heat and cooling applied to manage steady-state
temperatures. In another embodiment, the R2 reactor design is
tailored to utilize a combination of the isothermal method and
adiabatic methods. In another embodiment, the R2 reactor design
utilizes a unique cooling feature of the inner core of the reactor
to stabilize the response to exothermic reactions.
[0141] The R2 reactor design may also utilize a variety of methods
to support the regeneration of its catalysts. In one embodiment, a
series of R2 reactors is used to alternate between active
oligomerization processing and offline catalyst regeneration
processing. In the preferred embodiment, the R2 reactor design
utilizes a fluidized bed-style reactor with a continuous
regeneration process employed to refresh the catalyst with
sufficient turbidity and stabilized heat management without
interrupting the process flow. In another embodiment, the R2
reactor design utilizes a static bed in combination with a
fluidized bed reaction method to minimize latent heat and thereby
reduce the utility cost of the reactor. In yet another embodiment,
the R2 reactor design utilizes a static bed plug flow method is the
lowest cost method due to no moving parts thereby offering a more
predictable management of contact time between the flow and the
catalyst. Other reactor designs known to those skilled in the art
of catalytic processing are included in the available range of
reactor designs for the R2 oligomerization process.
Reactor Regeneration--R2
[0142] Operability of the catalytic reactor is dependent upon
reactor and catalyst life-cycles, and the resulting amount of
deactivation or thermal resistance that may occur from carbon
build-up on catalysts or reactor walls. Regeneration of any such
reactor or catalyst operating at high temperatures involves a
unique series of steps to restore active levels and prevent
permanent catalytic deactivation of the downstream zeolite-based
catalytic reactor. It has been determined that the regeneration
methods previously described herein are also useful with the R2
catalytic reactor(s), and the timing of regeneration may be
determined on a similar basis.
[0143] Both regeneration methods outlined herein can be tailored to
operate in any suitable reactor, especially any Thermal Olefination
reactor or any zeolite based catalytic reactor. For the R2
reactor(s) these methods beneficially restore the catalytic
activity of the zeolite with the advantage of eliminating loss of
active sites caused by traditional steam cracking methods resulting
in steam dealumination.
LG2F System
[0144] Referring to FIG. 3, there is shown a process flow for the
LG2F Process. Feedstock stream (1) comprises mostly C.sub.2-C.sub.5
paraffin-rich alkanes. Pretreatment (not shown) of the feed (1) can
be conducted to remove excess methane if necessary (via membrane
system or purging), C6+ hydrocarbons (via liquid-vapor flash drum),
or any contaminants to support gasoline and diesel fuel production
and/or to optimize feed composition. Feedstock stream (1) is
combined with a recycled light stream (13) comprised of a
C.sub.1-C.sub.5 mixture primarily including n-paraffins and
i-paraffins with some olefins and the combined stream (2) is fed
into heat exchanger (EX-1). As described later, light gas
feedstreams that have primarily olefin-rich content (e.g., FCC
off-gases, propylene, etc.) may be fed directly into R-2 via line
(7), bypassing the Thermal Olefination step. The combined stream
(2) is cross exchanged in EX-1 with stream (8), to recover heat
produced in the catalytic reactor R-2. The outlet stream (3) of
EX-1 is fed into another cross exchanger, EX-2, to further pre-heat
the feed for R-1.
[0145] The pre-heated stream (4) is fed into a Thermal Olefination
furnace (R-1) typically operating at 600-1100.degree. C. and 0-1500
psig. Thermal Olefination reactor (R-1) conducts an endothermic
reaction to produce olefinic compounds via carbon cracking and
dehydrogenation. Excess heat from the reaction is used as the hot
stream (5) for EX-2. The hot stream (6) exiting EX-2 may require
additional cooling for the second reaction stage (R-2). EX-3 is an
optional air-water or refrigerant-based cooling unit for the system
depending upon heating requirements. It is useful here to conduct
the appropriate heat transfer step to ensure proper set-point R-2
inlet conditions. A bypass can be implemented between streams (6)
and (7) and streams (9) and (10) in lieu of cooling utility for
EX-3 and EX-4 for dynamic operability between diesel and gasoline
production. An optional knockout step may be incorporated prior to
the R-2 reactor in stream (7) to capture entrained liquid droplets
and remove all C6+ compounds from entering R-2. See FIG. 4.
[0146] R-2 is catalytic reactor, typically operating at
200-1000.degree. C. and 0-1500 psig, that cracks, oligomerizes, and
under some conditions cyclizes olefinic compounds in
multi-iterative reactions to produce a broad spectrum of
n-paraffins, i-paraffins, naphthenes, and aromatics primarily
across the C.sub.4 to C.sub.16+ range, resulting in high-octane
gasoline or high-cetane diesel spectrum products. Depending upon
the final product desired, excess C.sub.2 to C.sub.12 compounds
from this catalytic reaction can be recycled into fuel grade
constituents. The reaction is very exothermic and can be configured
with or without inter-stage or integrated cooling to prevent
overheating. The excess heat from the reacted stream (8) is used in
EX-1 as the hot stream inlet to step up temperature for the
combined feed (2).
[0147] The hot outlet (9) can support optional cooling for proper
flashing in flash drum D-1. For this reason, EX-4 may not be
required but it could be an air-cooler, water cooler, etc. to
conduct appropriate heat exchange. The flash drum feed (10) is kept
at the pressure of the system and is used to purge targeted light
components from the mixed product stream. The primary function of
D-1 is to control the pressure of the system. Light components (11,
14) consist of mostly H2 and C1-C3 compounds that can either be
purged (14) from the system or directly recycled (11) back into the
system by combining with the flash drum (D-2) lights stream (16)
prior to compressor, C-1.
[0148] D-1 light streams will have H2 and C1 components which are
unreactive for the system and will cause accumulation in the
recycle if not properly removed. H2 and C1 can be purged (14) with
other light components to stabilize the recycle system or a
separator, such as a membrane, can be utilized to selectively
remove H2 and C1. The liquid bottoms (15) from D-1 are fed into D-2
which is set at a lower pressure to remove mostly C3 and C4
compounds from the liquid stream (15). Lights (16) from D-2 are
combined with lights (11) from D-1 to form stream (12) which is
compressed in C-1 and recycled for further reaction. Recyclable
light hydrocarbons (16) from D-2 (typically C2-C4 if targeting
gasoline; C2-C10 if targeting diesel) will be fed back to the
thermal reaction, unless the constituents are olefin-rich which can
optionally be fed directly into R-2 to increase process efficiency.
The resulting flashed liquid stream (17) exiting the bottoms of D-2
is the final product of the process which can be targeted to
produce any range of C4-C12 high-octane gasoline blendstock or
C.sub.9-16+ high-cetane diesel fuel blendstock.
Recycle
[0149] Following the R2 catalytic reaction, the alkane-rich light
gas recycle stream exiting the flash drum condensation unit can be
directed back to the C.sub.2+ Thermal Olefination reactor to be
merged with other incoming light hydrocarbon streams as depicted in
the process flow FIG. 1. The constituents outside the selected
array are gathered into a single-loop recycling configuration. This
recycle process maximizes the yield profile and performance
properties of any type of the liquid effluent produced for
transportation fuel use. Typically, for all compounds not used in a
targeted gasoline range or diesel fuel range the process will
direct the lighter byproducts (e.g. .ltoreq.C.sub.5 for gasoline or
.ltoreq.C.sub.8 for diesel) to be recycled for further upgrading.
Operating with a continuous recycle loop with R2 effluent achieves
high product yields, for example ranging from 65% to 95%.
[0150] Each recycle loop is continuous to allow the random
redistribution of C.sub.6+ liquid hydrocarbons yielded from the
LG2F Process to unite in various formations (e.g., paraffins,
olefins, aromatics) needed for a fuel based upon specific
performance characteristics. Such performance characteristics for
gasoline might include octane, vapor pressure, density, net heat of
combustion, etc., while such characteristics for diesel fuel might
include cetane, thermal stability, cold flowability, and
others.
[0151] Referring to FIG. 4, there is shown a simplified schematic
for an LG2F system in accordance with the present invention. The
system is generally the same as shown in FIG. 3, except a
"Knockout" is provided between reactors R1 and R2. As previously
mentioned, the Knockout unit operates to remove entrained liquids
and C6+ compounds from entering R2.
[0152] By way of example, the fully-recycled thermal and chemical
reactions from processing a feed of 80% C2 (ethane) and 20% C5
(pentane) are depicted in a material balance as shown below in
Table 3a. The process follows the steps in FIG. 4.
[0153] The resulting C.sub.6+ gasoline compounds yielded a 66% mass
conversion of high-performance gasoline with a 25% (17/66% mass as
aromatics) from the C.sub.2/C.sub.5 feed and resulted in an
unexpectedly high 101.7 Research Octane number (using ASTM D2699
Test Method). This illustration using C2 and C.sub.5 as the feed to
Thermal Olefination demonstrates the broad range of gasoline blend
compositions that are possible.
TABLE-US-00016 TABLE 3a Production of Gasoline Blendstock from C2
& C5 feedstock LG2F w/C2 + Process Step C5 w 4 6 8 Recycle 1 2
3 R2 5 Flash 7 Lights 9 Lb/hr Feed R1 Out Knockout Feed R2 Out Tops
Recycle Purge Gasoline H2 5.59 5.59 5.59 5.59 5.59 C1 19.10 19.10
19.11 19.11 19.11 C2 80 148.82 148.82 149.68 149.68 149.68 C2=
75.43 75.43 0.00 C3 0.65 0.65 5.55 5.55 5.55 C3= 9.54 9.54 0.00 C4
0.61 0.61 14.24 14.24 14.24 C4= 2.21 2.21 2.65 2.65 2.65 C5 20 0.00
0.00 14.27 14.27 C5= 0.97 0.97 4.15 4.15 C6 0.13 0.13 11.19 11.19
C7 7.33 7.33 C8 6.01 6.01 C9 4.07 4.07 C10 1.46 1.46 C11 0.48 0.48
C12 0.61 0.61 A6 4.83 4.83 0.19 0.19 A7 1.60 1.60 1.45 1.45 A8 3.64
3.64 A9 5.45 5.45 A10 4.17 4.17 A11 0.94 0.94 Unknown 2.65 2.65
0.82 0.82 Total 100 272.13 9.08 263.05 263.05 196.82 172.12 24.69
66.23
[0154] A similar example shown in Table 3b depicts 100% C2 (ethane)
with an 84% mass conversion to C5+ gasoline (for standard RVP) with
a 25% (21/84% mass as aromatics) and a RON octane value of 93 and a
vapor pressure of 11.6 psi. This demonstrates the broad spectrum of
molecular outcomes typical of all C2-5 feedstreams. The C.sub.2 to
C.sub.5 feedstocks can be fully recycled and converted to gasoline
range molecules based upon the unique operating conditions of the
reactor. The process follows the steps in FIG. 4.
TABLE-US-00017 TABLE 3b Production of Premium Gasoline Blendstock
from C2 (ethane) feedstock LG2F: Process Step C2 w/ 4 6 8 Recycle 1
2 3 R2 5 Flash 7 Lights 9 Lb/hr Feed R1 Out Knockout Feed R2 Out
Tops Recycle Purge Gasoline H2 4.67 4.67 4.67 4.67 4.67 C1 10.68
10.68 10.69 10.69 10.69 C2 100 238.41 238.41 239.32 239.32 239.32
C2= 108.32 108.32 0.00 0.00 0.00 C3 1.11 1.11 7.36 7.36 7.36 C3=
2.33 2.33 C4 0.88 0.88 18.71 18.71 18.71 C4= 1.77 1.77 3.39 3.39
3.39 C5 22.94 22.94 C6 0.22 0.22 14.35 14.35 C7 9.39 9.39 C8 7.70
7.70 C9 5.22 5.22 C10 1.87 1.87 C11 0.62 0.62 C12 0.78 0.78 A6 0.39
0.39 0.24 0.24 A7 1.86 1.86 A8 4.66 4.66 A9 6.99 6.99 A10 5.35 5.35
A11 1.21 1.21 Unknown 1.05 1.05 Total 100 368.78 0.39 368.39 368.39
284.14 268.78 15.36 84.25
[0155] This illustration also depicts how specific operating
conditions can be used to control the resulting slate of compounds.
The temperature of Reactor 2 was 250.degree. C. which resulted in a
25% m/m aromatic content. The aromatic content is variable and can
be used to increase octane values of gasoline blendstocks. Surplus
C6+ aromatics can be captured from the knockout as byproducts for
petrochemical processing. Increasing the temperature of reactor 2
from 250.degree. C. to 400.degree. C. doubles the content of
desirable aromatics in the gasoline blendstock and thereby
increases the resulting octane. The lights purge (via flash drum
and membrane separation) allows methane and hydrogen byproducts to
be reused in other downstream processes. Table 3c is similar for a
C6+ compounds (>98 RON with vapor pressure of 7.8 psi) gasoline
with a total yield of 79% from 100% ethane; aromatics were 35%
(28/79) of the total yield. The process follows the steps in FIG.
4.
TABLE-US-00018 TABLE 3c Production of Gasoline from C2 (ethane)
feedstock (high-octane, low RVP) LG2F: Process Step C2 w/ 4 6 8
Recycle 1 2 3 R2 5 Flash 7 Lights 9 Lb/hr Feed R1 Out Knockout Feed
R2 Out Tops Recycle Purge Gasoline H2 6.09 6.09 6.09 6.09 6.09 C1
13.94 13.94 13.95 13.95 13.95 C2 100 311.16 311.16 312.63 312.63
312.63 C2= 141.38 141.38 C3 1.45 1.45 9.61 9.61 9.61 C3= 3.04 3.04
C4 1.15 1.15 24.94 24.94 24.94 C4= 2.31 2.31 4.45 4.45 4.45 C5
29.68 29.68 29.68 C6 0.28 0.28 18.60 18.60 C7 12.17 12.17 C8 9.98
9.98 C9 6.76 6.76 C10 2.42 2.42 C11 0.80 0.80 C12 1.01 1.01 A6 0.51
0.51 0.31 0.31 A7 2.42 2.42 A8 6.04 6.04 A9 9.06 9.06 A10 6.93 6.93
A11 1.57 1.57 Unknown 1.36 1.36 Total 100 481.31 0.51 480.80 480.80
401.36 381.31 20.05 79.44
Enhanced R2 Reactor--Dual Phase Catalytic Quench
[0156] This invention includes a new reactor design shown in FIG.
19, featuring a dual phase catalytic quench (DPCQ) method of
processing gas and liquid phase feedstreams in a cross-current
technique whereby the liquid phase compounds effectively wash the
oligomerization catalyst held in a static-bed configuration and
vaporous gases pass in a counterflow direction through the reactor
chamber. This technique can be operated at 300-1200 psi but
preferable from 400-600 psi with operating temperatures near the
dew point of the liquid feed at such pressure, but generally at
250-450.degree. C. Our research has found that the combination of
catalytic reaction and molecular absorption methods in a
non-adiabatic chamber tends to slow the activity level of the
exothermic reaction, thereby allowing greater control over the
product selectivity. Our research shows that the key aspects of
this DPCQ technique include a) longer catalyst life with virtually
no catalytic regeneration required due to the effect of washing the
catalyst, b) a decrease in catalytic activity levels thereby
improving product selectivity and fuel quality without modifying
the chemistry of the catalyst, and c) a lower projected total cost
of operation by consolidating the catalytic reactor(s) and
absorption functions into a single static-bed design that operates
with greater than 50% less operational downtime.
[0157] This DPCQ technique can be applied to any appropriate R2
related oligomerization-type reactions in the LG2F process used to
make targeted hydrocarbon end-product such as gasoline and diesel
fuel.
Product Selectivity
[0158] The LG2F process uses the feed composition, the Thermal
Olefination reaction, and the zeolite catalyst operating conditions
(T, P, SV) to establish a predictable result to various fuel
performance criteria described on industry fuel specifications. The
following outlines how this technique is achieved. Also, see FIGS.
5 and 6.
[0159] In one aspect, the process is configured to produce a
desirable, broad-range of fuel products. The fuel products are
typically in the C5-24+ range of hydrocarbon fuels or fuel
blendstocks. The range of fuel products depends in part on the
C2-C5 alkane feedstream and is controlled based on operation of the
LG2F Process. In one approach, the fuel products are determined in
the following manner. First, the available feedstream is analyzed
in relation to the desired fuel target. Then a baseline is
established taking into account the nature of the feedstream and
typical operating conditions for the LG2F Process. For example, it
can be established that a given feedstream, e.g., 100% ethane, will
produce a predictable array of fuel products with the operation of
the Process at certain conditions of temperature, pressure, space
velocity and recycle.
[0160] It can further be determined that changes to these
conditions will move the product mix in one direction or another.
For example, raising the temperature in the zeolite-catalytic
reactor R2 will increase cracking of the hydrocarbons and the
production of lighter aromatics, resulting in a lower final boiling
point of the targeted fuel. A higher pressure, used for example in
a secondary R2 reaction will increase the chain-length of middle
distillate compounds produced, also impacting the final boiling
point of diesel fuel. Higher space velocities result in a higher
exotherm temperature which produces lighter compounds (as depicted
in FIGS. 5a and 6a). Higher reactor temperatures at a fixed space
velocity and pressure reflect a similar tendency to produce lighter
compounds (as depicted in FIGS. 5b and 6b). In this manner, it is
possible to identify baseline reactor operating conditions and then
adjust from there to produce differing product mixes.
Upper Boiling Limit
[0161] The temperature of the R2 reactor(s), particularly the
second R2 reactor if used in series, is used to prescribe the
cut-point of the fuel product, which determines the limit of the
final boiling point of the fuel. For example, a fuel specification
may call for a final boiling point of 340.degree. C. or 225.degree.
C. or 180.degree. C. and the reactor conditions can be set to limit
the upper boiling condition to a specific temperature.
TABLE-US-00019 TABLE 4 Upper Boiling Point Reason R2 - Zeolite
Operating Condition To include C12 FBP 225.degree. C. Baseline R2
Reactor - 275-325.degree. C. (less cracking) To include C11 FBP
215.degree. C. Baseline R2 Reactor - 325-375.degree. C. To include
C10 FBP 200.degree. C. Baseline R2 Reactor - 400.degree. C.
(hot/more cracking) To include C18 Mid Cetane Baseline R2 Reactor -
(hot/more aromatics) To include C17 Best Pour Point Baseline R2
Reactor - (less hot) To include C16 High Cetane Baseline R2 Reactor
- (cool/less aromatics)
Lower Boiling Limit
[0162] The use of a single stage flash-drum with a preset
liquid-vapor temperature limit can establish any lower bound to the
liquid fuel without the expense of cryogenics or complex
multi-stage fractionation columns. The flash-drum temperature is
set at a predetermined point (e.g. for C4 butane (high RVP) for the
preferred liquid/vapor cut. The level of precision can be enhanced
by using a 2-stage drum.
TABLE-US-00020 TABLE 5 Low Boiling Point Reason Flash Cut Point To
include C4 High RVP set flash at 0.degree. C. To include C5 Mid RVP
set flash at 27.degree. C. To include C6 Low RVP set flash at
50.degree. C. To include C7 Aromatic Cut Set flash at 105.degree.
C. To include C9 High Cetane set flash at 125.degree. C. To include
C10 High Cetane set flash at 150.degree. C.
Benzene Knock-Out Feature
[0163] The Thermal Olefination reaction is known to produce small
amounts of benzene, which typically has a control limit in fuels.
Accordingly, the LG2F Process utilizes an optional liquid-vapor
knockout separation technique set at or below the boiling point of
benzene at the appropriate pressure to capture any light aromatics
exiting Thermal Olefination. In some embodiments, benzene be
separated prior to the R2 reaction. In some embodiments, benzene
may alhydrate with olefins in the R2 reaction. In some embodiments,
the knockout feature may be undesired as BTX aromatics may be the
preferred product for use as a petrochemical feedstock. Since C2-C5
hydrocarbons are generally cracked into C5 and smaller compounds,
the primary exception to this is the production of the liquid C6H6
aromatic (albeit valued in select markets) which can then be
largely eliminated from the final fuel. This compound can be
marketed as BTX or reacted with olefins to make C7+ alky-aromatics
to increase octane in gasoline.
Aromatics Content in Gasoline
[0164] The temperature of the R2 Reactor is used to pre-determine
the level of activation which directly effects aromatic production.
Accordingly, the higher octane gasoline formulations favor a C7-C10
aromatic content of up to 50%.
This results in the following operating conditions:
TABLE-US-00021 TABLE 6 Activation Level Reason Aromatics in
Gasoline High High octane Up to 55% C7+ aromatics; (RON > 95)
Baseline + 60-100.degree. C. Medium Mid octane Up to 20% C7+
aromatics; (RON > 91) Baseline + 20-60.degree. C. Low Low octane
Up to 15% C7+ aromatics; (RON > 89) Baseline reactor at
320.degree. C.
Aromatics Content in Distillate
[0165] The temperature of the R2 reactor is used to pre-determine
the level of activation which directly affects aromatic production.
Accordingly, the higher cetane formulations favor lower aromatic
content of less than 25%. The aromatic content of diesel fuel is
limited to not exceed 35% and the presence of C16+ aromatics can
impede the cetane performance. So the diesel fuel spectrum is
generally targeted to C9-C16 range compounds and aromatic content
is limited to <35%. This results in the following operating
conditions:
TABLE-US-00022 TABLE 7 Activation Level Reason Aromatics in
Distillate High Low cetane Up to 35% C9+ aromatics in distillate;
(<40) Baseline + 100-175.degree. C. Medium Mid cetane Up to 30%
C9+ aromatics in distillate; (>40) Baseline + 50-100.degree. C.
Low High cetane Up to 25% C9+ aromatics in distillate; (>45)
Baseline reactor conditions
[0166] Gasoline performance was measured using ethylene with
baseline operating at 320.degree. C., atm (0 psig) and 0.75 WHSV.
Space velocity graphs using aliphatics and aromatics were performed
at atm (0 psig) at temperature 284.degree. C., 293.degree. C.,
318.degree. C. and 343.degree. C. All results demonstrate the core
principles for determining the appropriate R2 reactor operating
conditions to produce performance fuels. The actual operating
parameters will vary depending upon the feedstream. Diesel fuels
follow the same basic chemistry and thermodynamic principles as
gasoline spectrum reactions.
[0167] Control of operating parameters (Temperature, Pressure,
Space Velocity) can directly impact the scope and range of
molecules produced in a catalytic oligomerization unit. Temperature
directly impacts the level of cracking that occurs during
oligomerization. An increased temperature causes more cracking to
occur which will result in smaller molecules to be produced. Lower
temperature will produce longer chained molecules as they crack
less while coupling still occurs.
[0168] High pressures are preferred for diesel range production as
a higher gas concentration will allow for more opportunities for
coupling. Locally, more molecules will occupy a given area at high
pressure allowing for more reactions to occur in a given time
frame. Modifying pressure will have a direct impact on the boiling
point of the product as more pressure would create longer
molecules. However, more reactions due to high pressure will
significantly increase the exotherm so the energy would need to be
removed at the rate of generation to minimize cracking.
[0169] The same applies for space velocity where an increased space
velocity gives a shorter duration of residence time on the catalyst
but more reactions per second that will increase temperature as
well. Chain propagation can be reduced at high space velocities at
the expense of an increased exotherm. Thus, proper heat management
can dynamically control product slate, distribution and final
boiling point while modifying pressure and space velocity.
Recovery from Entrained C3+ Hydrocarbons from Gas Flows
[0170] This invention utilizes a novel technique to maximize liquid
volume yield by extracting H2 and all vapor-phase entrained
hydrocarbons from a light gas stream comprised of any combination
of C1-C5+ hydrocarbons at near ambient temperatures. The preferred
embodiment of this liquid separation process uses a quench tower to
strip all C3+ vapor-phase hydrocarbons and H2 at temperatures
ranging from about 8.degree. C.-40.degree. C. thereby eliminating
the need to require cryogenic or subzero processing temperatures
that could greatly increase utility costs. This is in direct
contrast to traditional absorber technology methods known to those
schooled in the art of gas processing which require repeated
low-temperature cooling cycles as gases are absorbed from the
stream which results in the need for a repetitive, capital
intensive process of subzero cooling.
[0171] This invention operates the quench tower (stripper) shown in
FIG. 20 below at pressures up to 1000 psi, but preferably at about
400 psi. However, the downstream stabilizer and recycle loop
feeding the Thermal Olefination reactor (R1) are stepped down to
lower pressures ranging from 14 to 140 psi. Our research experience
for the R1 Thermal Olefination reactor shows that sending a recycle
stream at high pressures (e.g. above about 140 psi) to be operated
at temperatures above 500.degree. C. will result in lower olefin
conversions and trigger serious challenges in the metallurgy of the
reactor tubes that could also damage the welds, joints and
junctions to the downstream transfer line exchanger. For this
reason, the recycle stream feeding R1 necessitates a low-pressure
operation. Accordingly, the preferred operating condition of the
Thermal Olefination reaction is a low-pressure environment
operating at no more than 140 psi. The preferred embodiment of this
liquid separation process utilizes a compressor upstream of the
quench tower (stripper) to provide effective operating conditions
for maximizing the extraction of all light vapor-phase components,
while lowering the pressure of the stabilizer (14-140 psi).
Accordingly, this low-pressure environment for the stabilizer also
prevents unnecessary vaporizing and recycling of valuable liquid
product.
[0172] This unique design utilizes a quench tower and stabilizer
with low cost utilities while eliminating the capital-intensive
cost of cryogenics. The higher cost of subzero cooling, cryogenics
and compression are not cost-justified for merely extracting the
last marginal portion of entrained liquids from the gas stream.
[0173] The unique design also depicts the partial separation of
methane and hydrogen for alternate uses including powering the LG2F
utilities. Also, a balanced portion of these gases is used as a
diluent in the R1 reaction to control effective heat duty.
[0174] In one aspect of the liquid recovery design, if liquid
streams being produced in the quench tower become overly saturated,
i.e. C4/C5 lights overflow to heavies, then a flash drum can be
used to separate the C4/C5 compounds to re-stabilize the quench
process. In this case, the C4/C5 compounds exiting the flash drum
can be quenched and commingled with the feed to the stabilizer.
Also in this case, the remaining heavies can be split between the
stabilizer and the remaining majority (i.e. 50-98% of the split
volume) being merged and fed into the quench column.
Commercial Significance
[0175] The LG2F Process and System allows for the midstream or
refinery production of performance-grade fuels which are tailored
to meet ever-changing industry performance criteria in areas where
stranded light hydrocarbons are not accessible to traditional fuel
and petrochemical supply chains. The US NGL market currently
rejects approximately 407,000 BPD of ethane (.about.10% of the
total production NGL's) by selling ethane as natural gas where an
ethane market does not exist, despite ethane's higher volumetric
BTU value.
[0176] Eliminating the "ethane rejection" mode opens up the
opportunity for more cost efficient gasoline and diesel fuel
production from NGL's and streamlines otherwise stranded, shut-in,
or flared methane gas reserves. LG2F also offers a low-cost pathway
to upgrade ethane, propane and butane+ compounds to
performance-grade fuel values or in some cases petrochemical
feedstocks. Producing gasoline and diesel to a fuel performance
standard reduces unnecessary logistics costs and allows fuels to
enter markets via the existing finished product fuel supply
chains.
[0177] The LG2F Thermal Olefination reaction (R1) along with the
catalytic reaction (R2) and recycle loop can be used independently
and can be interchangeably tailored based upon feedstock
composition and desired end products to produce gasoline
blendstocks and/or diesel fuel blendstocks. The process is flexible
to allow the reactor operating conditions to be established to
produce the desired blend components and compositional features to
meet fuel performance requirements (e.g. aromatics for gasoline
octane value, cetane for diesel performance). The byproducts of the
reaction may include methane and hydrogen.
[0178] The tailoring effects of the gasoline and diesel fuel
reactions include a variety of factors including the final boiling
point cut-off of the product, the lower cut-off of the
product--both of which are based on the operating conditions for
any given feedstream. Other factors include the % m/m of C6
aromatics, the % of C5 used in the gasoline (RVP index), the cetane
number, the % aromatics, the % C18+ compounds, etc.
[0179] A major feature of the LG2F Process is the targeting of
performance grade fuel products. Rather than indiscriminately
producing a stream of random hydrocarbons, this invention serves to
tailor the process and operating conditions for specific purposes.
For example, when targeting gasoline, C4 and C5 compounds typically
have higher vapor pressure and lower octane values than preferred
C6-C12 compounds, so too much concentration of C4/C5 compounds in
the targeted fuel will result in a low-grade off-spec fuel.
Similarly, high-performance gasoline with more than 50% aromatics,
while high in octane, can be undesirable for environmental
emissions. Yet other users of the process may prefer to produce a
very high concentration of aromatics in a constrained market--only
to be used as blendstocks with other surplus components (e.g.
before blending into a final fuel at a refinery). In yet another
example, the presence of excess benzene can also be on operating
limitation to some fuel specifications. Diesel fuel requires a high
proportion of C9-C16 compounds with relatively high cetane values;
diesel also requires hydrocarbons that do not form wax (solids) at
lower temperatures. Accordingly, this invention offers a wide
variety of process techniques and optionality for the user to
configure the catalytic operating conditions to meet the intended
performance-grade product outcomes.
[0180] An optional feature of LG2F is to produce C4 and C5 alkanes
which may be useful for increasing the volatility and raising the
vapor pressure in gasoline, although often at the expense of octane
levels. Thus, some or all the C4-5 alkanes may be targeted for
production into the gasoline blendstock. Alternatively, C4 or C4-05
production may be avoided, in which case the process directs
.ltoreq.C.sub.4 or .ltoreq.C.sub.5 byproducts to be recycled for
further upgrading.
[0181] It will be appreciated that the LG2F Process can include
split multi-iterative variations of both R1 and R2 that may require
more than a single recycle loop for optimal operation. As an
example, R2 may be separated into two or more reaction sequences
with some form of separation between and after the operations. The
separation off-gas may be merged or recycled independently and at
different locations from one another.
LG2F Products
[0182] The process configuration utilizes a recycle loop to produce
a specified range, for example C.sub.5 to C.sub.12 gasoline
compounds or C.sub.9 to C.sub.20 diesel fuel compounds for use as
blendstocks in high grade transportation fuels. Using the LG2F
process, the liquid yields using recycling can range from 65% to
95+% of the initial feedstream depending upon the severity of
operating conditions. This process offers flexibility in making
paraffinic molecules of higher yield, or olefinic molecules and
aromatic hydrocarbons of somewhat lower yields for gasoline range
products, or alternatively, it can be switched to create a blend of
middle distillates (primarily paraffins, olefins and aromatics)
primarily for diesel range products. As an alternative, excess
methane can be used as process fuel or recycled into fuels.
Gasoline Blendstocks
[0183] In one aspect the LG2F Process is tailored to the production
of gasoline blendstocks, as exemplified in the foregoing
discussion. As used herein, the term "gasoline blendstock" refers
to a formulation comprising n-paraffins, iso-paraffins,
cyclo-paraffins, olefins and aromatics having 4 to 12 carbons. The
gasoline blendstocks from this invention preferably have 5-12
carbons, and more preferably comprise 6-11 or 7-10 carbons. The
gasoline blendstocks also typically have branched-chain paraffins
and aromatic hydrocarbons having 6 to 11 carbons, preferably 7 to
10 carbons. In preferred embodiments, the LG2F Process yields a
product containing at least about 65% C5-10 branched-chain
paraffins and at least 25% C7-9 aromatic hydrocarbon compounds. The
following examples further demonstrate the ability to tailor the
LG2F Process depending on the C2-5 feedstream and the desired end
product(s).
TABLE-US-00023 TABLE 8 Typical Gasoline Composition Typical
Gasoline Constituents C4 C5 C6 C7 C8 C9 C10 C11 C12 n-paraffins X X
X X .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. iso-paraffins X X X X X X X .largecircle.
.largecircle. cyclo-paraffins X X X X X X .largecircle.
.largecircle. olefins X X X X X X .largecircle. .largecircle.
aromatics X X X X X .largecircle. .largecircle.
[0184] While the gasoline blendstocks described as the products of
LG2F in this invention may be comprised of varying chemical
compounds, the compounds output from this invention is not randomly
indiscriminate. This is accomplished as described herein by, inter
alia, selection of C2-5 Alkane Feedstreams, operating parameters
and recycle between the R1 and R2 reactors. The production of
high-performance gasoline requires the adherence to a minimum set
of performance conditions for gasoline grade products. The LG2F
Process produces, for example, fuel compositions and blendstocks
including the following:
[0185] In one embodiment, the gasoline compound is .gtoreq.95
research octane number (RON) with no ethanol, with a .gtoreq.9 psi
vapor pressure (RVP) but .ltoreq.13.5 psi, aromatic content
.ltoreq.50% m/m and with benzene content below 1.30% (v/v), and a
final boiling point <225.degree. C.
[0186] In one embodiment, the gasoline compound is >95 RON with
no ethanol, with a vapor pressure .gtoreq.9 psi but .ltoreq.13.5
psi, aromatic content <55% m/m and with benzene content below
1.30% (v/v), and a final boiling point <225.degree. C.
[0187] In one embodiment, the gasoline compound is .gtoreq.91
[using R+M/2] with no ethanol, with a vapor pressure .gtoreq.9 psi
but .ltoreq.13.5 psi, aromatic content .gtoreq.35% m/m and with
benzene content below 1.30% (v/v), and a final boiling point
<225.degree. C.
[0188] In one embodiment, the gasoline compound is .gtoreq.89
[using R+M/2] with no ethanol, with a vapor pressure .gtoreq.9 psi
but .ltoreq.13.5 psi, aromatic content .gtoreq.35% m/m and with
benzene content below 1.30% (v/v), and a final boiling point
<225.degree. C.
[0189] In one embodiment, the gasoline compound is .gtoreq.87
[using R+M/2] with no ethanol, with a vapor pressure .gtoreq.9 psi
but .ltoreq.13.5 psi, aromatic content .ltoreq.30% m/m and with
benzene content below 1.30% (v/v), and a final boiling point
<225.degree. C.
[0190] In one embodiment, the gasoline compound is .gtoreq.84
[using R+M/2] with no ethanol, with a vapor pressure .gtoreq.9 psi
but .ltoreq.15.0 psi, aromatic content .ltoreq.25% m/m and with
benzene content below 1.30% (v/v), sulfur content below 0.008%
(m/m), and a final boiling point <225.degree. C.
C2-5 Hydrocarbons to C6-8 Aromatics
[0191] In an embodiment, the LG2F Process is tailored by isolating
the catalytic R2 reaction to convert C2-C5 light olefin feedstocks
into aromatic hydrocarbons comprising a narrow range of C6 to C8
aromatics for use as a high-octane fuel blendstock or petrochemical
use. This is done by use of operating conditions to obtain an
aromatic yield up to the upper boiling limit of o-xylene, for
example 145.degree. C., and recycling all byproducts in the flash
drum with boiling points below benzene at 80.degree. C. The yield
of C6 to C8 aromatics is valuable to the petrochemical market as a
base aromatic feedstream to aromatics fractionation or as an
alternative, if the BTX product stream is first processed by a
hydrodealkylation step to decouple and remove ethyl-propyl and
butyl-aromatic constituents leaving only methyl-aromatic
products.
C2-5 Hydrocarbons to C7-8 Aromatics
[0192] In another embodiment, this invention can be tailored by
isolating the catalytic R2 reaction to convert C.sub.2-C.sub.5
light olefin feedstocks into aromatic hydrocarbons in a narrow
range of C.sub.7 to C.sub.8 aromatics. Again, this is done by
targeting the aromatic yield up to the upper boiling limit of
o-xylene, for example 145.degree. C., and recycling all byproducts
in the flash drum with boiling points below toluene at 110.degree.
C. The yield of C.sub.7 and C.sub.8 aromatics have a very
high-octane value and a very high energy density in the absence of
benzene and are useful gasoline blendstocks to meet premium
high-octane grades.
C2-5 Hydrocarbons to C8 Aromatics
[0193] In another embodiment, the LG2F Process is tailored by
isolating the catalytic R2 reaction to convert C.sub.2-C.sub.5
light olefin feedstocks into aromatic hydrocarbons in a narrow
range of solely C.sub.8 aromatics by targeting operating conditions
for the aromatic yield up to the upper boiling limit of o-xylene,
for example 145.degree. C., and recycling all byproducts in the
flash drum with boiling points below p-xylene at 138.degree. C. The
yield of C.sub.8 aromatics will have a very high-octane value and a
very high energy density which can be a useful gasoline blendstock
to meet premium high-octane grades. In addition, these C.sub.8
compounds may be further valuable to the petrochemical market,
particularly if they are produced by a hydrodealkylation step to
decouple and remove any close-boiling ethyl-aromatic constituents
and produce methyl-aromatic products.
C2-5 Hydrocarbons to C7-9 Aromatics
[0194] In one embodiment, this invention is tailored by isolating
the catalytic R2 reaction to convert C.sub.2-C.sub.5 light olefin
feedstocks into aromatic hydrocarbons in the C.sub.7 to C.sub.9
range by specifying operating conditions for the aromatic yield up
to the upper boiling limit of trimethylbenzenes, for example
175.degree. C., and recycling all byproducts in the flash drum with
boiling points below toluene at 110.degree. C. The yield of C.sub.7
to C.sub.9 aromatics will have a very high-octane value and a very
high energy density, without the presence of benzene, and can be a
useful gasoline blendstock to meet premium high-octane grades.
C2-5 Hydrocarbons to High-Octane Aliphatic Compounds
[0195] One specialized technique to produce high-octane gasoline
blendstocks is the use of LG2F in a tailored fashion to limit the
production of aromatics and instead produce high-octane aliphatic
compounds by the targeted conversion and/or dimerization of C2-C4
alkanes and olefins without coupling or cyclizing of the reaction
to produce fuels without the expense of complex fractionation. This
is achieved without traditional high-toxicity HF and H2S type
alkylation methods by setting the synthesis protocol and operating
conditions of the catalytic R2 chemical reaction(s) to produce the
desired product stream. All light hydrocarbon gases below a lower
targeted boiling point limit are recycled to maximize the yield
potential of this technology. This technique allows production of a
simple narrow band of desirable of C6, C7, or C8+ hydrocarbons (in
one preferred case C7 trimethylpentenes) from C2+ light gases that
may be particularly valuable to the high-octane gasoline blending
process while avoiding the production or use of benzene and C7-C9
aromatics traditionally used by refiners to increase the octane
value of the fuel.
[0196] This version of the LG2F process is particularly tailored to
selectively convert or dimerize C2-C4 feedstreams with catalysts at
low activity levels to make higher carbon products while minimizing
cycling and coupling of the molecules during the R2 catalytic
reactions to make aliphatic hydrocarbons. This technique will serve
to maximize the yield of targeted high-octane gasoline blendstocks
comprised of C6, C7 or C8+ aliphatic hydrocarbons or in some
configurations longer-chain diesel fuel blendstocks comprised of
C9-C16+ aliphatic hydrocarbons.
[0197] The choice of feedstream may include those comprising a)
light C2-C4 alkanes (e.g. from wet gas processing or industrial
sources), or b) light C2-C4 alkenes (e.g. from refinery FCC units,
specifically as byproducts of a ZSM-5 catalytic reaction).
[0198] In one aspect using wet-gas supply sources, feedstreams
comprised of C2+ alkane-rich hydrocarbons flow into the R1 Thermal
Olefination reaction producing C2+ alkenes which are subsequently
passed to a R2 catalytic reaction to be dimerized by one or more
sequential R2 reactions using various specialized zeolite catalysts
including those in proton form. A wide range of available zeolite
catalyst processes are known to those schooled in the art. In
addition, non-zeolite catalysts (e.g. Cobalt/triethyl-aluminum,
Ni-MFU-41, etc.), may also be utilized for selective dimerization
reactions targeting C4+ alkenes. The R2 effluent may then pass into
an optional skeletal isomerization technique using ZSM-35 to
created high-valued iso-alkanes for specialized uses. Unreacted C1+
alkanes comprised in the R1 effluent can be carried throughout each
of the catalytic reactions and the light-ends extracted by the
liquid recovery module can be recycled back to R1 to be merged with
fresh feedstreams to optimize the overall process and maximize
yields. Unreacted light alkenes can be recycled while the C6+
liquid streams can optionally then be hydrogenated for use as
high-octane gasoline blendstocks and/or C9+ liquid streams for
diesel fuel. A truncated version of this aliphatic production
process can occur when concentrated sources of either ethene or
butene are available to be fed directly into the R2 catalytic
reaction(s) (i.e. bypassing the need for Thermal Olefination) again
using the R2 dimerization process with the specialized catalysts
including those in proton form, with or without skeletal
isomerization, followed by the liquid recovery process and light
gas recycle loop back to R2 catalytic reaction process, after which
the C6+ aliphatic liquids are recovered, with or without a
hydrogenation step as may be required for fuel quality.
[0199] In one aspect using refinery processes, light gas
feedstreams comprised of C2+ alkene-rich hydrocarbons are captured
as a byproduct of adding ZSM-5 catalyst to any refinery Fluid Cat
Cracking (FCC) process to effectively crack C7+n-paraffin compounds
typically produced in such processes. This inventors prior art has
shown that these C7+n-paraffins have very low octane values.
Refiners often avoid such n-paraffin cracking in the FCC unit (and
the use of ZSM-5 zeolites) as it reduces the FCC liquid yield via
the production of large amounts of unwanted light C3-C4 alkenes.
However, this LG2F invention selectively captures these C2-C4 light
alkene gases (preferably propene and butene) and converts them into
high-value C6, C7 and C8+ liquid aliphatic hydrocarbons--notably
without the formation of aromatics--for use in gasoline. The
alkene-rich feedstreams comprised of C3 and C4 alkenes pass
directly into an R2 catalytic reaction process at appropriate
temperature (up to 550.degree. C.) and pressure (up to 750 psi)
using weak-acidic catalysts generating lower activity levels by
using post-transition metals and/or metalloids, preferably Ga(III),
Zn(II), In(III), B(III), Ge(IV) or Bi(V). Reactor design is any
variety of plug-flow, semi-regen or continuous regeneration
capability using fixed or fluidized bed design based upon the best
practices of those skilled in the art. The resulting R2 liquid
effluent is condensed via the quench and stabilization process
resulting in a C6+ liquid admixture comprising high-octane
di-methyl or tri-methyl alkenes (i.e. typically -butene and/or
-pentenes); see chart. This fuel blendstock may be used directly as
a fuel blendstock or it may be further hydrogenated or mixed with
antioxidants depending upon the degree of tailoring needed in the
finished blendstock. The resulting upgrade from C7+n-paraffins to
C3-C4 alkenes to C6+ high octane fuel by this invention is coupled
with the benefit that the n-paraffin octane "penalty" of the FCC
liquid stream is erased via ZSM-5 cracking, making the resulting
FCC liquid effluent (containing aromatics) a higher octane refined
product admixture as well, thereby providing a double benefit.
TABLE-US-00024 Admix C6+ Compounds # Carbons ASTM Motor Octane
Number 2,3-Dimethyl-1-butene 6 128 2,4-Dimethyl-2-pentene 7 123
2,3,3-Trimethyl-1-butene 7 130 2,4,4-Trimethyl-1-pentene 8 156
Example Alkene Compounds in the C6+ Aliphatic Admixture
[0200] In one embodiment of the LG2F process tailored to produce
high-octane non-aromatic fuels, a hydrocarbon feedstream comprised
of >80% isobutane is processed by the R1 Thermal Olefination
reaction operating at about 400-700.degree. C. to form an effluent
comprised of high concentrations of isobutene along with unreacted
iso-alkanes which is then enters the R2 catalytic reaction and the
iso-alkenes are dimerized using specialized zeolite catalysts
including in a proton form configured with or without particular
metals (e.g. B, Ga, Zn, Ni, Co, Ca, etc.) to directly convert the
isobutene to an aliphatic liquid comprised of C8 trimethylpentenes.
The preferred embodiment of the R2 reaction utilizes a dealuminated
zeolite H-beta catalyst with Si/Al ratio of 30, operating below 150
psi at 30-100.degree. C., to selectively dimerize isobutene. The R2
catalytic reaction converts at least 50% of the isobutene to C8
alkenes per pass. Any non-olefin hydrocarbon byproducts comprised
in the R1 effluent are unreacted in the R2 catalytic process. This
R2 reaction is tailored to limit the dimerization of n-olefins if
they exist that might otherwise reduce octane values in the
targeted C8 stream of trimethylpentanes. The R2 effluent is then
processed by one or more liquid recovery processes (e.g. quench and
stabilization) to recycle the light ends of the R2 effluent
comprised of unreacted alkanes and olefins. The R2 effluent >C4
is then hydrogenated in preparation to produce effective fuel grade
blendstocks and is then separated to isolate the C8 branched
alkanes from the >C8 branched alkanes. As an alternative, the
.ltoreq.C4 light gas recycle stream may be hydrogenated prior to
recycling to increase the presence of alkanes in the merge stream
prior to reentering the R1 Thermal Olefination process, but this is
an economic decision. The hydrogenated liquid effluent from R2 is
then passed via simple separation, either via knock-out or
optionally under higher pressure to condense the liquids, to
isolate the C8 stream comprised of high octane trimethylpentanes
from >C8 stream comprised of C12 and higher alkanes desirable
for diesel fuel. The hydrogenation step may utilize hydrogen from
the membrane separation process or from any available hydrogen
source.
[0201] In another embodiment tailored to produce non-aromatic fuel
compounds, shown in FIG. 21, a feedstream comprising >80% of the
combination of n-butane and isobutane in a ratio of 0-1:1.0, the
alkanes are fed single pass in the absence of a recycled stream
into the R1 Thermal Olefination process whereby n-butenes and
isobutenes are produced with >80% alkane conversion and passed
to the specialized R2 dimerization process using specialized
zeolite catalysts including in a proton form to convert the
isobutenes to isooctenes and higher while leaving the n-butenes
virtually unreacted. In this case, unconverted C4-alkanes and
n-butenes are high-vapor pressure byproducts of this reaction
useful for selective gasoline blending.
[0202] In another embodiment, a feedstream comprising >80% (wt)
of the combination of n-butane and isobutane in any ratio ranging
from 0-1:1.0 respectively is fed into the R1 Thermal Olefination
process operating at about 400-700.degree. C. whereby an effluent
stream comprised of proportional amounts of n-butene and isobutene
results in >80% "fresh" alkane conversion. This R1 effluent is
then passed to the specialized R2 alkene dimerization process using
specialized zeolite catalysts including in a proton form configured
with or without particular metals (e.g. B, Ga, Zn, Ni, Co, Ca,
etc.) to directly convert the isobutene to an aliphatic liquid
comprised of C8 trimethylpentenes, while n-butenes are unreacted.
The preferred embodiment of the R2 reaction utilizes a dealuminated
zeolite H-beta catalyst with Si/Al ratio of 30, operating below 150
psi at 30-100.degree. C., to selectively dimerize isobutene. The R2
catalytic reaction converts at least 50% of the isobutene to C8
alkenes per pass. Unreacted light gases exiting the R2 catalytic
reaction are isolated during the liquid recovery (quench) process
and those comprising n-butenes and isobutene are then passed
without fractionation directly to a specialized single or
multi-loop n-butene isomerization reaction to increase the
proportion of isobutene in this admixture by up to 20-50%. This
skeletal isomerization process preferably utilizes a dealuminated
ZSM-35 zeolite catalyst operating at about 400.degree. C. with WHSV
5 h-1 or other preferred methods known to those skilled in the art
of n-butene isomerization. Iso-alkanes and iso-alkenes in this
specialized isomerization process are unreacted. The resulting
isomerized effluent, now comprised of a higher concentration of
isobutene, is then recycled and merged to re-enter either the R1
Thermal Olefination reaction (if the merged stream is alkane-rich)
or the R2 catalytic reaction (if the merged stream is alkene-rich)
to maximize C8+ liquid product yield. The C5+ liquid recovered from
the R2 effluent is then hydrogenated and passed via simple
separation, either via knock-out or optionally under higher
pressure to stabilize and condense the liquids, to isolate the C8
stream comprised of high octane trimethylpentanes from >C8
stream comprised of C12 and higher alkanes desirable for diesel
fuel. The hydrogenation step may utilize hydrogen from the membrane
separation process if utilized for system equilibrium or from any
available hydrogen source.
[0203] In another embodiment, a refinery FCC unit is tailored to
use zeolite catalysts to generate a surplus of isobutene gas. This
stream of light gas comprising >80% (wt) isobutene is then
isolated from the remaining FCC effluent and passed directly to the
R2 catalytic process (not depicted). In this example, the R1
Thermal Olefination process is unnecessary and the LG2F recycle
loop following the R2 reaction can merge and reenter the R2
catalytic reaction. In one case, methane and hydrogen may accompany
the isobutene stream from the source to provide an equilibrium for
fuel, as diluent and for hydrogenation proposes. In a different
case, "on-purpose" methane or hydrogen can be supplied to balance
the LG2F process needs and thereby avoid the need for the membrane
separation process.
[0204] In a similar embodiment, any available feedstream comprised
of >80% isobutene gas can utilize the LG2F process using the
methods outlined above.
[0205] In another embodiment, a alkane-rich hydrocarbon feedstream
comprised of >80% ethane is converted via the R1 Thermal
Olefination reaction to an C2+ effluent stream comprised of ethene
and unreacted compounds which then enters the specialized R2
catalytic reaction to be dimerized, isomerized and selectively
re-dimerized in a combination of reaction steps to produce a high
portion of C8+ olefins. The specialized catalytic process includes
a combination of selective dimerization and isomerization
techniques in a three-part sequence to convert C2 alkenes to C4
alkenes to a high proportion of C4 iso-alkenes which are finally
re-dimerized to yield C8+ iso-alkenes. These iso-alkenes are then
hydrogenated, condensed, and separated via a simple knock-out
technique to yield a high proportion of C8 trimethylpentanes useful
for high-octane gasoline (without aromatics) and a remaining liquid
portion comprised of C12 to C16 alkanes very useful as premium
diesel fuel blendstocks. The specialized dimerization process can
be adjusted to raise or lower the proportion of C8's vs the C12-16
range of products yielded from this catalytic protocol.
[0206] One such example of the optionality is the targeting of
isobutane, a high-octane compound typically used to add vapor
pressure (RVP) to gasoline blending, but also used as a feedstock
to any traditional paraffin alkylation process. The catalytic R2
chemical reaction favors the production of branched-chain
paraffins, which reduces the likelihood of producing n-paraffins
which boil on either side of isobutane. Accordingly, as a result of
the tailored LG2F R2 reaction, isobutane (C.sub.4H.sub.10) can be
isolated using a high-pressure separation vessel. The target is a
narrow boiling range of between -40.degree. C. and -2.degree. C. at
atmospheric conditions, which can be pressurized to partially
liquify the stream and extract C.sub.4 iso-paraffins. All the
lights below -40.degree. C. (notably ethane and propane) are
recycled to maximize the yield of branched paraffins within the
temperature band.
[0207] In a similar example, the LG2F R1 Thermal Olefination
reactor in this invention can be targeted to produce any
combination of C.sub.3-C.sub.5 olefins (propene, butene and/or
amylene) from any C.sub.3-C.sub.5 light gas alkanes which can then
be directly applied into any traditional paraffin alkylation unit
with the additional feed of isobutane (from any source) for
production of high-octane, branched-chain paraffinic hydrocarbons,
particularly 2,2,4-trimethylpentane (Isooctane).
[0208] In a combined example, the LG2F R1 Thermal Olefination
reaction can be processed using any C3-C5 alkane gases to produce
C3-C5 olefins. The .ltoreq.C3 stream can be extracted and processed
by R2 (with the option to add additional light olefin streams) to
target the production of isobutane or isobutene as described above.
Any C6+ byproducts from the R1 reaction can be captured by
liquid-vapor knockout for surplus gasoline or reuse. This tailored
configuration results in the critical feedstreams necessary for
input to paraffin alkylation.
Diesel Blendstocks
[0209] Diesel fuel has several key performance characteristics
which depend upon the chemical composition of the fuel. Diesel
fuels are generally comprised of n-paraffins, iso-paraffins,
cycloparaffins and aromatics in such a way as to meet key
performance requirements of the fuel. For example, in a diesel
engine, cetane number is the measure of the speed of the
compression ignition upon injection of the fuel, as well as the
quality of the fuel burn in the combustion chamber. Accordingly, a
high-performance diesel fuel is preferred to have an aggregate
cetane index value (using ASTM D613) of at least 40 and as high as
60.
[0210] In addition, very low sulfur levels are also highly
desirable in diesel fuel to eliminate corrosive wear-and-tear and
prevent engine emission control system issues. Jet fuel and diesel
fuel, both derived from middle distillates, share many common
features. See FIG. 7 and FIG. 8. However, ASTM International fuel
specifications call for different performance-based fuel test
results impacting cetane, lubricity, viscosity, low temperature
flowability, sulfur content, heating value, and more. The
performance requirements are what dictate the composition and
operating requirements to produce the desired fuel.
[0211] Generally, C.sub.9+ n-paraffins, iso-paraffins and
cycloparaffins have higher cetane values than aromatics and are key
constituents in the diesel blendstock to achieving high cetane
measures (e.g. 40-60) for good fuel performance. Cetane Values for
various n-paraffins are shown below in Table 8.
TABLE-US-00025 TABLE 8 C9+ n-Paraffin Compounds Have Highest Cetane
Values Boiling Melting Pt Pt Cetane C9 to C20 n-Paraffins Formula
(.degree. C.) (.degree. C.) # N-NONANE C9H20 150 -48 72 N-DECANE
C10H22 174 -30 76 N-UNDECANE C11H24 196 -26 81 N-DODECANE C12H26
216 -10 87 N-TRIDECANE C13H28 235 -5 90 N-TETRADECANE C14H30 254 6
95 N-PENTADECANE C15H32 271 10 96 N-HEXADECANE C16H34 287 18 100
N-HEPTADECANE C17H36 302 22 105 N-OCTADECANE C18H38 316 28 106
N-NONADECANE C19H40 336 32 110 N-EICOSANE C20H42 344 36 110
[0212] However, while C14+n-paraffins have high Cetane Values,
their melting point is above low ambient temperatures leading to
wax crystals forming in the fuel, which can foul or block fuel
lines in cold weather, for example. See Table 10. Specialized pour
point, cloud point and cold filter plugging tests often call for a
reduction of heavier n-paraffinic compounds in middle distillates
(often via dewaxing) to improve the cold flowability and
operability of a diesel fuel. In addition, n-paraffins have lower
volumetric heating value (btu/gal) in comparison to aromatics.
TABLE-US-00026 TABLE 10 C14+ n-Paraffin Compounds Melting Points
Boiling Melting Pt Pt Cetane C9 to C20 n-Paraffins Formula
(.degree. C.) (.degree. C.) # N-NONANE C9H20 150 -48 72 N-DECANE
C10H22 174 -30 76 N-UNDECANE C11H24 196 -26 81 N-DODECANE C12H26
216 -10 87 N-TRIDECANE C13H28 235 -5 90 N-TETRADECANE C14H30 254 6
95 N-PENTADECANE C15H32 271 10 96 N-HEXADECANE C16H34 287 18 100
N-HEPTADECANE C17H36 302 22 105 N-OCTADECANE C18H38 316 28 106
N-NONADECANE C19H40 336 32 110 N-EICOSANE C20H42 344 36 110
[0213] Unlike gasoline for spark-ignited piston engines, which
depend upon C.sub.7-C.sub.9 high-octane aromatics to retard early
ignition, C.sub.10 to C.sub.20 aromatics provide diesel engines
thermal stability, heating value (btu/gallon) and desirable
elastomer swell characteristics. Unfortunately, these aromatics
generally have low cetane values which can impede effective diesel
engine performance. The right balance of aromatic vs. aliphatic
compounds will impact the performance characteristics of the diesel
blendstock. See Table 11.
TABLE-US-00027 TABLE 11 C10+ Aromatic Compounds Cetane Values
Boiling Melting Pt Pt Cetane C10 to C20 Aromatics Formula (.degree.
C.) (.degree. C.) # N-BUTYLBENZENE C10H8 183 -88 6
1-METHYLNAPHTHALENE C11H10 245 -30 0 N-PENTYLBENZENE C11H16 205 -75
8 N-HEXYLBENZENE C12H18 226 -61 19 N-HEPTYLBENZENE C13H20 246 -48
35 1-N-BUTYLNAPHTHALENE C14H16 289 -20 6 N-OCTYLBENZENE C14H22 264
-36 32 N-NONYLBENZENE C15H24 282 -24 50 N-DECYLBENZENE C16H26 298
-14 N-UNDECYLBENZENE C17H28 313 -5 2-N-OCTYLNAPHTHALENE C18H24 352
-2 18 N-DODECYLBENZENE C18H30 328 3 68 N-TRIDECYLBENZENE C19H32 341
10 N-TETRADECYLBENZENE C20H34 354 16 72
It is therefore desirable to be able to produce diesel blendstocks
that primarily contain high Cetane Value components (e.g.
C.sub.9-C.sub.16+ n-paraffins) with lesser targeted amounts of
aromatics (e.g. C.sub.9-C.sub.16) whose lower melting points help
increase cold flowability of the fuel.
[0214] Olefins are also a product of the R1 and R2 reactions and
play a key role in diesel fuel blendstocks. The Cetane Values of
C.sub.9 to C.sub.20 olefins are moderately high (above 50) and the
C.sub.9-C.sub.15 melting points tend to be cooler than ambient
temperatures helping to improve cold flowability, making them ideal
compounds for diesel fuel. See Table 12.
TABLE-US-00028 TABLE 12 Boiling Melting Pt Pt Cetane Olefin
Compounds Formula .degree. C. .degree. C. # 1-NONENE C9H18 146.87
-81 51 1-DECENE C10H20 170.57 -66 56 1-UNDECENE C11H22 192.67 -49
65 1-DODECENE C12H24 213.36 -35 71 1-TRIDECENE C13H26 232.78 -13
1-TETRADECENE C14H28 251.10 -12 80 1-PENTADECENE C15H30 268.39 -3
1-HEXADECENE C16H32 284.87 4 86 1-HEPTADECENE C17H34 300.33 11
1-OCTADECENE C18H36 314.82 14 90 1-NONADECENE C19H38 329.10 23
1-EICOSENE C20H40 342.40 26
[0215] These varying factors and fuel requirements call for
flexibility in the compositions of diesel fuels. In an aspect, the
LG2F Process is tailored to the production of diesel blendstocks.
As used herein, the term "diesel blendstock" refers to a
formulation comprising n-paraffins, iso-paraffins, cyclo-paraffins,
olefins and aromatics having 9 to 24 carbons. The diesel
blendstocks preferably have 10-20 carbons preferably have less than
35 wt % aromatic hydrocarbons, and more preferably less than 30 wt
%. The following discussion further demonstrates the ability to
tailor the LG2F Process depending on the C2-5 feedstream and the
desired diesel product(s).
[0216] This invention can be tailored by isolating the LG2F R2
chemical reaction to convert C.sub.2-C.sub.5 light olefin-rich
feedstocks into any range of C.sub.9 to C.sub.24+ middle distillate
hydrocarbons used in jet fuel/kerosene, heating oil, marine gasoil,
and ideally for high-value diesel fuel blending. When using
olefin-rich feedstocks from any source with the LG2F R2 reactor for
producing diesel fuel blendstocks, the zeolite-based chemical
reaction produces a broad-spectrum of paraffin, iso-paraffin,
cycloparaffin, olefin and aromatic output in a normal (gaussian)
distribution. The distribution of the final product can be widened
(e.g. C.sub.9 to C.sub.24+) or narrowed (e.g. C.sub.10 to C.sub.17)
depending upon the desired performance characteristics of the
middle distillate blendstock.
[0217] For example, one embodiment targets the LG2F finished
product yield by setting the operating conditions to produce
hydrocarbons up to the upper boiling limit of n-hexadecane for
example 295.degree. C. and recycling all byproducts in the flash
drum with boiling points just above C.sub.9 n-nonane at for example
145.degree. C. This will yield a very high cetane blendstock with
limited need for dewaxing. This can be a very useful premium diesel
fuel blendstock, particularly if processed in the absence of any
sulfur contaminates (e.g. using the optional C.sub.2-C.sub.5 light
gas feeds from any hydrotreated alkane streams). The lower carbon
paraffins have low freezing points which improve fuel flowability
in cold weather (pour point). Many other LG2F R2 operating
conditions may also be modified to optimize the fuel performance
characteristics (e.g. cetane, pour point, density, heat of
combustion, thermal stability, etc.) of the LG2F final product as a
fuel blendstock in comparison with other possible middle distillate
blending components. The LG2F R1 and R2 reactions can be used
together in a recycle loop or independently depending upon the
availability of the alkane or alkene light gas feedstreams.
Assessing the middle distillate product requirements in relation to
the feedstream quality available will determine the targeted
operating conditions and product yields from LG2F processing. Table
8 depicts the varying range of carbon numbers that would include
n-paraffin, iso-paraffins, cyclo-paraffins, olefins and aromatic
compounds found in the middle distillate fuel. Using the operating
conditions to select the upper boiling point and lower boiling
point directly impacts the resulting cetane values, melting point
and flowability attributes of the all-hydrocarbon blendstock.
Selecting 3 ranges of carbon numbers C9-C14 results in excellent
low-temperature flowability characteristics, selecting C10-C20 has
a lower cetane value, selecting C12-C16 is a boutique diesel fuel
blend with very high cetane values.
TABLE-US-00029 TABLE 13 Targeting C9-20 Paraffins, Olefins &
Aromatics Carbon Broad Low Temp Custom High # Spectrum Flowability
Blend Cetane 9 X X 10 X X X 11 X X X 12 X X X X 13 X X X X 14 X X X
X 15 X X X 16 X X X 17 X X 18 X X 19 X X 20 X X 21 X 22 X 23 X
[0218] In one embodiment, the LG2F Process is tailored to produce a
narrow range of C9 to C14, high-cetane paraffins with few
low-melting compounds, thereby minimizing any need for dewaxing.
This product is a desirable diesel fuel blendstock due to its speed
of starting, clean combustion and low temperature flowability.
Examples--Diesel Blendstocks
[0219] This same fully-recycled LG2F Process can be operated at
conditions to produce any targeted range (e.g. C.sub.9+) of
hydrocarbons for use as middle distillate, marine fuel, jet fuel or
for diesel fuel blendstocks. The Thermal Olefination reaction
depending upon the feed content creates a spectrum of C.sub.2 to
C.sub.5 olefinic hydrocarbons, and the zeolite-catalyzed R2
reactor(s) uses operating conditions, particularly a low-pressure
R2 reaction followed by a high-pressure R2 reaction sequence with
recycling, which favor the C.sub.9 to C.sub.24+ range of
hydrocarbon compounds used in diesel fuel blendstocks largely via
the dimerization, trimerization, etc. of reacted C2-C5 olefin
compounds. Selecting the C.sub.2 to C.sub.8 range of molecules
output from the R2 catalytic reaction for recycle or aromatic
reuse, and setting the appropriate operating conditions (T, P,
WHSV) allows a tailored outcome of middle distillate with high
cetane and low pour point values ideal for diesel fuel blendstocks.
Byproducts of the reaction include methane, hydrogen and aromatic
surplus.
[0220] In one embodiment, the R2 feedstream is comprised of
.gtoreq.60% m/m ethene and is subjected to a high-pressure,
low-temperature catalytic reaction just above activation energy to
allow additional thermodynamic control over the reaction. This
embodiment utilizes an integrated cooling/dilution mechanism and/or
a deactivating agent to minimize the exothermic reaction.
[0221] In one embodiment, the R2 feedstream is comprised of
.gtoreq.40% m/m ethene and .gtoreq.10% propene and is subjected to
a high-pressure, low-temperature catalytic reaction just above
activation energy to allow additional thermodynamic control over
the reaction. This embodiment utilizes an integrated
cooling/dilution mechanism and/or a deactivating agent to minimize
the exothermic reaction.
[0222] In one embodiment, the R2 feedstream is comprised of
.gtoreq.50% m/m any C2/C3 olefins and is subjected to a
high-pressure, low-temperature catalytic reaction just above
activation energy to allow additional thermodynamic control over
the reaction. This embodiment utilizes an integrated
cooling/dilution mechanism and/or a deactivating agent to minimize
the exothermic reaction.
[0223] In one embodiment, the R2 feedstream is comprised of
.gtoreq.50% m/m any C3/C4 olefins and is subjected to a
high-pressure, low-temperature catalytic reaction just above
activation energy to allow additional thermodynamic control over
the reaction. This embodiment utilizes an integrated
cooling/dilution mechanism and/or a deactivating agent to minimize
the exothermic reaction.
[0224] In one embodiment, the R2 feedstream is comprised of
.gtoreq.50% m/m any C3-C5 olefins and is subjected to a
high-pressure, low-temperature catalytic reaction just above
activation energy to allow additional thermodynamic control over
the reaction. This embodiment utilizes an integrated
cooling/dilution mechanism and/or a deactivating agent to minimize
the exothermic reaction.
By-Products
[0225] In all LG2F embodiments, excess methane and hydrogen are
byproducts of the Thermal Olefination reaction. Since methane and
hydrogen are unreactive to the LG2F process, there is no
restriction on their being present in the light hydrocarbon gas
feedstream.
[0226] The LG2F Process will produce varying amounts of methane
(e.g. 5-20%) subject to operational and economic choices, which may
have utility as process fuel particularly in remote operating
locations or returned for credit as dry gas to pipelines or
refineries. Depending upon the C.sub.2+ feedstock quality, the LG2F
process provides the option of extracting excess methane and
hydrogen via membrane separation. Byproduct methane can also be
recycled via MTO to maximize finished product yields from a given
light gas feedstream.
[0227] Produced H.sub.2 is highly desirable if reusable as a
byproduct, particularly in refining and petrochemical applications.
If membrane separation is not feasible then a purge stream of the
same composition as the recycle loop can be drawn to prevent
byproduct accumulation.
Middle Distillates--R2
Low-Pressure/High Pressure Catalytic Reaction
[0228] The LG2F catalytic reaction sequence can also be configured
to combine a low-pressure and high pressure reaction sequence to
target the conversion of light olefinic gases (e.g.,
C.sub.2-C.sub.5) from the Thermal Olefination reaction, to
chemically transform into longer-chain components through
intermediary low-molecular coupling. This pressure and conversion
control method produces high-grade distillates used particularly in
middle distillates, jet fuel and diesel fuel blendstocks with added
quality control by utilizing a high-pressure catalytic reaction
sequentially following a low-pressure catalytic reactor.
[0229] In one such embodiment, the R1 Thermal Olefination reaction
occurs upon receipt of alkane-rich C.sub.2 to C.sub.5 light gases
at high temperatures (e.g., above 700.degree. C.) operating at low
pressure (e.g., 0-200 psig) and producing a C.sub.2+ olefin-rich
mixed gaseous yield. These gases are cooled and proceed to the
initial R2 catalytic reactor which operates at temperatures between
about 200-500.degree. C. and low pressure (e.g. 0-200 psig) to
avoid using expensive compression techniques. Using R2 with a WHSV
above 30 and a residence time <1.0 second produces many
molecular combinations (dimers, trimers, etc.) in the R2 gas-phase
effluent.
[0230] A compressor is utilized downstream of R2 and the pre
heat-exchanger to compress the gas phase effluent into a phase
separation flash drum whereby condensed liquids are captured,
methane and hydrogen are separated or purged, and C.sub.2-C.sub.4+
residual light gases are recycled back to R1. The liquid phase from
R2's condensed effluent, which comprises C4+ hydrocarbons (a
marketable low grade gasoline product), can be further pressurized
by a pump operating at from 100 to 1000+ psig for processing into
another zeolite-catalytic reactor R2. This secondary R2 reactor
(depicted as R2L in the graphics) operates at similar temperatures
(e.g. 150-300.degree. C.) and uses a zeolite catalyst which may be
the same or different as used in initial R2 reactor, but in a
high-pressure environment, resulting in a high concentration
reaction. This high concentration reaction maximizes long-chain
molecule formation (e.g., C.sub.8+ which are ideal for various
middle distillates). The resulting R2 reactions from the secondary
reactor produce an effluent which then undergoes vapor/liquid flash
drum separation to remove C.sub.4 and lighter gaseous components
for recycle back upstream of R2, and yields performance grade
diesel fuel or targeted C.sub.6-C.sub.10 gasoline blendstocks. This
low-pressure/high-pressure catalytic method provides a more
controllable coupling of light olefinic gases to produce
longer-chain molecules thereby enhancing the tailoring of middle
distillates, particularly those used in any targeted range of
C.sub.9 to C.sub.16+ diesel fuel blendstocks or tailored gasoline
blendstocks. See FIG. 9.
[0231] Similar to the previously described two-reaction (R1 and R2)
sequence, there also exists an acceptable configuration for R1 plus
two R2 zeolite reactions operating in series with a low and
high-pressure configuration for increased molecular concentration
thereby improving longer-chain hydrocarbon yield, suitable for
middle distillates, especially diesel fuels.
[0232] The R1 feedstream is similarly comprised of the indicated
C2-C5 light alkane components that render the process productive.
These alkanes are combined with recycled light alkanes that are
unreacted or formed downstream. A combined feed is then preheated
in a heat exchanger (E-100) with the recycled gas outlet from R1
and then fed into the Thermal Olefination reactor (R1). R1 has
operating conditions similar to previous embodiments where this
high temperature reaction is conducted between 600 and 1100.degree.
C. and 0-1500 psig. R1's products consist of thermally
dehydrogenated alkenes that are suitable for the next iteration of
reactions. The outlet of the reactor has integrated heat with E-100
as described during heat exchange previously. It is expected that
the stream will need to be further cooled after cross exchange
before entering the Zeolite-Catalytic reactor (R2). E-101 will
further cool the stream to an appropriate operation temperature and
pressure for R2. R2 operates to largely dimerize, trimerize, and
tetramerize the incoming olefinic components to produce a partially
condensable stream at high pressure.
[0233] The R2 effluent is then combined with a recycle stream
originating downstream in the final flash drum (D-101). There
should be enough suction head from C-100 to return the compressed
gas from the downstream drum otherwise additional compression may
be necessary. The combined stream is then compressed to a pressure
resulting in some initial liquification of C3+ components (200-1000
psig) that are then further liquified in a cooler (E-102). It shall
be appreciated that further heat integration can occur to
increasingly preheat the feed into the first reactor as the
temperature will notably increase post compression. A flash
separator (D-100) is used to remove any vaporous light alkanes that
can be further processed by R1. The light alkane stream that
contains mostly ethane, propane, methane, and hydrogen is fed into
a compressor (C-101) to ensure consistent flow through the recycle
loop. C-101 may be unnecessary depending on operating conditions
and this high-pressure gas may have enough head to proceed through
the loop unaided before being stepped down with a valve. The outlet
of C-101 is led into a separator (S-100) where it can either be
simply purged or passed through a membrane(s) to remove methane and
hydrogen byproducts. After mass removal the first recycle loop is
then fed back upstream in the process.
[0234] The high-pressure liquid of D-100 is pumped (P-100) to
very-high-pressure (>1000 psig) as a liquid to mitigate the need
for expensive very-high-pressure compression. This
very-high-pressure liquid is fed into a third reactor (R2L) where
the liquid is vaporized and further oligomerized to heavy molecular
weight components. A heated expansion chamber pre-R2L may be needed
to ensure appropriate vaporization. Heavy molecular weight
production under this pressure will result in a largely condensed
stream down-flow of the third reactor. This heavy molecular weight
stream exiting the third reactor is then cooled in E-103 where it
is further cooled/liquified to a temperature that is appropriate
for vapor/liquid separation. D-101 separates the unliquified gases
that may contain some mid-range olefinic components. Regardless of
alkane/alkene composition, the tops of D-101 are fed upstream to be
re-compressed, cooled, and separated. Any recycled byproducts
downstream that are C2 or less will consequently be recycled
through the initial recycle loop. Finally, a liquid stream is
recovered from D-101 that resembles a diesel or gasoline spectrum
product produced via a three-reactor, pressure swing process for
very-high-pressure and high concentration oligomerization. In a
related embodiment, a source comprising about 70% ethane gas can be
processed in the R1 Thermal Olefination reactor to primarily
produce ethylene which is then processed in R2 at low pressure with
a fast residence time to create dimers, trimers and tetramers from
the olefin-rich feedstream. The exiting light gases are then
cleaved away for recycle and the remaining C4+ liquid, a low-grade
natural gasoline product, is available for the next processing
step. The R2 liquid effluent from the low-pressure reaction may
optionally serve as a finished product in this example with higher
value than ethane, or it may be further processed as a pressurized
liquid at high concentration into the secondary R2 reactor where
longer-chain coupling occurs. The high molecular concentration in
the liquid phase and the low residence time of the secondary R2
reaction produce a premium grade distillate for use in diesel fuel
blendstocks or targeted gasoline blendstocks. The unused compounds
from R2 are recycled based upon targeted hydrocarbon cut-points and
moved upstream of the liquid/gas condenser and the liquid pump.
Unprocessed light gases from R2 are recycled back to R1 and methane
and hydrogen are purged for reuse.
[0235] In a similar embodiment, a low-value ethane/propane mixture
is processed into R1 and the same options and features of the
invention result in either C.sub.5+ gasoline grade fuel blendstocks
(from R2) and/or high-performance distillate (from a secondary R2
reactor) which can be targeted to produce any range of fuel grade
molecules, e.g., C.sub.9 to C.sub.16+ for use in diesel fuel
blendstocks or targeted gasoline blendstocks. In processing R2 for
diesel fuel, the C8 and lighter pressurized stream is recycled for
reprocessing. The light compounds from R2 are recycled, and the
byproduct methane and hydrogen are purged for reuse.
[0236] In another embodiment, any two R2 reactors performing in
series can be operated at the same pressure as R1 Thermal
Olefination with intermediary separation of light gases. This will
increase the concentration of hydrogen and methane in the gaseous
stream for easier membrane separation or less yield loss from
purge. Generated byproducts in the second R2 catalytic reactor can
then be recycled directly into R1 without removal of unreactive
hydrogen and methane since they will be unremarkable in stream
composition.
[0237] In an environmentally distinct embodiment, a modification of
the gas phase reaction of R2 can be conducted as a
very-high-pressure liquid or supercritical phase reaction (>500
psig) to even further increase its concentration past that of
high-pressure gas.
[0238] Configurationally, the LG2F system can also operate with
multiple R1 Thermal Olefination reactions and a single R2 catalytic
reaction. Stepping temperature up and down from the first R1 to the
second R1 will give more selective control of olefinic product
distributions and also serve to limit heavy coking of a single R1
reactor system.
[0239] A further embodiment is the LG2F process is a multi-stage R1
configuration and multi-stage R2 catalytic reactions with low/high
pressure optionality to produce a more optimized product
distribution and yield. These two-, three- and four-step LG2F
reactor designs may utilize any commercially viable process
technique known in the art (e.g. fixed bed, moving bed, or fluid
bed) embodied herein allow for the interchangeable production of
C4-C12 gasoline blendstocks and/or C9-C16+ diesel fuel blendstocks
from alkane-rich light gases.
[0240] The LG2F process conditions are easily convertible to switch
processing methods which offers a unique capability to adjust the
production of key transportation fuels depending upon ever-changing
market conditions. A particular feature of the LG2F process is the
option to produce gasoline blendstocks at one set of operating
conditions and/or switch to produce middle distillate blendstocks
at a different set of (R2) reactor operating conditions. Depending
upon the availability of downstream processing often available at
refining plants, the timing of the process switching can be
tailored using distinctive cuts to eliminate the need for any
distillation of the blendstocks.
[0241] In one embodiment, the process is solely devised to produce
middle distillate grade product blendstocks of a high cetane and
net heat value. In a different embodiment, the process is solely
devised to produce higher octane gasoline blendstocks. In yet
another embodiment, the process is set to produce higher octane
gasoline blendstocks during one period, then switched and
reconfigured to produce middle distillate blendstocks in another
period. In yet another embodiment, the process is set to produce a
full spectrum of, for example, C.sub.5+ or C.sub.6+ or C.sub.7+
fuel products which could be distilled downstream for different
commercial uses. Once again, the preferred end product of the
reaction (e.g., the targeted performance requirements of a fuel
blendstock) may have a determining factor on the ideal operating
conditions (T,P,WHSV) and choice of the R2 catalyst.
[0242] While the diesel fuel blendstocks described as the products
of LG2F in this invention may be comprised of varying chemical
compounds, targeted performance grade diesel fuels can be tailored
by feed characteristics, catalyst choices and operating conditions
to achieve a minimum set of performance conditions for diesel grade
products.
[0243] In one embodiment, the diesel fuel product is .gtoreq.40
cetane number, with aromatic content .ltoreq.35% m/m, satisfactory
cloud point and cold temperature flowability, lubricity .ltoreq.520
microns at 60.degree. C., and distillation temperature
.ltoreq.338.degree. C. at 90% point.
[0244] In one embodiment, the diesel fuel product is .gtoreq.50
cetane number, with aromatic content .ltoreq.35% m/m, satisfactory
cloud point and cold temperature flowability, lubricity .ltoreq.520
microns at 60.degree. C., and distillation temperature
.ltoreq.338.degree. C. at 90% point,
[0245] In one embodiment, the diesel fuel product is .gtoreq.55
cetane number, with aromatic content .ltoreq.35% m/m, satisfactory
cloud point and cold temperature flowability, lubricity .ltoreq.520
microns at 60.degree. C., and distillation temperature
.ltoreq.338.degree. C. at 90% point.
[0246] Another distinguishing feature of the LG2F process is that
the composition and performance characteristics of the C9+
distillate products do not require a hydrogenation step. However,
some tailored fuel applications may favor a more paraffinic
composition in which case a hydrogenation reaction is included as
an optional embodiment. In this case, hydrogen can be supplied by
the LG2F process. In the case of excess hydrogen from the LG2F
process, the hydrogen byproduct may be highly valued by other
markets, e.g. refining.
[0247] The LG2F process also offers a wide range of modular
configurations (e.g., to eliminate benzene or increase octane or
increase energy density or increase net heat of combustion or lower
vapor pressure) when processing C2 to C5 light gases which allows
for the tailoring of the operating conditions resulting in a
specified composition of gasoline blendstock. In one embodiment,
the LG2F R1+R2 reaction with recycling is specified to produce only
C7 to C10 aliphatic and aromatic hydrocarbons between the boiling
point range of 85.degree. (above benzene) up to 200.degree. C. This
results in a well-balanced high-octane gasoline blendstock with no
benzene. In another embodiment, the LG2F R1+R2 reactions with
recycling is specified to produce C5 to C10 aliphatic (favoring
paraffins and olefins) with virtually no aromatics. This results in
a lower octane blendstock, but with higher volumetric yields. In
another embodiment, the LG2F R1+R2 reaction is specified to produce
primarily C7 to C10 high octane aromatics with only a minor content
of aliphatic hydrocarbons. This results in a high-octane gasoline
blendstock, in the absence of benzene, and a high energy
density.
[0248] This modular functionality in designing tailored hydrocarbon
product streams from C2-C5 light gas streams is a major feature of
this invention. This tailoring can be applied to adjust to
ever-changing market conditions and locational arbitrage
opportunities. The LG2F R1 and R2 reactors can operate
independently or in an integrated fashion. Any available source of
olefins can be used in the R2 reaction once the feedstock
composition is assessed for the ideal temperature, pressure and
reaction time for a given product specification. The product high
(final) boiling point is specified by the R2 operating conditions
and the product low (initial) boiling point is set by the flash
drum cut point which eliminates any need for distillation.
Combining R1 Thermal Olefination with an R2 Reactor
[0249] There is an added feature of this invention to combine the
benefits of Thermal Olefination and the basic Oligomerization,
Dimerizing and Trimerizing features of R2 into a single catalytic
reaction. This bi-functional reaction feature is called an
"Oli-Par" process whereby a single reactor produces an olefin and
paraffin cocktail which can be separated using knockout techniques
described herein. The olefins can pass to a downstream R2
reactor(s) to complete the conversion to distillate fuels while the
paraffins can be used as high-quality gasoline or aromatic
products. This bi-functional reactor process reduces costs and
allows operational flexibility for the producer of gasoline and
distillate types fuels, particularly for those who may prefer to
produce more than one finished product. A key advantage of the
Oli-Par process is operating temperatures of the catalytic reaction
are generally 500 C to 750 C thereby reducing some of the
operational severity of the Thermal Olefination process that may
otherwise harm certain catalysts.
[0250] In one embodiment, the Oli-Par process receives feedstreams
comprised of at least 90% C2+ alkanes, operating at 600 C with a
light gas (<C4) recycle loop to produce a cocktail comprising
.gtoreq.C4+ olefins and .gtoreq.C8+ paraffins. Following a targeted
knockout step, the C4+ olefins are then passed to a downstream R2
reactor for further processing to produce longer-chain distillate
fuels. Depending upon the tailored cut, any C6+, C7+ or C8+
paraffins can be used for gasoline blendstocks, fuels and/or
aromatic uses. The proportion of olefins to paraffins can vary
depending upon the operating conditions of the Oli-Par process. A
simple liquid/vapor knockout separator is used to separate the two
constituent product types which do not need to be of high purity
for fuel uses. In some embodiments, the use of hydrogen (H2) as a
feed to a secondary R2 reaction can increase the performance
characteristics of the distillate fuel products by increasing
cetane values of the fuel.
Combining Refinery Processes and LG2F
[0251] Another aspect of the LG2F Process is the ability to combine
the process with any other hydrocarbon process which provides a
source of C2-5 hydrocarbons useful as a feed to the LG2F Process.
In addition to the light gas offtake from NGL plants (e.g.
demethanizers), this could include the light gas byproducts from a
catalytic reforming, hydrodealkylation, paraffin cracking, fluid
catalytic cracking (producing olefin byproducts), a coking unit, or
any similar example with sufficient access to C2-C5 light
hydrocarbons, (One such process is described in a co-pending
application, U.S. Ser. No. 16/242,465, also owned by Applicant.
This process is called "I2FE" and comprises a long-chain paraffin
cracking technique that generates C2+ byproducts as a feedstream to
LG2F. This combined process is presented in FIG. 10.)
[0252] In one combined embodiment, a paraffin cracking process
(I2FE) can be designed to consume a small amount of hydrogen to
maintain the longevity of the metal catalyst. Depending upon design
configurations, hydrogen byproduct from LG2F may offset on-purpose
hydrogen consumed in I2FE, if these two processes are used
together. The design of both units can be balanced and optimized to
be hydrogen natural or a net producer of hydrogen, depending upon
the needs of the business operation.
[0253] In another combined embodiment, the LG2F Process converts
the clean light gas compounds (typically C3+) specifically from any
appropriate refining process to produce C6+ blendstocks using
Thermal Olefination (R1) followed by a multi-iterative,
acid-catalyzed cracking, oligomerizing and/or cyclizing reactions
(R2) in a single or multi-bed reactor configuration with a recycle
loop. In another embodiment from a catalytic reformer, the process
is used to yield any range of C.sub.9 to C.sub.24+, zero-sulfur,
middle distillate compounds with effective performance properties
for use in diesel fuel and other transportation fuel blendstocks.
The same process can be performed targeting a narrower range of
middle distillate compounds such as C.sub.10-C.sub.20, or
C.sub.12-C.sub.18, or C.sub.9-C.sub.14, etc. depending upon the
performance requirements of the finished product. A byproduct of
this process depending upon the configuration is unused hydrogen,
methane and surplus aromatics.
[0254] Another embodiment of this LG2F invention converts the clean
light gas compounds (C.sub.2+) specifically from the I2FE process,
with or without reformer off-gases, to produce gasoline range
blendstocks using only Thermal Olefination and a multi-iterative
acid-catalyzed zeolite reaction oligomerization, cyclization and
cracking reaction in a single or multi-bed reactor configuration
with a recycle loop. This process is designed to handle excess
hydrogen to yield any C.sub.4 to C.sub.12 range gasoline compounds
(i.e., paraffins, olefins and aromatics) for use with other
gasoline blendstocks. All gasoline products in this embodiment are
very-low benzene, sulfur-free and nitrogen-free. A byproduct of
this process depending upon the configuration is unused hydrogen,
methane and surplus aromatics.
[0255] Another embodiment of this LG2F invention converts the clean
light gas compounds (C.sub.2+) specifically from the I2FE process
to produce gasoline range blendstocks using thermal cracking (R1)
and multi-iterative, acid catalyzed reactions (R2) in a single or
multi-bed reactor configuration along with a recycle loop. This
process is designed without excess hydrogen to yield C.sub.4 to
C.sub.12 range gasoline compounds (i.e., paraffins, olefins and
aromatics) for use with other gasoline blendstocks. All gasoline
products in this embodiment are sulfur-free and nitrogen-free.
Alternatively, this process is designed to provide excess hydrogen
for reuse. Depending upon the configuration, methane and surplus
aromatics may be byproducts of the reaction.
Direct Alkene Feeds
[0256] The LG2F Process is also useful with other sources of the
C2-C5 alkenes processed in the catalytic reactor (R2). For example,
FCC cat-cracked gasoline byproducts including C.sub.3 alkenes and
LPG can be utilized as feedstocks directly into the catalytic
reactor of the LG2F Process. Another source comes from any methane
activation process, such as oxidative coupling of methane, or
methane pyrolysis and hydrogenation of acetylene, or any other
technique known in the art to produce ethene from methane. The
presence of greater than about 20% alkenes in the light hydrocarbon
feedstock allows the use first of the zeolite-catalyzed R2 reaction
in the LG2F process. The unconverted paraffins are then recycled to
the Thermal Olefination reactor (R1).
[0257] Referring to FIG. 11, the basic LG2F Process is shown.
However, the Process is augmented by having the C2-5 alkene feed
directed first into the R2 catalytic reactor, bypassing the Thermal
Olefination reactor and going straight into the multi-iterative,
acid-catalyzed reactions in a single or multi-bed reactor
configuration with a recycle loop. This feedstream is processed as
previously described to yield C6+ fuel-grade blendstocks. Light
gases from the catalytic process (often containing C.sub.3+
olefinic compounds, e.g., propylene) are then sent to the R1
reactor to proceed through the system as previously described,
thereby producing additional gasoline range blendstocks. This
process is designed to provide excess hydrogen to yield C.sub.6 to
C.sub.11 range gasoline compounds (i.e., paraffins, olefins and
aromatics) for use with other gasoline blendstocks. All gasoline
products in this embodiment are very-low benzene, sulfur-free and
nitrogen-free. A byproduct of this process is unused hydrogen.
[0258] As an illustration of the processing of alkene gases, a
single pass yield of the C.sub.2+ acid-based chemical reaction,
shown in FIG. 12, is from a C.sub.3 olefin feedstock and
demonstrates the production of gasoline grade compounds. This
reaction was made at 45 psig and 3 WHSV across a range of
temperatures. As illustrated, the aromatic hydrocarbon content
(A.sub.6+) varied by the reaction temperature, which can be used to
increase octane values of gasoline blendstocks.
[0259] Another embodiment of this LG2F invention receives the
byproduct light gases from the catalytic cracking process (often
containing C.sub.3+ olefinic compounds, e.g. propylene) to produce
diesel range fuel blendstocks. This embodiment again bypasses the
initial Thermal Olefination and goes straight into the
multi-iterative, acid-catalyzed reactions in a single or multi-bed
reactor configuration with an R2 catalyst tailored for the
feedstream before re-entering the LG2F recycle loop. This process
is designed to provide excess hydrogen and to yield any specified
range of C.sub.4 to C.sub.12 gasoline blendstocks or C.sub.9 to
C.sub.24 middle distillate for use as diesel fuel blendstocks. A
byproduct of this process is unused hydrogen.
[0260] The foregoing processes are examples of a range of processes
using alkene feeds, further including the following: [0261]
C.sub.2+ alkene gas streams exiting the catalytic cracking unit are
transformed to C.sub.6+ gasoline constituents first via LG2F
chemical reaction (R2), followed by a recycle loop that restarts
Thermal Olefination and a chemical reaction loop resulting in
higher liquid gasoline yields; [0262] C.sub.2+ light hydrocarbon
streams with primarily olefinic compounds are merged to increase
the available volume of light gas compounds for conversion via R2
processing with recycle loops to R1+R2 to produce gasoline
blendstocks using the LG2F process; [0263] C.sub.2+ light
hydrocarbon streams with primarily olefinic compounds are merged to
increase the available volume of light gas compounds for conversion
to light gas oil or diesel fuel blendstocks using LG2F.
Reducing Benzene
[0264] Another major feature of this light gas transformation to
transportation fuel is the selective reduction of benzene, which
makes the resulting products excellent for gasoline blending due to
low specification limits placed on benzene for use in fuels. In the
case where there is an unwanted surplus of benzene-rich C6+
aromatics extracted by liquid-vapor knockout from the R1 Thermal
Olefination effluent, an added feature of LG2F is to combine light
alkene compounds (e.g. C2-C3) from the R1 reaction with the surplus
C6+ aromatic compounds into a simple low-temperature acid-catalyzed
reaction to create alkyl-benzenes. See FIG. 13. This processing
will convert benzene via electrophilic substitution to become
productive gasoline grade blendstocks that adhere to existing
limitations in gasoline specifications for high-octane aromatic
compounds. This process may utilize aluminum chloride and hydrogen
chloride catalysts. This process will further increase the value of
the gasoline blendstock.
[0265] Another aspect of this invention is a simplified method to
dewax paraffinic compounds from C.sub.14 to C.sub.40 hydrocarbon
streams using a single-stage, low-severity, acid-catalyzed reaction
process to both hydrocrack and hydrotreat middle-to-heavy grade
distillate feedstocks to produce a higher-value, higher-grade
middle distillate with higher fuel performance properties.
[0266] Catalytic dewaxing is typically referred to as a process
that selectively removes C.sub.14+ paraffinic compounds from
middle- to heavy-distillate hydrocarbon streams. This technology is
usually applied to hydrocarbons used in diesel fuel and heating
oils to improve its physical properties including cloud point, pour
point and cold flowability. Increasing quality reduces the need of
using fuel additives to improve properties and allows for more
detailed control of blending specifications. The primary
alternative technology to catalytic dewaxing is solvent based
dewaxing which applies a solvent extraction method to heavy
paraffinic compounds that preserves the chemical structure.
[0267] Configurations of traditional dewaxing units vary but are
most often categorized in two categories: a single or dual bed
reactor. The choice in configuration depends on preference for
hydrotreating integration into the dewaxing catalytic system. The
inlet streams have higher concentrations of sulfur and nitrogen
which will deactivate noble metal catalysts. So, a hydrotreating
bed is typically integrated before the dewaxing catalyst to ensure
minimal degradation of performance.
Traditional Dewaxing Methods
[0268] Traditional refinery dewaxing catalysts are nickel- or
platinum-based selective zeolites, which is a molecular sieve
catalyst. By controlling pore size, these methods control the types
of molecules that enter the catalytically active sites.
Specifically, the pore sizes are set to allow n-paraffinic
compounds but not isoparaffinic compounds (0.6 nm). Traditional
hydrotreating catalysts commonly use Ni/Mo metal combination to
perform the hydrogenation of nitrogen and sulfur-based compounds.
The configuration of these catalyst depends on the level of
protection needed in a dewaxing unit. If there are lower than
normal catalyst poisons, then a single reactor can be used with a
protective bed above the dewaxing bed. However, if poisons are an
issue then a separate hydrotreating bed will be beneficial to
sustained catalyst life. A comparison between typical single and
dual bed catalysts is shown in Table 14.
TABLE-US-00030 TABLE 14 Single stage Second stage Product
distribution (wt %) (SDD-800) (SDD-821) C1-C4 4.3 0.2
C5-177.degree. C. 9.2 5.9 177.degree. C.+ 86.7 94.5 Total 100.2
100.6
[0269] Traditional methods for dewaxing require a separation
between two catalytic beds with one performing hydrotreating and
the other selectively cracking n-paraffinic compounds. Noble metal
catalysts propose too high of a risk for poisoning from hydrogen
sulfide and ammonia, hence the removal of these gases before
dewaxing. However, base metal catalysts lack the activity needed to
dewax a hydrocarbon stream effectively and require larger utility
costs.
[0270] This invention utilizes a unique, low-severity method for
hydrocracking the C.sub.14- to C.sub.40+ paraffins or any targeted
range of n-paraffins compounds using a specialized zeolite catalyst
with the capability to simultaneously hydrotreat the feedstream
thereby removing the sulfur and nitrogen-based compounds and
cracking the low-melting paraffins in a single step process. This
unique method reduces total costs of processing and eliminates the
need for additives used in the field. The main target is cracking
broad scope n-paraffinic compounds since even n-tetradecane
(C.sub.14) melts above low ambient temperatures. Having even a
single branch significantly reduces the melting point by .about.80
F while still having a cetane value of 67.
[0271] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiment has been shown
and described and that all changes, equivalents, and modifications
that come within the spirit of the inventions defined by following
claims are desired to be protected.
* * * * *