U.S. patent application number 14/039036 was filed with the patent office on 2015-04-02 for systems and methods for producing fuel from a renewable feedstock.
This patent application is currently assigned to UOP LLC. The applicant listed for this patent is UOP LLC. Invention is credited to Jonathan Arana, Daniel L. Ellig, Geoffrey William Fichtl.
Application Number | 20150094506 14/039036 |
Document ID | / |
Family ID | 52740779 |
Filed Date | 2015-04-02 |
United States Patent
Application |
20150094506 |
Kind Code |
A1 |
Fichtl; Geoffrey William ;
et al. |
April 2, 2015 |
SYSTEMS AND METHODS FOR PRODUCING FUEL FROM A RENEWABLE
FEEDSTOCK
Abstract
Methods and systems are provided for producing a fuel from a
renewable feedstock. The method includes deoxygenating the
renewable feedstock in a deoxygenation zone to produce hydrocarbons
with normal paraffins. The hydrocarbons with normal paraffins are
isomerized to produce hydrocarbons with branched paraffins. The
hydrocarbons with branched paraffins are fractionated to produce a
naphtha at a naphtha outlet, where the naphtha is further
isomerized.
Inventors: |
Fichtl; Geoffrey William;
(Chicago, IL) ; Arana; Jonathan; (Chicago, IL)
; Ellig; Daniel L.; (Arlington Heights, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Des Plaines |
IL |
US |
|
|
Assignee: |
UOP LLC
Des Plaines
IL
|
Family ID: |
52740779 |
Appl. No.: |
14/039036 |
Filed: |
September 27, 2013 |
Current U.S.
Class: |
585/310 ;
422/187 |
Current CPC
Class: |
C10G 65/043 20130101;
Y02P 30/20 20151101; C10G 2300/1011 20130101; C10G 3/50 20130101;
C10G 3/42 20130101 |
Class at
Publication: |
585/310 ;
422/187 |
International
Class: |
C10G 3/00 20060101
C10G003/00 |
Claims
1. A method of producing fuel from a renewable feedstock, the
method comprising the steps of: deoxygenating the renewable
feedstock in a deoxygenation reaction zone to produce hydrocarbons
comprising normal paraffins; isomerizing the hydrocarbons
comprising normal paraffins to produce hydrocarbons comprising
branched paraffins; fractionating the hydrocarbons comprising
branched paraffins to produce a naphtha at a naphtha outlet; and
isomerizing the naphtha from the naphtha outlet.
2. The method of claim 1 wherein isomerizing the hydrocarbons
comprising normal paraffins further comprise isomerizing the
hydrocarbons comprising normal paraffins in a first isomerization
reaction zone at isomerization conditions; and wherein isomerizing
the naphtha further comprises isomerizing the naphtha in the first
isomerization reaction zone.
3. The method of claim 2 wherein isomerizing the naphtha further
comprises adding the naphtha to the first isomerization reaction
zone such that the naphtha bypasses a portion of an isomerization
catalyst positioned within the first isomerization reaction
zone.
4. The method of claim 2 wherein isomerizing the naphtha further
comprises isomerizing the naphtha in a second isomerization
reaction zone.
5. The method of claim 1 wherein isomerizing the naphtha further
comprises isomerizing the naphtha in a second isomerization
reaction zone.
6. The method of claim 1 wherein deoxygenating the renewable
feedstock further comprises deoxygenating the renewable feedstock
wherein the renewable feedstock comprises glycerides or free fatty
acids.
7. The method of claim 1 wherein deoxygenating the renewable
feedstock further comprises deoxygenating the renewable feedstock
wherein the renewable feedstock comprises oil extracted from a
plant or an animal.
8. The method of claim 1 further comprising sulfiding a
deoxygenation catalyst in the deoxygenation reaction zone.
9. The method of claim 1 further comprising: contacting the
renewable feedstock with a guard bed catalyst at pretreatment
conditions.
10. The method of claim 1 further comprising: pre-cleaning the
renewable feedstock in a pre-cleaning zone.
11. A method of producing fuel from a renewable feedstock, the
method comprising the steps of: contacting the renewable feedstock
with a deoxygenation catalyst to produce hydrocarbons comprising
normal paraffins; contacting the hydrocarbons comprising normal
paraffins with an isomerization catalyst to produce hydrocarbons
comprising branched paraffins; fractionating the hydrocarbons
comprising branched paraffins to produce a naphtha at a naphtha
outlet; and isomerizing the naphtha from the naphtha outlet.
12. The method of claim 11 wherein contacting the hydrocarbons
comprising normal paraffins with the isomerization catalyst further
comprises contacting the hydrocarbons comprising normal paraffins
with the isomerization catalyst wherein the isomerization catalyst
is within a first isomerization reaction zone; and wherein
isomerizing the naphtha further comprises contacting the naphtha
with the isomerization catalyst in the first isomerization reaction
zone.
13. The method of claim 12 wherein isomerizing the naphtha further
comprises adding the naphtha to an isomerization reactor at a side
inlet of the isomerization reactor, wherein the isomerization
catalyst is positioned within the isomerization reactor and wherein
the side inlet is positioned such that the naphtha bypasses some of
the isomerization catalyst within the isomerization reactor.
14. The method of claim 12 wherein isomerizing the naphtha further
comprises contacting the naphtha with the isomerization catalyst in
a second isomerization reaction zone.
15. The method of claim 11 wherein contacting the hydrocarbons
comprising normal paraffins with the isomerization catalyst further
comprises contacting the hydrocarbons comprising normal paraffins
with the isomerization catalyst wherein the isomerization catalyst
is within a first isomerization reaction zone; and wherein
isomerizing the naphtha further comprises isomerizing the naphtha
in a second isomerization reaction zone different than the first
isomerization reaction zone.
16. The method of claim 11 wherein contacting the renewable
feedstock with the deoxygenation catalyst further comprises
contacting the renewable feedstock with the deoxygenation catalyst
wherein the renewable feedstock comprises glycerides or free fatty
acids.
17. The method of claim 11 wherein contacting the renewable
feedstock with the deoxygenation catalyst further comprises
contacting the renewable feedstock with the deoxygenation catalyst
wherein the renewable feedstock comprises oil extracted from a
plant or an animal.
18. The method of claim 11 further comprising sulfiding the
deoxygenation catalyst.
19. The method of claim 1 further comprising: pre-cleaning the
renewable feedstock in a pre-cleaning zone.
20. A system for producing fuel from a renewable feedstock
comprising; a renewable feedstock feed system; a deoxygenation
reaction zone coupled to the renewable feedstock feed system; a
first isomerization reaction zone coupled to the deoxygenation
reaction zone; a fractionation zone coupled to the first
isomerization reaction zone, wherein the fractionation zone
comprises a naphtha outlet; and an isomerization reactor, wherein
the naphtha outlet is coupled to the isomerization reactor.
Description
TECHNICAL FIELD
[0001] The present disclosure generally relates to systems and
methods for producing fuels from renewable feedstocks, and more
particularly relates to systems and methods for converting
renewable feedstocks into branched paraffins useful as fuel.
BACKGROUND
[0002] Many existing processes for converting renewable feedstocks
into diesel fuels or jet fuels produce a naphtha stream as a
co-product. The naphtha stream often includes many normal paraffin
compounds, which are straight chain paraffins, that have a
relatively low octane value. The octane value can be increased by
isomerizing the normal paraffins into branched paraffins, because
branched paraffins produce higher octane values. Increasing the
octane value of the naphtha stream increases the value of the
naphtha stream, and a more valuable naphtha stream increases the
value of the overall process for converting renewable feedstocks
into fuel.
[0003] Accordingly, it is desirable to develop methods and systems
for increasing the degree of isomerization of naphtha produced as a
co-product with other fuels from renewable feedstocks. In addition,
it is desirable to develop methods and systems for increasing the
octane value of naphtha produced from renewable feedstocks.
Furthermore, other desirable features and characteristics of the
present embodiment will become apparent from the subsequent
detailed description and the appended claims, taken in conjunction
with the accompanying drawings and this background.
BRIEF SUMMARY
[0004] A method is provided for producing fuel from renewable
feedstocks. The renewable feedstock is deoxygenated in a
deoxygenation zone to produce hydrocarbons with normal paraffins.
The hydrocarbons with normal paraffins are isomerized to produce
hydrocarbons with branched paraffins. The hydrocarbons with
branched paraffins are fractionated to produce a naphtha at a
naphtha outlet, where the naphtha is further isomerized.
[0005] Another method is provided for producing a fuel from a
renewable feedstock. The renewable feedstock is contacted with a
deoxygenation catalyst to produce hydrocarbons with normal
paraffins. The hydrocarbons with normal paraffins are contacted
with an isomerization catalyst to produce hydrocarbons with
branched paraffins. The hydrocarbons with branched paraffins are
fractionated to produce a naphtha at a naphtha outlet, and the
naphtha is then isomerized.
[0006] A system is also provided for producing a fuel from a
renewable feedstock. The system includes a renewable feedstock feed
system coupled to a deoxygenation reaction zone. A first
isomerization reaction zone is coupled to the deoxygenation
reaction zone, and a fractionation zone is coupled to the first
isomerization reaction zone. The fractionation zone includes a
naphtha outlet, and the naphtha outlet is coupled to an
isomerization reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Various embodiments will hereinafter be described in
conjunction with the following figures, wherein like numerals
denote like elements, and wherein:
[0008] FIG. 1 is a schematic diagram of an exemplary embodiment of
a system and method for producing fuel from a renewable feedstock;
and
[0009] FIG. 2 is a schematic diagram illustrating an exemplary
embodiment of a system and method for fractionating and isomerizing
fuel products produced from a renewable feedstock.
DETAILED DESCRIPTION
[0010] The following detailed description is merely exemplary in
nature and is not intended to limit the application or uses of the
embodiment described. Furthermore, there is no intention to be
bound by any theory presented in the preceding technical field,
background, brief summary, or the following detailed
description.
[0011] Various processes for converting renewable feedstocks into
fuels, especially into diesel fuel or jet fuel, also produce a
naphtha co-product. The naphtha co-product is primarily hydrocarbon
molecules with 5 to 8 carbon atoms and boils at a lower temperature
than diesel or jet fuel. The naphtha co-product could be used for
gasoline or other fuels, but it has a significant component of
straight chain (normal) paraffins that have a low octane value. The
octane value of the naphtha is increased by isomerizing the normal
paraffins to produce branched paraffins, and the higher octane
value increases the monetary value of the naphtha co-product.
[0012] Reference is now made to the exemplary embodiment
illustrated in FIG. 1. A renewable feedstock 10 is processed to
produce various types of fuel, such as diesel fuel, jet fuel,
gasoline, liquid propane gas (LPG), etc. The term renewable
feedstock 10 is meant to include feedstocks other than those
derived from petroleum crude oil, and includes oils extracted from
plants or animals. The renewable feedstocks 10 as contemplated
herein are any of those which include glycerides or free fatty
acids (FFA). Most of the glycerides will be triglycerides, but
monoglycerides and diglycerides may be present and processed as
well. Examples of these renewable feedstocks 10 include, but are
not limited to, canola oil, corn oil, rapeseed oil, soybean oil,
colza oil, tall oil, sunflower oil, hempseed oil, olive oil,
linseed oil, coconut oil, castor oil, peanut oil, palm oil, mustard
oil, camelina oil, pennycress oil, tallow, yellow and brown
greases, lard, train oil, jatropha oil, fats in milk, fish oil,
algal oil, sewage sludge, and the like. Additional examples of
renewable feedstocks 10 include non-edible vegetable oils, such as
oils from Madhuca indica (mahua), Pongamia pinnata, and Azadirachta
indica (neem).
[0013] The glycerides and FFAs of the typical vegetable or animal
fat contain aliphatic hydrocarbon chains in their structure which
have about 8 to about 24 carbon atoms. The majority of the fats and
oils contain high concentrations of fatty acids with 16 to 18
carbon atoms, and many types of oils contain aliphatic hydrocarbon
chains within a limited range, such as 14 to 18. Only a limited
number of oil types include aliphatic hydrocarbon chains covering
the entire range from about 8 carbon atoms to about 24 carbon
atoms, so the 8 to 24 carbon atoms range is meant to encompass
mixtures of all types of oils. Co-feeds, or mixtures of renewable
feedstocks 10 and petroleum derived hydrocarbons, may also be used
as the feedstock. Other feedstock components that may be used,
especially as a co-feed component in combination with the above
listed feedstocks, include spent motor oils and industrial
lubricants; used paraffin waxes; liquid derived from the
gasification of coal, biomass, or natural gas followed by a
downstream liquefaction step such as Fischer-Tropsch technology;
liquids derived from depolymerization (thermal or chemical) of
waste plastics such as polypropylene, high density polyethylene,
and low density polyethylene; and other synthetic oils generated as
byproducts from petrochemical and chemical processes. Mixtures of
the above feedstocks may also be used as co-feed components. One
advantage of using a co-feed component is the transformation of
what may have been a waste product into a valuable co-feed
component to the current process.
[0014] The renewable feedstock 10 is stored and delivered for
processing by a renewable feedstock feed system 12. In an exemplary
embodiment, the renewable feedstock feed system 12 includes a
renewable feedstock storage tank 14, renewable feedstock pump 16,
and associated piping. The renewable feedstock feed system 12
delivers a renewable feedstock feed stream 18 for further
processing. Other embodiments of the renewable feedstock feed
system 12 exist, such as a pipeline from a different source, and a
pressurized renewable feedstock storage tank 14 without a renewable
feedstock pump 16.
[0015] Many renewable feedstocks 10 that can be used herein contain
a variety of impurities. For example, tall oil is a byproduct of
the wood processing industry, and includes esters and rosin acids
in addition to FFAs. Rosin acids are cyclic carboxylic acids. The
renewable feedstocks 10 may also contain contaminants such as
alkali metals, (e.g. sodium and potassium), phosphorous, various
solids, water, and detergents. In some embodiments, the renewable
feedstock 10 is pre-cleaned in an optional pre-cleaning zone 20 to
improve downstream processing operations, and several different
types of pre-cleaning are possible. For example, the pre-cleaning
zone 20 may be configured to provide a mild acid wash by contact
with dilute sulfuric, nitric, citric, phosphoric, or hydrochloric
acid in a reactor. The acid wash can be a continuous process or a
batch process, and the dilute acid contact can be at ambient
temperature and atmospheric pressure. Other possible pre-cleaning
steps include, but are not limited to, contacting the renewable
feedstock 10 with an ion exchange resin such as Amberlyst.RTM.-15,
subjecting the renewable feedstock 10 to a caustic treatment,
bleaching the renewable feedstock 10 with an adsorbent, filtration,
solvent extraction, hydro processing, or combinations of the
above.
[0016] In some embodiments, a sulfiding agent 22 is added to the
renewable feedstock 10. Several reactors described more fully below
use catalysts of various types, and one or more of these catalysts
can be used in a sulfided state in various embodiments. Sulfur is
added to the process to maintain the catalysts in the sulfided
state. The sulfiding agent 22 is added at a sulfiding agent inlet
24. The sulfur is measured as elemental sulfur, regardless of the
compound containing the sulfur, and can be added in many forms. For
example, suitable sulfiding agents 22 include, but are not limited
to, dimethyl disulfide, dibutyl disulfide, and hydrogen sulfide.
The sulfur may be obtained from various sources, such as part of a
hydrogen stream from a hydrocracking unit or hydro treating unit,
or sulfur compounds removed from kerosene or diesel, and disulfide
oils removed from sweetening units such as Merox.RTM. units. A
deoxygenation catalyst is described more fully below, and sulfur
concentrations of less than 2,000 ppm are typically sufficient to
maintain the deoxygenation catalyst and the other catalysts
described below in a sulfided state. FIG. 1 illustrates adding the
sulfiding agent 22 to the renewable feedstock feed stream 18, but
other embodiments are possible. For example, some renewable
feedstocks 10 contain sufficient sulfur to maintain the catalysts
in a sulfided state. Sulfur can also be added to the renewable
feedstock storage tank 14, the reactors containing the catalysts,
or other locations.
[0017] In an exemplary embodiment, a recycle hydrogen stream 80
(described more fully below) is added to the renewable feedstock
feed stream 18 and flows downstream to a guard bed 26. A portion of
a hot separator bottoms stream 50 (described more fully below) is
also added to the renewable feedstock feed stream 18 before entry
into the guard bed 26. The guard bed 26 removes metals from the
renewable feedstock 10 by contacting the renewable feedstock feed
stream 18 with a guard bed catalyst 28 at pretreatment conditions.
The guard bed catalyst 28 may initiate a deoxygenation reaction of
the renewable feedstock feed stream 18 to some degree, as described
more fully below. In some embodiments, the guard bed catalyst 28 is
alumina, either with or without demetallation catalysts such as
nickel or cobalt, but other guard bed catalysts 28 are also
possible. The guard bed 26 is operated at a temperature from about
40.degree. C. to about 400.degree. C., for example from about
150.degree. C. to about 300.degree. C. Operating pressures for the
guard bed 26 are from about 690 kilopascals (kPa) absolute (100
pounds per square inch absolute (psia)) to about 13,800 kPa
absolute (2,000 psia), for example from about 1,380 kPa absolute
(200 psia) to about 6,900 kPa absolute (1,000 psia). A portion of
the hot separator bottoms stream 50 may be added at various
locations in the guard bed 26 to aid in temperature control,
hydrogen solubility, or other purposes, but in other embodiments
different streams or no streams are added at side locations in the
guard bed 26.
[0018] After the optional guard bed 26, a guard bed effluent 30
flows downstream to a deoxygenation reaction zone 40 including one
or more catalyst beds in one or more reactors. In the deoxygenation
reaction zone 40, the guard bed effluent 30 is contacted with a
deoxygenation catalyst 42 (sometimes referred to as a hydrotreating
catalyst) in the presence of hydrogen at deoxygenation conditions.
The hydrogen for this reaction is provided from the recycle
hydrogen stream 80 added to the renewable feedstock feed stream 18.
Under these conditions, the olefinic or unsaturated portions of
n-paraffinic chains are hydrogenated. Additionally, any
deoxygenation reactions that did not take place in the guard bed 26
are completed in the deoxygenation reaction zone 40. In some
embodiments, a portion of the hot separator bottoms stream 50 is
added at various locations in the deoxygenation reaction zone 40 to
aid in temperature control, hydrogen solubility, and other
purposes. In other embodiments, streams other than the hot
separator bottoms stream 50 (or even no streams) are added at side
locations in the deoxygenation reaction zone 40. A deoxygenation
effluent 44 exits the deoxygenation reaction zone 40.
[0019] Deoxygenation catalysts 42 are any of those well known in
the art, such as nickel, nickel/molybdenum, or cobalt/molybdenum
dispersed on a high surface area support. Other deoxygenation
catalysts 42 include one or more noble metal catalytic elements
dispersed on a high surface area support. Non-limiting examples of
noble metals include platinum (Pt) and/or palladium (Pd).
Deoxygenation conditions include a temperature of about 40 degrees
centigrade (.degree. C.) to about 400.degree. C., and a pressure of
about 690 kilopascals (kPa) absolute (100 psia) to about 13,800 kPa
absolute (2,000 psia). In another embodiment the deoxygenation
conditions include a temperature of about 200.degree. C. to about
300.degree. C., and a pressure of about 1,380 kPa absolute (200
psia) to about 6,900 kPa absolute (1,000 psia). Other operating
conditions for the deoxygenation reaction zone 40 can also be used.
A sulfiding agent 22, such as from the sulfiding agent inlet 24 or
from the renewable feedstock 10, maintains the deoxygenation
catalyst 42 in a sulfided state.
[0020] The deoxygenation catalysts 42 discussed above are also
capable of catalyzing decarboxylation, decarbonylation and/or
hydrodeoxygenation of the renewable feedstock 10 to remove oxygen.
Decarboxylation, decarbonylation, and hydrodeoxygenation are herein
collectively referred to as "deoxygenation reactions", and the
deoxygenation reactions and the olefin hydrogenation reactions
simultaneously occur in the deoxygenation reaction zone 40.
Deoxygenation conditions include a relatively low pressure of about
3,450 kPa (500 psia) to about 6,900 kPa (1,000 psia), a temperature
of about 200.degree. C. to about 400.degree. C., and a liquid
hourly space velocity of about 0.2 to about 10 hr.sup.-1. In
another embodiment the deoxygenation conditions include the same
relatively low pressure of about 3,450 kPa (500 psia) to about
6,900 kPa (1,000 psia), a temperature of about 290.degree. C. to
about 350.degree. C., and a liquid hourly space velocity of about 1
to about 4 hr.sup.-1.
[0021] Deoxygenation is an exothermic reaction, so the temperature
in the deoxygenation reaction zone 40 increases as the hydrocarbons
from the renewable feedstock 10 pass through. Decarboxylation and
hydrodeoxygenation reactions begin to occur as the temperature
increases. The rate of the deoxygenation reactions increases from
the front of the bed to the back of the bed as the temperature
increases. The deoxygenation reaction zone 40 can include one or
more reactors in series, and can also include parallel reactors or
sets of reactors.
[0022] The hydrodeoxygenation reaction consumes hydrogen and
produces water as a byproduct, while the decarbonylation and
decarboxylation reactions produce carbon monoxide (CO) or carbon
dioxide (CO.sub.2) without consuming hydrogen. However, hydrogen is
present for all the reactions in the deoxygenation reaction zone
40, regardless of whether the reaction consumes hydrogen or not.
The product from the deoxygenation reactions includes a liquid
portion and a gaseous portion. The liquid portion present in the
deoxygenation effluent 44 includes hydrocarbon compounds that are
largely normal paraffin compounds (n-paraffins) having a high
cetane number. The gaseous portion includes hydrogen, carbon
dioxide (CO.sub.2), carbon monoxide (CO), water vapor, propane, and
perhaps sulfur components such as hydrogen sulfide. It is possible
to separate and collect the liquid portion (the hydrocarbons
including n-paraffins) as a diesel fuel product without further
reactions. However, in most climates, at least a portion of the
liquid n-paraffins can be isomerized to produce branched paraffins,
which improves the cold flow properties of the fuel.
[0023] In an exemplary embodiment, the deoxygenation effluent 44
passes to an optional hot separator 46 downstream from the
deoxygenation reaction zone 40. One purpose of the hot separator 46
is to separate at least some of the gaseous portion from the liquid
portion of the deoxygenation effluent 44. Much of the gaseous
portion, including the recovered hydrogen, exits the hot separator
46 in a hot separator overhead stream 48, and the liquid portion
exits the hot separator in a hot separator bottoms stream 50. The
separated hydrogen is recycled back to the deoxygenation reaction
zone 40 in some embodiments, as described more fully below. The
liquid hydrocarbons including the n-paraffins exit the hot
separator 46 in the hot separator bottoms stream 50.
[0024] In some embodiments, water, CO, CO.sub.2, and any ammonia or
hydrogen sulfide are stripped in the hot separator 46 using
hydrogen. In some embodiments (not shown), additional hydrogen is
used as the stripping gas, but other gases could also be used. The
temperature is controlled to achieve the desired separation, and
the pressure can be maintained at approximately the same pressure
as the deoxygenation reaction zone 40 and the isomerization
reaction zone (described below) to minimize both investment and
operation costs. Energy is required to change the temperature or
pressure, which increases operating costs, and additional equipment
is needed to enable the process to change the temperature of
pressure, which increases the investment cost. The hot separator 46
may be operated at conditions ranging from a pressure of about 690
kPa absolute (100 psia) to about 13,800 kPa absolute (2,000 psia),
and a temperature of about 40.degree. C. to about 350.degree. C. In
another embodiment, the hot separator 46 may be operated at
conditions ranging from a pressure of about 1,380 kPa absolute (200
psia) to about 6,900 kPa absolute (1,000 psia), or about 2,410 kPa
absolute (350 psia) to about 4,880 kPa absolute (650 psia), and a
temperature of about 50.degree. C. to about 350.degree. C.
[0025] The paraffinic components of the hot separator bottoms
stream 50 are primarily n-paraffins which range from about 8 to
about 24 carbon atoms depending on the type of renewable feedstock
10 used. Different renewable feedstocks 10 will result in different
distributions of paraffins. The hot separator bottoms stream 50 is
divided and transferred to various locations in different
embodiments. A portion of the hot separator bottoms stream 50 may
be recycled and added to the guard bed 26 at various locations, and
to the deoxygenation reaction zone 40 at various locations, as
described above. In alternate embodiments, other streams or no
streams are recycled in place of the hot separator bottoms stream
50.
[0026] In an exemplary embodiment, the hot separator bottoms stream
50 also flows to an enhanced hot separator 52 to further separate
the gaseous and liquid components of the deoxygenation effluent 44.
Additional gases are removed from the liquid hydrocarbons with the
n-paraffins, and the gases are vented in an enhanced hot separator
overhead stream 54, which is combined with the hot separator
overhead stream 48. The enhanced hot separator 52 operates at
similar conditions as the hot separator 46. The enhanced hot
separator operating conditions range from a pressure of about 690
kPa absolute (100 psia) to about 13,800 kPa absolute (2,000 psia),
and a temperature of about 40.degree. C. to about 350.degree. C. In
another embodiment, the enhanced hot separator 52 may be operated
at conditions ranging from a pressure of about 1,380 kPa absolute
(200 psia) to about 6,900 kPa absolute (1,000 psia), or about 2,410
kPa absolute (350 psia) to about 4,880 kPa absolute (650 psia), and
a temperature of about 50.degree. C. to about 350.degree. C.
[0027] An enhanced hot separator bottoms stream 56 flows from the
enhanced hot separator 52 downstream to a first isomerization
reaction zone 60. The enhanced hot separator bottoms stream 56 is
primarily made up of the liquid hydrocarbons, including the
n-paraffins, from the deoxygenation reaction zone 40. Fresh
hydrogen is added to the enhanced hot separator bottoms stream 56
from a hydrogen feed line 36, so additional hydrogen is fed to the
first isomerization reaction zone 60. In other embodiments, the
hydrogen could be fed to the first isomerization reaction zone 60
in other manners, such as from a feed line piped directly into a
reactor in the first isomerization reaction zone 60.
[0028] Isomerization can be carried out in a separate bed of the
same reactor used in the deoxygenation reaction zone 40, or the
isomerization can be carried out in a separate isomerization
reactor 58. For ease of description, the following will address the
embodiments where a separate reaction zone is employed for the
first isomerization reaction zone 60. In an exemplary embodiment,
the first isomerization reaction zone 60 includes an isomerization
catalyst 62 positioned within an isomerization reactor 58, and is
operated at isomerization conditions. The hydrocarbons with the
n-paraffins in the enhanced hot separator bottoms stream 56 are
contacted with the isomerization catalyst 62 in the presence of
hydrogen to convert at least some of the n-paraffins into branched
paraffins. Only minimal branching is required to overcome the poor
cold-flow characteristics of the n-paraffins used in diesel or jet
fuel. In some embodiments, the predominant isomerized paraffin
product is a mono-branched hydrocarbon, because process conditions
that produce significant branching also increase the risk of
excessive cracking that reduces the yield of diesel or jet fuel.
The hydrocarbons used in diesel and jet fuel generally have more
carbons than the hydrocarbons used in gasoline, on average, and
have a higher average boiling point. Besides improving the cold
flow properties of diesel fuel, branched paraffins also increase
the octane rating of gasoline fuels.
[0029] An isomerization effluent 64, which exits the first
isomerization reaction zone 60, is a hydrocarbon stream rich in
branched paraffins. By the term "rich" it is meant that the
isomerization effluent 64 has a greater concentration of branched
paraffins than the stream entering the first isomerization reaction
zone 60, and in some embodiments includes greater than 50 mass
percent branched paraffins. The isomerization effluent 64 may
contain 70, 80, or 90 mass percent branched paraffins in some
embodiments, but lower concentrations of branched paraffins are
present in other embodiments. The degree of isomerization can be
changed by adjusting the isomerization conditions. For example, a
lower reactor temperature will decrease the degree of
isomerization, and also decrease the degree of cracking in the
first isomerization reaction zone 60.
[0030] The isomerization of the n-paraffins can be accomplished by
using a variety of suitable catalysts. The first isomerization
reaction zone 60 includes one or more beds of isomerization
catalyst 62, and the catalyst beds can be in series and/or
parallel. A single isomerization reactor 58 may include one or more
catalyst beds, so the first isomerization reaction zone 60 can also
include one or more isomerization reactors 58. In some embodiments,
the first isomerization reaction zone 60 is operated in a
co-current mode of operation. Fixed bed trickle down flow or fixed
bed liquid upward flow modes are both suitable. In some
embodiments, the isomerization catalyst 62 is not sulfided, so no
sulfiding agents are added to streams entering the first
isomerization reaction zone 60 downstream from the deoxygenation
reaction zone 40. In alternate embodiments, the isomerization
catalyst is sulfided.
[0031] Suitable isomerization catalysts 62 include a metal of Group
VIII (IUPAC 8-10) of the Periodic Table and a support material.
Suitable Group VIII metals include platinum and palladium, each of
which may be used alone or in combination. The support material may
be amorphous or crystalline, and many different support materials
can be used. Suitable support materials include, but are not
limited to, amorphous alumina, amorphous silica-alumina,
ferrierite, metal aluminumsilicophosphates, laumontite, cancrinite,
offretite, the hydrogen form of stillbite, the magnesium or calcium
form of mordenite, and the magnesium or calcium form of partheite,
each of which may be used alone or in combination. Many natural
zeolites, such as ferrierite, that have an initially reduced pore
size can be converted to forms suitable for olefin skeletal
isomerization by removing associated alkali metals or alkaline
earth metals by ammonium ion exchange and calcination to produce a
substantial hydrogen form. The isomerization catalyst 62 may also
include one or more modifiers, such as those selected from the
group of lanthanum, cerium, praseodymium, neodymium, samarium,
gadolinium, terbium, and mixtures thereof
[0032] The isomerization reaction occurs when hydrocarbons pass
through the isomerization catalyst 62 at isomerization conditions.
Isomerization conditions include a temperature of about 150.degree.
C. to about 420.degree. C. and a pressure of about 1,720 kPa
absolute (250 psia) to about 4,720 kPa absolute (700 psia). In
another embodiment, the isomerization conditions include a
temperature of about 300.degree. C. to about 360.degree. C. and a
pressure of about 2,400 kPa absolute (350 psia) to about 3,800 kPa
absolute (550 psia). Other operating conditions for the first
isomerization reaction zone 60 can also be used.
[0033] The hydrocarbons with the branched paraffins in the
isomerization effluent 64 are processed through one or more
separation steps to obtain a hydrocarbon stream useful as a fuel,
and the separation steps vary in different embodiments. The
isomerization effluent 64 includes both a liquid component and a
gaseous component, various portions of which can be recycled, so
multiple separation steps may be employed. For example, in some
embodiments the isomerization effluent 64 is separated in an
isomerization effluent separator 66 positioned downstream from the
first isomerization reaction zone 60. Hydrogen exits the
isomerization effluent separator 66 in an isomerization effluent
separator overhead stream 68, and the liquid portion exits in an
isomerization effluent separator bottoms stream 70. The
isomerization effluent separator overhead stream 68 is fed to the
enhanced hot separator 52 in some embodiments, so the gaseous
portions are combined with the gases in the enhanced hot separator
overhead stream 54. In other embodiments (not shown), the
isomerization effluent separator overhead stream 68 bypasses the
enhanced hot separator 52 and is eventually used as recycled
hydrogen or processed in other ways.
[0034] Suitable operating conditions of the isomerization effluent
separator 66 include, for example, a temperature of about
280.degree. C. to about 360.degree. C. and a pressure of about
4,100 kPa absolute (600 psia), but other operating conditions are
also possible. If there is a low concentration of carbon oxides, or
the carbon oxides are removed, the hydrogen may be directly
recycled and re-used in the process. Hydrogen is a reactant in the
deoxygenation reaction zone 40 and the first isomerization reaction
zone 60, and different renewable feedstocks 10 will consume
different amounts of hydrogen. Additional hydrogen can be added for
feeds that consume more hydrogen. Furthermore, at least a portion
of the isomerization effluent separator bottoms stream 70 can be
recycled to the first isomerization reaction zone 60 (not shown) to
increase the degree of isomerization, to aid in temperature
control, or for other purposes.
[0035] The remainder of the isomerization effluent separator
bottoms stream 70 still has liquid and gaseous components and can
be cooled by various techniques, such as air cooling or water
cooling. The liquid portion of the isomerization effluent separator
bottoms stream 70 is hydrocarbons, including the branched
paraffins, as well as some n-paraffins that were not isomerized
into branched paraffins. After cooling, the isomerization effluent
separator bottoms stream 70 is passed to a cold separator 72 where
the liquid component is separated from the gaseous component. The
hot separator overhead stream 48 and the enhanced hot separator
overhead stream 54 are also fed to the cold separator 72, and can
be combined with the isomerization effluent separator bottoms
stream 70 upstream from the cold separator 72. Suitable operating
conditions of the cold separator 72 include, for example, a
temperature of about 40.degree. C. to about 60.degree. C. (about
100.degree. F. to about 140.degree. F.) and a pressure of about
3,800 kPa absolute to about 5,300 kPa absolute (about 550 to about
770 psia), but other operating conditions are also possible. A
water byproduct stream is also separated in the cold separator 72
(not shown). A cold separator overhead stream 74 and a cold
separator bottoms stream 76 exit the cold separator 72.
[0036] The cold separator overhead stream 74, or the gaseous
components separated in the cold separator 72, is mostly hydrogen
and the carbon dioxide from the decarboxylation reaction. Other
components such as CO, propane, and hydrogen sulfide or other
sulfur containing components may be present as well. Water, CO, and
CO.sub.2 can negatively impact the catalyst performance in the
first isomerization reaction zone 60. It is desirable to recycle
the hydrogen, but if the CO.sub.2 and other components are not
removed, their concentrations can build up and negatively affect
the operation of the first isomerization reaction zone 60. A
recovery gas cleaner 78 can be used to increase the purity of the
cold separator overhead stream 74. The carbon dioxide can be
removed from the hydrogen by several different processes, including
but not limited to absorption with an amine, reaction with a hot
carbonate solution, pressure swing absorption, etc. If desired,
essentially pure carbon dioxide can be recovered by regenerating
the spent absorption media. A sulfur containing component, such as
hydrogen sulfide, may also be present. The sulfur containing
component may be used to help control the relative amounts of the
decarboxylation reaction and the hydrogenation reaction in the
deoxygenation reaction zone 40. The amount of sulfur is generally
controlled, so the sulfur is also removed before the hydrogen is
recycled. Various methods can be used, such as absorption with an
amine or a caustic wash, and the carbon dioxide and sulfur
containing components (as well as other components) are removed in
a single separation step in some embodiments.
[0037] A recycle hydrogen stream 80 exits the recovery gas cleaner
78 after the impurities have been removed. A recycle hydrogen
compressor 82 urges the hydrogen back into the process. As
discussed above, the recycle hydrogen stream 80 may be fed into the
renewable feedstock feed stream 18, but the recycle hydrogen stream
80 could be routed into the process in other locations as well,
such as routed directly into the reactors of the deoxygenation
reaction zone 40 or the first isomerization reaction zone 60. The
recycle hydrogen stream 80 supplies the hydrogen for the guard bed
26 and the deoxygenation reaction zone 40, as discussed above.
[0038] The cold separator bottoms stream 76, or the liquid
component separated in the cold separator 72, contains the liquid
hydrocarbons with the branched paraffins useful as jet fuel and/or
diesel fuel, as well as smaller amounts of naphtha, liquid propane
gas (LPG), and other hydrocarbons. The cold separator bottoms
stream 76 may be recovered as diesel boiling range fuel or it may
be further purified in a fractionation zone 84 that fractionates
the various components of the cold separator bottoms stream. In one
embodiment, the fractionation zone 84 includes a product stripper
86 or a product fractionator (not shown) that can be operated, for
example, with a vapor temperature of from about 20.degree. C. to
about 200.degree. C. and a pressure from about 0 kPa (0 psia) to
about 1,380 kPa absolute (200 psia) at the overhead of the product
stripper 86. In alternate embodiments, the fractionation zone 84
includes a plurality of fractionators and/or separators to divide
the cold separator bottoms stream 76 into various fractions. The
fractionation zone 84 separates the cold separator bottoms stream
76 into a fractionation zone overhead stream 88, a naphtha product
that exits the fractionation zone 84 at a naphtha outlet 92, and a
fractionation zone bottoms stream 94. The naphtha outlet 92 is
split into a naphtha fraction 90 that is collected as a product,
and a naphtha reisomerization stream 93.
[0039] The fractionation zone overhead stream 88 includes LPG and
lighter hydrocarbons, such as ethane or methane, and it may include
butanes. The fractionation zone overhead stream 88 can be further
fractionated and sold as a product, used as a fuel gas, or used in
other processes such as the feed to a hydrogen production facility,
a co-feed to a reforming process, or a fuel blending component. The
fractionation zone bottoms stream 94 can be used a diesel range
fuel or further fractionated and used as a jet fuel. The naphtha
fraction 90 includes hydrocarbons with about 5 to 8 carbon atoms,
and boils from about 20.degree. C. to about 150.degree. C., where
the hydrocarbons are primarily a mixture of n-paraffins and
branched paraffins. In some embodiments, the naphtha is lightly
isomerized after making one pass through an isomerization reactor
58, so it includes relatively few branched paraffins. The naphtha
fraction 90 can be used as a component in gasoline, but it has an
octane value of about 60 to about 70 after a single pass through
the isomerization reactor 58, so a higher octane value would
increase the value of the naphtha fraction 90 for use in gasoline.
Most gasoline sold commercially has an octane value of about 85 to
about 95. The octane value can be increased by converting
n-paraffins into branched paraffins.
[0040] In an exemplary embodiment, some of the naphtha product from
the naphtha outlet 92 is further isomerized to convert n-paraffins
into branched paraffins by routing the naphtha reisomerization
stream 93 back to the first isomerization reaction zone 60. Some of
the naphtha product is removed from the process in a naphtha
fraction 90 to prevent the naphtha from building up in the system.
The isomerization catalyst 62 in the first isomerization reaction
zone 60 will crack some of the hydrocarbons in the naphtha into
smaller molecules, which decreases the yield of the final naphtha
fraction 90. However, cracking of the hydrocarbons in the naphtha
is minimized by reducing the contact time with the isomerization
catalyst 62 in the first isomerization reaction zone 60. The
naphtha reisomerization stream 93 may be added to the first
isomerization reaction zone 60 by coupling the naphtha outlet 92 to
a side inlet 96 of an isomerization reactor 58 in the first
isomerization reaction zone 60, where the side inlet 96 is
positioned with some of the catalyst bed upstream from the side
inlet 96 and some of the catalyst bed downstream from the side
inlet 96. The position of the side inlet 96 can be adjusted to
optimize the degree of isomerization of the naphtha with the degree
of cracking, and in some embodiments the naphtha reisomerization
stream 93 is coupled to the inlet of the isomerization reactor 58
and contacted with the entire isomerization catalyst bed. A side
inlet 96 configured so the naphtha bypasses some of the
isomerization catalyst 62 also minimizes any dilution effect by the
naphtha on the isomerization of the hydrocarbons with n-paraffins
in the enhanced hot separator bottoms stream 56.
[0041] Reference is now made to the exemplary embodiment
illustrated in FIG. 2, which begins with the cold separator bottoms
stream 76. In this embodiment, the fractionation zone 84 includes a
product stripper 86 with a fractionation zone overhead stream 88
and a fractionation zone bottoms stream 94. The fractionation zone
overhead stream 88 is fed into a light gas separator 98. A lean gas
stream 100 exits the light gas separator as a gas, and a light gas
separator bottoms stream 102 exits as a liquid. The light gas
separator bottoms stream 102 from the light gas separator 98
includes the LPG 104 and the hydrocarbons in the naphtha fraction
118. The LPG 104 and hydrocarbons in the naphtha fraction 118
(prior to isomerization) are further separated in a debutanizer 106
that produces the LPG 104 as an overhead stream and the naphtha
reisomerization stream 93 as a bottom stream. The naphtha
reisomerization stream 93 exits the debutanizer 106 at the naphtha
outlet 92. The debutanizer 106 can be operated, for example, at a
vapor temperature of about 20.degree. C. to about 200.degree. C.
and a pressure from about 0 to about 2,760 kPa absolute (0 to 400
psia) at the debutanizer overhead, but other conditions are also
possible.
[0042] The naphtha outlet 92 from the debutanizer 106 is coupled to
an isomerization reactor 114 in a second isomerization reaction
zone 110 to further isomerize the paraffins in the naphtha fraction
118. In some embodiments, the second isomerization reaction zone
110 includes an isomerization catalyst 116 and operates at
isomerization conditions. The second isomerization reaction zone
110 can be operated to match the feed from the naphtha outlet 92,
and a suitable isomerization catalyst 116 and isomerization
conditions can be used. In an exemplary embodiment, the
isomerization catalyst 116 includes about 0.01 to about 3 weight
percent of a metal on an inorganic oxide carrier, and includes a
halide as a promoter. Suitable inorganic oxide carriers include
alumina, silica, zirconia, magnesia, thoria, and combinations
thereof, but other carriers can also be used. Suitable metals
include Ruthenium, Rhodium, Palladium, Osmium, Iridium, and
Platinum, and the weight percent is determined based on the weight
of the metal, regardless of the form of the metal on the carrier.
The halide promoter is present at about 0.1 to about 10 weight
percent, and includes chlorides or other halides. Suitable
isomerization conditions include a temperature from about
120.degree. C. to about 200.degree. C. (about 250.degree. F. to
about 400.degree. F.), and pressures from about 2,400 kPa to about
3,800 kPa (about 350 PSIG to about 550 PSIG).
[0043] The second isomerization reaction zone 110 can be used in
place of, or in conjunction with, a naphtha recycle through the
first isomerization reaction zone. The naphtha reisomerization
stream 93 is the primary feed to the second isomerization reaction
zone 110, so the size of the isomerization reactor 114 and catalyst
bed, the quantity of isomerization catalyst 116 used, and the
isomerization conditions can be optimized for the naphtha
reisomerization stream 93. A second isomerization reaction zone
hydrogen line 112 can be used to introduce hydrogen for the
isomerization reaction. The naphtha fraction 118 then exits the
second isomerization reaction zone 110 with a higher level of
branched paraffins than the feed to the second isomerization
reaction zone 110. An optional separator (not shown) can be
installed downstream from the second isomerization reaction zone
110 to vent hydrogen and light gases produced by cracking in the
isomerization reactor 114, and the vented hydrogen can be reused in
a similar manner to the hydrogen collected in the hot separator
overhead stream.
[0044] Reference is now made to FIG. 1 again. The exemplary
embodiments described above include many optional processes, or
processes that can be modified or arranged in different manners. In
a very simplified form, the renewable feedstock feed system 12 is
coupled to the deoxygenation reaction zone 40, because the
renewable feedstock 10 flows to the deoxygenation reaction zone 40.
The deoxygenation reaction zone 40 is likewise coupled to the first
isomerization reaction zone 60, which is coupled to the
fractionation zone 84, even though several vessels or processes are
positioned between the different zones. The naphtha is recovered
from the fractionation zone 84 and re-isomerized to increase the
concentration of branched paraffins. Several vessels and steps are
used to recover and reuse hydrogen throughout the manufacturing
process.
[0045] It should be appreciated that the embodiment or embodiments
illustrated are only examples, and are not intended to limit the
scope, applicability, or configuration of the application in any
way. Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing one
or more embodiments, it being understood that various changes may
be made in the function and arrangement of elements described
without departing from the scope as set forth in the appended
claims.
* * * * *