U.S. patent application number 15/729927 was filed with the patent office on 2018-02-01 for combined solid adsorption-hydrotreating process for whole crude oil desulfurization.
The applicant listed for this patent is Saudi Arabian Oil Company. Invention is credited to Esam Zaki HAMAD, Yuguo X. WANG.
Application Number | 20180030359 15/729927 |
Document ID | / |
Family ID | 44787404 |
Filed Date | 2018-02-01 |
United States Patent
Application |
20180030359 |
Kind Code |
A1 |
HAMAD; Esam Zaki ; et
al. |
February 1, 2018 |
COMBINED SOLID ADSORPTION-HYDROTREATING PROCESS FOR WHOLE CRUDE OIL
DESULFURIZATION
Abstract
A whole crude oil desulfurization system and process includes a
combination of an adsorption zone and a hydroprocessing zone. This
combined process and system reduces the requisite throughput for
the hydroprocessing unit, conventionally a very costly and process
both in terms of energy expenditures and catalyst depletion. By
first contacting the whole crude oil feedstock with an adsorbent
for the sulfur-containing compounds, the adsorption effluent having
a relatively lower sulfur content can be collected and provided to
refiners without further treatment. The adsorbates, including
adsorbed organosulfur compounds, are solvent desorbed resulting in
a stream containing high levels of organosulfur compounds and a
solvent. Following recovery of the solvent, the volume of the
sulfur-containing feedstream that remains to be desulfurized in the
hydroprocessing zone is substantially less than the original amount
of whole crude oil feedstock.
Inventors: |
HAMAD; Esam Zaki; (Dhahran,
SA) ; WANG; Yuguo X.; (Dhahran, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saudi Arabian Oil Company |
Dhahran |
|
SA |
|
|
Family ID: |
44787404 |
Appl. No.: |
15/729927 |
Filed: |
October 11, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13090584 |
Apr 20, 2011 |
|
|
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15729927 |
|
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61325898 |
Apr 20, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 25/003 20130101;
C10G 67/06 20130101; C10G 2300/202 20130101; C10G 2300/4093
20130101; C10G 25/05 20130101; C10G 2300/1033 20130101; C10G 25/12
20130101; C10G 2300/44 20130101; C10G 2300/207 20130101 |
International
Class: |
C10G 25/12 20060101
C10G025/12; C10G 67/06 20060101 C10G067/06; C10G 25/00 20060101
C10G025/00; C10G 25/05 20060101 C10G025/05 |
Claims
1. A process for treating whole crude oil containing organosulfur
compounds comprising: a. contacting, upstream of a crude
distillation unit, a whole crude oil feed stream containing
organosulfur compounds with a solid porous adsorbent material
having average pore diameter in the mesoporous range to about 50
nanometers, wherein organosulfur compounds are adsorbed by the
adsorbent material; b. recovering a treated effluent stream having
a reduced level of organosulfur compounds; c. desorbing at least a
portion of the organosulfur compounds from the adsorbent material,
and recovering a purge stream having an increased level of
organosulfur compounds from the adsorbent material; and d.
hydroprocessing the purge stream and recovering a hydroprocessed
stream having a reduced level of organosulfur compounds.
2. The process as in claim 1, wherein the adsorbent material is
contained in at least one fixed bed.
3. The process of claim 1, wherein the hydroprocessed stream is
combined with the treated effluent stream.
4. The process of claim 1, wherein the treated effluent stream is
further subjected to a fractionation process to remove a gas phase
that contains at least hydrogen sulfide gas.
5. The process of claim 1, wherein the treated effluent stream
contains at least about 5 to 53 weight percent less organosulfur
compounds than the whole crude oil stream.
6. The process of claim 1, wherein the treated effluent stream
contains at least about 30 to 53 weight percent less organosulfur
compounds than the whole crude oil stream.
7. The process of claim 1, wherein the desorbing step employs a
stripping solvent.
8. The process of claim 7, wherein the purge stream contains at
least a portion of the stripping solvent, and organosulfur
compounds, and wherein at least a portion of the stripping solvent
in the desorbed purge stream is distilled and recycled.
9. The process of claim 7, wherein the stripping solvent comprises
a solvent selected from the group consisting of toluene, hexane,
butane, pentane and combinations comprising at least one of the
foregoing solvents.
10. The process of claim 7, wherein the stripping solvent comprises
toluene.
11. The process of claim 1, wherein the desorbing step employs a
supercritical fluid.
12. The process of claim 11, further comprising recovering the
desorbed purge stream containing at least a portion of the
supercritical fluid and the increased organosulfur compound purge
stream, and wherein at least a portion of the supercritical fluid
in the desorbed purge stream is compressed and reused as the
stripping solvent.
13. The process of claim 11, wherein the supercritical fluid
comprises a supercritical fluid selected from the group consisting
of supercritical carbon dioxide, ethane, supercritical ethylene,
supercritical propane, supercritical butane and combinations
comprising at least one of the foregoing supercritical fluids.
14. The process of claim 11, wherein the supercritical fluid
comprises supercritical carbon dioxide.
15. The process of claim 1, wherein the adsorbent material has an
adsorbent capacity, and wherein contacting comprises: passing the
whole crude oil feed stream through a first adsorbing bed
containing adsorbent material until the adsorbent material in the
first adsorbing bed has reached a predetermined percentage of its
adsorbent capacity; and passing the whole crude oil feed stream
through a second adsorbing bed containing adsorbent material when
the adsorbent material in the first adsorbing bed has reached the
predetermined percentage of its adsorbent capacity.
16. The process of claim 15, further comprising desorbing the first
adsorbing bed while the whole crude oil feed stream is passed
through the second adsorbing bed.
17. The process of claim 15, wherein the predetermined percentage
is greater than at least 95%.
18. The process of claim 1, wherein the adsorbent material is
selective to organosulfur compounds including benzothiophenes
dibenzothiophenes, other multi-ring thiophenes, and combinations
comprising at least one of the foregoing organosulfur
compounds.
19. The process of claim 1, wherein the adsorbent material is
selected from the group of materials consisting of Y-zeolites,
active carbon powders and a combination comprising at least one of
the foregoing materials.
20. The process of claim 1, wherein hydroprocessing is selected
from the group consisting of hydrodesulfurization, hydrocracking,
hydrodenitrification, hydrodealkylation and hydrotreating.
Description
RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 13/090,584 filed on Apr. 20, 2011,
which is related to and claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/325,898 filed on Apr. 20, 2010,
which are incorporated by reference herein in their entireties.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] This invention relates to improvements in whole crude oil
processing, and in particular to an improved method for the
desulfurization of whole crude oil.
Description of Related Art
[0003] Natural petroleum and crude oil deposits are found worldwide
over land and sea, having been created based on significantly
different ecological and geological conditions since the time
before fossil records on Earth. It follows that the compositions
and constituents of extracted crude oil is different, and in some
cases vastly different. However, virtually all crude oils contain
some level of sulfur compounds, including inorganically combined
sulfur and organically combined sulfur, i.e., organosulfur
compounds. Whole crude oil that contains a relatively low level of
sulfur compounds is commonly referred to as "sweet." Often,
recovered whole crude oil contains a substantial level of sulfur
compounds, such as hydrogen sulfide, sulfur dioxide, and
organosulfiir compounds such as mercaptans, organic sulfides,
organic sulfoxides, organic sulfones, thiophenes, benzothiophenes,
and dibenzothiophenes, which are commonly referred to as
"sour."
[0004] Crude oil is generally converted in refineries by
distillation, followed by cracking and/or hydroconversion
processes, to produce various fuels, lubricating oil products,
chemicals, and chemical feedstocks. Fuels for transportation are
generally produced by processing and blending distilled fractions
from crude oil to meet the particular product specifications.
Conventionally, distilled fractions are subject to various
hydrocarbon desulfurization processes to make sulfur-containing
hydrocarbons more marketable, attractive to customers and
environmentally acceptable.
[0005] The discharge into the atmosphere of sulfur compounds during
processing and end-use of the petroleum products derived from
sulfur-containing sour crude oil pose health and environmental
problems. The stringent reduced-sulfur specifications applicable to
transportation and other fuel products have impacted the refining
industry, and it is necessary for refiners to make capital
investments to greatly reduce the sulfur content in gas oils to 10
parts per million by weight (ppmw) or less. In the industrialized
nations such as the United States, Japan and the countries of the
European Union, refineries for transportation fuel have already
been required to produce environmentally clean transportation
fuels. For instance, in 2007 the United States Environmental
Protection Agency required the sulfur content of highway diesel
fuel to be reduced 97%, from 500 ppmw (low sulfur diesel) to 15
ppmw (ultra-low sulfur diesel). The European Union has enacted even
more stringent standards, requiring diesel and gasoline fuels sold
in 2009 to contain less than 10 ppmw of sulfur. Other countries are
following in the footsteps of the United States and the European
Union and are moving forward with regulations that will require
refineries to produce transportation fuels with an ultra-low sulfur
level.
[0006] Furthermore, the price differential between sour crude oil
and sweet crude oil is increasing in favor of sweet crude oil.
Hydrocarbon desulfurization processes are required to reduce the
sulfur content. However, most desulfurization processing occurs
after varying levels of refining of the crude oil. Therefore sour
crude oil is sold at a lower price because the purchaser must
undertake the expense of desulfurization.
[0007] The most common hydrocarbon desulfurization process is
hydrotreating, or hydrodesulfurization. In typical hydrotreating
processes, hydrogen and a specific distilled hydrocarbon fraction
are introduced to a fixed bed reactor that is packed with a
hydrodesulfurization catalyst, commonly under elevated operating
conditions, which can vary depending on the specific fraction, type
and ratio of catalyst, requisite degree of desulfurization, and
other factors known to those of ordinary skill in the art. Notably,
the temperature and pressure conditions must be further elevated to
achieve the low and ultra low sulfur content requirements. However,
these operational and capital costs for these elevated conditions
are higher, and these elevated conditions often promote conversion
of the feed into less desirable intermediates.
[0008] Most known advances in the industry for minimizing these
undesirable effects include development of more robust
hydrotreating catalysts and advanced hydrodesulfurization reactor
designs. Alternative processes have also been developed to meet the
requirements of decreased sulfur levels in fuels and other
petrochemical products.
[0009] Conventionally, most oil refineries remove sulfur compounds
after the whole crude oil has been fractionated. For example, U.S.
Pat. Nos. 6,683,024, 6,864,215, 6,869,522, 6,930,074, 6,955,752 and
7,105,140, and Patent Publication US2001/002931 describe sorbent
compositions that are used to desulfurize cracked-gasoline and
diesel fuel. U.S. Pat. Nos. 7,0743,24 and 7,291,259 disclose
desulfurization of cracked-gasoline and diesel fuel and other
refinery fractions. Patent Publication US2005/0075528 describes the
use of spent hydrotreating catalyst as adsorbent to treat specific
fractions, including gasoline, gas oil, kerosene, or an atmospheric
distillation residue.
[0010] Other processes are described in which adsorption techniques
are used to remove hydrogenatable hydrocarbons, primarily in the
context of halogenated hydrocarbons. For instance, U.S. Pat. Nos.
4,952,746 and 4,747,937 generally disclose recovering compounds
that can be chemically modified by addition hydrogen. Hydrogentable
compounds are adsorbed, and then hydrogenated in a hydrotreating
reaction zone. Spent adsorbent is regenerated with an elution
solvent, and the combined stream including solvent is processed in
a hydrotreating zone. However, such a system only marginally
reduces the flow requirements for a hydrotreating zone, since the
elution solvent is hydrotreated along with the hydrogenatable
compounds. In addition, there is no teaching in U.S. Pat. Nos.
4,952,746 and 4,747,937 of treating whole crude oil to remove
organosulfur compounds.
[0011] Patent Publication US2005/0205470 discloses a process for
selectively removing sulfur from feedstocks such as FCC cracked
naphtha, jet fuel or diesel using adsorption. Traditional
hydrotreating is suitable for oil fractions, but not for whole
crude. However, this is not suitable for treating whole crude oil,
as adsorption alone will result in a substantial loss in the
overall crude oil volume.
[0012] Importantly, none of the above-described references that
incorporate adsorption disclose processes that are capable of
desulfurizing whole crude oil, prior to refining into its
constituent products. As a result, the previously proposed and
currently practiced methodologies require relatively greater
complexity downstream in operations, due to the need to remove
larger amounts of sulfur from naphtha, diesel fuel and other
refinery products. In addition, according to the process of the
above-described references in which adsorbent materials are used to
treat various fractions, no economic benefit is realized at the
level of providing whole crude oil to refineries, e.g., directly
from the pipeline or the tanker. Furthermore, none of the processes
and systems described above reduces the requisite capacity of a
hydroprocessing unit, typically an operation where substantial
processing costs are directly proportional to the overall volume of
crude oil that is processed in a given period of time.
[0013] It is therefore an object of this invention to provide a
whole crude oil desulfurization process that can reduce the sulfur
content while minimizing the required capacity of a hydroprocessing
reactor.
[0014] It is another object of the invention to balance the expense
of whole crude oil desulfurization with the price gain of the
product delivered to refiners.
[0015] As used herein, the term "whole crude oil" is to be
understood to mean a mixture of petroleum liquids and gases,
including impurities such as sulfur, as distinguished from refined
fractions of hydrocarbons.
[0016] As used herein, the term "hydroprocessing" is to be
understood to include hydrodesulfurization, hydrocracking,
hydrodenitrification, hydrodealkylation and hydrotreating.
SUMMARY OF THE INVENTION
[0017] A primary objective of whole crude oil desulfurization is to
convert sour grades of crude oil to more marketable and valuable
products for refinery operators. The present invention is directed
to a whole crude oil desulfurization system and process that
included a combination of an adsorption zone and a hydroprocessing
zone. This combined process and system reduces the requisite
throughput for the hydroprocessing unit, conventionally a very
costly process to operate both in terms of energy expenditures and
catalyst depletion.
[0018] By first treating the whole crude oil feedstock in the
adsorption zone, the adsorption effluent can be collected and
provided to refiners without further treatment, and the adsorbates,
which include adsorbed organosulfur compounds, are desorbed
resulting in a stream containing high levels of organosulfur
compounds and a solvent. The solvent is selected such that a major
proportion thereof can be conveniently separated and recovered, for
instance, by distillation. Accordingly, the volume of liquid feed
to be desulfurized in the hydroprocessing zone is substantially
less than the original volume of whole crude oil feedstock. This is
highly desirable, since a substantial cost of operating a
hydroprocessing unit is proportional to the feed volume and not
highly sensitive to the sulfur content. Since the cost of an
adsorption unit is typically much less than the cost of a
hydroprocessing unit, such as a hydrodesulfurization unit,
technologically mature units can be operated with desirable cost
savings using the novel process and system of the present
invention.
[0019] In a preferred embodiment, the process of the present
invention is operated upstream of the crude distillation unit in a
typical crude processing operation. It can be operated, for
instance, downstream of the wellhead, before or after the Gas-Oil
Separation Plant, upstream of the refinery limits, or within the
refinery limits prior to the crude distillation unit.
[0020] In the system and process of the present invention, a whole
crude oil feedstock is contacted with an adsorbent, typically in an
adsorbent bed, on which sulfur-containing compounds are selectively
adsorbed. The discharge is generally in the range of about 70% to
about 99% of the total volume of the initial feedstock, in which
the lower end of the range is applicable to feedstocks containing
higher levels of sulfur-containing compounds. The adsorbent is then
desorbed with a solvent to extract the adsorbates and regenerate
the bed.
[0021] In a preferred embodiment of the present invention, at least
two parallel adsorbent beds are used to operate continuously, so
that while one adsorbent bed is adsorbing the sulfur-containing
compounds from the whole crude oil feedstock, referred to herein as
an "adsorption cycle," the other adsorbent bed is regenerated,
referred to herein as a "desorption cycle."
[0022] Solvent is recovered and recycled from the mixture of
solvent and sulfur-containing adsorbates. The separated hydrocarbon
stream containing a relatively higher level of organosulfur
compounds is fed to a hydroprocessing unit for desulfurization to
produce a low sulfur content effluent. The low sulfur content
effluent recovered from the hydroprocessing zone can be recombined
with the low sulfur content effluent from the adsorption cycle, or
sent to a separate processing pool.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The foregoing summary, as well as the following detailed
description of preferred embodiments of the invention will be
better understood when read in conjunction with the appended
drawings. For the purpose of illustrating the invention, there are
shown in the drawings embodiments which are presently preferred. It
should be understood, however, that the invention is not limited to
the precise arrangements and instrumentalities shown. In the
drawings the same numeral is used to refer to the same or similar
elements, in which:
[0024] FIG. 1 is a schematic diagram of one embodiment of an
improved whole crude oil desulfurization system in accordance with
the invention;
[0025] FIG. 2 is a schematic diagram of another embodiment of an
improved whole crude oil desulfurization system in accordance with
the invention; and
[0026] FIG. 3 is a schematic diagram of a further embodiment of an
improved whole crude oil desulfurization system in accordance with
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0027] A process for treating whole crude oil containing
organosulfur compounds is generally described with respect to FIG.
1. A system 10 includes an adsorption zone 14 and a hydroprocessing
zone 20. The process includes contacting a whole crude oil feed
stream 12 containing organosulfur compounds with a solid adsorbent
material in the adsorption zone 14, wherein organosulfur compounds
are adsorbed by the adsorbent material. A treated effluent stream
16 having a reduced organosulfur compound content is recovered from
the adsorption zone 14.
[0028] When the adsorbent material has reached a predetermined
percentage of its adsorption capacity, organosulfur compounds are
desorbed from the adsorbent material, e.g., by contacting the
adsorbent material with a solvent for the organosulfur compounds.
An increased organosulfur compound purge stream 18 is recovered.
The increased organosulfur compound purge stream 18 is then
desulfitrized in the hydroprocessing zone 20, from which a reduced
organosulfur compound hydroprocessed stream 22 is recovered.
Accordingly, the treated effluent stream 16 having a reduced
organosulfur compound content (as compared to the whole crude oil
feed stream 12) bypasses the hydroprocessing zone 20. In certain
embodiments, the reduced organosulfir compound hydroprocessed
stream 22 and the treated effluent stream 16 recovered from the
adsorption zone 14 can be collected in a common location 24 or
stream 24 (e.g., reservoir, tanker, pipeline, refinery crude feed
stream). Alternatively, (not shown), the hydroprocessed stream 22
and the treated effluent stream 16 are collected or transported
separately.
[0029] The sequence of hydroprocessing after adsorption allows the
use of commercial hydroprocessing plant reactors and equipment such
as hydrotreating units and provides a significant economic
advantage. The cost of building and operating a hydroprocessing
unit is generally proportional to the feed volume, and is generally
not sensitive to the sulfur content up to about 6 wt %. Therefore,
since the cost of adsorption, desorption and other unit operations
equipment is generally much less than the cost of hydroprocessing
equipment such as hydrotreating units, the same amount of whole
crude oil can be desulfurized at a reduced cost using relatively
smaller hydrotreating units downstream of the adsorption unit(s),
as compared to using only a relatively larger hydrotreating unit to
achieve the same or similar level of desulfurization of a give
whole crude oil feedstream.
[0030] The adsorbent zone 14 can include any type of adsorbent bed
or other structure and associated systems for containing adsorbent
material. In certain embodiments, the adsorbent material is
contained in at least one fixed bed. The adsorbent zone 14 can also
be a plurality of fixed beds in parallel, series, or a combination
including parallel and series; one or more agitated or non-agitated
slurry vessels; or one or more moving bed adsorbers. The whole
crude oil feed 12 can be treated in batch, semi-continuous or
continuous operation, depending on the type and number of adsorbing
units in the adsorption zone 14.
[0031] The adsorbent material is characterized by a high capacity
and high selectivity for the sulfur compounds that are present in
whole crude oils. In general, the adsorbent material has an
adsorbent capacity suitable to remove at least about 5 to about 53
weight percent of the organosulfur compounds contained in the
original whole crude oil feed stream 12. In certain preferred
embodiments, the adsorbent material has an adsorbent capacity
suitable to remove at least about 30 weight percent, and in certain
embodiments higher levels, of the organosulfur compounds contained
in the whole crude oil feed stream 12.
[0032] In addition, a suitable adsorbent material can be readily
regenerated for repeated use if the adsorption unit. For instance,
suitable adsorbent material can be used for at least about 50
cycles, preferably at least about 200 cycles of adsorption and
desorption.
[0033] Further, the adsorbent material preferably does not react
with sulfur gases that can be present in the whole crude oil stream
12, such as hydrogen sulfide gas. Accordingly, unlike other prior
art processes that use beds of catalytic to remove hydrogen
sulfide, generally by oxidation, organosulfur compounds are
adsorbed in a manner that utilizes the "purge" stream to recover
whole crude oil, in a purge stream 18 having increased levels of
organosulfur compounds.
[0034] The adsorbent material/materials can include materials such
as zinc oxide. manganese oxide, metals over high surface area
supports like silica, alumina, zeolites, activated carbon,
mesoporous silica molecular sieves (e.g., Al-MCM-41), and bauxite.
Particularly suitable adsorbents that have been identified as
having suitable adsorbent capacity for adsorbing organosulfur
compounds from whole crude oil streams include alumino silicates
such as type Y zeolite (metal promoted, ion-exchanged and other
forms) and activated carbon powders. In certain embodiments, a
combination comprising at least one of the above mentioned
adsorbent materials can be used. For instance, these different
adsorbent materials can be admixed, or in staged sections or
adsorbent beds (in the case of series adsorbent beds).
[0035] The adsorbent preferably includes properties such as pore
size that permits the large organosulfur compounds access to the
internal adsorption sites. For instance, in a preferred embodiment,
adsorbent material is selected that has an average pore diameter of
about 10 to about 50 nanometers, a surface area of about 100 to
about 500 square meters per gram, a pore volume of about 0.5 to
about 0.8 cubic centimeters per gram, and a bulk density of about
0.55 to about 0.75 grams per cubic centimeter. In addition,
preferred adsorbent particles are extrudates having a diameter of
about 1 to about 5 millimeters and a length of about 0.5 to about
2.5 centimeters.
[0036] In preferred embodiments, large pressure drops (e.g.,
greater than about 0.25 bar/meter) are avoided by selection of
suitable adsorbent material (including selection of suitable
particle size), and suitable operating conditions such as
temperature, pressure and space flow velocity. Operating conditions
during adsorption can include: a temperature of ambient to about
70.degree. C., and in certain embodiments ambient to about
50.degree. C.; a pressure of ambient to about 5 bars, and in
certain embodiments ambient to about 3 bars; and a liquid hourly
space velocity of about 0.5/hour to about 10/hour, and in certain
embodiments about 1.0/hour to about 8.0/hour.
[0037] The organosulfur compounds from the whole crude oil stream
can include mercaptans, organic sulfides, organic sulfoxides,
organic sulfones, thiophenes, multi-ring thiophenes,
benzothiophenes, dibenzothiophenes and other sulfur-containing
organic compounds, and combinations comprising at least one of the
foregoing organosulfur compounds. During hydroprocessing, the
amount of organosulfilr compounds in the purge stream 18 having
increased levels of organosulfur compounds are converted to the
reduced organosulfur compound hydroprocessed stream 22.
[0038] In certain embodiments, sulfurous gases (such as hydrogen
sulfide gas) can be removed from the treated effluent 16 with a
fractionation process to further reduce the overall sulfur content,
as in known to those of ordinary skill in the in the art of
hydrotreating. The elemental sulfur can be recovered for commercial
sale.
[0039] Referring now to FIG. 2, an embodiment of a process and
system for desulfurizing whole crude oil (more generally shown with
respect to FIG. 1) is shown. A whole crude oil desulfurizing system
110 generally includes at least two parallel adsorption units 34,
54 in an adsorption zone 114. During the adsorption cycle, in which
one adsorption unit 54 is adsorbing organosulfur compounds from the
whole crude oil stream 32, the other adsorption unit 34 is in the
desorption cycle, where it is desorbing the previously adsorbed
organosulfur compounds into an increased organosulfur compound
purge stream 38.
[0040] During an adsorption cycle of the adsorption unit 34, a
treated effluent stream 36 having a reduced organosulfur compound
content is recovered from the adsorption unit 34. Likewise, during
an adsorption cycle of the adsorption unit 54, a treated effluent
stream 56 having a reduced organosulfur compound content is
recovered from the adsorption unit 54. The treated effluent streams
36, 56 can be directed, for instance, into a treated effluent
stream 116.
[0041] During a desorption cycle, shown with respect to the
adsorption unit 34 in FIG. 2, the adsorbates (including
organosulfur compounds adsorbed to the adsorbent material) are
desorbed to remove the increased organosulfur compound purge stream
38. A desorption cycle is also carried out in the adsorption unit
54 (not shown). The desorption cycle can commence, for instance,
when the adsorbent material in the adsorption unit 34 or 54 has
reached a predetermined percentage of its adsorbent capacity. In
certain embodiments, the whole crude oils stream 32 is adsorbed
until the level of organosulfur compounds has been reduced by a
predetermined percentage. The amount of sulfur reduction can be
monitored in the treated effluent stream 36, by various processes
including but not limited to X-ray florescence.
[0042] A semi-continuous operation can be established by adsorbing
in the adsorption unit 54 during the desorption cycle of adsorption
unit 34, where the whole crude oil stream 32 is directed to the
adsorption unit 54 for adsorptive desulfurization. The process can
cycle between desorption and adsorption as needed.
[0043] The adsorption bed 34 can be regenerated by various methods.
Furthermore, upon regeneration of the adsorbent material, at least
about 95%, preferably at least about 99%, of the adsorbate is
removed.
[0044] In the schematic diagram of FIG. 2, the desorption cycle
employs a stripping solvent. The stripping solvent used in the
process of the present invention is characterized by the following
properties: [0045] a. the ability to dissolve sulfur organic
compounds; [0046] b. it is in a liquid phase or supercritical state
at the stripping conditions; and [0047] c. sufficiently volatile
for reuse after separation of sulfur compounds. In addition,
economic considerations are important. Examples of suitable
stripping solvents include toluene, hexane, butane, pentane, or
combinations comprising at least one of the foregoing solvents. In
certain embodiments, toluene is a desirable stripping solvent as it
is an inexpensive aromatic solvent, thereby increasing the
solubility of a greater portion of aromatic organosulfur compounds.
Hexane, pentane and butane will dissolve a smaller portion of the
aromatic sulfur compounds, especially those with multiple aromatic
rings and nitrogen heteroatoms, in addition to sulfur, but energy
savings in recovering the solvent are realized.
[0048] The adsorbent in the adsorption unit 34 is contacted with a
stripping solvent in a desorbing stream 128. The purge stream 38
from the desorption cycle therefore includes organosulfur compounds
and stripping solvent. All or a substantial portion of the
stripping solvent used in the purge stream 38 is recovered, for
instance, in a distillation unit 126.
[0049] The effluent from the distillation unit 126, a hydrocarbon
stream 118 having an increased level of organosulfur compounds, is
then processed in the hydroprocessing zone 120 for desulfurization.
A hydroprocessed stream 122 having a reduced level of organosulfur
compounds is recovered.
[0050] In certain embodiments, the hydroprocessed stream 122 and
the treated effluent stream 116 recovered from the adsorption zone
114 can be collected in a common location 124 or stream 124.
Alternatively, (not shown), the hydroprocessed stream 122 and the
treated effluent stream 116 are collected or transported
separately.
[0051] Operating conditions during desorption, for instance using
toluene as a stripping solvent, can include: a temperature of
ambient to about 70.degree. C., and in certain embodiments ambient
to about 50.degree. C.; a pressure of ambient to about 5 bars, and
in certain embodiments ambient to about 3 bars; and a liquid hourly
space velocity of about 0.5/hour to about 10/hour, and in certain
embodiments about 1.0/hour to about 8.0/hour.
[0052] The operating conditions for adsorption and desorption can
be similar, realizing process economics and configuration
advantages related to heating or cooling the bed. Since typical
stripping solvents have relatively low viscosity levels, there is a
lower pressure drop across the bed, or a higher velocity at the
same pressure drop. For butane and lighter hydrocarbons, stripping
can be accomplished in a liquid phase or supercritical state, and
the pressure and temperature conditions should be set accordingly,
i.e., such that the fluid is in its liquid state with the
temperature below the solvent's critical temperature and the
pressure above the solvent's vapor pressure, and such that the
fluid is in the supercritical state with the temperature slightly
above the solvent's critical temperature point and the pressure
around the solvent's critical pressure.
[0053] In a further embodiment of a process and system for
desulfurizing whole crude oil, and referring now to FIG. 3, a
system 210 is shown similar to system 110 described with respect to
FIG. 2, with the use of compressed gas or supercritical solvent.
For instance, system 210 can use as a stripping agent one or more
of supercritical carbon dioxide, supercritical ethane,
supercritical ethylene, supercritical propane and supercritical
butane.
[0054] During a desorption cycle, shown with respect to the
adsorption unit 34 in FIG. 3, the adsorbates (including
organosulfur compounds adsorbed to the adsorbent material) are
desorbed to remove purge stream 38 having an increased level of
organosulfur compounds. A desorption cycle is also carried out in
the adsorption unit 54 (not shown). The desorption cycle can
commence, for instance, when the adsorbent material in the
adsorption unit 34 or 54 has reached a predetermined percentage of
its adsorbent capacity. In certain embodiments, the whole crude
oils stream 32 is adsorbed until the level of organosulfur
compounds has been reduced by a predetermined percentage, for
instance, ranging from about 5 to 53 weight percent, preferably
about 30 to 53 percent.
[0055] A solvent desorbing stream 228 is passed through the
adsorption unit 34. The purge stream 38 from the desorption cycle
therefore includes desorbed adsorbate, i.e., organosulfur
compounds, and solvent. At least a portion, and preferably,
substantially all, of the solvent used in the desorption cycle
purge stream 38 is recovered, for instance, in a separation unit
226, such as a distillation unit. The solvent is recompressed in a
compressor 230, for instance, during continued desorption in a
desorption cycle, or when needed in a subsequent desperation cycle.
The increased organosulfur compound whole crude oil stream 118 can
then be processed in the hydroprocessing zone 120 for
desulfurization, and a hydroprocessed stream 122 having a reduced
level of organosulfur compounds is recovered, as discussed
above.
[0056] Operating conditions during desorption, for instance using
supercritical carbon dioxide as a stripping solvent, can include a
temperature of generally about 31.degree. C. to about 70.degree. C.
and a pressure of about 72 to about 1000 bars with a liquid hourly
space velocity of about 0.5/hour to about 20/hour. In preferred
embodiments, operating conditions during adsorption can include a
temperature of generally about 31.degree. .degree. C. to about
70.degree. C. and a pressure of about 72 bars to about 200 bars
with a liquid hourly space velocity of about 1.0/hour to about
0/hour.
[0057] In the processes described herein, unlike conventional
desulfurization processes, gaseous sulfur components of the whole
crude oil stream (such as hydrogen sulfide) are not the targets of
the adsorption process. Rather, organosulfur compounds, mercaptans,
organic sulfides, organic sulfoxides, organic sulfones, thiophenes,
benzothiophenes, multi-ring thiophenes such as dibenzothiophenes,
and other sulfur-containing organic compounds are the desired
adsorbates, and hydrogen sulfide is substantially not adsorbed.
Thus, the reduced organosulfur compound adsorbent effluent stream
is discharged having substantially the same amount of hydrogen
sulfide gas as the whole crude oil stream. This treated effluent
stream can be further subjected to a fractionation process to
remove the gas phase containing hydrogen sulfide gas prior to
delivery, storage or combination with the hydrotreated
desultfurized stream described herein.
EXAMPLES
[0058] The following examples illustrate specific embodiments of
the method(s) of this invention. The scope of this invention is not
to be considered as limited by the specific embodiments described
therein, but rather as defined by the claims.
Example 1
[0059] In this example, 3 grams of type Y zeolite powder was
activated in a vacuum oven at 175.degree. C. and a gauge pressure
of 14 psig overnight. The Y zeolite powder was then cooled to room
temperature and placed in a 100 ml wide-mouth bottle, to which 15
grams of crude oil having a total sulfur content of 3.01 wt % was
added. The mixture was mechanically shaken for 8 hours to reach
adsorption equilibrium. After the shaking was stopped, the zeolite
powder was allowed to settle by gravity and the upper liquid layer
was analyzed for total remaining sulfur which was found to be 1.4
wt %. The liquid was then decanted from the bottle and the
remaining solid was washed with 30 grams of toluene. Analysis by
X-ray fluoresce indicates that the toluene removed 67% of the total
sulfur from the adsorbent.
Example 2
[0060] Example 1 was repeated, except that Ni--Y zeolite powder
(prepared by ion exchange) was employed as the adsorbent. The
remaining total sulfur in the liquid was 1.2 wt % and toluene
removed 54 wt % of the total sulfur from the adsorbent.
Example 3
[0061] Example 1 was repeated, except that 1-Y zeolite pellets were
employed as the adsorbent. The remaining total sulfur in the liquid
was 2.87 wt % and toluene removed almost 100 wt % of the total
sulfur from the adsorbent.
Example 4
[0062] Example 1 was repeated, except that activated carbon powder
was employed as the adsorbent. The remaining total sulfur in the
liquid was 2.61 wt % and toluene removed 100 wt % of the total
sulfur from the adsorbent.
[0063] The process of the invention has been described and
explained with reference to the schematic process drawings and
examples. Additional variations and modifications will be apparent
to those of ordinary skill in the art based on the above
description and the scope of the invention is to be determined by
the claims that follow.
* * * * *