U.S. patent application number 12/741261 was filed with the patent office on 2010-10-21 for membrane desulfurization of liquid hydrocarbon feedstreams.
Invention is credited to Ahmad Abdullah Bahamdan, Esam Zaki Hamad.
Application Number | 20100264065 12/741261 |
Document ID | / |
Family ID | 40801520 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100264065 |
Kind Code |
A1 |
Hamad; Esam Zaki ; et
al. |
October 21, 2010 |
MEMBRANE DESULFURIZATION OF LIQUID HYDROCARBON FEEDSTREAMS
Abstract
The process of the present invention is directed to the
desulfurization of a sulfur-containing unrefined hydrocarbon stream
with a membrane separation apparatus, where sulfur compounds are
concentrated in a sulfur-rich stream on a permeate side of the
membrane, and a sulfur-lean stream is recovered as a retentate. The
sulfur-rich stream, which has a small volume relative to the
original unrefined hydrocarbon stream, is conveyed to a subsequent
desulfurization apparatus or system, such as a hydrotreating
system, to recover the hydrocarbons associated with the
organosulfur compounds. The stream desulfurized by conventional
processes, such as hydrotreating, and the hydrocarbons desulfurized
by the membrane separation apparatus may be combined to provide a
low sulfur hydrocarbon effluent with minimal or no loss of the
original volume.
Inventors: |
Hamad; Esam Zaki; (Dhahran,
SA) ; Bahamdan; Ahmad Abdullah; (Dhahran,
SA) |
Correspondence
Address: |
ABELMAN, FRAYNE & SCHWAB
666 THIRD AVENUE, 10TH FLOOR
NEW YORK
NY
10017
US
|
Family ID: |
40801520 |
Appl. No.: |
12/741261 |
Filed: |
December 23, 2008 |
PCT Filed: |
December 23, 2008 |
PCT NO: |
PCT/US08/14075 |
371 Date: |
May 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61009016 |
Dec 24, 2007 |
|
|
|
Current U.S.
Class: |
208/87 ;
208/208R; 208/91 |
Current CPC
Class: |
C10G 31/11 20130101;
B01D 2311/13 20130101; C10G 53/14 20130101; B01D 61/362 20130101;
C10G 67/02 20130101 |
Class at
Publication: |
208/87 ; 208/91;
208/208.R |
International
Class: |
C10G 25/00 20060101
C10G025/00; C10G 45/00 20060101 C10G045/00 |
Claims
1. A process for reducing the sulfur content of an unrefined liquid
hydrocarbon feedstream containing sulfur compounds, the process
comprising: providing a membrane separation unit containing a
membrane having a porous substrate with a sulfur-selective material
retained upon the surface of the substrate and/or within the pores
of the substrate; introducing the unrefined liquid hydrocarbon
feedstream into the membrane separation unit; concentrating the
sulfur compounds in a first unrefined hydrocarbon stream as a
liquid permeate of the membrane unit; recovering as a liquid
retentate of the membrane separation unit a second unrefined
hydrocarbon separation product stream of reduced sulfur content;
recovering and subjecting the first unrefined hydrocarbon stream to
a hydrodesulfurization process step and recovering a third stream
that is substantially free of sulfur compounds; and mixing the
second unrefined hydrocarbon stream and the third product stream to
provide a final product stream of low sulfur content.
2. The process of claim 1 in which the membrane separation unit is
operated with a sweep stream on the permeate side of the membrane
at a temperature between about 15.degree. C. and about 60.degree.
C.
3. The process of claim 1 in which the membrane separation unit is
operated with an imposed pressure differential across the membrane
of between about 1 psi and about 15 psi.
4. A process for reducing the sulfur content of a hydrocarbon feed
stream comprising: a. providing a membrane separation unit
containing a membrane having a porous substrate with a
sulfur-selective material upon the surface of the substrate and/or
within the pores of the substrate, the membrane having a first side
and a second side; b. conveying an unrefined liquid hydrocarbon
feedstream past the first side of the membrane; c. recovering a
liquid permeate unrefined hydrocarbon stream from the second side
of the membrane, the permeate unrefined hydrocarbon stream having a
higher sulfur concentration than the unrefined hydrocarbon stream;
and d. recovering a liquid retentate unrefined hydrocarbon stream
from the first side of the membrane, the retentate unrefined
hydrocarbon stream having a lower sulfur concentration than the
unrefined hydrocarbon stream.
5. A process for reducing the sulfur content of a hydrocarbon feed
that includes a first desulfurization stage and a second
desulfurization stage, the process comprising: a. providing a
membrane separation unit containing a membrane having a porous
substrate with a sulfur-selective material upon the surface of the
substrate and/or within the pores of the substrate, the membrane
having a first side and a second side; b. conveying an unrefined
liquid hydrocarbon stream past the first side of the membrane; c.
recovering a liquid retentate unrefined hydrocarbon stream from the
first side of the membrane, the retentate unrefined hydrocarbon
stream having a lower sulfur content than the unrefined hydrocarbon
stream; and d. recovering a liquid permeate unrefined hydrocarbon
stream having a higher sulfur content than the unrefined
hydrocarbon stream from the second side of the membrane and
treating it the second desulfurization stage.
6. The process of claim 5, wherein the second desulfurization stage
includes a hydrodesulfurization step.
7. The process of claim 5, wherein the second desulfurization stage
includes an oxidative desulfurization step.
8. The process of claim 1, wherein the unrefined liquid hydrocarbon
feedstream is crude oil.
9. The process of claim 1, wherein the sulfur-selective material is
selective to thiophenes.
10. The process of claim 5, wherein the sulfur-selective material
is selective to dibenzothiophenes.
11. The process of claim 1, wherein the sulfur selective material
comprises an ionic liquid.
12. The process of claim 11, wherein the ionic liquid comprises a
methyl-pyridinium based ionic liquid.
13. The process of claim 12, wherein the methyl-pyridinium based
ionic liquid comprises N-butyl-3-methyl-pyridinium methyl
sulfate.
14. The process of claim 11, wherein the ionic liquid comprises an
imidazolium-based ionic liquid.
15. The process of claim 4, wherein the unrefined liquid
hydrocarbon feedstream is crude oil.
16. The process of claim 4, wherein the sulfur-selective material
is selective to thiophenes.
17. The process of claim 5, wherein the unrefined liquid
hydrocarbon feedstream is crude oil.
18. The process of claim 5, wherein the sulfur-selective material
is selective to thiophenes.
19. The process of claim 4, wherein the sulfur selective material
comprises an ionic liquid.
20. The process of claim 19, wherein the ionic liquid comprises a
methyl-pyridinium based ionic liquid.
21. The process of claim 20, wherein the methyl-pyridinium based
ionic liquid comprises N-butyl-3-methyl-pyridinium methyl
sulfate.
22. The process of claim 19, wherein the ionic liquid comprises an
imidazolium-based ionic liquid.
23. The process of claim 5, wherein the sulfur selective material
comprises an ionic liquid.
24. The process of claim 23, wherein the ionic liquid comprises a
methyl-pyridinium based ionic liquid.
25. The process of claim 24, wherein the methyl-pyridinium based
ionic liquid comprises N-butyl-3-methyl-pyridinium methyl
sulfate.
26. The process of claim 23, wherein the ionic liquid comprises an
imidazolium-based ionic liquid.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This patent application claims the benefit of U.S.
Provisional Application Ser. No. 61/009,016, filed Dec. 24, 2007,
the content of which is incorporated by reference herein in its
entirety.
FIELD OF THE INVENTION
[0002] The invention relates to processes for desulfurization of a
hydrocarbon feed using membrane separation, and more particularly
to desulfurization of an unrefined hydrocarbon feed using membrane
separation.
BACKGROUND OF THE INVENTION
[0003] Compositions of natural petroleum or crude oils vary
significantly, generally based upon the source. 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
substantial concentration of sulfur compounds, such as hydrogen
sulfide, sulfur dioxide, and organosulfur compounds such as
mercaptans, thiophenes, benzothiophenes, and dibenzothiophenes is
referred to as "sour," whereas whole crude oil that does not
contain a substantial concentration of sulfur compounds is referred
to as "sweet."
[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 evolution of sulfur compounds during processing and
end-use of the petroleum products derived from sour crude oil poses
safety and environmental problems. Laws have been enacted to reduce
sulfur content of fuels, including diesel and gasoline. For
instance, in 2007 the United States Environmental Protection Agency
required sulfur content of highway diesel fuel to be reduced 97%,
from 500 parts per million (low sulfur diesel) to 15 parts per
million (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 parts per million of
sulfur.
[0006] Furthermore, the price differential between sour crude oil
and sweet crude oil (crude oil having relatively low level of
sulfur compounds) favors sweet crude oil. sweet crude oil commands
a higher price than sour crude oil because it has fewer
environmental problems and requires less refining to meet sulfur
standards imposed on end product fuels. Hydrocarbon desulfurization
processes are required to reduce the sulfur content. However, most
desulfurization processing occurs after varying levels of refining
of the crude oil.
[0007] The most common hydrocarbon desulfurization process is
hydrotreating, or hydrodesulfurization. In typical hydrotreating
processes, oil and hydrogen are introduced to a fixed bed reactor
that is packed with a hydrodesulfurization catalyst, commonly under
elevated operating conditions, including temperatures of about 300
to 400.degree. C. and pressures of about 30 to 130 atmospheres. The
temperatures and pressures in hydrotreating processes must be
further elevated to achieve the low and ultra low sulfur content
requirements. However, under these more severe conditions,
hydrocarbons are typically converted to less desirable
intermediates or products.
[0008] Typical advances in the industry for minimizing these
undesirable effects include development of more robust
hydrotreating catalysts and advanced hydrodesulfurization reactor
designs. Alternative processes are also being developed to meet the
requirements of decreased sulfur levels in fuels and other
petrochemical products.
[0009] One alternate desulfurization process that has been proposed
for treating various refined fractions of hydrocarbons is membrane
separation. In general, membrane separation technology involves
selective transport of a material through the membrane, a permeate,
leaving behind a retentate on the feed side of the membrane.
Permeated components of the mixture are removed by various driving
forces. Membrane processes that rely upon pressure driving forces
are known as pervaporation processes, and membrane processes that
rely upon concentration gradients across the membrane are known as
perstraction processes. Membrane separation often relies on the
affinity of a specific compound or class of compounds for the
membrane. Components in a mixture having affinity for the membrane
will permeate the membrane. Membrane separation has been used for
desulfurization of refined hydrocarbon fractions.
[0010] Saxton et al. U.S. Pat. No. 6,702,945 and Minhas et al. U.S.
Pat. No. 6,649,061, both assigned to ExxonMobil, disclose reducing
the sulfur content in a hydrocarbon fraction, particularly light
cracked naphtha. The membrane system is operated under
pervaporation conditions in the examples. In addition, the process
discloses a transport agent (such as methanol) as an additive to
the hydrocarbon mixture to enhance the permeate flux through the
membrane.
[0011] White et al. U.S. Pat. No. 6,896,796, and related U.S. Pat.
Nos. 7,018,527, 7,041,212 and 7,048,846, all assigned to W.R. Grace
& Co., disclose a method for lowering the sulfur content of an
FCC light cat naphtha feed under pervaporation conditions. The
process proposes to minimize olefin and naphthene hydrogenation
during hydrotreating, particularly problematic in hydrotreating FCC
naphtha since the high olefin content is again prone to
hydrogenation.
[0012] Balko U.S. Pat. No. 7,267,761, also assigned to W.R. Grace
& Co., describes another process for treating naphtha streams
from an FCC unit, where the feedstream is treated in a
fractionation zone to produce a low boiling point fraction and a
second fraction, both containing sulfur. The low boiling point
fraction is treated in a membrane separation zone, where the
sulfur-enriched permeate is combined with the second fraction for
treatment in a hydrodesulfurization zone.
[0013] Plummer et al. U.S. Pat. No. 6,736,961, assigned to Marathon
Oil Company, discloses a process employing a solid membrane process
containing a transport facilitating liquid, identified as amines,
hydroxyamines, and alcohols. The feed is described as a refinery
hydrocarbon product such as naphtha or diesel.
[0014] Importantly, the hydrocarbon feed streams in all of the
above-mentioned references are products of upstream distillation
and cracking processes and/or other refining operations. However,
the use of unrefined petroleum products (e.g., crude oil) as a
feedstream to a membrane separation process remains heretofore
unknown to the inventors.
[0015] Another desulfurization process is described in Schoonover
U.S. Pat. No. 7,001,504, where hydrocarbon materials are contacted
with an ionic liquid to extract organosulfur compounds into the
ionic liquid. The ionic liquid is regenerated by various methods
including heating, gas stripping, oxidation, or extraction with
another solvent or supercritical carbon dioxide. However, this
process does not utilize membrane separation units to provide
relatively compact and efficient separation.
[0016] Therefore, it is an object of the invention to utilize
membrane separation to desulfurizing unrefined hydrocarbon
streams.
[0017] It is a further object of the invention to utilize membrane
separation for desulfurizing an unrefined hydrocarbon stream, and
to thereafter desulfurize the sulfur-rich retentate employing
conventional desulfurization processes such as hydrotreating.
[0018] A still further object of the invention is to utilize
membrane separation to desulfurize an unrefined hydrocarbon stream,
and to desulfurize the sulfur-rich retentate using conventional
desulfurization processes such as hydrotreating, while minimizing
the required capacity of the hydrotreating process.
[0019] Yet another object of the invention is to separate
heteroatom compounds such as sulfur compounds from a liquid
unrefined hydrocarbon into a liquid permeate and a liquid
retentate.
[0020] As used herein, the term "unrefined hydrocarbon" is to be
understood to mean a distillate product of crude oil (including
impurities such as sulfur) that has not been subjected to
hydroprocessing, hydrodesulfurization, hydrodenitrogenation,
catalytic processing, or cracking, and includes crude oil,
unrefined diesel, unrefined naphtha, unrefined gas oil, or
unrefined vacuum gas oil. Additionally, as used herein, the term
"crude oil" is to be understood to include a mixture of petroleum
liquids and gases (including impurities such as sulfur) as
distinguished from refined fractions of hydrocarbons.
SUMMARY OF THE INVENTION
[0021] The process of the present invention is directed to
desulfurization of a sulfur-containing unrefined hydrocarbon stream
with a membrane separation apparatus, where sulfur compounds are
concentrated in a sulfur-rich stream on a permeate side of the
membrane, and a sulfur-lean stream is recovered as a retentate. The
sulfur-rich stream, which has a small volume relative to the
original unrefined hydrocarbon stream, is subsequently conveyed to
a desulfurization apparatus or system, such as a hydrotreating
system, to recover the hydrocarbons associated with the
organosulfur compounds. The stream desulfurized by conventional
processes, such as hydrotreating, and the hydrocarbon stream
desulfurized by the membrane separation apparatus can be combined
to provide a low sulfur hydrocarbon effluent with minimal or no
significant loss of the original volume.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Further advantages and features of the present invention
will become apparent from the detailed description of a preferred
embodiment of the invention and reference to the accompanying
drawings, in which:
[0023] FIG. 1 is a schematic diagram of a combined membrane
separation and alternate desulfurization process according to
embodiments of the invention; and
[0024] FIG. 2 is a schematic diagram of a membrane separation
system used in the experimental analysis described herein.
DETAILED DESCRIPTION OF THE INVENTION
[0025] With reference to FIG. 1, a schematic overview of a
desulfurization process 10 is described. An unrefined hydrocarbon
feedstream 12 containing organosulfur compounds is introduced into
a membrane separation unit 14 where the feedstream 12 is separated
into streams 16, 18. Sulfur-containing hydrocarbon compounds
permeate a membrane of the membrane separation system 14 and are
concentrated into an unrefined sulfur-rich hydrocarbon stream 16.
The portion of the feedstream remaining on the feed side of the
membrane, the retentate, is conveyed as an unrefined sulfur-lean
hydrocarbon stream 18. The unrefined sulfur-lean hydrocarbon stream
18 has a substantially reduced concentration of sulfur-containing
compounds as compared to the feedstream 12. The unrefined sulfur
rich stream 16, typically a small volume relative to the original
feedstream 12, is transferred to a second stage desulfurization
system 20, such as a hydrotreating unit, to recover useful
hydrocarbons associated with the organosulfur compounds. Effluent
from the second stage desulfurization system 20, a second stage
unrefined sulfur-lean stream 22, and the membrane desulfurized
unrefined hydrocarbon stream 18, can be combined to provide a low
sulfur unrefined hydrocarbon stream 24 with minimal or no loss in
volume. In an alternative embodiment of the process, the second
stage unrefined sulfur-lean stream 22 that may be rich in aromatics
is transferred to one or more subsequent processing steps.
[0026] The combined membrane separation process 10 described herein
advantageously is conducted as a liquid separation process. The
unrefined hydrocarbon feedstream 12, the unrefined sulfur-rich
hydrocarbon stream 16 and the unrefined sulfur-lean hydrocarbon
stream 18 are all maintained in the liquid phase. The feedstream
12, which can be a crude oil feedstream, an unrefined diesel
feedstream, an unrefined naphtha feedstream, an unrefined gas oil
feedstream, or an unrefined vacuum gas oil feedstream, is generally
in the liquid phase initially, and the permeate and retentate
remain in the liquid phase, without conversion into vapors and
subsequent condensation, thereby conserving energy. A majority of
hydrocarbon gases that are in the feedstream, in particular a crude
oil feedstream, are generally dissolved in the liquid and do not
pass through the membrane, thus remain in the unrefined sulfur-lean
hydrocarbon stream 18. Accordingly, the prior art pervaporation
operations described relating to processes for separation of
particular fractions using sulfur-selective membranes and which
consume large amounts of energy due to vaporization and vacuum
maintenance, are not required.
[0027] The sequence of a membrane separation zone followed by
second stage desulfurization zone is also conducive to integration
with existing commercial hydrotreating units. This sequence
realizes substantial economic savings, since the cost of operating
a hydrotreating unit is proportional to the feed volume and is
generally not sensitive to the sulfur content of the feed. The cost
of a membrane separation unit is generally much less than the cost
of a hydrotreating unit; therefore, technically mature
hydrodesulphurization units can be employed with the attendant
economic savings. The use of common and well understood processing
units in combination will facilitate the capability for rapid
scale-up or development of unrefined hydrocarbon feedstream
desulfurization.
[0028] The overall performance of the integrated process and system
generally depends on the performance of the membrane separation
unit, which in turn is enhanced by the selectivity and permeability
of the membrane used. Accordingly, the membrane material is
selected based on the permeation rate and selectivity for the range
of sulfur compounds that are present in the unrefined hydrocarbon
stream. The selection of the type of membrane can also increase
efficiency and reliability of the separation unit, and hence
increase efficiency and reliability of the overall process.
[0029] The membrane is generally a substrate coated with a solid or
a liquid material that is selective for the sulfur compounds
present in the unrefined feedstream. The coating may be upon the
major surfaces of the substrate and/or within pores of the
substrate. Coating within the pores preferably is a relatively thin
layer, to maintain pore openings and minimize mass transfer
resistance and thereby increase flux. Furthermore, desired sulfur
selective materials used as coatings exhibit effective adhesion to
the substrate. Liquid coatings preferably include molecules with
functional groups that cause them to be anchored to the substrate,
thereby minimizing or avoid the loss of liquid sulfur-selective
material over the life of the membrane.
[0030] Substrate materials upon or within which the selective
sulfur compounds can be coated include ultrafiltration and
microfiltration membranes, for instance, formed of polymeric
materials such as polyethersulfone (PES), polycarbonate,
polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),
including hydrophilic PVDF, polyester, fluorinated polyimide,
polyethyl-oxazoline, Nafion.RTM., nylon, hydrophobically modified
nylon, and polyether terephthalate (PET).
[0031] The substrate has pore sizes of about 0.01 to about 2
micrometers, preferably about 0.05 to about 1 micrometer and more
preferably about 0.1 to about 0.5 micrometers. Suitable substrates
have molecular weight cut-off values of about 5,000 to about
1,000,000, preferably about 30,000 to about 500,000, and more
preferably about 30,000 to about 100,000. The substrate can also be
hydrophilic, for instance, with the inclusion of wetting agents
such as polyvinylpyrrolidone (PVP)). The thickness of the substrate
can be from about 100 to about 500 micrometers, preferably about
100 to about 300 micrometers, and more preferably about 100 to
about 200 micrometers. The area of the membrane (e.g., diameter in
the case of circular membranes in flat mounted sheet
configurations) can be selected based upon the requisite processing
volume demands.
[0032] The sulfur selective compounds suitable for use as membrane
coating materials can include functionalities with affinity to the
aromatic sulfur compounds, complexation agents, or acidic
functional groups. For example, sulfur selective compounds can
comprise ionic liquids including, but not limited to,
N-butyl-3-methyl-pyridinium methyl sulfate, imidazolium-based ionic
liquids, and methyl-pyridinium based ionic liquids. In certain
preferred embodiments, the sulfur selective compounds are selective
to organosulfur compounds including thiophenes, dibenzothiophenes
and other refractory sulfur compounds commonly found in untreated
hydrocarbon feedstreams.
[0033] The driving force for separation can be a concentration
gradient across the membrane, which is enhanced by a sweep stream
on the permeate side. Suitable sweep stream liquids include
paraffins such as isooctane, dodecane and hexadecane; or liquid
hydrocarbon mixtures such as naphtha and desulfurized diesel. The
particular sweep liquid should be low in organic sulfur compounds,
of paraffinic origin and be a liquid at room temperature and
ambient pressure conditions.
[0034] In contrast to pervaporation techniques commonly known in
the art, the membrane separation system for separating sulfur
compounds from unrefined hydrocarbon feeds can operate at
temperatures of about 15.degree. C. to about 60.degree. C.,
preferably about 20.degree. C. to about 50.degree. C., more
preferably about 25.degree. C. to about 35.degree. C., and
pressures of 1 pound per square inch (psi) to about 30 psi,
preferably about 5 psi to about 20 psi, more preferably about 10
psi to about 15 psi.
[0035] In alternative embodiments, the driving force for separation
is a pressure gradient across the membrane. Notably, the pressure
gradient required is not as severe as that required for
pervaporation conditions, as the feed, retentate and permeate are
maintained in liquid phase. For instance, suitable pressure
gradients across the membrane can be about 1 psi to about 15 psi,
preferably about 5 psi to about 15 psi, and more preferably about 5
psi to about 10 psi.
[0036] Operating temperatures in embodiments using a pressure
gradient as the driving force for separation can be about
15.degree. C. to about 60.degree. C., preferably about 20.degree.
C. to about 50.degree. C., more preferably about 25.degree. C. to
about 35.degree. C. In this embodiment, where liquid supported
membranes are employed, it is desirable that the liquid be
chemically anchored to the substrate to prevent the loss of mobile
liquid. Suitable liquids coatings for membranes operating under
pressure gradients include any of the ionic liquids mentioned above
coated after plasma treatment of the mentioned substrates.
[0037] The membrane unit can be in any suitable configuration. For
instance, the membrane unit can be in a spirally wound
configuration, a hollow fiber configuration, a plate and frame
configuration, or a tubular configuration. In certain preferred
embodiments, the membrane unit is in a spirally wound or a hollow
fiber configuration. In addition, a plurality of membrane units can
optionally be operated in parallel or series. In the parallel
configuration, one or more membrane units can be decommissioned for
maintenance without disrupting the continuity of the
desulfurization process.
[0038] The stream desulfurized by conventional processes, such as
hydrotreating, and the hydrocarbons desulfurized by the membrane
separation apparatus, can be combined to provide a low sulfur
hydrocarbon effluent with minimal or no loss of the original
volume. This low sulfur hydrocarbon effluent can serve as a
feedstream for subsequent fractioning in a downstream process.
Alternatively, the low sulfur hydrocarbon effluent may be sold as
sweet crude oil, thereby taking advantage of the price differential
between sweet and sour crude oils.
EXAMPLES
[0039] The following tests were conducted using the membrane
substrate/coating combinations described below in a membrane
separation system 50 configured as shown in FIG. 2. In particular,
the system 50 included a membrane 52 having a retentate side 54 and
a permeate side 56. The apparatus included a sulfur-lean portion 58
in for receiving retentate from the retentate side 54, and a
sulfur-rich portion 60 for receiving permeate from the permeate
side 56. A reservoir 62 initially included the feedstream that is
conveyed to the membrane, which was converted into an unrefined
sulfur-lean hydrocarbon retentate. A reservoir 64 initially
included a sweep solution, and the unrefined sulfur-rich
hydrocarbon permeate filled the reservoir 64. The feedstream was
pumped to the membrane retentate side 54 with a gear pump 66. The
sweep solution was pumped via a gear pump 68 across the permeate
side 56 of the membrane 52.
[0040] In the following examples, the selected membranes were
coated with ionic liquid (N-butyl-3-methyl pyridinium) using a spin
coater. The prepared membranes were mounted in a testing flow cell
as illustrated in FIG. 2. The three feeds were (1) a model
solution, (2) an unrefined diesel, and (3) crude oil obtained from
a refinery. The respective feeds were pumped to contact the
membrane surface tangentially on the retentate side 54.
Example 1
[0041] A polyethersulfone ultrafiltration filter, with a molecular
weight cutoff of 100,000 and having a 47 millimeter diameter
(commercially available from GE Osmonics Labstore, Minnetonka,
Minn., USA) was coated with the ionic liquid. This ionic liquid
exhibits an affinity for aromatic sulfur compounds. The membrane
was configured in a system schematically shown in FIG. 2.
[0042] Untreated diesel with 1% total sulfur content (10,000 parts
per million) is introduced tangentially to the retentate side of a
membrane cell shown in FIG. 2 that included the membrane prepared
as described above. A liquid sweep stream of light treated naphtha
with 100 ppm sulfur was conveyed across the membrane in the
permeate side. After 72 hours of operation, the sweep stream sulfur
concentration increased to 1000 ppm, yielding a sulfur-compound
flux of 0.1 kg/hr/m.sup.2.
Example 2
[0043] Example 1 was repeated using a feed consisting of Arabian
crude oil having an American Petroleum Institute (API) gravity of
about 27 and a sulfur concentration of 2.85%. After 72 hours of
operation, the average sulfur-compound flux of 0.05 kg/hr/m.sup.2
is achieved.
Example 3
[0044] A polycarbonate membrane filter with 0.1 micron pores having
a diameter of 47 millimeters (GE PCTE commercially available from
GE Osmonics Labstore, Minnetonka, Minn., USA) was prepared. The
membrane included polyvinylpyrrolidone (PVP) as a wetting agent
that imparts hydrophilicity. The membrane was coated with ionic
liquid and tested with a seven component model feed described in
Table 1, using a dodecane carrier. The receiving side (permeate)
included a dodecane solution to sweep accumulated permeate from the
surface of the membrane. A gear pump was connected to each side
while samples were extracted from the reservoirs to measure the
change in composition on both sides. The samples collected were
analyzed by gas chromatography, and for total sulfur by the ASTM D
5453 method. The process was performed at a low flow rate (10
milliliters per min) for 48 hours.
TABLE-US-00001 TABLE 1 Feed temperature (.degree. C.) 24
Cyclohexane, parts per million (ppm) 4029 Iso-octane, ppm 7290
Toluene, ppm 5611 N-Hexanes, ppm 4826 DBT, ppm 7874 Thiophene, ppm
4559 Total Sulfur, ppm 2265 Permeate flux, kilograms sulfur per
0.0013 hour per square meter (kgS/hr/m.sup.2) Selectivity of
Thiophene/Hexanes 156 Selectivity of DBT/Hexanes 142 Selectivity of
Thiophene/Toluene 2.8 Selectivity of DBT/Toluene 2.6
Example 4
[0045] A PTFE membrane filter with 0.2 micron pores having a
diameter of 47 millimeters (Omnipore.TM. commercially available
from Millipore, Billerica, Mass.) was prepared. The membrane was
coated with ionic liquid and tested with a seven component model
feed described in Table 2 using a dodecane carrier. The receiving
side (permeate) included a dodecane solution to sweep accumulated
permeate on the surface of the membrane. A gear pump was connected
to each side while samples were extracted from the reservoirs to
measure the change in composition on both sides. The samples
collected were analyzed by gas chromatography, and total sulfur
methods. The process was performed at a low flow rate (10
milliliters per min) for 48 hours.
TABLE-US-00002 TABLE 2 Feed temperature (.degree. C.) 24
Cyclohexane, ppm 2723 Iso-octane, ppm 4208 Toluene, ppm 2859
N-Hexanes, ppm 2859 DBT, ppm 8764 Thiophene, ppm 1618 Total Sulfur,
ppm 2889 Permeate flux, kgS/hr/m.sup.2 0.001 Selectivity of
Thiophene/Hexanes 139 Selectivity of DBT/Hexanes 38 Selectivity of
Thiophene/Toluene 7.3 Selectivity of DBT/Toluene 2.0
[0046] The results set forth in Tables 1 and 2 above indicate that
aromatic sulfur compounds can be selectively removed from the feed
without removing aliphatic compounds. Selectivity is expressed as
the ratio of organosulfur compound to the other mixture components
in the permeate. The coated ionic liquid membrane exhibited
selective permeation for thiophene and dibenzothiophene (DBT) over
other aliphatic and aromatic compounds.
[0047] 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.
* * * * *