U.S. patent application number 11/290668 was filed with the patent office on 2007-05-31 for combination of zeolite and alumina impregnated with a noble metal(s) for cos and tht removal at low temperatures (<40 degree c) in fuel cell processor applications.
This patent application is currently assigned to Sud-Chemie Inc.. Invention is credited to William M. Faris, R. Steven Spivey, Eric J. Weston.
Application Number | 20070119751 11/290668 |
Document ID | / |
Family ID | 38086386 |
Filed Date | 2007-05-31 |
United States Patent
Application |
20070119751 |
Kind Code |
A1 |
Weston; Eric J. ; et
al. |
May 31, 2007 |
Combination of zeolite and alumina impregnated with a noble
metal(s) for COS and THT removal at low temperatures (<40 degree
C) in fuel cell processor applications
Abstract
The present invention is a process for removing
sulfur-containing compounds from gaseous fuels and hydrocarbons,
such as natural gas, at temperatures of less than about 100.degree.
C. The sulfur-contaminated feedstream is placed in intimate contact
with a catalyst-sorbent which comprises a noble metal, a zeolite,
and an alumina in a single reactor bed.
Inventors: |
Weston; Eric J.;
(Shepherdsville, KY) ; Spivey; R. Steven;
(Louisville, KY) ; Faris; William M.; (Louisville,
KY) |
Correspondence
Address: |
SUD-CHEMIE INC.
1600 WEST HILL STREET
LOUISVILLE
KY
40210
US
|
Assignee: |
Sud-Chemie Inc.
|
Family ID: |
38086386 |
Appl. No.: |
11/290668 |
Filed: |
November 30, 2005 |
Current U.S.
Class: |
208/213 |
Current CPC
Class: |
C10G 25/05 20130101 |
Class at
Publication: |
208/213 |
International
Class: |
C10G 45/04 20060101
C10G045/04; C10G 25/00 20060101 C10G025/00; C10G 45/60 20060101
C10G045/60 |
Claims
1. A process for removing sulfur compounds from a gaseous
hydrocarbon feedstream comprising contacting said mixture with a
catalyst-sorbent comprising at least one noble metal, at least one
zeolite, and at least one oxide support, wherein said
catalyst-sorbent is packed into a reactor bed and said reactor bed
is maintained at a temperature of from about 0.degree. C. to about
100.degree. C.
2. The process of claim 1 wherein said noble metal is selected from
the group consisting of ruthenium, rhodium, palladium, osmium,
iridium, platinum, alloys thereof, mixed metal compounds thereof,
and combinations thereof.
3. The process of claim 2 wherein said noble metal comprises both
palladium and platinum in a ratio Pd:Pt of between about 1:1 and
about 6:1.
4. The process of claim 1 wherein said noble metal comprises from
about 0.1 wt % to about 5 wt % defined in terms of total
catalyst-sorbent weight.
5. The process of claim 4 wherein said noble metal comprises from
about 0.5 wt % to about 2 wt % defined in terms of total
catalyst-sorbent weight.
6. The process of claim 1 wherein said zeolite comprises zeolite X,
zeolite Y, zeolite beta, a zeolite having a BEA structure, a
zeolite having a MOR structure, or a combination thereof.
7. The process of claim 1 wherein said zeolite comprises from about
50 wt % to about 90 wt % defined in terms of total catalyst-sorbent
weight.
8. The process of claim 1 wherein said oxide support is selected
from alumina, silica, titania, zirconia, and combinations
thereof.
9. The process of claim 8 wherein said oxide support comprises
alumina.
10. The process of claim 1 wherein said oxide support comprises
from about 10 wt % to about 50 wt % defined in terms of total
catalyst-sorbent weight.
11. The process of claim 1 wherein said catalyst-sorbent has a pore
volume of at least about 0.3 cm.sup.3/g.
12. The process of claim 1 wherein said catalyst-sorbent has a
specific surface area of at least 300 m.sup.2/g.
13. The process of claim 1 wherein said reactor bed temperature is
less than about 60.degree. C.
14. The process of claim 1 where the gas hourly space velocity is
less than about 3000 h.sup.-1.
15. The process of claim 1 wherein said gaseous hydrocarbon
feedstream comprises natural gas, methane, propane, or liquefied
petroleum gas, and said feedstream comprises at least one sulfur
compound selected from the group consisting of carbonyl sulfide,
thiols, disulfides, saturated heterocyclic sulfur compounds,
tetrahydrothiophene and combinations thereof.
16. A process for removing sulfur compounds selected from the group
consisting of carbonyl sulfide, thiols, disulfides, saturated
heterocyclic sulfur compounds, tetrahydrothiophene and combinations
thereof, from a gaseous feedstream comprising hydrocarbons selected
from natural gas, methane, propane, liquefied petroleum gas, and
combinations thereof, wherein said process comprises contacting
said feedstream with a catalyst-sorbent comprising at least one
noble metal selected from the group consisting of ruthenium,
rhodium, palladium, osmium, iridium, platinum, alloys thereof,
mixed metal compounds thereof, and combinations thereof, and at
least one zeolite, and at least one oxide support, wherein said
catalyst-sorbent is packed into a reactor bed and said reactor bed
is maintained at a temperature of from about 0.degree. C. to about
100.degree. C.
17. The process of claim 16 wherein said noble metal comprises from
about 0.1 wt % to about 5 wt % defined in terms of total
catalyst-sorbent weight, and said zeolite comprises from about 50
wt % to about 90 wt % defined in terms of total catalyst-sorbent
weight, and said oxide support comprises from about 10 wt % to
about 50 wt % defined in terms of total catalyst-sorbent
weight.
18. The process of claim 16 wherein said noble metal comprises both
palladium and platinum in a ratio Pd:Pt of between about 1:1 and
about 6:1.
19. The process of claim 16 where the gas hourly space velocity is
less than about 3000 h.sup.-1.
20. A process for removing sulfur compounds selected from the group
consisting of carbonyl sulfide, thiols, disulfides, saturated
heterocyclic sulfur compounds, tetrahydrothiophene and combinations
thereof, from a gaseous feedstream comprising hydrocarbons selected
from natural gas, methane, propane, liquefied petroleum gas, and
combinations thereof, wherein said process comprises contacting
said feedstream with a catalyst-sorbent comprising from about 0.1
wt % to about 5 wt % of at least one noble metal, and from about 50
wt % to about 90 wt % of at least one zeolite, and from about 10 wt
% to about 50 wt % of at least one oxide support, wherein said
catalyst-sorbent is packed into a reactor bed and said reactor bed
is maintained at a temperature of from about 0.degree. C. to about
100.degree. C.
Description
BACKGROUND
[0001] The present development is a method for removing
sulfur-containing compounds from fluids, such as gaseous fuels and
hydrocarbons. More specifically, the method comprises placing a
feedstream in contact with a catalyst-sorbent which comprises a
noble metal, a zeolite, and an alumina. The method is suitable for
removing carbonyl sulfide and saturated heterocyclic sulfur
compounds such as tetrahydrothiophene as well as thiols and
hydrogen sulfide.
[0002] The presence of sulfur compounds in fuels is problematic for
a number of reasons. Burning such fuels produces sulfur oxides
which are a form of pollution. Sulfur-laden exhaust also poisons
the catalysts used to remove other harmful substances from the
exhaust, resulting in additional pollution. Many of the catalysts
used in refining and processing fuels are also subject to sulfur
poisoning. The electrocatalysts used in fuel cells to extract
energy from the fuel are highly sensitive to sulfur. Consequently,
sulfur content in fuels used to power fuel cells must be rigorously
restricted.
[0003] It may also be necessary, for one reason or another, to
remove sulfur from fluids other than fuels. Ethylene used for
polymerization, for example, must be of high purity and have a low
sulfur content. The same can be said for the hydrogen used in
ammonia synthesis.
[0004] The removal of carbonyl sulfide (COS) is particularly
troublesome because it is resistant to many desulfurization
processes. Thus, the ability to remove COS is a desirable feature
in a desulfurization process. Typically, COS is removed by
adsorption, hydrolysis, or a combination of the two.
[0005] Other sulfur compounds that may need to be removed include
hydrogen sulfide, thiols, and organic compounds containing a
C--S--C or C--S--S--C linkage, such as diethyl sulfide, diethyl
disulfide, and tetrahydrothiophene (THT). These compounds may be
naturally co-occurring with the combustible hydrocarbons in the
fuel, or may be added as odorants to allow humans to detect
dangerous leaks of otherwise odorless gases. In either case, these
sulfur compounds must be removed when the fuel is used certain
applications, such as in a fuel cell. It is known in the art that
hydrogen sulfide is relatively easy to remove by adsorption
relative to organic sulfur compounds. As a result, a process that
converts carbonyl sulfide and organic sulfur compounds to hydrogen
sulfide is useful, even if the overall sulfur content does not
appreciably change.
[0006] It is known in the art to remove sulfur compounds from
hydrocarbons at elevated temperature and high partial pressures of
hydrogen, a process referred to as hydrotreating or
hydrodesulfurization. Typically temperatures of 150.degree.
C.-400.degree. C. and hydrogen partial pressures in excess of 1 MPa
are used in hydrodesulfurization processes. For example, U.S. Pat.
No. 6,855,653 teaches a hydrodesulfurization process that uses a
catalyst which is similar in composition to the catalyst-sorbent of
the present development. However, the process of the '653 patent
relies on relatively high temperature and pressure, and requires
hydrogen to be present in the process stream in order to effect
sulfur compound removal.
[0007] Methods for removing noxious impurities, such as sulfur
compounds, from a fluid by contacting the fluid with a solid
material are well known in the art. Whether the solid material acts
by adsorption, catalysis, or a combination of the two, it is
necessary to ensure efficient and effective contact between the
catalyst-sorbent and the fluid, and to make sure that substantially
all of the fluid has been brought into effective contact with the
catalyst-sorbent. Examples of some methods to achieve this can be
found in the literature of chemical engineering and petroleum
engineering, including in the three articles "Adsorption",
"Adsorption, Gas Separation", and "Adsorption, Liquid Separation"
in the Kirk-Othmer Encyclopedia of Chemical Technology, 5.sup.th
Edition, and in the three chapters "Adsorption and Ion Exchange,"
"Liquid-Gas Systems," and "Solids Drying and Gas-Solid Systems" in
Perry's Chemical Engineers' Handbook, 6.sup.th Edition. These three
articles from Kirk-Othmer and three chapters from Perry's Handbook
are hereby incorporated by reference.
[0008] Sulfur compounds can be absorbed metals or metal oxides,
such as metallic nickel, nickel oxide, and zinc oxide. This type of
desulfurization process does not require high partial pressures of
hydrogen, but does require elevated temperatures. Nickel-based
sorbents, for example, typically work at a temperature range of
200.degree. C.-400.degree. C. In some situations, such as during
startup of a fuel cell system designed for intermittent use,
removal of sulfur compounds at about room temperature is
needed.
[0009] U.S. Pat. No. 4,455,446 teaches a method for removing
carbonyl sulfide from propylene which comprises passing the
propylene stream through a bed of platinum sulfide supported on
alumina. Unlike the present development, the catalyst-sorbent used
in the process claimed in the '446 patent does not include a
zeolite. The method described in the '446 patent can be performed
at temperatures only slightly above ambient (35.degree. C. to
65.degree. C.), but requires rather high pressures (200 psia to 450
psia). Alternatively, the process can be carried out at
near-atmospheric pressure but at elevated temperatures (135.degree.
C. to 260.degree. C.).
[0010] U.S. Patent Application 2002-0121093 teaches a process using
a Pt/Al.sub.2O.sub.3 catalyst to hydrolyze COS present in synthesis
gas. The temperature 300.degree. F. (150.degree. C.) is stated to
be a typical process temperature. As with the '446 patent, the
catalyst-sorbent in the '093 application includes a noble metal and
alumina, but does not include a zeolite. In addition, an elevated
temperature is required for the hydrolysis of COS.
[0011] U.S. Pat. No. 6,843,907 teaches a process for removing
carbonyl sulfide at near-ambient temperatures (15.degree. C. to
100.degree. C.) from a hydrocarbon stream which uses a generic,
regenerable sorbent. The sorbent is preferably an
alkali-impregnated alumina, a zeolite, or a combination thereof.
Thus the process taught in the '907 patent uses zeolite and an
alumina, but lacks a noble metal.
[0012] U.S. Patent Application 2004-0007506 teaches a process for
deep desulfurization of hydrocarbon fuels, primarily liquid fuels.
The fuel stream is contacted with any of a number of sulfur
sorbents which work at temperatures ranging from 10.degree. C. to
340.degree. C. In claims 3, 4, and 5 of the '506 application,
adsorbents containing mixed base-metal noble-metal chlorides
supported on MCM-41, silica gel, activated carbon, or zeolites are
mentioned. But the desulfurization process taught in the '506
application requires a narrow class of noble metal compounds
supported on alumina or zeolite.
[0013] Japanese Patent JP H04-106194 (to Kawasaki Steel Corp.,
1992) teaches a process for removing organic sulfur compounds from
coke oven gas. The gas to be treated is passed first over a bed of
Pd/Al.sub.2O.sub.3, then through a bed of zeolite. The process
temperature in the JP'194 patent is 250.degree. C.-350.degree.
C.
SUMMARY OF THE INVENTION
[0014] The present invention is a process for removing
sulfur-containing compounds, such as carbonyl sulfide, thiols,
disulfides, and saturated heterocyclic sulfur compounds, including
tetrahydrothiophene, from gaseous fuels and hydrocarbons, such as
natural gas. The process includes at least a step in which a
gaseous sulfur-contaminated feedstream is placed in contact with a
catalyst-sorbent which comprises a noble metal, a zeolite, and an
alumina in a single reactor bed. Use of a single bed reactor is
advantageous when conserving space or weight is desirable. Further,
the process is intended to operate at near-ambient temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present development is a method for removing
sulfur-containing compounds from gaseous feedstreams. The sulfur
compounds are removed from the feedstream by allowing the
feedstream to have intimate contact with a catalyst-sorbent
comprising a noble metal, a zeolite and an oxide compound. During
the period of feedstream contact with the catalyst-sorbent, the
temperature of the catalyst-sorbent is maintained at from about
0.degree. C. to about 100.degree. C. and the feedstream is fed to
the catalyst-sorbent at a gas hourly space velocity of less than
about 3000 h.sup.-1.
[0016] The term catalyst-sorbent, as used herein, denotes a solid
substance which by catalysis, absorption, adsorption, or any
combination thereof changes the composition of the stream passed
over it. For purposes of discussion herein, the term may be used
interchangeably with "catalyst."
[0017] The term noble metal, as used herein, denotes any one or
more of the elements ruthenium, rhodium, palladium, osmium,
iridium, and platinum, or any alloys or compounds containing at
least one of these elements.
[0018] The term oxide comprises compounds of oxygen and at least
one other element. In particular the term as used herein includes
hydroxides and hydrated oxides. Similarly, the term alumina
includes aluminum oxides, hydrated aluminum oxides, aluminum
hydroxides, and aluminum oxide hydroxides.
[0019] The term desulfurization refers to any process designed to
lower the total sulfur content or the concentration of particular
sulfur compounds or classes of sulfur compounds. When used with the
preposition "of", the noun phrase after the "of" indicates the
substance or mixture from which sulfur or its compounds are to be
removed.
[0020] The term gaseous when applied to fuels, chemical compounds,
or mixtures indicates that said fuel, compound, or mixture has a
vapor pressure of greater than or equal to about 100 kPa at
25.degree. C. The physical state under process conditions is
irrelevant.
[0021] The process of the invention may be used wherever a fluid in
the gaseous state contains excessive amounts of total sulfur, or of
particular sulfur compounds, or of classes of sulfur compounds,
including without limitation, carbonyl sulfide, thiols, disulfides,
and saturated heterocyclic sulfur compounds, including
tetrahydrothiophene, which the catalyst-sorbent is able to remove.
In fuel cell processor train applications, the sulfur levels must
be low enough to prevent premature degradation of the catalysts
used to convert the fuel into a pure hydrogen stream and of the
electrocatalyst in the fuel cell itself. Other situations may arise
in which the reduction in total sulfur or of particular sulfur
compounds or classes of sulfur compounds is desirable for one
reason or another.
[0022] The process of the invention is particularly well suited for
removing sulfur compounds from gaseous fuels such as natural gas,
methane, propane, and liquefied petroleum gas (LPG). These gases
often contain sulfur compounds as impurities, either naturally
occurring or deliberately added as odorants. A sulfur concentration
of 20 ppm to 500 ppm is typical for pipeline natural gas. When
sulfur-containing gases are fed into a fuel cell processor train,
the sulfur can poison the reforming catalyst(s), water-gas-shift
catalyst(s), and other catalysts required to convert the fuel into
a pure hydrogen stream. Sulfur poisoning of the fuel cell
electrocatalyst itself can also occur.
[0023] The catalyst-sorbent used in the process of the invention
has three necessary components: at least one noble metal, at least
one zeolite, and at least one oxide support. In an exemplary
embodiment of the catalyst, the noble metal comprises from about
0.1 wt % to about 5 wt % of the total catalyst weight, the zeolite
comprises from about 50 wt % to about 90 wt % of the total catalyst
weight, and the oxide support comprises from about 10 wt % to about
50 wt % of the total catalyst weight. In a more preferred
embodiment of the catalyst, the noble metal comprises from about
0.5 wt % to about 2 wt % of the total catalyst weight, the zeolite
comprises from about 75 wt % to about 85 wt % of the total catalyst
weight, and the oxide support comprises from about 25 wt % to about
35 wt % of the total catalyst weight. The pore volume of the
catalyst-sorbent is preferably at least about 0.3 cm.sup.3/g, and
the specific surface area, measured by the BET procedure, is
preferably at least 300 m.sup.2/g.
[0024] The noble metal may be selected from the group consisting of
ruthenium, rhodium, palladium, osmium, iridium, platinum, alloys of
these elements, other compounds containing at least one of these
elements, and combinations thereof. The amount of noble metal to be
added can vary and may, for example, be chosen to balance the need
for a high activity with the cost of the metal(s). If noble metals
are combined, for example if the catalyst-sorbent comprises
platinum and palladium, the concentration of the combined noble
metals will be from about 0.1 wt % to about 5 wt % of the total
catalyst weight. The relative ratio of the noble metals may also
vary as necessary to obtain a balance of performance versus cost.
In an exemplary embodiment, palladium and platinum having a Pd:Pt
ratio of from about 1:1 to about 6:1 is used. The noble metal or
noble metals may be added to the zeolite and/or the support by
standard methods of catalyst preparation which are known in the
art, such as impregnation, ion exchange, chemisorption, or vapor
deposition.
[0025] Zeolites are microporous materials having a framework
comprising oxygen, silicon, and aluminum. The framework has a
formal negative charge, which is balanced by adsorbed cations. One
property of zeolites is that these cations can be exchanged for
other cations, for example, Na.sup.+ ions can be replaced by
NH.sub.4.sup.+ ions. It is found that aluminosilicate zeolites of
the BEA and FAU structures (including zeolites .beta., X, and Y)
are suitable zeolite components for the catalyst-sorbent.
Preparative procedures for several zeolites can be found in the
monograph Verified Syntheses of Zeolitic Materials, edited by H.
Robson (Amsterdam; N.Y.: Elsevier, 2001), which is hereby
incorporated by reference. Zeolite Y containing Na.sup.+
exchangeable cations (commonly known as "NaY") is preferred.
[0026] The oxide support is typically alumina, silica, titania,
zirconia, or mixtures thereof. Alumina is preferred. If alumina is
used, it can be obtained in various forms with differing surface
areas (high- or low-surface-area), differing levels of hydration,
and different crystallographic phases (alpha, gamma, kappa, etc.)
Any one or more of these forms may be used to prepare the
catalyst-sorbent, and any one or several of these forms may be
present in the final product. As is known in the art, some forms of
alumina are more suitable for use in catalysts and sorbents than
other forms. In general, high surface areas and crystallographic
phases other than the alpha phase are more catalytically active and
have higher sorbent capacity. This is especially important in fuel
cell processor trains, where weight or space is often at a
premium.
[0027] The process is suitable for use at near-ambient conditions.
That is, a process wherein the catalyst-sorbent bed temperature is
held below about 100.degree. C. is preferred; a catalyst-sorbent
bed temperature below about 60.degree. C. is more preferred; and a
catalyst-sorbent bed temperature below 40.degree. C. is most
preferred. A catalyst-sorbent bed temperature above 0.degree. C. is
preferred. No hydrogen is required for the process. If hydrogen is
present, it is preferable that the partial pressure of hydrogen at
the catalyst-sorbent bed be less than about 500 kPa, and more
preferably less than about 50 kPa. The gas hourly space velocity of
the feedstream as it is fed into the catalyst-sorbent bed is
preferably less than about 3000 h.sup.-1, more preferably less than
about 1500 h.sup.-1.
[0028] The following example illustrates and explains the present
invention, but is not to be taken as limiting the present invention
in any regard:
[0029] In an exemplary process, a catalyst-sorbent is prepared by
physically mixing gamma-alumina and zeolite NaY such that the ratio
of alumina to zeolite is approximately 1:4, and the alumina-zeolite
mixture is then extruded. Palladium and platinum are impregnated
onto the extruded alumina-zeolite pieces to produce a catalyst
precursor having a Pd to Pt ratio of about 3:1 and a combined noble
metal loading of between 1.0% and 1.5%. The precursor is dried at
about 120.degree. C. for about 12 hours, then calcined at about
550.degree. C. for about 4 hours. The resulting catalyst-sorbent
comprises about 37.49 wt % A;.sub.2O.sub.3, 57.08 wt % SiO.sub.2,
4.49 wt % Na.sub.2O, 0.83 wt % Pd, 0.30 wt % Pt, 0.029 wt % C and
0.003 wt % S, and has a pore volume of 0.48 cm.sup.3/g, a BET
specific surface area of 481 m.sup.2/g, and a loss of ignition at
1000.degree. F. (540.degree. C.) of 23.07%. The catalyst-sorbent
has about an 86% NaY content according to X-ray diffraction. The
catalyst-sorbent is packed into a tubular reactor having a diameter
of about 1.9 cm and a catalyst bed volume of about 10 cm.sup.3. The
catalyst bed is heated to a temperature of about 38.degree. C. and
this temperature is maintained as a hydrocarbon feedstream
comprising about 93 vol % methane, 3 vol % ethane, 2 vol % propane,
0.25 vol % butane, 1 vol % nitrogen, 1 vol % carbon dioxide, 5 ppm
carbonyl sulfide, 5 ppm mercaptan, 5 ppm tetrahydrothiophene, and 5
ppm hydrogen sulfide is fed to the reactor at a gas hourly space
velocity (GHSV) of about 3000.sup.-hr, and at a gas pressure of
about 15 psig. After about 50 hours on stream, at the reactor
outlet, the gaseous feedstream comprises by volume less than about
0.1 ppm mercaptan, less than about 0.1 ppm tetrahydrothiophene,
about 3 ppm carbonyl sulfide, and about 10 ppm hydrogen
sulfide.
[0030] The present invention has the advantage of being able to
remove mercaptans, tetrahydrothiophene, and carbonyl sulfide in a
single step. However, the catalyst-sorbent used in the invention is
not designed to absorb hydrogen sulfide; in fact the hydrogen
sulfide level of the process stream may increase due to hydrolysis
of other sulfur compounds, such as carbonyl sulfide. Because of
this, it is almost always preferable to include a subsequent step
in which hydrogen sulfide is removed. For example, a bed of
H.sub.2S-specific sorbent may be used downstream from the claimed
catalyst-sorbent.
[0031] It is understood that the composition of the
catalyst-sorbent and the specific processing conditions may be
varied within limits known in the art without exceeding the scope
of this development.
* * * * *