U.S. patent application number 10/790920 was filed with the patent office on 2004-09-02 for attrition resistant, zinc titanate-containing, reduced sorbents and methods of use thereof.
This patent application is currently assigned to Research Triangel Institute. Invention is credited to Gupta, Raghubir P., Turk, Brian S., Vierheilig, Albert A..
Application Number | 20040170549 10/790920 |
Document ID | / |
Family ID | 33302427 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040170549 |
Kind Code |
A1 |
Vierheilig, Albert A. ; et
al. |
September 2, 2004 |
Attrition resistant, zinc titanate-containing, reduced sorbents and
methods of use thereof
Abstract
Reduced sulfur gas species (e.g., H.sub.2S, COS and CS.sub.2)
are removed from a gas stream by compositions wherein a zinc
titanate ingredient is associated with a metal oxide-aluminate
phase material in the same particle species. Nonlimiting examples
of metal oxides comprising the compositions include magnesium
oxide, zinc oxide, calcium oxide, nickel oxide, etc.
Inventors: |
Vierheilig, Albert A.;
(Savannah, GA) ; Gupta, Raghubir P.; (Durham,
NC) ; Turk, Brian S.; (Durham, NC) |
Correspondence
Address: |
WILMER CUTLER PICKERING HALE AND DORR LLP
300 PARK AVENUE
NEW YORK
NY
10022
US
|
Assignee: |
Research Triangel Institute
PO Box 12194 3040 Conrwallis Road
Research Triangle Park
NC
27709
INTERCAT, INC.
P.O. BOX 412
Sea Girt
NJ
08750-0412
|
Family ID: |
33302427 |
Appl. No.: |
10/790920 |
Filed: |
March 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10790920 |
Mar 2, 2004 |
|
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09541204 |
Apr 3, 2000 |
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Current U.S.
Class: |
423/244.06 |
Current CPC
Class: |
B01D 53/83 20130101;
B01J 20/28004 20130101; B01D 2257/304 20130101; B01J 20/06
20130101; B01J 20/2803 20130101; B01J 20/28057 20130101; B01J
20/28011 20130101; B01D 53/48 20130101; B01D 2257/308 20130101;
B01J 20/08 20130101; Y10S 502/504 20130101; Y10S 502/517 20130101;
B01J 20/28019 20130101; B01J 20/30 20130101; B01D 53/508 20130101;
B01J 20/041 20130101; B01D 53/52 20130101 |
Class at
Publication: |
423/244.06 |
International
Class: |
B01D 053/50 |
Goverment Interests
[0002] This invention was made with United States Government
support under Grant number DE-FG02-96ER82189 awarded by the
Department of Energy. Consequently, the United States Government
has certain rights in this invention.
Claims
What is claimed is:
1. A process for removing a reduced sulfur gas from a process
stream, said process comprising contacting the process stream with
a reduced sulfur gas sorbing composition comprising, in the same
particle, zinc titanate and a metal oxide-aluminate phase in order
to remove at least a portion of the reduced sulfur gas from the
process stream.
2 The process according to claim 1, wherein the metal
oxide-aluminate phase of the sulfur sorbing composition has the
general formula MO, wherein M is a metal selected from the group
consisting of magnesium, zinc, nickel and calcium, and O is
oxygen.
3. The process according to claim 1, wherein the metal
oxide-aluminate phase is zinc oxide-aluminate.
4. The process according to claim 1, wherein the metal
oxide-aluminate phase is calcium oxide-aluminate.
5. The process according to claim 1, wherein the metal
oxide-aluminate phase is magnesium oxide-aluminate.
6. The process according to claim 1, wherein the reduced sulfur gas
sorbing composition, after sorption of a reduced sulfur gas, is
contacted with an oxygen-containing gas at an elevated temperature
in order to desorb a reduced sulfur gas and thereby regenerate the
reduced sulfur gas sorbing composition for subsequent reduced
sulfur gas sorption duty.
7. The process according to claim 1, wherein the composition
further comprises a binder material.
8. The process according to claim 1, wherein the composition is in
the form of microspheroidal particles.
9. The process according to claim 1, wherein the composition is
constantly recirculated in a fluid bed reactor to effect sorption
of the reduced sulfur gas.
10. The process according to claim 1, further comprising
regeneration of the composition by extracting a portion of
partially sorbed particles and subjecting said particles to
regeneration.
11. The process according to claim 1, further comprising
regeneration of the composition by ceasing a gas flow in said
process and then subjecting the sorbent to a regeneration
process.
12. The process according to claim 1, wherein a reduced sulfur gas
is removed from a coal gas stream.
13. The process according to claim 1, wherein a reduced sulfur gas
is removed from a hydrocarbon gas stream.
14. A process for removing a reduced sulfur species from a process
stream, comprising: (a) providing an attrition-resistant
particulate sorbent comprising a plurality of substantially uniform
particles comprising a zinc titanate phase and a zinc
oxide-aluminate phase, said zinc titanate phase being present in an
amount of from about 5 w. % to about 80 w. % of said particles,
said zinc oxide-aluminate phase being present in an amount of from
about 20 w. % to about 95 w. % of said particles, said zinc
titanate and zinc oxide-aluminate phases constituting at least
about 80 w. % of said particles, and said particles being
substantially free of unreacted alumina; and (b) contacting the
process stream with said particulate sorbent under conditions
sufficient to cause sorption of sulfur by said particulate
sorbent.
15. The process according to claim 14, further comprising:
contacting the particulate sorbent with an oxygen-containing gas at
an elevated temperature after sorption of sulfur to remove sulfur,
thereby regenerating the particulate sorbent for subsequent
sorption duty.
16. The process according to claim 15, wherein the steps of
contacting the process stream with said particulate sorbent and
contacting the particulate sorbent with the oxygen-containing gas
are each conducted in a fluid bed reactor.
17. The process according to claim 16, wherein the particulate
sorbent is recirculated from the step of contacting the particulate
sorbent with the oxygen-containing gas to the step of contacting
the process stream with said particulate sorbent.
18. The process according to any one of claims 14, 16 or 17,
wherein said process stream is a coal gas stream.
19. The process according to any one of claims 14, 16 or 17,
wherein said process stream is a hydrocarbon gas stream.
20. A method of stabilizing an unreacted alumina support so as to
be chemically nonreactive with zinc atoms from a zinc-containing
compound comprising a reduced sulfur sorbent composition, said
method comprising: chemically reacting a metal oxide with alumina
to form a metal oxide-aluminate phase material under elevated
temperature conditions, said metal oxide-aluminate phase-forming
chemical reaction reducing or eliminating deactivation of the
zinc-containing compound comprising the reduced sulfur sorbent
composition at the elevated temperature.
21. The method according to claim 20, wherein the metal oxide
comprises a divalent metal.
22. The method according to claim 21, wherein the divalent metal is
selected from magnesium, calcium, zinc, or nickel.
23. The method according to claim 20, wherein the alumina support
comprises an alumina binder.
24. The method according to claim 20, wherein the zinc containing
compound is zinc titanate.
25. The method according to claim 24, wherein the reduced sulfur
sorbent composition comprises from about 5 w. % to about 80 w. %
zinc titanate and from about 20 w. % to about 95 w. % of the metal
oxide-aluminate phase.
26. The method according to claim 25, wherein the zinc titanate and
the metal oxide-aluminate phase comprise the same particle.
27. The method according to claim 26, wherein the particle
comprises a microspheroidal particle.
28. The method according to claim 20, wherein the temperature is
greater than about 300.degree. C.
Description
[0001] This patent application is a divisional of application U.S.
Ser. No. 09/541,204, filed on Apr. 3, 2000, and claims benefit of
application U.S. Serial No. 60/075,680, filed on Feb. 24, 1998.
FIELD OF THE INVENTION
[0003] This invention generally relates to zinc titanate-containing
compositions used to remove reduced sulfur gases such as H.sub.2S,
COS, and CS.sub.2 from gas streams. More specifically, it relates
to those zinc titanate-containing compositions that, aside from
their chemical reactivity toward reduced sulfur gases, also have
the physical attributes of toughness and attrition resistance.
BACKGROUND OF THE INVENTION
[0004] Reduced sulfur gases are present in many industrial
processes. For example, reduced sulfur gases are found in flue gas,
coal gas and fuel gas streams. They are also found in industrial
product gas streams such as olefin-containing gas streams, which
are a component of petroleum refining operations. These gases are
often removed from such gas streams by use of various metal oxides
that have the ability to capture a reduced sulfur-containing gas
component from such gas streams. In order to capture such a gas
from certain industrial processes (such as packed-bed,
fluidized-bed or moving-bed reactors), the metal oxide, reduced
sulfur gas sorbent materials must be used in forms that are
mechanically strong and resistant to attrition. Otherwise,
problems, such as pressure drops through a process reactor unit,
particulate matter elutriation and/or clogging of valves or other
mechanical components will take place.
[0005] Moreover, almost all industrial processes that deal with
reduced sulfur gases also are confronted with the problem of
desorbing these gases from the metal oxide sorbent material so that
the sorbent material can be used over and over again in order to
obtain its maximum economic benefit. Other problems associated with
the presence of reduced sulfur gases (such as H.sub.2S, COS and
CS.sub.2) in gas streams such as fuel gases, flue gases and waste
gases arise from the fact that reduced sulfur gases are corrosive
toward ferrous metals. They are especially corrosive toward steel
turbine blades. Therefore, the presence of reduced sulfur gases in
those hot fuel gases used to power turbines results in their severe
corrosion. Oxidation of hot fuel gases also serves to oxidize any
reduced sulfur gases contained therein. The resulting sulfur oxide
gases (e.g., SO.sub.2, and SO.sub.3, which are commonly referred to
as "SO.sub.x" gases) also are highly corrosive toward ferrous
metals. Moreover, upon release to the atmosphere, SO.sub.x gases
form so-called "acid-rain." Therefore, the concentration of reduced
sulfur gases contained in those hot fuel gases introduced into
power-producing equipment, such as turbines and fuel cells, must be
brought to very low concentrations, e.g., a few parts per million
(ppm), before they are combusted in equipment of this kind.
[0006] Next, it should be noted that in the case of sulfur oxide
sorbents--as opposed to the reduced sulfur sorbents that form the
subject matter of this patent disclosure--the subject sulfur oxide
is normally usually captured in an oxidizing atmosphere such as
those extant in the catalyst regenerator of a FCC unit. This is
done through use of various metal oxide particles having an
affinity for a given sulfur oxide-containing gas. These particles
are often entrained in a "fluidized" process. For example, sulfur
oxide (e.g., SO.sub.2 or SO.sub.3) sorption is often carried out
through the use of fluidized microspheroidal magnesium-containing
particles that can withstand the hot (e.g., 1350.degree. F.)
oxidizing conditions present in the catalyst regenerator units of
those fluid catalytic conversion ("FCC") processes used to refine
petroleum. Conversely, release of such sorbed sulfur-containing
gases usually occurs in the reducing environment of a FCC reactor.
The sulfur component of such gases is released as hydrogen sulfide
H.sub.2S. This released H.sub.2S gas is readily captured downstream
of the reactor and normally does not create an environmental
hazard.
[0007] Again, however, the processes of the present patent
disclosure are different from such SOX sorption processes in that
applicant's compositions are specifically designed to capture
chemically reduced forms of sulfur (e.g., those in H.sub.2S, COS
and CS.sub.2) rather than chemically oxidized forms of sulfur
(e.g., those in SO.sub.2 and SO.sub.3). Thus, applicant's capture
of reduced sulfur gases must take place under chemical reduction
conditions, rather than under chemical oxidizing conditions.
[0008] Many different zinc-containing compounds have been used in
both fixed bed and fluid bed systems in order to remove one or more
species of reduced sulfur gases from various industrial gas streams
(e.g., fuel gases, such as those derived from the gasification of
coal, flue or waste gases and/or industrial product gases, such as
those that contaminate olefin-type gases). Such zinc-containing
compounds have included zinc oxide, zinc titanate and zinc
aluminate. Zinc oxide, for example, has been used as a sorbent for
selectively removing hydrogen sulfide gas, H.sub.2S, from certain
industrial gas streams. This metal oxide is normally used by
placing it in contact with a hydrogen sulfide-containing gas stream
at elevated temperatures. Zinc oxide, in and of itself, has not,
however, proven to be a particularly effective hydrogen sulfide
sorbent for many industrial applications. For example, its hydrogen
sulfide sorption ability is relatively limited, especially at lower
temperatures. It also suffers from the drawback of not being easily
regenerated. This drawback follows from the relatively high
thermodynamic stability of the zinc sulfide product of zinc
oxide-hydrogen sulfide reactions. Zinc oxide also lacks the
qualities of hardness, toughness and/or attrition resistance that
are needed for many industrial applications.
[0009] Regeneration of the zinc sulfide product of zinc
oxide-hydrogen sulfide reactions requires subsequent oxidation of
the sulfur component of the zinc sulfide reaction product. This
must be done at relatively high temperatures (e.g., 900.degree. F.
to 1500.degree. F.). Unfortunately, the relatively high
temperatures needed to oxidize zinc sulfide back to zinc oxide also
tend to degrade the already inherently low mechanical strength
and/or toughness of these zinc oxide-based materials. Consequently,
zinc oxide sorbents tend to quickly disintegrate when they are
repeatedly used and regenerated.
[0010] Therefore, in order for zinc oxide-containing compounds to
be effectively used in the harsh environments where they are needed
(e.g., in the high temperature/high velocity particle impact
environments of fluid, fixed or bubbling bed processes), they must
be combined with other tougher and more attrition resistant metal
oxide components in order to produce overall zinc oxide/metal oxide
compositions having the requisite mechanical strength, hardness,
durability, toughness and attrition resistance that they will need
to function as reduced sulfur gas sorbents.
[0011] Generally speaking, this has been accomplished by mixing
certain prescribed proportions of a relatively soft zinc oxide
component with certain prescribed portions of another, relatively
harder, tougher, metal oxide component in the same particle. The
most effective and widely used metal oxide used for this
hardening/toughening purpose has been unreacted alumina
(Al.sub.2O.sub.3). Such use of alumina as a catalyst support for
zinc oxide sorbents follows from the unusually high degree of
hardness this material imparts to such compositions, as well as
from the excellent binding capabilities of many forms of so-called
"gelling" or "sol" alumina forms. Examples of such aluminas are the
various grades of VISTA CATAPAL.RTM. and CONDEA DISPERAL.RTM.
aluminas. Such aluminas have been used in producing relatively
harder, tougher and more attrition resistant extrudate, granule,
microsphere, powder, particle, pellet, bead, etc. forms of zinc
oxide/unreacted alumina compositions.
[0012] Improvements in the sorption, regeneration and physical
attributes of zinc oxide-containing compositions are described, for
example, in U.S. Pat. No. 4,088,736 ("the '736 patent") which
discloses a reduced sulfur sorbent comprised of homogeneous
mixtures of zinc oxide, alumina, silica, and Group II-A metal
oxide(s). The alumina and silica components of the compositions
taught by the '736 patent serve to impart toughness and attrition
resistance to the therein disclosed compositions.
[0013] Other patent disclosures teach the use of other
zinc-containing compounds, i.e., other than zinc oxide, as the
"active," reduced sulfur gas-capturing agent in such compositions.
For example, U.S. Pat. No. 4,263,020 ("the '020 patent") discloses
the reduced sulfur gas-capturing abilities of metal aluminate
spines having the general formula MAl.sub.2O.sub.4 wherein the M
component can be chromium, iron, cobalt, nickel, copper, cadmium or
mercury. Zinc aluminate spinel, ZnAl.sub.2O.sub.4, is a
particularly preferred member of this group of compounds. The '020
patent also discloses that the zinc atoms of such a zinc aluminate
spinel form simple adsorption bonds with reduced sulfur gases.
These adsorption bonds are sufficient to remove a reduced sulfur
gas, such as hydrogen sulfide, from a recycle hydrogen gas stream.
The '020 patent also discloses that, unlike the chemical mechanism
involved in the removal of reduced sulfur gas (e.g., hydrogen
sulfide) from a recycle hydrogen gas stream by the use of zinc
oxide-based sorbents, there is no chemical reaction in the process
of the '020 patent wherein zinc sulfide is ever formed from these
MAl.sub.2O.sub.4 compounds. Consequently, they can be regenerated
by simply purging or sweeping the physically sorbed, reduced sulfur
gas from these MAl.sub.2O.sub.4 compounds with a hot, inert gas
such as nitrogen.
[0014] Zinc titanate has also been used as a reduced sulfur
compound sorbent. Indeed, it has been used in sorbents having no
binder component other than the zinc titanate itself.
Unfortunately, zinc titanate (like zinc oxide) also suffers to some
degree from the drawback of being a relatively "soft" material.
Consequently, most zinc titanate-containing compositions (like zinc
oxide-containing compositions) employ an unreacted alumina
component as a binder material in order to create hard, tough,
attrition resistant zinc titanate/unreacted alumina
compositions.
[0015] Still other zinc titanate-containing, reduced sulfur sorbent
compositions do not employ unreacted alumina, but rather employ
other kinds of toughness-imparting binder materials. For instance,
U.S. Pat. No. 5,254,516 ("the '516 patent") teaches various zinc
titanate-based sorbent materials that further comprise a
combination of inorganic and organic materials that are used as a
binder for the active zinc titanate ingredient. These inorganic
binder materials include clays, such as kaolinite and bentonite
(which are aluminosilicates), feldspar, sodium silicate, forsterite
and calcium sulfate. The more preferred organic binders used to
create the tough binder materials disclosed in the '516 patent are
methylcellulose-based compositions such as that commercially
available as METHOCEL.RTM..
[0016] Those skilled in this art also will appreciate that zinc
titanate-containing compositions tend to lose more and more of
their capacity to absorb reduced sulfur gases as more and more of
the binder ingredients (e.g., clay, alumina, organics, etc.) are
used in these compositions. It might also be noted in passing here
that it was heretofore generally believed that the reason for this
loss in reduced sulfur gas capturing ability was simply due to the
fact that less zinc titanate is present in those compositions
having relatively greater proportions of binder materials.
[0017] The present invention addresses a need in the art for new
and improved materials with sulfur gas capturing capacity and
provides such materials and methods of production and use
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 depicts, by Thermogravimetric Analysis (TGA) traces,
the hydrogen sulfide sorption ability of a prior art composition
comprised of a zinc titanate sorbent supported by an unreacted
alumina binder. The TGA traces for both a fresh sample and a
reacted sample of the sorbent compositions are given for
comparative purposes.
[0019] FIG. 2 shows the x-ray diffraction (XRD) pattern of a
composition comprised of a zinc titanate ingredient that is
supported by an unreacted alumina binder material before said
composition was subjected to multiple sorption/regeneration cycles
in a high temperature, high pressure (HTHP) reactor.
[0020] FIG. 3 shows the x-ray diffraction pattern of zinc titanate
supported by an unreacted alumina binder composition whose XRD
pattern is shown in FIG. 2, after this composition was subjected to
multiple cycles of HTHP reactor testing.
[0021] FIG. 4 shows the x-ray-diffraction pattern of a composition
comprised of zinc titanate supported by zinc aluminate. The traces
for the materials are shown before and after being subjected to 10
cycles of HTHP reactor testing.
[0022] FIG. 5 shows the TGA pickup trace of the H.sub.2S gas pickup
ability of a composition comprised of zinc titanate sorbent
supported by a zinc oxide-aluminate phase material. The traces for
both fresh and reacted forms of this composition are given for
comparative purposes.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Applicant has learned that the reduced sulfur-capturing
capacity of materials prior to this invention, as discussed
hereinabove, is only partially due to the reduced concentrations of
the disclosed sulfur sorbent materials. Indeed, Applicant has
established that the reduction of sulfur sorbing capacities in such
materials is largely caused by certain adverse chemical interaction
between the zinc titanate and the other components of the sorbent
particle (such as their binder and filler ingredients). Applicant
has also discovered the most undesirable of these reactions is one
that occurs between zinc titanate and unreacted alumina. That is to
say that even though certain metal oxides, and especially unreacted
alumina, have proven to be especially effective binders for zinc
titanate-based compositions because they serve to greatly improve
the mechanical strength and attrition resistance of the resulting
zinc titanate/unreacted alumina particles, Applicant has found that
such use of unreacted alumina results in overall reduced sulfur gas
sorbent compositions that exhibit progressively lower reduced
sulfur gas capturing activity--not only because more and more
unreacted aluminum-containing compounds (such as alumina, clay,
etc.) are added to these compositions in order to make them harder,
tougher and more attrition resistant--but because some of the
aluminum component of the unreacted alumina has chemically reacted
with some of the zinc component of the zinc titanate.
[0024] In other words, Applicant has found the reason behind the
fact that, despite the improvements in the physical attributes of
zinc titanate-containing particles in general, and especially those
brought about by use of "optimal" proportions of unreacted alumina
binders, prior art reduced sulfur sorbent compositions are
characterized by the fact that they, all too soon, lose their
reduced sulfur-containing gas sorbent ability and/or their physical
integrity, as they are repeatedly used, regenerated and reused.
Armed with this understanding, Applicant has produced reduced
sulfur gas sorbents that are characterized by their relatively
better reduced sulfur gas sorbent abilities and physical hardness,
toughness, durability and/or attrition resistance qualities. It is
therefore an object of the present invention to describe certain
reduced sulfur sorbent compositions that are simultaneously capable
of readily reversibly sorbing, and releasing, relatively large
amounts of reduced sulfur gas without losing their sulfur sorbing
ability and/or quickly succumbing to the harsh conditions where
these particles are employed.
[0025] Applicant's reduced sulfur gas sorbent compositions even
tend to gain in their reduced sulfur gas sorbent abilities as these
compositions are repeatedly used over many successive sorption and
regeneration cycles. Hence, the reduced sulfur sorbent compositions
of this patent disclosure are especially well suited for use in a
wide variety of production and/or pollution control process streams
(e.g., removing a reduced sulfur gas from a hydrocarbon stream,
e.g., removing H.sub.2S from an olefin stream, removing reduced
sulfur gases from flue gases, etc., removing sulfur from coal gases
before they are introduced into a turbine, etc.). Applicant's
compositions are especially useful in those bubbling and fluid bed
processes wherein the mechanical stresses imparted to particles of
such reduced sulfur sorbent compositions are severe, and, if not in
some way guarded against, would result in high elutriation losses
from any process employing these compositions under such adverse
conditions.
[0026] Thus, the more desirable properties of the reduced sulfur
sorbents taught by this patent disclosure include their improved
(1) hardness, toughness and attrition resistance, (2) ability to
capture reduced sulfur gases (such as H.sub.2S) from a variety of
gaseous streams, (3) ability to release the sorbed sulfur species,
(4) ability to minimize sorbent deactivation over relatively more
cycles of sorbing and releasing various reduced sulfur species, (5)
ability to form into special shapes (i.e. microspheroidal
particles) that are particularly useful for certain applications,
(6) ability to remove reduced sulfur gases from a stream of a
commercially valuable gas product (e.g., remove H.sub.2S from an
olefin stream), and (7) special suitability for capturing reduced
sulfur gases from hot fuel gas streams, such as those used to power
turbines and fuel cells (e.g., removing reduced sulfur gas from a
coal gas stream before it is introduced into a turbine).
[0027] Applicant's experimental work has established that the loss
of activity of zinc titanate/unreacted alumina compositions with
respect to their ability to pick-up reduced sulfur gases is due, in
large measure, to formation of a zinc aluminate phase in such
compositions during their use in high temperature environments
(e.g., those higher than about 500.degree. F.). This zinc aluminate
phase forms from the zinc component of the zinc titanate active
ingredient and from the aluminum component of those unreacted
alumina ingredient(s) normally used as binder ingredients for the
zinc titanate in most known, reduced sulfur sorbent compositions.
Applicant also has found that this zinc aluminate phase is not
normally formed under the sorption cycle in which the chemically
reduced sulfur gas is sorbed, but rather is, for the most part,
formed during the subsequent relatively higher temperature,
regeneration cycle wherein the sorbed, reduced sulfur gases are
driven off the composition so that it can be reused over and over
again.
[0028] Applicant also found that this zinc aluminate forming
chemical reaction is virtually irreversible under the catalyst
regeneration temperature conditions that exist in most processes
wherein such zinc titanate/unreacted alumina compositions are
employed. In effect, this loss of activity toward reduced sulfur
gases follows from the fact that the newly-formed zinc aluminate
phase possesses significantly lower reduced sulfur gas capturing
ability relative to that of the original zinc titanate ingredient
of such compositions. Indeed, Applicant's experimental work
indicates that the reduced sulfur gas activity of this zinc
aluminate phase is often as much as an order of magnitude less than
that of the original zinc titanate ingredient. In other words, this
newly formed zinc aluminate phase can be thought of as "poisoning"
the sulfur sorbing zinc titanate ingredient of such zinc
titanate-containing compositions. Worse yet, this poisoning effect
becomes more and more pronounced as these compositions experience
repeated sorption/regeneration cycles.
[0029] Thus, this invention is particularly concerned with
preventing degradation of the active, reduced sulfur gas capturing,
zinc titanate phase in those zinc titanate-containing reduced
sulfur gas sorbent compositions that also employ aluminum
ingredients (e.g., alumina-based ingredients) in order to give such
compositions the hardness, toughness and attrition resistant
qualities they need to survive in the harsh environments where they
are employed. Applicant's invention also may be considered as
teaching a method of producing attrition resistant zinc
titanate-containing compositions (e.g., microspheroidal particles)
by using a metal oxide-aluminate phase to support (bind, etc.) the
active zinc titanate phase, as opposed to using an unreacted
alumina phase for this support (binding, etc.) function.
[0030] The improved reduced sulfur gas capturing ability and
desired physical characteristics of Applicant's compositions are
simultaneously achieved by chemically incorporating another
metal-containing compound into an aluminum-containing binder
component--and especially into an unreacted alumina binder
component--of an overall zinc titanate/metal oxide-aluminate phase
composition. That is to say that a chemical reaction is produced
between at least a portion of an aluminum-containing component
(such as unreacted alumina) and a metal-oxide containing compound
(such as magnesium oxide) so that a resulting metal oxide-aluminate
phase (e.g., MgO.Al.sub.2O.sub.3) will not thereafter chemically
react with any zinc oxide driven off the zinc titanate component
during regeneration of these sulfur sorbents at those elevated
temperatures (e.g., those greater than about 700.degree. F.) at
which these sulfur sorbents are normally regenerated.
[0031] In other words, the metal oxide component of Applicant's
metal oxide-aluminate phase ingredient is further characterized by
the fact that it is, to some degree, already chemically reacted
with an aluminum-containing compound such as unreacted alumina when
the sulfur sorbent experiences the high temperatures at which these
sulfur sorbents are regenerated. It is emphasized that this binder
component of these overall compositions is not merely a mixture of
the metal oxide (e.g., MgO) and unreacted alumina
(Al.sub.2O.sub.3), but rather is a compound formed from these
chemicals, through Applicant's use of the expression "metal oxide
aluminate phase". That these chemical reactions have, in fact,
occurred can be verified in several ways. For example, the XRD
pattern for the resulting metal oxide-aluminate phase will differ
from the XRD pattern of the subject metal oxide compound (e.g.,
MgO) itself, as well as from the XRD pattern of the subject
unreacted aluminum-containing compound (e.g., Al.sub.2O.sub.3)
itself. For example, if the metal oxide is magnesium oxide (MgO)
and the unreacted aluminum-containing compound is alumina
(Al.sub.2O.sub.3), the XRD pattern of Applicant's resulting metal
oxide-aluminate (MgO.Al.sub.2O.sub.3) phase will differ from that
of the metal oxide (MgO) and from that of the unreacted alumina
(Al.sub.2O.sub.3). Thus, Applicant's overall zinc titanate/metal
oxide-aluminate phase composition may be thought of as a zinc
titanate phase that is combined, mixed, associated, etc. with a
metal oxide-aluminate phase in the same particle. Again, the object
of Applicant's processes is to prevent chemical reactions between
the zinc component of a zinc titanate and the aluminum component of
the unreacted alumina (Al.sub.2O.sub.3) under those high
temperature conditions where reduced sulfur gas sorbents are
employed. Applicant's reduced sulfur gas sorbent composition also
may contain certain optional ingredients hereinafter more fully
described.
[0032] It should also be noted that an excess metal oxide phase or
an excess alumina phase may be present in Applicant's overall
reduced sulfur gas sorbent compositions (that is to say that
complete chemical reaction between all of Applicant's
aluminum-containing compound (e.g., unreacted alumina) and all of
Applicant's metal oxide (e.g., MgO, ZnO, etc.) is not necessary for
effective formulation of the overall compositions that constitute
the subject matter of this patent disclosure. Complete chemical
reaction between these metal oxide and alumina ingredients may in
many cases be preferred.
[0033] Examples of the metal oxide-aluminate phases that can be
used in Applicant's sulfur sorbent compositions are varied and
extensive. Indeed, such metal oxide-aluminate phases can be made
with any metal or metal compound (e.g., a metal oxide) that can, to
some extent, chemically react with alumina. These metals may
include, but are not limited to, Mg.sup.2+, Ca.sup.2+, Zn.sup.2+,
Ni.sup.2+. Bivalent metals are, however, particularly preferred for
this purpose. The oxides of these metals (e.g., MgO, CaO, ZnO,
NiO), as well as their nitrate, acetate, etc., forms, can be used
as starting materials for Applicant's formulations. Those skilled
in this art will, however, appreciate that the non-oxide forms of
these metal compounds (e.g., their nitrates, acetates, etc.) will
be converted to oxide forms, (e.g., MgO, CaO, ZnO, NiO, etc.) when
these non-oxide metal compounds are subsequently subjected to
certain high temperature processes (e.g., calcining) that may be
used in the manufacture of these reduced sulfur gas sorbents, or
which may be encountered (e.g., in high temperature regeneration
units) during actual use of these sorbents.
[0034] It should be noted that Applicant also has found that, if
the metal oxide-aluminate compound used in the processes of this
patent disclosure is zinc aluminate, ZnAl.sub.2O.sub.4, the
resulting zinc titanate/zinc oxide-aluminate composition is not
poisoned by the original presence of the zinc aluminate. Without
wishing to be bound by theory, Applicant believes that this
seemingly anomalous result follows from the fact that since the
zinc aluminate phase is already present in the zinc titanate-zinc
aluminate sorbent particle, it prevents the zinc component of the
zinc titanate from reacting with the aluminum component of the zinc
aluminate. Consequently, following release of the sorbed sulfur
species from such compositions, the zinc component of the zinc
titanate compound again recombines with the titania to once again
form zinc titanate which is again ready for reduced sulfur gas
sorbing duty in a subsequent sorption cycle. In effect, this
particular metal oxide-alumina chemical reaction produces a phase
(a metal oxide-aluminate) that is not reactive toward the zinc
titanate active ingredient.
[0035] Applicant's sulfur sorbent compositions will preferably
contain, in the same particle, from about 5 to about 80 weight
percent (w. %) zinc titanate, and from about 20 to about 95 weight
percent of the metal oxide-aluminate phase. The most preferred
concentration will, in large part, depend on the particular end use
intended. For instance, in those environments that employ a fluid
bed process, the particles require maximum attrition resistance.
Consequently, a high concentration of the metal oxide-aluminate
phase may be required. Conversely, in fixed bed applications, the
attrition resistance of the sorbent particles is relatively less
important, while the overall sulfur sorption capacity is relatively
more important.
[0036] It is also noted here that, for purposes of this patent
disclosure, the term(s) "particle(s)" will be employed to describe
any one of, or all of, the extrudate, granule, microsphere, powder,
particle, pellet or bead forms of the compositions of this patent
disclosure. These particles also may contain minor amounts (e.g.,
less than twenty weight percent) of other auxiliary ingredients
such as other binder materials (i.e., other than the metal
oxide-aluminate phase), fillers, fluxes, surfactants and gas
evolution agents.
[0037] In some cases, the resulting metal oxide-aluminate phase
component of Applicant's overall zinc titanate phase/metal
oxide-aluminate phase composition may have some capacity to remove
reduced sulfur gases in its own right, while in other cases, the
resulting metal oxide-aluminate phase will possess no reduced
sulfur gas sorption capabilities whatsoever. In either case,
however, the resulting zinc titanate phase/metal oxide-aluminate
phase, sulfur sorbent compositions of this patent disclosure will
have improved reduced sulfur sorbent capabilities relative to known
compositions comprised of similar concentrations of zinc titanate
and unreacted alumina that exist as a mixture of zinc titanate and
a mixture of metal oxide (e.g., MgO) and alumina (Al.sub.2O.sub.3)
that have not been chemically reacted.
[0038] Indeed, the properties (chemical as well as physical) of
Applicant's reduced sulfur gas sorbents compare very favorably to a
wide variety of sulfur sorbent compositions prepared by various
known methods. For example, Applicant has established that the
sulfur sorbent compositions of this patent disclosure have better
reduced sulfur gas activities and attrition characteristics
relative to those based upon the use of (1) binderless zinc
titanate compositions, (2) compositions comprised of zinc titanate
and unreacted alumina mixtures, and (3) compositions based upon the
combined use of zinc titanate and other commonly used inorganic
binder materials such as kaolin and bentonite.
[0039] Another extremely important aspect of the present invention
is the fact that Applicant's zinc titanate/metal oxide-aluminate
phase compositions will actually improve in their activity toward
reduced sulfur gas species over repeated cycles of use. This
behavior with respect to the effects of regeneration upon
Applicant's reduced sulfur capturing compositions stands in stark
contrast to the fact that, under otherwise comparable conditions,
repeated cycling of all prior art compositions known to Applicant
(such as those based upon the use of mixtures of zinc titanate and
unreacted alumina) leads to their early, accelerating and very
significant deactivation with respect to their ability to pick up
reduced sulfur gases. The reason why Applicant's compositions
actually become better reduced sulfur-capturing agents upon
repeated use is not fully understood; however, without wishing to
be bound by theory, Applicant believes this phenomenon may be due
to certain synergistic effects between the zinc titanate and the
metal oxide-aluminate phase that take place upon successive
sorption/regeneration cycles. Indeed, this improvement in reduced
sulfur gas sorbing ability may be taken as some evidence that a
chemical reaction has been carried out between Applicant's metal
oxide and alumina ingredients. In improved reduced sulfur gas
capturing ability over success use also may be due, at least in
part, to increased "activation" of the zinc titanate or metal-oxide
aluminate phase with successive sorption/regeneration cycles. One
experimental result supporting the latter view was Applicant's
repeated observation of an increase in overall surface area of such
compositions following multiple sorption/regeneration cycles. Those
skilled in this art will appreciate that an increase in the surface
area of such a sulfur sorbent particle may serve to increase its
reduced sulfur gas sorbent capabilities. Some additional
experimental data (e.g., XRD traces for the zinc titanate component
of these compositions) also suggests that a decrease in the
crystallite sizes of the zinc titanate is taking place. This too,
may play some role in the improved sulfur-capturing ability of
Applicant's compositions as they are repeatedly used.
[0040] Applicant believes that the reason(s) for the relatively
faster and more severe chemical deactivation of those prior art
zinc titanate sorbents used in conjunction with an unreacted
alumina that is used as the zinc titanate's binder material can be
summarized by the following generalized reactions:
1TABLE IA Zinc Titanate Compositions Only Sorption ZT + H.sub.2S
.fwdarw. ZnS + TiO.sub.2 + H.sub.2O Regeneration ZnS + TiO.sub.2 +
O.sub.2 .fwdarw. ZT + SO.sub.2
[0041]
2TABLE IB Zinc Titanate + Alumina Binder Sorption ZT +
Al.sub.2O.sub.3 + H.sub.2S .fwdarw. ZnS + TiO.sub.2 +
Al.sub.2O.sub.3 + H.sub.2O Regeneration ZnS + TiO.sub.2 +
Al.sub.2O.sub.3 + .fwdarw. ZT + ZA + TiO.sub.2 + SO.sub.2
O.sub.2
[0042] In these tables, ZT represents a zinc titanate phase and ZA
represents a zinc aluminate phase. Again, a ZT phase material made
and employed according to the scheme of Table IA is generally
characterized by both a relatively high reactivity toward reduced
sulfur gas species and by a relatively low degree of toughness and
attrition resistance. Conversely, those prior art
ZT+Al.sub.2O.sub.3, compositions depicted in the chemical reaction
scheme of Table IB are generally characterized by their relatively
greater toughness and attrition resistance, but relatively lower
chemical activity toward reduced sulfur gas species--especially
over repeated cycles of use (relative to the materials depicted in
Table IA). By way of contrast, Applicant believes that the chemical
reaction mechanism of the compositions of the present patent
disclosure (as they undergo chemical reaction with a reduced
sulfur-containing gas species such as H.sub.2S) can be generally
described by the reaction schemes depicted in Table IIA and Table
IIB.
[0043] In Table IIA, the metal oxide-aluminate component of such
compositions is assumed to be substantially inactive toward reduced
sulfur gas species, while in Table IIB, such a metal
oxide-aluminate phase is assumed to be chemically active toward
such reduced sulfur species.
3TABLE IIA Metal Aluminate Not Reactive Sorption ZT + MOA +
H.sub.2S .fwdarw. ZnS + TiO.sub.2 + MOA + H.sub.2O Regeneration ZnS
+ TiO.sub.2 + MOA + .fwdarw. ZT + MOA + SO.sub.2 O.sub.2
[0044]
4TABLE IIB Metal Aluminate Reactive Sorption ZT + MOA + H.sub.2S
.fwdarw. ZnS + MS + TiO.sub.2 + Al.sub.2O.sub.3 + H.sub.2O
Regeneration ZnS + TiO.sub.2 + Al.sub.2O.sub.3 + .fwdarw. ZT + MOA
+ SO.sub.2 O.sub.2
[0045] In these tables, ZT represents a zinc titanate phase, MS
represents a metal sulfide phase and MOA represents a metal
oxide-aluminate phase. In either case, however, no significant
reduction in the ZT phase results following successive
sorption/regeneration cycles. Hence, no zinc aluminate is formed.
Consequently, the zinc titanate (ZT) phase is not "poisoned".
[0046] Next, it should be noted that the zinc titanate/metal
oxide-aluminate phase compositions of this patent disclosure can be
made by two general methods. The first general method involves
pre-reacting a zinc-containing compound with a titanium-containing
compound at a sufficient temperature to effect a transformation of
the zinc and titanium containing species into a zinc titanate
compound. The various techniques for doing this are well known to
this art. Indeed, in each of the two general methods for making
Applicant's zinc titanate/metal oxide-aluminate compositions, the
zinc titanate ingredient may be obtained from commercial
sources.
[0047] In any case, Applicant's first production method (A), starts
with mixing zinc titanate and one or more metal oxide-aluminate
phase compounds in the presence of various inorganic binders and
one or more liquid binder solution(s). A zinc titanate phase/metal
oxide-aluminate phase precursor composition resulting from such
mixtures is then formed into desired shapes, such as extrudates,
microspheres, granules, pellets, powders, or powders. The resulting
physical forms of these materials are then subjected to a
temperature greater than about 300.degree. C. for a time period of
greater than about 1 minute to convert the precursor components
into a zinc titanate/metal oxide-aluminate composition with the
desired physical properties (e.g., toughness, attrition resistance,
macroporosity and surface area). More preferably, however, the
heating period will be from about 1 to about 2 hours (at
temperatures ranging from about 300.degree. C. to about
1200.degree. C.). Alternatively, where the targeted process
operates at sufficiently high temperatures to effect the desired
chemical phase transformations, this heat treatment step may occur
within the process reactor vessel itself.
[0048] In the second manufacturing method (B), a zinc-containing
compound, an aluminum-containing compound (and especially an
unreacted alumina-containing compound) and the metal
oxide-containing compound are mixed with various liquids to form a
slurry, paste, etc. The resulting composition is then formed into a
desired shape, e.g., extrudates, microspheres, granules, pellets or
powders. The resulting physical forms of these compositions are
then subjected to a temperature greater than about 300.degree. C.
for a time period greater than 1 minute to convert the precursor
components into the zinc titanate/metal oxide aluminate phase
composition with the desired physical properties such as toughness,
attrition resistance, macroporosity and surface area. Preferably,
this heating period will be from about 1 to about 2 hours at
temperatures ranging from about 300.degree. C. to about
1300.degree. C. Alternatively, where the process in which
Applicant's sulfur sorbents is to be used operates at sufficiently
high reactor and/or regenerator temperatures (e.g., above about
300.degree. C.) to effect the desired chemical phase
transformations, this heat treatment step, likewise, may occur
within the process reactor vessel itself.
[0049] These two production methods A and B, can be carried using
the following generalized step-by-step procedures:
[0050] Method A.
[0051] a) Pre-react a zinc-containing compound with a
titanium-containing compound at sufficient temperature to effect a
transformation of the Zn- and Ti-containing species into a zinc
titanate compound.
[0052] b) Combine the zinc titanate compound prepared in step (a)
with a metal-containing compound and an aluminum-containing
compound.
[0053] c) Form the material resulting from step (b) into a desired
shape such as extrudates, microspheres, granules, pellets, or
powder.
[0054] d) Heat the resulting formed material to a temperature of
>300.degree. C. for a time of greater than 1 minute.
[0055] Method B.
[0056] a) Combine a zinc-containing compound, an aluminum
containing compound and a metal oxide-containing compound to form a
slurry, paste, etc.
[0057] b) Form the material resulting from step (a) into a desired
shape, such as extrudates, microspheres, granules, pellets, or
powder.
[0058] c) Heat the resulting formed material to a temperature of
>300.degree. C. for a time of greater than 1 minute.
[0059] It also should be noted that either of these two general
methods A and B can include the use of minor amounts (e.g., less
than about 20%) of other components such as binders, fluxes,
surfactants and gas evolution agents. These compositions can also
include other minor components, and especially those used to assist
in the regeneration of the sorbed, reduced sulfur gas species. For
example, such compositions may include compounds containing Ni, Co,
Mo, Cn, Tn, Mn, Fe, V, Cu and combinations thereof. These other
minor components also can be added to the resulting composition
(e.g., by impregnation or spraying particles of such compositions),
or they can be employed by their inclusion in the respective
starting ingredient formulations.
[0060] Thus, in general terms, Applicant has discovered a process
for removing a reduced sulfur gas from a process stream wherein
said process comprises contacting a process stream with a reduced
sulfur gas sorbing composition comprising, in the same particle, a
zinc titanate phase and a metal oxide-aluminate phase in order to
remove at least a portion of the reduced sulfur gas from the
process stream. The metal oxide-aluminate phase of Applicant's
sulfur sorbing compositions have the general formula MO, wherein M
is preferably a metal selected from the group consisting of
magnesium, zinc, nickel and calcium and 0 is oxygen. For example,
the metal oxide-aluminate phase may be zinc oxide-aluminate,
calcium oxide-aluminate, magnesium oxide-aluminate, and so on.
Indeed, this metal may be selected from a wide variety of divalent
and/or trivalent metals.
[0061] In some preferred embodiments of this invention, the reduced
sulfur gas composition, after sorption of a reduced sulfur gas, is
regenerated by contacting it with an oxygen-containing gas (such as
air) at an elevated temperature, in order to desorb the reduced
sulfur species and thereby regenerate the sulfur sorbing
composition for subsequent reduced sulfur gas sorption duty.
Preferably, the reduced sulfur gas sorbing composition has a weight
ratio of zinc titanate to metal oxide-aluminate phase ranging
between about 5:80 and about 95:20.
[0062] These sulfur sorbent compositions may be prepared from a
zinc titanate ingredient and at least one metal oxide-aluminate
having the general formula MAlO, where M is a metal selected from
the group consisting of magnesium, zinc, nickel and calcium, Al is
aluminum, O is oxygen, and where the zinc titanate ingredient and
metal oxide-aluminate ingredient are in weight ratios of from about
5:80 to about 95:20. Such compositions may further comprise an
inorganic binder in an amount such that it constitutes from about
2.0 to about 15.0 weight percent of the composition. Preferably
such inorganic binder(s) will be selected from the group consisting
of finely-sized bentonite, kaolinite, forsterite, vermiculite,
feldspar, Portland cement, oil shale, calcium sulfate and mixtures
thereof.
[0063] These compositions may be made by two general processes. The
first process generally involves: (a) pre-reacting a zinc
containing compound with a titanium-containing compound at
sufficient temperature to effect a transformation of zinc and
titanium-containing ingredients into a zinc titanate compound; (b)
combining the zinc titanate compound prepared in step (a) with a
metal oxide-containing compound and an aluminum-containing
compound; (c) forming the zinc titanate/metal oxide aluminate
composition created in step (b) into a desired shape such as
extrudates, microspheres, granules, pellets, or powder; and (d)
heating shaped particles created in step (c) to a temperature
greater than about 300.degree. C. for a time of greater than one
minute. In the alternative, the zinc titanate compound may be
obtained from commercial sources.
[0064] Applicant's second general process generally involves: (a)
combining a zinc-containing compound, an aluminum-containing
compound, a titanium-containing compound and a metal
oxide-containing compound to form a slurry, paste, etc.; (b)
forming the resulting zinc titanate/metal oxide-aluminate precursor
material into a desired shape; and (c) heating the resulting shaped
material to a temperature greater than about 300.degree. C. for a
time of greater than one minute.
[0065] In some of the more preferred embodiments of this invention,
the use of Applicant's compositions may be improved through such
measures as (1) constantly recirculating the composition in a fluid
bed reactor to effect sorption of the reduced sulfur gas; (2)
extracting a portion of partially sorbed particles and subjecting
them to a regeneration step; and (3) regeneration of the
composition by ceasing a gas flow in said process and then
subjecting the sorbent composition to a regeneration step.
EXAMPLES
[0066] The following provides examples of the invention and its
embodiments, which are not intended to limit the invention in any
way.
[0067] FIG. 1 shows the TGA sorption capacity of a prior art zinc
titanate/unreacted alumina sorbent before and after multiple cycles
in a bench-scale, high temperature, high pressure (HTHP) reactor
unit. As can be readily seen in FIG. 1, after such multi-cycle
testing, the performance of the "reacted" prior art sorbent is
degraded by about a factor of two.
[0068] FIG. 2 depicts an x-ray diffraction pattern generated by a
sample of a zinc titanate/unreacted alumina composition before
multi-cycle HTHP testing. This x-ray diffraction pattern indicates
that, prior to testing, the sample contained zinc titanate and
alumina. By way of comparison, FIG. 3 depicts the XRD pattern of
the FIG. 2 sample material after it was HTHP tested. FIG. 3 shows a
significant reduction in the original zinc titanate phase. This was
accompanied by a corresponding increase in a zinc aluminate phase
and a titanium dioxide phase.
[0069] Given these findings, the present invention also may be
thought of as a method of stabilizing unreacted alumina binders in
order to render them chemically inactive toward chemical reaction
with those zinc atoms that emanate from a zinc-containing compound,
such as a zinc titanate component of such sulfur sorbent
compositions, under the high temperature conditions existing in
those processes where these compositions are typically employed.
Thus, Applicant's invention also may be thought of as a
"stabilization agent" comprised of a metal oxide (which will
usually, but not necessarily, be a divalent metal such as
Mg.sup.2+, Ca.sup.2+, Zn.sup.2+, etc., which is chemically reacted
with alumina to form a metal oxide-aluminate phase material. As a
result of this metal oxide-aluminate phase-forming chemical
reaction, deactivation of the zinc titanate ingredient of the
reduced sulfur sorbent composition can be eliminated or, at the
very least, greatly decreased.
[0070] Applicant's XRD analysis of various samples that were
subjected to HTHP testing shows that the zinc titanate phase of an
overall zinc titanate/metal oxide-aluminate phase composition was
essentially unchanged with repeated cycles of pickup and release of
reduced sulfur gases (for example, compare the "before and after"
graphs of FIG. 4). Consequently, the activity of the overall
sorbent composition (comprised of zinc titanate, metal
oxide-aluminate, binder, etc.) does not degrade with multiple
sorption/regeneration cycles. This phenomenon also is clearly shown
by the TGA traces of FIG. 5. In fact, FIG. 5 shows that the reduced
sulfur capturing activity of this zinc titanate/metal
oxide-aluminate composition actually improved with repeated HTHP
cycling. Again, this is the very opposite behavior to that
displayed by the zinc unreacted/unreacted alumina composition that
generated the TGA trace shown in FIG. 1. As previously noted, the
increase in reduced sulfur sorbent activity after repeated cycles
of use that is exhibited by Applicant's reduced sulfur sorbent
composition is believed to result, at least in part, from the fact
that no degradation of the zinc titanate phase by the mechanism
described above has taken place.
[0071] Moreover, an increase in surface area in these materials was
observed. It also is noted that increased line broadening of the
XRD trace of the zinc titanate component strongly indicates that a
decreased crystallite size of the zinc titanate phase may be
brought about by successive sorption/regeneration cycles. The
result of this decrease in crystallite size of the zinc titanate
phase may well explain the increase in sorption activity. Another
possible factor in the improved reduced sulfur gas pickup ability
of the hereindescribed compositions may be reduced sulfur sorption
by the metal oxide component of the metal oxide-aluminate compounds
in these compositions. Regardless of the chemical mechanism(s) that
produce these phenomena, the fact remains that Applicant's zinc
titanate/metal oxide-aluminate phase compositions represent a very
significant advance in the art of capturing reduced sulfur
gases.
[0072] Description of Test Equipment
[0073] Two pieces of equipment were used to determine the ability
of a given sorbent to sorb H.sub.2S species, and then to release
the sorbed species as SO.sub.2. This sorption and release
constitutes one cycle of a test. The first piece of equipment was a
high temperature, high pressure (HTHP) bench reactor, which is, in
effect, a bench-scale fixed fluidized bed reactor unit that has the
capability to vary the temperature, pressure and atmosphere of the
reactor over a given series of test cycles. At the end of a given
cyclic test, the subject sulfur sorbent materials were removed from
the reactor and subjected to a TGA test to determine the amount of
deactivation experienced by the subject material as a result of the
cyclic testing.
[0074] The TGA test was performed on a Dupont 1090 thermal analysis
system at constant temperature and at atmospheric pressure. The TGA
technique, as described herein, measures a change in weight of a
sample as a sorbent gas is passed into the reaction chamber
containing the sample. A test gas, composed of H.sub.2S and
nitrogen, was used in these studies and the sample mass increased
as the subject sulfur sorbent material reacts with the H.sub.2S gas
to form zinc sulfides. Such tests were performed for about 30-50
minutes, at which point introduction of the H.sub.2S-containing gas
was discontinued.
[0075] The x-ray diffraction tests used by Applicant were performed
on both fresh and HTHP unit-reacted materials using a Scintag
XDS-2000 theta-theta XRD unit with copper K.alpha. radiation. Scans
were performed over the two-theta range of 5 to 72.degree..
[0076] Applicant's attrition testing was performed on a 3-hole
air-jet test unit. Such testing is fully compliant with the ASTM
standard D5757. The values reported in this patent disclosure are
the loss per hour during hour two of the test. The experimental
results from the first hour were discarded since this part of the
test produces a material that generally contains a great many fine
particles which were not produced as a result of attrition of the
sorbent material, but are merely present due to the original
particle size distribution of the particles being tested. For harsh
environments, such as those extant in circulating fluid bed
processes, i.e., integrated gasification combined cycle (IGCC), hot
gas desulfurization, FCC, etc., acceptable attrition resistance
values range from about 0.1 to about 12. For further reference, a
typical equilibrium catalyst (ECAT) from an FCC unit measures in
the range of 0.2-0.6 by the above attrition test method.
[0077] Formulation Methods
[0078] The formulation methods employed by Applicant generally
involved first pre-reacting a zinc oxide component with a titanium
oxide component and heat treating the resulting mixture such that
the desired zinc titanate phase was produced. A commercial source
of zinc titanate could have been utilized as well. The finished
zinc titanate phase was then incorporated into a binder material
and formed into a desired shape. If the zinc oxide, titanium oxide
and alumina were all mixed and reacted to temperatures sufficient
to convert the zinc oxide and titanium oxide to the desired zinc
titanate phase, a zinc oxide-aluminate phase would invariably form
along with the zinc titanate phase.
[0079] In the practice of Applicant's invention, it is also
possible to form a zinc titanate/metal oxide-aluminate phase
composition by a one-step process, without any deleterious effect
on the formation of the zinc titanate phase. Applicant prepared
zinc titanate/zinc oxide aluminate compounds via this "one step"
formulation process. The procedure is found in Example 5 of this
patent disclosure. Following calcination at 950.degree. C. for 2
hours, x-ray diffraction analysis was performed on the resulting
materials. This x-ray diffraction testing confirmed that the only
phases present were zinc titanate and zinc oxide-aluminate. The
success of such one step formulations may be somewhat more
dependent (relative to Applicant's other formulation methods) on
the proportions of the starting ingredients being as close to the
stoichiometric proportions as possible (i.e., it is preferred that
there be no excess alumina, zinc oxide or metal oxide). This same
result was found for a two-step process such as the one described
in Example 4. The aforementioned one-step process not only results
in an easier overall manufacturing process, but also results in
more attrition resistant and dense particles relative to those made
by Applicant's two-step process. Applicant's tests also involved
systematic comparisons between counterpart compositions prepared by
applicant's one-step process and two-step process.
Example 1
[0080] A zinc titanate compound containing no binder material was
produced by mixing 2637 grams of water, 548 grams of zinc oxide
(Zinc Corporation of America, Grade: KADOX.RTM. 911) and 359 grams
of titanium oxide (Dupont, Grade: TI-PURE.RTM. R-900) in a
container under strong shear conditions. The resulting slurry was
spray dried to form microspheroidal particles. The resulting
particles were then heat treated at 900.degree. C. for two hours.
X-ray diffraction analysis confirmed zinc titanate was the only
phase present in such particles.
Example 2
[0081] A zinc titanate compound containing 3 weight percent
bentonite binder was produced by mixing 2637 grams of water, 532
grams of zinc oxide (Zinc Corporation of America, Grade: KADOX.RTM.
911), 348 grams of titanium oxide (Dupont, Grade: TI-PURE.RTM.
R900) and 27.2 grams of Bentonite in a container under strong shear
conditions. The resulting slurry was spray dried to form
microspheroidal particles. The resulting particles were then heat
treated at 900.degree. C. for two hours. X-ray diffraction analysis
confirmed zinc titanate was formed in such particles.
Example 3
[0082] A zinc titanate-containing composition containing alumina as
the binder was made by first preparing a zinc titanate compound as
in Example 1. This zinc titanate was then reduced to an average
particle size of about 2.5 micrometers. In a separate container, a
12% solids slurry of hydratable alumina (CONDEA PLURAL SB.RTM.) was
prepared by slurrying 499 grams of alumina in 1895 grams of water
under high shear conditions. To this slurry, 25 grams of formic
acid were added and agitated unit alumina became gelled. The gelled
alumina was then combined with the zinc titanate and water such
that the amount of zinc titanate contained in the finished product
was 30 weight percent. The slurry was then spray dried at 13%
solids to form microspheroidal particles that were then heat
treated at 700.degree. C. for one hour.
Example 4
[0083] A zinc titanate/zinc oxide aluminate phase composition was
made by first preparing the zinc titanate compound as in Example 1.
The zinc titanate was then reduced in particle size to an average
particle size of about 2.5 micrometers. In a separate container, a
12 weight percent solids alumina sol was prepared by dispersing
under high shear conditions 544.3 grams of CONDEA DISPERAL P3.RTM.
alumina in 2379 grams of water containing 25.3 grams acetic acid.
The zinc titanate, alumina sol and zinc oxide (Zinc Corporation of
America, Grade: KADOX.RTM. 911) were combined in water such that
the zinc titanate concentration in the finished product was 30
weight percent and the zinc aluminate was prepared at an 0.5 Zn/Al
ratio. The resulting slurry was spray dried at 13% solids to form
microspheroidal particles that were then heat treated at
950.degree. C. for two hours.
Example 5
[0084] A zinc titanate-zinc aluminate composition was prepared in a
single-step process by combining zinc oxide (Zinc Corporation of
America, Grade: KADOX.RTM. 911), alumina sol (prepared as in
Example 4), and titanium oxide (Dupont, Grade: TI-PURE-900.RTM.)
such that a slurry was formed. The zinc oxide, alumina sol and
titanium oxide were formulated such that the zinc titanate
concentration in the finished product was 30 weight percent and the
zinc aluminate was prepared at an 0.5 Zn/Al ratio. The slurry was
then spray dried at 13% solids to form microspheroidal particles
that were then heat treated at 950.degree. C. for two hours. X-ray
diffraction confirmed that zinc titanate and zinc aluminate were
the only phases present.
Example 6
[0085] A zinc titanate-calcium aluminate composition was prepared
by mixing in a container water, calcium carbonate, zinc titanate
(prepared as in Example 1) and alumina sol (prepared as in Example
4). The zinc oxide, alumina sol and calcium carbonate were
formulated such that the zinc titanate concentration in the
finished product was 30 weight percent and the calcium aluminate
was prepared at an 0.5 Ca/Al ratio. The slurry was then spray dried
to form microspheroidal particles that were then heat treated at
700.degree. C. for two hours.
Example 7
[0086] A zinc titanate-magnesium aluminate composition was prepared
by mixing water, magnesium acetate solution (Fisher Chemical), zinc
titanate (prepared as in Example 1) and alumina sol (prepared as in
Example 4). The zinc titanate, alumina sol and magnesium acetate
were formulated such that the zinc titanate concentration in the
finished product was 30 weight percent and the magnesium aluminate
was prepared at an 0.5 Mg/Al ratio. The slurry was then spray dried
to form microspheroidal particles that were then heat treated at
700.degree. C. for two hours.
Example 8
[0087] A zinc titanate-zinc aluminate composition was prepared in a
single-step process by combining water, zinc oxide, alumina sol
(prepared as in Example 4), and titanium oxide such that a slurry
was formed. The zinc oxide (Zinc Corporation of America, Grade:
KADOX.RTM. 911), alumina sol and titanium oxide (Dupont, Grade:
TI-PURE.RTM. R-900) were formulated such that the zinc titanate
concentration in the finished product was 40 weight percent and the
zinc aluminate was prepared at an 0.5 Zn/Al ratio. The slurry was
then spray dried at 13% solids to form microspheroidal particles
that were then heat treated at 900.degree. C. for 1.5 hours. X-ray
diffraction confirmed that zinc titanate and zinc aluminate were
the only phases present.
Example 9
[0088] A zinc titanate-zinc aluminate composition was prepared in a
single-step process by combining water, zinc oxide (Zinc
Corporation of America, Grade: KADOX.RTM. 911), alumina sol
(prepared as in Example 4), and titanium oxide (Dupont, Grade:
TI-PURE.RTM. R-900) such that a slurry was formed. The zinc oxide,
alumina sol and titanium oxide were formulated such that the zinc
titanate concentration in the finished product was 50 weight
percent and the zinc aluminate was prepared at an 0.5 Zn/Al ratio.
The slurry was then spray dried at 13% solids to form
microspheroidal particles that were then heat treated at
900.degree. C. for 1.5 hours. X-ray diffraction confirmed that zinc
titanate and zinc aluminate were the only phases present.
Example 10
[0089] A zinc titanate-zinc aluminate composition was prepared in a
single-step process by combining water, zinc oxide (Zinc
Corporation of America, Grade: KADOX.RTM. 911), alumina sol
(prepared as in Example 4), and titanium oxide (Dupont, Grade:
TI-PURE.RTM. R-900) such that a slurry was formed. The zinc oxide,
alumina sol and titanium oxide were formulated such that the zinc
titanate concentration in the finished product was 60 weight
percent and the zinc aluminate was prepared at an 0.5 Zn/Al ratio.
The slurry was then spray dried at 13% solids to form
microspheroidal particles that were then heat treated at
900.degree. C. for 1.5 hours. X-ray diffraction confirmed that zinc
titanate and zinc aluminate were the only phases present.
Example 11
[0090] A zinc titanate/zinc aluminate phase composition was
prepared in a single-step process by combining water, zinc oxide
(Zinc Corporation of America, Grade: KADOX.RTM. 911), alumina sol
(prepared as in Example 4), and titanium oxide (Dupont, Grade:
TI-PURE.RTM. R-900) such that a slurry was formed. The zinc oxide,
alumina sol and titanium oxide were formulated such that the zinc
titanate concentration in the finished product was 60 weight
percent and the zinc aluminate was prepared at an 0.5 Zn/Al ratio.
The slurry was then spray dried at 13% solids to form
microspheroidal particles that were then heat treated at
900.degree. C. for 1.5 hours. X-ray diffraction confirmed that zinc
titanate and zinc aluminate were the only phases present.
Example 12
[0091] Comparative Tests
[0092] Examples of certain physical and chemical properties of
representative zinc titanate-containing particles described in the
prior art are given in Table III.
5 TABLE III Active Component Example 1 Example 2 Example 3 6036A
6036B 6072C Zinc Titanate Zinc Titanate Zinc Titanate
Support/Binder None Bentonite Alumina Attrition >25 >25 4.5
Resistance, % loss/hr. Apparent Bulk 0.86 0.86 0.64 Density, g/cc
Surface Area, 3.6 3.2 150 m.sup.2/g XRD Phase ZT ZT ZT +
Alumina
[0093] Examples of certain physical properties of zinc
titanate-containing compositions described in the present invention
are given in Table IV.
6 TABLE IV Active Component Example 4 Example 7 Example 6 6147D2
6036B 6072C Zinc Titanate Zinc Titanate Zinc Titanate
Support/Binder Zinc Aluminate Magnesium Calcium Aluminate Aluminate
Attrition 3.2 4.3 3.0 Resistance, % loss/hr. Apparent Bulk 0.76
0.63 0.66 Density, g/cc Surface Area, 26 163 124 m.sup.2/g XRD
Phase ZT + ZA ZT + MA ZT + CA
[0094] A comparison of properties of compositions made by the
one-step and two-step methods of manufacture of the zinc
titanate/metal oxide-aluminate materials of this patent disclosure
is summarized in Table V.
7 TABLE V Example 4 Example 5 6147D2 7003A Process Technique
Two-Step One-Step Attrition Resistance, 3.2 1.3 % loss/hr. Apparent
Bulk Density, 0.76 1.4 g/cc Surface Area, m.sup.2/g 26 11 XRD Phase
ZT + ZA ZT + ZA
[0095] A comparison of properties of compositions made by the
one-step method of manufacture with increasing amounts of zinc
titanate in the composition is summarized in Table VI.
8 TABLE VI Example No. ID 5 7003A 8 9 10 Zinc Titanate 30% 40% 50%
60% Attrition Resistance, 1.3 3.2 5.2 11 % loss/hr. Apparent Bulk
1.4 1.4 1.4 1.4 Density, g/cc Surface Area, m.sup.2/g 11 13 12 11
XRD Phase ZT + ZA ZT + ZA ZT + ZA ZT + ZA
[0096] While applicant's invention has been described with respect
to various theories, specific examples and a spirit which is
committed to the concept of use of zinc titanate phase material and
metal oxide-aluminate phase material in the same particle as a
reduced sulfur sorbent, and wherein the occurrence of a chemical
reaction between a metal oxide ingredient and an alumina ingredient
produce the metal oxide-aluminate phase material, the full scope of
this invention is limited only by the patent claims which
follow.
* * * * *