U.S. patent number RE29,771 [Application Number 05/834,528] was granted by the patent office on 1978-09-19 for flue gas desulfurization sorbent.
This patent grant is currently assigned to Exxon Research & Engineering Co.. Invention is credited to Neville L. Cull, Warren M. Smith.
United States Patent |
RE29,771 |
Cull , et al. |
September 19, 1978 |
Flue gas desulfurization sorbent
Abstract
Sulfur dioxide is removed from gas mixtures such as flue gas
containing the same by contacting the gas mixture with a solid
sorbent comprising a porous gamma-alumina base, about 2 to 20
percent by weight (based on alumina) of a coating of a refractory
oxide such as titanium dioxide, zirconium dioxide, or silica, and
an active material, such as copper oxide, which is capable of
selective removal of sulfur oxides from a gas mixture.
Inventors: |
Cull; Neville L. (Baker,
LA), Smith; Warren M. (Baton Rouge, LA) |
Assignee: |
Exxon Research & Engineering
Co. (Linden, NJ)
|
Family
ID: |
24154534 |
Appl.
No.: |
05/834,528 |
Filed: |
September 19, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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315590 |
Dec 15, 1972 |
|
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Reissue of: |
540225 |
Jan 10, 1975 |
04039478 |
Aug 2, 1977 |
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Current U.S.
Class: |
502/242; 252/189;
252/190; 423/244.04; 502/244; 502/246; 502/258; 502/263; 502/406;
502/407; 502/415; 95/137 |
Current CPC
Class: |
B01D
53/02 (20130101); C01B 17/60 (20130101) |
Current International
Class: |
B01D
53/02 (20060101); C01B 17/00 (20060101); C01B
17/60 (20060101); B01J 029/06 (); B01J
023/08 () |
Field of
Search: |
;252/455R,463,464 ;55/73
;423/244 |
References Cited
[Referenced By]
U.S. Patent Documents
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2749216 |
June 1956 |
Dinwiddie et al. |
2943066 |
June 1960 |
Arnold et al. |
3014020 |
December 1961 |
Batthis, Jr. |
3338666 |
August 1967 |
Sanchez et al. |
3501897 |
March 1970 |
Van Helden et al. |
3502595 |
March 1970 |
Johnson et al. |
3776854 |
December 1973 |
Dautzenberg et al. |
|
Foreign Patent Documents
Primary Examiner: Dees; Carl F.
Attorney, Agent or Firm: Luecke; Jerome E.
Parent Case Text
This is a division of application Ser. No. 315,590, filed Dec. 15,
1972 and now abandoned.
Claims
What is claimed is:
1. A process for preparing alumina base catalysts and sorbents
which comprises:
a. forming on particles of porous alumina a liquid surface coating
containing a hydrolyzable organic compound .Iadd.of a metal
selected from the group consisting of silicon and Group IIIB, IVB
and VB metals .Iaddend.which forms a refractory oxide on hydrolysis
.Iadd.and subsequent calcination.Iaddend.;
b. hydrolyzing and calcining said hydrolyzable organic compound to
said refractory oxide, thereby forming a coating of said oxide on
said alumina base;
c. impregnating said coated alumina base with a solution of a
decomposable compound of a desired active metal selected from the
group consisting of iron and copper; and
d. converting said compound to the oxide of the desired active
metal.
2. A process according to claim 1 in which said hydrolyzable
organic compound is an organometallic compound.
3. A process according to claim 2 in which said hydrolyzable
organic compound is a compound of a Group IV-B metal.
4. A process according to claim 3 in which said Group IV-B metal is
titanium.
5. A process according to claim 3 in which said Group IV-B is
zirconium.
6. A process according to claim 1 in which said hydrolyzable
organic compound is a silicon compound.
7. A process according to claim 1 in which said hydrolyzable
organic compound is an ester of an inorganic acid which has a
refractory oxide as its anhydride.
8. A process according to claim 1 in which said liquid surface
coating is formed by immersing said particles of porous alumina in
a liquid medium containing said hydrolyzable compound.
9. A process according to claim 1 in which the immersed particles
of porous alumina are heat treated at a temperature of at least
about 50.degree. C. but not exceeding the boiling point of said
liquid medium.
10. A process according to claim 1 in which said hydrolyzable
organic compound is hydrolyzed in a moist gaseous atmosphere.
11. A process according to claim 1 in which said liquid surface
coating is formed by vapor deposition of said hydrolyzable organic
compound on the surfaces of said porous alumina particles.
12. A process according to claim 1 in which said active metal is
copper.
13. A porous non-acidic solid sorbent for flue gas desulfurization
comprising:
a. a porous alumina base;
b. a coating of .Iadd.up to about 5% by weight, based on said
alumina, of silica, said silica being formed in situ by hydrolysis
and subsequent calcination of a hydrolyzable silicon compound or a
coating of .Iaddend.about 2% to about 20% by weight, based on said
alumina, of a refractory oxide, said oxide being formed in situ by
hydrolysis .Iadd.and subsequent calcination .Iaddend.of a
hydrolyzable organic compound .Iadd.of a metal selected from the
group consisting of Group IIIB, IVB and VB metals.Iaddend., the
coated alumina base being non-acidic; and
c. a material active for the selective removal of sulfur oxides
from gas mixtures, said active material being a metal or metal
oxide.
14. A composition according to claim 13 in which the refractory
oxide coating is a refractory metal oxide.
15. A composition according to claim 14 in which said refractory
metal oxide is an oxide of a Group IV-B metal.
16. A composition according to claim 15 in which said Group IV-B
metal is titanium.
17. A composition according to claim 15 in which said Group IV-B
metal is zirconium.
18. A composition according to claim 13 in which said refractory
oxide is silica, the amount of said silica not exceeding about 5%
by weight, based on alumina.
19. A composition according to claim 13 in which the active
material is copper oxide.
Description
BACKGROUND OF THE INVENTION
This invention relates to solid flue gas desulfurization sorbents
and their preparation, and to methods of removing sulfur oxides
from gas mixtures using the same.
Sulfur dioxide is an atmospheric pollutant which is present in
small amounts in various waste gas mixtures, such as flue gas and
certain smelter gases. Flue gases may also contain small amounts
(usually only trace quantities) of sulfur trioxide. Sulfur dioxide
and sulfur trioxide will be referred to collectively herein as
"sulfur oxides." Processes for the selective removal of sulfur
oxides from flue gas and other waste gas streams are known. Most of
these processes are cyclic regenerative processes employing either
a solid sorbent or an aqueous solution which selectively removes
sulfur oxides.
Examples of cyclic regenerative processes using a dry solid sorbent
or acceptor are described in British Pat. Nos. 1,089,716,
1,154,009, and 1,160,662, and in U.S. Pat. No. 3,501,897. British
Patent Nos. 1,089,716 and 1,160,662 describe the use of copper
oxide on gamma-alumina as the sorbent; British Pat. No. 1,154,009
discloses the use of potassium oxide and vandium pentoxide on
porous alumina; and U.S. Pat. No. 3,501,897 discloses both types of
sorbents. In the processes of all of these patents, flue gas
containing SO.sub.2 and oxygen is contacted with the solid sorbent
or acceptor until breakthrough of SO.sub.2 into the effluent gas
occurs. The sorbent is then generated with a reducing gas. Removal
of SO.sub.2 is accomplished in these processes by reaction of
SO.sub.2 and oxygen with the active component of the sorbent; thus,
copper oxide is partially converted to copper sulfate. The
sulfation of the active materials in nearly all cases is incomplete
at the time that breakthrough occurs. Breakthrough may be defined
as occurring when a stated percentage of the SO.sub.2 in the
incoming gas, e.g., 10% over a whole cycle, passes into the
effluent gas. Other contact masses, such as copper oxide on silica
have also been tried but found to be less satisfactory than copper
oxide on alumina.
Although gamma-alumina is a good carrier material from the
standpoint of sorbent activity in flue gas desulfurization
sorbents, it has been found to be subject to attrition, even in
fixed beds, after numerous flue gas desulfurization cycles, as
reported for example in British Pat. No. 1,160,662. To improve the
hardness and attrition resistance of the sorbent, British Pat. No.
1,160,662 suggests the use of about 1 to 20% by weight, calculated
on the solid carrier material, of colloidal silica as a reinforcing
material.
The preparation of coated or reinforced high surface area catalysts
for other processes is well known. U.S. Pat. Nos. 3,502,595 and
3,615,166 are cited as two examples of such catalysts and their
methods of preparation. U.S. Pat. No. 3,502,595 describes a process
of preparing cracking catalyst having an acidic support such as
silica-alumina or titania-alumina by reacting gamma alumina which
is at least slightly hydrated with an alkyl ester, such as ethyl
orthosilicate, in an orgaic solvent medium, and separating the
solid alumina-inorganic oxide particles from the solvent and the
alcohol produced in the reaction, U.S. Pat. No. 3,615,166 describes
coated catalysts comprising a high surface area refractory core
material (e.g., alumina) and a coating oxide (e.g., zirconia or
thoria), which are prepared by dispersing colloidal size particles
of the core material in an aqueous solution of a zirconium or
thorium salt, adding an alkaline reagent to precipitate zirconia or
thoria, drying and calcining. The products of both U.S. Pat. Nos.
3,502,595 and 3,615,166 can be impregnated with other catalytically
active metals (e.g., platinum) by known techniques. Reactions of
metal alkoxides (which can also be considered as alkyl esters of
inorganic acids) are also discusssed in D. C. Bradley, "Metal
Alkoxides," ACS Monograph No. 23, "Metal Organic Compounds" pp.
10-37 (1959).
SUMMARY OF THE INVENTION
Porous solid sorbents of improved strength and strength maintenance
comprising a gamma alumina carrier coated with a refractory oxide
and impregnated with an active metal or metal oxide are prepared
according to this invention by forming on particles of a porous
gamma alumina carrier a liquid surface coating containing a
hydrolyzable organic compound which on hydrolysis and calcination
yields the desired oxide coating material, hydrolyzing and
calcining the organo metallic compound to the corresponding oxide,
impregnating the coated carrier with a solution of a salt of a
desired active metal, and drying and calcining the impregnated
carrier in order to convert the active metal salt to the
corresponding active metal oxide. The coating is a refractory
oxide, preferably a refractory metal oxide such as titanium dioxide
or zirconium dioxide. Silica is an alternative coating material.
This coating is deposited in situ on the alumina carrier by
hydrolysis of a decomposable compound such as tetrabutyl zirconate,
tetraisopropyl titanate, or ethyl silicate.
Sulfur dioxide is removed from gases such as flue gas according to
this invention by contacting the gas with a sorbent as above
described.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The alumina carrier or base in the contact materials of this
invention is porous gamma alumina, having a surface area (BET) of
at least about 80 square meters per gram and preferably at least
about 100 square meters per gram. The alumina carrier is in the
form of preformed particles of any desired shape, such as spheres,
extrudates, rings or saddles. The carrier particles may be of any
desired size. Various commercial catalyst and sorbent grade
aluminas which fulfill these requirements are available.
The alumina base is coated according to this invention with about 2
to about 20% by weight, based on the weight of alumina, of a second
refractory oxide. Preferably, this refractory oxide is a metal
oxide. The choice of metal oxide is based on the properties of the
metal oxide and the ease of preparation of the metal alkoxide from
which the metal oxide coating is laid down. Thus, oxides of
titanium and zirconium (Group IV-B metals) are preferred because of
their properties and the availability of the corresponding
alkoxides. The acidic refractory oxides, i.e., refractory oxides of
nonmetals, are ordinarily less desirable because of lower flue gas
desulfurization activity. Thus, silica can be used as a coating
material, but the maximum loading should not be more than about 5%
by weight based on alumina in order not to impair sulfur dioxide
removal activity significantly. Boria has been found unacceptable
as a coating material because flue gas desulfurization activity is
greatly impaired. The Group IV-B metal oxides, and particularly
titania, are especially preferred. Other preferred refractory metal
oxides are those of Groups III-B (e.g. rare earths and actinide
series metals) and V-B (e.g. vanadium). The Group numbers refer to
the Periodic Table according to H. G. Deming, "Periodic Chart of
the Elements" as reproduced, for example, in Lange's Handbook of
Chemistry. Eighth Edition, pp. 56 and 57 (1952).
In forming the refractory oxide coating, the alumina particles are
first coated under anhydrous conditions with a hydrolyzable organic
compound which yields the desired refractory oxide coating material
on hydrolysis and calcination. This may be done by immersing the
particles in a liquid medium containing the compound, or by vapor
deposition. The liquid medium can be either the hydrolyzable
compound in bulk or a solution of the compound in a suitable
solvent.
Preferred hydrolyzable compounds are esters of an alcohol or phenol
and an inorganic acid corresponding to the desired oxide coating
material. The alcohol or phenol corresponding to the ester is an
alcohol or phenol containing up to about 8 carbon atoms. Suitable
lower alkyl esters include tetraisobutyl zirconate, tetraisopropyl
titanate, tetra-n-butyl titanate, tetra-sec.-butyl titanate,
tetra-tert.-butyl titanate, tetrakis(2-ethyl hexyl) titanate,
tetrabuyl zirconate, tetraethyl orthosilicate, etc. Cycloalkyl
esters include tetracyclohexyl titanate. In general, alkyl esters
in which the alkyl groups contain from 2 to 4 carbon atoms are
preferred because of the greater ease of hydrolysis. The ease of
hydrolysis decreases with increasing carbon number. When the
desired oxide coating is a metal oxide, the corresponding
hydrolyzable organic compound is an organometallic compound.
The esters may be represented by the general formula:
where M is an element forming a refractory oxide, R is a lower
alkyl, cycloalkyl, aryl, or aralkyl radical containing from 1 to
about 8 carbon atoms, and n is the valence of M. M is preferably a
transition metal of Group IIIB, IV-B or V-B and most preferably of
Group IV-B, e.g., titanium or zirconium. R is preferably a lower
alkyl radical containing from 2 to 4 carbon atoms. Alternatively,
the alkyl esters herein can be named as metal alkoxides or as
alkoxy derivatives of silane.
Suitable solvents for the hydrolyzable organic compound include
hydrocarbons such as hexane and heptane, and alcohols such as
isopropyl alcohol and butanol. In the case of alcohol solvents, the
solvent alcohol is usually the same as the alcohol moiety of the
ester.
The amount of oxide coating material deposited is controlled by
variations in the concentration of the organic compound, the length
of time of immersion, the temperature of immersion, or any
combination of these. Variations in the solution concentration
provide particularly good control over the coating weight attained.
The temperature of immersion may vary from room temperature or
lower up to the boiling point of the solution; but is preferably
from about 50.degree. C. up to the boiling point. Excellent results
have been obtained using immersion temperatures of about 50.degree.
to about 60.degree. C. Immersion times ordinarily run from a few
minutes up to about one hour; good results have been obtained using
immersion times of about 1/2 hour. The solution concentration may
be varied anywhere from about 20 to 100% by weight of hydrolyzable
organic compound, based on the total weight of solution; the value
of 100%, of course, represents the use of a decomposable organic
compound in bulk. The carrier particles may be separated from the
liquid medium by suitable means, such as decantation, when the
desired immersion time has been reached.
The alternative method of applying the liquid coating containing
the hydrolyzable organic compound is by vapor deposition. The
organic compound is vaporized and is allowed to condense on the
alumina particle surfaces.
Next, the wet carrier material containing the liquid coating of
hydrolyzable organic compound is treated with water vapor in order
to hydrolyze the hydrolyzable organic compound. This may be
accomplished by exposing the carrier particles to a moist gaseous
atmosphere such as air of normal moisture content for a suitable
length of time. For example, exposure of the soaked carrier
particles to moisture-containing air which preferably has a
relative humidity of about 50 to about 100% for periods of about 16
hours (i.e., overnight) and at room temperature have resulted in
the desired hydrolysis. Neither relative humidity, temperature nor
time are critical. However, use of air having a relative humidity
below and 50% requires longer hydrolysis times. Moist nitrogen can
also be used. Accelerated hydrolysis can be obtained if desired
using steam or using air of high relative humidity at elevated
temperatures; however, these expedients are not necessary. After
hydrolysis, the composite carrier of alumina with the coating
thereon may be dried and then calcined to give the desired oxide
coating. It is believed that a high molecular weight inorganic
polymer coating is formed during air hydrolysis and
calcination.
The above coating procedure can be repeated where a single
application of hydrolyzable organic compound followed by hydrolysis
and calcination does not give a coating of sufficient
thickness.
The amount of coating material deposited on the alumina surfaces
can be approximated by the weight gain in the carrier particles by
treatment with the hydrolyzable organic metal compound, followed by
hydrolysis, drying and calcination as above described. Coating
weights in this application were obtained by this method unless
otherwise indicated. In some cases, the amount of coating material
has been determined both by this weight gain method and by
conventional quantitative analysis techniques; the latter usually
indicate a greater percentage of coating material weight. Thus, the
coating material weight as reported herein may be somewhat lower
than actual values.
After the oxide coating has been applied to the alumina base, the
resulting coated carrier material can be impregnated with a
decomposable compound of a desired active metal according to
conventional techniques. Thus, when a sorbent having copper oxide
as its active material is desired, the coated alumina may be
impregnated with a suitable copper salt, such as copper nitrate, in
aqueous solution, and the impregnated sorbent may then be dried and
calcined in order to convert the copper nitrate to copper oxide.
Other active metal oxides may be similarly applied by appropriate
choice of metal salts. Where the active material is desired in the
form of a free metal rather than the metal oxide, the metal oxide
may be reduced to the free metal with a suitable reducing agent
such as hydrogen according to means known in the art. The choice of
active material of course depends on the use to which the contact
mass is to be put. Copper oxide is the preferred active material in
the case of flue gas desulfurization sorbents, although flue gas
desulfurization sorbents containing a mixture of potassium oxide
and vanadium pentoxide as the active material are known as earlier
indicated.
Catalysts and sorbents for other reactions can also be prepared
according to this invention, using active materials which are known
in the art. Thus, for example, platinum catalysts for oxidation and
hydrogenation reactions can be prepared by applying platinum to a
coated carrier which has been prepared as described above. A
catalyst of either iron oxide or copper oxide titania-coated
alumina can be used for the selective removal of nitrogen oxides
from gases such as flue gas. Other active materials, depending on
the intended use of the finished catalyst or sorbent, include the
oxides of chromium, manganese, cobalt and nickel, as well as other
active catalytic and sorbent materials which are known in the
art.
The contact masses, i.e., catalysts and sorbents, produced
according to this invention are particularly useful in processes,
such as the removal of sulfur dioxide from flue gases or other
gases containing the same, where attrition of conventional
catalysts or sorbents comprising an active material on alumina is a
problem. The catalysts and sorbents prepared according to this
invention exhibit improved strength and strength maintenance as
compared to catalysts and sorbents having the same active material
on alumina but with the coating oxide omitted. Improved strength,
i.e. crushing strength, and strength maintenance, i.e. strength of
a particle of catalyst or sorbent after the catalyst or sorbent has
been in service for a measured length of time, can be correlated
with improved attrition resistance in service. Sorbent activity of
the contact materials prepared according to this invention is in
most cases comparable to the activity of the corresponding material
in which the coating oxide is omitted. In some cases, the activity
of materials produced according to the present invention are
slightly lower than the activities of the corresponding materials
in which the oxide coating is omitted; however, in most cases no
significant loss of activity is encountered. Activity in the case
of flue gas desulfurization sorbents is indicated by the percentage
of active material which is sulfated in a normal operating cycle at
the time that maximum desirable sulfur dioxide breakthrough into
the effluent occurs.
Flue gas desulfurization using the sorbents of the present
invention can be carried out under desulfurizing conditions known
in the art. Thus, for example, a conventional
sulfation-regeneration cycle may be used. During the sulfation
period, flue gas or other gas stream containing sulfur dioxide and
oxygen is contacted with the contact mass at a suitable inlet
temperature, e.g., approximately 600.degree.-900.degree. F. in the
case of copper oxide sorbents, and slightly higher, e.g., about
700.degree.-1000.degree. F. in the case of K.sub.2 O--V.sub.2
O.sub.5 sorbents. When maximum desirable breakthrough of sulfur
dioxide into the effluent occurs, e.g., when the amount of sulfur
dioxide in the effluent, as measured over a whole operating cycle,
reaches 10% of the amount of SO.sub.2 in the incoming gas, the
sulfation (or sorption) period is stopped and the sorbent is
regenerated. The preferred regeneration gas is a reducing gas, such
as hydrogen, carbon monoxide, mixtures of these, or a hydrocarbon
such as methane, ethane, propane, butane or heavier hydrocarbons
such as octane, decane, etc. The reducing gas or gas mixture may be
mixed with steam if desired. Hydrogen-steam mixtures are especially
preferred. The regeneration gas inlet temperature is preferably
about the same as the flue gas inlet temperature. This minimizes
sorbent attrition. The sorbent is preferably in a fixed bed, and
both the gas to be treated for removal of SO.sub.2 and the
regeneration gas are passed through the fixed bed at a suitable
space velocity. In the case of SO.sub.2 -containing gas, suitable
space velocities are generally in the range of about 1000 to about
10,000 v/v/hr. The sorbent bed may be purged with a suitable inert
gas such as steam or nitrogen after either the sorption period, the
regeneration period, or both, as desired.
While the removal of sulfur oxides has been particularly described
with respect to removal of sulfur dioxide, it will be evident that
any sulfur trioxide which is contained in the incoming gas mixture
will be removed under conditions which achieve removal of sulfur
dioxide.
The invention will now be described in further detail with
reference to the examples which follow.
EXAMPLE 1
This example describes the coating of calcined alumina particles
with oxides of titanium, zirconium and silicon, and strength tests
on the coated particules. A few samples in this example were also
impregnated with copper oxide.
The alumina base in this example consisted of 1/2-inch alumina
saddles, having the shape shown in U.S. Pat. No. 2,639,909, which
had been previously calcined at 1000.degree. F. for 3 hours, and
which had a surface area (BET) of 303 square meters per gram and a
pore volume (BET) of 0.59 cubic centimeters per gram. This material
will be designated A-1.
A portion of the above saddles was impregnated by immersion in an
aqueous solution of copper nitrate [27% by weight of
Cu(NO.sub.3).sub.2 .multidot.3H.sub.2 O] for 10 minutes. The
saddles were removed from the impregnated solution, blotted to
remove excess liquid, air dried for 20 hours, and then calcined for
3 hours at 800.degree. F. This material is designated A-2.
Three batches of the above-described alumina saddles, each batch
weighing about 25 grams, were coated with varying quantities of
titanium dioxide according to the following procedure: A batch of
alumina saddles was weighed and charged to a reactor. Liquid
tetraisopropyl titanate, either in bulk or in a 50% (by weight)
solution in hexane, was added to the reactor in sufficient quantity
to cover completely the alumina saddles. The concentrations of the
solution were varied in order to give different coating weights of
TiO.sub.2. The reactor and its contents were heated to about
50.degree. to 60.degree. C. and held at this temperature for about
30 minutes. The reactor and its contents were then cooled to room
temperature, and the solution was decanted off. The saddles were
allowed to hydrolyze in air for 16 hours at room temperature, were
then dried in a forced air oven at 117.degree. C. for 6 hours, and
were then calcined overnight at 590.degree. C. (1100.degree. F.).
This treatment converted the tetraisopropyl titanate condensation
product to titanium dioxide. The saddles were again weighed, and
the weight gain of the treated saddles, based on the weight of the
untreated alumina, was computed. These sorbents are designated A-3,
A-4 and A-5. A portion of sorbent A-5 was impregnated with a 27%
(by weight) aqueous solution of copper nitrate by immersion for 10
minutes. The saddles were removed, blotted dry, air dried for 20
hours, and then calcined for 3 hours at 800.degree. F. These
saddles are designated A-6.
Two batches of saddles were coated with zirconium oxide according
to the above procedure except that a 50% (wt.) solution of
tetraisobutyl zirconate in butanol was used in place of
tetraisobutyl titanate-solution. These batches are designated A-7
and A-8. A portion of the saddles in batch A-8, after coating with
zirconium oxide, were immersed in a 27and calcined (wt.) aqueous
copper nitrate solution for 10 minutes, blotted dry, air dried for
20 hours andcalcined for 3 hours at 800.degree. F. The
copper-impregnated saddles are designated A-9.
Two batches, designated A-10 and A-11, were coated with silica in
the same manner as above. In coating A-10, 100% tetraethyl silicate
was used whereas in A-11 a 50% (wt.) solution of tetraethyl
silicate in hexane was used.
A portion of the saddles A-11 were impregnated with copper by
immersion in a 27% (by weight) aqueous solution of copper nitrate
for 10 minutes. The saddles were then removed, blotted to remove
excess solution, air dried for 20 hours, and calcined for 3 hours
at 800.degree. F. The copper impregnated sorbent was designated
A-12.
Oxide coating weights, coating solution concentrations, and amounts
of copper where present are shown in Table I below. In Table I,
oxide coating weights are based on the weight of uncoated and
unimpregnated alumina. The amount of copper present is quoted as
Cu, based on finished sorbent, although the copper is actually in
the form of copper oxide.
TABLE I ______________________________________ Coating Coating
Material Wt. % Sample Coating Material Conc. Cu
______________________________________ A-1 None -- -- -- A-2 None
-- -- 5.2 A-3 14% TiO.sub.2 Ti(OPr).sub.4 100% -- A-4 15% TiO.sub.2
Ti(OPr).sub.4 100% -- A-5 9% TiO.sub.2 Ti(OPr).sub.4 50%(hexane) --
A-6 9% TiO.sub.2 Ti(OPr).sub.4 50%(hexane) 4.6 A-7 9% ZrO.sub.2
Zr(OBu).sub.4 50% (butanol) -- A-8 8.8% ZrO.sub.2 Zr(OBu).sub.4 50%
(butanol) -- A-9 8.8% ZrO.sub.2 Zr(OBu).sub.4 50% (butanol) 4.6
A-10 11% SiO.sub.2 Si(OEt).sub.4 100% -- A-11 9.2% SiO.sub.2
Si(OEt).sub.4 50% (hexane) -- A-12 9.2% SiO.sub.2 Si(OEt).sub.4 50%
(hexane) 5.0 ______________________________________
In Table I above, Et = ethyl, Pr = isopropyl, and Bu = butyl.
EXAMPLE 2
This example describes the crushing strength and strength
maintenance testing of samples of saddles taken from batches A-1,
A-3 and A-7, prepared as described in Example 1. All samples,
except for the "as received" sample from batch A-1, were calcined
for 16 hours at 1100.degree. F., The as received sample from batch
A-1 was not calcined. In addition, one sample from each batch was
acid treated by immersion overnight in 15% HCl. Each sample
included 25 saddles.
The crushing strength of each saddle was determined as follow:
The crushing strength of a saddle is determined by measuring the
force, in pounds, required to crush a single saddle between two
polished flat steel plates. The strength tester consisted of a
stationary bottom plate of circular cross section and a movable top
plate of the same diameter as the bottom plate. Both plates had
polished flat steel surfaces. The top plate was connected to a
pressure gauge having an indicator which retained its reading from
the moment of crush until reset to zero. Readings were in psig,
which were converted to force in pounds from a chart which is
previously obtained by calibration of the tester. Saddle strength
is expressed as an average of the strengths of all the saddles
tested plus a high and a low value. The saddle is placed in a
standing upright (inverted U) position for testing. The moisture
content of these saddles was standardized by allowing the saddles
to remain overnight in the ambient air atmosphere followed by
calcination for 3 hours at 650.degree. F. Calcined saddles were
transferred to bottles, the bottle tops sealed, and the saddles
cooled down to room temperature for testing. The average, high and
low crushing strengths, in pounds, of the saddles from each sample
are recorded in Table II below. The strength retention of acid
treated samples in percent, measured by dividing the average
strength of acid treated saddles by the average strength of saddles
from the same batch which were not acid treated, is also given in
Table II.
TABLE II ______________________________________ % Strength, lbs.
Strength Batch Coating Treatment Avg. High Low Retained
______________________________________ A-1 None As received 7 14 4
C 10 13 6 C + AT 5 9 1 50 A-3 14% TiO.sub.2 C 19 29 9 C + AT 10 17
7 53 A-7 9% ZrO.sub.2 C 18 26 10 C + AT 19 29 9 55
______________________________________ *C = calcined C + AT =
calcined and acid treated
Calcined saddles, which were coated with either titania or
zirconia, had appreciably higher strengths than the calcined
uncoated alumina saddles, as Table II shows. Acid treatment caused
appreciable weakening of the titania- and zirconia-coated alumina
saddles, as well as of the uncoated alumina saddles. Percentage
strength losses as the result of acid treating were not appreciably
different. However, the acid titania- and zirconia-coated saddles
were appreciably stronger than the uncoated alumina saddles which
were not acid treated.
EXAMPLE 3
This example describes strength and strength maintenance of five
batches of coated saddles and one control bath of uncoated alumina
saddles, prepared as described in Example 1, under flue gas
desulfurization conditions.
Simulated cyclic flue gas desulfurization runs were carried out as
follows: A batch of saddles to be tested was charged to a tubular
reactor having an inside diameter of 3 inches and a length of 26
inches. Simulated flue gas, containing 2700 ppm of sulfur dioxide,
2.5% by volume of oxygen, balance nitrogen, was passed through the
reactor at an inlet temperature of 650.degree. F. and a space
velocity of 2000 v/v/hr. for 20 minutes. Then a regeneration gas
consisting of 40% by volume of hydrogen and 60% by volume of steam
was passed through the reactor at an inlet temperature of
650.degree. F. and a space velocity of 600 v/v/hr. for a period of
3 minutes. Repeated cycles were carried out in this manner for a
period of three weeks. The effluent sulfur dioxide contents in the
simulated flue gases were not measured, and it is assumed that
little or no sulfur dioxide was removed, since no copper was
present in the saddles used in this test. The crushing strength of
25 saddles from each batch were measured before and after the test
in the manner described in Example 2. In all batches except one,
the saddles were noted to be stronger at the end of the test than
at the beginning. The strength of the saddles after each test was
compared with the strength of the uncoated alumina saddles (batch
A-1) before the test, and the result is reported as percentage
gain. Results are given in Table III below.
TABLE III ______________________________________ Avg. Particle %
Gain relative Strength, lb. to uncoated Batch Coating Before After
base ______________________________________ A-1 None 13 14 + 8 A-4
15% TiO.sub.2 15 18 +38 A-5 9% TiO.sub.2 17 16 +23 A-8 8.8%
ZrO.sub.2 17 19 +46 A-10 11% SiO.sub.2 13 17 +31 A-11 9.2%
SiO.sub.2 18 20 +54 ______________________________________
It will be noted from Table III above that the initial strengths of
all coated samples were greater than the initial strength of the
uncoated alumina saddles in batch A-1. Also, all batches of saddles
except batch A-5 were found to be stronger after the tests than
before. Differences of .+-. 1 pound are probably not significant;
the reproducibility of test results is probably about .+-.10%.
EXAMPLE 4
This example gives strength and strength maintenance data of four
supported copper oxide sorbents prepared as described in Example 1,
including batches (A-6, A-9 and A-12) of copper oxide on coated
alumina and one batch (A-2) of copper oxide on uncoated alumina
under flue gas desulfurization conditions.
A series of flue gas desulfurization runs (one for each batch) was
carried out using the same reactor and the same desulfurization and
regeneration conditions as those described in Example 3. The flue
gas and regeneration gas compositions were also the same as in
Example 3.
A total of 1151 cycles was carried out in this manner in each run.
The particle strengths (average, high and low) before and after
each run were determined by taking 25 saddles from each batch
before the run and 25 saddles from each batch after the run, and
carrying out the strength test described in Example 2. From these
data, strength retention was computed as the average particle
strength from a given batch after the test, divided by the average
particle strength before the same test, multiplied by 100. Results
are given in Table IV below.
TABLE IV ______________________________________ Wt. Strength
Strength % % Before, lb. After, lb. Str. Batch Coating Cu Avg. H L
Avg. H L Ret. ______________________________________ A-2 None 5.2
15 24 6 10 20 5 67 A-6 9% TiO.sub.2 4.6 16 31 7 16 32 7 100 A-9
8.8% ZrO.sub.2 4.6 17 26 5 15 40 4 88 A-12 9% SiO.sub.2 5 21 33 11
18 35 7 86 ______________________________________
It will be noted that the saddles having coated alumina carriers
(batches A-6, A-9 and A-12) were only slightly stronger at the
start of the test than the saddles (batch A-2) having an uncoated
alumina carrier, but exhibited considerably better strength
retention. The saddles of copper oxide on titania-coated alumina
exhibited the best retention of all, followed by the saddles of
copper oxide on zirconia-coated alumina. Sulfur dioxide removal
from the simulated flue gas was not measured in this test. However,
sulfur dioxide was removed from flue gas and the sorbent was
regenerated, in each cycle.
It will be noted that the strength retention results in this
example were not quite as good as those in Example 3. Thus, while
the sorbents in Example 3, which contained no copper, actually
gained strength during the simulated flue gas desulfurization test,
the sorbents in this example, with the exception of sorbent A-6,
show some strength loss. This can probably be accounted for by
greater cycle variation in temperature in this example, due to the
exothermic nature of both the desulfurization and the regeneration
reactions.
EXAMPLE 5
This example describes the preparation and testing, under flue gas
desulfurization conditions, of a sorbent of copper oxide on
silica-coated alumina, and a control sorbent of copper oxide on
alumina.
The alumina carier in this example consisted of 1/8-inch
cylindrical extrudates, manufactured by the Harshaw Chemical
Company of Cleveland, Ohio, having a surface area of 214 m.sup.2
/g. and a pore volume of 0.74 cc/g. These extrudates were calcined
for 16 hours at 1000.degree. F. prior to further treatment
according to this example.
Sixty grams of the alumina extrudates described above were
impregnated with 18.3 grams of copper nitrate trihydrate dissolved
in 41.0 grams of water (30.9% by weight copper nitrate trihydrate
concentration). The extrudates were air dried overnight and
calcined for 3 hours at 800.degree. F. The resulting sorbent
contained 8% Cu by weight based on the alumina. This sorbent is
designated B-1.
Thirty grams of the above sorbent, B-1, were immersed in a solution
of tetraethyl silicate (25% by weight) in hexane for 30 minutes at
50.degree.-60.degree. C. The excess solution was decanted off and
the extrudes were allowed to hydrolyze in air for 48 hours. The
extrudates were then calcined for 3 hours at 900.degree. F. This
sorbent contained about 3% by weight of silica, as determined by
weight gain, and is designated B-2.
Each of the batches of extrudates was evaluated for strength both
before and after a cyclic flue gas desulfurization run which was
carried out in the manner described in Example 3, using simulated
flue gas and regeneration gas having the same respective
compositions as those described in Example 3. Results are shown in
Table V below:
TABLE V ______________________________________ Average Particle %
Gain Wt. % Strength Based on Batch Coating Cu Before After Control
______________________________________ B-1 None 8 18 20 +11 B-2 3%
SiO.sub.2 8 21 26 +44 ______________________________________
The strength gain in Table V above is based on the average particle
strength of the control particles (batch B-1) before the flue gas
desulfurization run. Both the control sorbent and the test sorbent
were stronger after the flue gas desulfurization test than
before.
EXAMPLE 6
This example shows the preparation and activity testing of copper
oxide on silica-coated alumina sorbents. A control sorbent of
copper oxide on uncoated alumina was also prepared and tested.
The alumina base used in this example was a commercially available
alumina (made by Harshaw Chemical Company, Cleveland, Ohio) in the
form of 1/8-inch extrudates, which had been previously calcined for
16 hours at 800.degree. F., having a surface area of 232 m.sup.2
/g. and a pore volume of 0.79 cc g.
One batch of the above alumina extrudates was impregnatd with
aqueous 25.4% by weight copper nitrate [Cu(NO.sub.3).sub.2
.multidot.3H.sub.2 O] solution, dried and calcined. This gave a
sorbent containing 6% by weight of copper, based on the weight of
alumina. This sorbent was designated C-1.
A second batch of alumina extrudates was immersed in a quantity of
17.4% (by volume) solution of tetraethyl silicate in hexane
sufficient to fill the pore volume of the alumina, and was allowed
to stand overnight in a stoppered flask. The extrudates were then
hydrolyzed in air for 24 hours and calcined for 16 hours at
1100.degree. F. The resulting silica-coated alumina extrudates were
impregnated with 25.4% copper nitrate solution, dried and calcined
for 3 hours at 800.degree. F. The percentage silica (by weight
gain) was 2.6%, based on untreated alumina, and the percentage of
copper by analyses was 6.1%, based on total sorbent. The sorbent
was designated C-2.
A second batch of copper oxide on silica-coated alumina extrudates,
designated as C-3, was prepared by immersing the alumina extrudates
in an excess of 17.4% by volume) of tetraethyl silicate solution in
hexane, allowing it to stand for one hour, decanting off the
excess, then allowing the extrudates to stand overnight in a
stoppered flask, followed by air hydrolysis, calcination, copper
impregnation, drying, and calcination as in the case of batch C-2.
This batch of saddles contained 4.1% by weight of silica (by weight
gain based on untreated alumina and 6.4% by weight of copper, after
impregnation based on total sorbent.
A fourth batch of alumina extrudates was first coated with silica
by treating the alumina with vapor phase tetraethyl silicate. This
was accomplished by placing the extrudates (about 50 grams) in a
plastic beater, the bottom of which contained a plurality of
drilled holes so that vapor could pass through but the extrudates
could not. This plastic container was placed on top of a beaker
containing 3 grams of tetraethyl orthosilicate (100%). These two
beakers were placed in a pint jar which was capped and heated in an
oven at 190.degree. F. for 24 hours. The beakers and their contents
were cooled down, and the extrudates were then removed. These
extrudates were coated with liquid tetraethyl orthosilicate. The
extrudates were then allowed to hydrolyze in air for 24 hours, and
then were calcined in air for 16 hours at 1100.degree. F. The
percentage of silica by weight gain was 2.3% by weight based on
alumina. The coated alumina was then impregnated with an aqueous
copper nitrate solution [25.4% of Cu(No.sub.3).multidot.3H.sub.2 O
by weight], air dried and calcined for 3 hours at 800.degree. F.
This sorbent was designated C-4.
All of the sorbents in this test had nominal copper contents of 6%
Cu by weight. The copper contents of batches C-1, C-2 and C-3 as
determined by analysis have been indicated; batch C-4 was not
analyzed for copper content.
The sulfur dioxide removal activity of each of the above sorbents
was evaluated in a flue gas desulfurization run consisting of three
sorption-generation cycles. During the sorption period of each
cycle, synthetic flue gas containing 2700 ppm by volume of
SO.sub.2, 2.5% by volume of oxygen, balance nitrogen, was passed
through a fixed bed of the sorbent contained in a tubular reactor
12 inches long and one inch in diameter at an inlet temperature of
650.degree. F. and a space velocity of 5000 v/v hr. The sorption
period was stopped when the amount of SO.sub.2 in the effluent flue
gas reached 10% of the amount of SO.sub.2 in the incoming flue gas
(i.e. 90% SO.sub.2 removal). The length of time of the sorption
period was recorded as the breakthrough time. The sorbent was then
regenerated with a mixture of 20% by volume of hydrogen and 80% by
volume of steam at an inlet temperature of 650.degree. F. Then a
new cycle was begun.
Results are shown in Table VI below.
TABLE VI ______________________________________ Sorption Wt. %
Coating Wt. % Cu Time % Cu Batch SiO.sub.2 Method Nom. Anal. Min.
Utilization ______________________________________ C-1 None -- 6
6.4 11 20 (19) C-2 2.6 solution 6 6.1 11 19.5 (19) C-3 4.1 solution
6 6.2 10 18 (17) C-4 2.3 vapor 6 -- 11 19 phase
______________________________________
Copper utilization values in parentheses in Table VI above
represent utilization based on analyzed values for copper.
As Table VI shows, breakthrough times using copper impregnated
silica-coated sorbents of this invention are above the same as, or
only slightly shorter than the breakthrough times using the control
sorbent (C-1) of copper oxide on uncoated alumina. Copper
utilization percentages (which are the percentages of copper oxide
converted to copper sulfate during the sorption period) are only
slightly worse in the case of silica-coated alumina sorbents C-2,
C-3 and C-4 than in the case of the uncoated alumina sorbent C-1.
Thus, the improvement in strength and strength maintenance in
copper oxide on silica-coated alumina sorbents, as compared to the
copper oxide on uncoated alumina sorbents, noted in earlier
examples, is gained with only minimal reduction in activity.
EXAMPLE 7
This example describes the preparation and activity testing of
copper oxide on titania-coated alumina and copper oxide on
zirconia-coated alumina extrudates. A control sorbent of copper
oxide on uncoated alumina extrudates was also prepared and
tested.
The alumina base used in this example was a commercially available
alumina in the form of 1/8-inch extrudates, made by Harshaw
Chemical Company of Cleveland, Ohio. These extrudates were calcined
for 16 hours at 800.degree. F.; the calcined extrudates had a
surface area of 223 m.sup.2 /g. and a pore volume of 0.79 cc/g.
Control sorbent D-1 was prepared by impregnating 30 grams of the
above-described alumina base with 6.8 aams of copper nitrate,
Cu(NO.sub.3).sub.2 .multidot.3H.sub.2 O, dissolved in 20 ml of
water. The impregnated sorbent was air dried for 48 hours, calcined
for 3 hours at 800.degree. F. The nominal copper content was 6%;
the copper content by analysis was 6.4%.
Sorbent D-2, which was copper oxide on titania-coated alumina, was
prepared as follows: 52 grams of the above-described alumina
extrudates were flooded with a 40 volume % solution of
tetraisopropyl titanate in neptane. The solution was heated to
about 50.degree.-60.degree. C. for 30 minutes, allowed to cool
down, and the excess solution was decanted off. The extrudates were
allowed to hydrolyze slowly in air at ambient temperature
overnight. The extrudates were then calcined overnight by heating
slowly to 1100.degree. F. and then maintaining this temperature.
The percentage of TiO.sub.2 by weight gain was 11.7%; the
percentage of TiO.sub.2 by analysis was 9.3%. Thirty grams of the
coated sorbent were impregnated with 6.85 grams of copper nitrate,
[Cu(NO.sub.3).sub.2 .multidot.3H.sub.2 O] dissolved in 20 cc of
water. The impregnated sorbent was air dried for 72 hours and then
calcined for 3 hours at 800.degree. F.
Sorbent D-3, consisting of copper oxide on zirconia-coated alunina,
was prepared as follows: 45 grams of the above-described alumina
extrudates were immersed in a 50% by volume solution of tetrabutyl
zirconate in butanol, heated to 50.degree.-60.degree. C. for 30
minutes, and the excess solution decanted. The extrudates were then
hydrolyzed in air at ambient temperature overnight, then calcined
overnight by slowly heating the extrudates to 1100.degree. F. and
maintaining this temperature. The amount of ZrO.sub.2 by weight
gain was 10.3% based on the weight of untreated alumina. Thirty
grams of the coated sorbent were impregnated with 6.85 grams of
copper nitrate dissolved in 20 cc of water. The impregnated sorbent
was air dried for 72 hours and calcined for 3 hours at 800.degree.
F.
The reactor, desulfurization and regeneration conditions, and flue
gas and regeneration gas compositions, were the same as in Example
6.
The above sorbents, D-1, D-2 and D-3 were tested for flue gas
desulfurization activity in a one-inch diameter tubular glass
reactor using synthetic flue gas containing 2700 ppm by volume of
SO.sub.2 and 2.5% by volume of oxygen, balance nitrogen. Each of
the sorbents was evaluated in a cyclic flue gas desulfurization run
which consisted of three sorption-regeneration cycles. During the
sorption step of each cycle, the synthetic flue gas was passed
through the reactor at an inlet temperature of 650.degree. F. at a
space velocity of 5000 v/v/hr.; the sorption period was stopped
when the amount of SO.sub.2 in the effluent gas reached 10% of the
amount of SO.sub.2 in the incoming gas, as measured over the whole
sorption period. The sorbent was then regenerated with a gas
mixture of 20% by volume of hydrogen and 80% by volume of steam at
an inlet temperature of 650.degree. F. A new cycle was then carried
out.
Table VII below gives the coating oxide and amount thereof, the
amount of copper as determined by analysis (in each sorbent, the
nominal amount of copper was 6% by weight, based on the weight of
carrier base), the average length of sorption period, and the
percentage of copper utilization (i.e. the average percentage of
copper in the form of copper sulfate at the end of the sorption
period) based on both nominal and actual copper content (the latter
being shown in parentheses).
The titania and zirconia contents in batches D-2 and D-3 as shown
in Table VII are both by weight gain.
TABLE VII ______________________________________ Sorption Wt. % Cu
Time, Cu Utili- Batch Coating Nom. Anal. Min. zation %
______________________________________ D-1 None 6 6.4 12 20(19) D-2
11.7% TiO.sub.2 6 4.9 13 21 (26) D-3 10.3% ZrO.sub.2 6 -- 13 20
______________________________________
Copper utilization values in parentheses represent utilization
based on analyzed values for Cu.
From the data in Table VII, it can be seen the equivalent or
slightly superior activity for SO.sub.2 removal was obtained by
using titania-coated alumina or zirconia-coated in place of
uncoated alumina as the carrier. In view of improved strength
maintenance data as shown in earlier examples using titania-coated
alumina and zirconia-coated alumina carriers, sorbents of this
invention comprising copper oxide on either a titania-coated
alumina or a zirconia-coated alumina carrier are superior to copper
oxide on conventional alumina carriers. Copper oxide on
titania-coated alumina is especially desirable.
* * * * *