U.S. patent application number 13/611164 was filed with the patent office on 2013-01-03 for process for preparation of a catalyst carrier.
This patent application is currently assigned to SD LIZENZVERWERTUNGSGESELLSCHAFT MBH & CO. KG. Invention is credited to Nabil Rizkalla.
Application Number | 20130006002 13/611164 |
Document ID | / |
Family ID | 37743249 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130006002 |
Kind Code |
A1 |
Rizkalla; Nabil |
January 3, 2013 |
PROCESS FOR PREPARATION OF A CATALYST CARRIER
Abstract
This invention relates to catalyst carriers to be used as
supports for metal and metal oxide catalyst components of use in a
variety of chemical reactions. More specifically, the invention
provides a process of formulating a low surface area alpha alumina
carrier that is suitable as a support for silver and the use of
such catalyst in chemical reactions, especially the epoxidation of
ethylene to ethylene oxide. A precursor for a catalyst support
comprises an admixture of an alpha alumina and/or a transition
alumina; a binder; and either a solid blowing agent which expands,
or propels a gas upon the application of sufficient heat, and
optionally contains talc and/or water soluble titanium
compound.
Inventors: |
Rizkalla; Nabil; (Rivervale,
NJ) |
Assignee: |
SD LIZENZVERWERTUNGSGESELLSCHAFT
MBH & CO. KG
Munchen
DE
|
Family ID: |
37743249 |
Appl. No.: |
13/611164 |
Filed: |
September 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11201253 |
Aug 10, 2005 |
|
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13611164 |
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Current U.S.
Class: |
549/534 ;
423/628; 502/216; 502/231; 502/243; 502/348; 502/439; 502/63 |
Current CPC
Class: |
C07D 301/10 20130101;
B01J 21/04 20130101; B01J 23/50 20130101; B01J 37/0018 20130101;
C07D 301/08 20130101 |
Class at
Publication: |
549/534 ;
502/439; 502/63; 502/348; 502/216; 502/231; 423/628; 502/243 |
International
Class: |
B01J 21/04 20060101
B01J021/04; B01J 21/08 20060101 B01J021/08; C07D 301/10 20060101
C07D301/10; B01J 27/02 20060101 B01J027/02; B01J 27/06 20060101
B01J027/06; C01F 7/02 20060101 C01F007/02; B01J 21/16 20060101
B01J021/16; B01J 23/50 20060101 B01J023/50 |
Claims
1. A process for producing a catalyst support which comprises: a)
preparing a precursor for a catalyst support which comprises an
admixture of an alpha alumina and/or a transition alumina; a
binder; a solid blowing agent which expands, or propels a gas upon
the application of sufficient heat, and water; thereafter b)
molding the resultant precursor into a structure; thereafter c)
heating said structure for a sufficient time and at a sufficient
temperature to cause the blowing agent to form a porous structure,
and thereafter d) heating the porous structure for a sufficient
time and at a sufficient temperature to fuse the porous structure
and thereby form a porous catalyst support.
2. The process of claim 1 wherein the blowing agent comprises a
composition of thermoplastic shells which encapsulate a
hydrocarbon, which hydrocarbon expands the thermoplastic shells
upon the application of sufficient heat.
3. The process of claim 1 wherein the blowing agent comprises a
granular blowing agent which propels a gas upon the application of
sufficient heat.
4. The process of claim 3 wherein the solid blowing agent comprises
a material selected from the group consisting of
p-toluenesulfonylhydrazide, benzenesulfonylhydrazide, and
azodicarbonamide, H.sub.2NCO--N.dbd.N--CONH.sub.2, and combinations
thereof.
5. The process of claim 1 wherein the alpha alumina and/or a
transition alumina component comprises one or more alpha aluminas,
and optionally one or more transition aluminas.
6. The process of claim 1 wherein the binder comprises a material
selected from the group consisting thermally decomposable organic
compounds, clays, silica, silicates of elements of Group II of the
Periodic Table of the elements, and combinations thereof.
7. The process of claim 1 wherein step c), step d) or both step c)
and step d) are conducted in an atmosphere of an inert gas, and
optionally an oxidizing gas.
8. A process for producing a catalyst which comprises: a) preparing
a precursor for a catalyst support which comprises an admixture of
an alpha alumina and/or a transition alumina; a binder; a solid
blowing agent which expands, or propels a gas upon the application
of sufficient heat, and water; thereafter b) molding the resultant
precursor into a structure; thereafter c) heating said structure
for a sufficient time and at a sufficient temperature to cause the
blowing agent to form a porous structure, thereafter d) heating the
porous structure for a sufficient time and at a sufficient
temperature to fuse the porous structure and thereby form a porous
catalyst support; and then e) depositing a catalytically effective
amount of silver onto a surface of the catalyst support.
9. The process of claim 8 wherein the blowing agent comprises a
composition of thermoplastic shells which encapsulate a
hydrocarbon, which hydrocarbon expands the thermoplastic shells
upon the application of sufficient heat.
10. The process of claim 8 wherein the blowing agent comprises a
granular blowing agent which propels a gas upon the application of
sufficient heat.
11. The process of claim 10 wherein the solid blowing agent
comprises a material selected from the group consisting of
p-toluenesulfonylhydrazide, benzenesulfonylhydrazide, and
azodicarbonamide, H.sub.2NCO--N.dbd.N--CONH.sub.2, and combinations
thereof.
12. The process of claim 8 wherein the alpha alumina and/or a
transition alumina component comprises one or more alpha aluminas,
and optionally one or more transition aluminas.
13. The process of claim 8 wherein the binder comprises a material
selected from the group consisting of thermally decomposable
organic compounds, clays, silica, silicates of elements of Group II
of the Periodic Table of the elements, and combinations
thereof.
14. The process of claim 8 wherein step c), step d) or both step c)
and step d) are conducted are conducted in an atmosphere of an
inert gas, and optionally an oxidizing gas.
15. The process of claim 8 further comprising depositing a
promoting amount of a promoter onto the surface of the catalyst
support, the promoter comprising one or more alkali metal
containing compounds, one or more transition metal containing
compounds, one or more sulfur components, one or more fluorine
containing components, or combinations thereof.
16. The catalyst produced by the process of claim 3.
17. The catalyst produced by the process of claim 8.
18. A process for the oxidation of ethylene to ethylene oxide which
comprises the vapor phase oxidation of ethylene with molecular
oxygen in a fixed bed, tubular reactor, in the presence of the
catalyst produced by the process of claim 8.
19. A process for the oxidation of ethylene to ethylene oxide which
comprises the vapor phase oxidation of ethylene with molecular
oxygen in a fixed bed, tubular reactor, in the presence of the
catalyst produced by the process of claim 15.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. Ser.
No. 11/201,253 filed on Aug. 10, 2005. The entire contents of the
aforementioned U.S. application are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to catalyst carriers to be used as
supports for metal and metal oxide catalyst components of use in a
variety of chemical reactions. More specifically, the invention
pertains to a process of formulating catalyst having a low surface
area alpha alumina carrier that is suitable as a support for
silver, and the use of such catalyst in chemical reactions,
especially the epoxidation of ethylene to ethylene oxide.
[0004] 2. Description of the Related Art
[0005] Alumina is well known to be useful as a catalyst support for
the epoxidation of olefins. It is particularly useful as a support
for a catalyst comprising silver which is employed in the oxidation
of ethylene to ethylene oxide. Support materials are made by fusing
high purity aluminum oxide, with or without silica. For this
purpose the support material often comprises 90 percent or more, by
weight, alpha alumina and up to 6 percent, by weight, silica. They
are usually very porous and have a high or low surface area
depending on the use to be made of them.
[0006] In known processes of making a support, alpha alumina and/or
transition alumina (alpha alumina precursors) is thoroughly mixed
with temporary and permanent binders. The temporary binders hold
together the components of the carrier precursor during its
processing. The permanent binders are inorganic materials having
fusion temperatures below that of the alumina and induce fusion at
the points of contact of the alumina particles which impart
mechanical strength to the finished support. After thorough
dry-mixing, sufficient water is added to the mass to form the mass
into a: paste-like substance. The catalyst support particles are
then formed from the paste by conventional means such as high
pressure extrusion, tableting, granulation or other ceramic forming
processes. The particles are then dried and are subsequently fired
at an elevated temperature.
[0007] In the firing step, the temporary binders are burnt or
thermally decomposed to carbon dioxide and water, and are
volatilized. It is known in the art that ceramic carriers based
catalysts comprise inert, solid supports such as alpha alumina.
Such have been described in U.S. Pat. Nos. 3,664,970; 3,804,781;
4,428,863 and 4,874,739. U.S. patents which describe the making of
alumina supports include U.S. Pat. Nos. 2,499,675; 2,950,169 and
3,172,866. Other patents such as U.S. Pat. Nos. 3,222,129;
3,223,483 and 3,226,191 show the preparation of active aluminas.
Methods of making highly porous aluminas are disclosed in U.S. Pat.
Nos. 3,804,781; 3,856,708; 3,907,512 and 3,907,982. Alumina
carriers having high thermal stability are disclosed in U.S. Pat.
No. 3,928,236. Other methods of making catalyst carriers are
discussed in U.S. Pat. Nos. 3,987,155; 3,997,476; 4,001,144;
4,022,715; 4,039,481; 4,098,874 and 4,242,233. U.S. Pat. No.
3,664,970 discloses a carrier containing mainly alumina and also
contains silica, magnesia and titania. U.S. Pat. No. 4,410,453
discloses that the performance of a silver on alumina catalyst for
the oxidation of ethylene to ethylene oxide is improved by the
inclusion of an oxide, or oxide precursor, of zinc, lanthanum, or
magnesium. U.S. Pat. No. 4,200,552 discloses a carrier that is made
of a-alumina and at least one of the compounds
Si0.sub.2,Ti0.sub.2,Zr0.sub.2, CaO, MgO, B.sub.20.sub.3, Mn0.sub.2,
or Cr.sub.20.sub.3, as a sintering agent. U.S. Pat. No. 4,455,392
discloses the composition of an alumina carrier that contains
silica and magnesia as components of the bonding material. U.S.
Pat. No. 5,100,859 discloses a carrier that contains an alkaline
earth metal silicate, which may be added as an original component
or generated in situ by the reaction of silica, or silica
generating compounds, with compounds that decompose to alkaline
earth metal oxide upon heating. U.S. Pat. No. 5,512,530 discloses a
process for the production of a catalyst carrier which is based on
mixing alpha alumina, burnout material, and titania. U.S. Pat. No.
5,380,697 discloses a carrier containing a ceramic bond comprises
60% wt. silica, 29% wt. alumina, 3% wt. calcium oxide, 2% magnesia,
4% wt. alkali metal oxides and less than 1% wt. each of ferric
oxide and titania. U.S. Pat. No. 5,733,840 and U.S. Pat. No.
5,929,259 disclose a titania-modification of formed carriers. The
treatment involved impregnating the pre-formed carrier with a
solution of titanyl oxalate, titanium (IV) bis(ammonium
lactato)dihydroxide, or similar organic salts and then the
impregnated carrier is calcined at a temperature from about 450 to
700.degree. C. The patents disclosed that if titania is added
during the carrier's preparation, it tend to affect the
densification of the carrier structure which can lead to
unacceptable properties. U.S. Pat. No. 4,368,144 states that better
catalytic performance was obtained with carriers that contain no
more than 0.07% Na. U.S. Pat. No. 6,103,916 discloses that catalyst
performance was improved when the carrier was washed by boiling in
pure water until the water resistivity is more than 10,000
.OMEGA.cm.
[0008] One of the problems with the catalysts that are based on
porous carriers is that they have an insufficiently uniform pore
structure. U.S. Pat. No. 4,022,715 attempts to solve this problem
by using an organic solution of a blowing agent, mixed with a
carrier precursor composition. It has now been found that an
improved carrier pore structure can be formed by employing a
precursor for a catalyst support which comprises an admixture of an
alpha alumina and/or a transition alumina; a binder; and either a
solid blowing agent which expands, or propels a gas upon the
application of sufficient heat, talc and/or a water soluble
titanium compound.
[0009] The catalyst support of this invention has excellent crush
strength, porosity, and surface area. The optimum porosity insures
the absence of diffusional resistances for reactants and product
gases under reaction conditions. A minimum surface area is
important because it provides the structure on which the catalytic
component will be deposited. Crush strength is a parameter of the
physical integrity of the carrier. This physical strength is
essential for the catalyst ability to withstand handling as well as
its long life in a commercial reactor. It has been discovered that
the novel pore forming agent in combination with a bonding agent
demonstrate a great influence in controlling the specifications of
the finished carrier. A carrier that has the optimum surface area
and porosity may be deficient in its crush strength, and vice
versa. The balance between the different physical specifications of
the carrier is important.
SUMMARY OF THE INVENTION
[0010] The invention provides a precursor for a catalyst support
which comprises an admixture of an alpha alumina and/or a
transition alumina; a binder; and a solid blowing agent which
expands, or propels a gas upon the application of sufficient
heat.
[0011] The invention also provides a process for producing a
catalyst support which comprises: [0012] a) preparing a precursor
for a catalyst support which comprises an admixture of an alpha
alumina and/or a transition alumina; a binder; a solid blowing
agent which expands, or propels a gas upon the application of
sufficient heat, and water; thereafter [0013] b) molding the
resultant precursor into a structure; thereafter [0014] c) heating
said structure for a sufficient time and at a sufficient
temperature to cause the blowing agent to form a porous structure,
and thereafter [0015] d) heating the porous structure for a
sufficient time and at a sufficient temperature to fuse the porous
structure, and thereby form a porous catalyst support.
[0016] The invention further provides a process for producing a
catalyst which comprises: [0017] a) preparing a precursor for a
catalyst support which comprises an admixture of an alpha alumina
and/or a transition alumina; a binder; a solid blowing agent which
expands, or propels a gas upon the application of sufficient heat,
and water; thereafter [0018] b) molding the resultant precursor
into a structure; thereafter [0019] c) heating said structure for a
sufficient time and at a sufficient temperature to cause the
blowing agent to form a porous structure, thereafter [0020] d)
heating the porous structure for a sufficient time and at a
sufficient temperature to fuse the porous structure and thereby
form a porous catalyst support; and then [0021] e) depositing a
catalytically effective amount of silver onto the surface of the
catalyst support.
[0022] The invention still further provides a precursor for a
catalyst support which comprises an admixture of an alpha alumina
and/or a transition alumina; a binder; and talc.
[0023] The invention further provides a process for producing
catalyst support which comprises: [0024] a) preparing a precursor
for a catalyst support which comprises an admixture of an alpha
alumina and/or a transition alumina; a binder; talc and water;
thereafter [0025] b) molding the resultant precursor into a
structure; thereafter [0026] c) heating said structure for a
sufficient time and at a sufficient temperature to form a porous
structure, and thereafter [0027] d) heating the porous structure
for a sufficient time and at a sufficient temperature to fuse the
porous structure and thereby form a porous catalyst support.
[0028] The invention further provides a precursor for a catalyst
support which comprises an admixture of an alpha alumina and/or a
transition alumina; a binder; and a water soluble titanium
compound.
[0029] The invention further provides a process for producing a
catalyst support which comprises: [0030] a) preparing a precursor
for a catalyst support which comprises an admixture of an alpha
alumina and/or a transition alumina; a binder; a water soluble
titanium compound; and water; [0031] b) molding the resultant
precursor into a structure; thereafter [0032] c) heating said
structure for a sufficient time and at a sufficient temperature to
form a porous structure, and thereafter [0033] d) heating the
porous structure for a sufficient time and at a sufficient
temperature to fuse the porous structure and thereby form a porous
catalyst support.
DETAILED DESCRIPTION OF THE INVENTION
[0034] In one embodiment of the invention, the precursor for a
catalyst support is prepared by forming a physical admixture of an
alpha alumina and/or a transition alumina; a binder; and a solid
blowing agent which expands, or propels a gas upon the application
of sufficient heat.
[0035] The precursor may comprise an aluminum oxide such as
alpha-alumina and/or a transition alumina. The preferred carriers
are prepared from alpha-alumina particles. Transition alumina may
comprise an aluminum hydroxide such as gibbsite, boehmite,
diaspore, bayerite and combinations thereof. The alpha alumina
and/or a transition alumina may be present in an amount of from
about 80 weight % to about 100 weight % based on the weight of the
finished carrier. It is preferably present in an amount of from
about 90 weight % to about 99 weight % based on the weight of the
finished carrier, more preferably from about 97 weight % to about
99 weight percent based on the weight of the finished carrier.
[0036] The precursor further comprises a binder which may be a
temporary binder, a permanent binder, or both. The temporary
binders are thermally decomposable organic compounds of moderate to
high molecular weight. The permanent binders are inorganic
clay-type materials that impart mechanical strength to the finished
support.
[0037] Temporary binders, and burnout materials, include polyolefin
oxides, oil, e.g mineral oil, acacia, carbonaceous materials such
as coke, carbon powders, graphite, cellulose, substituted
celluloses, e.g. methylcellulose, ethylcellulose, and
carboxyethylcellulose, cellulose ethers, stearates, such as organic
stearate esters, e.g. methyl or ethyl stearate, waxes, powdered
plastics such as polyolefins, particularly polyethylene and
polypropylene, polystyrene, polycarbonate, sawdust, starch, and
ground nut shell flours, e.g. pecan, cashew, walnut and filbert
shells, and the like which burn at the firing temperatures
employed. Burnout material is used primarily to ensure the
preservation of the structure during the green, or unfired phase in
which the mixture may be shaped into particles by molding or
extrusion processes and also provide the desired porosity to the
finished product. When employed, a temporary binder is essentially
totally removed during the firing to produce the finished support.
The supports of the invention are preferably made with the
inclusion of a permanent binder material to ensure preservation of
the porous structure after the carrier is fired. Permanent binders,
include inorganic clay materials, silicas, silica with an alkali
metal compound, silicates of elements of Group II of the Periodic
Table of the elements, and combinations thereof. Useful clays
non-exclusively include kaolinite. A convenient binder material
which may be incorporated with the alumina particles is a mixture
of boehmite, stabilized silica sol and a soluble sodium salt. The
binder may be present in the precursor in an amount of from about
0.1 weight % to about 15 weight % based on the weight of the
precursor preferably from about 0.2 weight % to about 10 weight %
based on the weight of the precursor, and more preferably from
about 0.5 weight % to about 5 weight % based on the weight of the
precursor.
[0038] The precursor then comprises a solid blowing agent which
expands, or propels a gas upon the application of sufficient heat.
In one embodiment, the blowing agent comprises a composition of
microspheres which include thermoplastic shells which encapsulate a
hydrocarbon. The hydrocarbon expands the thermoplastic shells upon
the application of sufficient heat. Such blowing agents comprise
gas-tight thermoplastic shells that may encapsulate a hydrocarbon
in liquid form. Upon heating, the hydrocarbon is gasified and
increases its pressure while the thermoplastic shell softens,
resulting in an increase in the volume of the microspheres.
Examples of expandable microspheres are Advancell,
acrylonitrile-based spheres, commercially available from Sekisui
Chemical Co. (Osaka, Japan) and Expancel.RTM. micro spheres,
commercially available from Expancel, Stockviksverken, Sweden.
Expancel is available in unexpanded and expanded microsphereforms.
Unexpanded microspheres have a diameter of from about 6 to about 40
.mu.m, depending on grade. When heated, these microspheres expand
to from about 20 to about 150 .mu.m in diameter. The preferred
hydrocarbon inside the shell is isobutane or isopentane. The shell
is preferably a copolymer of monomers, e.g. vinylidene chloride,
acrylonitrile and methyl methacrylate. In another embodiment, the
blowing agent may be a solid, granular chemical blowing agent which
decomposes upon heating, releasing a considerable amount of gaseous
decomposition products and resulting in pore formation. Chemical
blowing agents are preferably solid forms of hydrazine derivatives
that will release gases such as C02 and nitrogen. Examples of
chemical blowing agents are p-toluenesulfonylhydrazide,
benzenesulfonylhydrazide, and azodicarbonamide,
H.sub.2NCO--N.dbd.N--CONH.sub.2. Azodicarbonamide decomposes at
200.degree. C., into N.sub.2, CO, and CO.sub.2.
[0039] A suitable amount of blowing agent to provide the desired
porosity may be in the range of from about 0.1 weight % to about 30
weight % by weight of the overall precursor. Preferably, the amount
of the blowing agent ranges from about 1 weight % to about 20
weight % and more preferably from about 3 weight % to about 15
weight percent based on the weight of the precursor. The amount of
blowing agent is a function of its type, the type of alpha alumina
and/or a transition alumina components used, as well as the nature
of the porosity that is desired in the finished product.
[0040] After thorough dry-mixing of the alpha alumina and/or a
transition alumina material, binder and blowing agent, sufficient
water is added to the precursor mass to form a paste-like
substance. Water and/or a water-containing substance is added to
the starting precursor in order to give plasticity to the mixture.
The plastic mixture is then formed into the desired shape via
standard ceramic processing methods, e.g. tableting or extrusion.
The amount of water added to the carrier precursor will be a
function of the method used to form the paste.
[0041] Extrusion may require the addition of a higher level of
water to gain the optimum level of plasticity. Where particles are
formed by extrusion it may be desirable to include conventional
extrusion aids such as lubricants, for example petroleum jelly, or
mineral oil. The lubricant may be present in the precursor in an
amount of from about 0.1 weight % to about 10 weight percent based
on the weight of the precursor, preferably from about 0.5 weight %
to about 5 weight % based on the weight of the precursor, and more
preferably from about 1 weight % to about 3 weight % based on the
weight of the precursor. The amounts of the components to be used
are to some extent interdependent and will depend on a number of
factors that relate to the equipment used. However these matters
are well within the general knowledge of a person skilled in the
art of extruding ceramic materials. Preparation of a catalyst
carrier generally uses a step of kneading the precursor material
into a desired shape and a desired size. The catalyst support
particles are then formed from the paste by conventional means such
as, for example, pelletizing, high pressure extrusion, granulation
or other ceramic forming processes. For use in commercial ethylene
oxide production applications, the supports are desirably formed
into regularly shaped pellets, spheres, rings, particles, chunks,
pieces, wagon wheels, cylinders, trilobes, tetralobes and the like
of a size suitable for employment in fixed bed reactors. Desirably,
the support particles may have "equivalent diameters" in the range
of from about 3 mm to about 20 mm and preferably in the range of
from about 4 mm to about 12 mm, which are usually compatible with
the internal diameter of the tube reactors in which the catalyst is
placed. "Equivalent diameter" is the diameter of a sphere having
the same external surface (i.e. neglecting surface within the pores
of the particle) to volume ratio as the support particles being
employed. The particles are then dried and are subsequently fired
at an elevated temperature. The function of the drying step is to
remove the water from the shaped pellets. The formed carrier
precursor is dried to at a temperature of from about 80.degree. C.
to about 150 DC for a time sufficient to remove substantially all
of the water. Then the extruded material is calcined under
conditions sufficient to remove the burnout agents and the organic
binding agents and to fuse the alpha alumina particles into a
porous, hard mass. The carrier is heated at a temperature that is
high enough to sinter the alumina particles and produce a structure
with physical properties adequate to withstand the environment in
which it is expected to operate. The calcination temperature and
duration should be high enough to convert any transition alumina
into alpha alumina and to induce grain boundary fusion. Controlling
the calcination process is essential to obtain a carrier having the
optimum balance between surface area, porosity and strength.
Typically the calcination temperature is higher than 1000 DC,
preferably is in the range of 1150 DC to about 1600 DC. The holding
times at these maximum temperatures typically range from about 0
hour to 10 hours, preferably from about 0.1 hour to about 10 hours
preferably from about 0.2 hour to about 5 hours to form the
support.
[0042] The final carrier has a water pore volume ranging from about
0.2 cc/g to about 0.8 cc/g, preferably from about 0.25 cc/g to
about 0.6 cc/g. The BET surface area of the finished carrier is
preferred to be in the range of 0.4-4.0 m.sup.2/g more preferably
from about 0.6 to about 1.5 m.sup.2g. The suitable value of crush
strength is about 8 pounds and higher, and preferably about 10
pounds and higher.
[0043] In another embodiment of the invention, the precursor for a
catalyst support is prepared as above except the admixture
comprises an alpha alumina and/or a transition alumina as above and
in the same amounts; and talc instead of or in addition to the
permanent binder component. The talc may be present in the
precursor in an amount of from about 0.1 weight % to about 15
weight % based on the weight of the precursor, preferably from
about 0.5 weight % to about 10 weight % based on the weight of the
precursor, and more preferably from about 1 weight % to about 8
weight % based on the weight of the precursor. The support is then
formed in a manner similar to that described above.
[0044] In another embodiment of the invention, the precursor for a
catalyst support is prepared as above except the admixture
comprises an alpha alumina and/or a transition alumina as above and
in the same amounts; and a water soluble titanium compound instead
of or in addition to the permanent binder. Suitable water soluble
titanium compounds non-exclusively include titanyl oxalate, and
titanium IV) bis(ammonium lactato)dihydroxide. The water soluble
titanium compound may be present in the precursor in an amount of
from about 0.01 weight % to about 10 weight percent based on the
weight of the precursor, preferably from about 0.1 weight % to
about 8 weight percent based on the weight of the precursor, and
more preferably from about 0.2 weight % to about 5 weight percent
based on the weight of the precursor. The support is then formed in
a manner similar to that described above.
[0045] In order to produce a catalyst for the oxidation of ethylene
to ethylene oxide, a support formed above is then provided with a
catalytically effective amount of silver thereon. The catalysts are
prepared by impregnating the supports with silver ions, compounds,
complexes and/or salts dissolved in a suitable solvent sufficient
to cause deposition of silver precursor compound onto the support.
The impregnated carrier is then removed from the solution and the
deposited silver compound is reduced to metallic silver by high
temperature calcination. Also preferably deposited on the support
either prior to, coincidentally with, or subsequent to the
deposition of the silver are suitable promoters in the form of
ions, compounds and/or salts of an alkali metal dissolved in a
suitable solvent. Also deposited on the carrier either prior to,
coincidentally with, or subsequent to the deposition of the silver
and/or alkali metal, suitable transition metal compounds, complexes
and/or salts dissolved in an appropriate solvent.
[0046] The supports as formed above are impregnated with a silver
impregnating solution, preferably an aqueous silver solution. The
support is also impregnated at the same time or in a separate step
with various catalyst promoters. Preferred catalysts prepared in
accordance with this invention contain up to about 45% by weight of
silver, expressed as metal, deposited upon the surface and
throughout the pores of a porous support. Silver contents,
expressed as metal, of from about I to about 40% based on weight of
total catalyst are preferred, while silver contents of from about 8
to about 35% are more preferred. The amount of silver deposited on
the support or present on the support is that amount which is a
catalytically effective amount of silver, i.e., an amount which
economically catalyzes the reaction of ethylene and oxygen to
produce ethylene oxide. As used herein, the term "catalytically
effective amount of silver" refers to an amount of silver that
provides a measurable conversion of ethylene and oxygen to ethylene
oxide and selectivity and activity stability within catalyst life.
Useful silver containing compounds non-exclusively include silver
oxalate, silver nitrate, silver oxide, silver carbonate, a silver
carboxylate, silver citrate, silver phthalate, silver lactate,
silver propionate, silver butyrate and higher fatty acid salts and
combinations thereof.
[0047] This catalyst comprises a catalytically effective amount of
silver, a promoting amount of alkali metal, a promoting amount of a
transition metal supported on a porous, support. As used herein the
term "promoting amount" of a certain component of a catalyst refers
to an amount of that component that works effectively to provide an
improvement in one or more of the catalytic properties of that
catalyst when compared to a catalyst not containing said component.
The exact concentrations employed, of course, will depend upon,
among other factors, the desired silver content, the nature of the
support, the viscosity of the liquid, and solubility of the silver
compound.
[0048] In addition to silver, the catalyst also contains an alkali
metal promoter selected from lithium, sodium, potassium, rubidium,
cesium or combinations thereof, with, cesium being preferred. The
amount of alkali metal deposited on the support or catalyst or
present on the support or catalyst is to be a promoting amount.
Preferably the amount will range from about 10 ppm to about 3000
ppm, more preferably from about 50 ppm to about 2000 ppm and even
more preferably from about 100 ppm to about 1500 ppm and yet even
more preferably from about 200 ppm to about 1000 ppm by weight of
the total catalyst, measured as the metal.
[0049] The catalyst also preferably contains a transition metal
promoter which comprises an element from Groups 4b, 5b, 6b, 7b and
8 of the Periodic Table of the Elements, and combinations thereof.
Preferably the transition metal comprises an element selected from
Group 6b, and 7b of the Periodic Table of the Elements. More
preferred transition metals are rhenium, molybdenum, and tungsten,
with molybdenum and rhenium most preferred. The amount of
transition metal promoter deposited on the support or catalyst or
present on the support or catalyst is to be a promoting amount. The
transition metal promoter may be present in an amount of from about
0.1 micromoles per gram to about 10 micromoles per gram, preferably
from about 0.2 micromoles per gram to about 5 micromoles per gram,
and more preferably from about 0.5 micromoles per gram to about 4
micromoles per gram of total catalyst, expressed as the metal.
[0050] The silver solution used to impregnate the support may also
comprise an optional solvent or complexing/solubilizing agent such
as are known in the art. A wide variety of solvents or
complexing/solubilizing agents may be employed to solubilize silver
to the desired concentration in the impregnating medium. Useful
complexing/solubilizing agents include amines, ammonia, or lactic
acid. Amines include alkylene diamines, and alkanol amines having
from 1 to 5 carbon atoms. In one preferred embodiment, the solution
comprises an aqueous solution of silver oxalate and ethylene
diamine. The complexing/solubilizing agent may be present in the
impregnating solution in an amount of from about 0.1 to about 5.0
moles of ethylene diamine per mole of silver, preferably from about
0.2 to about 4.0 moles, and more preferably from about 0.3 to about
3.0 moles of ethylene diamine for each mole of silver.
[0051] When a solvent is used it may be water-based, or
organic-based, and may be polar or substantially or totally
non-polar. In general, the solvent should have sufficient solvating
power to solubilize the solution components. At the same time, it
is preferred that the solvent be chosen to avoid having an undue
influence on or interaction with the solvated promoters. The
concentration of silver salt in the solution is in the range of
from about 1% by weight to the maximum permitted by the solubility
of the particular salt/solubilizing agent combination employed. It
is generally very suitable to employ silver salts solutions
containing from 5% to about 45% by weight of silver with silver
salt concentrations of from 10 to 35% by weight being
preferred.
[0052] Impregnation of the selected support is achieved in
conventional manners by excess solution impregnation, incipient
wetness, etc. Typically the support material is placed in the
silver solution until a sufficient amount of the solution is
absorbed by the support. Preferably the quantity of the silver
solution used to impregnate the porous support is no more than is
necessary to fill the pore volume of the support. The silver
containing liquid penetrates by absorption, capillary action and/or
vacuum into the pores of the support. A single impregnation or a
series of impregnations, with or without intermediate drying, may
be used, depending in part on the concentration of the silver salt
in the solution. Impregnation procedures are described in U.S. Pat.
Nos. 4,761,394, 4,766,105, 4,908,343, 5,057,481, 5,187,140,
5,102,848, 5,011,807, 5,099,041 and 5,407,888, which are
incorporated herein by reference. Known prior procedures of
pre-deposition, co-deposition and post-deposition of various
promoters can be employed.
[0053] Examples of catalytic properties include, inter alia,
operability (resistance to runaway), selectivity, activity,
conversion, stability and yield. It is understood by one skilled in
the art that one or more of the individual catalytic properties may
be enhanced by the "promoting amount" while other catalytic
properties may or may not be enhanced or may even be diminished. It
is further understood that different catalytic properties may be
enhanced at different operating conditions. For example, a catalyst
having enhanced selectivity at one set of operating conditions may
be operated at a different set of conditions wherein the
improvement shows up in the activity rather than the selectivity
and an operator of an ethylene oxide plant will intentionally
change the operating conditions in order to take advantage of
certain catalytic properties even at the expense of other catalytic
properties in order to optimize conditions and results by taking
into account feedstock costs, energy costs, by-product removal
costs and the like. The particular combination of silver, support,
alkali metal promoter, and transition metal promoter of the instant
invention will provide an improvement in one or more catalytic
properties over the same combination of silver and support and
none, or only one promoter.
[0054] After impregnation, the support impregnated with silver
precursor compound and the promoters is calcined or activated, for
a time sufficient to reduce the silver component to metallic silver
and to remove the solvent and volatile decomposition products from
the silver containing support. The calcination is accomplished by
heating the impregnated support, preferably at a gradual rate, to a
temperature in the range of from about 200.degree. C. to about
600.degree. C., preferably from about 230.degree. C. to about
500.degree. C., and more preferably from about 250.degree. C. to
about 450.degree. C., at a reaction pressures in the range of from
0.5 to 35 bar, for a time sufficient to convert the contained
silver to silver metal and to decompose all or substantially all of
present organic materials and remove the same as volatiles. In
general, the higher the temperature, the shorter the required
calcination period. A wide range of heating periods have been
suggested in the art to thermally treat the impregnated support,
e.g., U.S. Pat. No. 3,563,914 suggests heating for less than 300
seconds, U.S. Pat. No. 3,702,259 discloses heating from 2 to 8
hours at a temperature of from 100.degree. C. to 375.degree. C. to
reduce the silver salt in the catalyst; usually for from about 0.5
to about 8 hours, however, it is only important that the reduction
time be correlated with temperature such that substantially
complete reduction of silver salt to catalytically active metal is
accomplished. A continuous or step-wise heating program may be used
for this purpose.
[0055] The impregnated support is maintained under an atmosphere
comprising an inert gas and optionally an oxygen containing
oxidizing component. In one embodiment the oxidizing component is
present in an amount of from about 10 ppm to about 5% by volume of
gas. For purposes of this invention, inert gases are defined as
those which do not substantially react with the catalyst producing
components under the catalyst preparation conditions chosen. These
include nitrogen, argon, krypton, helium, and combinations thereof,
with the preferred inert gas being nitrogen. In a useful
embodiment, the atmosphere comprises from about 10 ppm to about 1%
by volume of a gas of an oxygen containing oxidizing component. In
another useful embodiment, the atmosphere comprises from about 50
ppm to about 500 ppm of a gas of an oxygen containing oxidizing
component.
[0056] Ethylene Oxide Production
[0057] Generally, the commercially practiced ethylene oxide
production processes are carried out by continuously contacting an
oxygen containing gas with ethylene in the presence of the present
catalysts at a temperature in the range of from about 180.degree.
C. to about 330.degree. C. and preferably about 200.degree. C. to
about 325.degree. C., more preferably from about 210.degree. C. to
about 270.degree. C., at a pressure which may vary from about
atmospheric pressure to about 30 atmospheres depending on the mass
velocity and productivity desired. Higher pressures may, however,
be employed within the scope of the invention. Residence times in
large-scale reactors are generally on the order of about 0.1-5
seconds. Oxygen may be supplied to the reaction in an oxygen
containing stream, such as air or as commercial oxygen. The
resulting ethylene oxide is separated and recovered from the
reaction products using conventional methods. However, for this
invention, the ethylene oxide process envisions the normal gas
recycle encompassing carbon dioxide recycle in the normal
concentrations, e.g., about 0.1-15 volume percent. A usual process
for the oxidation of ethylene to ethylene oxide comprises the vapor
phase oxidation of ethylene with molecular oxygen in the presence
of the inventive catalyst in a fixed bed, tubular reactor.
Conventional commercial fixed bed ethylene oxide reactors are
typically in the form of a plurality of parallel elongated tubes
(in a suitable shell) approximately 0.7 to 2.7 inches O.D. and 0.5
to 2.5 inches I.D. and 15-45 feet long filled with catalyst.
[0058] The inventive catalysts have been shown to be particularly
selective catalysts in the oxidation of ethylene with molecular
oxygen to ethylene oxide. The conditions for carrying out such an
oxidation reaction in the presence of the catalysts of the present
invention broadly comprise those described in the prior art. This
applies, for example, to suitable temperatures, pressures,
residence times, diluent materials such as nitrogen, carbon
dioxide, steam, argon, methane, the presence or absence of
moderating agents to control the catalytic action, for example,
ethyl chloride, 1,2-dichloroethane, or vinyl chloride, the
desirability of employing recycle operations or applying successive
conversion in different reactors to increase the yields of ethylene
oxide, and any other special conditions which may be selected in
processes for preparing ethylene oxide. Molecular oxygen employed
as a reactant may be obtained from conventional sources. The
suitable oxygen charge may be relatively pure oxygen, a
concentrated oxygen stream comprising oxygen in major amount with
lesser amounts of one or more diluents such as nitrogen, argon,
etc., or another oxygen containing stream such as air. The use of
the present catalysts in ethylene oxidation reactions is in no way
limited to the use of specific conditions among those which are
known to be effective.
[0059] The resulting ethylene oxide is separated and recovered from
the reaction products by conventional methods known and used in the
art. Use of the silver catalysts of the invention in ethylene oxide
production processes gives higher overall ethylene oxidation
selectivities to ethylene oxide at a given ethylene conversion than
are possible with conventional catalysts.
[0060] In the production of ethylene oxide, reactant feed mixtures
may contain 0.5 to 45% ethylene and 3 to 15% oxygen, with the
balance comprising comparatively inert materials including such
substances as nitrogen, carbon dioxide, methane, ethane, argon and
the like. In a preferred application of the silver catalysts of the
invention ethylene oxide is produced when an oxygen containing gas
of about 95% or more of oxygen. Only a portion of the ethylene
usually is reacted per pass over the catalyst and after separation
of the desired ethylene oxide product and the removal of
appropriate purge stream and carbon dioxide to prevent uncontrolled
build up of inerts and/or by-products, unreacted materials are
returned to the oxidation reactor. For purposes of illustration
only, the following are conditions that are often used in current
commercial ethylene oxide reactor units. GHSV -1500-10,000; Inlet
pressure -150-400 psig; Inlet Feed: ethylene 1-40%; 02 -3-12%; CO2
-0.1-40%; ethane 0-3%; argon and/or methane and/or nitrogen:
balance, 0.3-20 ppmv total diluent chlorohydrocarbon moderator;
[0061] coolant temperature -180-315.degree. C.
[0062] The following non-limiting examples serve to illustrate the
invention.
EXAMPLE 1
[0063] Step 1 The following components were mixed thoroughly:
TABLE-US-00001 250 g alpha alumina(I) * 250 g alpha alumina(II) **
15 g K15M Methocel (methyl cellulose) 2 g Acacia 28.8 g Expancel 25
g Petroleum Jelly 8 g 50% Ti solution (as titanium bis-ammonium
lactato dihydroxide) 20 g Talc 107 g Water * Alpha Alumina(I) is a
highly pure alpha alumina that has a BET surface area of 0.7
m.sup.2/g and Na contents of less than 0.3%. ** Alpha Alumina(II)
is a highly pure alpha alumina that has a BET surface area of 11
m.sup.2/g and Na contents of less than 0.15%.
[0064] All the dry components were mixed together in a dry powder
mixer (US Stoneware Model M93120DC). The dry mixture was
transferred to a high shear mixer (Lancaster Model 530PO). There it
was blended with the water and the water-soluble components and
mixing continued for 15 more minutes.
[0065] Step 2
[0066] The plastic mixture was extruded into 8 mm hollow cylinders,
using a Killion extruder (Model 4321111282).
[0067] Step 3
[0068] The shaped pellets were dried at 120.degree. C. for 3 hours
followed by firing in a slow and programmed scheme. The firing
process involved heating the green ware in a high temperature
furnace, using a CM furnace (Model 1720). The firing scheme
involved temperature ramping at a rate of 4.degree. C./min up to
1275.degree. C. The temperature of the furnace was held at this
level for 2 hours and then it was allowed to cool down at a rate of
6.degree. C./min. This carrier is designated as carrier A. Testing
the carrier showed that it has the following specifications:
TABLE-US-00002 Crush strength 27.6 lb Water absorption 30 ml/100 g
BET surface area 1.3 m.sup.2/g
EXAMPLE 2
[0069] The following components were mixed thoroughly:
TABLE-US-00003 150 g alpha alumina(I)* 150 g alpha alumina(III)***
9 g K15M Methocel (methyl cellulose) 1.2 g Acacia 2.9 g Expancel
7.5 g Graphite 15 g Petroleum Jelly 4.7 g 50% Ti solution (as
titanium bis-ammonium lactato dihydroxide) 0.5 g Boric acid 20 g
Talc 80 g Water *Alpha Alumina(l) is a highly pure alpha alumina
that has a BET surface area of 0.7 m.sup.2/g and Na contents of
less than 0.3%. ***Alpha Alumina(III) is a highly pure alpha
alumina that has a BET surface area of 9 m.sup.2/g and Na contents
of less than 0.4%.
[0070] Mixing, shaping, and drying these components followed the
same procedure as in Example 1.
[0071] The firing scheme involved temperature ramping at a rate of
3.degree. C./min. up to 800.degree. C. The temperature of the
furnace was held at this level for 30 minutes. The temperature was
ramped up again at a rate of 4.degree. C./min up to 1325.degree. C.
The temperature of the furnace was then held at this level for 2
hours before it was allowed to cool down at a rate of 5.degree.
C./min. This carrier is designated as carrier B. Testing the
carrier showed that it has the following specifications:
TABLE-US-00004 Crush strength 17.6 lb Water absorption 33.8 ml/100
g BET surface area 1.13 m.sup.2/g
EXAMPLE 3
[0072] The following components were mixed thoroughly:
TABLE-US-00005 250 g alpha alumina(I)* 250 g alpha alumina(II)** 15
g K15M Methocel (methyl cellulose) 2 g Acacia 4.8 g Expancel 25 g
Petroleum Jelly 0.85 g Boric acid 10 g Talc 115 g Water *Alpha
Alumina(I) is a highly pure alpha alumina that has a BET surface
area of 0.7 m.sup.2/g and Na contents of less than 0.3%. **Alpha
Alumina(II) is a highly pure alpha alumina that has a BET surface
area of 11 m.sup.2/g and Na contents of less than 0.15%.
[0073] Mixing, shaping, and drying these components followed the
same procedure as in Example 1. The shaped pellets were dried at
120.degree. C. for 3 hours followed by firing in a slow and
programmed scheme. The firing process involved heating the green
ware in a high temperature furnace, using CM furnace (Model 1720).
The firing scheme involved temperature ramping at a rate of
4.degree. C./min up to 1275.degree. C. The temperature of the
furnace was held at this level for 2 hours and then it was allowed
to cool down at a rate of 5.degree. C./min. This carrier is
designated as carrier C. Testing the carrier showed that it has the
following specifications:
TABLE-US-00006 Crush strength 36.6 lb Water absorption 25.3 ml/100
g BET surface area 1.33 m.sup.2/g
EXAMPLE 4
[0074] The following components were mixed thoroughly:
TABLE-US-00007 250 g alpha alumina(l)* 250 g alpha alumina(II)** 15
g K15M Methocel (methyl cellulose) 2 g Acacia 4.8 g Expancel 7.8 g
50%Ti solution (as titanium bis-ammonium lactato dihydroxide) 25 g
Petroleum Jelly 109 Talc 107 g Water *Alpha Alumina(l) is a highly
pure alpha alumina that has a BET surface area of 0.7 m.sup.2/g and
Na contents of less than 0.3%. **Alpha Alumina(II) is a highly pure
alpha alumina that has a BET surface area of 11 m.sup.2/g and Na
contents of less than 0.15%.
[0075] Mixing, shaping, drying and firing these composite followed
the same procedure as in Example 3. This carrier is designated as
carrier D. Testing the carrier showed that it has the following
specifications:
TABLE-US-00008 Crush strength 32.9 lb Water absorption 26 ml/100 g
BET surface area 1.12 m.sup.2/g
EXAMPLE 5
[0076] The following components were mixed thoroughly:
TABLE-US-00009 250 g alpha alumina(I)* 250 g alpha alumina(II)**
37.5 g Alumina sol (20% colloidal alumina in water) 15 g K15M
Methocel (methyl cellulose) 2 g Acacia 4.8 g Expancel 25 g
Petroleum Jelly 7.8 g 50%Ti solution (as titanium bis-ammonium
lactato dihydroxide) 109 Talc 95 g Water
[0077] Mixing, shaping, and drying these components followed the
same procedure as in Example 1. The firing scheme involved
temperature ramping at a rate of 4.degree. C./min up to
1225.degree. C. The temperature of the furnace was held at this
level for 2 hours before it was allowed to cool down at a rate of
5.degree. C./min. This carrier is designated as carrier E. Testing
the carrier showed that it has the following specifications:
TABLE-US-00010 Crush strength 30.4 lb Water absorption 27.4 ml/100
g BET surface area 1.25 m.sup.2/g
EXAMPLE 6
[0078] The following components were mixed thoroughly:
TABLE-US-00011 250 g alpha alumiria(I)* 250 g alpha alumina(I)** 15
g KI5M Methocel (methyl cellulose) 2 g Acacia 25 g azodicarbonamide
25 g Petroleum Jelly 7.8 g 50%Ti solution (as titanium bis-ammonium
lactato dihydroxide) 10 g Talc 107 g Water
[0079] Mixing, shaping, drying and firing this composite followed
the same procedure as in Example 1. This carrier is designated as
carrier F. Testing the carrier showed that it has the following
specifications:
TABLE-US-00012 Crush strength 30.1 lb Water absorption 29.1 ml/100
g BET surface area 1.39 m.sup.2/g
EXAMPLE 7
[0080] Step 1 The following components were mixed thoroughly:
TABLE-US-00013 225 g alpha alumina(I) * 75 g alpha alumina(II)** 9
g KI5M Methocel (methyl cellulose) 1.2 g Acacia 2.8 g Expancel 15 g
Petroleum Jelly 4.7 g 50%Ti solution (as titanium bis-ammonium
lactato dihydroxide) 6 g Talc 80 g Water
[0081] Mixing, shaping, and drying these components followed the
same procedure as in Example 1. The firing scheme involved
temperature ramping at a rate of 4.degree. C./min up to
1275.degree. C. The temperature of the furnace was held at this
level for 2 hours before it was allowed to cool down at a rate of
5.degree. C./min. This carrier is designated as carrier G. Testing
the carrier showed that it has the following specifications:
TABLE-US-00014 Crush strength 41.7 lb Water absorption 27.3 ml/100
g BET surface area 1.35 m.sup.2/g
EXAMPLE 8
[0082] Step 1 The following components were mixed thoroughly:
TABLE-US-00015 250 g alpha alumina(I)* 250 g alpha alumina(II)** 15
g K15M Methocel (methyl cellulose) 2 g Acacia 4.8 g Expancel 25 g
Petroleum Jelly 1.25 g ammonium hexafluorotitanate 10 g Talc 115 g
Water
[0083] Mixing, shaping, and drying these components followed the
same procedure as in Example 1. The firing scheme involved
temperature ramping at a rate of 4.degree. C./min up to
1275.degree. C. The temperature of the furnace was held at this
level for 2 hours before it was allowed to cool down at a rate of
5.degree. C./min.
[0084] This carrier is designated as carrier H. Testing the carrier
showed that it has the following specifications:
TABLE-US-00016 Crush strength 22.6 lb Water absorption 29.4 ml/100
g BET surface area 1.15 m.sup.2/g
EXAMPLE 9
[0085] Step 1 The following components were mixed thoroughly:
TABLE-US-00017 250 g alpha alumina(I)* 250 g alpha alumina(II)'' 15
g KI5M Methocel (methyl cellulose) 2 g Acacia 25 g mineral oil 7.8
g 50%Ti solution (as titanium bis-ammonium lactato dihydroxide) l0
g 10 g Talc 115 g Water
[0086] Mixing, shaping, and drying these components followed the
same procedure as in Example 1. The firing scheme involved
temperature ramping at a rate of 4.degree. C./min up to
1375.degree. C. The temperature of the furnace was held at this
level for 2 hours before it was allowed to cool down at a rate of
5.degree. C./min. This carrier is designated as carrier I. Testing
the carrier showed that it has the following specifications:
TABLE-US-00018 Crush strength 14.4 lb Water absorption 33.3 ml/100
g BET surface area 0.88 m.sup.2/g
EXAMPLE 10
[0087] Step 1 The following components were mixed thoroughly:
TABLE-US-00019 176 g alpha alumina(II)** 232 g Hydrated alumina
(Gibssite) 48 g Boehmite 12 g K1SM Methocel (methyl cellulose) 2 g
Acacia 80 g azodicarbonamide 25 g mineral oil 6.2 g 50%Ti solution
(as titanium bis-ammonium lactato dihydroxide)10 g 16 g Talc 108 g
Water
[0088] Mixing, shaping, and drying these components followed the
same procedure as in Example I. The firing scheme involved
temperature ramping at a rate of 4.degree. C./min up to
1375.degree. C. The temperature of the furnace was held at this
level for 2 hours before it was allowed to cool down at a rate of
5.degree. C./min. This carrier is designated as carrier J. Testing
the carrier showed that it has the following specifications:
TABLE-US-00020 Crush strength 17.4 lb Water absorption 29.6 ml/100
g BET surface area 1.03 m.sup.2/g
EXAMPLE 11
[0089] Step 1 The following components were mixed thoroughly:
TABLE-US-00021 250 g alpha alumina(I)* 250 g alpha alumina(IV)****
15 g K15M Methocel (methyl cellulose) 2 g Acacia 4.8 g Expancel 25
g Petroleum Jelly 24 g 34% Colloidal silica suspended in water 0.84
g Boric acid 10 g Magnesium stearate 116 g Water ****Alpha Alumina
(IV) is a highly pure alpha alumina that has a BET surface area of
14 m.sup.2/g and Na contents of less than 0.4%
[0090] Mixing, shaping, and drying these components followed the
same procedure as in Example 1. The firing scheme involved
temperature ramping at a rate of 4.degree. C./min up to
1450.degree. C. The temperature of the furnace was held at this
level for 2 hours before it was allowed to cool down at a rate of
5.degree. C./min. This carrier is designated as carrier K. Testing
the carrier showed that it has the following specifications:
TABLE-US-00022 Crush strength 36.3 lb Water absorption 25.1 ml/l00
g BET surface area 0.89 m.sup.2/g
EXAMPLE 12
[0091] Step 1 The following components were mixed thoroughly:
TABLE-US-00023 1075 g alpha alumina (1)* 1075 alpha alumina
(IV)**** 65 g K15M Methocel (methyl cellulose) 9 g Acacia 124 g
Expancel 110 g Petroleum Jelly 3.6 g Boric acid 43 g Magnesium
stearate 516 g Water ****Alpha Alumina (IV) is a highly pure alpha
alumina that has a BET surface area of 14 m.sup.2/g and Na contents
of less than 0.4%.
[0092] Mixing, shaping, and drying these components followed the
same procedure as in Example 1. The firing scheme involved
temperature ramping at a rate of 4.degree. C./min up to
1500.degree. C. The temperature of the furnace was held at this
level for 2 hours before it was allowed to cool down at a rate of
5.degree. C./min. Testing the carrier showed that it has the
following specifications:
TABLE-US-00024 Crush strength 16.1 lb Water absorption 42.8 ml/100
g BET surface area 1.32 m.sup.2/g
EXAMPLE 13
[0093] a. Preparation of a Stock Solution of Silver/Amine
Complex:
[0094] A silver solution was prepared using the following
components
[0095] (parts are by weight):
[0096] Silver oxide--834 parts
[0097] Oxalic acid--442 parts
[0098] De-ionized water--1180 parts
[0099] Ethylenediamine--508 parts
[0100] Silver oxide was mixed with water, at room temperature,
followed by the gradual addition of the oxalic acid. The mixture
was stirred for 15 minutes and at that point, the color of the
black suspension of silver oxide had changed to the light brown
color of silver oxalate. The mixture was filtered and the solids
were washed with 3 liters of de-ionized water.
[0101] The sample was placed in an ice bath and stirred while
ethylenediamine and water (as a 66%/34% mixture) were added slowly
in order to maintain the reaction temperature lower than 33.degree.
C. After the addition of all the ethylenediamine/water mixture, the
solution was filtered at room temperature. The clear filtrate was
utilized as a silver/amine stock solution for the catalyst
preparation.
[0102] b. Promoters Addition:
[0103] The clear stock solution was diluted with the 66/34 mixture
of ethylenediamine/water. In addition, Cs hydroxide and ammonium
hydrogen sulfate were added to the diluted silver solution in order
to prepare a catalyst containing 11% silver, and the suitable
amount of cesium and sulfur.
[0104] c. Catalyst Impregnation:
[0105] A 150 g sample of the carrier was placed in a pressure
vessel and then exposed to vacuum until the pressure was reduced to
50 mm Hg. 200 ml of the adjusted silver/promoters solution was
introduced to the flask while it is still under vacuum. The
pressure of the vessel was allowed to rise to atmospheric pressure
and its contents were shaken for few minutes. The catalyst was
separated from the solution and was now ready for calcination.
[0106] d. Catalyst Calcination:
[0107] Calcination, deposition of silver, was induced by heating
the catalyst up to the decomposition temperature of the silver
salt. This was achieved via heating in a furnace that has several
heating zones in a controlled atmosphere. The catalyst was loaded
on a moving belt that entered the furnace at ambient temperature.
The temperature was gradually increased as the catalyst passed from
one zone to the next. It was increased, up to 400.degree. C., as
the catalyst passed through seven heating zones. After the heating
zones, the belt passed through a cooling zone that gradually cooled
the catalyst to a temperature lower than 100.degree. C. The total
residence time in the furnace was 22 minutes. The atmosphere of the
furnace was controlled through the use of nitrogen flow in the
different heating zones.
[0108] e. Catalyst Testing:
[0109] The catalysts were tested in a stainless steel tube that was
heated by a molten salt bath. A gas feed mixture containing 15%
ethylene, 7% oxygen, and 78% inert, mainly nitrogen and carbon
dioxide, was used to test the catalyst at 300 p.s.i.g. The
temperature of the reaction was adjusted in order to obtain a
standard ethylene oxide productivity of 160 Kg per hour per m.sup.3
of catalyst.
EXAMPLE 14
[0110] Carriers A-K were used to prepare catalysts for the
oxidation of ethylene to ethylene oxide in an identical procedure
to that illustrated in example 13. The results of the catalyst
testing are summarized in Table 1.
TABLE-US-00025 TABLE 1 Results of catalyst testing Reaction
Catalyst Carrier Selectivity Temp .degree. C. 14-a A 83.5 235 14-b
B 83.6 223 14-c C 82.6 230 14-d D 83.6 236 14-e E 83.3 233 14-f F
83.2 230 14-g G 83 233 14-h H 83 226 14-i I 82.5 247 14-j J 84 240
14-k K 82 243
[0111] While the present invention has been particularly shown and
described with reference to preferred embodiments, it will be
readily appreciated by those of ordinary skill in the art that
various changes and modifications may be made without departing
from the spirit and scope of the invention. It is intended that the
claims be interpreted to cover the disclosed embodiment, those
alternatives which have been discussed above and all equivalents
thereto.
* * * * *