U.S. patent application number 10/133058 was filed with the patent office on 2003-03-06 for sulfur absorbents.
This patent application is currently assigned to Phillips Petroleum Company. Invention is credited to Bonnell, Ralph E., Khare, Gyanesh P..
Application Number | 20030042646 10/133058 |
Document ID | / |
Family ID | 25246914 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030042646 |
Kind Code |
A1 |
Khare, Gyanesh P. ; et
al. |
March 6, 2003 |
Sulfur absorbents
Abstract
A composition and method of making a strength enhanced
composition are described. The composition comprises zinc oxide,
silica and colloidal oxide solution. The colloidal oxide solution
is utilized as a binding agent to provide a strength enhanced
absorbent composition that can be utilized in an absorption process
for the purpose of removing sulfur contaminants from fluid
streams.
Inventors: |
Khare, Gyanesh P.;
(Bartlesville, OK) ; Bonnell, Ralph E.; (Dewey,
OK) |
Correspondence
Address: |
RICHMOND, HITCHCOCK,
FISH & DOLLAR
P.O. Box 2443
Bartlesville
OK
74005
US
|
Assignee: |
Phillips Petroleum Company
Bartlesville
OK
|
Family ID: |
25246914 |
Appl. No.: |
10/133058 |
Filed: |
April 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10133058 |
Apr 26, 2002 |
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09047677 |
Mar 25, 1998 |
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6432873 |
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09047677 |
Mar 25, 1998 |
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08694975 |
Aug 9, 1996 |
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5780001 |
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08694975 |
Aug 9, 1996 |
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07826567 |
Jan 27, 1992 |
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Current U.S.
Class: |
264/117 ;
502/253; 502/405; 516/79 |
Current CPC
Class: |
B01D 53/52 20130101;
B01J 20/06 20130101; B01D 2253/106 20130101; B01J 20/18 20130101;
B01D 2255/20707 20130101; B01D 2255/20792 20130101; B01J 20/28011
20130101; B01D 2255/20738 20130101; B01D 2255/20784 20130101; B01J
20/3078 20130101; B01D 53/02 20130101; B01D 2253/304 20130101; B01J
20/0244 20130101; B01D 2255/20769 20130101; B01J 20/28004 20130101;
B01J 20/28019 20130101; B01D 2255/20761 20130101; B01J 20/103
20130101; B01D 2255/2061 20130101; B01D 2255/20753 20130101; B01D
2258/02 20130101; B01D 2255/2098 20130101; B01D 2255/20715
20130101; B01J 20/2803 20130101; B01D 2259/402 20130101; B01J 20/14
20130101; B01D 2259/4009 20130101; B01D 2257/304 20130101; B01D
2253/1124 20130101; B01D 2255/2073 20130101; B01D 2255/20776
20130101; B01D 2255/2094 20130101; B01J 20/12 20130101; B01J
2220/42 20130101; B01J 20/28033 20130101 |
Class at
Publication: |
264/117 ; 516/79;
502/253; 502/405 |
International
Class: |
B29B 009/08; B01J
021/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 1993 |
CA |
2,087926 |
Claims
That which is claimed is:
1. A composition comprising: zinc oxide, silica, and colloidal
oxide solution.
2. A composition as recited in claim 1 wherein said colloidal oxide
solution comprises finely divided, colloidal-size particles of a
metal oxide compound that is uniformly dispersed in a liquid
medium.
3. A composition as recited in claim 2 wherein the ratio of zinc
oxide to silica is in the range of from about 0.25:1 to about 4:1
and wherein the amount of colloidal oxide solution present in said
composition is such that the metal oxide compound content of said
composition is in the range of from an amount effective for
providing an agglomerate of said composition having a crush
strength at least about 3 lb.sub.f to about 30 weight percent of
the total weight of said composition.
4. A composition as recited in claim 3 wherein said finely divided,
colloidal-size particles have a medium particle size in the range
of from about 50 angstroms to about 10,000 angstroms and wherein
said liquid medium comprises water and wherein the concentration of
said finely divided, colloidal-size particles in said colloidal
oxide solution is in the range of from about 1 weight percent to
about 30 weight percent.
5. A composition as recited in claim 4 wherein said metal oxide
compound is selected from the group consisting of alumina, silica,
titania, zirconia, tin oxide, antimony oxide, cesium oxide, yttrium
oxide, copper oxide, iron oxide, manganese oxide, molybdenum oxide,
tungsten oxide, chromium oxide and mixtures of any two or more
thereof.
6. A composition as recited in claim 5 wherein said composition is
in the form of a dried agglomerate.
7. A composition as recited in claim 6 wherein said composition is
in the form of a calcined agglomerate.
8. A composition as recited in claim 7 further comprising a group
VIII metal oxide promoter.
9. A composition as recited in claim 8 wherein said group VIII
metal oxide promoter is present in said composition in the range of
from about 0.1 weight percent to about 15 weight percent.
10. A composition as recited in claim 9 wherein said group VIII
metal oxide promoter is nickel oxide.
11. A composition as recited in claim 10 wherein the crush strength
of said composition is at least about 5 lb.sub.f.
12. An absorption composition comprising a mixture consisting
essentially of zinc oxide, silica, and colloidal oxide solution,
said mixture having been dried to remove the liquid medium of said
colloidal oxide solution thereby forming a dried mixture having a
crush strength of at least 3 lb.sub.f and a sulfur loading capacity
of at least about 11 weight percent.
13. An absorption composition as recited in claim 12 wherein said
colloidal oxide solution comprises finely divided, colloidal-size
particles of a metal oxide compound selected from the group
consisting of alumina, silica, titania, zirconia, tin oxide,
antimony oxide, cesium oxide, yttrium oxide, copper oxide, iron
oxide, manganese oxide, molybdenum oxide, tungsten oxide, chromium
oxide and mixtures of any two or more thereof having a medium
particle size in the range of from about 50 angstroms to about
10,000 angstroms uniformly dispersed in an aqueous solvent.
14. An absorption composition as recited in claim 13 wherein the
ratio of zinc oxide to silica in said mixture is in the range of
from about 0.25:1 to about 4:1 and wherein the amount of said metal
oxide compound present in said dried mixture is present in the
range of from about 1 weight percent to about 30 weight percent of
the total weight of said dried mixture.
15. An absorption composition as recited in claim 14 wherein said
dried mixture further consists essentially of a group VIII metal
oxide promoter which is present in said dried mixture in the range
of from about 0.1 weight percent to about 15 weight percent.
16. An absorption composition as recited in claim 15 wherein said
group VIII metal oxide promoter is nickel oxide and wherein said
dried mixture is further calcined to produce a promoted calcined
mixture having a crush strength of at least about 5 lb.sub.f.
17. A method for preparing a high crush strength absorption
composition comprising the step of: spraying a colloidal oxide
solution onto a homogeneous mixture comprising zinc oxide and
silica during tumbling agglomeration to form an agglomerate.
18. A method as recited in claim 17 wherein the ratio of zinc oxide
to silica in said homogeneous mixture is in the range of from about
0.25:1 to about 4:1.
19. A method as recited in claim 18 wherein said colloidal oxide
solution comprises finely divided, colloidal-size particles of a
metal oxide compound that is uniformly dispersed in a liquid
medium.
20. A method as recited in claim 19 wherein said finely divided,
colloidal-size particles have a medium particle size in the range
of from about 50 angstroms to about 10,000 angstroms and wherein
said liquid medium comprises water and wherein the concentration of
said finely divided, colloidal-size particles in said colloidal
oxide solution is in the range of from about 1 weight percent to
about 30 weight percent.
21. A method as recited in claim 20 wherein the amount of said
colloidal oxide solution utilized in said spraying step is such to
provide said agglomerate with a content of said metal oxide
compound of from an amount effective for providing said agglomerate
having a crush strength at least about 3 lb.sub.f to about 30
weight percent of the total weight of said agglomerate.
22. A method for preparing a high crush strength absorption
composition comprising: agglomerating a homogeneous powder mixture
comprising zinc oxide and silica by spraying a colloidal oxide
solution upon said homogeneous powder mixture while tumbling said
homogeneous powder mixture within a inclined rotating disk having a
rim to form an agglomerate substantially in the shape of a
sphere.
23. A method as recited in claim 22 further comprising: drying said
agglomerate to form a dried agglomerate.
24. A method as recited in claim 23 further comprising: calcining
said dried agglomerate to form a calcined agglomerate having a
crush strength of at least about 3 lb.sub.f.
25. A method as recited in claim 24 wherein the ratio of zinc oxide
to silica in said homogeneous powder mixture is in the range of
from about 0.25:1 to about 4:1 and wherein the amount of colloidal
oxide mixture utilized is such to provide said calcined agglomerate
with a metal oxide compound content in the range of from about 0.1
weight percent to about 30 weight percent of the total weight of
said calcined agglomerate.
26. A method as recited in claim 25 further comprising: adding a
Group VIII metal oxide promoter to said dried agglomerate in an
amount such as to give a metal oxide compound content in said dried
agglomerate in the range of from about 1 weight percent to about 30
5 weight percent to give a promoted agglomerate.
27. A method as recited in claim 26 further comprising: calcining
said promoted agglomerate to give a promoted calcined agglomerate
having a crush strength of at least 5 lb.sub.f.
28. A method for preparing a high crush strength absorption
composition comprising the steps of: (a) mixing zinc oxide and
silica with water to form a mixture; (b) drying said mixture to
form a dried mixture; (c) milling said dried mixture to form a
powder; (d) spraying said powder with a colloidal oxide solution
during tumbling agglomeration to form an agglomerate; (e) drying
said agglomerate to form a dried agglomerate; and (f) calcining
said dried agglomerate to form a calcined to agglomerate.
29. A method as recited in claim 28 wherein said agglomerate or
calcined agglomerate, or both, is substantially in the shape of a
sphere.
30. A method as recited in claim 29 wherein said calcined
agglomerate has a crush strength of at least about 3 lbs.
31. A method as recited in claim 30 wherein said colloidal oxide
solution comprises finely divided, colloidal-size particles of a
metal oxide compound selected from the group consisting of alumina,
silica, titania, zirconia, tin oxide, antimony oxide, cesium oxide,
yttrium oxide, copper oxide, iron oxide, manganese oxide,
molybdenum oxide, tungsten oxide, chromium oxide and mixtures of
any two or more thereof that is uniformly dispersed in a liquid
medium.
32. A method as recited in claim 31 wherein said finely divided,
colloidal-size particles have a medium particle size in the range
of from about 50 angstroms to about 10,000 angstroms and wherein
said liquid medium is water and wherein the concentration of said
finely divided, colloidal-size particles in said colloidal oxide
solution is in the range of from about 1 weight percent to about 30
weight percent.
33. A method as recited in claim 32 wherein the ratio of zinc oxide
to silica utilized in mixing step (a) is in the range of from about
0.25:1 to about 4:1.
34. A method as recited in claim 33 wherein the amount of colloidal
oxide solution utilized in spraying step (d) is such to provide
said calcined agglomerate of step (f) or said dried agglomerate of
step (e) with a metal oxide compound content in the range of from
about 0.1 weight percent to about 30 weight percent of the total
weight of either said dried agglomerate or said calcined
agglomerate.
35. A method as recited in claim 34 wherein the spraying step (d)
utilizes an amount of said colloidal oxide solution that is
effective in producing said calcined agglomerate of step (f) having
a crush strength of at least about 3 lbs.
36. A product prepared by the method of claim 17.
37. A product prepared by the method of claim 18.
38. A product prepared by the method of claim 19.
39. A product prepared by the method of claim 20.
40. A product prepared by the method of claim 21.
41. A product prepared by the method of claim 22.
42. A product prepared by the method of claim 23.
43. A product prepared by the method of claim 24.
44. A product prepared by the method of claim 25.
45. A product prepared by the method of claim 26.
46. A product prepared by the method of claim 27.
47. A product prepared by the method of claim 28.
48. A product prepared by the method of claim 29.
49. A product prepared by the method of claim 30.
50. A product prepared by the method of claim 31.
51. A product prepared by the method of claim 32.
52. A product prepared by the method of claim 33.
53. A product prepared by the method of claim 34.
54. A product prepared by the method of claim 35.
55. A process for absorbing hydrogen sulfide from a fluid stream,
said process comprising: (a) mixing zinc oxide and silica to
provide a dry homogeneous mixture; (b) providing said dry
homogeneous mixture within a pan of a tumbling agglomerator; (c)
spraying a colloidal oxide solution, wherein said colloidal oxide
solution comprises particles of a metal oxide compound dispersed in
a liquid medium said metal oxide compound comprises colloidal-size
particles having a median particle size in a range from about 50
angstroms to about 10,000 angstroms upon said dry homogeneous
mixture while rotating said pan to thereby form pellets; (d) drying
said pellets to provide dried pellets; and (e) contacting said
dried pellets with a fluid stream containing hydrogen sulfide under
conditions suitable for absorbing hydrogen sulfide.
56. A process for absorbing hydrogen sulfide from a fluid stream,
said process comprising: (a) mixing zinc oxide and silica to
provide a dry homogeneous mixture; (b) providing said dry
homogeneous mixture within a pan of a tumbling agglomerator; (c)
spraying a colloidal oxide solution, wherein said colloidal oxide
solution comprises particles of a metal oxide compound dispersed in
a liquid medium said metal oxide compound comprises colloidal-size
particles having a median particle size in a range from about 50
angstroms to about 10,000 angstroms upon said dry homogeneous
mixture while rotating said pan to thereby form pellets; (d)
calcining said dried pellets to provide calcined pellets; and (e)
contacting said calcined pellets with a fluid stream containing
hydrogen sulfide under conditions suitable for absorbing hydrogen
sulfide.
57. A process as recited in claim 55 wherein the ratio of zinc
oxide to silica in said dry homogeneous mixture is in the range of
from about 0.25:1 to about 4:1 and wherein the amount of colloidal
oxide present in said pellets is such that the metal oxide content
of said pellets is in the range of from an amount effective for
providing said dried pellets with a crush strength of at least
about 3 lb.sub.f to about 30 weight percent.
58. A process as recited in claim 56 wherein the ratio of zinc
oxide to silica in said dry homogeneous mixture is in the range of
from about 0.25:1 to about 4:1 and wherein the amount of colloidal
oxide present in said pellets is such that the metal oxide content
of said pellets is in the range of from an amount effective for
providing said calcined pellets with a crush strength of at least
about 3 lb.sub.f to about 30 weight percent.
59. A process as recited in claim 55 wherein said colloidal-size
particles in said colloidal oxide solution are in the range of from
about 1 weight percent to about 30 weight percent.
60. A process as recited in claim 56 wherein said colloidal-size
particles in said colloidal oxide solution are in the range of from
about 1 weight percent to about 30 weight percent.
61. A process as recited in claim 59 wherein said metal oxide
compound is selected from the group consisting of alumina, silica,
titania, zirconia, tin oxide, antimony oxide, cesium oxide, yttrium
oxide, copper oxide, iron oxide, manganese oxide, molybdenum oxide,
tungsten oxide, chromium oxide and mixtures of any two or more
thereof.
62. A process as recited in claim 60 wherein said metal oxide
compound is selected from the group consisting of alumina, silica,
titania, zirconia, tin oxide, antimony oxide, cesium oxide, yttrium
oxide, copper oxide, iron oxide, manganese oxide, molybdenum oxide,
tungsten oxide, chromium oxide and mixtures of any two or more
thereof.
63. A process as recited in claim 61 wherein said dried pellets
further comprise a Group VIII metal oxide.
64. A process as recited in claim 62 wherein said calcined pellets
further comprise a Group VIII metal oxide.
65. A process as recited in claim 63 wherein said Group VIII metal
oxide is present in said dried pellets in the range of from about
0.1 weight percent to about 15 weight percent.
66. A process as recited in claim 64 wherein said Group VIII metal
oxide is present in said calcined pellets in the range of from
about 0.1 weight percent to about 15 weight percent.
67. A process as recited in claim 65 wherein said Group VIII metal
oxide is nickel oxide.
68. A process as recited in claim 66 wherein said Group VIII metal
oxide is nickel oxide.
69. A process as recited in claim 67 wherein the crush strength of
said dried pellets is at least about 5 lb.sub.f.
70. A process as recited in claim 68 wherein the crush strength of
said calcined pellets is at least about 5 lb.sub.f.
Description
[0001] This is a continuation of application Ser. No. 07/826,567
filed on Jan. 27, 1992.
[0002] This invention relates to sulfur-absorbent compositions, the
manufacture of sulfur absorbents and their use.
[0003] The removal of sulfur from fluid streams can be desirable or
necessary for a variety of reasons. If the fluid stream is to be
released as a waste stream, removal of sulfur from the fluid stream
can be necessary to meet the sulfur emission requirements set by
various air pollution control authorities. Such requirements are
generally in the range of about 10 ppm to 500 ppm of sulfur in the
fluid stream. If the fluid stream is to be burned as a fuel,
removal of sulfur from the fluid stream can be necessary to prevent
environmental pollution. If the fluid stream is to be processed,
removal of the sulfur is often necessary to prevent the poisoning
of sulfur sensitive catalysts or to satisfy other process
requirements.
[0004] Various absorption compositions have been used to remove
sulfur from fluid streams when the sulfur is present as hydrogen
sulfide. These absorption compositions can be manufactured by a
variety of methods which include, for example, extrusion production
techniques. A problem that is often encountered in the production
of these absorption compositions is equipment wear caused by the
abrasive nature of the absorption materials being manufactured. In
certain attempts to produce commercial quantities of absorbent
compositions, excessive equipment wear and downtime caused by the
abrasive characteristics of the absorption material components
have, in effect, rendered the production commercially unviable.
[0005] It is desirable for an absorbent composition to not only
have a high sulfur-absorption capacity but also to have sufficient
mechanical strength to permit its use as a contact material that is
placed as an absorbent bed within a contact vessel. A low
mechanical strength or low crush strength of an absorbent
agglomerate can lead to excessive attrition thereby causing
undesirable operating difficulties in commercial processes which
utilize such absorbent agglomerates.
[0006] A further property of which it is desirable for absorption
compositions to have is the ability to absorb large quantities of
sulfur. This capability to absorb large amounts and maintain high
concentrations of sulfur is sometimes referred to as "sulfur
loading" and is generally reported in terms of percent sulfur
loading. The term "percent sulfur loading" is generally defined as
the parts by weight of sulfur absorbed upon the surface or within
the pores of an absorption composition per parts by weight of the
total absorbent composition multiplied by a factor of 100. It is
desirable to have an absorption composition with the largest
possible sulfur loading capacity.
[0007] An additional property desirable for an absorption
composition is the ability to be regenerated to its original
absorbing composition state after the absorbing composition has
become spent. An absorbing composition generally becomes spent when
its sulfur loading capacity has essentially been used up. It is
desirable for the absorbing composition to be able to undergo
numerous regeneration cycles without losing its sulfur loading
capacity and other desirable properties.
[0008] Even though many absorbing compositions can effectively
absorb hydrogen sulfide from fluid streams containing hydrogen
sulfide, it is not uncommon for many of these absorbing
compositions to effectively oxidize significant amounts of hydrogen
sulfide to sulfur dioxide when contacted with such fluid streams.
The resulting sulfur dioxide is not removed from the fluid stream
by the absorbent composition and thus passes through the absorbent
material with the contacted fluid stream. This phenomena is
sometimes called "sulfur slippage". It is desirable to have an
absorption material that has a high capacity to absorb sulfur from
a fluid stream but which minimizes the amount of sulfur
slippage.
[0009] In some absorption compositions, the addition of a promoter
compound can be used to allow for easier regeneration of the
absorbing material.
[0010] It is, thus, an object of the present invention to provide
an improved absorption composition capable of removing certain
sulfur compounds from fluid streams.
[0011] Another object of this invention is to provide an absorption
process for the removal of sulfur from fluid streams.
[0012] Yet another object of the present invention is to provide an
absorption composition characterized by exceptional mechanical
strength and an improved process for the production of such
composition.
[0013] A still further object of this invention is to provide a
method of manufacturing an absorption composition that minimizes
equipment wear and that produces an absorption composition having a
high mechanical strength.
[0014] In accordance with one aspect of this invention, there is
provided a composition comprising zinc oxide, silica and a
colloidal oxide solution. In accordance with another aspect of this
invention, there is provided a method for preparing a high crush
strength absorption composition comprising the step of spraying a
colloidal oxide solution onto a homogeneous mixture comprising zinc
oxide and silica during tumbling agglomeration to form an
agglomerate. Another aspect of the present invention includes an
absorption process wherein a fluid stream is contacted under
absorption conditions with an absorption composition comprising
zinc oxide, silica and a colloidal oxide solution.
[0015] Other objects, advantages and features of this invention
will become apparent from a study of this disclosure, the appended
claims and the drawings in which:
[0016] FIG. 1 is a schematic process flow diagram illustrating a
preferred embodiment of the inventive process for removing sulfur
compounds from contaminated fluid streams; and
[0017] FIG. 2 is a schematic representation of the inventive method
for preparation of an absorption composition illustrating certain
features of the present invention.
[0018] The composition of matter of the present invention can
suitably comprise, consist of, or consist essentially of, zinc
oxide, silica and colloidal oxide solution. It has been found that
an absorption composition having certain exceptional physical
properties can be produced when a colloidal oxide solution is
utilized in the production of the absorption composition or
absorption material. In particular, the absorption composition can
have improved mechanical strength, or crush strength, by the
utilization of a colloidal oxide solution when the material is
manufactured. A further advantage from the utilization of a
colloidal oxide solution as a component of the composition of
matter of this invention is that it permits the use of tumbling
agglomeration techniques in the production of an agglomerate,
rather than the use of extrusion techniques, to agglomerate the
material components of the composition of matter of this invention.
Experience has demonstrated that the use of silica compounds as a
component of absorbent compositions causes excessive equipment wear
when agglomerates are formed by use of extrusion equipment. The
excessive equipment wear that results from the abrasive
characteristics of silica components of the agglomerate materials
has rendered the production of such absorbent agglomerates
commercially unviable. The use of a colloidal oxide solution as a
binder material in the manufacture of the absorbent composition
permits the production of the agglomerates by use of tumbling
agglomeration techniques, while at the same time, it provides the
unexpected result of producing an agglomerate material that has a
higher crush strength than an agglomerate produced by extrusion
agglomeration techniques.
[0019] In another embodiment of this invention, there is provided a
composition suitably comprising, consisting of, or consisting
essentially of zinc oxide, silica and colloidal oxide solution
wherein the ratio of zinc oxide to silica in the composition is in
the range of from about 0.25 to 1 (0.25:1) to about 4 to 1 (4:1).
Preferably, the ratio of zinc oxide to silica in the composition of
matter of this invention can be in the range of from about 0.5 to 1
(0.5:1) to about 1.5 to 1 (1.5:1); but, most preferably, the ratio
of zinc oxide to silica should range from 0.75 to 1 (0.75:1) to
1.25 to 1 (1.25:1).
[0020] The colloidal oxide solution component of the composition of
matter described herein should be present in an amount which is
effective for providing sufficient binding properties to give a
final agglomerate of the components of the composition of this
invention, which has been dried or calcined, or both, having a
crush strength of at least about 3 lbs force (lb.sub.f). The final
agglomerate can preferably have a crush strength in the range of
from about 3 lb.sub.f to about 6 lb.sub.f; but, most preferably,
the crush strength can range from 3.5 lb.sub.f to 5.5 lb.sub.f. The
term "crush strength" as used herein when referring to the
mechanical properties of the absorbent agglomerates is that which
is determined by standard ASTM method, D4179-88A, entitled
"Standard Test Method For Single Pellet Crush Strength of Formed
Catalyst Spheres". The Standard Test Method ASTM D4179-88A is
incorporated herein by reference.
[0021] Alternatively, it is desirable for the amount of colloidal
oxide solution component of the composition of the invention to be
such that the metal oxide compound content of the composition is in
the range of from an amount effective for providing an agglomerate
of said composition having a crush strength at least about 3
lb.sub.f to about 30 weight percent of the total weight of said
composition. Preferably, however, the amount of colloidal oxide
solution component of the composition of matter of this invention
is such that the metal oxide compound content is in the range of
from about 5 weight percent to about 20 weight percent; but, most
preferably, the metal oxide content shall range from 5 weight
percent to 15 weight percent.
[0022] The composition comprising, consisting of, or consisting
essentially of, zinc oxide, silica and colloidal oxide solution can
additionally be dried to form a dried agglomerate or calcined to
form a calcined agglomerate or alternatively, both dried and
calcined. The drying step is used generally to remove the liquid
medium of the colloidal oxide solution from the composition of
matter of this invention. The drying of the composition can be
conducted at any suitable temperature for removing the liquid
medium of the colloidal oxide solution; but, preferably, the drying
step should be conducted in the range of from about 150.degree. F.
to about 550.degree. F. More preferably, however, the drying step
shall range from about 190.degree. F. to about 480.degree. F.
Generally, the time period for such drying shall range from about
0.5 hour to about 4 hours, and more preferably, the drying time
shall range from about 1 hour to about 3 hours.
[0023] The composition comprising, consisting of, or consisting
essentially of, zinc oxide, silica and colloidal oxide solution can
be calcined, after undergoing a drying step, to form a calcined
agglomerate. The calcination of the composition or agglomerate can
be conducted under any suitable calcination conditions; but,
preferably, the composition shall be calcined in the presence of
either oxygen or an oxygen-containing fluid at a temperature
suitable for achieving the desired degree of calcination.
Generally, the temperature shall range from about 700.degree. F. to
about 1400.degree. F.; and, more preferably, the calcination
temperature shall range from about 900.degree. F. to about
1300.degree. F. The calcining step can be conducted for a period of
time suitable for achieving the desired degree of calcination, but
generally, the time for calcination shall range from about 0.5
hours to about 4 hours. Most preferably, the calcination time shall
range from about 1 hour to about 3 hours to produce a calcined
absorbing composition.
[0024] It can further be desirable to add a Group VIII metal oxide
promoter to the composition comprising, consisting of, or
consisting essentially of, zinc oxide, silica and colloidal oxide
solution, which has previously been either dried or calcined, or
both, to produce the aforementioned dried agglomerate or calcined
agglomerate. It has been found that the addition of certain metal
promoters provide certain improved physical and chemical properties
to the absorbent composition. These improved properties include,
for example, the ability of the composition to hydrogenate sulfur
oxide species to hydrogen sulfide and an improved ability of the
absorbent composition to easily be regenerated after becoming
spent. A further improvement to the composition resulting from the
addition of metal promoters is in the mechanical strength of the
composition once it has been promoted and subsequently dried, or
calcined, or both. By incorporating a metal oxide promoter into the
composition of matter described herein followed by drying and/or
calcining the material, the resultant agglomerate will have an
improved mechanical strength or crush strength of at least about 5
lbs.sub.f Preferably, however, the crush strength of the promoted
composition shall range from about 6 lbs.sub.f to about 14
lbs.sub.f, and most preferably, the crush strength shall range from
about 7 lbs.sub.f to about 13 lbs.sub.f.
[0025] An alternative composition of matter of this invention
includes a composition comprising a mixture comprising, consisting
of, or consisting essentially of, zinc oxide, silica and colloidal
oxide solution that has undergone a drying step or a calcining
step, or both. The drying of the mixture results in removing from
the composition or mixture, the liquid medium of the colloidal
oxide solution to thereby form a dried mixture; or in the case
where the composition is either both dried and calcined or merely
calcined, the calcining of the composition or mixture suitably
provides a calcined agglomerate. The dried mixture or the calcined
agglomerate can optionally be impregnated with a metal oxide
promoter for the purposes of improving performance of the
composition as an absorbent and for improving crush strength of the
composition by producing a promoted calcined mixture. The metal
oxide promoted composition, having undergone a further calcining
step, can have a crush strength of at least about 5 lbs.sub.f.
Preferably, the crush strength of the metal oxide promoted
absorbent composition, which has been calcined, can range from
about 6 lbs.sub.f to about 14 lbs.sub.f, most preferably, however,
the crush strength shall range from 7 lbs.sub.f to 13
lbs.sub.f,
[0026] As for the amount of colloidal oxide solution utilized in
the mixture comprising, consisting of, or consisting essentially of
zinc oxide, silica and colloidal solution, it is such that the
amount of metal oxide compound present in the dried mixture will
preferably range from about 1 weight percent to about 30 weight
percent of the total weight of the dried mixture. Preferably,
however, the amount of colloidal oxide solution utilized in the
mixture should be such that the metal oxide content of the dried
mixture shall range from about 5 weight percent to about 20 weight
percent. Most preferably, the quantity of colloidal oxide solution
present in the mixture of this invention will be such that the
amount of metal oxide content in the final dried mixture shall
range from 5 weight percent to 15 weight percent.
[0027] The ratio of zinc oxide to silica in the mixture of the
absorption composition can be in the range of from about 0.25 to 1
(0.25:1) to about 4 to 1 (4:1). Preferably, the ratio of zinc oxide
to silica in the mixture of the absorption composition can range
from about 0.5 to 1 (0.5:1) to about 1.5 to 1 (1.5:1); but, most
preferably, the ratio of zinc oxide to silica in the mixture of the
absorption composition can range from 0.75 to 1 (0.75:1) to about
1.25 to 1 (1.25:1).
[0028] The silica component of the compositions described herein
can be any suitable form of silica, including, but not limited to,
naturally occurring silica, such as a diatomaceous earth, which is
also called kieselguhr or diatomite or celite, and synthetic
silica, such as zeolites, high silica zeolites, precipitated or
spray dried silicas or clay and plasma-treated silica or clay.
Furthermore, the silica can be in the form of one or more silica
compounds that are convertible to silica under the conditions of
absorption composition preparation described herein. Examples of
other suitable types of silica that can be used include diatomite,
silicate, silica colloid, flame hydrolyzed silica, hydrolyzed
silica, and precipitated silica. Examples of silicon compounds that
are convertible to silica under the production conditions used in
the preparation of the absorption composition described herein
include, silicic acid, sodium silicate, and ammonium silicate.
[0029] Generally, zinc oxide is the primary active component of the
compositions of the invention, and the zinc oxide will be present
in the compositions in an amount suitable for providing the desired
absorption capacity. The zinc oxide component of the absorption
composition can be either in the form of zinc oxide or in the form
of one or more zinc compounds that are convertible to zinc oxide
under the conditions of preparation described herein. Examples of
such zinc compounds include zinc sulfide, zinc sulfate, zinc
hydroxide, zinc carbonate, zinc acetate, and zinc nitrate.
Preferably, zinc oxide is in the form of a powdered zinc oxide.
[0030] The colloidal oxide solution component of the compositions
of matter described herein is generally a chemical sol comprising a
metal oxide compound or material contained in a solution or a
liquid medium. It is preferred that the colloidal oxide solution
comprise finely divided, colloidal-size particles of a metal oxide
compound that is uniformly dispersed in a liquid medium. The finely
divided particles are not necessarily in the molecular state, but
they are generally polymolecular particles having a size of which
99 percent of such particles will be in the size range of from
about 10 angstroms to about 10,000 angstroms. It is generally
preferred, however, that 99 percent of the particles have a size in
the range of from about 50 angstroms to about 10,000 angstroms;
and, most preferably, 99 percent of the particles shall have a size
in the range of from 50 angstroms to 5,000 angstroms. As for the
medium particle size of the colloidal oxide compounds, it is
desirable to have a medium size in the range of from about 50
angstroms to about 10,000 angstroms. Preferably, the medium
particle size should range from about 10 angstroms to about 1000
angstroms, and most preferably, the medium particle size can range
from 100 angstroms to 500 angstroms.
[0031] Typical solid concentrations in a colloidal oxide solution
can range from about 1 weight percent to about 30 weight percent
solids, with the weight percent of solids being defined as a
fraction of the weight of solids to the total weight of the
colloidal oxide solution multiplied by a factor of 100. The
solution pH can range from about 2 to about 11 depending upon the
method of preparation of the colloidal oxide solution. It is
preferred that the invention use a colloidal oxide solution
comprising a metal oxide selected from the group consisting of
alumina, silica, titania, zirconia, tin oxide, antimony oxide,
cerium oxide, yttrium oxide, copper oxide, iron oxide, manganese
oxide, molybdenum oxide, tungsten oxide, chromium oxide and
mixtures of any two or more thereof It is presently preferred that
the colloidal oxide solution be one of either a colloidal alumina
solution or a colloidal silica solution or some mixture thereof.
The solvent or liquid medium is preferably water which serves as an
aqueous solvent.
[0032] The compositions described herein can optionally be promoted
with any suitable metal oxide promoter. Examples of such suitable
metal oxide promoters include the oxides of manganese, rhenium,
copper, molybdenum, tungsten, Group VIII metals of the Periodic
Table, and any other metal oxide that is known to have
hydrogenation ability of the type necessary to reduce sulfur oxide
species to hydrogen sulfide. Preferably, the metal oxide promoter
is a Group VIII metal oxide promoter with the Group VIII metal
being from the group consisting of iron, cobalt, nickel, ruthenium,
rhodium, palladium, osmium, iridium and platinum. In the most
preferred embodiment of the present invention, the absorbing
composition is promoted with nickel oxide.
[0033] The metal oxide promoter can be added to the absorbing
composition in the form of the elemental metal, metal oxide, and/or
metal-containing compounds that are convertible to metal oxides
under the calcining conditions described herein. Some examples of
such metal-containing compounds include metal acetates, metal
carbonates, metal nitrates, metal sulfates, metal thiocyanates and
mixtures of any two or more thereof.
[0034] The elemental metal, metal oxide, and/or metal-containing
compounds can be added to the absorbing composition by any method
known in the art. One such method is the impregnation of the
absorbing composition with a solution, either aqueous or organic,
that contains the elemental metal, metal oxide, and/or
metal-containing compounds. After the elemental metal, metal oxide,
and/or metal-containing compounds have been added to the absorbing
composition, the promoted composition is dried and calcined, as
described hereinafter.
[0035] The elemental metal, metal oxide, and/or metal-containing
compounds can be added to the absorbing composition as components
of the original mixture, or they can be added after the absorbing
composition has been dried and calcined. If the metal oxide
promoter is added to the absorbing composition after it has been
dried and calcined, then the now-promoted composition is dried and
calcined a second time to form the promoted absorbing composition.
The now-promoted composition is preferably dried at a temperature
in the range of about 150.degree. F. to about 570.degree. F., but
more preferably, the drying temperature will range from 190.degree.
F. to 480.degree. F., for a period of time generally in the range
of from about 0.5 hour to about 8 hours, more preferably in the
range of from about 1 hours to about 5 hours. The dried, promoted
composition is then calcined in the presence of oxygen or an
oxygen-containing inert gas generally at a temperature in the range
of from about 700.degree. F. to about 1400.degree. F., and more
preferably in the range of from 930.degree. F. to 1330.degree. F.,
until volatile matter is removed and the elemental metal and/or the
metal-containing compounds are substantially converted to metal
oxides. The time required for this calcining step will generally be
in the range of from about 0.5 hour to about 4 hours, and will
preferably be in the range of from about 1 hour to about 3
hours.
[0036] The metal oxide promoter will generally be present in the
absorbing composition in an amount in the range of from about 0.1
weight percent to about 15 weight percent, and will more preferably
be in the range of from about 2.0 weight percent to about 7.5
weight percent, most preferably in the range of from 5 to 7 weight
percent.
[0037] Once the absorbent composition components are properly mixed
and agglomerated, the mixture can advantageously undergo a drying
step for removing certain quantities of the liquid medium of the
colloidal oxide solution component of the compositions described
herein. The drying of the agglomerates can be conducted at any
suitable temperature for removing excess quantities of liquid; but
preferably, the drying temperature will range from about
150.degree. F. to about 550.degree. F. More preferably, however,
the drying temperature shall range from about 190.degree. F. to
about 480.degree. F. Generally, the time period for such drying
shall range from about 0.5 hour to about 8 hours and, more
preferably, the drying time shall range from about 1 hour to about
5 hours. The method and apparatus used for performing the optional
drying step are not critical aspects of this invention and any
suitable methods and apparatuses known in the art can be used.
Examples of many of the methods and apparatuses suitable for use in
this invention for drying an agglomerate are described at length in
Perry's Chemical Engineers' Handbook, pages 20-3 through 20-75 (6th
edition, 1984).
[0038] Molybdenum compounds suitable for use as a source for a
promoter metal are ammonium molybdate, potassium molybdate,
molybdenum oxides such as molybdenum (IV) oxide and molybdenum (VI)
oxide and the like and mixtures of any two or more thereof.
[0039] Tungsten compounds suitable for use as a source for a
promoter metal are ammonium tungstate, potassium tungstate,
tungsten oxides such as tungsten (IV) oxide and tungsten (VI) oxide
and the like and mixtures of any two or more thereof.
[0040] Another embodiment of the invention includes a method for
preparing a high crush strength absorption composition which avoids
the problems with excessive equipment wear caused by the abrasive
nature of certain absorption components, such as silica. This novel
method eliminates the problems with high equipment wear by allowing
the use of tumbling agglomeration methods to form agglomerates of
the compositions described herein. The use of tumbling-type or
disk-type agglomerators to form agglomerates is well known in the
art. Description of methods and apparatuses used for performing
such tumbling-type agglomeration procedures can be found in various
art references, such as, for example, Perry's Chemical Engineer's
Handbook (6th edition 1984), wherein at pages 8-65 through 8-68
such methods and apparatuses are described at length. When referred
to herein, the term "agglomeration" is that process whereby small
particles are gathered together into larger particles of relatively
permanent masses. These permanent masses can be any suitable shape,
such as irregular pellets or balls, but tumbling agglomeration
methods generally provide substantially spherically shaped
agglomerates. While the utilization of tumbling-type agglomerators
is well known in the art, the use of certain binders to assist in
the formation of agglomerates and the effects of such binders upon
the mechanical properties of the final agglomerates are not always
generally known by those in the art. In particular, a novel aspect
of the method for preparing high crush strength absorption
compositions is the use of a colloidal oxide solution as a binding
agent during tumbling agglomeration of the absorbent components of
the compositions described herein. The art does not teach the use
of colloidal oxide solution as a suitable agent for binding the
absorbent compounds of zinc oxide and silica. Furthermore, in
addition to the unexpected binding properties of colloidal oxide
solutions, there is also the result that the final agglomerates
have unexpectedly good mechanical properties.
[0041] In one embodiment of the methods of preparing a high crush
strength absorption composition, a colloidal oxide solution is
sprayed, in a spraying step, onto a homogeneous mixture comprising,
consisting of, or consisting essentially of, zinc oxide and silica
during tumbling agglomeration of the homogeneous mixture to form an
agglomerate. Any suitable method for forming a spray of the
colloidal oxide solution can be used in this invention. The spray
can generally be in the form of small droplets or dispersed
droplets which serve to wet the homogeneous mixture during tumbling
agglomeration so as to permit the formation of spheres or
balls.
[0042] The ratio of zinc oxide to silica in the homogeneous mixture
can range from about 0.25:1 to about 4:1. Preferably, the ratio of
zinc oxide to silica in the homogeneous mixture can be in the range
of from 0.5:1 to about 1.5:1; but, most preferably, the ratio can
range from 0.75:1 to 1.25:1. Additionally, the homogeneous mixture
can be a mixture comprising, consisting of, or consisting
essentially of, zinc oxide and silica in the form of a fine powder.
This homogeneous powder mixture can suitably be agglomerated by
spraying of the colloidal oxide solution upon such homogeneous
powder mixture while tumbling the homogeneous powder mixture within
an inclined rotating disk agglomerator, which is equipped with a
rim. As earlier mentioned, this tumbling agglomeration results in
the formation of an agglomerate that is substantially in the shape
of a sphere.
[0043] The colloidal oxide solution utilized in the method of
preparing a high strength absorption composition has the same
properties as the colloidal solution or sol earlier described
herein. The amount of the colloidal oxide solution utilized in the
agglomeration of the homogeneous mixture or the homogeneous powder
mixture is to be such to provide an agglomerate, either in a dry
form or a calcined form, having a content of the metal oxide
compound from an amount that is effective for providing an
agglomerate having a crush strength of at least 3 lbs.sub.f to
about 30 weight percent of the total weight of the agglomerate.
Preferably, however, the amount of colloidal oxide solution
utilized in the agglomeration step should be such that the metal
oxide content of either the dried agglomerate or calcined
agglomerate shall range from about 5 weight percent to about 20
weight percent. Most preferably, the quantity of colloidal oxide
solution utilized in the agglomeration of the composition will be
such that the amount of metal oxide content in either the dried
agglomerate or the calcined agglomerate shall range from 5 weight
percent to 15 weight percent.
[0044] As earlier mentioned, the novel method described herein for
preparing a high crush strength absorption composition gives a
final agglomerate, which has been either dried or calcined, or
both, having an exceedingly high crush strength of at least 3
lbs.sub.f. The final agglomerate can preferably have a crush
strength of from about 3 lbs.sub.f to about 6 lbs.sub.f; but
preferably, the crush strength can range from 3.5 lbs.sub.f to 5.5
lbs.sub.f.
[0045] It has further been discovered that by adding a Group VIII
metal compound promoter to a dry agglomerate prepared by the
methods described herein and subsequently calcining the thus
promoted agglomerate, an improvement in the crush strength of an
unpromoted calcined agglomerate can be achieved. This metal oxide
promoted agglomerate has substantially improved mechanical
properties over that of the unpromoted agglomerate in that such a
metal oxide promoted agglomerate, after having undergone a further
calcining step, can have a crush strength of at least 5 lbs.sub.f.
Preferably, the crush strength of such metal oxide promoted
absorbent composition, which has subsequently been calcined, can
range from about 6 lbs.sub.f to about 14 lbs.sub.f; most
preferably, however, the crush strength can range from 7 lbs.sub.f
to 13 lbs.sub.f.
[0046] The metal oxide promoters can be added to the agglomerates
produced by the methods herein by any method known in the art. One
preferred method for adding a promoter to the agglomerates
described herein is by the impregnation of the agglomerates by a
standard incipient wetness procedure, whereby the agglomerates are
impregnated by either an aqueous or an organic solution containing
the desirable amount of promoter metal that has been diluted with a
volume of the aqueous or organic solvent that is equal to the total
pore volume of the absorbent material or the agglomerate material
being impregnated. Suitable metal oxide promoters have been earlier
described herein. The amount of metal oxide promoter that can be
added to the agglomerate should be such that the amount in the
final calcined or dried agglomerate is in the range of from about
0.1 weight percent to about 15 weight percent, and will more
preferably be in the range of from about 2 weight percent to about
7.5 weight percent, most preferably, the metal oxide promoters will
be in the range of from 5 to 7 weight percent. The operating
conditions for drying and calcining of the agglomerates has
thoroughly been described hereinabove.
[0047] As an additional embodiment of the present method for
preparing a high crush strength absorption composition, a
homogeneous powder mixture prepared by mixing zinc oxide and silica
with water to form a mixture, undergoes a drying step to form a
dried mixture, which subsequently is milled to form a homogeneous
mixture. The milled homogeneous mixture can be utilized in the
methods described hereinabove. Any suitable method for mixing the
zinc oxide and silica components with water can be used, and it can
be done in a batch-wise fashion or a continuous fashion, provided
that the components are thoroughly and intimately mixed prior to
further processing. Suitable types of batch mixers include, but are
not limited to, change-can mixers, stationary-tank mixers,
double-armed kneading mixers, having any suitable agitator or
blades, such as sigma blades, dispersion blades, multi-wiping
overlap blades, single curve blades, double-nabin blades and the
like. Suitable types of continuous mixers can include, but are not
limited to, single or double screw extruders, trough-and-screw
mixers and pugmills. To achieve the desired dispersion of the
materials, they are mixed until a homogeneous mixture is formed.
The mixing time should be sufficient to give a uniform mixture and
generally will be less than about 45 minutes. Preferably, the
mixing time will be in the range of from about 2 minutes to about
15 minutes.
[0048] Following the mixing of water with the absorbent components
comprising, consisting essentially of, or consisting of, zinc oxide
and silica, the thus-formed mixture is dried to remove the water
utilized in the mixing step. Any suitable method for drying can be
used and should be such that a substantially dry mixture is formed.
The operating conditions for the drying step have been earlier
described herein.
[0049] The dried mixture of zinc oxide and silica can further be
reduced in size preferably to the form of a homogeneous powder
mixture by any suitable or known method of size reduction. There
are many known methods and apparatuses for size reduction and
reference is hereby made to the examples shown and described at
length in Perry's Chemical Engineer's Handbook, (6th edition 1984),
pages 8-20 to 8-48. Any of these size reduction methods and
apparatuses can be used for milling purposes and for the purposes
of forming a powder for subsequent use in tumbling agglomeration to
form an agglomerate by the aforementioned methods of spraying a
colloidal oxide solution onto such powder.
[0050] The sulfur removal processes of the present invention can be
carried out by means of any apparatus whereby there is achieved an
alternate contact of the absorbing composition with a
sulfur-containing gaseous feed stream and, thereafter, of the
absorbing composition with oxygen or an oxygen-containing gas which
is utilized to regenerate the absorbing composition. The sulfur
removal process is in no way limited to the use of a particular
apparatus. The sulfur removal process of this invention can be
carried out using a fixed bed of absorbing composition, a fluidized
bed of absorbing composition, or a moving bed of absorbing
composition. Presently preferred embodiment is the use of a fixed
bed of absorbing composition.
[0051] In order to avoid any casual mixing of the gaseous feed
stream containing sulfur compounds with the oxygen or
oxygen-containing gas utilized in the regeneration step, provision
is preferably made for terminating the flow of the gaseous feed
stream to the reactor and subsequently injecting an inert purging
fluid such as nitrogen, carbon dioxide or steam. Any suitable purge
time can be utilized but the purge should be continued until all
hydrocarbon and/or hydrogen sulfide are removed. Any suitable flow
rate of the purge fluid can be utilized. A presently preferred
purge fluid flow rate is one which will give a gaseous hourly space
velocity (GHSV) in the range of from about 800 GHSV to about 1200
GHSV. As used herein, the term "gaseous hourly space velocity" is
defined as the ratio of the gaseous volumetric flow rate, at
standard conditions of 60.degree. F. and one atmosphere of
pressure, to the reactor volume.
[0052] The composition of matter of this invention can be utilized
to remove trace quantities of sulfur compounds from any suitable
type of gaseous feed steam containing contaminating quantities of
sulfur compounds. Such gaseous streams can contain sulfur compounds
in the concentration range upwardly to about 2 mole percent. The
sulfur compounds are generally of the type consisting of hydrogen
sulfide, sulfur dioxide, carbonyl sulfide, carbon disulfide, and
mixtures of two or more thereof. One preferred embodiment of the
invention includes the processing of Claus plant tail gas streams.
Of these Claus plant tail gas streams, they can be from either a
Claus process operated in a mode for minimizing sulfur dioxide or
the tail gas stream can undergo a prior hydrogenation step whereby
the sulfur compounds within the tail gas stream are reduced to
hydrogen sulfide. The sulfur dioxide minimization operating mode of
the Claus process is conducted by providing the reaction zone with
a slight excess of hydrogen sulfide above the stoichiometric
requirement for the Claus reaction. This slight stoichiometric
excess of hydrogen sulfide results in minimizing the amount of
sulfur dioxide that is present in a Claus tail gas. If the ratio of
hydrogen sulfide to sulfur dioxide in the reaction zone of a Claus
plant approximates 2:1, then the ratio of hydrogen sulfide to
sulfur dioxide in the Claus tail gas will also approximate 2:1.
Generally, the concentration of sulfur compounds in a Claus tail
gas stream will be less than 2 mole percent; the carbon dioxide
will be present in the tail gas stream at a concentration in the
range of from about 5 to about 60 mole percent. Water normally will
be present in the range of from about 10 mole percent to about 40
mole percent, nitrogen will be present in the range of from about
20 mole percent to about 50 mole percent and hydrogen will be
present in the range upwardly to about 2 mole percent.
[0053] The gaseous stream containing a concentration of sulfur
compounds is contacted with the novel absorption compositions
described herein to produce a treated effluent stream having a
substantially reduced concentration of sulfur compounds.
Preferably, the substantially reduced concentration of the sulfur
compounds in the treated effluent stream can be less than 0.5 mole
percent of the treated effluent stream. Most preferably, the
substantially reduced concentration of sulfur compounds in the
treated effluent stream can be less than 0.02 mol percent of the
treated effluent stream.
[0054] Any suitable temperature for the sulfur-removal processes of
the present invention can be utilized which will achieve the
desired removal of sulfur from a gaseous feed stream. The
temperature will generally be in the range of from about
300.degree. F. to about 1110.degree. F. and will, more preferably,
be in the range of from about 390.degree. F. to about 840.degree.
F.
[0055] Any suitable temperature can be utilized which will
regenerate the absorbing composition from its sulfided form back to
the original absorbing composition form. The regeneration
temperature will generally be in the range of from about
700.degree. F. to about 1500.degree. F. The regeneration
temperature is preferably in the range of from about 800.degree. F.
to about 1400.degree. F. Most preferably, the regeneration
temperature should range from about 800.degree. F. to about
1300.degree. F.
[0056] Any suitable pressure can be utilized for the processes of
the present invention. The pressure of the gaseous feed stream
being treated is not believed to have an important effect on the
absorption process of the present invention, and will generally be
in the range of from about atmospheric pressure to about 2,000 psig
during the treatment.
[0057] Any suitable residence time for the sulfur-containing
gaseous feed stream in the presence of the absorbing composition of
the present invention can be utilized. The residence time expressed
as volumes of gas at standard temperature and pressure per volume
of absorbing composition per hour will generally be in the range of
about 10 to about 10,000 and will, more preferably, be in the range
of about 250 to about 2500.
[0058] In the preferred embodiment of the invention, the Claus
plant effluent stream having a concentration of sulfur compounds
can be introduced into an absorption zone containing any of the
novel absorbent compositions described herein to remove at least a
portion of the concentration of sulfur compounds to produce a
treated effluent stream having a substantially reduced
concentration of the sulfur compounds to produce a laden absorbent
composition. Periodically, the laden absorbent composition can be
regenerated by passing an oxygen-containing gas in contact with the
laden absorbent composition to produce both a regenerated absorbent
and a regeneration effluent stream. Claus processes are well known
in the art and any references herein to Claus processes or Claus
plants refers to those conversion processes for recovering
elemental sulfur from fluid streams, sometimes referred to as acid
gas streams, containing primarily hydrogen sulfide and carbon
dioxide. These acid gas streams are generally fluid streams having
their origin from a main gas treating system used to remove
hydrogen sulfide and carbon dioxide from fluid streams containing
such. The acid gas stream is charged to the thermal zone of a Claus
plant wherein a portion of the hydrogen sulfide is combusted in the
presence of air. In the thermal zone of the Claus plant, the
hydrogen sulfide will generally react with oxygen to form sulfur
dioxide and water by the following reaction equation:
2H.sub.2S+3O.sub.2.fwdarw.2SO.sub.2+2H.sub.2O.
[0059] In order to convert the sulfur compounds contained in the
acid gas stream to elemental sulfur, the effluent from the Claus
plant thermal zone will pass to a Claus plant sulfur recovery zone
or reaction zone wherein the sulfur dioxide is reacted with the
unconverted hydrogen sulfide to form elemental sulfur and water in
accordance with the following equation:
2H.sub.2S+SO.sub.2.fwdarw.3S+2H.sub.2O.
[0060] For the optimum recovery of sulfur from the hydrogen sulfide
in the acid gas stream, it is most desirable to maintain a ratio of
hydrogen sulfide to sulfur dioxide in the fluid stream to the Claus
reactor zone of about 2:1. In order to achieve this optimum ratio,
the amount of air charged to the Claus plant thermal zone will be
controlled so as to react a sufficient amount of HS with oxygen to
form the necessary ratio of SO. The Claus plant effluent stream or
tail gas will generally have only trace quantities of sulfur
compounds which include hydrogen sulfide and sulfur dioxide. Other
possible sulfur compounds contained within the tail gas stream can
include carbon disulfide and carbonyl sulfide. As earlier
described, the Claus process can be operated in a sulfur dioxide
minimization mode or, alternatively, the tail gas can further
undergo a hydrogenation step whereby sulfur compounds are reduced
to hydrogen sulfide prior to downstream processing. Preferably, the
concentration of sulfur compounds can be less than about 2 mole
percent of the tail gas stream.
[0061] The Claus plant effluent stream or tail gas stream having a
concentration of sulfur compounds is introduced into a vessel
defining an absorption zone containing the novel absorbent
composition described herein. Within the absorption zone, at least
a portion of the concentration of the sulfur compound contained
within the tail gas stream is removed to produce a treated effluent
stream having a substantially reduced concentration of the sulfur
compounds, but, preferably having a concentration of sulfur
compounds of less than about 0.5 mol percent and, most preferably,
less than about 0.1 mol percent. The removed sulfur compounds will
be absorbed upon the surfaces and within the pores of the absorbent
composition to produce a laden absorbent composition. The chemical
changes that are believed to occur in the absorption composition
during the absorption or removal step are summarized in the
following equation:
ZnO+H.sub.2S.fwdarw.ZnS+H.sub.2O.
[0062] Once the absorbent composition becomes substantially
completely sulfided, it is a laden absorbent requiring a
regeneration in order to restore the composition to its original
form. The regeneration is conducted periodically by terminating the
fluid flow to the absorption zone followed by passing an
oxygen-containing gas in contact with the laden absorbent to
produce a regenerated absorbent in a regeneration effluent stream.
It is believed that the regeneration step occurs by the following
equation:
ZnS+O.sub.2.fwdarw.ZnO+SO.sub.X.
[0063] The regeneration effluent stream which contains the sulfur
oxide compounds can, optionally, be recycled to be mixed with the
acid gas stream being charged to the Claus plant thermal zone. This
regeneration effluent stream is mixed with the acid gas stream
prior to introducing the acid gas stream into the Claus plant
thermal zone. The benefit from recycling the regeneration effluent
stream comes from the ability to use the sulfur oxide compound as a
reactant with the unconverted HS to form elemental sulfur and water
in accordance with the above equations.
[0064] Referring now to FIG. 1, there is provided a schematic
representation of process 10 for removing sulfur compounds from
contaminated fluid streams. An acid gas stream having a
concentration of hydrogen sulfide is introduced via conduit 12 to
furnace 14, which defines a w thermal zone of a Claus plant,
wherein at least a portion of the hydrogen sulfide of the acid gas
stream is combusted with oxygen that is contained within the air
that is introduced into the thermal zone defined by furnace 14 via
conduit 16. The resultant product from the thermal zone is
introduced into reactor 18, which defines a reactor zone of the
Claus plant, wherein elemental sulfur is recovered through conduit
20, and a Claus effluent stream is produced and passes by way of
conduit 22 to heating means or heat exchanger 24. The Claus plant
effluent stream is, optionally, heated to a desired temperature and
then passes by way of conduit 26 to absorber vessels 28a and 28b,
which respectively define two separate absorption zones. Contained
within the absorption zones are any of the novel absorbent
compositions described herein. Within the absorption zones, at
least a portion of the sulfur compounds contained within the Claus
plant effluent stream are absorbed by the absorbent composition or
removed from the effluent stream to produce a treated effluent
stream which is conveyed from absorber vessel 28a or 28b, or both,
via conduit 30. The treated effluent stream will generally have a
substantial reduction in the concentration of the sulfur compounds.
Preferably, the amount sulfur compounds contained within the
treated effluent stream will be less than about 0.5 mole percent
and, most preferably, the concentration of sulfur compounds in the
treated effluent stream will be less than 0.1 mole percent.
[0065] It is generally desirable to have at least two separate
absorption zones in order to permit the simultaneous regeneration
of one absorption zone while utilizing another absorption zone for
removing or absorbing sulfur compounds from the Claus plant tail
gas stream. Having at least two absorbent zones permits the
periodic regeneration of a laden absorbent composition by passing
an oxygen or oxygen-containing gas, such as air, in contact with
the ladened absorbent to produce a regenerated absorbent and a
regeneration effluent stream. The oxygen-containing gas is
introduced into absorber vessel 28a or 28b, or both, via conduit
32. Optionally, disposed within conduit 32 is heating means or heat
exchanger 34 which, if desired, permits the heating of the
oxygen-containing gas prior to passing the gas into at least one of
the absorption zones. The regeneration effluent stream passes from
absorber vessel 28a or 28b, or both, through conduit 36 to be mixed
with the incoming acid gas stream passing through conduit 12 prior
to introducing the thus formed mixture to the thermal zone.
[0066] FIG. 2 is provided to illustrate the use of a typical
inclined pan or disk type agglomerator used in the method for
preparing the compositions of this invention. As shown in FIG. 1, a
feeder device 110 is provided so that material can be charged to
pan 112 of the agglomerator. Any suitable feeder for charging
material can be used. That which is shown in FIG. 2, however, is a
belt type conveyor on which the agglomerate charge material 114
comprising the absorbent components is conveyed and discharged to
pan 112 by a moving belt 116. Pan 112 comprises a disk 118 that is
equipped with a rim 120 attached to the outer perimeter edge of
disk 118 so as to form an essentially open-end, cylindrically
shaped device. To promote the lifting and cascading of the material
in pan 112, the inside surface of disk 118 can optionally be
provided with a rough surface by any suitable means including, for
example, expanded metal, abrasive coatings or metallized surfaces.
Disk 118 can be any suitable diameter necessary for giving the
required capacity and can range from less than one foot in diameter
to more than twenty feet in diameter. The depth of pan 112 is set
by the height of rim 120, which can be any suitable height that
will promote the desired agglomeration. Generally, the height of
rim 120 will approximate twenty percent of the diameter of disk
118.
[0067] Provided on disk 118 is rotation means 122 which permits the
rotation of pan 112 about its axis. Rotation means 112 is connected
by linking means 124 for transmitting power from power means 126 to
rotation means 122. Power means 126 can be any suitable device for
imparting the power necessary for rotating pan 112 about its axis
and can include electrical motors of any type, engines of any type
or turbines of any type. Preferably, however, power means 126 is an
electrical motor with linking means 124 being any suitable device
including those devices which can permit variable speed control of
pan 112.
[0068] Pan 112 can be inclined at an angle from the horizontal
plane, as depicted in FIG. 2 and as referred to in FIG. 2 by the
Greek letter theta (.theta.), in the range of from about 15.degree.
to about 75.degree.; but, generally, the angle of inclination will
range from about 30.degree. to about 65.degree.. The agglomerate or
pellet size is significantly influenced by the angle of inclination
of pan 112.
[0069] To treat and agglomerate the absorption composition, the
absorbent component materials or agglomerating charge 114 is fed to
pan 112. As disk 118 is rotated about its axis, the material on
disk 118 undergoes a tumbling action. A colloidal oxide solution is
sprayed through nozzle 128 upon the materials while disk 118 is
rotating. While FIG. 2 illustrates spray nozzle 128 as the means by
which the colloidal oxide solution is contacted with the
agglomerate material, any suitable method known in the art for
spraying or contacting a liquid onto the dry agglomerate powder can
be used. The agglomerating charge is moistened by the colloidal
oxide solution that assists in the formation of pellets. The
tumbling action of the materials within rotating pan 112 causes
what is sometimes referred to as a "snowballing" effect whereby the
moistened material agglomerates as the dampened particles come w
into contact with other particles thereby forming spheroids. The
colloidal oxide solution used in this process not only provides
moisture, which causes adhesion of the particles by capillary
attraction of the particle surfaces, but it also gives the
unexpected result of providing a final absorption composition
agglomerate having improved mechanical properties.
[0070] There are various operating factors of rotating pan 112
which affect the ultimate size of the spheroids formed. Some of
these operating factors can include, but are not limited to, the
rotational speed of pan 112, the angle of inclination (.theta.) of
pan 112, the location and rate of introduction of both liquid feed
and solid feed and the ratio of the height of rim 120 to the
diameter of disk 118. These factors, among others, are to be
adjusted to provide the desired agglomerate or pellet size.
[0071] To more fully illustrate and to assist in understanding the
invention, the following examples are provided.
EXAMPLE I
[0072] This calculated Example I provides calculated ranges for the
various operating conditions, process flows and stream compositions
in the operation of one embodiment of the herein-described
invention.
1TABLE I Typical Operating Conditions, Flows and Compositions
(Calculated) Range Acid Gas Feed Stream (12) Composition (mole
percent on dry basis) Hydrogen Sulfide 10-98 Carbon Dioxide 0-90
Carbon Sulfide 0-2 Hydrocarbon 0-2 Air Stream 1:1 to 2:1 Ratio of
Oxygen-to-Hydrogen Sulfide preferably 0.5:1 Thermal Zone (14)
Operating Conditions Temperature (.degree. C.) 760-1260 Pressure
(psig) 5-30 Reaction Zone (18) Operating Conditions Temperature (C.
.degree.) 150-400 Pressure (psig) 5-30 Claus Plant Effluent Stream
(22) Composition (mole percent) Sulfur Compounds less than 2 Water
10-40 Hydrogen 0-2 Nitrogen 20-50 Carbon Dioxide 5-60 Total
Effluent Stream (30) Composition (mole percent) Sulfur Compounds
0.1-0.5 Regeneration Effluent Stream (36) Composition (mole
percent) Sulfur Oxides 5-25 Nitrogen 70-90 Water 1-5
EXAMPLE II
[0073] This Example II describes the method of preparing the
absorbent compositions along with the components of such
compositions and pertinent physical property data of the prepared
compositions.
[0074] Spheres comprising about 38 weight percent celite silica,
about 50 weight percent zinc oxide (ZnO) and about 12 weight
percent alumina were prepared as follows. First, ZnO and celite
powders were mixed for a period of approximately 45 minutes in a
sufficient amount of water to form a mixture and then dried at a
temperature of about 300.degree. F. for 6 to 12 hours. The dried
material was broken up to a fine powder in a ball mill. The
resulting powder was then sprayed with a colloidal solution of
Dispal.RTM. 18N4-20 alumina (Vista Chemicals) in a sufficient
amount to incorporate about 5.25 weight percent alumina in the
resultant mixture which was thereafter dried to form a dried
powder. A portion of this dried powder was placed in a Dravo
Corporation pelletizing disk or pelletizer for forming an
agglomerate. While the pelletizing disk was being rotated, an
additional amount of the fine powder was continuously fed to the
pelletizer using a powder feed and the mixture in the disk was
continuously sprayed with a colloidal solution of Dispal.RTM.
alumina in water to effect sphere formation. The amounts of powder
feed and colloidal alumina solution sprayed onto the powder was
adjusted to yield spheres with the composition stated above. The
disk angle and its revolution was manipulated to yield spheres of
desired size.
[0075] The spheres were dried at about 275.degree. F. for about 3
hours and then calcined at about 1175.degree. F. for about two
hours. The dried and calcined spheres were impregnated by use of an
incipient wetness method with a sufficient amount of
Ni(NO.sub.3).sub.2.multidot.6H.sub.2O dissolved in water to yield
about 7.5 weight percent nickel oxide in the product. This was
followed by another drying and calcination step as described above.
The physical characteristics of the material before and after
nickel impregnation are shown in Table II. Comparative data are
also provided in Table II for a composition similar to that of the
inventive composition but which was prepared by extrusion methods
instead of disk agglomeration methods and which such comparative
composition did not utilize a colloidal solution as a binder or
binding agent. The data presented in Table II show that the
spherical product has high mechanical strength while still
maintaining pore volume and bulk density similar to those of the
comparative composition or material.
2TABLE II Physical Properties of HS Absorbents Before Ni
Impregnation Bulk Water After Ni Impregnation Cr. Str. Density Pore
Volume Cr. Str. (lb.sub.f/p) (g/cc) (cc/g) (lb.sub.f/p) Control
Composition Extrudates: 3 0.78 0.40 8 (50 parts ZnO, 40 parts
Celite, 10 parts Al.sub.2O.sub.3, 7.5 parts NiO) Invention Spheres:
31/2 mesh 4 0.75 0.38 13 4-5 mesh 5 0.74 0.43 11 5-14 mesh 4 0.74
0.42 7
EXAMPLE III
[0076] This Example III describes the use of the novel material in
a process for removing HS from a HS-contaminated fluid stream and
makes a comparison between the novel material and a control
material when both are utilized in an HS absorption process.
[0077] The novel absorbent described in Example II above was
subjected to an absorption test in which the absorbent was
alternately contacted with a gaseous stream containing HS mixed
with an inert gas until the sulfur loading capacity of the
absorbent was reached followed then by a regeneration of the
sulfur-loaded absorbent to its original ZnO form by contacting the
absorbent with air. The reactor temperature for the contacting step
was maintained at about 800.degree. F. and the regeneration
temperature was maintained at about 1100.degree. F. The sulfur
loading capacity of the absorbent was determined to be reached when
hydrogen sulfide was detected in the effluent stream; at which
point, the sulfided material was regenerated in air. The SO.sub.2
concentration was measured at 10 minutes after the start of the
absorption step and at breakthrough (BT). The test data for the
inventive composition is included in Table III. The absorbent of
this invention exhibited similar sulfur removal ability to that of
the control material while exhibiting much improved mechanical
strength as demonstrated in Example II above. Even after 100
absorbing and regeneration cycles, only a minor loss in sulfur
removal capacity was noted. The spherical shape of this product is
preferred for commercial operation for a number of reasons
including the improved pressure drop characteristics that result
from the use of spherical absorbent masses.
3TABLE III Hydrogen Sulfide Absorption Test Results Composition
(weight parts) ZnO/Celite/ Cycle Sulfur Loading Sample
Al.sub.2O.sub.3/NO Number 10 min. BT (Wt %) A (Control)
50/40/10/7.5 1 180 60 10.6 14 13.2 20 950 630 13.1 Invention
50/38/12/7.5 1 30 11.3 2 715 470 12.4 15 805 530 12.4 20 845 555
12.7 100 470 11.0 BT = Breakthrough
[0078] It is understood that the foregoing detailed description is
given merely by way of illustration and that many variations may be
made herein without departing from the spirit of this
invention.
* * * * *