U.S. patent application number 09/748734 was filed with the patent office on 2002-06-27 for method and apparatus for removing trace impurities from a gas using superactivated carbon material.
Invention is credited to Fraenkel, Dan, Funke, Hans H., Houlding, Virginia.
Application Number | 20020078825 09/748734 |
Document ID | / |
Family ID | 25010690 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020078825 |
Kind Code |
A1 |
Funke, Hans H. ; et
al. |
June 27, 2002 |
Method and apparatus for removing trace impurities from a gas using
superactivated carbon material
Abstract
Trace impurities such as organic compounds and carbon monoxide
are reduced to sub-ppb levels in gases such as nitrogen, helium and
argon, by gas purifying systems that contain an ultra-low emission
(ULE) carbon material. Ultra-low emission (ULE) carbon materials
can be made from commercially available carbon materials in the
form of pellets, extrudates and beads and is capable of removing
impurities from a gas stream down to parts-per-billion (ppb) and
sub-ppb levels without concurrently emitting other impurities such
as moisture or carbon dioxide to the purified gas stream. The
carbon material is superactivated by heating the carbon to
temperatures from 300.degree. to about 800.degree. degrees C. in an
ultra-dry, inert gas stream. The ultra-low emission (ULE) carbon
material is handled and stored in an environment that minimizes
contamination from moisture and other oxygenated species in order
to maintain its ppb and sub-ppb impurity removal and low emission
properties. The ultra-low emission (ULE) carbon material can be
used as "stand-alone" purifier material or in combination with
other scavenging materials that are capable of removing large
quantities of impurities such as oxygen and moisture that are not
removed or only marginally removed by the ultra-low emission (ULE)
carbon material.
Inventors: |
Funke, Hans H.; (Boulder,
CO) ; Fraenkel, Dan; (Boulder, CO) ; Houlding,
Virginia; (Boulder, CO) |
Correspondence
Address: |
Sarah O'Rourke
Hogan & Hartson, LLP
Suite 1500
1200 17th Street
Denver
CO
80202
US
|
Family ID: |
25010690 |
Appl. No.: |
09/748734 |
Filed: |
December 26, 2000 |
Current U.S.
Class: |
95/117 ; 502/416;
95/139; 95/140; 95/141; 96/108; 96/133 |
Current CPC
Class: |
C01B 7/0725 20130101;
B01D 53/02 20130101; C01B 7/0743 20130101; C01B 7/093 20130101;
Y02C 20/40 20200801; B01D 2253/102 20130101; B01J 20/20 20130101;
C01C 1/024 20130101; Y10S 502/519 20130101; Y02C 10/08
20130101 |
Class at
Publication: |
95/117 ; 95/139;
95/140; 95/141; 96/108; 96/133; 502/416 |
International
Class: |
B01D 053/02 |
Claims
We claim:
1. An ultra-low emission carbon material capable of removing
impurities from a gas containing said impurities to produce an
ultra-pure gas, wherein the concentrations of said impurities in
said ultra-pure gas are less than 1 part-per-billion, and wherein
said ultra-low emission carbon material is stored in a
substantially non-contaminating environment until contacted with
said gas containing said impurities.
2. The ultra-low emission carbon material of claim 1, wherein said
impurities comprise water.
3. The ultra-low emission carbon material of claim 1, wherein said
impurities comprise carbon dioxide.
4. The ultra-low emission carbon material of claim 1, wherein said
impurities comprise carbon monoxide.
5. The ultra-low emission carbon material of claim 1, wherein said
impurities comprise organic compounds.
6. The ultra-low emission carbon material of claim 5, wherein said
organic compounds comprise straight chain or branched chain
hydrocarbons.
7. The ultra-low emission carbon material of claim 1, wherein said
organic compounds comprise aromatic hydrocarbons.
8. The ultra-low emission carbon material of claim 6, wherein said
hydrocarbon is hexane.
9. The ultra-low emission carbon material of claim 7, wherein said
aromatic hydrocarbon is benzene, or ethylbenzene.
10. The ultra-low emission carbon material of claim 1, wherein the
concentration of said impurities in said ultra-pure gas is measured
by Atmospheric Pressure Ion Mass Spectrometry.
11. A process of producing an ultra-low emission carbon material
comprising: a) placing a carbon material containing trace amounts
of water in a reactor having a gas inlet and a gas outlet; b)
heating a carbon material in said reactor for at least twenty four
hours at a temperature between about 300.degree. C. and 800.degree.
C. under a flow of ultra-dry inert gas; c) measuring the amount of
water in said inert gas exiting said reactor; d) terminating said
heating when the concentration of water in said inert gas exiting
said reactor is below about ten parts-per-million, whereby said
ultra-low emission carbon material is produced; and e) maintaining
said ultra-low emission carbon material in a substantially
non-contaminating environment.
12. The process of claim 11, further comprising: f) providing a
container having a gas inlet port, a gas outlet port, and a
receiving port; g) purging said container with an ultra-dry inert
gas; h) transferring a portion of said ultra-low emission carbon
material from said reactor to said container while flowing an
ultra-dry inert gas through said container; and i) closing said
receiving port while maintaining the flow of inert gas through said
container; and j) closing said inlet and outlet ports, whereby said
ultra-low emission carbon material is maintained in said container
in an ultra-dry inert atmosphere.
13. The process of claim 11, wherein said carbon material is a high
hardness carbon material.
14. The process of claim 11, wherein the amount of water in said
inert gas exiting said reactor is measured with a hygrometer.
15. The process of claim 11, wherein the amount of water in said
inert gas exiting said reactor is measured with Atmospheric
Pressure Ion Mass Spectrometry instrumentation.
16. The process of claim 11, wherein said heating is terminated
when the concentration of water in said inert gas exiting said
reactor is below one part-per-billion when said carbon material is
at room temperature.
17. The process of claim 11, wherein said carbon material is heated
for between about two days and five days.
18. The process of claim 11, wherein said carbon material is heated
at a temperature between about 500.degree. and 700.degree. C.
19. The process of claim 11, wherein said ultra-low emission carbon
material is capable of reducing trace amounts of impurities in a
process gas to less than about one part-per-billion.
20. The process of claim 19, wherein said impurities are selected
from organic compounds, carbon dioxide, carbon monoxide and
water.
21. The ultra-low emission carbon material of claim 20, wherein
said organic compounds comprise straight chain or branched chain
hydrocarbons.
22. The ultra-low emission carbon material of claim 20, wherein
said organic compounds comprise aromatic hydrocarbons.
23. The ultra-low emission carbon material of claim 21, wherein
said hydrocarbon is hexane.
24. The ultra-low emission carbon material of claim 22, wherein
said aromatic hydrocarbon is benzene, or ethylbenzene.
25. The process of claim 12, wherein said container is adapted for
use in a gas purifying system.
26. An ultra-low emission carbon material produced according to the
method comprising: a) placing a carbon material containing trace
amounts of water in a reactor having a gas inlet and a gas outlet;
b) heating a carbon material in said reactor for at least twenty
four hours at a temperature between about 300.degree. C. and
800.degree. C. under a flow of ultra-dry inert gas; c) measuring
the amount of water in said inert gas exiting said reactor; d)
terminating said heating when the concentration of water in said
inert gas exiting said reactor is below about one part-per-million,
whereby said ultra-low emission carbon material is produced; and e)
maintaining said ultra-low emission carbon material in a
substantially non-contaminating environment.
27. The ultra-low emission carbon material of claim 19, wherein
said method farther comprises: f) providing a container having a
gas inlet port, a gas outlet port, and a receiving port; g) purging
said container with an ultra-dry inert gas; h) transferring a
portion of said ultra-low emission carbon material from said
reactor to said container while flowing an ultra-dry inert gas
through said container; and i) closing said receiving port while
maintaining the flow of inert gas through said container; and j)
closing said inlet and outlet ports, whereby said ultra-low
emission carbon material is maintained in said container in an
ultra-dry inert atmosphere.
28. The process of claim 27, wherein said container is adapted for
use in a gas purifying system.
29. The process of claim 26, wherein said carbon material is heated
for between about two days and five days.
30. The process of claim 26, wherein said carbon material is heated
at a temperature between about 500.degree. and 700.degree. C.
31. The process of claim 26, wherein the amount of water in said
inert gas exiting said reactor is measured with a hygrometer or
Atmospheric Pressure Ion Mass Spectrometry instrumentation.
32. The process of claim 26, wherein said ultra-low emission carbon
material is capable of reducing trace amounts of impurities in a
process gas to less than about one part-per-billion.
33. The process of claim 32, wherein said impurities are selected
from organic compounds, carbon dioxide, carbon monoxide and
water.
34. The ultra-low emission carbon material of claim 33, wherein
said organic compounds comprise straight chain or branched chain
hydrocarbons.
35. The ultra-low emission carbon material of claim 33, wherein
said organic compounds comprise aromatic hydrocarbons.
36. The ultra-low emission carbon material of claim 34, wherein
said hydrocarbon is hexane.
37. The ultra-low emission carbon material of claim 35, wherein
said aromatic hydrocarbon is benzene, or ethylbenzene.
38. A method for removing impurities from process gas stream
comprising: contacting the gas stream with an ultra-low emission
carbon material, wherein said ultra-low emission carbon material
reduces the concentration of the impurities to less than 1 part per
billion by volume.
39. The method of claim 38, wherein the concentration of said
impurities in said ultra-pure gas is less than 100 parts per
trillion.
40. The method of claim 38, wherein said impurities comprise
organic compounds.
41. The ultra-low emission carbon material of claim 40, wherein
said organic compounds comprise straight chain or branched chain
hydrocarbons.
42. The ultra-low emission carbon material of claim 40, wherein
said organic compounds comprise aromatic hydrocarbons.
43. The ultra-low emission carbon material of claim 41, wherein
said hydrocarbon is hexane.
44. The ultra-low emission carbon material of claim 42, wherein
said aromatic hydrocarbon is benzene, or ethylbenzene.
45. The method of claim 38, wherein said impurities comprise carbon
dioxide.
46. The method of claim 38, wherein said impurities comprise carbon
monoxide.
47. The method of claim 38, wherein said impurities comprise
water.
48. A gas purifier system comprising: an ultra-low emission carbon
material capable of removing impurities from a gas stream to less
than 1 part-per-billion concentration by volume to produce an
ultra-pure gas; and a container for holding said carbon material,
wherein said container comprises an gas stream inlet and a gas
stream outlet to allow said gas stream to flow through said
container, wherein said container maintains said ultra-low emission
carbon material in a substantially non-contaminating environment
until said carbon material is contacted with said gas stream.
49. The gas purifier system of claim 48, wherein the concentration
of impurities in said ultra-pure gas is less than 100 parts per
trillion.
50. The gas purifier system of claim 48, wherein said impurities
comprise organic compounds.
51. The ultra-low emission carbon material of claim 50, wherein
said organic compounds comprise straight chain or branched chain
hydrocarbons.
52. The ultra-low emission carbon material of claim 50, wherein
said organic compounds comprise aromatic hydrocarbons.
53. The ultra-low emission carbon material of claim 51, wherein
said hydrocarbon is hexane.
54. The ultra-low emission carbon material of claim 52, wherein
said aromatic hydrocarbon is benzene, or ethylbenzene.
55. The gas purifier system of claim 48, wherein said impurities
comprise carbon dioxide.
56. The gas purifier system of claim 48, wherein said impurities
comprise carbon monoxide.
57. The gas purifier system of claim 48, wherein said impurities
comprise water.
58. A gas purifier system comprising: a first container comprising
a first gas inlet and a second gas inlet and containing a scavenger
material capable of adsorbing oxygen and/or moisture from a gas
stream; an ultra-low emission carbon material capable of removing
impurities from a gas stream to less than 1 part-per-billion
concentration by volume to produce an ultra-pure gas:; a second
container comprising a second gas stream inlet and a second gas
stream outlet for holding said carbon material, wherein said second
container is positioned downstream of said first container and said
second gas inlet is connected to said first gas outlet, wherein
said second container maintains said ultra-low emission carbon
material in a substantially non-contaminating environment until
said carbon material is contacted with said gas stream.
59. The gas purifier system of claim 58, wherein said scavenger
material comprises a metallated macroreticular polymer, wherein
said polymer is metallated with Group IA or Group IIB alkyl or aryl
organometallic compounds.
60. The gas purifier system of claim 58, wherein said scavenger
material is selected from the group consisting of Groups IIA, IVA,
IIIB and IVB metal oxides.
61. The gas purifier system of claim 60, wherein said oxide is
alumina or an alumina-based material.
62. The gas purifier system of claim 61, wherein said oxide is
modified by a metal salt or a metal oxide.
63. The gas purifier system of claim 60, wherein said oxide is
silica or a silica-based material.
64. The gas purifier system of claim 63, wherein said oxide is
modified by a metal salt or a metal oxide.
65. The gas purifier system of claim 60, wherein the scavenger
material is a zeolite molecular sieve.
66. The gas purifier system of claim 58, wherein the concentration
of impurities in said ultra-pure gas is less than 100 parts per
trillion.
67. The gas purifier system of claim 58, wherein said impurities
comprise organic compounds.
68. The ultra-low emission carbon material of claim 67, wherein
said organic compounds comprise straight chain or branched chain
hydrocarbons.
69. The ultra-low emission carbon material of claim 67, wherein
said organic compounds comprise aromatic hydrocarbons.
70. The ultra-low emission carbon material of claim 68, wherein
said hydrocarbon is hexane.
71. The ultra-low emission carbon material of claim 69, wherein
said aromatic hydrocarbon is benzene, or ethylbenzene.
72. The gas purifier system of claim 58, wherein said impurities
comprise carbon dioxide.
73. The gas purifier system of claim 58, wherein said impurities
comprise carbon monoxide.
74. The gas purifier system of claim 58, wherein said impurities
comprise water.
75. A gas purifier system comprising: a container for holding gas
purifying materials, wherein said container comprises an gas stream
inlet and a gas stream outlet to allow said gas stream to flow
through said container, wherein said gas purifying materials
comprise a scavenger material capable of adsorbing oxygen and/or
moisture from a gas stream, and an ultra-low emission carbon
material capable of removing impurities from a gas stream to less
than 1 part-per-billion concentration by volume to produce an
ultra-pure gas, said carbon material located downstream of said
scavenger material, wherein said container maintains said ultra-low
emission carbon material in a substantially non-contaminating
environment until said carbon material is contacted with said gas
stream.
76. The gas purifier system of claim 75, wherein said scavenger
comprises a metallated macroreticular polymer, wherein said polymer
is metallated with Group IA or Group IIB alkyl or aryl
organometallic compounds.
77. The gas purifier system of claim 75, wherein said scavenger
material is selected from the group consisting of Groups IIA, IVA,
IIIB and IVB metal oxides.
78. The gas purifier system of claim 77, wherein said oxide is
alumina or an alumina-based material.
79. The gas purifier system of claim 78, wherein said oxide is
modified by a metal salt or a metal oxide.
80. The gas purifier system of claim 77, wherein said oxide is
silica or a silica-based material.
81. The gas purifier system of claim 80, wherein said oxide is
modified by a metal salt or a metal oxide.
82. The gas purifier system of claim 75, wherein the scavenger
material is a zeolite molecular sieve.
83. The gas purifier system of claim 75, wherein the concentration
of impurities in said ultra-pure gas is less than 100 parts per
trillion.
84. The gas purifier system of claim 75, wherein said impurities
comprise organic compounds.
85. The ultra-low emission carbon material of claim 84, wherein
said organic compounds comprise straight chain or branched chain
hydrocarbons.
86. The ultra-low emission carbon material of claim 84, wherein
said organic compounds comprise aromatic hydrocarbons.
87. The ultra-low emission carbon material of claim 85, wherein
said hydrocarbon is hexane.
88. The ultra-low emission carbon material of claim 86, wherein
said aromatic hydrocarbon is benzene, or ethylbenzene.
89. The gas purifier system of claim 75, wherein said impurities
comprise carbon dioxide.
90. The gas purifier system of claim 75, wherein said impurities
comprise carbon monoxide.
91. The gas purifier system of claim 75, wherein said impurities
comprise water.
92. A gas purifier system comprising: a bed comprising a mixture of
an ultra-low emission carbon material capable of removing
impurities from a gas stream to less than 1 part-per-billion
concentration by volume and a scavenger material capable of
adsorbing oxygen and/or moisture from a gas stream to produce an
ultra-pure gas; a container for holding said bed, wherein said
container comprises an gas stream inlet and a gas stream outlet to
allow said gas stream to flow through said container, wherein said
container maintains said ultra-low emission carbon material in a
substantially non-contaminating environment until said carbon
material is contacted with said gas stream.
93. The gas purifier system of claim 92, wherein said scavenger
comprises a metallated macroreticular polymer, wherein said polymer
is metallated with Group IA or Group IIB alkyl or aryl
organometallic compounds.
94. The gas purifier system of claim 92, wherein said scavenger
material is selected from the group consisting of Groups IIA, IVA,
IIIB and IVB metal oxides.
95. The gas purifier system of claim 93, wherein said oxide is
alumina or an alumina-based material.
96. The gas purifier system of claim 94, wherein said oxide is
modified by a metal salt or a metal oxide.
97. The gas purifier system of claim 93, wherein said oxide is
silica or a silica-based material.
98. The gas purifier system of claim 96, wherein said oxide is
modified by a metal salt or a metal oxide.
99. The gas purifier system of claim 92, wherein the scavenger
material is a zeolite molecular sieve.
100. The gas purifier system of claim 92, wherein the concentration
of impurities in said ultra-pure gas is less than 100 parts per
trillion.
101. The gas purifier system of claim 92, wherein said impurities
comprise organic compounds.
102. The ultra-low emission carbon material of claim 101, wherein
said organic compounds comprise straight chain or branched chain
hydrocarbons.
103. The ultra-low emission carbon material of claim 101, wherein
said organic compounds comprise aromatic hydrocarbons.
104. The ultra-low emission carbon material of claim 102, wherein
said hydrocarbon is hexane.
105. The ultra-low emission carbon material of claim 103, wherein
said aromatic hydrocarbon is benzene, or ethylbenzene.
106. The gas purifier system of claim 92, wherein said impurities
comprise carbon dioxide.
107. The gas purifier system of claim 92, wherein said impurities
comprise carbon monoxide.
108. The gas purifier system of claim 92, wherein said impurities
comprise water.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to the field of gas purification, and
more specifically to the removal of trace impurities from inert
gases such as nitrogen, helium, and argon using solid scavenger
adsorption materials. More particularly, this invention comprises a
method of reducing concentrations of trace impurities, such as
hydrocarbons, carbon monoxide, and carbon dioxide, from process
gases to parts-per-billion and sub-parts-per-billion levels using
an ultra-low emission carbon based scavenger. This invention
further relates to reducing concentrations of impurities such as
organic compounds including, but not limited to, substituted and
unsubstituted hydrocarbons, wherein said hydrocarbons include
saturated, unsaturated, and aromatic hydrocarbons, carbon monoxide,
and carbon dioxide, as well as other impurities such as oxygen and
larger quantities of moisture (H.sub.2O), from process gases by
combining an ultra-low emission carbon material of this invention
and a second scavenger material capable of removing oxygen and/or
moisture from the process gas.
[0003] 2. Description of the Prior Art
[0004] Numerous products and processes require pure gases. One
known method of gas purification involves the adsorption of process
gas impurities on a bed or column of solid scavenger material. In
these solid adsorption methods, impurities are caught by the
surface of the scavenger material while the process gas preferably
passes unaltered through the bed or column.
[0005] Commonly used solid scavenger adsorption materials include
alumina, activated carbon, silica, adsorption clays, and secondary
scavengers. Activated carbon, for example, is used in PSA (Pressure
Swing Adsorption) plants and for solvent recovery from air in
painting facilities (See, for example, Wood and Stampfer, Carbon,
30:593 (1992); Wood and Stampfer, Carbon, 31:195 (1993); Nelson et
al., Am. Ind. Hyg. Assoc. J., 33:797 (1972); and Nelson et al., Am.
Ind. Hyg. Assoc. J., 52:235 (1991)). These techniques are known to
reduce selected impurities in a gas stream down to single digit
percentages, and perhaps even as low as ppm (parts per million)
concentrations. However, the use of solid scavenger adsorption
materials operating at ambient conditions to reduce
parts-per-billion (ppb) levels of impurities, particularly
hydrocarbons, to sub-ppb levels without contaminating the gas
stream with other impurities such as moisture is not known.
[0006] For most applications, reducing impurities in gases down to
the ppm level is satisfactory. However, ultra-pure gases having
impurity concentrations not exceeding ppt (parts-per-trillion (ppt)
levels are required in a growing number of industries. For example,
in semiconductor fabrication processes, gases such as nitrogen,
helium and argon are often required to not have more than low ppb
or sub-ppb impurity levels to ensure that the impurities do not
degrade the quality, and hence the performance of the semiconductor
chips. Gas purification systems are therefore widely used in the
manufacture of semiconductors to remove process gas impurities to
very low, trace concentrations.
[0007] The desire to develop methods to reduce impurities in
process gases down to sub-ppb concentrations is further driven by
the present ability to measure impurities at extremely low levels.
Modern chemical instrumentation such as Atmospheric Pressure Ion
Mass Spectrometry (APIMS) permits the detection of process gas
impurities such as carbon monoxide, carbon dioxide, oxygen, and
moisture (H.sub.2O) at sub-ppb concentrations.
[0008] The advances in the detection of trace levels of
hydrocarbons with APIMS has motivated researchers to further reduce
the levels of these impurities in ultra-pure process gases to
bellow the limits of detection of this supersensitive
instrumentation. One challenge has been to develop gas purification
materials and techniques that remove hydrocarbon impurities from an
ultra-pure gas without adding trace amounts of other
impurities.
[0009] Conventionally activated carbon, for example, is known as a
very effective adsorbent for removing hydrocarbon impurities from
gases. However, conventionally activated carbon is typically
activated at 200.degree. C. to 400.degree. C. in gas streams
contaminated with ppm levels of impurities such as moisture and
CO.sub.2. After conventional activation, the carbon material
contains trace amounts of water and CO.sub.2 that are either not
completely removed during activation or re-adsorbed in the
contaminated environment of the treatment process. The carbon
material may also produce trace amounts of moisture and CO.sub.2
during thermal activation due to chemical reaction of residual
functional groups or adsorbed species, such as by dehydroxylation
or decarboxylation reactions. The residual water and CO.sub.2 in
the conventionally activated carbon material are then released in
small quantities into a gas stream during a gas purification
process, thereby causing significant contamination of the gas and
rendering the effluent gas useless for high purity applications. In
some cases, conventionally activated carbon is characterized as
"hydrophobic" (repels or fails to adsorb water), even though
traditionally activated carbon has been shown to weakly adsorb
moisture upon exposure of a gas containing several hundreds to
several thousands of ppm of moisture (see, for example, Barton et
al., Carbon, 22:22 (1984), which is specifically incorporated
herein by reference). However, this adsorbed moisture, is also
easily released into a process gas stream during purification of
the gas. Thus, reducing hydrocarbon impurities in a process gas to
sub-ppb levels while maintaining very low levels of water vapor and
CO.sub.2 has proven extremely difficult.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is an object of this invention to provide a
method for reducing the concentration of hydrocarbon impurities as
well as other impurities in a process gas to sub-parts-per-billion
(sub-ppb) levels, while at the same time not emitting higher levels
of other contaminants, such as water vapor and CO.sub.2, into the
process gas being purified.
[0011] Another object of this invention is to provide "ultra-low
emission" (ULE) carbon materials for reducing trace impurities such
as organic compounds including, but not limited to, substituted and
unsubstituted hydrocarbons, wherein said hydrocarbons include
saturated, unsaturated, and aromatic hydrocarbons, carbon monoxide
(CO), carbon dioxide (CO.sub.2), and small amounts water vapor from
process gas streams such as helium (He), nitrogen (N.sub.2) and
argon (Ar) to parts-per-billion (ppb) and sub-parts-per-billion
(sub-ppb) levels.
[0012] Another object of this invention is to provide a method of
producing ultra-low emission (ULE) carbon materials capable of
reducing the concentration of organic compounds including, but not
limited to, substituted and unsubstituted hydrocarbons, wherein
said hydrocarbons include saturated, unsaturated, and aromatic
hydrocarbons, carbon monoxide (CO), carbon dioxide (CO.sub.2), and
water vapor (H.sub.2O) from a process gas to ppb and sub-ppb
levels.
[0013] It is a further object of the present invention to provide a
method of purifying gases with ultra-low emission (ULE) carbon
materials prepared according to the method of this invention,
wherein the method reduces trace amounts of hydrocarbon, carbon
monoxide (CO), carbon dioxide (CO.sub.2), and water vapor
(H.sub.2O) impurities to ppb and sub-ppb levels.
[0014] It is a further object of the present invention to provide a
one-component gas purifier system comprising a bed of an ultra-low
emission (ULE) carbon material of this invention capable of
reducing trace levels of organic compounds including, but not
limited to, substituted and unsubstituted hydrocarbons, wherein
said hydrocarbons include saturated, unsaturated, and aromatic
hydrocarbons, carbon monoxide, carbon dioxide, oxygen and water
vapor from a process gas to ppb and sub-ppb levels.
[0015] Yet another object of this invention is to provide a
two-component gas purifier system comprising an ultra-low emission
(ULE) carbon material of this invention and a secondary scavenger
material to remove impurities such as oxygen and larger quantities
of moisture that are not scavenged by the ultra-low emission (ULE)
carbon material. The two-component purifier system of this
invention acts as a combination gas purifier capable of producing a
purified gas with only sub-ppb levels of impurities such as organic
compounds including, but not limited to, substituted and
unsubstituted hydrocarbons, wherein said hydrocarbons include
saturated, unsaturated, and aromatic hydrocarbons, CO, CO.sub.2,
O.sub.2, and water vapor. In one embodiment, the secondary purifier
is a chemical scavenger material that removes a variety of
impurities such as moisture and oxygen from gas streams but does
not remove hydrocarbons. In one embodiment, the secondary purifier
is an organometallic resin as disclosed in U.S. Pat. No. 4,603,148,
which is specifically incorporated herein by reference. Other
materials that are suitable for use as secondary purifiers for the
removal of moisture include, but are not limited to, inorganic
high-surface-area solids such as oxides and mixed oxides, e.g.,
alumina, silica, silica-alumina, aluminosilicate zeolites and other
molecular sieves. These materials may be modified by salts, oxides
or hydroxides of the Group IA or IIA metals, and preferably are
thermally activated, as described in copending U.S. Provisional
Patent Application No. 60/251,000, filed Dec. 4, 2000, which is
specifically incorporated herein by reference. The secondary
purifier material is referred to herein as a "secondary
scavenger".
[0016] To achieve the foregoing and other objects and in accordance
with the purposes of the present invention, as embodied and broadly
described therein, one embodiment of this invention provides a
method for producing an ultra-low emission (ULE) carbon material,
comprising heating a carbon material under inert conditions at a
temperature and for a time sufficient to remove substantially all
of the water and carbon dioxide (CO.sub.2) contained in the carbon
material to produce an ultra-low emission (ULE) carbon material,
and transferring the ultra-low emission (ULE) carbon material to a
container under conditions that do not allow moisture, carbon
dioxide, or other atmospheric contaminants to be reintroduced into
the ultra-low emission (ULE) carbon material.
[0017] To further achieve the foregoing and other objects and in
accordance with the purposes of the present invention, as embodied
and broadly described therein, another embodiment of this invention
comprises a method for removing impurities such as organic
compounds including, but not limited to, substituted and
unsubstituted hydrocarbons, wherein said hydrocarbons include
saturated, unsaturated, and aromatic hydrocarbons, small amounts of
water vapor, carbon monoxide (CO), and carbon dioxide (CO.sub.2)
from process gases, the method comprising contacting a process gas
with a one-component gas purifying system comprising an ultra-low
emission (ULE) carbon material produced according to this
invention, wherein the concentrations of the trace impurities in
the process gas are reduced to below about one part-per-million
(ppm), and preferably to below about one part-per-billion (ppb)
upon contacting the process gas with the ultra-low emission (ULE)
carbon material of this invention.
[0018] To further achieve the foregoing and other objects and in
accordance with the purposes of the present invention, as embodied
and broadly described therein, another embodiment of this invention
comprises a two-component gas purifying system comprising a
canister containing ULE carbon material of this invention connected
in series with, and downstream of, a canister that contains a bed
of a secondary scavenger capable of removing larger amounts of
moisture and carbon dioxide from a process gas, the
series-connected canisters forming a two-component gas purifier
that operates to purify an input gas stream.
[0019] To further achieve the foregoing and other objects and in
accordance with the purposes of the present invention, as embodied
and broadly described therein, another embodiment of this invention
comprises a two-component gas purifier system comprising a canister
having an upstream portion that contains a bed of secondary
scavenger material capable of removing larger amounts of moisture
and carbon dioxide from a process gas, and a downstream portion
that contains a bed of ultra-low emission (ULE) carbon material of
this invention.
[0020] To further achieve the foregoing and other objects and in
accordance with the purposes of the present invention, as embodied
and broadly described therein, another embodiment of this invention
comprises a two-component gas purifier system comprising a canister
containing a secondary scavenger material intermixed with an
ultra-low emission (ULE) carbon material of the present
invention.
[0021] Additional objects, advantages and novel features of this
invention shall be set forth in part in the description that
follows, and in part will become apparent to those skilled in the
art upon examination of the following specification or may be
learned by the practice of the invention. The objects and
advantages of the invention may be realized and attained by means
of the instrumentalities, combinations, and methods particularly
pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The accompanying drawings, which are incorporated herein and
form a part of the specification, illustrate preferred embodiments
of the present invention, and together with the description, serve
to explain the principles of the invention.
[0023] In the Drawings:
[0024] FIG. 1 is a schematic representation of the production of an
ultra-low emission (ULE) carbon material according to the method of
this invention, including the transport of the ultra-low emission
(ULE) carbon material to a canister.
[0025] FIG. 2 is a schematic representation of a one-component gas
purifying system of this invention comprising a canister containing
an ultra-low emission (ULE) carbon material of this invention.
[0026] FIG. 3 is a schematic representation of a two-component gas
purifier system comprising a canister containing an ultra-low
emission (ULE) carbon material of this invention connected in
series with, and downstream of, a canister containing secondary
scavenger beads.
[0027] FIG. 4 is a schematic representation of an alternative
embodiment of a two-component gas purifier system of the invention
comprising a canister having an upstream layer of secondary
scavenger beads and a downstream layer of an ultra-low emission
(ULE) carbon material of this invention.
[0028] FIG. 5 is a schematic representation of an alternative
embodiment of a two-component gas purifier system of the invention
comprising a canister having a mixture of an ultra-low emission
(ULE) carbon material of this invention and secondary scavenger
beads.
[0029] FIG. 6 is a graph plotting moisture (H.sub.2O) emission
(thin line) and temperature (thick line) in an exhaust gas in
counts per second versus time (days) during the production of the
ultra-low emission (ULE) carbon beads, as measured by APIMS.
[0030] FIG. 7 is a graph plotting hexane concentration in
parts-per-billion versus time in hours for various hexane
challenges in a stream of argon flowing through a ultra-low
emission (ULE) carbon material of this invention, as measured by
APIMS.
[0031] FIG. 8 is a graph plotting moisture (H.sub.2O) concentration
measured by an AMETEK 5850 hygrometer versus time for a gas stream
that initially bypasses an ultra-low emission (ULE) carbon bed and
then is directed through the ultra-low emission (ULE) carbon bed
until moisture breakthrough occurs.
[0032] FIG. 9 is a graph plotting the response of APIMS in
counts-per-second (cps) versus time in minutes of a nitrogen stream
challenged with a mixture of benzene (m/z=78) and ethylbenzene
(m/z=106) that initially bypasses an ultra-low emission (ULE) bed
and then is directed through a bed of ultra-low emission (ULE)
carbon material of this invention.
[0033] FIG. 10 is a graph plotting the moisture response of APIMS
in counts per second (cps) versus time in minutes of a nitrogen
stream initially bypassing and then passing through a carbon bed
activated in situ by Advanced Technology Materials Incorporated in
an air tight canister.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The present invention provides ultra-low emission (ULE)
carbon materials for purifying process gases such as nitrogen
(N.sub.2), argon (Ar) and helium (He), and a method for producing
the ultra-low emission (ULE) carbon materials. As used herein, the
term "ultra-low emission (ULE)" carbon material refers to a carbon
material that is sufficiently dehydrated to display strong
hydrophilic properties and that, upon contact with a process gas
containing sub-ppm amounts of water vapor (H.sub.2O), produces a
purified gas having a water concentration below at least
parts-per-billion (ppb) levels, and preferably at
sub-parts-per-billion (sub-ppb) levels. The ULE carbon material of
this invention is further able to reduce the concentrations of
trace impurities such as organic compounds, carbon monoxide (CO)
and carbon dioxide (CO.sub.2) from a process gas contaminated with
such impurities to sub-ppb levels.
[0035] As used herein, the term organic compounds includes, but is
not limited to, substituted and unsubstituted compounds including,
but not limited to, alkanes, alkenes, alkynes, aromatic compounds
including arenes and heteroarenes, alcohols, thiols, ketones,
ethers, amines, and organic acids. The terms "alkanes, " ,
"alkenes," and "alkynes" include straight chain and branched chain
alkyls, alkenes, and alkynes. The term "aromatic" compounds
includes arenes and heteroarenes. As used herein, "arenes," is
intended to mean any stable monocyclic, bicyclic or tricyclic
carbon ring, wherein at least one ring is aromatic. The term
"heteroarene", as used herein, represents a stable 5- to 7-membered
monocyclic or stable 8- to 11-membered bicyclic heterocyclic ring
which is either saturated or unsaturated, and which consists of
carbon atoms and from one to four heteroatoms selected from the
group consisting of N, O, and S, and including any bicyclic group
in which any of the above-defined heterocyclic rings is fused to a
benzene ring. As used herein, the term "substituted" organic
compound refers to the above-listed compounds having one or more
substituents, including, but are not limited to, halo (fluoro,
bromo, chloro, iodo), hydroxy, nitro, amino, thio, alkoxy, aryloxy,
and oxo.
[0036] As stated above, conventionally activated carbon retains
enough moisture (H.sub.2O) and carbon dioxide (CO.sub.2) to add
significant amounts of water vapor and CO.sub.2 to the ultra-pure
gas stream during removal of the hydrocarbon impurities from the
gas stream. Thus, reducing hydrocarbon impurities in a process gas
to sub-ppb levels while maintaining very low levels of water vapor
and CO.sub.2 has proven extremely difficult. However, the inventors
discovered that when conventional carbon material is heated in an
ultra-dry, inert environment at a sufficient temperature and for a
sufficient time according to the method of this invention as
described below in detail, water and CO.sub.2 molecules that
normally occupy a significant number of sites on the conventional
carbon material are driven out of the carbon material. As a result
of the method of this invention, sites in the carbon material
normally occupied by water and CO.sub.2 in conventionally activated
carbon are freed up, thereby producing an ultra-low emission (ULE)
carbon material. These freed up sites are believed to have a high
affinity for moisture and CO.sub.2. Thus, unlike conventionally
activated carbon, the ultra-low emission (ULE) carbon material of
the present invention has freed up sites capable of efficiently
trapping and retaining trace amounts of moisture along with other
impurities from a gas stream, without concurrently emitting equal
or greater amounts of moisture (H.sub.2O) and carbon dioxide
CO.sub.2 back into the gas being purified. In other words, the
method of the present invention changes the properties of
conventionally activated carbon by transforming a conventional
hydrophobic carbon material, which has most or all of its available
hydrophilic sites occupied by water and other sites occupied by
CO.sub.2, to an ultra-low emission (ULE) carbon material, wherein a
significant number of the strong hydrophilic sites capable of
holding water molecules are unoccupied, and wherein a significant
number of sites normally occupied by CO.sub.2 are now
unoccupied.
[0037] As stated above, since the ultra-low emission (ULE) carbon
material of the present invention is strongly hydrophilic, it
adsorbs small amounts of moisture very efficiently, even in
relatively dry (sub-ppm levels of moisture) environments. However,
since the moisture capacity of the ultra-low emission (ULE) carbon
material of the present invention is small, the ultra-low emission
(ULE) carbon material can quickly become saturated with moisture
(H.sub.2O) upon contact with very small amounts of moisture. For
example, the relatively dry atmosphere of a conventional glove box
can still contain enough water vapor to saturate the hydrophilic
sites of the ultra-low emission (ULE) carbon material of the
present invention in a matter of seconds. Typically, glove boxes
have moisture levels of about 0.5-10 ppm, sometimes higher. Thus,
if the ultra-low emission (ULE) carbon material becomes
contaminated (i.e., saturated) with moisture, the carbon material
is rendered useless as a gas purifier, since the moisture-saturated
carbon would reemit moisture into the process gas stream that is
being purified. Accordingly, the method of the present invention
further includes an enclosed transport and filling mechanism (i.e.,
a "transfill system") for transferring the ultra-low emission (ULE)
carbon material from a high-temperature activation reactor to a gas
purifier container, wherein the transfill system is in an
atmosphere having moisture levels much lower than those in a
conventional glove box. Thus, the transfill system prevents
recontamination of the ultra-low emission (ULE) carbon material
after its production and the container maintains the ultra-low
emission (ULE) carbon material in a substantially contaminant-free
environment.
[0038] Briefly, to prepare an ultra-low emission (ULE) carbon
material according to the present invention, a carbon material is
placed in a reactor and is activated while in the reactor by
subjecting the carbon material to a relatively high temperature for
a given time period. In this superactivating process, as the
reactor temperature is lowered, the activation period (i.e., the
time required to produce an ultra-low emission (ULE) carbon
material of this invention) must be increased accordingly. An
ultra-dry inert gas flows through the carbon material contained in
the reactor during the activation process, and the exhaust gas
exiting the reactor may be directed to an instrument that measures
the amount of water in the exhaust gas. According to the present
invention, carbon materials are determined to be ultra-low emission
(ULE) carbon materials when the concentration of water emitted by
the carbon material (i.e., the water present in the exhaust gas) is
about 1 part-per-billion (ppb) or less, more preferably 100 ppt or
less, as measured for example with a hygrometer or Atmospheric
Pressure Ion Mass Spectrometry (APIMS) after the ultra-low emission
(ULE) carbon material has been cooled to room temperature. The
ultra-low emission (ULE) carbon material of this invention is
capable of removing impurities such as organic compounds, carbon
dioxide, and carbon monoxide from process gases to produce
ultra-pure gases, wherein the concentrations of all of the
impurities in the ultra-pure gases are reduced to parts-per-billion
(ppb) and sub-parts-per-billion (sub-ppb) levels.
[0039] The Carbon Material:
[0040] The ultra-low emission (ULE) carbon materials of the present
invention are preferably made from commercially available activated
carbon materials in the form of beads, pellets or extrudates.
Preferably ultra-low emission (ULE) carbon materials are prepared
from a high-hardness carbon that produces only small amounts of
carbon dust under typical working conditions for gas purification
processes such as space velocities (volume of gas at standard
temperature and pressure flowing per hour per unit volume of
purifier) up to 10,000 hr.sup.-1. Low dust emission avoids the
blockage of particle filters that are typically installed
downstream of purifier beds, and thus prevents the gas stream from
being interrupted by a blocked particle filter. An ultra-low
emission (ULE) carbon of the present invention can be derived from
commercially available carbon materials, which may be activated or
non-activated carbon. Suitable carbon materials for use in the
present invention include carbon beads supplied by Advanced
Technology Materials Incorporated ("ATMI" carbon), designed for
safe delivery systems (SDS) for hazardous and reactive gas storage.
ATMI carbon material is preactivated by Advanced Technology
Materials Incorporated at 800.degree. C. but is neither maintained
in a suitable fashion after activation to meet the criterion for
ultra-low emission (ULE) carbon nor analyzed for emissions. Another
suitable carbon material for the production of ultra-low emission
(ULE) carbon material is Norit.RTM. activated carbon supplied by
the Aldrich Chemical Company.
[0041] Activated carbon is commercially available, and in fact such
a commercial product is a preferred starting material for use in
accordance with this invention to produce an ultra-low emission
(ULE) carbon material of this invention. However, as stated above,
such commercially available activated carbon is too contaminated
with moisture, CO.sub.2 and other impurities to be suitable for the
gas purification requirements of the present invention. While
commercially available carbon material is effective for removing
hydrocarbon impurities from a process gas, it simultaneously emits
water vapor and other oxygenated impurities into the process gas
during a gas purification process at levels well above 1 ppb. The
activation of conventional carbon material to produce ultra-low
emission (ULE) carbon materials according to the method of the
present invention overcomes the deficiencies of conventional carbon
material, in that the ultra-low emission (ULE) carbon material is
capable of producing purified process gases while concurrently
keeping moisture levels in the purified gas well below one
part-per-billion (ppb). That is, ultra-low emission (ULE) carbon
materials of the present invention do not add water vapor to a gas
stream that passes though the ultra-low emission (ULE) carbon
material during a gas purification process.
[0042] In one preferred embodiment of this invention, an ultra-low
emission (ULE) carbon material is prepared from ATMI carbon beads.
ATMI carbon beads are spherical and have a diameter of about
0.7-1.0 millimeter. The spherical shape of the beads permits a high
packing density in a canister of a gas purifier system without
causing a significant pressure drop as gas flows through the
densely packed beads during a gas purification process.
Additionally, the ATMI carbon beads are very hard, and produce no
visible amount of dust during gas purification.
[0043] Production of ultra-low emission (ULE) carbon materials
[0044] While the method of superactivating carbon materials to make
the ultra-low emission (ULE) carbon materials as described below
utilizes ATMI carbon beads, such a description is merely for ease
of explanation. Thus, it will be understood by those of skill in
the art that other carbon materials may be likewise suitable for
use in the method of this invention.
[0045] In one embodiment of this invention, ATMI carbon beads are
activated to remove moisture (H.sub.2O) and CO.sub.2 from the beads
by heating the beads in a reactor at a sufficient temperature,
preferably from 300.degree. C. to 800.degree. C., and more
preferably from 500.degree. C. to 700.degree. C. During the heat
activation, an ultra-dry inert gas such as nitrogen, helium or
argon, or any combination thereof, is flowed through the reactor.
As used herein, an ultra-dry inert gas refers to an inert gas that
has been purified by flowing the gas through a suitable purifier
such as the one disclosed in U.S. Pat. No. 4,603,148, to decrease
the level of moisture impurity in the inert gas to below about 1
ppb. The carbon beads are heated under the inert gas flow for at
least several hours, more preferably between about twenty four
hours and five days, depending on the temperature.
[0046] During the activation process performed according to the
method of this invention, the levels of impurities (e.g., moisture
and CO.sub.2) emitted from the carbon beads into the inert gas are
preferably monitored using a hygrometer or Atmospheric Pressure Ion
Mass Spectrometry (APIMS) instrumentation. Activation of the carbon
beads is determined to be complete when the moisture (H.sub.2O) and
CO.sub.2 levels measured in the inert gas stream exiting the
reactor at the activation temperature indicate that moisture and
CO.sub.2 concentrations are sufficiently low to be acceptable for
ultra high purity applications, i.e., less than about 1 ppb at room
temperature. Typically, emissions of about 10 ppm or less of
moisture as measured at carbon bead temperatures above 500.degree.
C. are sufficient to guarantee that an ultra-low emission carbon
material (ULE) has been produced and that the material will perform
as an ultra-low emission carbon material when at ambient
temperature.
[0047] FIG. 1 illustrates one embodiment of the present invention
for producing an ultra-low emission (ULE) carbon material in
accordance with this invention and for transporting the ultra-low
emission (ULE) carbon material to a canister for use in a gas
purifier system. In FIG. 1, heat reactor 12 contains a supply of
carbon beads 14 that are to be superactivated in accordance with
the invention. A dry, purified inert gas 18 such as helium,
nitrogen, or argon, enters reactor 12 through inlet valve 22 and
flows through carbon beads 14 during the activation process. Carbon
beads 14 within heat reactor 12 are subjected to a high
temperature, preferably from about 300.degree. C. to 800.degree.
C., and more preferably from about 500.degree. C. to 700.degree.
C., for at least several hours, more preferably between about
twenty four hours and five days, depending on the temperature, as
ultra-dry inert gas 18 flows continuously through carbon beads 14
in heat reactor 12. Inert gas 18 exits heat reactor 12 at outlet
ball valve 26 and continues on through valve 30 to instrumentation
38. Instrumentation 38 monitors the chemical content of inert gas
18 exiting reactor 12 to determine when the activation of carbon
beads 14 is complete. In one embodiment, instrumentation 38 is a
hygrometer commercially available from Meeco, Ametek, or
Panametrics, which monitors inert gas 18 exiting reactor 12 for
moisture content. When the moisture (H.sub.2O) content of inert gas
18 exiting reactor 12 at the activation temperature is reduced to
the levels where sub-ppb emissions of moisture (H.sub.2O) from the
ultra-low emission (ULE) at room temperature are guaranteed,
typically less than 10 ppm at 500.degree. C., activation of carbon
beads 14 is complete. The ultra-low emission (ULE) carbon beads 14
are then cooled, preferably to ambient temperature, while in
reactor 12. Room temperature emissions of moisture and CO.sub.2 can
be verified at sub-ppb levels by replacing hygrometer
instrumentation 38 with APIMS instrumentation.
[0048] Transfill of the ultra-low emission (ULE) carbon:
[0049] In order to minimize the contamination of the ultra-low
emission (ULE) carbon by re-adsorption of moisture and other
oxygenated materials such as O.sub.2 and CO.sub.2, the present
invention provides a completely enclosed transfer and filling
("transfill") system. The transfill system, illustrated in FIG. 1,
comprises an environmentally sealed, contamination-free transfer
system that operates to physically transport a portion of the
ultra-low emission (ULE) carbon beads 14 from the reactor to
individual canisters while maintaining the ultra-low emission (ULE)
carbon material in a substantially contaminant free environment.
That is, the transfill system allows the ultra-low emission (ULE)
carbon material to be transferred to individual containers without
allowing moisture, carbon dioxide, or other contaminants to come
into contact with the ultra-low emission (ULE) carbon material. The
individual containers can then be incorporated into gas purifier
systems.
[0050] Referring again to FIG. 1, the ultra-low emission (ULE)
carbon beads 14 are first transferred from the reactor 12 through
opened ball valve 26 to a calibrated glass cylinder 44 via gravity
fill. Specialized ball valves such as ball valve 26 are desirable
in order to minimize contamination of the ultra-low emission (ULE)
carbon beads 14. A flexible line 40 allows the orientation of
reactor 12 to be changed from the horizontal position used for
activation of the carbon beads to a vertical position for the
transfill process. The ultra-low emission (ULE) carbon beads 14 are
transferred to calibrated cylinder 44 for volume determination
under and ultra-dry inert gas flow 18 which flows through opened
valves 22 and 26 and is vented through open valve 48, while all
other valves in the system remain closed.
[0051] After the desired amount of ultra-low emission (ULE) carbon
beads 14 is collected in the calibrated cylinder 44, ball valve 26
is closed and ball valve 52 is opened to allow the ultra-low
emission (ULE) carbon beads 14 to flow through a flexible line 56
into a gas purifier canister 64. Canister 64 comprises a gas inlet
valve 68, a gas outlet valve 76, and a receiving port 70 through
which a portion of the ultra-low emission (ULE) carbon beads are
transferred into canister 64. This transfer process from calibrated
cylinder 44 to canister 64 is conducted under an ultra-dry inert
gas flow 18 through opened valve 22, which is vented through opened
diaphragm valve 76. A thorough cross purge with inert gas 72
through canister 64, calibrated cylinder 44, and vent lines to
instrumentation 38 is necessary to remove moisture (H.sub.2O),
CO.sub.2, and O.sub.2 contamination from the canister and the
transfill system prior to the filling procedure of the canister 64
in order to purge the transfill lines and the canister 64, thereby
ensuring that the ultra-low emission (ULE) carbon material is not
contaminated by residual impurities in the transfill system or the
canister.
[0052] Once all of the ultra-low emission (ULE) carbon beads 14 are
transferred from calibrated cylinder 44 to canister 64 having a gas
inlet valve 68, a gas outlet valve 76, with outlet valve 76 closed,
and a slow reverse ultra-dry inert gas stream 72 is initiated
through valve 68 and vented though valve 48. The flow of inert gas
72 should remain small to prevent blowing the ultra-low emission
(ULE) carbon beads out of canister 64 and back into the system.
Flexible hose 56 is then disconnected from canister 64 at fitting
60 while inert gas 72 flows through valve 68 and vents through the
disconnected fitting 60 to minimize contamination. The
disconnection procedure is preferentially performed in a glove box
or with a plastic purge bag that is inflated by an ultra pure inert
gas and is attached above and below the fitting 60 to completely
surround the fittings. The plastic bag provides a "micro
environment" of a clean purge gas and further minimizes exposure to
ambient contaminants. The open fitting 60 is then closed with a
plug (not shown) while maintaining the inert gas purge 72. Canister
64, filled with ultra-low emission (ULE) carbon beads, is then
ready for installation in a gas purifying system.
[0053] The exact details of construction of transfill system as
illustrated in FIG. 1 are not critical to the invention, since a
transfill system of this invention can take a number of physical
forms. Thus it will be understood by those of skill in the art that
a transfill system of this invention will be constructed and
arranged so as to prevent contamination of carbon beads 14. That
is, the transported ultra-low emission (ULE) carbon beads 14
residing in a canister 64 remain generally as highly activated as
they were at the end of their activation within heat reactor
12.
[0054] Gas Purification Systems
[0055] One embodiment of a portion of a gas purification system of
the present invention is illustrated in FIG. 2. This gas
purification system comprises a one-component canister 64
containing ultra-low emission (ULE) carbon material 14. Canister 64
is prepared by the transfill process described above, and is then
installed in a gas purification system for purification of gas
100.
[0056] An alternative embodiment of a portion of a gas purification
system of the present invention is illustrated in FIG. 3. The
system shown in FIG. 3 is a two-component gas purifier system for
the purification of gas 100, wherein the two-component gas purifier
comprises canister 64 containing ultra-low emission (ULE) carbon
beads 14 connected in series with, and downstream of, a canister
164 containing secondary scavenger 82 for removing larger
concentrations of moisture and oxygen that may be present in the
impure process gas. The ultra-low emission (ULE) carbon material
does not remove oxygen and has only a small capacity for water
vapor. The water capacity is only about 0.1% of that of typical
chemical scavengers and thus, ultra-low emission (ULE) carbon will
not address the requirements of typical high purity gas
applications, where oxygen (O.sub.2) and larger amounts of moisture
are key impurities. A combined bed, however, has the benefit of
large oxygen and/or moisture capacities as well as the capabilities
to remove organic compounds and carbon monoxide (CO).
[0057] In one embodiment of the gas purification system illustrated
in FIG. 3, the secondary scavenger material 24 comprises a
metallated macroreticular polymer, wherein the polymer is
metallated with a Group IA or Group IIB alkyl or aryl
organometallic compound, as described in U.S. Pat. No. 4,603,148 to
Tom, which is specifically incorporated herein by reference. In
another embodiment, the secondary scavenger is a zeolite molecular
sieve.
[0058] Alternatively, the secondary scavenger comprises, but is not
limited to, inorganic high-surface-area solids such as oxides and
mixed oxides, for example, alumina, silica, silica-alumina,
aluminosilicate zeolites and other molecular sieves. These
materials may be modified by salts, oxides or hydroxides of the
Group IA or IIA metals, and preferably are thermally activated, as
described in copending U.S. Provisional Patent Application No.
60/251,000, filed Dec. 4, 2000, which is specifically incorporated
herein by reference. In one embodiment, the secondary scavenger
comprises a Group IIA, IVA IIIB or IVB metal oxide such as an
alumina oxide, alumina-based oxide, silica, or a silica-based
oxide. Preferably, the metal oxide has a high surface area of at
least about 30 m.sup.2/g. In another embodiment, the secondary
scavenger is an alumina oxide, alumina-based oxide, silica, or a
silica-based oxide that has been modified by a salt, oxide, or
hydroxide of a Group IA or Group IIA metal as described in
copending U.S. Provisional Patent Application Ser. No. 60/251,000,
filed Dec. 4, 2000, supra. In this embodiment, the modifier
comprises between about 1 to 20 percent weight of the modified
material.
[0059] In the two-component gas purifier embodiment shown in FIG.
3, preparation of canister 164 containing secondary scavenger beads
82 involves the transfill process described above from container 80
containing secondary scavenger beads 82. Referring again to FIG. 1,
reservoir 80 containing secondary scavenger beads 82 is
incorporated into the transfill system. The secondary scavenger
beads 82 are first transferred by gravity fill into calibrated
cylinder 44 through flexible line 40, during which a stream of
inert gas 84 flows through valve 88 and vents through valve 48.
Once a measured amount of secondary scavenger beads 82 has been
transferred to cylinder 44, valve 52 is opened to allow secondary
scavenger beads 82 to be transferred through flexible line 56 into
canister 164, while a flow of inert gas 84 through cylinder 44 and
canister 164 is maintained. After secondary scavenger beads 82 have
been completely transferred to canister 164, line 56 is
disconnected from canister 164 at fitting 60 while a stream of
inert gas 72 flows through canister 164. Fitting 60 is closed with
a plug (not shown) while the inert gas purge 72 is maintained,
after which canister 164 containing resin beads 120 is ready for
use in the gas purifying system as illustrated in FIG. 3.
Alternatively, canister 164 can be prepared according to standard
filling procedures in a glove box. This is due to the fact that the
large moisture and oxygen capacity of the secondary scavenger beads
causes the beads to be less sensitive to exposure of small levels
of contaminants during filling than the ultra-low emission (ULE)
carbon material.
[0060] Canister 164 with the secondary scavenger beads 82 is then
connected to canister 64 filled with the ultra-low emission (ULE)
carbon material. The connection is preferentially performed while
flowing an ultra-dry inert gas through canister 64 while keeping
the inlet and outlet of canister 164 closed, to purge contaminants
from the connection with an ultra-dry inert gas prior to closing
the connection.
[0061] FIG. 4 shows a portion of another embodiment of a
two-component gas purifier system of the invention. The gas
purifier system illustrated in FIG. 4 includes a canister 264
having an upstream portion of secondary scavenger beads 82 selected
from the materials described above and a downstream portion of
ultra-low emission (ULE) carbon beads 14.
[0062] Canister 264 is prepared using the transfill system
illustrated in FIG. 1. One embodiment of preparing canister 264
comprises first partially filling canister 264 with a measured
amount of ultra-low emission (ULE) carbon beads 14 using the
transfill system as described above, followed by filling the
remaining volume of canister 264 with the secondary scavenger beads
82 using the transfill as described above. The transfill system for
preparing canister 264 includes the appropriate inert gas purges as
described above to prevent contamination of canister 264 by
moisture (H.sub.2O), O.sub.2 and CO.sub.2.
[0063] FIG. 5 illustrates an alternative embodiment of a
two-component gas purifier system of this invention. The
two-component gas purifier shown in FIG. 5 comprises canister 364
containing a mixture of ultra-low emission (ULE) carbon beads 14
and secondary scavenger beads 82 selected from the materials
described above. Canister 364 is prepared using the above-described
transfill system for preparing canister 264. The mixing of ULE
carbon beads 14 and secondary scavenger beads 82 can be performed
by mechanical agitation while beads 14 and 82 are contained within
calibrated cylinder 44 (FIG. 1), or after beads 14 and 82 have been
transferred to canister 364.
[0064] The foregoing description is considered as illustrative only
of the principles of the invention. Further, since numerous
modifications and changes will be readily apparent to those skilled
in the art, it is not desired to limit the invention to the exact
construction and process shown as described above. Accordingly, all
suitable modifications and equivalents may be resorted to falling
within the scope of the invention as defined by the claims that
follow.
[0065] The words "comprise," "comprising", "include," "including,"
and "includes" when used in this specification and in the following
claims are intended to specify the presence of stated features,
integers, components, or steps, but they do not preclude the
presence or addition of one or more other features, integers,
components, steps, or groups thereof.
EXAMPLES
[0066] Example 1: Production of an ultra-low emission (ULE)
carbon
[0067] ATMI carbon beads (10 mL) were heated stepwise in a reactor
over several days in an ultra-dry nitrogen atmosphere at a 2 slpm
(standard liters per minute) flow rate, and the concentrations of
moisture and carbon dioxide (CO.sub.2) in the exhaust stream were
monitored by APIMS. FIG. 6 shows the results obtained during
monitoring of moisture emission, where the thin line represents the
moisture emission levels, and the thick line represents temperature
of the reactor.
[0068] The initial levels of moisture in the exhaust gas at ambient
temperature decreased slowly over several days. An increase of the
activation temperature from room temperature to 110.degree. C.
increased the amount of moisture in the exhaust gas stream by a
factor of about 500. After cooling back to room temperature, the
moisture level in the exhaust gas stream rapidly dropped to
concentrations below that observed prior to heating. Further
heating to 300.degree. C. and to 500.degree. C. resulted in an
additional release of significant amounts of moisture (H.sub.2O)
from the carbon material. After activation of the carbon at
500.degree. C. for five days, the moisture levels emitted into the
exhaust gas stream at 500.degree. C. approached concentrations
observed in the exhaust stream at ambient temperature prior to the
activation procedure, that is, about 500-1000 counts/s. After
cooling to room temperature, the moisture response dropped to about
100 counts/s, indicating sub-ppb moisture concentrations. The
carbon dioxide emission followed similar trends to the moisture
emission (data not shown).
[0069] Example 2: Removal of straight-chain hydrocarbons from a gas
stream using an ultra-low emission (ULE) carbon material
[0070] A gas purifier comprising a densely packed bed of ultra-low
emission (ULE) carbon beads (60 cc) prepared according to the
method of this invention was installed downstream of a calibration
system capable of adding trace amounts of hydrocarbons vapors into
a gas stream. The efficiency of the ultra-low emission (ULE) carbon
beads in removing the trace hydrocarbons from an ultra-dry argon
stream was studied using APIMS instrumentation that was installed
downstream of the bed of ultra-low emission (ULE) carbon beads.
FIG. 7 shows the results after flowing argon containing trace
amounts of hexane (i.e., between about 0.6 ppb and 6.3 ppm) through
a bed of ultra-low emission (ULE) carbon beads at a flow rate of 2
slpm. Initially, the gas purifier containing the ultra-low emission
(ULE) carbon beads was bypassed to establish a 5 ppb hexane
concentration in the argon gas stream. When the argon gas stream
containing the hexane impurity was directed through the gas
purifier, the hexane concentration in the exhaust argon gas stream
exiting the purifier dropped to below the detection limit of the
APIMS instrumentation. That is, the concentration of hexane in the
exhaust stream was less than 100 ppt.
[0071] While flowing through the purifier, the hexane challenge was
varied between 0.6 ppb and 6.3 ppm. A slight breakthrough of about
0.5 ppb hexane was observed at the high challenge of 6.3 ppm,
corresponding to a removal of hexane vapor by a factor of more than
10,000. Below a challenge of about 50 ppb the hexane concentration
in the exhaust gas stream was not distinguishable from the
baseline.
[0072] Example 3: Removal of moisture (H.sub.2O) from a gas stream
using an ultra-low emission (ULE) carbon beads
[0073] FIG. 8 shows the removal of a about 5 ppm moisture challenge
in nitrogen at 500 cc/min flow by a purifier containing 60 cc of
ultra-low emission (ULE) carbon beads. The measurements were
performed with an AMETEK 5850 moisture analyzer (Ametek, Paoli,
Pa). The detection limit of the setup was about 0.5 ppm. The
elimination of the water challenge confirmed that the ultra-low
emission (ULE) carbon beads were strongly hydrophilic. The amount
of water vapor removed until breakthrough occurred was about 0.01
liter water vapor at standard conditions per liter ultra-low
emission (ULE) carbon beads.
[0074] Example 4: Removal of aromatic species from a gas stream
using an ultra-low emission (ULE) carbon beads
[0075] FIG. 9 shows the removal of trace amounts of the aromatic
species benzene (m/z=78) and ethylbenzene (m/z=106) from a nitrogen
stream at 2000 cc/min by a purifier filled with 10 cc of ultra-low
emission (ULE) carbon beads. The measurements were performed by
APIMS. The instrument response at m/z=78 and m/z=106 while flowing
the contaminated nitrogen through the purifier was identical to the
background response obtained with a nitrogen gas stream free of
benzene and ethylbenzene.
[0076] Example 5: Moisture level measurements of an ATMI carbon
sample activated and shipped in air-tight vessel
[0077] A sample of ATMI carbon that had been activated and packaged
by Advanced Technology Materials Incorporated was tested for
moisture content. FIG. 10 shows moisture outgassing of a 50 cc
carbon sample contained in an air-tight stainless steel reactor and
which had been activated by Advanced Technology Materials
Incorporated in-situ using cylinder quality helium (99.999% purity)
as purge gas. Activation conditions used by Advanced Technology
Materials Incorporated comprised heating the ATMI carbon at
800.degree. C. for 8 hrs under 200 sccm helium flow.
[0078] Outgassing of moisture from the ATMI carbon was investigated
using APIMS instrumentation and a nitrogen matrix at 2 slpm. After
the system was dried in an ultra-dry inert gas stream to obtain a
moisture response of less than about 100 counts/s (400-500
counts/s, which corresponds to about 1 ppb), the vessel containing
the ATMI carbon was switched in line and a moisture spike of about
30,000 counts/s was observed. After 14 hours of dry down, the
response decreased to about 200 counts/s. The temperature was then
increased to 100.degree., 300.degree. and 500.degree. C., causing
further emission of significant quantities of water. The results
indicated that ATMI carbon as activated and stored by Advanced
Technology Materials Incorporated is not sufficient to meet the
requirements for ultra-low emission (ULE) carbon material.
Impurities in the 5.5 grade helium purge gas, such as low ppm
moisture levels, as well as insufficient conditioning times were
suspected as main contributors to the observed outgassing of
moisture.
* * * * *