U.S. patent application number 10/911868 was filed with the patent office on 2005-02-17 for process and apparatus for enriching ammonia.
This patent application is currently assigned to The BOC Group. Invention is credited to Ji, Wenchang, Sadkowski, Piotr J., Shirley, Arthur I..
Application Number | 20050034479 10/911868 |
Document ID | / |
Family ID | 33567979 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050034479 |
Kind Code |
A1 |
Ji, Wenchang ; et
al. |
February 17, 2005 |
Process and apparatus for enriching ammonia
Abstract
A process for enriching a crude ammonia stream having moisture
and/or metal impurities and/or gas impurities therein. The crude
ammonia stream is condensed to form a crude liquid ammonia stream.
A distillation membrane or pervaporation membrane is contacted with
the crude liquid ammonia stream to form an enriched ammonia vapor
stream, which is removed as a permeate. When the crude ammonia
stream originates from a manufacturing tool, the enriched ammonia
vapor stream may be recycled to the manufacturing tool. There is
also an apparatus for enriching a crude ammonia stream.
Inventors: |
Ji, Wenchang; (Basking
Ridge, NJ) ; Shirley, Arthur I.; (Hillsborough,
NJ) ; Sadkowski, Piotr J.; (Ash, GB) |
Correspondence
Address: |
Paul D. Greeley, Esq.
Ohlandt, Greeley, Ruggiero & Perle, L.L.P.
10th Floor
One Landmark Square
Stamford
CT
06901-2682
US
|
Assignee: |
The BOC Group
|
Family ID: |
33567979 |
Appl. No.: |
10/911868 |
Filed: |
August 5, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60494729 |
Aug 13, 2003 |
|
|
|
Current U.S.
Class: |
62/617 ;
62/606 |
Current CPC
Class: |
B01D 61/362 20130101;
B01D 61/364 20130101; C01C 1/024 20130101 |
Class at
Publication: |
062/617 ;
062/606 |
International
Class: |
C10G 009/00; C10G
011/00; C10G 047/00; C10G 049/22; C10G 015/00; F25J 003/00; F25J
001/00 |
Claims
What is claimed is:
1. Process for enriching a crude ammonia stream having moisture
and/or metal impurities and/or gas impurities therein, which
comprises: condensing said crude ammonia stream to form a crude
liquid ammonia stream; and contacting a distillation membrane or
pervaporation membrane with said crude liquid ammonia stream,
wherein an enriched ammonia vapor stream is removed as a
permeate.
2. The process of claim 1, wherein said crude ammonia stream
originates from a manufacturing tool, and wherein said enriched
ammonia vapor stream is recycled to said manufacturing tool.
3. The process of claim 1, wherein said enriched ammonia vapor
stream contacts a gas separation membrane, wherein a
further-enriched ammonia vapor stream is removed as a permeate.
4. The process of claim 3, wherein said crude ammonia stream
originates from a manufacturing tool, and wherein said
further-enriched ammonia vapor stream is recycled to said
manufacturing tool.
5. The process of claim 3, wherein said crude ammonia stream
contacts a thermal swing adsorber prior to condensation.
6. A process for enriching a crude ammonia stream having moisture
and/or metal impurities and/or gas impurities therein, which
comprises: separating said crude ammonia stream via a first
separator into a first crude ammonia liquid stream and a first
crude ammonia vapor stream; contacting a gas separation membrane
with said first crude ammonia vapor stream, wherein a first
enriched ammonia vapor stream is removed as a permeate; passing
said first enriched ammonia vapor stream to said first separator;
separating said first crude ammonia liquid stream via a second
separator into a second crude ammonia liquid stream and a second
enriched ammonia vapor stream as a product stream; contacting a gas
distillation membrane with said second crude ammonia liquid stream,
wherein a third enriched ammonia vapor stream is removed as a
permeate; and passing said third enriched ammonia vapor stream to
said first separator.
7. The process of claim 6, wherein said crude ammonia stream
originates from a manufacturing tool, and wherein said product
stream is recycled to said manufacturing tool.
8. A system for enriching a crude ammonia stream having moisture
and/or metal impurities and/or gas impurities therein, which
comprises: a condenser for condensing said crude ammonia stream to
form a crude liquid ammonia stream; and a distillation membrane or
pervaporation membrane that produces an enriched ammonia vapor
permeate from said crude liquid ammonia stream.
9. The system of claim 8, further comprising a manufacturing tool
from which said crude ammonia stream originates and a conduit
capable of recycling said enriched ammonia vapor stream to said
manufacturing tool.
10. The system of claim 8, further comprising a gas separation
membrane with which produces a further-enriched ammonia vapor
permeate from said enriched ammonia vapor.
11. The system of claim 10, further comprising a manufacturing tool
from which said crude ammonia stream originates, and a conduit
capable of recycling said further-enriched ammonia vapor stream to
said manufacturing tool.
12. The system of claim 10, further comprising a thermal swing
adsorber disposed upstream of said condenser.
13. A system for enriching a crude ammonia stream having moisture
and/or metal impurities and/or gas impurities therein, which
comprises: a first separator which is capable of forming a first
crude ammonia liquid stream and a first crude ammonia vapor stream
from said first crude ammonia stream; a gas separation membrane
which is capable of separating a first enriched ammonia vapor
stream from said first crude ammonia vapor stream; a first conduit
for conveying said first enriched ammonia vapor stream to said
first separator; a second conduit for conveying said first crude
ammonia liquid stream to a second separator, wherein said second
separator is capable of separating a second crude ammonia liquid
stream and a second enriched ammonia vapor stream from said first
crude ammonia liquid stream; a gas distillation membrane which is
capable of separating from said second crude ammonia liquid stream
a third enriched ammonia vapor stream; and a third conduit for
conveying said third enriched ammonia vapor stream to said first
separator.
14. The system of claim 13, further comprising a manufacturing tool
from which said crude ammonia stream originates, and wherein a
fourth conduit recycles said product stream to said manufacturing
tool.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
[0001] The present application claims priority from U.S.
Provisional Application 60/494,729, filed Aug. 13, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a process and apparatus for
enriching a crude ammonia stream having metal impurities and/or gas
impurities and/or moisture therein.
[0004] 2. Description of the Prior Art
[0005] In semiconductor manufacturing, ammonia is used to remove a
wide variety of contaminants, including moisture, gas impurities,
and metals. Gas impurities include oxygen, nitrogen, hydrogen,
carbon monoxide, and carbon dioxide. Metals include sodium,
potassium, aluminum, calcium, iron, nickel, chromium, copper,
manganese, and zinc.
[0006] It would be desirable to recover and recycle ammonia used in
semiconductor manufacturing. Recovery and recycle would save raw
material costs and reduce process effluent. The presence of
contaminants in the ammonia prevents direct recovery and
recycle.
[0007] U.S. Pat. No. 6,065,306 describes a method for removing
contaminants from crude ammonia streams. A crude ammonia stream is
enriched by removal of moisture via a temperature swing adsorption
unit and removal of gas impurities via a gas separation
membrane.
[0008] It would be desirable to have a process and apparatus for
recovering and recycling ammonia. It would further be desirable to
have a process and apparatus for enriching a crude ammonia stream.
It would still be further desirable to have a process and apparatus
for removing moisture, metals, and gas impurities from a crude
ammonia stream. It would still be further desirable to have a
process and apparatus for enriching a crude ammonia stream in a
semiconductor manufacturing process.
[0009] It was surprisingly found there could be a process and
apparatus for recovering and recycling ammonia. It was further
surprisingly found there could be a process and apparatus for
recovering and recycling ammonia in a semiconductor manufacturing
process. It was still further surprisingly found there could be a
process and apparatus for enriching a crude ammonia stream. It was
yet further surprisingly found there could be a process and
apparatus for enriching ammonia and removing moisture, metal
impurities, and gas impurities.
SUMMARY OF THE INVENTION
[0010] A process for enriching a crude ammonia stream having
moisture and/or metal impurities and/or gas impurities therein. The
crude ammonia stream is condensed to form a crude liquid ammonia
stream. A distillation membrane or pervaporation membrane is
contacted with the crude liquid ammonia stream to form an enriched
ammonia vapor stream, which is removed as a permeate. When the
crude ammonia stream originates from a manufacturing tool, the
enriched ammonia vapor stream may be recycled to the manufacturing
tool.
[0011] A process for enriching a crude ammonia stream having
moisture and/or metal impurities and/or gas impurities therein. The
process has the following steps: a) conveying the crude ammonia
stream to a first separator maintained under conditions sufficient
to form a first crude ammonia liquid stream and a first crude
ammonia vapor stream; b) contacting a gas separation membrane with
the first crude ammonia vapor stream to form a first enriched
ammonia vapor stream removed as a permeate; c) conveying the first
enriched ammonia vapor stream to the first separator; d) conveying
the first crude ammonia liquid stream to a second separator
maintained under conditions sufficient to form a second crude
ammonia liquid stream and a second enriched ammonia vapor stream as
a product stream; e) contacting a gas distillation membrane with
the second crude ammonia liquid stream to form a third enriched
ammonia vapor stream removed as a permeate; and f) conveying the
third enriched ammonia vapor stream to said first separator.
[0012] An apparatus for enriching a crude ammonia stream having
moisture and/or metal impurities and/or gas impurities therein. The
apparatus has a) a condenser for condensing the crude ammonia
stream to form a crude liquid ammonia stream and b) a distillation
membrane or pervaporation membrane that separates a permeate stream
of an enriched ammonia vapor from said crude liquid ammonia
stream.
[0013] An apparatus for enriching a crude ammonia stream having
moisture and/or metal impurities and/or gas impurities therein. The
apparatus has a) a first separator which is capable of forming a
first crude ammonia liquid stream and a first crude ammonia vapor
stream; b) a gas separation membrane which is capable of separating
a first enriched ammonia vapor stream from the first crude ammonia
vapor; c) a first conduit for conveying the first enriched ammonia
vapor stream to the first separator; d) a second conduit for
conveying said first crude ammonia liquid stream to a second
separator wherein the second separator is capable of separating a
second crude ammonia liquid stream and a second enriched ammonia
vapor stream as a product stream from said first crude ammonia
liquid stream; e) a gas distillation membrane which is capable of
separating from said second crude ammonia liquid stream a third
enriched ammonia vapor stream; and f) a third conduit for conveying
the third enriched ammonia vapor stream to the first separator.
DESCRIPTION OF THE FIGURES
[0014] Embodiments of the present invention are generally
illustrated by reference to the several figures herein.
[0015] FIG. 1 illustrates a schematic diagram of an embodiment of a
process and apparatus according to the present invention.
[0016] FIG. 2 illustrates a schematic diagram of another embodiment
of a process and apparatus according to the present invention.
[0017] FIG. 3 illustrates a schematic diagram of yet another
embodiment of a process and apparatus according to the present
invention.
[0018] FIG. 4 illustrates a schematic diagram of still another
embodiment of a process and apparatus according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] When originating from manufacturing tooling, crude ammonia
typically takes the form of a vapor. The vapor can be condensed to
a substantially liquid state by reducing temperature and/or raising
pressure. The condensing means (condenser) can take the form of any
condensing and/or pressure vessel wherein temperature and/or
pressure and/or volume can be regulated. The temperature range will
typically vary from about -30.degree. C. to about 10.degree. C. The
pressure range will typically vary from about 1.18 to about 6.075
atmospheres absolute. The crude ammonia liquid can take any known
thermodynamic form, such a critical liquid or a conventional
liquid.
[0020] After condensation, the crude ammonia liquid is contacted
with a distillation membrane or pervaporation membrane to yield an
enriched ammonia vapor. The distillation membrane or pervaporation
membrane evolves ammonia vapor but retains a substantial proportion
of metal impurities and/or moisture as a retentate.
[0021] Pervaporation membranes typically operate by adsorbing
liquid at the retentate side, diffusing through the membranes, and
then desorbing at the permeate side. Distillation membranes
typically operate by evaporation and diffusion through the membrane
microporous structure. The operating temperature range will
typically vary from about -30.degree. C. to about 10.degree. C. At
-30.degree. C., the operating pressure range will typically be at
least about 1.18 atmospheres absolute. At 10.degree. C., the
operating pressure will typically be at least about 6.075
atmospheres absolute. Preferably, the operating temperature of the
membrane is in a range of about 0.degree. C. to about 5.degree. C.
at a pressure selected such that the ammonia at the temperature
will liquefy. For membrane distillation, at any operating
temperature, the ammonia pressure should not exceed ammonia
intrusion pressures of selected membranes at which ammonia would
penetrate into the membrane microporous structure.
[0022] Distillation membranes are typically comprised of
microporous materials, including microporous polymers. Distillation
membrane materials are hydrophobic. The surface of the membranes
typically cannot be wetted by water and ammonia. Typical pore size
of microporous membranes ranges from about 0.1 to about 100
microns. The preferred membrane pore size ranges from about 0.1 to
about 5 microns. The most preferred membrane pore size is about 0.2
microns. The microporous membranes can be made by various polymers,
including polyvinylidene fluoride (PVDF), Teflon (PTFE), and
polypropylene.
[0023] Pervaporation membrane materials are typically dense
materials of the kind used in gas separation membranes. If a
pervaporation membrane is used, there are no intrusion pressure
limitations since there is no intrusion pressure for dense
membranes.
[0024] The enriched ammonia vapor exiting the distillation membrane
or pervaporation membrane module may then optionally be further
enriched by passing it through a gas separation module to form a
further-enriched ammonia vapor by removing a substantial proportion
of the gas impurities. The module has a gas separation membrane
that permits the passage of ammonia vapor but retains a substantial
proportion of gas impurities as a retentate. Gas separation
membranes are typically comprised of dense membranes made of
polymeric materials. A preferred material is NAFION.RTM. polymer
(E.I. du Pont de Nemours and Co.). NAFION.RTM. is a copolymer of
tetrafluoroethylene and perfluoro 3,6-dioxa-4-methyl-7-octen-
e-sulfonic acid. Another useful material is ethane-propene
terpolymer and polychloroprene.
[0025] In the gas separation module, the contaminated ammonia
product stream is compressed with a process compressor or other
means to raise the feed pressure to a pressure calculated to
prevent the ammonia from liquefying at the temperature at which the
process will be conducted. The process may be conducted at
temperatures ranging from between about -30.degree. C. to about
30.degree. C. Preferably, the temperatures range from -30.degree.
C. to 10.degree. C. At -30.degree. C., the pressure should be less
than about 1.18 atmospheres absolute. At 10.degree. C., the
pressure should be less than about 6.075 atmospheres absolute. The
most preferred temperature range is about 0.degree. C. to about
5.degree. C. The ammonia stream is cooled prior to its introduction
into the at least one membrane. If the process is carried out at
sub-ambient temperatures, the compressed feed stream can be cooled
within a heat exchanger. One type of heat exchanger, for example,
is a two pass, plate-fin device in which a liquid coolant, such as
obtained from a liquid coolant tank, is fed as a coolant stream
through the heat exchanger. The cooled feed stream is fed to a
membrane module, which can be housed within a cold box filled with
insulating materials. The gas separation module can be a single
module or unit or be a series of two or more of such modules or
units.
[0026] If recycle of ammonia is desired, the enriched ammonia vapor
is conveyed directly or indirectly to the manufacturing tool by any
means known in the art. Typically, enriched ammonia vapor exiting
the distillation membrane, pervaporation membrane, or the gas
separation membrane will be of relatively low temperature and
pressure. Also, some ammonia will have been lost in retentate
streams and other process losses. Thus, it is desirable to
transform the enriched ammonia vapor to a higher temperature and
pressure and replenish lost ammonia prior to return to the
manufacturing tool.
[0027] In a preferred process, enriched ammonia vapor exiting the
distillation membrane, pervaporation membrane, or the gas
separation membrane is condensed and makeup ammonia added thereto
to form an enriched ammonia liquid. The enriched ammonia liquid is
then vaporized and conveyed to the manufacturing tool for use. The
condensing means employed to form the enriched ammonia liquid may
be any condensing means (condenser) known in the art, including
those condensing means described above. A preferred condensing
means for this application is a heat pump condenser. Condensing
temperatures and pressures are as described above. The vaporizing
means employed to form the enriched ammonia vapor may be any
vaporizing means known in the art such as a heat pump vaporizer or
a two-pass, plate fin heat exchanger. A preferred vaporizing means
is a heat pump vaporizer.
[0028] Although crude ammonia streams encountered in industrial
practice will vary in contaminate content, a typical crude ammonia
exiting semiconductor manufacturing tooling will typically have
about 100 parts per million of impurities in the feed. Such
impurities typically include nitrogen, oxygen, hydrogen, carbon
monoxide, carbon dioxide, hydrocarbons, organics, moisture, and
metals. Processed ammonia product streams from processes of the
present invention will typically have about 10 parts per million or
less of such impurities.
[0029] An embodiment of the apparatus of the present invention is
seen in FIG. 1 and is generally referenced by the numeral 10.
Apparatus 10 represents a semiconductor manufacturing process or
other manufacturing process wherein ammonia is used for cleaning
purposes and is continuously recycled. Apparatus 10 has tools 14
and 18, which generally and schematically represent manufacturing
tooling that produces crude ammonia as a process by-product. The
specific structure or function of tools 14 and 18 or the number of
tools is not critical to the invention. Crude ammonia in
substantially vapor form is conveyed to a condensing vessel 22
through conduits 16 and 19, which converge into conduit 20. If
desired or necessary, a compressor(s) (not shown) or a filter(s)
(not shown) may be installed between tools 14/18 and condensing
vessel 22. In condensing vessel 22, the crude ammonia is condensed
to a substantially liquid state by reducing temperature and/or
raising pressure. The crude ammonia liquid is conveyed to a
distillation membrane or pervaporation membrane module 26 through a
conduit 24. If desired or necessary, a compressor(s) (not shown)
may be installed between condensing vessel 22 and module 26. Module
26 has a membrane 29, which has a retentate side 28 and a permeate
side 30. A retentate stream 31 is withdrawn from the retentate side
28 of membrane 29. The retentate stream 31 is a concentrate of
ammonia along with an elevated level of metal and/or moisture
contaminants. The relative level of metal and moisture contaminates
in the retentate stream 31 is higher than in the condensed crude
ammonia. Ammonia evaporates at the permeate side 30 in the form of
a first enriched ammonia vapor and through conduit 32 to a heat
pump condenser 34. The first enriched ammonia vapor is condensed at
condenser 34 via temperature reduction and/or pressure increase.
Makeup ammonia is added at condenser 34 to form an enriched ammonia
liquid, which is conveyed through a conduit 36 to a heat pump
vaporizer 38. In vaporizer 38, the enriched ammonia liquid is
vaporized to form a second enriched ammonia vapor, which is
conveyed through a conduit 40 to tools 14 and 18 for use in the
manufacturing process. Apparatus 10 has valves 15, 17, 33, 39, and
41 for regulating the flow of the various process streams
therethrough.
[0030] Another embodiment of the apparatus of the present invention
is seen in FIG. 2 and is generally referenced by the numeral 42.
Apparatus 42 represents a manufacturing process wherein ammonia is
used for cleaning purposes and is continuously recycled. Apparatus
42 has tools 46 and 50, which generally and schematically represent
manufacturing tooling that produces crude ammonia as a process
by-product. The specific structure or function of tools 42 and 50
or the number of tools is not critical to the invention. A crude
ammonia stream is conveyed to a condensing vessel 54 through
conduits 48 and 52, which converge into conduit 53. If desired or
necessary, a compressor(s) (not shown) or a filter(s) (not shown)
may be installed between tools 42/50 and condensing vessel 54. In
condensing vessel 54, the crude ammonia is condensed to a
substantially liquid state by reducing temperature and/or raising
pressure. The crude ammonia liquid is conveyed to a membrane
distillation or a pervaporation membrane module 58 through a
conduit 56. If desired or necessary, a compressor(s) (not shown)
may be installed between condensing vessel 54 and module 58. Module
58 has a membrane 61, which has a retentate side 60 and a permeate
side 62. A retentate stream 60 is withdrawn from the retentate side
60 of membrane 61. The retentate stream 59 is a concentrate of
ammonia and an elevated level of metal and moisture contaminants.
Ammonia vapor evaporates from the permeate side 62 in the form of a
first enriched ammonia vapor and is conveyed through a conduit 63
to a gas separation module 64. If desired or necessary, a
compressor(s) (not shown) may be installed between module 58 and
module 64. Module 64 has a retentate side 66, a membrane 67, and a
permeate side 68. A retentate stream 69 is withdrawn from the
retentate side 66 of membrane 67. Stream 69 has a vapor concentrate
of ammonia and an elevated level of gas impurities. The passing of
the first enriched ammonia vapor through module 64 results in a
further enriched ammonia vapor referred to as the second enriched
ammonia vapor, which is conveyed through a conduit 70 to a heat
pump condenser 72. The second enriched ammonia vapor is condensed
at condenser 72 via temperature reduction and/or pressure increase.
Makeup ammonia is added at condenser 72 to form an enriched ammonia
liquid, which is conveyed through a conduit 74 to a heat pump
vaporizer 76. In vaporizer 76, the enriched ammonia liquid is
vaporized to form a third enriched ammonia vapor, which is conveyed
through a conduit 78 to tools 46 and 50 for use in the
manufacturing process. Apparatus 42 has valves 85, 87, 115, 124,
and 126 for regulating the flow of the various process streams
therethrough.
[0031] Another embodiment of the apparatus of the present invention
is seen in FIG. 3 and is generally referenced by the numeral 80.
Apparatus 80 represents a semiconductor manufacturing process
wherein ammonia is used for cleaning purposes and is continuously
recycled. Apparatus 80 has tools 84 and 88, which generally and
schematically represent manufacturing tooling that produces crude
ammonia as a process by-product. The specific structure or function
of tools 84 and 88 or the number of tools is not critical to the
invention. A crude ammonia stream is conveyed to a TSA unit 92
through conduits 86 and 90, which converge into conduit 91. TSA
refers to a temperature swing adsorber. TSA unit 92 removes part of
or substantially all moisture from the crude ammonia stream. The
crude ammonia stream is conveyed from TSA unit 92 to a condensing
vessel 96 through conduit 94. If desired or necessary, a
compressor(s) (not shown) or a filter(s) (not shown) may be
installed between tools 84/88 and TSA unit 92 or condensing vessel
96. In condensing vessel 96, the crude ammonia stream is condensed
to a substantially liquid state by reducing temperature and/or
raising pressure to form a crude ammonia liquid. The crude ammonia
liquid is conveyed to a membrane distillation or pervaporation
membrane module 100 through a conduit 98. If desired or necessary,
a compressor(s) may be installed between vessel 96 and module 100.
Module 100 has a membrane 103, which has a retentate side 102 and a
permeate side 104. A retentate stream 99 is withdrawn from the
retentate side 102 of membrane 103. The retentate stream 99 is a
concentrate of ammonia and an elevated level of metal and moisture
contaminants. Ammonia vapor evaporates from the permeate side 104
in the form of a first enriched ammonia vapor and through a conduit
106 to a gas separation module 108. If desired or necessary, a
compressor(s) may be installed between module 100 and module 108.
Module 108 has a gas separation membrane 111. Membrane 111 has a
retentate side 110 and a permeate side 112. A retentate stream 113
is withdrawn from the retentate side 110 of membrane 111. Stream
113 is a vapor concentrate of ammonia and an elevated level of gas
impurities. Contacting membrane 111 with the first enriched ammonia
vapor results in a second enriched ammonia vapor, which is conveyed
though a conduit 114 to a heat pump condenser 116. The second
enriched ammonia vapor is condensed at condenser 116 via
temperature reduction and/or pressure increase. Makeup ammonia is
added at condenser 116 to form an enriched ammonia liquid, which is
conveyed through a conduit 118 to a heat pump vaporizer 120. In
vaporizer 120, the enriched ammonia liquid is vaporized to form a
third enriched ammonia vapor, which is conveyed through a conduit
122 to tools 84 and 88 for use in the manufacturing process.
Apparatus 80 has valves 85, 87, 115, 124, and 126 for regulating
the flow of the various process streams therethrough.
[0032] Another embodiment of the process of the present invention
is seen in the FIG. 4 and is generally referenced by the numeral
130. Apparatus 130 represents a manufacturing process wherein
ammonia is used for cleaning purposes and is continuously recycled.
Apparatus 130 has tools 134 and 138 which generally and
schematically represent manufacturing tooling that produces crude
ammonia as a process by-product. The specific structure or function
of tools 134 and 138 or the number of tools is not critical to the
invention. Crude ammonia vapor is conveyed through conduits 137 and
139, which converge into conduit 140. Conduit 140 merges into
conduit 142, which conveys the crude ammonia vapor through a filter
144 into condensing vessel 146. In condensing vessel 146, an
equilibrium is maintained between a vapor phase 148 and a liquid
phase 150 by regulation of temperature, volume, and pressure.
Desirably, the vapor phase 148 of vessel 146 is maintained at about
1.18 atmospheres absolute and the temperature is maintained at
about -30.degree. C. The ammonia vapor is conveyed from vessel 146
through conduit 152 to gas separation module 160. Module 160 has a
membrane 158 of a dense polymeric material. Membrane 158 has a
retentate side 154 and a permeate side 156. Membrane 158 permits
the passage of ammonia vapor but not gas impurities. A retentate
stream 162 is withdrawn from retentate side 154 of membrane 158.
Retentate stream 162 is a concentrate of ammonia vapor along with
an elevated or higher level of gas impurities. The enriched ammonia
exiting module 160 is conveyed through a conduit 168 via the action
of vacuum pump 170 into conduit 142 for return to condensing vessel
146. Liquid crude ammonia is conveyed from vessel 146 through
conduit 172 via pump 174 to heat pump vaporizer 176. In vaporizer
176, an equilibrium is maintained between a vapor phase 178 and a
liquid phase 180 by regulation of volume, temperature and pressure.
Desirably, vapor phase 178 of vaporizer 176 is maintained at about
750 psig and the temperature is maintained at about 90.degree. C.
The enriched ammonia vapor is conveyed from vaporizer 176 through
conduit 206 and filter 208 to tools 134 and 138 for use in the
manufacturing process. The crude ammonia liquid exiting vaporizer
176 is conveyed through conduit 182 to a distillation membrane or
pervaporation membrane module 186. Module 186 has a membrane 192,
which has a retentate side 188 and a permeate side 190. Membrane
192 is comprised of a dense or microporous polymeric material. A
retentate stream 194 is withdrawn from the retentate side 188 of
membrane 192. The retentate stream 194 has a concentrate of ammonia
along with an elevated level of metal impurities and water. The
relative level of metal impurities in the retentate stream 194 is
higher than in the crude ammonia liquid exiting vaporizer 176.
Ammonia evaporates at the permeate side 190 to form an enriched
ammonia vapor and is conveyed through conduit 198 to vessel 146 via
the action of vacuum pump 200. Makeup ammonia is added to vaporizer
176 through conduit 204. The operating conditions of the
distillation/pervaporation membrane module 186, gas separation
module 160, condenser 146, and vaporizer 176 are as previously
described. Apparatus 130 has valves 135, 136, 164, 184, 196, 202,
210, and 212 for regulating the flow of the various process streams
through the various conduits.
[0033] A first separator of the type disclosed in FIG. 4 retains
and maintains crude ammonia at conditions, i.e., a volume level,
temperature and pressure, sufficient to provide a vapor phase and a
liquid phase. The first separator is sized with respect to the
throughput of crude ammonia such that there is adequate headspace
to provide a vapor phase. The first separator can take the form of
any condensing and/or storage vessel or tank wherein temperature
and/or pressure can be regulated. A preferred first separator is a
condenser. Condenser temperature range will preferably range from
about -30.degree. C. to about 10.degree. C. At -30.degree. C., the
pressure should be about 1.18 atmospheres absolute. At this feed
pressure, a vacuum pump is needed at the permeate side of the
membrane unit in order to generate the driving force for membrane
permeation. At these conditions, a compressor is not required for
the condenser. At 10.degree. C., the pressure should be about 6.075
atmospheres absolute. At this temperature, a compressor is needed
to compress the ammonia stream prior to entering the condenser. At
these conditions, a vacuum pump is not required for the membrane
unit. The most preferable operating temperature range is about
0.degree. C. to about 5.degree. C. In any case, the operating
pressure of the membrane unit is maintained at less than ammonia
vapor pressure corresponding to the condensation temperature to
avoid ammonia condensation in the membrane unit. Operating pressure
is regulated by using a pressure restriction device and/or raising
the ammonia temperature slightly above the condensation
temperature.
[0034] A second separator of the type disclosed in FIG. 4 retains
and maintains crude ammonia at conditions, i.e., a volume level,
temperature and pressure, sufficient to provide a vapor phase and a
liquid phase. The second separator is sized with respect to the
throughput of ammonia such that there is adequate headspace to
allow a vapor phase. The operating temperature and pressure of the
second separator is typically higher than the operating temperature
and pressure of the first separator because of the desirability of
providing enriched ammonia vapor to the manufacturing tool at an
elevated temperature and pressure. A most preferred operating
pressure is about 750 pounds per square inch gauge (psig). The
second separator can take the form of any processing and/or storage
vessel or tank or a heat pump vaporizer wherein temperature and/or
pressure can be regulated. A heat pump vaporizer is most
preferred.
[0035] In the vaporizer of the type disclosed in FIG. 4, the
temperature can be set to any value corresponding to the vapor
pressure required by the manufacturing tools. For instance, if the
manufacturing tools require an inlet ammonia pressure of 750 psig,
vaporization temperature can be set at about 90.degree. C. Transfer
of ammonia liquid between the condenser and vaporizer can be
carried out with a compressor, preferably by a heat pump apparatus
as described in U.S. patent application Ser. No. 09/383,699.
[0036] The process of the present invention operates continuously
or semi-continuously as desired. Continuous operation is
preferred.
[0037] It will be apparent to one skilled in the art that the
process and apparatus of the present invention may have or employ
ancillary equipment such as pumps, compressors, flow regulators,
digital or analog gauges, thermocouples, and the like.
[0038] The present invention is useful in semiconductor
manufacturing processes. The present invention is particularly
useful in gallium nitride semiconductor manufacturing processes.
The present invention is also useful in other manufacturing
processes that employ ammonia as a cleaner and remover.
[0039] The following are non-limiting examples of the present
invention. Unless otherwise indicated, all percentages and parts
are by weight.
EXAMPLES
[0040] Tests were carried out to investigate the potential
performance of the gas separation membranes as described in this
invention. For a pressure across a membrane (fabricated from a
Nafion.RTM. polymer) at about 0.5 atmospheres, the ammonia
permeability was found to increase from about 16778 barrer to about
45015 barrer as the operating temperature was reduced from about
23.degree. C. to about 4.degree. C. The permeability enhancement
due to decreasing temperature increases with increasing drive force
(or feed pressure for a given downstream pressure).
[0041] Further tests were conducted to determine the permeation of
impurities. These results are summarized in the following
table.
Effect of Feed Temperature on Membrane Separation Efficiency
[0042]
1 23.degree. C. 2.degree. C. T (.degree. C.) Feed Permeate Feed
Permeate Gas Impurity (ppm) (ppm) (ppm) (ppm) H.sub.2 81.85 2.10
79.90 0.94 N.sub.2 80.33 0.44 86.12 0.49 O.sub.2 87.18 0.86 90.17
0.77 CO 74.71 0.32 73.46 0.25 CH.sub.4 82.36 0.5 80.32 0.33
NH.sub.3 Recovery 97.04 98.29 (%)
[0043] As can be seen from the foregoing, the percent recovery of
ammonia and ammonia purity increases with decreasing
temperature.
[0044] It should be understood that the foregoing description is
only illustrative of the present invention. Various alternatives
and modifications can be devised by those skilled in the art
without departing from the invention. Accordingly, the present
invention is intended to embrace all such alternatives,
modifications and variances that fall within the scope of the
appended claims.
* * * * *