U.S. patent application number 10/349065 was filed with the patent office on 2003-06-12 for process for producing ammonia with ultra-low metals content.
This patent application is currently assigned to Ashland Inc.. Invention is credited to Dershowitz, Daniel J., Dove, Curtis, Mahapatra, Sadhana, Mears, Ryan L., Schnaith, Jay F., Wadsworth, Kevin K..
Application Number | 20030108473 10/349065 |
Document ID | / |
Family ID | 25012706 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030108473 |
Kind Code |
A1 |
Dershowitz, Daniel J. ; et
al. |
June 12, 2003 |
Process for producing ammonia with ultra-low metals content
Abstract
Commercial grade ammonia is purified for use in production of
semiconductors by initially passing the liquid ammonia through a
liquid phase oil separation system. This removes the vast majority
of the impurities. The filtered liquid ammonia is then passed
through a vaporizer which quiescently forms ammonia vapor and
prevents entrainment of impurities within the ammonia vapor. The
vapor passes through a vapor filtration system and subsequently to
a bubble column. The bubble column is designed so that the bubbles
are small enough and travel at a rate which ensures that any
entrapped particle within the bubble will have time to migrate to
the surface of the bubble and thereby pass through the liquid
phase. The collected vapor is directed through subsequent vapor
filters and is collected. If anhydrous ammonia is desired, the
ammonia vapor is collected upstream of the bubble column.
Inventors: |
Dershowitz, Daniel J.;
(Columbus, OH) ; Mears, Ryan L.; (Mesquite,
TX) ; Schnaith, Jay F.; (Powell, OH) ; Dove,
Curtis; (Colorado Springs, CO) ; Mahapatra,
Sadhana; (Bridgewater, NJ) ; Wadsworth, Kevin K.;
(Columbus, OH) |
Correspondence
Address: |
WOOD, HERRON & EVANS, L.L.P.
2700 Carew Tower
441 Vine St.
Cincinnati
OH
45202
US
|
Assignee: |
Ashland Inc.
50 East River Center Boulevard
Covington
KY
41012-0391
|
Family ID: |
25012706 |
Appl. No.: |
10/349065 |
Filed: |
January 22, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10349065 |
Jan 22, 2003 |
|
|
|
09749201 |
Dec 27, 2000 |
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6534027 |
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Current U.S.
Class: |
423/352 ; 159/23;
159/47.1; 159/DIG.4 |
Current CPC
Class: |
C01C 1/024 20130101 |
Class at
Publication: |
423/352 ; 159/23;
159/47.1; 159/DIG.004 |
International
Class: |
C01C 001/02; F26B
007/00 |
Claims
This has been a description of the present invention along with the
preferred method of practicing the present invention. However, the
invention itself should only be defined by the appended claims
wherein I claim:
1. A method of purifying liquid ammonia comprising: passing said
liquid ammonia through an oil separator; directing said liquid
ammonia from said separator and quiescently vaporizing said ammonia
to form ammonia vapor; directing said ammonia vapor through a
bubble column, said bubble column including a saturated solution of
ammonium hydroxide; and collecting said ammonia vapor after passing
through said ammonium hydroxide.
2. The method claimed in claim 1 wherein said liquid ammonia is
passed through a first liquid filter before passing through said
oil separator and wherein said oil separator is a coalescer.
3. The method claimed in claim 2 wherein said ammonia is vaporized
in a vaporizer, wherein said vaporizer is tilted towards a drain
and whereby higher density impurities are drained from said
vaporizer.
4. The method claimed in claim 2 wherein said bubble column has a
height and bubbles are formed having a size small enough to provide
any particles entrained in said bubbles sufficient time while
passing through said bubble column to contact side walls of said
bubbles to thereby be captured by said liquid ammonium
hydroxide.
5. The method claimed in claim 3 wherein liquid ammonia is
introduced below a liquid surface of said vaporizer.
6. The method claimed in claim 5 wherein said vapor obtained from
said quiescent vaporizer is passed through a vapor filter
system.
7. The method claimed in claim 6 wherein said vaporous filter
system includes a first and a second vapor filter.
8. The method claimed in claim 5 further comprising passing said
vapor from said bubble column through a vapor filter system.
9. A method of purifying ammonia comprising passing liquid ammonia
through a liquid phase separator system to remove oil from said
liquid ammonia; passing said liquid ammonia to a vaporizer; and
separating vaporous ammonia from said liquid ammonia in said
vaporizer.
10. The method claimed in claim 9 wherein said vaporizer vaporizes
said liquid ammonia quiescently.
11. The method claimed in claim 10 further comprising passing
bubbles of ammonia gas through a bubble column and collecting
ammonia gas passing through said bubble column wherein the bubble
column has a length effective to permit solid impurities in said
bubbles to pass to a liquid phase in said bubble column.
12. A method of purifying liquid ammonia comprising: passing said
liquid ammonia through an oil separator; directing said liquid
ammonia from said separator and quiescently vaporizing said ammonia
to form ammonia vapor; directing said ammonia vapor through a vapor
filter; and collecting said ammonia vapor.
13. The method claimed in claim 12 wherein said liquid ammonia is
passed through a first liquid filter before passing through said
oil separator and wherein said oil separator is a coalescer.
14. The method claimed in claim 12 wherein said ammonia is
vaporized in a vaporizer, wherein said vaporizer is tilted towards
a drain and whereby higher density impurities are drained from said
vaporizer.
15. The method claimed in claim 12 wherein said ammonia is
vaporized at a rate less than 1 fps.
16. The method claimed in claim 15 wherein said ammonia is
vaporized at a rate less than 0.1 fps.
17. The method claimed in claim 16 wherein said ammonia is
vaporized at a rate less than 0.02 fps.
18. The method claimed in claim 15 further comprising passing said
ammonia vapor through a bubble column wherein said bubble column
has a height and bubbles are formed having a size small enough to
provide any particles entrained in said bubbles sufficient time
while passing through said bubble column to contact side walls of
said bubbles to thereby be captured by said liquid ammonium
hydroxide.
19. The method claimed in claim 14 wherein liquid ammonia is
introduced below a liquid surface of said vaporizer and in a
direction toward said drain.
20. The method claimed in claim 18 further comprising passing said
vapor from said bubble column through a vapor filter system.
21. A method of purifying ammonia comprising passing liquid ammonia
through a liquid phase separator system to remove oil from said
liquid ammonia; vaporizing said liquid ammonia to form ammonia
vapor; and passing bubbles of said ammonia vapor through a bubble
column and collecting ammonia vapor passing through said bubble
column wherein the bubble column has a length effective to permit
solid impurities in said bubbles to pass to a liquid phase in said
bubble column.
22. A vaporizer adapted to purify ammonia comprising an elongated
tank having a bottom surface; said tank tilted providing a first
end of said tank lower than a second end of said tank; a drain
located at said first end of said tank; and a heater adapter to
heat ammonia in said tank.
Description
BACKGROUND OF THE INVENTION
[0001] Ultra-high purity ammonium hydroxide is commonly used in the
manufacture of semiconductor products such as microprocessors. In
particular this is used as a cleaning solution in the formation of
integrated circuits. As these circuits become smaller and smaller,
impurities become less tolerable. In particular, the ammonium
hydroxide utilized must be free of any conducting contaminants and
in particular metallic contaminants. There is also an integrated
circuits market for high purity specialty gas ammonia.
[0002] Generally commercially produced ammonia is totally
unsuitable for such applications. The production of ammonia such as
for use in fertilizers introduces contaminants including oil and
metal particles. This commercial grade or fertilizer grade ammonia
may include up to 10 ppm free oil and several ppm cadmium, calcium,
sodium, iron, zinc and potassium. To be useful for integrated
circuit production the metal concentration should be less than
about 100 ppt.
[0003] There are a number of processes which are designed to purify
this commercial grade ammonia. However for various reasons, they
are not optimally designed. Hoffman et al., U.S. Pat. Nos.
5,496,778 and 5,846,386 disclose drawing ammonia vapor from a
liquid ammonia reservoir and passing the vapor through a filter
capable of filtering out particles. Due to the amount of impurities
in the ammonia, removing these impurities in the vapor phase is
inefficient and to a large extent ineffective. The small size of
many of the metal particles makes vapor filtration ineffective.
Further the evaporator design permits entrainment of the
impurities.
[0004] Japanese Patent 8-119626-A discloses passing ammonia gas
through a saturated aqueous solution of ammonia. This allows
entrainment in the mist and requires a subsequent mist separator.
Further due to the design of the device, particles are not given
sufficient time to be removed in the liquid bath. There are
filtration processes designed to remove oil from ammonia. But these
are not capable of to producing ultra high purity ammonia.
SUMMARY OF THE INVENTION
[0005] The present invention is premised on the realization that
ultra-pure ammonia can be obtained from commercial grade ammonia by
first filtering/coalescing liquid ammonia with a liquid phase
filter/coalescer to remove almost all of the oil and metal
particles which are carried by the oil. The partially cleaned
ammonia liquid is then directed to a quiescent evaporator which
promotes vapor formation without creating turbulence or bubbles
which would promote entrainment of impurities. After vapor phase
filtration, the ammonia vapor can be further directed to an aqueous
scrubber. The aqueous scrubber is particularly designed to provide
small bubbles which follow a path through a saturated water bath.
The path provides sufficient time for any particles within the
bubbles to contact the bubble wall and migrate into the aqueous
liquid. Further, this is done with minimum turbulence to prevent
again entrainment of impurities. The ammonia vapor collected from
the scrubber can be combined with ultrahigh purity water to form an
ultra-high purity solution of ammonium hydroxide suitable for use
in the semi-conductor industry. If ammonia gas on anhydrous ammonia
is the desired product, purified ammonia gas for this purpose can
be collected after vapor phase filtration.
[0006] This process can be practiced in a large free standing plant
or can be scaled down to provide on-site production of ammonium
hydroxide or ammonia gas.
[0007] The objects and advantages of the present invention will be
further appreciated in light of the following detailed description
and drawings in which:
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a diagrammatic depiction of the present
invention.
[0009] FIG. 2 is a cross-sectional view of the bubbler for use in
the present invention.
DETAILED DESCRIPTION
[0010] The present invention is a separation apparatus or system 10
adapted to produce ultrahigh purity ammonia. The system includes
first and second liquid filters/separators 12 and 14 which are
connected to a vaporizer 18. To the extent possible the parts are
made of materials which do not interfere with this process and are
generally stainless steel, Teflon or Teflon lined.
[0011] More particularly, ammonia tank 34, which can be a tanker
truck of ammonia or a portable tank of ammonia for smaller volume
requirements, provides liquid ammonia to apparatus 10. The ammonia
is directed to inlet 38 and through line 40 to the first liquid
separation prefilter 12. From the first filter 12 the ammonia is
directed through line 42 to liquid/liquid coalescer 14.
[0012] Preferably the prefilter 12 is a polypropylene filter which
removes solids which could disturb the ammonia oil emulsion. This
is a 1-10 micron filter (preferably 10) with a 15 psid maximum
pressure drop. The liquid/liquid coalescer 14 is designed for 8-10
ppm inlet and 1-2 ppm outlet (free oil). The coalescer can be a
horizontal coalescer having two stages. The primary stage will
cause small oil droplets to coalesce into larger droplets by
passing through a polypropylene filter element. This is designed
for use with emulsions having a surface tension of 0.5 to 40
dyne/cm. In the second stage, the larger droplets separate from the
continuous ammonia phase in a settling zone. The pressure drop
through coalescer 14 should be 0-10 psid preferably 0-15 psid. The
oil and other impurities separated in filter 12 and separator 14
are discarded through drains 44 and 46, respectively.
[0013] The liquid phase ammonia passes from the coalescer 14 to the
vaporizer 18. Vaporizer 18 is simply a tank which has a heat
exchanger such as a water jacket 50 located at a bottom portion of
the vaporizer. The ammonia enters the vaporizer through liquid
ammonia inlet 52 which directs the ammonia subsurface. The
vaporizer further has an ammonia vapor outlet 54.
[0014] As shown in the drawing, the tank 18 is tilted towards a
drain 58 which permits withdrawal of the denser component of the
liquid in vaporizer 18. Inlet 52 is a conduit having a bend 53
directed toward drain 58. Incoming ammonia encourages flow toward
drain 58. The denser component will be oil or an ammonia oil
emulsion along with metal particles. This denser component drains
through drain 58 to valve 60 directed to an ammonia blowdown pot
64. Periodically valve 60 may direct liquid through line 70 to pump
72 which forces the ammonia through line 74 back into inlet 38.
This can be used to recirculate portions of the liquid in vaporizor
18.
[0015] The outlet 54 from vaporizer 18 is directed to first and
second vapor phase filters 78 and 82 which include drains 84 and
86, respectively. The filters 78 and 82 are Teflon.RTM. coated
filters rated for 0.05 micron to 0.2 micron with a maximum pressure
drop of 15 psid. Ammonia vapor passes from filter 82 to a valve 81.
Valve 81 can direct vapor either to an outlet 83 or to a manifold
88 connected by conduits 90 to the bottom portion 92 of a bubble
column 94. Vapor directed to outlet 83 is collected for further use
as anhydrous ammonia.
[0016] The ammonia vapor when directed to conduits 90 is introduced
through the bottom of the bubble column through inlets 98 and
passes through a sparge plate 100 where ammonia bubbles are formed
and evenly distributed across the column. These bubbles travel up
the column 94 through the water 93 and then to head space 101 to a
vapor outlet 102.
[0017] The bubble column 94 is specifically designed to produce
small bubbles. The length of the column is further designed so that
the bubbles so produced will reside in the liquid for a sufficient
period of time to allow any particles in the bubbles to migrate
from within the bubble to the wall of the bubble via Stokes and
Brownian motion. Thus, the length of the column then will depend on
bubble size and the speed at which the bubbles pass through the
liquid in the column. To promote purification, the bubble size
should be small and the rate at which the ammonia vapor is
introduced should be controlled.
[0018] The solid Teflon.RTM. sparge plate 100 has as many small
holes 108 as possible. As an example with a column having a liquid
depth of about 10 feet and a vapor space of four feet, the diameter
of the holes 108 should be no greater than about {fraction (3/64)}"
so that for the gas flow of about 42 lbs/hr-ft.sup.2=lbs/hr.ft, any
impurities will separated into the liquid within the column.
[0019] Vapor outlet 102 is connected to third and fourth vapor
filters 104 and 106. These filters are preferably rated for 0.2
microns with a maximum pressure drop of 15 psi. Filter 106 directs
ammonia gas to either a collection unit or to a mixing unit where
it can be combined with high purity water and form ammonium
hydroxide.
[0020] According to this process, ammonia from tank 34 is
introduced into inlet 38 at ambient temperature where it passes
through filter 12 and liquid/liquid coalescer 14 which reduces the
oil content to less than about 1-2 ppm. Entrained metal particles
within the liquid oil will also be removed. Collected impurities
are drained through drains 44 and 46.
[0021] Pressure causes the remaining liquid ammonia to flow through
line 52 into vaporizer 18. A heater such as water jacket 50
maintains the temperature of the ammonia high enough to create
vaporous ammonia but not so high as to cause boiling of the
ammonia. The temperature of the heated water should be no greater
than about 55-65.degree. C. Heated water is supplied to waterjacket
50 through line 112 and drained through line 114. The vaporizer is
operated quiescently, i.e., with minimal agitation of the liquid
ammonia. Additionally, the vapor space above the liquid level in
the vaporizer is such that very low vapor velocities are formed.
Generally the maximum vapor velocity is 0.5 to 1.0 fps. Preferably
it is less than 0.1 fps and most preferably less than 0.02 fps
which provides added assurance that no liquid is entrained in the
vapor. This prevents liquid ammonia and any entrained impurities
from escaping the vaporizer.
[0022] Because tank 18 is tilted, denser impurities will collect at
drain 58. The collected impurities are directed to ammonia blowdown
pot 64.
[0023] The vapor that forms in head space 118 of evaporator 18
flows through vapor filters 78 and 82. The pressure in head space
118 is preferably about 100-125 psig. First vapor filter 78 is
designed to remove particles having a size of about 0.1 micron.
Second vapor filter 82 in turn is designed to remove impurities of
a particle size of about 0.05 microns. If desired, the vapor can be
directed by valve 81 to outlet 83 and collected.
[0024] Alternatively, the vapor can be directed by valve 81 to
manifold 88 which divides the gas stream into lines 90 leading into
the bottom portion 92 of bubble column 94. The pressure of the gas
as it enters column 94 is preferably about 50-60 psig.
[0025] The bubble column is filled with saturated high purity
ammonium hydroxide. The ammonia gas passes through the holes in
sparge plate 100 forming bubbles which rise through the ammonium
hydroxide solution.
[0026] A heat exchanger such as water jacket 120 maintains the
ammonium hydroxide in the column at a temperature of about 20 to
about 30.degree. C. The bubbles rise through the ammonium hydroxide
and the ammonia vapor passes from the bubble column through port
102. The bubbles migrate at a rate to prevent entrainment of liquid
ammonium hydroxide and impurities. The ammonia vapor flows from
column 94 through a third and fourth vapor filter 104 & 106,
which remove particles of a size of 0.2 microns.
[0027] The ammonia vapor is now ready to mix with high purity water
to form ammonium hydroxide. Alternately it can be collected for use
as a gas or anhydrous liquid. This ammonium hydroxide is suitable
for use in production of integrated circuits. Generally, it will
have no more than about 100 ppt metal particles, and preferably
much less.
[0028] Thus by utilization of the present invention, extremely pure
ammonia gas is formed without the problems encountered with the
prior art separation apparatus. In particular, by removing the
majority of the impurities in the liquid phase prior to
evaporation, entrainment of impurities is minimized. Further, by
using a quiescent evaporator, as opposed to a turbulent evaporator,
entrainment of impurities in the vapor phase is again minimized.
This permits further purification using vapor filters. Finally, the
bubble column is designed to minimize entrainment of impurities and
at the same time provide adequate separation time to allow any
entrained impurities to be gathered and retained by the liquid
phase in the bubble column.
* * * * *