Cryogenic rectification system for fluorine compound recovery

A cryogenic system for the recovery of fluorine compounds from a carrier gas stream such as an effluent stream from a semiconductor facility comprising a mass transfer contacting device, such as a cryogenic wash column, integrated with a cryogenic rectification column system.

TECHNICAL FIELD 
This invention relates to the separation and recovery of fluorine compounds 
from a fluorine compound-containing stream. It is particularly useful for 
recovering fluorine compounds from an effluent of a semiconductor 
production facility. 
BACKGROUND ART 
Fluorine compounds are used in many manufacturing processes. In particular, 
they are widely used in the manufacture of semiconductors. Fluorine 
compounds are among the more costly of the more commonly used chemicals in 
manufacturing processes and, moreover, are among the more environmentally 
detrimental of such chemicals. Accordingly there is a need for recovering 
fluorine compounds used in manufacturing processes so that they not cause 
environmental problems and also so that they may be reused. 
One method currently used by industry for ensuring that fluorine compounds 
are not released to the environment involves combustion of the fluorine 
compounds contained in an effluent stream. While this method effectively 
destroys the fluorine compounds thus preventing environmental pollution, 
it also makes it impossible to reuse the fluorine compounds. This method 
is also disadvantageous because it generates waste gases such as hydrogen 
fluoride and nitrogen oxides which require further treatment. Furthermore, 
combustion processes require fuel and oxidant to operate, adding further 
operating and capital costs to the manufacturing operation. 
Another method currently used by industry for the recovery of fluorine 
compounds is adsorption wherein the fluorine compounds are adsorbed onto 
adsorbent under elevated pressure and desorbed from the adsorbent under 
vacuum. This method is disadvantageous because very high power consumption 
is needed to carry out the requisite pressurization and depressurization. 
Moreover, the fluorine compound mixture from the desorption generally 
requires further purification before the components of the mixture can be 
reused. Still further, adsorption processes do not have the flexibility to 
deal with the dramatic changes in fluorine compound concentrations and 
flow rates which characterize manufacturing effluent streams such as those 
from a semiconductor manufacturing plant. 
Accordingly it is an object of this invention to provide an improved 
fluorine compound recovery system. 
It is another object of this invention to provide an improved fluorine 
compound recovery system which does not generate significant amounts of 
waste gas. 
It is a further object of this invention to provide a fluorine compound 
recovery system which can produce fluorine compound product without need 
for significant further separation or purification for reuse. 
It is yet another object of this invention to provide a fluorine compound 
recovery system which can operate effectively in spite of large changes in 
fluorine compound concentrations and flow rates in the stream to be 
treated. 
SUMMARY OF THE INVENTION 
The above and other objects which will become apparent to those skilled in 
the art upon a reading of this disclosure are attained by the present 
invention one aspect of which is: 
A method for recovering fluorine compounds comprising: 
(A) passing gaseous feed comprising carrier gas and fluorine compounds into 
a mass transfer contacting device, and passing wash liquid into the mass 
transfer contacting device; 
(B) passing fluorine compounds into the wash liquid within the mass 
transfer contacting device to produce vapor comprising carrier gas and 
fluorine compound-containing wash liquid; 
(C) passing the fluorine compound-containing wash liquid into a 
rectification column as column feed and separating the column feed within 
said rectification column by cryogenic rectification into fluorine 
compound-containing top vapor and bottom wash liquid; and 
(D) withdrawing fluorine compound-containing top vapor from the 
rectification column and recovering at least a portion thereof as product 
fluorine compounds. 
Another aspect of the invention is: 
Apparatus for the recovery of fluorine compounds comprising: 
(A) a mass transfer contacting device and means for passing fluorine 
compound-containing feed into the mass transfer contacting device; 
(B) means for passing wash liquid into the mass transfer contacting device; 
(C) a rectification column and means for passing liquid from the mass 
transfer contacting device into the rectification column; and 
(D) means for recovering fluorine compounds taken from the upper portion of 
the rectification column. 
Yet another aspect of the invention is: 
A method for recovering fluorine compounds comprising: 
(A) passing gaseous feed comprising carrier gas, high volatility fluorine 
compounds and low volatility fluorine compounds into a mass transfer 
contacting device, and passing wash liquid into the mass transfer 
contacting device; 
(B) passing high volatility fluorine compounds and low volatility fluorine 
compounds into the wash liquid within the mass transfer contacting device 
to produce vapor comprising carrier gas and wash liquid comprising high 
volatility and low volatility fluorine compounds; 
(C) passing the wash liquid comprising high volatility and low volatility 
fluorine compounds into a first rectification column as first column feed 
and separating the first column feed within said first rectification 
column by cryogenic rectification into top vapor comprising high 
volatility fluorine compounds and wash liquid comprising low volatility 
fluorine compounds; 
(D) withdrawing top vapor comprising high volatility fluorine compounds 
from the first rectification column and recovering at least a portion 
thereof as product fluorine compounds; 
(E) passing wash liquid comprising low volatility fluorine compounds into a 
second rectification column as second column feed and separating the 
second column feed within said second rectification column by cryogenic 
rectification into top vapor comprising low volatility fluorine compounds 
and residual wash liquid; and 
(F) withdrawing top vapor comprising low volatility fluorine compounds from 
the second rectification column and recovering at least a portion thereof 
as product fluorine compounds. 
A further aspect of the invention is: 
Apparatus for the recovery of fluorine compounds comprising: 
(A) a mass transfer contacting device and means for passing fluorine 
compound-containing feed into the mass transfer contacting device; 
(B) means for passing wash liquid into the mass transfer contacting device; 
(C) a first rectification column and means for passing liquid from the mass 
transfer contacting device into the first rectification column; 
(D) means for recovering fluorine compounds taken from the upper portion of 
the first rectification column; 
(E) a second rectification column and means for passing liquid from the 
lower portion of the first rectification column into the second 
rectification column; and 
(F) means for recovering fluorine compounds taken from the upper portion of 
the second rectification column. 
As used herein the term "fluorine compounds" means one or more compounds 
comprising fluorine. 
As used herein the term "high volatility fluorine compounds" means one or 
more fluorine compounds having a normal, atmospheric pressure, boiling 
point below 150.degree. K. Examples include carbon tetrafluoride 
(CF.sub.4) and nitrogen trifluoride (NF.sub.3). 
As used herein the term "low volatility fluorine compounds" means one or 
more fluorine compounds which are not high volatility fluorine compounds. 
Examples include hexafluoroethane (C.sub.2 F.sub.6), fluoroform 
(CHF.sub.3), methyl fluoride (CH.sub.3 F), pentafluoroethane (C.sub.2 
HF.sub.5) and sulfur hexafluoride (SF.sub.6). 
As used herein the term "wash column" means a trayed or packed column in 
which a gas mixture is contacted with a liquid for the purpose of 
preferentially dissolving one or more components of the gas to provide a 
solution of them in the liquid. The operation is also known as gas 
absorption. 
As used herein, the term "rectification column" means a distillation or 
fractionation column or zone, i.e., a contacting column or zone wherein 
liquid and vapor phases are countercurrently contacted to effect 
separation of a fluid mixture, as for example, by contacting of the vapor 
and liquid phases on a series of vertically spaced trays or plates mounted 
within the column and/or on packing elements such as structured or random 
packing. For a further discussion of rectification columns, see the 
Chemical Engineer's Handbook fifth edition, edited by R. H. Perry and C. 
H. Chilton, McGraw-Hill Book Company, New York, Section 13, The Continuous 
Distillation Process. 
Vapor and liquid contacting separation processes depend on the difference 
in vapor pressures for the components. The high vapor pressure (or more 
volatile or low boiling) component will tend to concentrate in the vapor 
phase whereas the low vapor pressure (or less volatile or high boiling) 
component will tend to concentrate in the liquid phase. Partial 
condensation is the separation process whereby cooling of a vapor mixture 
can be used to concentrate the volatile component(s) in the vapor phase 
and thereby the less volatile component(s) in the liquid phase. 
Rectification, or continuous distillation, is the separation process that 
combines successive partial vaporizations and condensations as obtained by 
a countercurrent treatment of the vapor and liquid phases. The 
countercurrent contacting of the vapor and liquid phases is generally 
adiabatic and can include integral (stagewise) or differential 
(continuous) contact between the phases. Separation process arrangements 
that utilize the principles of rectification to separate mixtures are 
often interchangeably termed rectification columns, distillation columns, 
or fractionation columns. Cryogenic rectification is a rectification 
process carried out, at least in part, at temperatures at or below 150 
degrees Kelvin (K). 
As used herein, the term "indirect heat exchange" means the bringing of two 
fluid streams into heat exchange relation without any physical contact or 
intermixing of the fluids with each other. 
As used herein the term "recovery as product" means removal from the 
system. Preferably fluorine compounds recovered by the practice of this 
invention are reused, either directly or after further processing. 
As used herein the terms "upper portion" and "lower portion" of a column 
mean those sections of a column respectively above and below the midpoint 
of the column. 
As used herein the term "dephlegmator" means a heat exchanger and a mass 
transfer device which is designed to operate with countercurrent flow of 
vapor and liquid within the passages of one or more streams. This results 
in mass transfer between the phases, which are removed from opposite ends 
of the exchanger, resulting in a separation of components.

DETAILED DESCRIPTION 
The invention will be described in detail with reference to the drawings. 
FIG. 1 illustrates an embodiment of the invention wherein the mass transfer 
contacting device is a wash column. Referring now to FIG. 1, gaseous feed 
1 which has been pressurized to a pressure of at least 18 and preferably 
at least 20 pounds per square inch absolute (psia) and has been treated to 
remove particulate and chemically active impurities such as hydrogen 
fluoride, carbon dioxide and water, and which comprises nitrogen carrier 
gas, high volatility fluorine compounds and low volatility fluorine 
compounds, is cooled by indirect heat exchange in heat exchanger 2 with 
return nitrogen-containing top vapor taken from the wash column to a 
temperature somewhat above that at which some of the fluorine compounds 
would begin to condense, either as solid or liquid. Generally such 
temperature is within to range of from 150.degree. to 130.degree. K. The 
carrier gas of the gaseous feed may comprise other gases in addition to or 
in place of nitrogen such as oxygen, argon, helium and/or hydrogen. 
Cooled gaseous feed 3 is then passed into the lower portion of wash column 
4. Temperature controller 5 controls valve 6 to ensure that the 
temperature of gaseous feed 3 is within the desired range. Wash liquid 7 
is passed into the upper portion of wash column 4. Wash liquid 7 has a 
freezing point lower than the temperature of the gaseous feed as it enters 
the mass transfer contacting device such as wash column 4 and has a vapor 
pressure at that temperature less than 1.0 mmHg and preferably less than 
0.01 mmHg. A preferred wash liquid is perfluoropropane (C.sub.3 F.sub.8). 
Other fluids which may be used as wash liquid 7 include propane, ethane 
and mixtures thereof. 
The gaseous feed flows up wash column 7 and the wash liquid flows down wash 
column 7 and in the process high volatility fluorine compounds and low 
volatility fluorine compounds pass from the gaseous feed into the 
downflowing wash liquid to produce nitrogen-containing top vapor and wash 
liquid comprising high volatility and low volatility fluorine compounds. 
In the embodiment illustrated in FIG. 1 upflowing gas, which has been 
partially depleted of fluorine compounds, is withdrawn from wash column 7 
as stream 8 and cooled by indirect heat exchange in heat exchanger 9. 
Resulting cooled stream 10, which may contain some liquid, is passed into 
wash column 7. The gas then continues up the wash column in countercurrent 
contact with the descending wash liquid to continue carrying out the 
aforesaid mass transfer of the fluorine compounds into the wash liquid. 
The nitrogen-containing vapor is withdrawn from the upper portion of wash 
column 7 as stream 11. Liquid cryogen such as nitrogen stream 17 is 
withdrawn from tank 16, passed through part of heat exchanger 9, through 
valve 18, and then combined with stream 11. The resultant stream is then 
passed through a portion of heat exchanger 9, and then combined with 
nitrogen vapor stream 13 which is supplied from tank 16 through valve 15. 
The combined stream is divided into streams 12 and 14. Stream 12 is 
passed, at least in part, through heat exchanger 2 to carry out the 
aforementioned cooling of gaseous feed 1 and is then passed out of the 
system. Stream 14 is employed in a downstream portion of the system as 
will be described later. 
Wash liquid comprising high volatility and low volatility fluorine 
compounds is withdrawn from the lower portion of wash column 4 as stream 
19 and preferably passed through valve 20 into first batch storage tank 21 
where it is stored for subsequent batch-wise processing. The use of tank 
21 is advantageous when there is a significant variance in the fluorine 
compound concentration in the gaseous feed and/or in the gaseous feed flow 
rate. Any liquid that is vaporized within tank 21 may be passed out from 
tank 21 through valve 22 in line 23 and combined with gaseous feed stream 
3 and then into wash column 4. Wash liquid comprising high volatility and 
low volatility fluorine compounds is passed from tank 21 in stream 24 
through valve 25 as first column feed into the lower portion of first 
rectification column 26 which is driven by external heat input through 
heat input line 27. 
The rectification steps may be operated in a batch mode. Within first 
rectification column 26 the first column feed is separated by cryogenic 
rectification into top vapor comprising high volatility fluorine compounds 
and wash liquid comprising low volatility fluorine compounds. It will be 
recognized by those skilled in the art that the top vapor from column 26 
may initially contain some carrier gas which has been dissolved in stream 
24, and may also contain some low volatility fluorine compounds. 
Similarly, the wash liquid from column 26 may contain some high volatility 
fluorine compounds. 
Top vapor comprising high volatility fluorine compounds is withdrawn from 
the upper portion of first rectification column 26 as stream 28 and at 
least a portion thereof is recovered as product fluorine compounds. In the 
embodiment illustrated in FIG. 1, stream 28 is passed through tank 16 in 
indirect heat exchange with the liquid within tank 16 and is partially 
condensed. A portion 29 of stream 28 may be passed through valve 30 so as 
to bypass tank 16. Resulting partially condensed stream 31 is then passed 
into phase separator 32. Vapor, comprised primarily of carrier gas, is 
passed out from phase separator 32 in stream 33, through valve 34 and 
combined with stream 10 and then into wash column 4. Liquid is withdrawn 
from phase separator 32 as stream 35. A portion 36 of stream 35 is passed 
through valve 37 and into the upper portion of first rectification column 
26 as reflux. After essentially all of the carrier gas has been exhausted 
from the first rectification column through stream 33, another portion 38 
of stream 35 is passed through valve 39 and recovered as product fluorine 
compounds comprising primarily high volatility fluorine compounds. 
Following removal of most of the high volatility fluorine compounds from 
column 26 through stream 38, wash liquid comprising low volatility 
fluorine compounds is withdrawn from the lower portion of first 
rectification column 26 as stream 42 and passed through valve 43 into 
second batch storage tank 44 where it is stored for subsequent batch-wise 
processing. The use of tank 44 is advantageous when there is a significant 
variance in the fluorine compound concentration in the gaseous feed and/or 
in the gaseous feed flow rate. Any liquid that is vaporized within tank 44 
may be passed out from tank 44 through valve 45 in line 46 and combined 
with first column feed stream 24 and then into first rectification column 
26. Wash liquid comprising low volatility fluorine compounds is passed 
from tank 44 in stream 47 through valve 48 as second column feed into the 
lower portion of second rectification column 49 which is driven by 
external heat input through heat input line 50. 
Within second rectification column 49 the second column feed is separated 
by cryogenic rectification into top vapor comprising low volatility 
fluorine compounds and residual wash liquid. Top vapor comprising low 
volatility fluorine compounds is withdrawn from the upper portion of 
second rectification column 49 as stream 51 and at least a portion thereof 
is recovered as product fluorine compounds. In the embodiment illustrated 
in FIG. 1, stream 51 is condensed by passage through heat exchanger 52 in 
indirect heat exchange with stream 14 which is then passed out of the 
system. Resulting stream 53 is withdrawn from heat exchanger 52 and a 
portion 54 is passed through valve 55 and into the upper portion of second 
rectification column 49 as reflux. Another portion 56 of stream 53 is 
recovered as product fluorine compounds. When more than one fluorine 
compound is to be recovered, each compound may be recovered sequentially. 
Residual wash liquid is withdrawn from the lower portion of second 
rectification column 49 as stream 61 and passed through valve 62 into wash 
liquid storage tank 63. From tank 63 the residual wash liquid is passed as 
stream 64 through tank 16 wherein it is cooled by indirect heat exchange 
with the liquid within tank 16 to a temperature below 100.degree. K. and 
preferably between 91.degree. and 93.degree. K. The resulting cooled wash 
liquid is passed from tank 16 into the upper portion of wash column 4 as 
stream 7. 
FIG. 2 illustrates another embodiment of the invention wherein the initial 
rectification steps are preferably carried out continuously. The numerals 
in FIG. 2 correspond to those of FIG. 1 for the common elements and these 
common elements will not be described again in detail. In the embodiment 
illustrated in FIG. 2, first rectification column feed 24 is passed into 
the upper portion of first rectification column 26. Stream 31 is passed 
into the upper portion of additional column 57 wherein it is separated by 
cryogenic rectification into carrier gas-containing vapor and into liquid 
containing high volatility fluorine compounds. The vapor is passed out 
from column 57 in stream 33, through valve 34 and combined with stream 10 
and then passed into wash column 4. The liquid is withdrawn from column 57 
and recovered as product fluorine compounds comprising primarily high 
volatility fluorine compounds. 
FIG. 3 illustrates another embodiment of the invention wherein the mass 
transfer contacting device is a dephlegmator. The numerals in FIG. 3 
correspond to those of FIG. 1 for the common elements. In the embodiment 
illustrated in FIG. 3, cooled gaseous feed 3 is passed into the lower 
portion of dephlegmator 58. Wash liquid 7 is passed into the upper portion 
of the same passages of dephlegmator 58. The gaseous feed flows up 
dephlegmator 58 and wash liquid flows down dephlegmator 58 and in the 
process high volatility fluorine compounds and low volatility fluorine 
compounds pass from the gaseous feed into the downflowing wash liquid to 
produce carrier gas-containing top vapor and wash liquid comprising high 
volatility and low volatility flourine compounds. The resulting vapor is 
withdrawn from dephlegmator 58 as stream 11, combined with stream 13 and 
further processed as described with the previous embodiments. Wash liquid 
comprising high volatility and low volatility fluorine compounds is 
withdrawn from the lower portion of dephlegmator 58 as stream 19 and 
further processed in a manner similar to that of the embodiment 
illustrated in FIG. 1. In the embodiment illustrated in FIG. 3, streams 12 
and 17 each pass through dephlegmator 58 as heat exchange streams. The 
resulting warmed streams are combined to form stream 59 which is passed at 
least in part through heat exchanger 2 to carry out the cooling of gaseous 
feed 1 and is then passed out of the system. Also, stream 33 is passed 
into stream 23 which is then combined with the cooled gaseous feed 3 
upstream of dephlegmator 58. 
FIG. 4 illustrates another embodiment of the invention wherein the mass 
transfer contacting means is a spray chamber. The numerals in FIG. 4 
correspond to those of FIG. 1 for the common elements. In the embodiment 
illustrated in FIG. 4, cooled gaseous feed 3 is passed into first spray 
chamber 70. Wash liquid 7 is also passed into first spray chamber 70 and 
the contact between the feed and the wash liquid produces a vapor enriched 
in carrier gas and a first liquid enriched in fluorine compounds. The 
vapor is withdrawn from first spray chamber 70 as stream 71. A portion is 
passed through heat exchanger 9 and combined with stream 33 to form stream 
10 which is passed into second spray chamber 72. A portion 73 of stream 71 
may be passed directly into second spray chamber 72. Wash liquid 7 is also 
passed into second spray chamber 72 wherein the resulting contact between 
the vapor and the liquid produces carrier gas-containing vapor and a 
second liquid enriched in fluorine compounds. The carrier gas-containing 
vapor is withdrawn from second spray chamber 72 as stream 11 and further 
processed similarly as described with the embodiment illustrated in FIG. 
1. The first and second liquids are withdrawn respectively from first and 
second spray chambers 70 and 72 as streams 74 and 75, passed respectively 
through valves 76 and 77, and combined to form stream 19 which is further 
processed as previously described. 
The embodiments of the invention illustrated in FIGS. 1-4 are preferred 
embodiments, in part, because they enable the separate recovery of high 
volatility fluorine compounds and low volatility fluorine compounds as the 
product fluorine compounds. When the incoming gaseous feed does not 
contain appreciable amounts of both high volatility and low volatility 
fluorine compounds, or when separate recovery of high volatility and low 
volatility fluorine compounds is not desired, the embodiment of the 
invention illustrated in FIG. 5 may be employed. The embodiment of the 
invention illustrated in FIG. 5 shows the invention employing a wash 
column although it will be recognized that the systems illustrated in 
FIGS. 2, 3 and 4 may also be employed with the embodiment illustrated in 
FIG. 5. 
Referring now to FIG. 5, gaseous feed 101 which has been pressurized to a 
pressure of at least 18 and preferably 20 psia and has been treated to 
remove particulate and chemically active impurities such as hydrogen 
fluoride, carbon dioxide and water, and which comprises nitrogen as the 
carrier gas and fluorine compounds, is cooled by indirect heat exchange in 
heat exchanger 102 with return nitrogen-containing top vapor taken from 
the wash column to a temperature somewhat above that at which some of the 
fluorine compounds would begin to condense, either as solid or liquid. 
Generally such temperature is within to range of from 150.degree. to 
130.degree. K. The carrier gas of the gaseous feed may comprise other 
gases in addition to or in place of nitrogen such as oxygen, argon, helium 
and/or hydrogen. 
Cooled gaseous feed 103 is then passed into the lower portion of wash 
column 104. Temperature controller 105 controls valve 106 to ensure that 
the temperature of gaseous feed 103 is within the desired range. Wash 
liquid 107 is passed into the upper portion of wash column 104. Wash 
liquid 107 has a freezing point lower than the temperature of the gaseous 
feed as it enters the mass transfer contacting device such as wash column 
104 and has a vapor pressure at that temperature less than 1.0 mmHg and 
preferably less than 0.01 mmHg. A preferred wash liquid is 
perfluoropropane (C.sub.3 F.sub.8). Other fluids which may be used as wash 
liquid 107 include propane, ethane and mixtures thereof. 
The gaseous feed flows up wash column 107 and the wash liquid flows down 
wash column 107 and in the process fluorine compounds pass from the 
gaseous feed into the downflowing wash liquid to produce 
nitrogen-containing top vapor and fluorine compound-containing wash 
liquid. In the embodiment illustrated in FIG. 5 upflowing gas, which has 
been partially depleted of fluorine compounds, is withdrawn from wash 
column 107 as stream 108 and cooled by indirect heat exchange in heat 
exchanger 109. Resulting cooled stream 110, which may contain some liquid, 
is passed into wash column 107. The gas then continues up the wash column 
in countercurrent contact with the descending wash liquid to continue 
carrying out the aforesaid mass transfer of the fluorine compounds into 
the wash liquid. 
The nitrogen-containing vapor is withdrawn from the upper portion of wash 
column 107 as stream 111. Liquid nitrogen stream 117 is withdrawn from 
tank 116, passed through part of heat exchanger 109, through valve 118 and 
then combined with stream 111. The resultant stream is then passed through 
a portion of heat exchanger 109, and then combined with nitrogen vapor 
stream 113 which is supplied from tank 116 through valve 115 to form 
stream 112. Stream 112 is passed, at least in part, through heat exchanger 
102 to carry out the aforedescribed cooling of gaseous feed 101 and is 
then passed out of the system. 
Fluorine compound-containing wash liquid is withdrawn from the lower 
portion of wash column 104 as stream 119 and preferably passed through 
valve 120 into batch storage tank 121 where it is stored for subsequent 
batch-wise processing. The use of tank 121 is advantageous when there is a 
significant variance in the fluorine compound concentration in the gaseous 
feed and/or in the gaseous feed flow rate. Any liquid that is vaporized 
within tank 121 may be passed out from tank 121 through valve 122 in line 
123 and combined with gaseous feed stream 103 and then into wash column 
104. Fluorine compound-containing wash liquid is passed from tank 121 in 
stream 124 through valve 125 as column feed into the lower portion of 
rectification column 126 which is driven by external heat input through 
heat input line 127. 
Within rectification column 126 the column feed is separated by cryogenic 
rectification into fluorine compound-containing top vapor and bottom wash 
liquid. 
The top vapor comprising fluorine compounds is withdrawn from the upper 
portion of rectification column 126 as stream 128 and at least a portion 
thereof is recovered as product fluorine compounds. In the embodiment 
illustrated in FIG. 5, stream 128 is passed through tank 116 in indirect 
heat exchange with the liquid such as liquid nitrogen within tank 116 and 
is partially condensed. A portion 129 of stream 128 may be passed through 
valve 130 so as to bypass tank 116. Resulting partially condensed stream 
131 is then passed into phase separator 132. Vapor, comprised primarily of 
carrier gas, is passed out from phase separator 132 in stream 133, through 
valve 134 and combined with stream 110 and then into wash column 104. 
Liquid is withdrawn from phase separator 132 as stream 135. A portion 136 
of stream 135 is passed through valve 37 and into the upper portion of 
rectification column 126 as reflux. After essentially all of the carrier 
gas has been exhausted from rectification column 126 through stream 128, 
another portion 138 of stream 135 is passed through valve 139 and 
recovered as product fluorine compounds. 
Bottom wash liquid is withdrawn from the lower portion of rectification 
column 126 as stream 142 and passed through valve 143 into wash liquid 
storage tank 144. Any liquid that is vaporized within tank 144 may be 
passed out from tank 144 through valve 145 in line 146 and combined with 
column feed stream 124 and then into rectification column 126. From tank 
144 the bottom wash liquid is passed as stream 147 through tank 116 
wherein it is cooled by indirect heat exchange with the liquid within tank 
116 to a temperature below 100.degree. K. and preferably between 
91.degree. and 93.degree. K. The resulting cooled wash liquid is passed 
from tank 116 into the upper portion of wash column 104 as stream 107. 
Now by the use of the cryogenic fluorine compound recovery system of this 
invention one can effectively and efficiently recovery fluorine compounds 
from a carrier gas stream, such as an effluent stream from a semiconductor 
production facility, without generating significant amounts of waste gas 
or requiring significant further separation to produce fluorine compound 
products suitable for use. Furthermore, the invention enables one to 
effectively handle a feed gas stream which has a highly variable flow rate 
and/or fluorine compound concentration. 
Although the invention has been described in detail with reference to 
certain embodiments, those skilled in the art will recognize that there 
are other embodiments of the invention within the spirit and the scope of 
the claims.