Separation of tetrafluoroethane isomers

Separation of CF.sub.3 CH.sub.2 F and CHF.sub.2 CHF.sub.2 from a mixture thereof is effectively achieved using either inorganic molecular sieves having suitable intermediate electronegaativities (compared to Zeolite Na-X) or activated carbon.

This application represents the U.S. national filing (371) of International 
Application No. PCT/US92/05851 filed Jul. 17, 1992 and published as 
WO94/02440 Feb. 3, 1994. 
FIELD OF THE INVENTION 
This invention relates to the separation of fluorocarbon products, more 
particularly to the separation of the isomers of tetrafluoroethane, 
CHF.sub.2 CHF.sub.2 (HFC-134) and CF.sub.3 CH.sub.2 F (HFC-134a). 
BACKGROUND 
Isomers of C.sub.2 H.sub.2 F.sub.4 (HFC-134s) are used as refrigeration 
fluids for a number of applications. HFC-134s can also be used as starting 
materials for producing various other halogenated hydrocarbons. Products 
containing isomers of C.sub.2 H.sub.2 F.sub.4 are produced in various 
degrees of isomer purity. One method of producing HFC-134s is by the 
hydrogenolysis of C.sub.2 C.sub.12 F.sub.4 isomers (CFC-114s). In the 
manufacture of C.sub.2 Cl.sub.2 F.sub.4 by the chlorofluorination of 
perchloroethylene the product typically consists of a mixture of the 
isomers, CClF.sub.2 CClF.sub.2 (CFC-114) and CF.sub.3 CCl.sub.2 F 
(CFC-114a) (see e.g., U.S. Pat. No. 4,605,798). If the CFC-114s are then 
used to produce CHF.sub.2 CClF.sub.2 (HCFC-124a), CF.sub.3 CHClF 
(HCFC-124), HFC-134 or HFC-134a by hydrodehalogenation, the products often 
consist of a mixture of C.sub.2 HClF.sub.4 and C.sub.2 H.sub.2 F.sub.4 
isomers (see e.g., GB 1,578,933). 
It has been found that for many applications, the presence of the second 
isomer of the isomer pair can significantly alter the physical and 
chemical properties of the desired isomer. For example, variation in the 
HFC-134/HFC-134a ratio in the product can result in dramatic variability 
in the thermodynamic properties critical for use in refrigeration 
applications. For use as a raw material feed, the presence of the unwanted 
isomer can result in yield loss due to increased side reactions. As a 
result, there has been a continually increasing demand for high isomer 
purity materials. Consequently, the separation of HFC-134 isomers 
represents a significant aspect of preparing these compounds for various 
applications. 
Purification of halogenated hydrocarbon products has been the subject of 
considerable research. Of particular interest are the challenges presented 
in separating desired halogenated hydrocarbon products from materials such 
as impurities in the starting materials used to produce the halogenated 
hydrocarbon, excess reactants, and reaction by-products and/or reaction 
co-products which are difficult to remove by standard separation methods 
such as distillation. Selective sorbents such as carbons and zeolites have 
been proposed for various separations. The effectiveness of separation 
using such sorbents varies with the chemical components and the sorbents 
involved. The successful design of sorbent based systems is considered 
highly dependent upon experimental determination of whether the relative 
sorbencies of the particular compounds are suitable for such systems. 
HFC-134 has a boiling point of -23.degree. C. and HFC-134a has a boiling 
point of -26.5.degree. C. Distillation is consequently relatively 
inefficient as a means for separating these two compounds. 
SUMMARY OF THE INVENTION 
We have found that mixtures of the isomers of C.sub.2 H.sub.2 F.sub.4 
(i.e., CHF.sub.2 CHF.sub.2 and CF.sub.3 CH.sub.2 F) can be substantially 
separated by using a sorbent for CHF.sub.2 CHF.sub.2 selected from the 
group consisting of (i) inorganic molecular sieves (e.g., zeolites) having 
greater intermediate electronegativities than Zeolite Na-X, and (ii) 
activated carbons. The present invention provides a process for separating 
a mixture of CHF.sub.2 CHF.sub.2 and CF.sub.3 CH.sub.2 F to provide a 
product wherein the mole ratio of CF.sub.3 CH.sub.2 F relative to 
CHF.sub.2 CHF.sub.2 is increased which comprises contacting said mixture 
with said sorbent at a temperature within the range of -20.degree. C. to 
300.degree. C. and a pressure within the range of 10 kPa to 3000 kPa and 
for a period of time sufficient to remove a substantial amount of the 
CHF.sub.2 CHF.sub.2. As a result, the mole ratio of CF.sub.3 CH.sub.2 F to 
CHF.sub.2 CHF.sub.2 increases (preferably by 25% or more); and a product 
wherein the mole ratio of CF.sub.3 CH.sub.2 F relative to CHF.sub.2 
CHF.sub.2 is increased, may thus be recovered. 
This invention also provides a process for separating a mixture of 
CHF.sub.2 CHF.sub.2 and CF.sub.3 CH.sub.2 F to provide a product wherein 
the mole ratio of CHF.sub.2 CHF.sub.2 relative to CF.sub.3 CH.sub.2 F is 
increased which comprises contacting said mixture with said sorbent as 
described above to remove a substantial amount of the CHF.sub.2 CHF.sub.2, 
and desorbing sorbed CHF.sub.2 CHF.sub.2 to provide a product which is 
enriched therewith. Another process of this invention for separating a 
mixture of CHF.sub.2 CHF.sub.2 and CF.sub.3 CH.sub.2 F to provide a 
product wherein the mole ratio of CHF.sub.2 CHF.sub.2 relative to CF.sub.3 
CH.sub.2 F is increased, comprises contacting said mixture with a sorbent 
for CF.sub.3 CH.sub.2 F selected from the group consisting of inorganic 
molecular sieves having intermediate electronegativities equal to or less 
than the intermediate electronegativity of Zeolite Na-X, at a temperature 
within the range of -20.degree. C. to 300.degree. C. and a pressure within 
the range of 10 kPa to 3000 kPa and for a period of time sufficient to 
remove a substantial amount of the CF.sub.3 CH.sub.2 F. 
Said process for producing a CF.sub.3 CH.sub.2 F enriched product and said 
processes for producing a CHF.sub.2 CHF.sub.2 enriched product may be 
integrated into an overall process (e.g., a thermal swing cycle process) 
whereby both of said products are provided. Said process for producing a 
CF.sub.3 CH.sub.2 F enriched product and/or said processes for producing a 
CHF.sub.2 CHF.sub.2 enriched product may also be used in conjunction with 
a process for producing HFC-134 and HFC-134a by the hydrogenolysis of 
CFC-114 and/or CFC-114a. 
DETAILS OF THE INVENTION 
The present invention provides for the separation of HFC-134 from HFC-134a. 
Isomer enriched products are provided in accordance with this invention by 
contacting a mixture of C.sub.2 H.sub.2 F.sub.4 isomers with a sorbent for 
CHF.sub.2 CHF.sub.2 selected from the group consisting of activated 
carbons and certain inorganic molecular sieves at a temperature and 
pressure suitable for sorption, for a period of time sufficient to remove 
a substantial amount of said CHF.sub.2 CHF.sub.2. CF.sub.3 CH.sub.2 F 
enriched product is thereby provided using CHF.sub.2 CHF.sub.2 sorption. 
Where CHF.sub.2 CHF.sub.2 enriched product is desired, the invention also 
includes a process involving desorbing sorbed CHF.sub.2 CHF.sub.2 to 
provide a product which is enriched therewith. The process based upon 
preferential CHF.sub.2 CHF.sub.2 sorption is particularly useful for 
purifying CF.sub.3 CH.sub.2 F which contains minor amounts of CHF.sub.2 
CHF.sub.2. Where the process is used for such purification of CF.sub.3 
CH.sub.2 F, the isomer mix to be purified by this process generally has a 
mole ratio of CF.sub.3 CH.sub.2 F to CHF.sub.2 CHF.sub.2 of at least about 
9:1, preferably at least about 19:1, and most preferably at least about 
99:1. 
A mix of the C.sub.2 H.sub.2 F.sub.4 isomers may result, for example, from 
a process involving the reaction of the CFC-114 and/or CFC-114a isomers 
with hydrogen. Unreacted starting materials and C.sub.2 HClF.sub.4 isomers 
may be recycled and reacted further with hydrogen to produce additional 
C.sub.2 H.sub.2 F.sub.4. Additional impurities may be present in these 
products. Distillation is typically used in order to remove impurities 
such as HCl, HF, under- and over-chlorinates and fluorinates to produce 
products that are at least 90% C.sub.2 H.sub.2 F.sub.4. Separation of 
C.sub.2 H.sub.2 F.sub.4 isomers in accordance with this invention to 
provide products which are enriched in HFC-134 and/or products which are 
enriched in HFC-134a then may be advantageously employed. This invention 
can thus be adapted for use in connection with production of C.sub.2 
H.sub.2 F.sub.4 by hydrogenolysis of materials such as C.sub.2 Cl.sub.2 
F.sub.4 such that after removal of a substantial amount of CHF.sub.2 
CHF.sub.2 using the sorbent, either (i) a product is recovered wherein the 
mole ratio of CF.sub.3 CH.sub.2 F relative to CHF.sub.2 CHF.sub.2 is 
increased, (ii) sorbed CHF.sub.2 CHF.sub.2 is desorbed to produce a 
product wherein the mole ratio of CHF.sub.2 CHF.sub.2 relative to CF.sub.3 
CH.sub.2 F is increased, or both (i) and (ii). 
Some embodiments of this invention use activated carbon as the sorbent. 
Commercially available activated carbon may be used. The effectiveness of 
the process can be influenced by the particular activated carbon employed. 
Moreover, the sorption efficiency and sorption capacity of an activated 
carbon bed depends upon the particle size of an activated carbon in a 
dynamic flow system. Preferably, the activated carbon has a particle size 
range of from about 4 to 325 mesh (from about 0.044 to 4.76 millimeters). 
More preferably, the activated carbon has a particle size range of from 
about 6 to 100 mesh (from about 0.149 to 3.36 millimeters). Most 
preferably, the activated carbon has a particle size range of from about 
10 to 30 mesh (from about 0.595 to 2.00 millimeters). 
An activated carbon obtained having a particle size range of about 
0.074.times.0.297 millimeters (50.times.200 mesh) is available from the 
Barneby & Sutcliffe Corp. as Activated Carbon Type UU (natural grain, 
coconut shell based). An activated carbon having a particle size of 0.595 
millimeters.times.1.68 millimeters (12.times.30 mesh) is available from 
the Calgon Corporation as Calgon BPL (bituminous coal based) activated 
granular carbon. An activated carbon having a particle size range of about 
0.450.times.1.68 millimeters (12.times.38 mesh) is available from Barnebey 
& Sutcliffe Corp. as Barneby & Sutcliffe Corp. Activated Carbon Type PE 
(natural grain, coconut shell carbon). An activated carbon having a 
particle size range of about 0.297.times.0.841 millimeters (20.times.50 
mesh) is available from Westvaco as Microporous Wood-Base Granular Carbon. 
Typically the activated carbon used will have a total content of from about 
0.1 to 10 weight percent of alkali and alkaline earth metals selected from 
lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, 
strontium and/or barium. The alkali and alkaline earth metal content of 
carbon can be regulated by techniques known in the art. For example, the 
metal content of carbon can be reduced by acid washing; and the metal 
content can be increased by standard impregnation techniques. In a 
preferred embodiment using preferential HFC-134 sorption, the activated 
carbon contains inherent alkali and/or alkaline earth metal(s) selected 
from the group consisting of lithium, sodium, potassium, rubidium, cesium, 
magnesium, calcium, strontium, barium, and combinations thereof. Inherent 
alkali metals (typically Na and/or K) are preferred. The presence of these 
metals, particularly as inherent metals in the range of from about 0.5 to 
3 percent by weight, is considered to improve the HFC-134 sorption 
efficiency. 
Some embodiments of this invention use inorganic molecular sieves. 
Molecular sieves are well known in the art and are defined in R. Szosak, 
Molecular Sieves-Principles of Synthesis and Identification, Van Nostrand 
Reinhold (1989) page 2. The inorganic molecular sieves used for 
preferentially sorbing HFC-134 in accordance with this invention include 
various silicates (e.g., titanosilicates and zeolites such as Zeolite Y, 
Zeolite A, Zeolite ZSM-5, and Zeolite ZSM-8), metalloaluminates and 
aluminophosphates, as well as other inorganic molecular sieve materials. 
The molecular sieves useful in the invention will typically have an 
average pore size of from about 0.3 to 1.5 nm. 
The Sanderson electronegativity model (see, R. T. Sanderson, "Chemical 
Bonds and Bond Energy", 2nd ed., Academic Press, New York, 1976) furnishes 
a useful method for classifying inorganic molecular sieves based on their 
chemical composition. In accordance with this invention the preferential 
sorption of tetrafluoroethane isomers by molecular sieves can be 
correlated with their intermediate electronegativity (i.e., their "Sint") 
as determined by the Sanderson method based on chemical composition. The 
Sint for Zeolite Na-X is about 2.38. 
Inorganic molecular sieves with Sints greater than the Sint for Zeolite 
Na-X (i.e., more electronegative or more acidic) may be used in accordance 
with this invention for increasing the mole ratio of CF.sub.3 CH.sub.2 F 
relative to CHF.sub.2 CHF.sub.2 by removing a substantial amount of 
CHF.sub.2 CHF.sub.2 ; and/or for increasing the mole ratio of CHF.sub.2 
CFH.sub.2 relative to CF.sub.3 CH.sub.2 F by desorbing sorbed CHF.sub.2 
CHF.sub.2 (i.e., CHF.sub.2 CHF.sub.2 is believed to sorb more strongly 
than CH.sub.2 FCF.sub.3). 
Inorganic molecular sieves with Sints no greater than the Sint for Zeolite 
Na-X (i.e., less electronegative or more basic) may be used in accordance 
with this invention for increasing the mole ratio of CHF.sub.2 CHF.sub.2 
relative to CF.sub.3 CH.sub.2 F by removing a substantial amount of 
CF.sub.3 CH.sub.2 F; and/or for increasing the mole ratio of CF.sub.3 
CH.sub.2 F relative to CHF.sub.2 CHF.sub.2 by desorbing sorbed CF.sub.3 
CH.sub.2 F (i.e., CF.sub.3 CH.sub.2 F is believed to sorb more strongly 
than CHF.sub.2 CHF.sub.2). Accordingly, this invention provides a process 
for separating a mixture of CHF.sub.2 CHF.sub.2 and CF.sub.3 CH.sub.2 F to 
provide a product wherein the mole ratio of CHF.sub.2 CHF.sub.2 relative 
to CF.sub.3 CH.sub.2 F is increased, which comprises the step of 
contacting said mixture with a sorbent for CF.sub.3 CH.sub.2 F selected 
from the group consisting of activated inorganic molecular sieves having 
intermediate electronegativities equal to or less than the intermediate 
electronegativity of Zeolite Na-X, at a temperature within the range of 
-20.degree. C. to 300.degree. C. and a pressure within the range of 10 kPa 
to 3000 kPa and for a period of time sufficient to remove a substantial 
amount of the CF.sub.3 CH.sub.2 F. Example Sint values are provided in 
Table I. 
TABLE I 
______________________________________ 
Intermediate Sanderson Electronegativities 
for Selected Molecular Sieves 
Molecular Sieve Sint 
______________________________________ 
Na-X 2.38 
Ca-A 2.56 
Na--Y 2.58 
ETS 2.60 
H--Y 2.97 
Na-ZSM-8 3.00 
H-ZSM-5 3.04 
H-ZSM-8 3.04 
______________________________________ 
Generally, for the inorganic molecular sieves, it is desirable to occupy 
acidic sites of the sieve material with alkali metal(s) and or alkaline 
earth metal(s) so long as the intermediate electronegativity remains 
suitable for the desired separation. In a preferred embodiment using 
preferential HFC-134 sorption the inorganic molecular sieve is a Zeolite Y 
which contains alkali or alkaline earth metal (s) selected from the group 
consisting of lithium, sodium, potassium, rubidium, cesium, magnesium, 
calcium, strontium and barium or combinations thereof. Alkali metals are 
preferred. It is preferred that alkali metals occupy from about 50% to 
100% of the accessible exchange sites in the zeolite. Particularly 
preferred zeolite molecular sieves include those having alkali metal to 
aluminum ratios of about 1:1, or alkaline earth metal to aluminum ratios 
of about 1:2. 
Suitable temperature ranges for sorption range from about -20.degree. C. to 
about 300.degree. C. Suitable pressures for sorption range from about 10 
kPa to about 3000 kPa. 
Contact with sorbent should be sufficient to achieve the desired degree of 
isomer enrichment. Preferably, the mole ratio of the enriched isomer to 
the second isomer is increased by at least about 25% relative to the mole 
ratio thereof in the initial mixture, most preferably by at least about 
50%. 
Where the process is used to purify CF.sub.3 CH.sub.2 F from a mixture of 
CF.sub.3 CH.sub.2 F and CHF.sub.2 CHF.sub.2 using preferential HFC-134 
sorption, preferably at least about 50 mole % of the CHF.sub.2 CHF.sub.2 
is removed. A particularly advantageous embodiment of this invention 
involves providing sufficient contact to produce CF.sub.3 CH.sub.2 F of at 
least about 99.99 mole percent purity. 
This invention can be practiced with the sorbent contained in a stationary 
packed bed through which the process stream whose components need 
separation is passed. Alternatively, it can be practiced with the sorbent 
applied as a countercurrent moving bed; or with a fluidized bed where the 
sorbent itself is moving. It can be applied with the sorbent contained as 
a stationary packed bed but the process configured as a simulated moving 
bed, where the point of introduction to the bed of the process stream 
requiring separation is changed, such as may be effected using appropriate 
switching valves. 
The production of a product enriched with respect to one C.sub.2 H.sub.2 
F.sub.4 isomer may be accompanied by the production of other products 
which are enriched with regard to the concentration of one or more other 
components of the initial mixture. Indeed, a typical process might include 
both a product which is enriched in CF.sub.3 CH.sub.2 F (e.g., essentially 
pure CF.sub.3 CH.sub.2 F) and another product which is enriched in 
CHF.sub.2 CHF.sub.2. The production of product enriched in CHF.sub.2 
CHF.sub.2 generally involves desorption of CHF.sub.2 CHF.sub.2. In any 
case, whether or not a CHF.sub.2 CHF.sub.2 enriched product is desired, 
the sorbent is typically regenerated following CHF.sub.2 CHF.sub.2 removal 
by desorption of sorbent materials. Desorption of components held by the 
sorbent may be effected with the sorbent left in place, or the sorbent may 
be removed and the desorption effected remotely from where the sorption 
step occurred. These desorbed components may exit the sorbent section in a 
direction either co-current (in the same direction as the original C.sub.2 
H.sub.2 F.sub.4 mixture feed was fed) or countercurrent (in the opposite 
direction of the original stream requiring separation). Desorption may be 
effected with or without the use of a supplemental purge liquid or gas 
flow. Where supplemental purge material is used, it may be a component of 
the feed, or some appropriate alternative material, such as nitrogen. Such 
supplemental purge materials may be fed either co-currently or 
countercurrently. 
In general, desorption can be effected by changing any thermodynamic 
variable which is effective in removing the sorbed components from the 
sorbent. For example, sorption and desorption may be effected using a 
thermal swing cycle, (e.g., where after a period of sorption, the sorbent 
is heated externally through the wall of the vessel containing it, and/or 
by the feeding of a hot liquid or gas into the sorbent, the hot gas being 
either one of the component materials or alternative materials). 
Alternatively, sorbed components can be removed by using a pressure swing 
cycle or vacuum swing cycle (e.g., where after a period of sorption the 
pressure is sufficiently reduced, in some embodiments to a vacuum, such 
that sorbed components are desorbed). Alternatively, the sorbed components 
can be removed by use of some type of stripping gas or liquid, fed 
co-currently or countercurrently to the original process feed material. 
The stripping material may be one of the process feed materials or another 
material such as nitrogen. 
One or several beds of sorbent may be used. Where several beds are used, 
they may be combined in series or in parallel. Also, where several beds 
are used, the separation efficiency may be increased by use of cycling 
zone sorption, where the pressure and or the temperatures of the beds are 
alternately raised and lowered as the process stream is passed through.

Practice of the invention will be further apparent from the following 
non-limiting Examples. 
EXAMPLE 1 
Metal tubing (0.18 inch I.D..times.12 inch, 0.46 cm I.D..times.30.5 cm) was 
packed with a carbon sorbent and installed in a gas chromatograph with a 
flame ionization detector. Helium was fed as a carrier gas at 33 sccm 
(5.5.times.10.sup.-7 m.sup.3 /s). Samples of the various compounds were 
then injected into the carrier stream at 200.degree. C. The results of 
these experiments using Barneby & Sutcliffe Type PE (3.75 g) carbon 
(Carbon A), Westvaco Microporous Wood-Based Granular Carbon (Carbon B), 
Barneby & Sutcliffe Type UU (3.85 g) carbon (Carbon C) and Calgon BPL 
(2.59g) carbon (Carbon D) are shown in Table 1. These data show that in 
each case the isomers had different retention times, and thus may be 
separated using the carbons of this Example. 
TABLE 1 
______________________________________ 
Retention 
Sample Time (min.) 
Separation 
Carbon 
mL.sup.(a) 
134.sup.(b) 
134a.sup.(c) 
Factor.sup.(d) 
Na.sup.(e) 
K.sup.(f) 
______________________________________ 
A 5 6.6 4.0 1.65 0.13% 1.09% 
200 4.36 3.16 1.36 0.13% 1.09% 
B 5 4.22 2.61 1.62 0.58% 75 ppm 
200 3.32 2.27 1.46 0.58% 75 ppm 
C 200 4.79 3.38 1.42 940 ppm 
0.93% 
D 5 2.32 1.75 1.32 660 ppm 
650 ppm 
200 2.01 1.59 1.26 660 ppm 
650 ppm 
______________________________________ 
.sup.(a) Volume of gas sample injected (microliters) 
.sup.(b) 134 = CHF.sub.2 CHF.sub.2 
.sup.(c) 134a = CF.sub.3 CH.sub.2 F 
.sup.(d) Separation Factor = 134 retention time/134a retention time 
.sup.(e) sodium content of carbon in weight percent or parts per million 
as indicated 
.sup.(f) potassium content of carbon in weight percent or parts per 
million as indicated 
It is evident from Table 1 that the relative sorption efficiency for 
HFC-134 is higher in the presence of the alkali metals Na and K. 
EXAMPLE 2 
Metal tubing (0.18 inch I.D..times.12 inch, 0.46 cm I.D..times.30.5 cm was 
packed with a carbon sorbent and installed in a gas chromatograph with a 
flame ionization detector. The experiment was repeated using the same 
carbon, but washing it with hydrochloric acid before using it for 
separations. The sodium content of Westvaco Microporous Wood-Based 
Granular Carbon (Not Acid-Washed, NAW) was 1.29%. After washing with 
hydrochloric acid the sodium content was 9 ppm. This carbon was designated 
Acid-Washed (AW). Helium was fed as a carrier gas at 33 sccm 
(5.5.times.10.sup.-7 m.sup.3 /s). Samples of 134 and 134a were then 
injected into the carrier stream at 200.degree. C. The results of these 
experiments are shown in Table 2. These data show that a more efficient 
separation was obtained with the carbon containing alkali metal; in this 
case sodium. 
TABLE 2 
______________________________________ 
Retention 
Time (min.) 
Separation 
Carbon Na Content 
134 134a Factor.sup.(a) 
______________________________________ 
NAW 1.29% 10.67 6.63 1.61 
AW 9 ppm 6.2 4.3 1.44 
______________________________________ 
.sup.(a) Separation Factor = 134 retention time/134a retention time 
EXAMPLE 3 
A packed tube (26 cm.times.2.12 cm I.D) containing Calgon BPL carbon (46.1 
g, 4.8.times.0.59 mm (12.times.30 mesh)) was purged with nitrogen 
continuously for 24 hours at 250.degree. C. and at 1 atmosphere pressure. 
While still being purged with nitrogen, the bed was cooled and was 
maintained at 25.degree. C. HFC-134a containing 1 wt % HFC-134 was then 
fed to the bed at 16.7 grams per hour. The results are shown in Table 3. 
TABLE 3 
______________________________________ 
Time 134a 134a 134 
(min) in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 0 0 0 
61 0.164 0 0 
65 0.175 0.011 0 
77 0.207 0.043 0 
89 0.239 0.075 0.61 
100 0.269 0.105 0.88 
112 0.301 0.137 0.96 
124 0.334 0.170 1.00 
______________________________________ 
.sup.(a) 134a in represents the total running sum of the moles of CF.sub. 
CH.sub.2 F fed to the column. 
.sup.(b) 134a out represents the total running sum of the moles of 
CF.sub.3 CH.sub.2 F exiting the column. 
.sup.(c) 134 out represents the instantaneous concentration of CHF.sub.2 
CHF.sub.2 in the CF.sub.3 CH.sub.2 F exiting the column, expressed as a 
multiple of the 1 wt. % feed (i.e., 0.5 would equal a 0.5 wt. % HFC134 
concentration in the HFC134a effluent). A zero is less than the detection 
limit of about 10 ppm. 
This example shows that carbon will selectively hold back HFC-134 allowing 
HFC-134a free of HFC-134 followed by HFC-134a containing reduced HFC-134 
concentrations to be obtained. 
EXAMPLE 4 
A packed tube (26 cm.times.2.12 cm I.D) containing Barneby & Sutcliffe Type 
PE carbon (50.3 g) was purged with nitrogen continuously for 12 hours at 
250.degree. C. and at atmosphere pressure. While still being purged with 
nitrogen, the bed was cooled and was maintained at 25.degree. C. HFC-134a 
containing 1 wt % HFC-134 was then fed to the bed at 16.7 grams per hour. 
The results are shown in Table 4. 
TABLE 4 
______________________________________ 
Time 134a 134a 134 
(min) in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 0 0 0 
69 0.186 0 0 
73 0.196 0.010 0 
85 0.229 0.043 0 
96 0.258 0.072 0 
108 0.291 0.105 0 
120 0.323 0.137 0.76 
132 0.355 0.169 0.94 
144 0.387 0.201 1.00 
______________________________________ 
.sup.(a) 134a in represents the total running sum of the moles of CF.sub. 
CH.sub.2 F fed to the column. 
.sup.(b) 134a out represents the total running sum of the moles of 
CF.sub.3 CH.sub.2 F exiting the column. 
.sup.(c) 134 out represents the instantaneous concentration of CHF.sub.2 
CHF.sub.2 in the CF.sub.3 CH.sub.2 F exiting the column, expressed as a 
multiple of the 1 wt. % feed (i.e., 0.5 would equal a 0.5 wt. % HFC134 
concentration in the HFC134a effluent). A zero is less than the detection 
limit of about 10 ppm. 
EXAMPLE 5 
A packed tube (26 cm.times.2.12 cm I.D) containing Westvaco Microporous 
Wood-Based Granular Carbon (46 g) was purged with nitrogen continuously 
for 12 hours at 250.degree. C. and at 1 atmosphere pressure. While still 
being purged with nitrogen, the bed was cooled and was maintained at 
25.degree. C. HFC-134a containing 1 wt % HFC-134 was then fed to the bed 
at 16.6 grams per hour. The results are shown in Table 5. 
TABLE 5 
______________________________________ 
Time 134a 134a 134 
(min) in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 0 0 0 
74 0.199 0.003 0 
82 0.221 0.025 0 
94 0.253 0.057 0 
106 0.285 0.089 0 
118 0.317 0.121 0.16 
130 0.350 0.154 0.65 
142 0.382 0.186 0.97 
155 0.417 0.221 1.00 
______________________________________ 
.sup.(a) 134a in represents the total running sum of the moles of CF.sub. 
CH.sub.2 F fed to the column. 
.sup.(b) 134a out represents the total running sum of the moles of 
CF.sub.3 CH.sub.2 F exiting the column. 
.sup.(c) 134 out represents the instantaneous concentration of CHF.sub.2 
CHF.sub.2 in the CF.sub.3 CH.sub.2 F exiting the column, expressed as a 
multiple of the 1 wt. % feed (i.e., 0.5 would equal a 0.5 wt. % HFC134 
concentration in the HFC134a effluent). A zero is less than the detection 
limit of about 10 ppm. 
EXAMPLE 6 
A packed tube (26 cm.times.2.12 cm I.D) containing Westvaco Microporous 
Wood-Based Granular Carbon (46 g) was purged with nitrogen continuously 
for 12 hours at 250.degree. C. and at 1 atmosphere pressure. While still 
being purged with nitrogen, the bed was cooled and was maintained at 
25.degree. C. HFC-134a containing 1 wt % HFC-134 was then fed to the bed 
at 16.6 grams per hour and at 4.7 atm. (476 kPa). The results are shown in 
Table 6. 
TABLE 6 
______________________________________ 
Time 134a 134a 134 
(min) in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 0 0 0 
54 0.261 0.013 0 
65 0.3125 0.067 0 
77 0.373 0.125 0 
89 0.431 0.183 0 
101 0.489 0.241 0.33 
113 0.547 0.299 0.47 
125 0.605 0.357 0.55 
137 0.663 0.415 0.82 
______________________________________ 
.sup.(a) 134a in represents the total running sum of the moles of CF.sub. 
CH.sub.2 F fed to the column. 
.sup.(b) 134a out represents the total running sum of the moles of 
CF.sub.3 CH.sub.2 F exiting the column. 
.sup.(c) 134 out represents the instantaneous concentration of CHF.sub.2 
CHF.sub.2 in the CF.sub.3 CH.sub.2 F exiting the column, expressed as a 
multiple of the 1 wt. % feed (i.e., 0.5 would equal a 0.5 wt. % HFC134 
concentration in the HFC134a effluent). A zero is less than the detection 
limit of about 10 ppm. 
Examples 3 through 6 show that these carbon based sorbents will selectively 
sorb HFC-134 allowing HFC-134a free of HFC-134, followed by HFC-134a 
containing reduced HFC-134 concentration to be obtained. Examples 3 
through 6 show that process material other than the components to be 
separated can be used to strip HFC-134 (i.e., in this case, nitrogen 
rather than HFC-134a is used to clear the bed of HFC-134). Also, examples 
5 and 6 show that the capacity or 134 increases with pressure, and 
illustrates the presence of pressure swing adsorption. 
EXAMPLE 7 
This is an example of a thermal swing cycle alternating a sorption step 
with a desorption step. The column and carbon packing are the same as that 
used in Example 4 above. During the sorption step, HFC-134a containing 1 
wt % 134 was fed to the packed column at 26.degree. C. and at a feed rate 
of 16.6 g/hr with a back-pressure setting of 1 atmosphere (101 kPa) in the 
column. When HFC-134 began to break through at the other end of the 
column, the flow of feed was stopped, and the ends of the column were 
sealed. The column was then heated to 150.degree. C., and gas was vented 
from the column in the direction countercurrent to the original direction 
of feed, to keep the pressure at 1 atmosphere (101 kPa). When the 
temperature reached 150.degree. C., HFC-134a containing less than 1 ppm of 
HFC-134 was fed in the direction countercurrent to the original feed to 
purge the bed, at 16.5 g/hr and with a back pressure setting of 1 
atmosphere (101 kPa). The column valves were then closed at both ends, and 
the column cooled to 26.degree. C. The cooling of the bed caused a partial 
vacuum. The pressure was then brought back to 1 atmosphere (101 kPa) using 
the high HFC-134 content HFC-134a and the cycle was started again. The 
sorption and desorption steps were then repeated. The results of the 
second sorption step are shown in Table 7A. 
TABLE 7A 
______________________________________ 
Time Temp HFC-134a HFC-134a 
HFC-134 
(Min) .degree.C. 
in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 26 0 0 0 
93 26 0.250 0.124 0 
117 26 0.315 0.189 0.77 
129 26 0.347 0.221 0.87 
140 26 0.377 0.251 0.96 
______________________________________ 
.sup.(a) HFC134a in represents the total running sum of the moles of 
HFC134a fed to the column. 
.sup.(b) HFC134a out represents the total running sum of the moles of 
HFC134a exiting the column. 
.sup.(c) HFC134 out represents the instantaneous concentration of the 
HFC134 in the HFC134a exiting the column, expressed as a multiple of the 
1% feed. A zero is less than the detection limit of about 10 ppm. 
The results of the desorption step which followed are shown in Table 7B. 
TABLE 7B 
______________________________________ 
Time Temp HFC-134a HFC-134a 
HFC-134 
(min) .degree.C. 
in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 25 0 0 0 
7 35 0 0.049 1.16 
12 98 0 0.107 1.51 
24 150 0 0.133 1.63 
36 150 0.032 0.165 1.67 
47 150 0.062 0.195 1.63 
71 150 0.126 0.259 0 
______________________________________ 
.sup.(a) HFC134a in represents the total running sum of the moles of 
HFC134a fed to the column. 
.sup.(b) HFC134a out represents the total running sum of the moles of 
HFC134a exiting the column. 
.sup.(c) HFC134 out represents the instantaneous concentration of the 
HFC134 in the HFC134a exiting the column, expressed as a multiple of the 
1% feed. A zero is less than the detection limit of about 10 ppm. 
Initially, no HFC-134a was fed, but HFC-134a and HFC-134 exited the column 
due to the let down of the pressure as the temperature was raised from 
26.degree. C. to 150.degree. C. Beginning at 24 minutes, when the 
temperature reached 150.degree. C., HFC-134a containing less than 1 ppm 
134 was fed at 16.5 g/hr. At 71 minutes, the HFC-134a flow was stopped. 
This example shows the use of a temperature swing cycle as a process 
concept to produce both HFC-134-free and HFC-134-reduced HFC-134a. 
EXAMPLE 8 
This is an example of a thermal swing cycle alternating a sorption step 
with a desorption step. The column and carbon packing were the same as 
that used in Examples 5 and 6 above. During the sorption step, HFC-134a 
containing 1 wt % 134 was fed to the packed column at 25.degree. C. and a 
134a feed rate of 16.6 g/hr with a back-pressure setting of 1 atmosphere 
(101 kPa) in the column. When the outlet HFC-134 concentration matched the 
inlet concentration, the flow of feed was stopped, and the ends of the 
column were sealed. The column was then heated to 150.degree. C., and gas 
was vented from the column in the direction countercurrent to the original 
direction of feed, to keep the pressure at 1 atmosphere (101 kPa). When 
the temperature reached 150.degree. C., HFC-134a containing less than 1 
ppm of HFC-134 was fed in the direction countercurrent to the original 
feed to purge the bed, at 16.5 g/hr and with a back pressure setting of 1 
atmosphere (101 kPa). The column valves were then closed at both ends, and 
cooled to 25.degree. C. The cooling of the bed caused a partial vacuum. 
The pressure was then brought back to 1 atmosphere (101 kPa) using the 
high HFC-134 content HFC-134a and the cycle was started again. The 
sorption and desorption steps were then repeated. 
The results of the second sorption step are shown in Table 8A. 
TABLE 8A 
______________________________________ 
Time Temp HFC-134a HFC-134a 
HFC-134 
(min) .degree.C. 
in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 25 0 0 0 
29 25 0.140 0 0 
73 25 0.353 0.213 0 
85 25 0.411 0.271 0.25 
97 25 0.469 0.329 0.80 
100 25 0.532 0.392 1.00 
______________________________________ 
.sup.(a) HFC134a in represents the total running sum of the moles of 
HFC134a fed to the column. 
.sup.(b) HFC134a out represents the total running sum of the moles of 
HFC134a exiting the column 
.sup.(c) HFC134 out represents the instantaneous concentration of HFC134 
in the HFC134a exiting the column, expressed as a multiple of the 1% feed 
A zero is less than the detection limit of about 10 ppm. 
The results of the desorption step which followed are shown in Table 8B. 
TABLE 8B 
______________________________________ 
Time Temp HFC-134a HFC-134a 
HFC-134 
(min) .degree.C. 
in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 25 0 0 0 
10 36 0 0.049 1.09 
22 78 0 0.105 1.31 
34 130 0 0.150 1.54 
46 150 0.015 0.170 1.65 
58 150 0.073 0.228 1.59 
71 150 0.136 0.291 1.56 
83 150 0.194 0.349 0.02 
95 150 0.252 0.407 0 
______________________________________ 
.sup.(a) HFC134a in represents the total running sum of the moles of 
HFC134a fed to the column. 
.sup.(b) HFC134a out represents the total running sum of the moles of 
HFC134a exiting the column. 
.sup.(c) HFC134 out represents the instantaneous concentration of the 
HFC134 in the HFC134a exiting the column, expressed as a multiple of the 
1% feed. A zero is less than the detection limit of about 10 ppm. 
Initially, no HFC-134a was fed, but HFC-134a and HFC-134 exited the column 
due to the let down of the pressure as the temperature was raised from 
25.degree. C. to 150.degree. C. Beginning at 34 minutes, when the 
temperature reached 150.degree. C., HFC-134a containing less than 1 ppm 
134 was fed at 16.5 g/hr. At 95 minutes, the HFC-134a flow was stopped. 
This example shows the use of a temperature swing cycle as a process 
concept to produce both HFC-134-free and HFC-134-reduced HFC-134a. 
EXAMPLE 9 
Metal tubing 0.18" (4.6 mm) I.D..times.2 ft. (0.51 m) was packed with 
zeolite sorbents as indicated in Table 9, and installed in a gas 
chromatograph with a flame ionization detector. The columns were heated at 
200.degree. C. in flowing helium for a minimum of 12 hours. Helium was fed 
as a carrier gas at 20 sccm (3.3.times.10.sup.-7 m.sup.3 /s). Samples (25 
.mu.L) of HFC-134 and HFC-134a were then injected into the carrier stream 
at different temperatures. The results of these experiments are shown in 
Table 9. Comparison of the 134/134a data for Na-Y and H-Y show a much 
enhanced separation on the more basic zeolite. 
TABLE 9 
______________________________________ 
Retention Times 
Temperature (min) Separation 
Zeolite (.degree.C.) 
134/134a Factor 
______________________________________ 
Na--Y 200 408/71.4 5.7 
H--Y 100 68.1/46.1 1.5 
H-ZSM-5.sup.(a) 
200 470/308 1.5 
5A 200 291/about 150 1.9 
______________________________________ 
.sup.(a) The flow rate for the HZSM-5 run was 35 sccm (5.8 .times. 
10.sup.-7 m.sup.3 /s 
EXAMPLE 10 
Metal tubing 0.18" (4.6 mm) I.D..times.2 ft. (0.51 m) was packed with 
zeolite sorbents as indicated in Table 10, and installed in a gas 
chromatograph with a flame ionization detector. The columns were heated at 
200.degree. C. in flowing helium for a minimum of 12 hours. Helium was fed 
as a carrier gas at 30 sccm (5.0.times.10.sup.-7 m.sup.3 /s). Samples (25 
to 500 .mu.L) of HFC-134 and HFC-134a were then injected into the carrier 
stream at different temperatures. Each test was run in duplicate. Methane 
(1% in nitrogen) was run as a standard at each temperature. The results of 
these experiments are shown in Table 10. 
TABLE 10 
______________________________________ 
Retention Times 
Temperature (min) Separation 
Zeolite (.degree.C.) 
134/134a Factor 
______________________________________ 
Na--Y 230 160/53.2 3.0 
240 128/45.1 2.8 
250 98.3/36.8 2.7 
H--Y 210 2.07/1.19 1.7 
220 1.78/1.06 1.7 
230 1.01/0.89 1.1 
H-ZSM-8 210 110/70.2 1.6 
220 79.7/51.1 1.6 
230 56.7/37.5 1.5 
5A 230 74.7/29.4 2.5 
240 64.1/24.9 2.6 
250 49.2/18.5 2.7 
______________________________________ 
EXAMPLE 11 
This is an example of a thermal swing cycle with countercurrent purge 
during desorption. A 1 inch (2.54 cm) diameter tube was packed with 63 
grams of the zeolite H-ZSM-5, and purged with nitrogen at 50 psig (450 
kPa). The nitrogen was then turned off, and the column fed with HFC-134a 
containing 1.2 mole % HFC-134 at 60 sccm (1.0.times.10.sup.-7 m.sup.3 /s) 
and 50 psig (450 kPa). The results of this test are shown in Table 11A. 
TABLE 11A 
______________________________________ 
Time Temp HFC-134 
(min) .degree.C. 
out.sup.(a) 
______________________________________ 
0 29 -- 
10 29 -- 
20 29 0* 
30 29 0 
40 29 0 
50 29 0 
60 29 0 
70 29 0 
80 29 0 
90 29 0.18 
100 29 0.34 
110 29 0.51 
120 29 0.69 
______________________________________ 
*Breakthrough of HFC134a occurs. 
.sup.(a) HFC134 out represents the instantaneous concentration of HFC134 
in the HFC134a exiting the column, expressed as a multiple of the origina 
1% feed. A zero is less than the detection limit of about 10 ppm. 
When the outlet concentration of the 134 matched the inlet concentration, 
the high 134 concentration 134a flow was stopped and the ends of the 
column were sealed. The column was then heated to 150.degree. C., and gas 
was vented from the column in the direction countercurrent to the original 
direction of feed, to keep the pressure at 1 atmosphere (100 kPa). When 
the temperature reached 150.degree. C., HFC-134a containing less than 1 
ppm 134 was fed in the direction countercurrent to the original feed at 
psig (450 kPa). The results are summarized in Table 11B. 
TABLE 11B 
______________________________________ 
Time Temp HFC-134 
(min) .degree.C. 
out.sup.(a) 
______________________________________ 
0 31 1.06 
10 86 1.19 
20 114 1.37 
30 126 1.56 
40 133 1.63 
50 133 1.67 
60 133 1.75 
70 134 1.61 
80 134 1.25 
90 134 0.78 
100 134 0.41 
110 134 0.18 
120 134 0 
______________________________________ 
.sup.(a) HFC134 out represents the instantaneous concentration of the 
HFC134 in the HFC134a exiting the column, expressed as a multiple of the 
original 1% feed. A zero is less than the detection limit of about 10 ppm 
 
EXAMPLE 12 
This is an example of a thermal swing cycle with countercurrent purge 
during desorption. A 0.93 inch (2.36 cm) diameter by 12 inch (30.48) long 
tube was packed with 80 grams of LZ-Y52 zeolite (a Na-Y zeolite), and 
purged with nitrogen at 50 psig (450 kPa). The nitrogen was then turned 
off, and the column fed with HFC-134a containing 1.5 mole % HFC-134 at 50 
psig (450 kPa) and 30.degree. C. The results of this test are shown in 
Table 12A. 
TABLE 12A 
______________________________________ 
HFC-134a HFC-134a HFC-134 
in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 0 0 
0.235 0.004 0 
0.958 0.717 0 
0.965 0.736 0.108 
0.987 0.758 0.221 
1.009 0.781 0.304 
1.032 0.803 0.379 
1.053 0.825 0.447 
1.071 0.843 0.460 
______________________________________ 
.sup.(a) HFC134a in represents the total running sum of the moles of 
HFC134a fed to the column. 
.sup.(b) HFC134a out represents the total running sum of the moles of 
HFC134a exiting the column. 
.sup.(c) HFC134 represents the instantaneous concentration of HFC134 in 
the HFC134a exiting the column, expressed as a multiple of the 1.5% feed. 
When the outlet concentration of the 134 reached of the feed concentration, 
the high 134 concentration 134a flow was stopped and the column heated to 
150.degree. C. The pressure generated from the heating was vented from the 
column in the direction countercurrent to the original direction of feed. 
During the temperature ramp, approximately 0.0514 moles of 134a and 0.0002 
moles of 134 were vented. When the temperature reached 150.degree. C., 
HFC-134 free HFC-134a was fed in the direction countercurrent to the 
original feed at psig (450 kPa) and 150.degree. C. The results are 
summarized in Table 12B. 
TABLE 12B 
______________________________________ 
HFC-134a HFC-134a HFC-134 
in.sup.(a) out.sup.(b) 
out.sup.(c) 
______________________________________ 
0 0 0 
0.0336 0.0321 3.26 
0.0673 0.0639 3.45 
0.1010 0.0958 3.48 
0.1347 0.1277 3.48 
0.1795 0.1702 3.26 
0.2118 0.2009 3.05 
0.2513 0.2380 2.48 
0.3545 0.3396 0.58 
______________________________________ 
.sup.(a) HFC134a in represents the total running sum of the moles of 
HFC134a fed to the column. 
.sup.(b) HFC134a out represents the total running sum of the moles of 
HFC134a exiting the column. 
.sup.(c) HFC134 represents the instantaneous concentration of HFC134 in 
the HFC134a exiting the column, expressed as a multiple of the 1.5% feed. 
EXAMPLE 13 
Metal tubing 0.18" (4.6 mm) I.D..times.2 ft. (0.51 m) was packed with 
zeolite sorbents as indicated in Table 13 and installed in a gas 
chromatograph with a flame ionization detector. The columns were heated at 
200.degree. C. in flowing helium for a minimum of 12 hours. Helium was fed 
as a carrier gas at 30 sccm (5.0.times.10.sup.-7 m.sup.3 /s). Samples (5 
to 25 .mu.L) of HFC-134 and HFC-134a were then injected into the carrier 
stream at different temperatures. Each test was run in duplicate. Methane 
(1% in nitrogen) was run as a standard at each temperature. The results of 
these experiments are shown in Table 13. 
TABLE 13 
______________________________________ 
Retention Times 
Temperature 
(min) Separation 
Zeolite (.degree.C.) 
134/134a Factor 
______________________________________ 
ETS-10.sup.(a) 
200 262.5/90.3 2.9 
Na-A 200 1.6/0.6 2.7 
Clinoptilolite 
200 1.0/0.8 1.3 
Ferrierite 
200 0.9/0.5 1.8 
______________________________________ 
.sup.(a) Sodium Potassium Titanosilicate 
EXAMPLE 14 
Metal tubing 0.18" (4.6 mm) I.D..times.4.5 in (11.4 cm) was packed with 
Zeolite Na-X as indicated in Table 14, and installed in a gas 
chromatograph with a flame ionization detector. The columns were heated at 
200.degree. C. in flowing helium for a minimum of 12 hours. Helium was fed 
as a carrier gas at 30 sccm (5.0.times.10.sup.-7 m.sup.3 /s). Samples (25 
.mu.L) of HFC-134 and HFC-134a were then injected into the carrier stream 
at different temperatures. Each test was run in duplicate. Methane (1% in 
nitrogen) was run as a standard at each temperature. The results of these 
experiments are shown in Table 14. The peaks were very broad and therefore 
the retention times were difficult to measure. However, it was clear that 
the relative retention times of the 134/134a isomers were reversed when 
compared to the previous examples. 
TABLE 14 
______________________________________ 
Retention Times 
Temperature 
(min) Separation 
Zeolite (.degree.C.) 
134/134a Factor 
______________________________________ 
Na-X 200 13.2/180.7 0.073 
Na-X 210 60.0/115.0 0.52 
______________________________________ 
The examples serve to illustrate particular embodiments of the invention. 
The invention is not confined thereto, but embraces embodiments which come 
within the scope of the claims.