Solvent extraction of I-141B from I-365

Partial or total separation of a mixture of 1,1,1,3,3-pentafluorobutane and 1,1-dichloro-1-fluoroethane by liquid-liquid extraction with solvents containing ethylene glycol, 2-butene-1,4-diol, ethanolamine, propylene glycol, or mixtures thereof, preferably ethylene glycol.

FIELD OF THE INVENTION 
This invention relates to a method of partially or totally separating a 
mixture of 1,1,1,3,3-pentafluorobutane ("I-365") and 
1,1-dichloro-1-fluoroethane ("I-141b") by liquid-liquid extraction with 
solvents containing ethylene glycol, 2-butene-1,4-diol, ethanolamine, 
propylene glycol, or mixtures thereof. 
BACKGROUND OF THE INVENTION 
I-365 is a byproduct formed during the manufacture of I-141b, a replacement 
for trichlorofluoromethane as a blowing agent. Since I-365 is a solvent 
and precursor for other chemicals, a method for its recovery is needed. 
Separation by conventional distillation means is extremely difficult, 
however, since I-365 and I-141b form an azeotrope. 
While liquid-liquid extraction has been reported in U.S. Pat. No. 4,031,148 
for separating chlorinated hydrocarbons by the use of water-miscible 
solvents and 0%-50% water, applicant is not aware of literature which 
discloses liquid-liquid extraction for separating HFC's 
(hydrofluorocarbons) such as I-365 from HCFC's (hydrochlorofluorocarbons) 
such as I-141b. Also, as noted in column 1, lines 53-56 of said U.S. Pat. 
No. 4,031,148, and as demonstrated by copending application Ser. No. 
07/751,014, filed on even date herewith, it is impossible to foresee which 
extraction agents will enable the separation of any two substances. 
SUMMARY OF THE INVENTION 
A method is provided for at least partial separation of a mixture of I-365 
and I-141b comprising liquid-liquid extraction on the mixture in the 
presence of a solvent containing ethylene glycol, 2-butene-1,4-diol, 
ethanolamine, propylene glycol, or mixtures thereof, preferably ethylene 
glycol. More specifically, the process comprises contacting the mixture of 
I-141b and I-365 with the extracting agent such that the agent extracts 
I-141b from the mixture and forms a separate phase therefrom, then 
separating the phases of I-141b-rich solvent and I-141b/I-365 mixture, 
which mixture now has a correspondingly reduced concentration of I-141b.

DETAILED DESCRIPTION OF THE INVENTION 
It has now been discovered that efficient separation of I-365 and I-141b 
can be achieved via liquid-liquid extraction using the aforementioned 
solvents, such as ethylene glycol alone or in admixture with 
2-butene-1,4-diol, ethanolamine, propylene glycol, propylene carbonate, or 
2-butene-1,4-diol and propylene glycol; 2-butene-1,4-diol alone or in 
admixture with propylene glycol, ethanolamine, or propylene carbonate; 
ethanolamine alone or with propylene glycol; or propylene glycol. These 
solvents are found to have a selectivity for I-141b (at 25.degree. C.) of 
from about 1.24 to 3.85. Other solvents, such as dipropylene glycol, may 
be incorporated as well as long as the selectivity is not substantially 
adversely affected. Subject to this proviso, the exact proportion of 
solvent components in the solvent mixtures is not critical. Examples of 
solvent mixtures containing dipropylene glycol ("DG") are DG in admixture 
with ethanolamine, 2-butene-1,4-diol, 2-butene-1,4-diol and ethanolamine, 
ethylene glycol and ethanolamine, or ethylene glycol and 
2-butene-1,4-diol. 
The separation can be carried out in a liquid-liquid extractor, as shown in 
FIG. 1, where a I-141b/I-365 mixture is shown as the heavier component 
entering the top of the extraction column 1 through line 2. The solvent, 
shown as the lighter component, enters column 1 at the bottom through line 
3 (for a solvent which is heavier, the two feed streams would come in the 
reversed ends). The purified (or partially purified) I-365 stream is 
removed from the bottom of column 1 through line 4, and the used, 
I-141b-enriched, solvent stream is removed from the top of column 1 
through line 5. Any solvent adsorbed into the I-365 stream is removed by 
distillation in column 6, producing a purified I-365 stream which exits 
the top of column 6 through line 7 and a small solvent recycle stream 
which exits the bottom of column 6 through line 8 for reintroduction to 
column 1. The used solvent stream is distilled in distillation column 9 to 
remove the I-141b (and any I-365) which exits at the top of column 9 
through line 10, and then the purified solvent stream is recycled back to 
column 1 via line 11. A pump 12 provides the power to circulate the 
solvent around the process. 
The extraction column can be designed from equilibrium data. For example, 
the Table below shows equilibrium concentrations for the ternary system of 
I-365, I-141b, and ethylene glycol at 25.degree. C. Plotting of the data 
as in FIG. 2 enables the design of an on column to reduce I-141b in an 
I-141b/I-365 stream from, for example, 99% to 92%. Referring to FIG. 2, 
the I-365 is fed to an extraction column (at point A). The solvent leaves 
the column (at point B) with 99% I-141b, in equilibrium with I-365 now 
having an I-141b concentration of only 98.3% (point C). Thus, after 
leaving the first equilibrium stage of the extraction column (from point A 
to point C), the I-141b concentration has been reduced from 99% to 98.3%. 
Using the same procedure (C to E, E to G, and G to I), it is seen that the 
concentration can be reduced to 92% in four equilibrium stages. 
TABLE 
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Equilibrium Data for I-141b, I-365, and 
and Solvent at 25.degree. C. (in Mole %) 
I-141b I-365 (*) 
Ethylene Glycol 
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(A) RAFFINATE 
98.9 1.1 (1.1) 
0.0 
97.8 2.2 (2.2) 
0.0 
96.0 4.0 (4.0) 
0.0 
93.1 6.9 (6.9) 
0.0 
90.5 9.5 (9.5) 
(B) EXTRACT 
7.8 0.02 (0.3) 
92.2 
8.2 0.13 (1.6) 
91.6 
7.4 0.19 (2.4) 
92.4 
6.3 0.27 (4.1) 
93.5 
6.1 0.36 (5.6) 
93.5 
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*Amounts in Parenthesis Show I365 On A SolventFree Basis