Process for purification of 1,1,1-trifluoro-2-chloroethane

Abstract: Hydrogen fluoride and 1,1,1-trifluoro-2-chloroethane forms an azeotropic mixture. A mixture comprising hydrogen fluoride and 1,1,1-trifluoro-2-chloroethane is phase separated when it is cooled to a temperature below 7 °C. 1,1,1-Trifluoro-2-chloroethane is purified effectively from the mixture by cooling the mixture to form an upper liquid phase and a lower liquid phase and distilling the lower liquid phase so that the hydrogen fluoride is removed as an azeotropic distillate and 1,1,1-trifluoro-2-chloroethane substantially free from hydrogen fluoride is obtained as a bottom product.

Description: The present invention relates to a process for the purification of 1,1,1,-trifluoro-2-chloroethane (hereinafter referred to as R-133a) by removing HF from a mixture comprising HF and R-133a. R-133a draws attention since it is one representative cooling medium which can replace dichlorodifluoromethane. Also R-133a is a suitable raw material of HFC-134a (1,1,1,2-tetrafluoroethane) and it is a suitable raw material of trifluoroethanol. Description of the Related Art R-133a is generally produced by reacting a carbon chloride such as trichloroethylene with HF. HF is removed from a reaction mixture comprising HF and R-133a as main components by washing the mixture with an aqueous solution (cf. EP-A-407961). This manner is not so suitable since a large amount of alkali is required to neutralize the washing solution. EP-A 353970 discloses the separation of HF from a mixture comprising FC-123 (1,1-dichloro-2,2,2-trifluoroethane) and FC-124 (1-chloro-1,2,2,2-tetrafluoroethane) in addition to HF, using phase separation and distillation. EP-A 98341 discloses a process for the recovery of 142b (1-chloro-1,1-difluoroethane) and HF as an azeotropic mixture using phase separation and azeotropic distillation. None of the above-cited prior art documents discloses the phase separation of R-133a and HF of the present invention. SUMMARY OF THE INVENTION We found that a mixture comprising HF and R-133a as main components is separated into two liquid phases, that is, an upper liquid phase rich in HF and a lower liquid phase rich in R-133a (the ratio HF/R-133a of the lower liquid phase is smaller than that of the original mixture before the liquid separation) when it is cooled to a temperature below 7 °C. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a process flow sheet of one preferred embodiment in which the present purification process is carried out. DETAILED DESCRIPTION OF THE INVENTION A two component system comprising HF and R-133a has the azeotropic mixture having the minimum boiling point. When the mixture comprising HF and R-133a as the main components is distilled at atmospheric pressure, no further concentration of HF from a molar ratio HF/R-133a of about 65/35 is possible. In other words, at such a molar ratio, the composition of the liquid phase is the same as that of the vapor phase which is in equilibrium with the liquid phase. The molar ratio HF/R-133a of the azeotropic mixture changes with a system pressure. For example, when the system pressures are 1.5 Kg/cm 2 G, 4.0 Kg/cm 2 G and 15 Kg/cm 2 G, the molar ratios (HF/R-133a) are about 60/40, about 55/45 and about 45/55, respectively. After cooling the mixture comprising HF and R-133a and separating into the two phases, the concentration of R-133a of the lower liquid phase is increased compared with that before the cooling. It has been found that when increased, the R-133a concentration of the lower liquid phase is deviated into a R-133a concentration greater than that of the azeotropic mixture. Cooling the mixture comprising HF and R-133a produces a lower liquid phase rich in R-133a and an upper liquid phase rich in HF. Merely cooling the mixture provides the upper liquid phase and the lower liquid phase each of which is rich in either component compared with the original mixture before the cooling. The concentration of R-133a in the lower liquid phase may be further increased when the obtained lower liquid phase is subjected to any proper treatment such as distillation, extraction, absorption, adsorption or neutralization with an alkali in which HF is preferentially removed so that R-133a is concentrated and purified. Since the upper liquid phase is rich in HF, it is subjected to any proper treatment in which R-133a is preferentially removed as in the case of the treatment of the lower liquid phase so that HF is concentrated and purified. Thus, merely cooling facilitates the first rough separation step. The temperature at which the mixture is cooled (cooling temperature) is below 7 °C. The mixture may not be liquid-separated at a temperature above 7 °C at any ratio of HF/R-133a. The preferred cooling temperature is below 5 °C. At a temperature above 5 °C, a composition of the upper liquid phase is not so different from that of the lower liquid phase, so that the density of the upper liquid phase is also not so different from that of the lower liquid phase, which may make the liquid separation insufficient. There is no specific lower limitation of the cooling temperature, provided that the temperature is higher than the solidifying point of R-133a (about -100 °C). Generally, the cooling temperature is preferably above about -50 °C. Operation at a temperature below -50 °C is uneconomical since much amount of energy is required for the cooling. The cooling temperature is more preferably in the range of -20 °C to 0 °C. HF may be separated from the mixture comprising R-133a and HF by directly distilling the mixture with the use of any type of a distillation apparatus. On such distillation, the azeotrope mixture of HF and R-133a is used as a reflux returned to the distillation apparatus during the distillation operation so that a distillate of the azeotropic mixture is efficiently obtained from the top of the distillation apparatus, and R-133a substantially free from HF is obtained from the bottom of the apparatus when the concentration of R-133a of the mixture fed into the apparatus is deviated into the R-133a concentration greater than that of the azeotropic mixture. The azeotropic distillation apparatus may be any type of distillation apparatus which has conventional means necessary for the usual distillation operation. For example, a distillation column having trays or a packed column may be preferably used. The azeotropic distillation may be carried out in a continuous operation or in a batch operation. In a preferred embodiment of the present invention, the mixture comprising HF and R-133a is cooled so that the mixture is divided into an upper liquid phase rich in HF and a lower liquid phase rich in R-133a, and then each liquid phase is subjected to the azeotropic distillation separately. The upper liquid phase is divided into a distillate of the azeotropic mixture of R-133a and HF distilled from the top of the distillation apparatus and the rest of HF substantially free from R-133a withdrawn as a bottom product from the apparatus, provided that the HF concentration of the upper liquid phase is deviated into a HF concentration which is greater than that of the HF concentration of the azeotropic mixture. Since the R-133a concentration of the lower liquid phase is deviated into the R-133a concentration which is larger than that of the azeotropic mixture, the lower liquid phase is divided into a distillate of the azeotrope mixture of R-133a and HF distilled from the top of the other distillation apparatus and the rest of R-133a substantially free from HF withdrawn as a bottom product from the apparatus. The present invention is useful for the removal of HF from a mixture produced in the reaction of trichloroethylene with HF in the liquid phase or in the vapor phase in the presence of a catalyst. One preferred embodiment of the present invention will be explained below. Figure 1 shows a flow sheet of one example of preferred purification plants which may be used in the present invention. Usually the mixture obtained from the reaction is withdrawn in the form of a gaseous phase. The mixture comprises R-133a, HF and hydrogen chloride in addition to small amounts of organic substances. Hydrogen chloride is removed from the mixture by distillation. Then, the mixture is cooled to a temperature below 7 °C, preferably below 5 °C, more preferably below 0 °C through a cooler and passed to a liquid phase separation device 1 such as a decanter to form the two liquid phases. There is R-133a substantially free from HF at the bottom of the distillation apparatus 3, which may be withdrawn as a bottom product. On the one hand, the lower liquid phase rich in R-133a from the separation device 1 may be supplied to a distillation apparatus 3 and an azeotropic mixture 5 is distilled from the top of the apparatus 3. During such distillation, a portion of the distilled azeotropic mixture is returned, as a reflux, to the top of the apparatus 3. The rest of the distillate is passed to the liquid separation device 1 after being cooled to a temperature below 7 °C at a cooler 11 and then above procedures are repeated. There remains R-133a substantially free from HF at the bottom of the distillation apparatus 3, which is withdrawn as a bottom product 9. On the other hand, the upper liquid phase rich in HF in the liquid separation device 1 may be returned to any reaction system, if possible. Alternatively, it may be distilled in the other distillation apparatus. In Figure 1, the upper liquid phase is supplied to another distillation apparatus 23 where it is divided into an azeotropic distillate 25 of HF and R-133a and a bottom product 29 of HF substantially free from R-133a. A portion of the distillate is returned, as a reflux 27, to the top of the distillation apparatus 23 as in the case of distillation apparatus 3. The rest of the distillate is cooled to a temperature below 7 °C at a cooler 31 and then returned to the liquid separation device 1. The bottom product 29 substantially free from R-133a may be reused. As described above, all HF is utilized while R-133a is purified. These procedures may be carried out in a continuous or a batch mode. The present invention will be further explained with reference to some Examples below. Example 1 HF and R-133a were charged into an evacuated vessel made of a fluorine plastic at a molar ratio HF/R-133a of 60/40 and then mixed together. The mixture was settled at 0 °C to be phase-separated. The molar ratio HF/R-133a of the separated lower liquid phase was measured and found to be 30/70. The molar ratio HF/R-133a of the upper liquid phase was also measured and found to be 84/16. Examples 2-4 Example 1 was repeated except that the phase separation temperature was changed. The separation temperatures and the molar ratio HF/R-133a of the lower phases are shown in Table 2 together with the results of Example 3. Example Sep. Temp. HF/R-133a Ratio (lower phase) 3 0 °C 30/70 4 -5 °C 20/80 5 -10 °C 10/90 6 5 °C 50/50 Note: Before the phase separation, the molar ratio HF/R-133a was 60/40. It is understood that the molar ratio HF/R-133a of the lower liquid phase is remarkably reduced after the phase separation. Example 5 HF (150 g, 7.5 mol) and R-133a (592.5 g, 5.0 mol) were charged into an evacuated vessel made of a fluorine plastic (effective volume 1000 ml) and cooled to -20 °C. After cooling, the mixture of HF and R-133a was phase-separated into a lower liquid phase and an upper liquid phase, and the lower phase was recovered which contained 1 g of HF (0.05 mol) and 435.5 g of R-133a (3.68 mol). Thus, the molar ratio HF/R-133a was 1.34/98.66, and the concentration of R-133a was greatly deviated into the R-133a concentration which is greater than that of the azeotropic mixture. Example 6 HF (150 g, 7.5 mol) and R-133a (592.5 g, 5.0 mol) were charged into an evacuated vessel made of the fluorine plastic (effective volume 1000 ml) and cooled to -20 °C. After cooling, the mixture of HF and R-133a was liquid-separated into a lower liquid phase and an upper liquid phase, and the upper phase was recovered which contained 149 g of HF (7.45 mol) and 157 g of R-133a (1.32 mol). Thus, the molar ratio HF/R-133a was 84.95/15.05, and the concentration of HF was greatly deviated into the HF concentration which is larger than that of the azeotropic mixture.

Claims: A process for the purification of 1,1,1-trifluoro-2-chloroethane which comprises the steps of cooling a mixture comprising hydrogen fluoride and 1,1,1-trifluoro-2-chloroethane to a temperature below 7°C, liquid-separating the mixture into an upper liquid phase rich in hydrogen fluoride and a lower liquid phase rich in 1,1,1-trifluoro-2-chloroethane, and recovering 1,1,1,-trifluoro-2-chloroethane containing a smaller amount of hydrogen fluoride from the lower liquid phase. A process according to claim 1 in which the mixture is cooled to a temperature below 5°C.

Inventors: IWASHITA NOBUYOSHI, KOMATSU SATOSHI, KOYAMA SATOSHI, TSUDA TAKEHIDE, IWASHITA, NOBUYOSHI, KOMATSU, SATOSHI, KOYAMA, SATOSHI, TSUDA, TAKEHIDE, IWASHITA, NOBUYOSHI, C/O YODOGAWA WORKS OF, KOMATSU, SATOSHI, C/O YODOGAWA WORKS OF, KOYAMA, SATOSHI, C/O YODOGAWA WORKS OF, TSUDA, TAKEHIDE, C/O YODOGAWA WORKS OF
Applicants: DAIKIN IND LTD, DAIKIN INDUSTRIES, LTD.
Application year: 1992
Main classification: C07C19
IPC codes: C01B7, C07C17