Process for the production of dichlorotrifluoroethane

Abstract

A process for the production of dichlorotrifluoroethane is described. The process comprises reacting perchloroethylene with hydrogen fluoride in the vapour phase at elevated temperature in at least one reactor in the presence of a fluorination catalyst to produce a composition comprising dichlorotrifluoroethane, hydrogen chloride, unreacted perchloroethylene and unreacted hydrogen fluoride. The composition that is produced is subjected to a separation step to recover a first fraction comprising dichlorotrifluoroethane and a second fraction comprising perchloroethylene and hydrogen fluoride. The second fraction is further separated into a hydrogen fluoride-rich fraction and a perchloroethylene-containing, organic-rich fraction which are then recycled. The dichlorotrifluoroethane that is recovered may be used to prepare pentafluoroethane.

1 . A process for the production of pentafluoroethane which comprises the steps of:
 (i) in a first reactor or a first plurality of reactors reacting perchloroethylene with hydrogen fluoride in the vapour phase at elevated temperature in the presence of a fluorination catalyst to produce a composition comprising dichlorotrifluoroethane, hydrogen chloride, unreacted perchloroethylene and unreacted hydrogen fluoride;   (ii) separating from the composition that is produced in step (i) a first fraction comprising at least 95 weight % of dichlorotrifluoroethane and less than 0.5 weight % of compounds having the formula C 2 Cl 6−x F x , where x is an integer of from 0 to 6, based on the total weight of organic compounds in the composition, and a second fraction comprising perchloroethylene and hydrogen fluoride;   (iii) separating the second fraction from step (ii) into a hydrogen fluoride-rich fraction and a perchloroethylene-containing, organic-rich fraction;   (iv) recycling the hydrogen fluoride-rich fraction and perchloroethylene-containing, organic-rich fraction back to step (i) of the process; and   (v) in a second reactor or a second plurality of reactors reacting the dichlorotrifluoroethane-containing first fraction recovered from step (ii) with hydrogen fluoride (HF) in the vapour phase at an elevated temperature in the presence of a fluorination catalyst to produce a composition comprising pentafluoroethane and less than 0.5 weight % of chloropentafluoroethane, based on the total weight of organic compounds in the composition.   
     
     
         2 . The process according to  claim 1 , wherein the composition that is produced in step (i) contains less that 2 weight % of chlorotetrafluoroathane and pentafluoroethane combined and less than 5 weight % of compounds having the formula C 2 Cl 6−x F x , where x is an integer of from 0 to 6, based on the total weight of organic compounds in the composition. 
     
     
         3 . The process according to  claim 2 , wherein the composition that is recovered from step (v) is passed to a still where it is separated into a top fraction comprising hydrogen chloride and pentafluoroethane and a bottom fraction comprising hydrogen fluoride. 
     
     
         4 . The process according to  claim 3 , wherein the bottom fraction also comprises chlorotetrafluoroethane and dichlorotrifluoroethane. 
     
     
         5 . The process according to  claim 4 , wherein the bottom fraction is recycled to step (v) of the process. 
     
     
         6 . The process according to  claim 5 , wherein the composition recovered from step (v) is combined with fresh hydrogen fluoride before it is passed to the still for purification. 
     
     
         7 . The process according to  claim 6 , wherein the amount of hydrogen fluoride added is sufficient to avoid the need to convey a separate hydrogen fluoride feed to the second reactor(s) in step (v) of the process.