Process for dehydrohalogenation of halogenated alkanes

Abstract

A process for the manufacture of halogenated olefins in semi-batch mode by dehydrohalogenation of halogenated alkanes in the presence of an aqueous base such as KOH which simultaneously neutralizes the resulting hydrogen halide. During the process, aqueous base is continuously added to the haloalkane which results in better yields, lower by-product formation and safer/more controllable operation.

1 . A process for preparing a hydrofluoroolefin comprising:
 a. introducing an alkali-metal hydroxide feed stream into a reactor charged with at least one halogenated propane having a structure according to Formula I:
   C 3 F x Cl y H 8-x-y   (Formula I)
 
 wherein x is 5 or 6 and y is 0 or 1, provided that x+y is ≦6; 
   b. reacting, in a liquid phase, said halogenated propane with said an aqueous base in said reactor to produce a halogenated propene having a structure according to Formula II:
   C 3 F z-1 H 7-z   (Formula I)
 
 wherein z is x−1; and 
   c. removing at least a portion of said halogenated propene from said reactor as a vapor product stream,
 wherein steps (a), (b), and (c) are at least partially performed simultaneously. 
   
     
     
         2 . The process of  claim 1  wherein x+y is 6 and said halogenated propene is HFO-1225. 
     
     
         3 . The process of  claim 2  wherein said halogenated propane is HFCF-235fa and said halogenated propene is HFO-1225zc. 
     
     
         4 . The process of  claim 2  wherein said halogenated propane is HFCF-236fa and said halogenated propene is HFO-1225zc. 
     
     
         5 . The process of  claim 2  wherein said halogenated propane is HFCF-236ea and said halogenated propene is HFO-1225ye. 
     
     
         6 . The process of  claim 1  wherein x+y is 5 and said halogenated propene is HFO-1234. 
     
     
         7 . The process of  claim 6  wherein said halogenated propane is HFCF-245eb and said halogenated propene is HFO-1234yf. 
     
     
         8 . The process of  claim 1  further comprises refluxing at least a portion of unreacted halogenated propane in said vapor product stream back to said reactor. 
     
     
         9 . The process of  claim 8  further comprises refluxing water in said vapor product stream back to said reactor. 
     
     
         10 . The process of  claim 1  wherein said reacting occurs at a temperature of about 40 to about 75° C. 
     
     
         11 . The process of  claim 10 , wherein said reacting occurs at a temperature of about 50 to about 60° C. 
     
     
         12 . The process of  claim 1 , wherein said aqueous base is an alkali metal hydroxide. 
     
     
         13 . The process of  claim 12 , wherein said alkali metal hydroxide is potassium hydroxide. 
     
     
         14 . The process of  claim 13 , wherein potassium hydroxide is present in a concentration of about 10 to about 50 wt. %. 
     
     
         15 . A process for dehydrohalogenating a compound comprising:
 a. providing a reaction admixture comprising potassium hydroxide and a halogenated propane having a degree of halogenation of M; and   b. reacting said potassium hydroxide with said halogenated propane to form a halogenated propene having a degree of halogenation of M−1.   
     
     
         16 . The process of  claim 15  wherein M is 5 or 6. 
     
     
         17 . The process of  claim 16  wherein said halogenated propane is at least pentafluorinated. 
     
     
         18 . The process of  claim 17  wherein said product is a hydrofluoroolefin.