Abstract:
A gas phase process for the preparation of 245fa is provided, wherein 1233zd is contacted with HF in the presence of a supported antimony catalyst.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the preparation of 1,1,1,3,3-pentafluoropropane (“245fa”) from 1,1,1-trifluoro-3-chloro-2-propene (“1233zd”), particularly to gas phase processes wherein said 1233zd is contacted with hydrogen fluoride (“HF”) in the presence of a supported antimony catalyst. 1,1,1,3,3-Pentafluoropropane is known to have utility as a foam blowing agent and refrigerant. 
     WO 97/24307 discloses a gas phase process for the conversion of 1233zd to 245fa via reaction with HF in the presence of a chrome catalyst, but does not achieve high conversions of the 1233zd (generally at or below about 80%) so that a major portion of the desired 245fa product becomes azeotroped with the unreacted 1233zd, causing product loss and/or major separation problems. A process is therefore needed which permits high conversions of the 1233zd starting material. 
     BRIEF SUMMARY OF THE INVENTION 
     A gas phase process for preparing readily recoverable 245fa is provided, which process comprises (a) contacting 1233zd with HF in the presence of a supported antimony halide catalyst (preferably antimony fluoride); and (b) recovering 245fa from the resulting reaction mixture. 
     DETAILED DESCRIPTION 
     It has now been discovered that the use of a supported antimony catalyst in the gas phase hydrofluorination of 1233zd permits high conversions of 1233zd to 245fa, typically on the order of 95% or more, with 99-100% selectivity for 245fa, so that product loss is mininized or avoided altogether. In addition to 245fa, the resulting reaction mixture also contains coproduct hydrogen chloride (HCl), together with unreacted HF and 1233zd. 
     The 1233zd starting material can be prepared by known processes, such as fluorination of 1,1,3,3-tetrachloro-2-propene (“1230za”) as taught in U.S. Pat. No. 5,616,819. 
     The HF:1233zd molar ratio is typically from about 0.5:1 to about 10:1, but is preferably from about 5:1 to 10:1. Temperatures of from about 110° C. to about 150° C. are typically used. Pressures are typically from about 0 to about 315 psig, preferably from about 115-170 psig. The contact time (total flow rate divided by the catalyst volume) is typically from about 1 to about 100 seconds, more typically from about 20 to about 60 seconds. 
     A supported antimony halide catalyst is used, the support typically being activated carbon, HF-treated activated carbon, graphite, fluorided graphite, alumina or fluorided alumina and the halide typically being chloride or, preferably, fluoride. The catalyst is typically prepared by adding an antimony V salt, such as antimony chloride, SbCl 5  to the support, loading the catalyst to a fixed bed reactor and activating the catalyst by feeding HF over the bed at about 50° C., resulting in conversion of the antimony chloride to antimony fluoride. 
     The HCl and HF can be separated from the resulting reaction mixture by conventional means. For example, the HCl can be distilled from the other compounds and the HF separated by scrubbing with water, metal fluoride adsorption, membrane separation or swing distillation. Metal fluoride adsorption can be conveniently out using an alkali metal fluoride such as KF or NaF to convert the HF to a metal fluoride. 
     A minor amount of the 245fa product will be azeotroped with unreacted 1233zd. However, since only a low level of 1233zd will be present, photochlorination can be used to convert the 1233zd to the high boiling 1,1,1-trifluoro-2,3,3-trichloropropane (b.p., 106° C.), which latter compound can be readily separated from the low boiling 245fa (b.p., 15° C.) by distillation. 
    
    
     The practice of the invention is illustrated in more detail in the following non-limiting examples. 
     EXAMPLE 1 
     Preparation of Antimony Halide Catalyst 
     Antimony (V) chloride was added to activated carbon, loaded to a fixed bed reactor, and activated with HF at 50° C. 
     EXAMPLE 2 
     Preparation of 245fa 
     A gas phase mixture of HF and 1233zd (molar ratio of 7.2:1) was fed over the catalyst bed of Example 1 at a temperature of 112° C. and a pressure of 151 psig for a contact time of 47 seconds, resulting in 96.6% conversion of the 1233zd, with selectivity of 99.7% for 245fa.