Method for preparing pentafluoroethane

Abstract

The invention discloses a method of preparing the pentafluoroethane (HFC-125), which adopts the hydrogen fluoride (HF) and the perchlorethylene (PCE) as the material, and takes two reactors and two steps of gas phase catalysis fluorination reaction. A first reactor fluorinates the PCE and synthesizes 2,2-dichlor-1,1,1-trifluoroethane(HCFC-123) and 2-chlorin-1,1,1,2-tetrafluorothane(HCFC-124), and the second reactor fluorinates HCFC-123 and HCFC-124 and synthesizes HFC-125. The unreacted PCE in the resultant flow of the first reactor is separated by a first distillation tower and then circulates to the first reactor; the HF, HCFC-126, HCFC-124, HFC-125 and HCL in the resultant flow of the first reactor and the second reactor are separated by a second distillation tower and a third distillation tower, and then the separated HF circulates to the first reactor and the second reactor, while the HCFC-123, the HCFC-124 and the HFC-134a circulate to the second reactor. The invention can prolong the service life of the catalyst and improve the one-way conversion of PCE as well as remarkably reduce the content of chloropentafluoroethane(CFC-115) in the desired product HFC-125.

Description

technical field [0001] The present invention relates to a preparation method of pentafluoroethane (HFC-125), in particular to a method for obtaining 2,2-dichloro-1,1,1-trifluoro through hydrogen fluoride gas-phase catalyzed fluorinated tetrachloroethylene (PCE). Ethane (HCFC-123) and 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124), and then further catalytic fluorination of HCFC-123 and HCFC-124 to obtain pentafluoroethane . Background technique [0002] Pentafluoroethane is a fluorinated hydrocarbon compound that is safe for the atmospheric ozone layer. It is mainly used as a substitute for chlorodifluoromethane (HCFC-22) refrigerants. In addition, it is also widely used as a blowing agent, solvent, propellant , fire extinguishing agent and dry etchant. [0003] At present, among the known methods for industrially preparing HFC-125, the preparation method of synthesizing HFC-125 by gas phase reaction in the presence of a catalyst using hydrogen fluoride and PCE as raw mater...

AI Technical Summary

Problems solved by technology

In this method, the reaction of fluorinating PCE to generate HCFC-123 and HCFC-124 is carried out in the same reactor as the synthesis of HFC-125 by fluorinating HCFC-123 and HCFC-124, and is affected by the intermediate products HCFC-123 and HCFC-124 , the reaction of fluorinated PCE to generate HCFC-123 and HCFC-124 is restricted, resulting in a relatively low single-pass conversion rate of PCE

In addition, in order to increase the space-time yield of HFC-125, the reaction needs to be carried out at a high temperature of about 350 ° C. Because the polymerization reaction of PCE is easy to occur at high temperature, the coking rate of the catalyst is accelerated, and the life of the catalyst is affected.

And the content of chloropentafluoroethane (CFC-115) in the product is higher, because of the azeotropic phenomenon of CFC-115 and HFC-125, brings difficulty to the purification of HFC-125, has increased production cost

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