Recycling HCFC-31 In The Production Of HFC-32 Using Dry Separation Technology

HFC-32 is the ideal substitute of the ozone depleting substance (ODS) and it has a good thermodynamic performance. The chemical name is difluoromethane and molecular formula is CH2F2. The boiling point is -51.65℃. The ozone depletion potential (ODP) is 0.11 which is about 100 times lower than that of HFC-134a, so it is a more environmentally refrigerant. HFC-32 as the main raw material with the HFC-134a or HFC-125 can be made from R410 or R407 which are the most environmentally refrigerant with excellent refrigerating effect. The refrigerant is used for large-scale air conditioning and will replace HCFC-22 and R502 eventually. In addition, they can be fully applicable to the compressor of normalization, and thermodynamic performance is 15% higher than that of HCFC-22, annual growth rate is expected to reach 25%.The synthesis methods of the HFC-32 include:fluorination of dichloromethane, hydrogenolysis and reduction of HCFCs, and formaldehyde oxidation, etc. wherein the fluorination of dichloromethane is the most common method. According to the different of the reaction phase, it can be divided into vapor and liquid fluorination.This paper mainly studied that high toxic by-product HCFC-31 recycling and utilization in the process route that use dichloromethane and the anhydrous hydrogen fluoride as the raw materials, SbCl5 as the catalyst to product HFC-32 in liquid-phase. The analysis showed, the reaction gas from the reaction reflux tower including:HFC-32, HC1, HCFC-31 and HF, and the amount of the HCFC-31 is about 4% of the product yield. According to the current single set of fluorination reactor where the yield of is 600 kg/h, design a heavier component recovery system that recovery HCFC-31. Reaction gas through the reaction reflux tower into the heavies recovery tower, when the content of the top of HFC-32 up to 99%, enter into the subsequent neutralization system, the HCFC-31 and the small amount of HFC-32 from tower bottoms into the fluorination reactor by liquid pressure difference or pump, and then completed the purpose of recycling HCFC-31.According to the preliminary design process about the HCFC-31 recovery system, the production processing and control points have been determined, a selection of major equipments has been made, the recovery system has been designed and installed, and established safety procedures. The result is good after operation, and the yield up 90%.