Intermolecular Mechanism Analysis and Process Design for the Separation of Fluorinated Mixed Refrigerants by Extractive Distillation to Produce Electronic-Grade Pentafluoroethane

Electronic-grade pentafluoroethane (R125), a new etching gas, is irreplaceable in advanced process precision cleaning, 3D NAND etching, and other scenarios. R125 is usually present in mixed azeotropic refrigerants. It is easy to form azeotropes with difluoromethane (R32) and pentafluorochloroethane (R115) during the recovery process. Conventional distillation has difficulty achieving efficient recovery of R125, necessitating the development of efficient separation and purification technologies. This work proposes a three-column extractive distillation process for the efficient separation of the R32-R125-R115 ternary system to purify and prepare electronic-grade R125. The optimal entrainer was determined based on relative volatility analysis and quantum chemical calculations, and the optimal process parameters for the three-column extractive distillation process (EDP) were obtained using a multiobjective optimization method based on genetic algorithms with the total annual cost (TAC) and greenhouse gas emissions as the objective functions. On this basis, two energy-saving process schemes were developed. Finally, the conventional distillation process (CDP), EDP, and its energy-saving schemes (HIEDP-1 and HIEDP-2) were comprehensively analyzed. The results showed that, compared with CDP, the EDP process significantly reduces TAC, gas emissions, and process energy consumption. Compared with EDP, the TAC of HIEDP-1 and HIEDP-2, which introduced energy-saving means such as heat integration and heat pumps, was reduced by 31.50% and 30.94%, respectively, and the process energy consumption was reduced by 54.59% and 46.78%, respectively, both of which significantly reduced the process energy consumption and saved the cost of equipment and utility works. In addition, the HIEDP-2 with heat pump-assisted heat integration saves the expensive cost of cooling the top of the EDC1 column compared to the HIEDP-1 with conventional heat integration, but the high compression ratio of the top vapor makes the equipment cost and energy consumption slightly higher. However, considering that HIEDP-1 is less flexible due to the limitation of fluctuations in the composition of the flow strands or the flow rate, the application potential of HIEDP-2 is greater if the higher investment cost is acceptable. This work verifies the feasibility of the recovery of fluorinated mixed refrigerants and the purification and separation of high-purity R125, which provides a valuable reference for the efficient recovery of fluorinated refrigerants and the preparation of high-value-added products by purification.