Study On Adsorption And Separation Of HFCs Mixture By Functional Microporous Materials

Hydrofluorocarbons（HFCs）are widely used as alternatives to ozone-depleting substances（ODS）,chlorofluorocarbons（CFCs）and hydrochlorofluorocarbons（HCFCs）,mainly as refrigerants or foaming agents for cooling and air conditioning.In the HFCs,CHF₃has the largest greenhouse potential and the longest atmospheric lifetime,posing a major climate problem if released into the atmosphere.CHF₃ is a by-product of the production of refrigerant CHCl F₂.However,CHCl F₂ is the basic raw material for the production of products such as TFE,PTFE,and HFCs,etc.The emissions of CHF₃ will inevitably continue.According to the actual CHCl F₂ production system,the emission gas composition of CHCl F₂is CHF₃:97%,N₂:3%.At present,CHF₃ is mainly disposed of by high-temperature incineration.So,the treatment cost is relatively high.In recent years,the utilization and conversion of CHF₃ into valuable chemicals have been paid more and more attention.These chemicals mainly include direct trifluoromethylation reagents,CF₃I,fluorine-containing alkanes,vinylidene fluoride,and halogenated hydrocarbons,etc.The separation and purification methods of CHF₃ mainly focus on low temperature distillation,absorption separation,membrane separation and adsorption separation.Compared with other technologies,adsorption separation technology has the advantages of low energy consumption,simple operation and high degree of automation.In this paper,SIFSIX-3-Ni,Ge FSIX-3-Ni and Ti FSIX-3-Ni were synthesized by changing the anion（M=Si,Ge,Ti）of MF₆^2-using the same organic ligand pyrazine.The pure component adsorption of CHF₃ and N₂ on different materials was investigated at 288K,298 K and 308 K.The experimental results show that SIFSIX-3-Ni is the most adsorptive material for CHF₃ and N₂ among the three MOFs at 288 K.The adsorption isotherms of CHF₃ and N₂ on SIFSIX-3-Ni were fitted with Langmuir model,and the selectivity of CHF₃and N₂ was calculated by IAST solution theory.The experimental results show that the fitting degrees of CHF₃ and N₂ are 98.70%and 98.55%,respectively,and the values of S_{（CHF3/N2）}are both greater than 20.It is proved that SIFSIX-3-Ni has good potential for the separation of CHF₃/N₂.Then the isomolar breakthrough experiment and the continuous breakthrough experiment of actual gas composition were carried out for CHF₃/N₂ mixture.The results showed that SIFSIX-3-Ni had good separation effect on CHF₃/N₂ mixture at 288 K and a total pressure of 10 bar,and SIFSIX-3-Ni had good reproducibility and stability.Using Aspen adsorption software to simulate the separation process of CHF₃/N₂.The separation process of CHF₃/N₂ by SIFSIX-3-Ni was designed.The effects of feed flow rate,adsorption pressure,adsorption time,pressure equalization time,blow down time and vacuum degree on the purity and recovery of CHF₃ were discussed and analyzed,and the separation performance of CHF₃/N₂ was evaluated.The PSA result show that the adsorption pressure is 1.5 bar,the feed flow is 0.6 m³/h,the adsorption time is 165 s,the pressure equalization time is 22 s,the blow down time is 95 s,and the vacuum degree is 0.1 bar.Under these conditions,the purity of CHF₃ is more than 99%（fire extinguishing agent grade）,and the recovery rate is more than 90%under the optimized operating conditions.In conclusion,PSA simulation confirms that SIFSIX-3-Ni has good separation performance for CHF₃/N₂ mixture.In addition,this work provides an effective strategy for designing and screening adsorbed materials for CHF₃/N₂ separation and recovery applications.