Study On The Separation Of HCFC-22/HFC-23 Gas Mixture By Membrane

HFC-23 is the byproduct in the producing process of HCFC-22, and it is a target gas for emission reduction in the Kyoto protocol. The global warming potential (GWP) of HFC-23 is 11700 times that of CO₂. Central incineration treatment for it is needed to avoid destroying the ecological environmentIn this paper, HCFC-22/HFC-23 gas mixture was separated by membrane technique on the background of the project in a company. The HFC-23 was enriched for incineration after the HCFC-22 was recovered.Firstly, the separation experiments for HCFC-22/HFC-23 gas mixture were done by home-made PDMS membrane, commercial PI membrane and commercial PSF membrane, respectively. The stability of membrane and the influences of feed concentration, feed pressure and stage-cut on the separation were also studied. The results show that the home-made PDMS membrane is more suitable for the separation of this gas mixture. The average separation factor for the tail gas can reach up to 2.34. The concentration and flux of retentate gas increase with the increasing concentration in feed gas. The concentration of HFC-23 in retentate gas and the recovery of HCFC-22 increase with the increasing feed pressure and stage-cut, while the separation factor declined because of the increasing degree of the concentration polarization.Secondly, the permeation mechanisms and permeation properties of HCFC-22 and HFC-23 through the membranes were analyzed. The variation of permeate rates of HCFC-22 and HFC-23 with the feed pressure and stage-cut were studied. The results show that pressure is the main factor which causes the variation of permeate rates. The permeate rates of HCFC-22 and HFC-23 through the PDMS membrane increase with the partial pressure and tend to steady gradually under the influence of swelling and concentration polarization.Thirdly, a new simulation method of membrane process was developed in HYSYS system, in which the variation of permeate rates with pressure were considered. The flow sheets for the separation of the tail gas were designed by HYSYS system. The simulation for the separation under fluctuant feed conditions was also done to observe the stability of the design. Simulation results show that the two step-three stage flow sheet can accomplish the separation task effectively. The concentration of HFC-23 can keep up around 97% under the fluctuant feed conditions, and the variation under different feed condition just answered for the experimental results.The membrane separation scheme proposed in this paper can effectively separate the HCFC-22/HFC-23 gas mixture according to the results of experiments and simulations. It provides a reliable foundation for the industrial application. Meanwhile, this paper puts forward a new method for researching the separation process of gas mixture by membrane.