Vacuum swing adsorption process for the separation of ethylene/ethane with AgNO3/clay adsorbent

The performance of the 4-bed and 3-bed VSA process using AgNO3/clay adsorbent for the ethylene separation from C2 fractionator feed (83.56% C2H4, 16.44% C2H6) was investigated experimentally and theoretically. With the 4-bed VSA process, extremely high recovery of ethylene, over 99%, was obtained at ethylene purity of 99.8%. The recovery of the 3-bed process was lower about by 1% than that of the 4-bed VSA process. But, the productivity of the 3-bed VSA was higher about by 33% than that of the 4-bed VSA process. The productivity of the 3-bed VSA process was 3.7 mol/kg/hr at the ethylene purity of 99.8%. Effects of the rinse flow rate in the 3-bed VSA process were investigated by both experiment and simulation. The purity of ethylene was not significantly improved by the increase of the rinse flow rate after it reached 99.8%. At the rinse flow rate where the purity was 99.9%, the recovery became 70%. It might be attributed to the slow diffusion of ethane. According to the simulation, ethylene purity of over 99.9% could be obtained with recovery of over 90% only when the mass transfer rate of ethane is lower than 1.0×10-4 s-1 or higher than 0.2 s-1. The productivity of the process could be improved by increasing the feed flow rate at the expense of the recovery. According to the simulation, at the feed flow rate of 5,000 ml/min, the productivity of 5.2 mol/kg/hr was obtained at the ethylene purity of 99.5%.