Propane/propylene separation by pressure swing adsorption using zeolite 4A

In this work we have studied Pressure Swing Adsorption (PSA) process for separation of propane/ propylene mixtures using zeolite 4A extrudates (CECA) as an alternative to distillation. Purified propylene is withdrawn in the blowdown step at 10 kPa because is the most adsorbed compound. The cycle used comprises five steps: pressurization, feed, purge with product, depressurization to intermediate pressure and counter-current blowdown for propylene recovery. Two mixtures with different propylene/propane ratios (54-46 and 85-15 diluted to 50% with nitrogen) corresponding to different sources of propylene production (steam cracking and Fluid Catalytic Cracking) were studied. The effects of the different step times in the performance of the PSA unit were evaluated. PSA performance was also studied using different operating conditions: process temperature and feed pressure. Also, the removal of inert from the process was studied. The simulation of the PSA unit was performed in gPROMS using a bi-LDF approximation for mass transfer. Experimental purities of propylene around 99.0% were obtained. The recovery of propylene in some of the runs reached values higher than 85% which is much higher than 30% obtained in previous studies. The best performance was obtained at 408 K where simulated purity was 99.43% with a recovery of 84.3% and a unit productivity of 2.57 mol/h.kg of zeolite.