Dow has developed new carbon molecular sieves (CMS) that show a high separation factor for olefin and paraffin. The new CMS was investigated for its propane - propylene separation performance via experimentation and computer simulation. Recent efforts have focused on improving the propylene product purity either by using a two stage PSA or alternate PSA cycle configurations.
Using the new CMS in a 4-step basic PSA cycle, propylene can be enriched to over 80% from a 25/75% propylene and propane mixture with over 95% propylene recovery. Adding co-current blowdown and propylene rinse steps to the 4-step basic PSA cycle increased the propylene product concentration to over 88% from the same mixture. A two stage PSA can readily enrich propylene to >98% when using 4-step PSA cycles and to>99% if the second stage PSA uses a cycle including co-current blowdown and propylene rinse steps.
Aspen models were developed for the base PSA cycles as well as the alternate cycle configurations. Model predictions are compared to PSA experimental results. Simulation results show very good agreement with experimental results.
