Economic Estimation of Various Membranes and Distillation for Propylene and Propane Separation

The separation of propylene and propane is very costly due to similar physical-chemical properties. In this study, the effect of various membranes on the economic performance of the olefin unit was evaluated. The Robeson's line cannot judge the economic performance of membrane separation systems. A precise model of cocurrent and counter-current hollow fiber membrane was developed and implemented in a commercial chemical engineering software to estimate the economics of the best inorganic (ZIF-8) and polymeric (6FDA-TrMPD) membranes compared with the existing distillation unit. At the same area, the cocurrent flows have higher recovery and the counter-current flows have higher purity. The use of the alternative polymer membrane results in a drastic increase in costs. The ZIF-8 membrane performance leads to a 30% increase in the total capital costs, while the annual cost considerably decreased by 46%. When the membrane performance is appropriate in terms of selectivity and permeability, the use of membrane processes alone is more economical than the use of membrane-distillation systems. But when this is mediocre, cost savings in hybrid systems are higher than the membrane system. Also, to achieve high purity, the use of high selectivity materials is more efficient than high permeability materials.