Cyclic distillation: a high-efficiency alternative for sustainable propane-propylene separation with reduced cost

Abstract

Separation of propane and propylene continues to be one of the petrochemical industry's most energy-demanding processes, with high capital cost, mainly because of the very small boiling point difference between them, which requires very challenging separation methods. Here, cyclic distillation is proposed especially for super fractionators, which provides outstanding separation efficiency while greatly reducing both equipment size and the amount of energy needed. The system realizes 99.9 % high-purity separation of both propane and propylene using 54 trays, compared to 140 trays in conventional systems, a 61 % reduction. Additionally, the reboiler duty is also decreased from 21 GJ/hr to 12 GJ/hr, which is 43 % less in terms of energy usage. The McCabe-Thiele analysis emphasizes the inherent benefits of cyclic operation in which periodic vapor-liquid dynamics make use of beneficial thermodynamic conditions to ensure high separation quality. Periodic operation also boosts internal efficiency by decreasing the pinch effect and accommodating lower flow rates of vapor, which further ensures an energy economy without compromising separation quality. It is the only distillation mode that has both features of continuous distillation as well as batch distillation, bringing about intensified phase contact, better use of energy, as well as enhanced separation efficiency, especially in the case of near-boiling constituents in the system.