Design of combined membrane and distillation processes

The performance of three hybrid membrane and distillation processes is compared theoretically, using the separation of propylene and propane as a representative case. For each system configuration the effect of the main design variables is illustrated through parametric studies. Results dealing with both design of new processes and retrofit of existing distillation-based separation processes are presented. The results show qualitative trends which may serve as guidelines for design of hybrid membrane and distillation processes. If the membrane is placed parallel to the column, the optimal position for the membrane feed stream is close to the column feed plate, which represents a potential pinch point in the column. The optimal membrane cut rate for this configuration is generally close to the molefraction of propylene in the membrane feed stream. The comparison of the systems performances indicates that placing the membrane in parallel or on the bottom stream of the column gives the best performance of the hybrid process, both in terms of compressor duty and in terms of installed membrane area.