A hybrid batch distillation/membrane process for high purification part 1: Energy efficiency and separation performance study for light impurities removal

High purification processes are usually characterized by high energy demand and unavoidable losses of a purified substance during removal of trace impurities. An unsteady-state hybrid separation method based on a batch distillation with integrated membrane gas separation was studied for high purification of liquefied gases. The performance of a hybrid process versus a standalone batch distillation was analyzed through simulations and experiments for the case of light impurities removal from ammonia. A model of a middle-vessel batch distillation column was built in Aspen Plus Dynamics (TM) with an integrated hollow fiber membrane model implemented in Aspen Custom Modeler (TM). The results of batch distillation simulations are validated against the experimental data. Among the considered aspects are the hydrodynamics study, the effect of operating conditions on column separation performance, and the dynamics of the purification process. The simulations were done at a varied impurity cut withdrawal rate, membrane area, stage cut, and membrane selectivity taking into account the effective (mixed gases) selectivity data for ammonia/impurity systems available in the open literature. The possibility of both reducing the total energy input and improving the product recovery is shown for a hybrid purification process involving the separation of the withdrawn impurity cut in a membrane module with recycling of the purified component back to the distillation column.