Relation between permeate pressure and operational parameters in VOC/nitrogen separation by a PDMS composite membrane

Transmembrane driving force, which can be produced by permeate pressure, is a significant element in the design of VOC/nitrogen separation processes. Studies on the impart of the pressure on the membrane performance and the separation mechanism can provide important information for the design of new membranes and separation processes. In this work, the effect of permeate pressure on membrane performance was studied for the separation of a cyclohexane/nitrogen mixture using a polydimethylsiloxane (PDMS)/polyamide (PA) composite membrane. The changing trends of the separation performance for the separation of VOCs with different saturated vapor pressures under different permeate pressures were analyzed. The variation in the transmembrane driving force for cyclohexane and nitrogen with different parameters, such as membrane thickness, were also investigated under various permeate pressures. The reason for the decrease in selectivity with increasing permeate pressure was discussed. It was demonstrated that permeate pressure affects the membrane performance mainly by weakening the cyclohexane flux, while having little influence on the nitrogen flux in the studied range due to their different saturated vapor pressures. Lastly, the energy consumption for the VOC/nitrogen separation, which provides fundamental insight for industrial membrane-based VOC recovery, was simulated keeping in consideration all the obtained experimental data.