Effects of membrane transport properties and structure parameter on pressure-retarded osmosis performance

For salinity gradient power generation, a pressure-retarded osmosis (PRO) process uses a semipermeable membrane as a means of energy conversion. The performance of a PRO membrane is evaluated by the power density determined in a particular PRO condition. The membrane power density, which is the power generated per unit membrane surface area, can be calculated from the experimentally measured water flux and operating pressure difference. To fabricate a high-performance PRO membrane, both the transport properties and the structure parameter of the membrane should be balanced delicately. Water permeability (A) and salt permeability (B) are both transport properties of the active layer, while the structure parameter (S) is a distinct feature of the support layer. Thus, the PRO membrane should be designed to have three good parameters together. In addition, these A, B, and S parameters can be used in a PRO performance simulation to verify experimental results. In this study, the magnitude of effective osmotic pressures and reverse salt buildup factor is analyzed and a systematic investigation of the effect of the membrane transport properties and structure parameter on PRO performance is presented. The numerical simulation was performed for a number of actual and imaginary membranes. The imaginary membranes were both on A and B trade-off relationship and off the relationship. The A and S values affected the water flux value at a low pressure difference, while the B and S values influenced the water flux at high pressure. In addition, the effect of the mass transfer coefficient (k) in close connection with the experimental condition was examined. The k value was not an important variable in simulation, but it will play a significant role in a real-life process.