Predicting power density of pressure retarded osmosis (PRO) membranes using a new characterization method based on a single PRO test

The characteristic parameters of pressure retarded osmosis (PRO) membranes (water permeability, A, solute permeability, B, and the structural parameter of the membrane support layer, S) were estimated by a single PRO test combined with a statistical approach. The single PRO test measures water and reverse solute flux ( Jw and Js) as functions of the hydraulic pressure in the draw solution (DS) using sodium chloride solutions as feed and draw solutions. The PRO test data were obtained from literatures. A statistical approach developed in this work finds the most appropriate parameters (A, B, and S) to predict Js/Jw and power density of the tested PRO membrane using the internal concentration polarization (ICP) model. The model prediction results of Js/Jw and power density using the PRO membrane parameters obtained from the single PRO test matched the experimental data better than those using the membrane parameters obtained from the conventional reverse osmosis (RO) and forward osmosis (FO) tests. The A and B parameters from the single PRO test were consistently higher than those from the RO and FO tests, which could be related to the membrane deformation under the highpressure PRO operation with the poor support by the spacer. © 2016 Published by Elsevier B.V.

The PRO method to characterize PRO membranes based on a single PRO test and a statistical approach using ICP model was developed and verified by the various experimental data obtained from literatures. The PRO membrane parameters (e.g., A, B, and S) obtained from the PRO method can predict the power density, water flux and reverse solute flux better than those from the conventional RO–FO method. There are two possible reasons for the poor prediction performance of the RO–FO method: (1) the water and solute transport in PRO mode operation fundamentally differs from those in FO or RO mode operation, and (2) the PRO membrane may be deformed under the high-pressure PRO operation with the poor support by the DS spacer (i.e., the characteristics of the PRO membrane evaluated by the RO–FO method and the PRO method are different due to the deformation during the PRO operation). In either case, the PRO method is a feasible solution to properly characterize the PRO membrane and has several advantages: (1) its good performance in the power density prediction was verified under the various FS and DS concentrations (although there is limitation in the prediction of the PRO membrane performance in a higher FS or DS concentrations due to the ignored ECP effect); (2) it is a fundamentally Please cite this article as: J. Lee, S. Kim, Predicting power density of pressure retarded osmosis (PRO) membranes using a new characterization Fig. 11. Comparison between the modeled and experimental power densities; (a) PEI-2# (DS: 1 M NaCl, FS: 40 mM NaCl), (b) PRO-TFC-HF (DS: 1 M NaCl, FS: 1 mM NaCl), (c) CTA-W (DS: 1 M NaCl, FS: 1 mM NaCl), (d) CTA-W (DS: 1 M NaCl, FS: 100 mM NaCl), (e) CTA-W (DS: 0.5 M NaCl, FS: 10 mM NaCl), (f) CTA-W (DS: 2 M NaCl, FS: 10 mM NaCl).