Theoretical estimation of semi-permeable membranes leading to development of forward osmosis membranes and processes as a future seawater desalination technology

摘要

Recently, forward osmosis (FO) process has been expected for the future seawater desalination method. In this study, the estimation of semi-permeable membranes leading to development of FO membranes and processes was investigated from the theoretical calculation view point. It is common to apply multivalent ionic materials to draw solution in FO membrane process. MgCl2, one of the common multivalent ionic materials, was used for calculating the relationship between pure water permeability (A value) and required FO membrane length. Two cases were assumedone as an ideal condition which was without any concentration polarization (CP), the other as an actual condition which was with external concentration polarization. In the case of non-CP condition, the membrane length decreased with increase the A value. On the other hand, in the case of CP condition, the membrane length converged to constant value with increase of the A value. From this phenomenon, there was the optimized relationship between A value and membrane length. For instance, under the condition of MgCl2 concentration at 12.9wt%, the A value over 2.0x10(-11) [ms(-1)Pa(-1)] was required while the membrane length was equal to eight elements. Moreover, the effect of mass transfer coefficient was estimated. It was suggested that the estimation was possible for the A value and the membrane length with any given mass transfer coefficients.