Modeling of transport phenomena in reverse osmosis membranes.

摘要

This dissertation has investigated the development and validity of a novel transport model for reverse osmosis, which does not have the serious shortcomings of the previous models. As a result, a mechanistic model, called the Modified Surface-Force-Pore Flow (MD-SF-PF) model, has been developed. The model assumes that transport through the membrane takes place in very fine pores, and the pores are modeled as perfect cylinders. This two-dimensional model incorporates a potential field inside the membrane which is responsible for the partitioning effect and, in part, determines the membrane performance. A computer code has been developed, based on the "orthogonal collocation" method of weighted residuals to solve the complicated differential equation of the transport model. The model has been extended with respect to temperature (temperature-extended model) and with respect to the type of system affinity (Extended MD-SF-PF model) which can describe or predict both solvent-membrane affinity systems, such as sodium chloride-water system, and solute-membrane affinity systems, such as toluene-water system).; The following experimental plan was undertaken using aromatic polyamide (FilmTec) FT30 membranes to test the validity of the derived model: (i) experiments with 2000-15 000 ppm aqueous solutions of sodium chloride (brackish water concentration) at 350-7000 kPa and 5-60 C; (ii) experiments with 2000 ppm potassium chloride, lithium chloride, and lithium nitrate at 25 C and 500-4000 kPa; and (iii) experiments with 35 000 ppm sodium chloride (sea water concentration) at 4000-7000 kPa and 5-60 C.; The average pore radii for the SW30HR and BW30 types of FT30 membranes were determined at about 1.0 and 1.2 nm, respectively. All the experimental data at other pressures and feed concentrations are well predicted by the MD-SF-PF model. The MD-SF-PF model also predicts well for the other 1-1 electrolytes. Temperature effects are reasonably predicted by the temperature-extended model. Compaction, which becomes more severe as temperature or pressure is increased, has no effect on predicting the membrane separation or flux ratio (i.e., ratio of total solution flux to pare solvent flux). The Extended MD-SF-PF model has been found to well describe the difficult case of strong solute-membrane affinity.