TABLE OF CONTENTS This application is based on the hydrophilicity of the ion exchange membrane. Though it is not essential to use an ion exchange membrane, [219] they show excellent performance in pervaporation for dehydration of organic solvents. Pervaporation is the separation of solvents on the basis of their different affinities for the membrane and different permeation speeds through the membrane phase. The system consists of a liquid mixture to be separated, which contacts one side of the membrane, and a gas phase to permeate under reduced pressure, which is on the other side of the membrane (Figure 6.37). Membrane performance is evaluated by a permeability coefficient (flux) and separation factor (selectivity coefficient). The permeability coefficient, Q, is the permeated solvent through the membrane per unit area and unit time (kg m ?2 h ?1). When a mixed solvent composed of components A and B is separated, the separation factor, ?, is defined as
where X A and X B are the weights (or moles) of components A and B respectively in the feed solution, and Y A and Y B are the weights (moles) of components A and B respectively in the permeate.
Permeability coefficients and separation factors between water and organic solvents have been evaluated using various cation and anion exchange membranes. [220] Both cation [221] and anion exchange membranes [222] are effective in the dehydration of water miscible organic...
