ABSTRACT
Gas streams containing organic vapors are produced by numerous industrial and commercial processes. The selectivities of composite membranes for organic vapors over air are typically of the order 20–100, enough to make membrane separation cost-competitive with other technologies in the appropriate concentration range. The bulk of the membrane vapor separation plants installed to date fall into two categories: the first category is small systems to recover CFCs, HCFCs, and other high-value solvent vapors from process vent streams. The second category is larger units to recover hydrocarbon vapors from petroleum transfer operations. The mathematical model used to predict vapor and gas membrane permeation behavior is the solution-diffusion model. The Henry's-law sorption coefficient can be plotted against boiling point or molar volume. In rubbery polymers, the sorption selectivity term is usually dominant, permeability increases with increasing permeant size, and larger molecules permeate preferentially. To make high-flux composite membranes, it is necessary to minimize the thickness of the selective layer.
