EFFECTS OF CHEMICAL IMPURITIES ON GAS PERMEATION AND DIFFUSION IN POLYMERIC MEMBRANES

Abstract

In recent years, polymeric membranes have been increasingly used in key unit operations such as gas separations. In theory, the performance of a polymeric membrane module depends solely on the chemical structure of the polymer and the feed gas composition. However, impurities in the feed stream (such as vapors from compressor oils) have been found to affect the productivity of the membrane module even at parts per million (ppm) levels. To understand the fundamental effects of such trace chemicals, commercial polymers were studied for their solubility and permeability characteristics in the presence and absence of such impurities. Two types of compressor oils were used in doping the polymers at three concentration levels. Permeabilities of N2, O2, CH4, and CO2 were measured in dense homogeneous films at 35°C. Selectivities of O2/N2 and CO2/CH4 were also calculated in the presence and absence of oil. The permeability data were used in conjunction with the sorption results as reported in previous papers to calculate diffusivities in the Henry's (D D) and Langmuir (D H) regions of the polymer. The effect of annealing on permeability and diffusivity in clean and doped samples of the polymers was also examined. Such thermal treatment reduced the diffusivity and permeability due to densification of the glassy structure. The effect was common to both clean and doped films. A good understanding of the effects of such trace chemicals on the permeability characteristics of the membrane will aid in designing effective polymeric membrane modules in the future.