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.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the financial support provided by MG Generon, Pittsburg, California and wish to thank Mr. Fred Coan, Mr. John Jensvold, and Mr. Tom Jeanes for their suggestions and help during the experimental phase of the project. The authors would also like to express their deep appreciation and gratitude to Mr. Tom Breese, Mr. Charles Cornwall, Mr. Barry King, and Mrs. Judy Kidd for their invaluable technical assistance and moral support throughout the entire course of this project. A special thanks goes to Dr. Roger Korus for the many insightful suggestions and comments made during the preparation of this manuscript.