Investigation of poly(pyrrolone-imide) materials for the olefin/paraffin separation



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The separation of olefin and paraffin gases is one of the most important processes in the petrochemical industry. Currently, this separation is done using low temperature distillation, which is very expensive and energy intensive. In an effort to decrease cost and save energy membrane separations have been considered as an attractive alternative. The present work examines behavior of poly(pyrrolone-imide) membrane materials for the olefin / paraffin separation based on mobility selectivity. It was found that rigid materials such as carbon molecular sieves and poly(pyrrolone-imides) exhibit a surprising C3H6/C3H8 selectivity maximum as the structure of the material is varied at fixed operating conditions. The structure of the carbon materials is controlled by the magnitude of the thermal treatment. Similarly, the structure of the poly (pyrrolone-imides) is varied by changing monomer stoichiometry. This work provides a fundamental understanding for this maximum in selectivity and continues to examine the utility of this behavior. This unexpected behavior is explained by a straightforward model, which considers a pore size distribution for the carbons, or a distribution of chain spacings for the rigid poly (pyrrolone-imides). This work has also demonstrated that swelling induced plasticization of rigid well-packed poly(pyrrolone-imides), as well as increases in temperature have resulted in a surprising increase in C3H6/C3H8 selectivity, as well as C3H6 permeability. Observation and understanding of this novel behavior provides potential uses for rigid materials that show undesirable transport properties under ambient and low pressure feed stream conditions. Furthermore, a fundamental understanding of this material behavior has been developed through modeling efforts, which take into account a distribution of selective entities within the material.