Development of polyphenylene oxide and modified polyphenylene oxide membranes for dehydration of methane

Abstract

The objective of this study was to systematically evaluate the suitability of polyphenylene oxide (PPO) and modified PPO as membrane material for separation of water vapor from methane gas. The objectives of the study also included the study of structure and performance relationship of both PPO and modified PPO in relation to separation of water vapor and methane mixture as well as the permeation of single gases. In particular, modification of PPO was achieved via sulfonation and bromination of the aromatic ring in the backbone of the polymer to various degrees of substitution. Two high molecular weight PPO polymers with intrinsic viscosities of 1.58 dL/g and 1.79 dL/g were chemically modified via addition of bromine (PPOBr) through aryl bromination; with degrees of substitution of up to 98% via addition of sulfonate groups (SPPO); with ion exchange capacities (IEC) of as high as 2.07 meq/g dry polymer, through aryl substitution and sequential addition of bromine and sulfonate substituents (SPPOBr) to the PPO backbone, followed by conversion of the sulfonate groups (-SO3H) to its sodium form (NaSPPO and NaSPPOBr) and dense homogeneous films were cast and tested. The results indicated that in the NaSPPO mutual interactions of water and methane and their interaction with the film material are dominating factors in their transport. The decrease in methane permeability was a result of increased water cluster size and increased interaction of water and methane. The permeability of water vapor showed an initial increase in NaSPPO films up to IEC of 1.69, followed by a decrease with increasing IEC. The decrease in water permeability was attributed to increased water-water and water-polymer interactions. In methane and water separation experiments the dominating factors were both the sieving effect of the material (diffusivity) and the interaction of the polymer with the penetrating species (solubility). In addition to these factors, the interaction between methane and water was found to further contribute to increased selectivity that was observed in these films. (Abstract shortened by UMI.)