Experimental research is proposed to investigate an overlooked issue in the pursuit of high-permeability, high- permselectivity membrane materials for carbon dioxide/hydrocarbon separations. Modified poly(1,6-dimethyl phenylene oxide) (PPO) is a promising material for the separation of carbon dioxide from hydrocarbons. More recently this research group discovered that substitution at the 3 and 5 positions in the repeat unit of PPO with bromine atoms increases the polymer's permeability to carbon dioxide while retaining the carbon dioxide/methane permselectivity. It was further found that the diffusivity-related selectivity of the modified polymer remains surprisingly high when compared with other glassy polymers, in sharp contrast to conventional wisdom that lowering interchain packing will bring about a loss in size-sieving power of the polymer. It is proposed that the relatively low carbon dioxide/methane permselectivity of the aryl-brominated PPOs is actually caused by their very low solubility-related selectivity. It is hypothesized that introduction of basic groups into the polymer repeat unit will enhance the solubility of carbon dioxide relative to methane in the polymer. Concurrently, if the packing density and torsional mobility of the polymer chain segments are also lowered (e.g. by bromine), the resulting polymer will exhibit both high carbon dioxide permeability and high permselectivity for carbon dioxide over methane. This project consists of a systematic experimental investigation of the above hypothesis. PPO polymers with different degrees of aryl-bromination, aryl- amination and aryl-phthalimidomethylation will be studied such that a wide range of packing densities and concentrations of basic groups is covered. Membrane gas separation technology will be one of the most important developing technologies of the next decade. Technological leadership in the area will also translate into increased manufacturing efficiency in all of the chemical process industry. This project, if the hypothesis described above is demonstrated to be correct, will constitute a major advance in membrane science which should translate into significant technical advances in membrane separations of gas mixtures.
