Abstract
Membrane gas separations require materials with high permeability and good selectivity. For glassy polymers, the gas transport properties depend strongly on the amount and distribution of free volume, which may be enhanced either by engineering the macromolecular backbone to frustrate packing in the solid state or by thermal conversion of a soluble precursor to a more rigid structure of appropriate topology. The first approach gives polymers of intrinsic microporosity (PIMs), while the second approach is used in thermally rearranged (TR) polymers. Recent research has sought to combine these approaches, and here a new range of thermally rearrangeable PIM-polyimides are reported, derived from dianhydrides incorporating a spiro center. Hydroxyl-functionalized polyimides were prepared using two different diamines: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (bisAPAF) and 4,6-diaminoresorcinol (DAR). Thermal treatment at 450 °C under N2 for 1 h yielded polybenzoxazole (PBO) polymers, which showed increas...
Highlights
Gas separation membranes already represent an established technology for some important industrial applications, such as the recovery of hydrogen in the production of ammonia, the separation of air to give a nitrogen-rich inert gas, and the removal of carbon dioxide from natural gas.[1,2] other applications, such as alkene/alkane separation and carbon dioxide capture from flue gases, require better membrane performance, in terms of productivity and product purity, if the potential of membrane processes for energy-efficient, costeffective separations is to be fully realized
For glassy polymers, which have been extensively investigated as membrane materials, the gas transport behavior is strongly influenced by the amount and distribution of free volume
The thermal imidization (T) method involves the production of a poly(amic acid) intermediate, from which the polyimide is subsequently formed by cyclodehydration at 300 °C
Summary
Gas separation membranes already represent an established technology for some important industrial applications, such as the recovery of hydrogen in the production of ammonia, the separation of air to give a nitrogen-rich inert gas, and the removal of carbon dioxide from natural gas.[1,2] other applications, such as alkene/alkane separation and carbon dioxide capture from flue gases, require better membrane performance, in terms of productivity and product purity, if the potential of membrane processes for energy-efficient, costeffective separations is to be fully realized. Productivity may be expressed in terms of a permeability coefficient, P, which in the simplest case is the product of a diffusion coefficient, D, and a solubility coefficient, S, i.e., P = DS. For glassy polymers, which have been extensively investigated as membrane materials, the gas transport behavior is strongly influenced by the amount and distribution of free volume. High free volume enhances D, and P, but the size and connectivity of free volume elements can strongly affect S and have a profound influence on the selectivity. In recent years various approaches have been employed in order to obtain polymers with high free volumes and desirable free volume distributions and to tailor the gas transport properties.[3,4]
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