Evaluation of Polymeric Membranes for Gas Separation Processes: Poly(ether-<I>b</I>-amide)(PEBAX® 2533) Block Copolymer

Abstract

The development of polymeric membranes for gas separations has provided an alternative to traditional energy-intensive processes, especially for hydrocarbon separations. Material studies of the membrane can provide insights to its formation and modification. Gas permeation behaviour through two types of polymeric membrane material is investigated herein. Though the main objective of our investigation was to determine the hydrocarbon gas permeation properties of poly(ether-<I>b</I>-amide) PEBAX®2533 copolymer membranes over a range of operating temperatures and pressures, we first tested a poly(ethylene oxide) (PEO) membrane for permeability of ethane and ethylene. The screening results from the tests of PEO membranes containing silver salts, indicate that although PEO membranes may possess high olefin/paraffin selectivity through facilitated transport, difficult membrane preparation and unstable structure remain major obstacles to their commercial use. However, the knowledge acquired on preparation technique and permeability testing from these trials was carried over to our study of PEBAX®2533 membranes. Permeability coefficients were determined at temperatures ranging from 25°C to 75°C, and pressures from 25 psig to 200 psig for ethane, ethylene, nitrogen, propane, propylene, and carbon dioxide. The PEBAX®2533 membranes showed high organic gas permeabilities. Plasticization effects on the membrane were pronounced with propane and propylene at elevated pressure (100 psig). Activation energies of permeation (E<i>p</i>) were determined. E<i>p</i> of nitrogen is nearly constant and is the highest among gases tested in the pressure range. E<i>p</i> shows a linear decreasing trend as pressure increases for hydrocarbons. Relatively high selectivities (12 to 26) were observed for the polar and non-polar gas pair CO2/N2. As temperature increased, the selectivity of CO2/N2 decreased. This study provides the groundwork for the use of PEO and PEBAX®2533 membranes for hydrocarbon separations.