Poly(ether urethane) and poly(ether urethane urea) membranes with high H2S/CH4 selectivity

The objective of this study was to synthesize rubbery polymers with a high H2S/CH4 selectivity for possible use as membrane materials for the separation of H2S from 'low-quality' natural gas. Two poly(ether urethanes), designated hereafter PU1 and PU3, and two poly(ether urethane ureas), designated PU2 and PU4, were synthesized and cast in the form of 'dense' (homogeneous) membranes. PU1 and PU2 contained poly(propylene oxide) whereas PU3 and PU4 contained poly(ethylene oxide) as the polyether component. The permeability of these membranes to two ternary mixtures of CH4, CO2, and H2S was measured at 35 degrees C, and for a PU4 membrane also at 20 degrees C, in the pressure range from 4 to 13.6 atm (4.05-13.78 x 10(5) Pa). PU4 is a very promising membrane material for H2S separation from mixtures with CH4 and CO2, having a H2S/CH4 selectivity greater than 100 at 20 degrees C as well as a very high permeability to H2S. Permeability measurements were also made with commercial PEBAX(TM) membranes for comparison. The possibility of upgrading low-quality natural gas to US pipeline specifications for HPS and CO2 by means of membrane processes utilizing both highly H2S-selective and CO2-selective polymer membranes is discussed.