Effects of hydrocarbon and water impurities on CO2/CH4 separation performance of ester-crosslinked hollow fiber membranes

High-performance ester-crosslinked hollow fiber membranes were evaluated for sensitivity to aggressive hydrocarbon and water impurities. The hollow fiber samples show improved separation productivity and hydrocarbon-induced antiplasticization resistance under extremely challenging feed conditions in comparison to previously reported cases. The CO2 permeance was improved from 10 GPU to 50 GPU with a CO2/CH4 selectivity of 28 in testing at an 800 psi 50/50 CO2/CH4 feed with 1000 ppm (molar) toluene, 35 °C. Moreover, membrane samples with different skin layer thicknesses show significantly different sensitivities to toluene. The thinner skinned samples are hypothesized to have higher fractional free volume (FFV) and hence show more tendency to antiplasticize when exposed to impurities as compared to thicker skinned samples. The high separation performance of crosslinked hollow fibers was fully recovered after removing the high-level contaminants, including toluene and heptane, and showed negligible changes over 100 h exposure to a 600 psi 50/50 CO2/CH4 feed with 750 ppm toluene, indicating a strong stability against contaminants. Furthermore, exposure to 101 ppm (molar) water impurity did not cause an apparent subsequent change in the separation properties. The excellent properties in the presence of hydrocarbon and water contaminants demonstrate that ester-crosslinked hollow fiber membranes are attractive for natural gas purification, even under more aggressive operating conditions.