Natural gas sweetening using a cellulose triacetate hollow fiber membrane illustrating controlled plasticization benefits

Plasticization is a well-understood drawback of polymer membranes in many applications; however, recent studies have demonstrated surprising advantages of this phenomenon for demanding natural gas sweetening for some glassy polymer dense film membranes. Moving beyond dense film membranes, the current study focuses on cellulose triacetate (CTA) hollow fiber membranes to use the benefits of controlled plasticization for realistic raw natural gas sweetening. Natural gas sweetening can be complicated by co-existence of condensable hydrocarbons, e.g. C2H6, C3H8 and toluene with the main H2S/CO2/CH4 ternary mixture; moreover, the operating temperature and pressure adds another dimension to this important separation. In this study, we consider an aggressive gas composition of high H2S (20 mol.%), low CO2 (5 mol.%), and significant amounts of C2H6 (3 mol.%) and C3H8 (3 mol.%) as well as trace amount of toluene (100–300 ppm) with CH4 comprising the rest of the feed. Various temperatures (35 °C and 50 °C) and pressures (6.9–31.3 bar) are also considered. We show a controlled plasticization benefit for the CTA hollow fiber membrane, with attractive CO2 and H2S permeance (>110 GPU) and selectivity (22–28) for CO2 and H2S over CH4 at 35 °C and 31.3 bar. The current study represents a major step forward in processes for membrane-based natural gas sweetening using practical asymmetric membranes.