CO2/CH4, CO2/N2 and CO2/H2 selectivity performance of PES membranes under high pressure and temperature for biogas upgrading systems

Abstract

Abstract Currently, thermal treatments are used extensively to convert millions of tons of biomass and municipal solid waste into energy products. Although biogas represents ∼ 50% of these energy products, usually disposed due to the difficulty to extract CH4 and H2 (main flammable compounds) from their complex composition contaminated by CO2, N2, etc. Recently, Polyethersulfone (PES) membranes have been employed for that purpose as an effective and cheap technology, however, their permeation properties under higher pressure and temperature are still undefined. Within this context, this research aims to study the influence of high temperatures and pressure on CO2/N2, CO2/H2 and CO2/CH4 selectivity performance of PES membranes and their potential applications in biogas upgrading systems. The experiments were started with preparation of the PES membranes using phase inversion methods, then observing their morphology, physical, chemical, thermal, and mechanical behaviors using SEM, XRD, FTIR, TGA, and universal testing machine. Consecutively, the initial gas separation experiments using CO2 gas were conducted to determine the maximum pressure and temperatures that the synthesized PES membranes can withstand without being damaged or thermally degraded. Based on the results of initial experiments, CO2/CH4, CO2/N2, and CO2/CH4 selectivity of the PES membranes was measured up to 60 °C and 6 bar (absolute pressure) using a set-up built especially for that purpose. Also, the effect of separation temperature and pressure on the separation mechanism were studied. The results revealed that the lowest pressure (1 bar) and the highest temperature (60 °C) can help to achieve the maximum selectivity performance for CO2/N2 (0.91), CO2/H2 (1.25), and CO2/CH4 (3.07), with improvement of 9, 20, and 17%, respectively. In addition, permeability of CO2 > N2 > H2 > CH4 increased by 13.2% (CO2), 15.1% (N2), 11% (H2), and 4.6% (CH4) at the same temperature. Based on that, pressure and temperature are considered as key factors that can be used to enhance the gas permeation and to control their pore shape. Also, PES membranes can be classified as a promising emerging technology for biogas upgrading with high selectivity, especially at high separation temperatures and low pressure.