Development and Analysis of Cellulose Acetate Based Membranes for CO2 Removal from Natural Gas

Abstract

The surge in human population and enduring economic development lead to an increase in the global energy demand. To meet an ever-increasing energy demand, fossil fuels are still counted as a significant source of energy. Amongst numerous fossil fuels, natural gas has been deemed as greener energy source because of its lesser carbon footprints. Nevertheless, depending on the geological location, raw natural gas may contain undesirable components such as CO2 and H2S, which can trigger pipeline corrosion and lessens the calorific value of the natural gas. Membrane-based technologies have offered an effective alternative for the exclusion of undesirable CO2 from raw natural gas. In particular, polymeric membranes have led to the commercialization of membrane gas separations for various applications including CO2 separation from natural gas. But the design of high-performance polymeric membrane is very exigent mainly due to the (1) inverse relationship between selectivity and permeability of the separating gases and (2) membrane plasticization under the highly condensable gases like CO2, resulting in the drastic reduction in separation selectivity. Various strategies have been proposed by the researchers to overcome these constraints and to design the novel membrane materials with high gas separation performance. Cellulose acetate (CA) has been linked with the membrane separation from the start. Both flat sheet and hollow fiber configurations have been employed for the design of industrial modules for natural gas processing. The success of CA is linked with its easy availability, low cost and good stability in terms of both mechanical and chemical properties. However, one of the foremost challenges faced by the CA membranes is the lower permeability compared to the other emerging polymers. Hence, the major objective of this PhD dissertation was to increase the CO2 permeability of pristine CA membrane without compromising its CO2/CH4 inherent selectivity. To achieve this objective, we have explored various techniques such as mixed matrix membranes (MMMs), polymer blends and composite membranes for CO2/CH4 separation. Both flatsheet and hollow fiber membrane configurations were investigated. Among all investigated strategies; best CO2/CH4 separation performance has been shown by dual-layer (DL) composite hollow fibers that displayed a CO2 permeance of xix 45 GPU and an ideal CO2/CH4 selectivity of 30.3 at 2 bar. The upshot of this research work is that it provides an ample data to design next generation of CA membranes for CO2 separation.