Membrane contactors modelled for process intensification post combustion solvent regeneration

Abstract

Membrane gas-solvent contactors are potentially more efficient at undertaking solvent regeneration in carbon capture applications compared to traditional desorber columns. This potential is investigated here through modelling of two experimentally reported membrane contactors based on Teflon AF1600 and polydimethylsiloxane active layers, by a simple approximate model and a one-dimensional mass transfer model. The respective membrane contactors could be operated at temperatures below that corresponding to the vaporisation of the solvent, due to the separation of the solvent and gas phase by the membrane. This required a steam sweep operating under vacuum conditions. The calculated module length for the Teflon AF1600 membrane varied between 8.9–70.2 m with decreasing regeneration temperature. This increase in required length was due to reductions in overall mass transfer coefficient and mass transfer driving force as temperature is lowered. It was determined that at 110 °C a PDMS contactor of length 1.1 m was required to regenerate the solvent, achievable with commercial modules. A comparison of the equipment volume footprint, known as process intensification, revealed that both the Teflon AF1600 and PDMS membranes required a lower volume than a standard packed column when operating at temperatures above 90 °C. Temperatures higher than 95 °C also designated the transition above which membrane contactors have a lower energy duty than the corresponding solvent column approach. This energy duty is a trade-off between the reduction in latent heat required to produce CO2 and regenerate the solvent at lower temperatures, countered by the work duty of the vacuum pump needed to operate the steam sweep at pressures below atmospheric. The investigation demonstrated that membrane contactors are a viable alternative technology for solvent regeneration.