Effect of capillary pressure on the CO2 flux in the pores of membrane contactor: Theory and simulation results

Abstract

A simulation model was made to evaluate the effect of the capillary pressure on the CO2 capture by membrane absorption. More specifically, the model calculated the changes in the interfacial pressure and CO2 flux as the interface of gas and liquid moves through the pore opening to its exit. Two cases were considered; hydrophilic or hydrophobic membrane materials with a respective contact angle of less or more than 90°. It was revealed that CO2 flux is about 70% higher for the hydrophilic membrane of 10−6 m radius and 50 × 10−6 m length than the hydrophobic membrane of equal pore radius and pore length, when nearly equal to 1.72 × 105 Pa is applied either on the feed side (hydrophilic membrane) or on the permeate side (hydrophobic membrane) to keep the membrane pore dry without gas bubble formation. It should be noted that CO2 flux is higher when a hydrophilic membrane is used, which is against the common belief that a hydrophobic membrane is preferable for membrane absorption. Also, the duration for the interface to get to the pore exit was determined. The effect of capillary pressure increases as the membrane pores become smaller, which turns into an increase in CO2 flux when the porosity and the pore length are maintained constant. It was also revealed that the CO2 flux can be significantly increased when water absorbent is replaced by 1 M monoethanolamine solution due to increased CO2 solubility. Thus, this work is the first attempt to study the effect of capillary pressure on the flux of membrane contactors. It is recommended to collect more data on membrane contactors by the hydrophilic membrane. Electronic structure calculations were also performed to investigate the reaction mechanism between CO2 and MEA, with a focus on non-conventional interactions such as hydrogen bonding and van der Waals interactions. This is to know the details of the reaction occurring between CO2 and MEA.