An ultrathin skinned hollow fibre module for gas absorption at elevated pressures

Abstract

An ultrathin skinned hollow fibre membrane module coupled with a liquid absorbent was investigated experimentally for the removal of CO2 from a gas mixture. The module consists of a bundle of hollow fibres having a dense skin layer at the outer edge of the fibre. The gas mixture containing 4% CO2 was introduced into the hollow fibre lumen and was in countercurrent contact with the liquid (either water or NaOH solution) fed into the module shell. The overall mass transfer coefficients of carbon dioxide were obtained in the gas phase. A study of mass transfer in the membrane module indicates that the overall mass transfer coefficients, KAG, are controlled by both the liquid film and membrane resistances. It was also shown experimentally that the use of the ultrathin skinned hollow fibre module for CO2 absorption has two advantages. Firstly, the dense skin layer of the hollow fibre membrane eliminates the wetting problem commonly encountered in microporous membranes. As a result, the mass transfer operations are stable with long term exposure of the membrane to the liquid absorbent. Secondly, operations of the feed pressure are flexible. The feed gas pressure of 200 kPa higher than the liquid pressure was maintained without any noticeable bubble formation in the liquid phase. The higher operating pressure in the gas phase suggests that the reduction of the mass transfer rate due to the higher membrane resistance could be compensated by an elevation of the feed gas pressure, i.e. increase of the driving force.