AN ULTRATHIN SKINNED HOLLOW-FIBER MODULE FOR GAS-ABSORPTION AT ELEVATED PRESSURES

An ultrathin skinned hollow fibre membrane module coupled with absorbe nt was investigated experimentally for the removal of CO2 from a gas m ixture. The module consists of a bundle of hollow fibres having a dens e skin layer at the outer edge of the fibre. The gas mixture containin g 4% CO2 was introduced into the hollow fibre lumen and was in counter current contact with the liquid (either water or NaOH solution) fed in to the module shell. The overall mass transfer coefficients of carbon dioxide were obtained in the gas phase. A study of mass transfer in th e membrane module indicates that the overall mass transfer coefficient s, K-AG, are controlled by both the liquid film and membrane resistanc es. It was also shown experimentally that the use of the ultrathin ski nned hollow fibre module for CO2 absorption has two advantages. Firstl y, the dense skin layer of the hollow fibre membrane eliminates the we tting problem commonly encountered in microporous membranes. As a resu lt, the mass transfer operations are stable with long term exposure of the membrane to the liquid absorbent. Secondly, operations of the fee d pressure are flexible. The feed gas pressure of 200 kPa higher than the liquid pressure was maintained without any noticeable bubble forma tion in the liquid phase. The higher operating pressure in the gas pha se suggests that the reduction of the mass transfer rate due to the hi gher membrane resistance could be compensated by an elevation of the f eed gas pressure, i.e. increase of the driving force.