Selection of microporous hydrophobic membranes for use in gas/liquid contactors: An experimental approach

Abstract

Contactors equipped with hydrophobic porous membranes were widely tested and operated in different separation processes. New applications, e.g. concentration of fruit juice or air conditioning, require an absolute reliable separation of the two contacting phases in order to avoid product pollution by the liquid absorbent. This can only be realized by applying coated membranes as a liquid tight semipermeable barrier. Because the dense layer of such membranes acts as an additive transport resistance its thickness has to be as thin as possible which requires porous support membranes with the porosity profile of ultrafiltration membranes. Testing of membranes in contactors under actual operation conditions is a very time-consuming approach. Therefore first of all a simple model gas/liquid contactor arrangement was applied for testing of porous hydrophobic microfiltration membranes. The temperature polarization arising during the absorption process was determined experimentally. The results show that neglecting the temperature polarization would result in underestimated membrane permeability values. By taking the temperature polarization into consideration the calculated membrane permeabilities were in good accordance with literature data. Using this model different structured poly(ether imide) hollow fiber membranes with ultrafiltration separation profile were characterized with respect to the water vapor permeability. The results document that these ultrafiltration membranes provide equivalent or even distinctly higher permeabilities, than commercial microfiltration membranes. The better performance is related to the asymmetric structure of these membranes. On basis of the obtained results it can be concluded that composite membranes with a pore-free thin coating can be prepared which offer performances comparable with porous hydrophobic microfiltration membranes. Furthermore the morphology of these membrane types can be tailored to contactor applications, which require high heat transfer (e.g. osmotic distillation) or low heat transfer (e.g. membrane distillation).