A study of mass transfer in the membrane air-stripping process using microporous polyproplylene hollow fibers

The mass transfer of water and chloroform in membrane air-stripping (MAS) w as studied using a microporous polypropylene hollow fiber membrane module, with air flow on the lumen side and liquid cross-flow on the shell side. Wa ter transport experiments showed that its mass transport decreased signific antly when the membrane had been in contact with water for prolonged period s. It was hypothesized that the increased mass transfer resistance was due to water condensation in a fraction of the membrane pores. MAS of chlorofor m from aqueous solutions confirmed the additional mass transfer resistance with prior exposure to water. It was concluded that membrane pores were eit her completely air-filled or partially wetted with water during the MAS pro cess, Existing models are able to predict the performance only for either c ompletely air-filled or liquid-filled pores. A modified model was proposed to take into account the diffusion through partially wetted pores. The mode l described the data well. This hypothesis also provided a plausible explan ation to the conflicting literature values of the membrane mass transfer re sistance. It was found that the membrane mass transfer resistance of the pa rtially wetted pores is two orders of magnitude higher than that of air-fil led pores. The overall mass transfer coefficient was constant for initial f eed chloroform concentrations ranging from 50 to 1000 ppm. Crown Copyright (C) 2000 Published by Elsevier Science B.V.