Chinese Journal of Chemical Engineering, Vol.26, No.11, 2337-2343, 2018
Mass transfer correlations for membrane gas-solvent contactors undergoing carbon dioxide desorption
Membrane gas-solvent contactors are a hybrid technology combining solvent absorption with membrane gas separation, which demonstrates potential for CO2 capture through the ability of the membrane to rigidly control the mass transfer area. Membrane contactors have been successfully demonstrated for CO2 absorption, and there is strong research interest in using membrane contactors for the complimentary CO2 desorption process to regenerate the solvent. However, understanding and modelling the various stages of mass transfer in the desorption process is less well-known, given the existing mass transfer correlations had been developed from absorption experiments. Hence, mass transfer correlations for membrane contactors are reviewed here, and their appropriateness for desorption analysed. This is achieved through simulating CO2 desorption through a membrane contactor from loaded 30wt% monoethanolamine solvent to enable comparison of the correlations. It was found that the most cited correlations by Yang and Cussler were valid for shell side parallel flow, while that of Kreith and Black was viable for shell side cross flow. A limitation of all of these correlations is that they assume single phase flow on both sides of the membrane; however, the high temperature of CO2 desorption can lead to partial solvent vaporisation and hence two phases present on one side of the membrane contactor during desorption. A mass transfer correlation is established here for two phase parallel flow on the shell side of a membrane contactor, based on experimental results for three composite and one asymmetric hollow fibre membrane contactors stripping CO2 from loaded MEA at 105-108 degrees C. This correlation is comparable to that reported in the literature for mass transfer in other two phase systems, but differs from the standard format for membrane contactors in terms of the exponent on the dimensionless Schmidt and Reynolds numbers. (C) 2018 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.