MICROPOROUS HOLLOW-FIBER MEMBRANE MODULES AS GAS-LIQUID CONTACTORS .1. PHYSICAL MASS-TRANSFER PROCESSES - A SPECIFIC APPLICATION - MASS-TRANSFER IN HIGHLY VISCOUS-LIQUIDS

Gas-liquid mass transfer has been studied in a membrane module with no n-wetted microporous fibres in the laminar flow regime. This new,type of gas/liquid contactor can be operated stabily over a large range of gas and liquid flows because gas and liquid phase do not influence eac h other directly. Therefore foam is not formed in the module, gas bubb les are not entrained in the liquid flowing out of the reactor and the separation of both phases can be achieved very easily. These phenomen a often limit the applicability of conventional contactors, e.g. a bub ble column which was also studied in the present work. The large mass transfer area of a bundle of small fibres offers the possibility of cr eating a compact gas/liquid mass exchanger. However, owing to the smal l channels in and around the fibres the flow of either gas or liquid b ecomes laminar which reduces the mass transfer capacity of the module. Therefore the mass transfer coefficients in the laminar flow regime w ere determined experimentally. For mass transfer determined by the tra nsport in the liquid phase it was found that the active mass transfer area is equal to the total membrane area, regardless the porosity of t he fibre. For processes with liquid flowing through the fibres, the in fluence of fibre diameter, diffusivity in the liquid, liquid viscosity and liquid velocity on mass transfer can be correlated extremely well with the Graetz-Leveque solution derived for the analogous case of he at transfer. For liquid flowing around regularly packed fibres mass tr ansfer was described satisfactory with a correlation derived from a nu merical solution for the similar heat transfer problem [ Miyatake and Iwashita, Int. J. Heat Mass Transf., 33 (1990) 416 ]. Correlating mass transfer in liquid flowing around irregularly packed fibres was not p ossible because of the undefined dimensions of the different channels between the fibres.