The performance of membrane solvent extraction in a parallel-plate module arranged, by inserting vertically several impermeable barriers in the flow channel, to create a device of multiple passes in the rafflinate phase, has been investigated. Increasing the pass number, as well as decreasing the cross-section area of flowing channels, will increase the fluid velocities, thereby leading to an increased mass-transfer coefficient. Considerable improvement of mass-transfer rate in a parallel-plate module of fixed dimensions is obtainable for low flow-rate operations if multiple passes, instead of single pass, are arranged in the phase (rafflinate phase or extract phase) where the mass transfer is dominated by its external film and not by the membrane resistance. It was also found that the increase in operating cost due to increasing pass number may be ignored, for low flow-rate operations.
