Fast mass transfer rate and short reaction time are required to reduce side product of the premixing reaction, in the SNIA Viscosa process, as a liquid-liquid competitive consecutive system. In order to obtain high selectivity, a microstructure device, named a membrane dispersion mini-reactor, was designed and tested at several operation conditions. The mass transfer rate of cyclohexanecarboxylic acid (CCA) was significantly increased by membrane dispersion in this mini-reactor compared with a traditional batch reactor and a membrane free one, just with a residence time less than 80 ms. The results showed that the nominal yield of side product was lower than 10% in the reaction products and about 5% lower than the traditional stirring method. Additionally, a theoretical model was developed to eliminate the mass transfer flux in this mini-reactor, and the calculation results fit well with the experimental data. (c) 2006 American Institute of Chemical Engineers.