Two CA membranes of different sizes -0.00159 m(2) and 0.0748 m(2)-were used for pervaporation separation of a methanol/C-5 mixture. They were placed in two modules with different structures, and then the current status of feed were disparate. The velocity distribution of the feed in both modules was simulated by ANSYS software. At the same current velocity, the holding time of the feed in the pilot plant module was longer than that in the laboratory module. There were more channels and dead angles in the pilot-plant module so as to cause a higher separation factor and lower flux.