Concentration of ginseng extracts aqueous solution by vacuum membrane distillation. 1. Effects of operating conditions

Vacuum membrane distillation (VMD) was employed to concentrate Ginseng extracts aqueous solution. Polytetrafluoroethylene (PTFE) micro-porous plate membranes, with average pore size of 0.2 µm and thickness of 50 µm, were used inVMD process. The effects of operating temperature, vacuum pressure and feed concentration were investigated using a plate membrane module. Furthermore, scanning electron microscopy analysis technology was used to observe membrane fouling. The experimental results showed that both initial flux and flux decline were affected obviously by the selected operating variable, i.e. temperature, vacuum pressure and concentration. When the vapor pressure difference between two sides of membrane was small enough to certain value, the permeation flux in VMD concentration of Ginseng extracts aqueous solution can keep in a stability condition. In this case, the SEM image indicated that membrane fouling did not take place. There is a critical pressure difference which prevents membrane from fouling. On the other hand, high operating temperature and high vacuum tightness resulted in high pressure difference and hence high initial flux. But the permeation flux decreased quickly. And a fouling layer on membrane surface was observed. When increasing feed concentration, the initial flux reduced, and the flux declined more quickly.