Study On The Treatment Of Traditional Chinese Medicine By Microfiltration And Membrane Distillation Technology

Membrane distillation(MD) has developed as a new seperation technology which applied hydrophobic membrane since 1980s.With the advantages of low energy consumption, less loss of heat-sensitive material,MD can increase the level of processing and product quality.This study mainly focus on the flat sheet membrane module and hollow fibre membrane module which applied in the concentration of traditional chinese medicine(TCM), Membrane flux was investigated under different parameter such as packing density, operating manners,bubbling manner during membrane distillation,and the reason of flux decline has been discussed. Measures have been taken to control the decline of flux.For the process of the flat sheet membrane module applied in the concentration of TCM, the mathematical model which consider the thermal resistance of fouling layer was established. Based on the measured trans-membrane mass flux, the variation of the thermal resistance of fouling layer and interface temperature was abtained. From the analysis of electronic microscope photograph, it was found that a porous fouling layer covers the membrane surface, introducing an additional thermal resistance to overall heat transfer in DCMD. The comparison of the relationships between fouling resistance and concentration ratio obtained under different conditions reveals that the growth of fouling layer can be effectively limited by increasing either the feed temperature or feed flow velocity.Membrane flux was measured under different parameters such as feed flow rate and packing density of hollow fibre membrane module. The theoretical analysis about flux decline was deduced accords with the experimental results.that is four filtration models were linear fitted experimental results and the experimentally observed flux decline under constant feed concentration agreed best with the cake filtration model.This indicates that the growth of fouling layer and flux decline in concentrating TCM extract by DCMD should be described by cake filtration model.To reduce the rate of transmembrane flux decline caused by membrane fouling, the study adopted the methods of microfiltration pre-treatment and two-phase flow caused in the feed side during the membrane distillation.The former reduce the concentration of foulants and control the membrane fouling effectively;bubbling was introduced in the latter,the movement of bubbles near the membrane surface enhanced the shearing.Furthermore, bubble disturbance between the membrane and liquid also weaken the effect of temperature polarization.The transmembrane flux was increased significantly by the favorable factors caused by the two-phase flow.