Concentrated On Traditional Chinese Medicine Extract, The Membrane Distillation

Membrane distillation is a relatively new kind of separation technology developed in recent years. It has been more and more investigated owing to its characteristics of low energy requirement and low operational temperature as well as high construction compactness. In this work, membrane distillation was used to concentrate the extracts of Chinese traditional medicine. The primary of this study is to overcome the disadvantages such as high operational temperature for the traditional concentration methods. Theoretical and experimental work of this study was supported by the Science and Technology Department of Zhejiang Province, and the main results and conclusions are described as follows.Direct contact membrane distillation and vacuum membrane distillation were compared under similar operate conditions. It was found that the water flux of the vacuum membrane distillation is much higher than that of the direct contact membrane distillation, therefore, the vacuum membrane distillation was chosen to concentrate the extracts of Chinese traditional medicine in this work. The effect of membrane distillation on the reservation ratio of active component in the Chinese traditional medicine was studied. Results indicate that the reservation ratio is higher than 80% and the rejection ratio to this active component should be 100%. The influences of membrane distillation conditions and the membrane properties on the water flux were studied also. It was found that the flux increases with the feed temperature and feed flow rate while decreases with the downstream pressure and packing density of the membrane module. Data also demonstrates that the flux is higher when the feed flows inside the hollow fibers while the outlet position of vapor in vacuum membrane distillation almost have no effect on the flux. The membrane properties can affect the flux greatly and higher porosity, larger pore size and thinner membrane thickness lead to higher flux. The membrane fouling in the concentration process was investigated too. It was found that, under our conditions, the fouling of the membrane can be well controlled. The ultrasonic was attempted to apply to the vacuum membrane distillation using polypropylene hollow fiber membranes. It canimprove the membrane distillation flux obviously. The flux increase enhances with the operate temperature while decreases with the feed flow rate. It also depends on the shell material of the membrane module.The theory of membrane distillation was investigated too. Several parameterssuch as the thermal conductivity of the membrane Km, the membrane mass transportcoefficient , the film heat transfer coefficient h, the temperature polarization coefficient and the evaporation efficiency EE under different conditions, for this process were obtained through the simulation of experiment data The temperature polarization of the direct contact membrane distillation and the vacuum membrane distillation was compared quantitatively.Finally, the mass transfer principle in the membrane micro pores was analyzed and the mass transfer models both for the direct contact membrane distillation and the vacuum membrane distillation were considered.