Preliminary Study On Concentration Of Radix Scutellariae And Other Different Chinese Herbal Decoctions Using Vacuum Membrane Distillation Based On PVDF Hydrophobic Membrane

Vacuum membrane distillation (VMD) is a novel membrane enrichment technology with bright prospect. VMD which has the advantages of simple operation, lower loss of active ingredients and high concentration ratio, can effectively compensate the disadvantages of conventional concentration methods. The key problem of MD process is the choice of hydrophobic membrane. Polyvinylidene fluoride (PVDF) is an ideal material for industrial applications of MD, with excellent hydrophobicity, heat resistance and chemical stability, reasonable price and simple preparation. This paper which selects PVDF hydrophobic hollow fiber membrane concentrates different Chinese herbal decoctions using VMD technology, and explores the application problems starting from the factors affecting the concentration process and physicochemical properties from different aspects. The study provided the basis for the amplification of industrialized application. The major content and results of this paper are as follows:Part one:Firstly, with water extract of Radix scutellariae for research system, we study the effects of different pretreatment methods on physicochemical parameters, macromolecule content, rejection rate of index component, HPLC specific chromatogram and membrane distillation properties. The test results show that 6,000-8,000 ultrafiltration after centrifugal is relatively reasonable pretreatment method.Part two:The experiments analysis the correlation of main operation parameters and membrane flux and the effects of concentration process on the nature of Chinese herbal decoctions, found that only vacuum degree and trans-membrane flux exists significant correlation. The single factor and full factorial experiments which analysis effects of operation parameter on MD performance are carried out, and found that with increasing feed temperature, vacuum degree and flow rate,the membrane flux increases. In addition, the influence of feed temperature on membrane flux was most remarkable, followed by vacuum degree, liquid flow rate.Part three:We researched the problem of reduce of membrane flux. Taking the decoction of Radix scutellariae, Radix Paeoniae Alba, Erding Kell as experimental system, the study investigated the change of membrane flux and temperature polarization coefficient in the concentration and constant concentration experiments and selected the appropriate cleaning method for hydrophobic membrane which take flux recovery rate and changes of the membrane surface structure as assessment index. Experimental results show that, temperature polarization effect can be neglected on VMD, and the main reason for membrane flux decline is saturated vapor pressure drop and increasing viscosity caused by the increase of liquid concentration. The acid and alkali cleaning method,which recovering ratio of membrane flux is up to 97.98% and no damage to the structure of membrane surface, can be as the main cleaning method later experiments.Part four: On the basis of studies of water extract of Radix scutellariae, a preliminary study on concentration process of 12 other kinds of Chinese herbal decoctions, which analyzed the correlation between physicochemical properties and membrane flux, and measured common physicochemical parameters before and concentration is carried out. It was found that physicochemical parameters of liquids had no significant effect on the membrane flux, and the process had little impact on pH, HPLC specific chromatogram. But the process has different influence on conductivity, viscosity, turbidity, solids content and rejection rate of index component.In order to select reasonable pretreatment and cleaning method, this experiment practically investigated the impact of different pretreatment methods, main operation parameters and cleaning methods on MD performance in the concentration process of water extract of Radix scutellariae. Further analysis of MD process of different Chinese herbal decoctions under different vacuum degree, and its impact on the complicated system of Chinese herbal decoctions are carried out, which provided the basis of process mechanism for further study of concentrating Chinese herbal decoctions using VMD technology.