Study On Membrane Mass Transfer Process Of Different TCM Extracts By Reverse Osmosis Integrated Vacuum Membrane Distillation

RO technology has been gradually used in the field of traditional Chinese medicine in recent years,with low operating temperature,can fully protect the heat-sensitive active ingredients from damage,but the concentration ratio is small.VMD technology has the advantages of simple operation,low loss of active ingredient and high concentration ratio,which can effectively compensate the deficiency of conventional concentration method,but it is far away from industrial application.Various defects caused by membrane process technical principles also affect their advantages.In order to improve the performance of the reverse osmosis in the process of TCM extract enrichment,this paper used RO-VMD integrated membrane process for the concentration of aqueous extract of TCM,and studied the correlation between rheological parameters and membrane dynamic parameters,and the threshold flux of the VMD process,the critical osmotic pressure of the RO process were used to optimize the membrane process.The "critical point" of RO-VMD integrated membrane process was studied with the main experimental system of traditional Chinese medicine aqueous extract of different medicinal parts,and evaluated the RO-VMD process.Optimizing the RO-VMD process had practical significance in the effective concentration of TCM extracts to achieve process control.The major content and results of this paper are as follows:Part one:Firstly,with extracts of dandelion and Sophora japonica for research system,concentrated by reverse osmosis(0.45 MPa,30 ?)for 200 min,the osmotic pressure of most of the extracts had exceeded the applied pressure,that is,the driving force of the membrane process was decreased to 0 MPa,the membrane process should be difficult to continue,otherwise it will have a greater damage to the membrane module.When the osmotic pressure reach the balance value,and the membrane process driving force is also just 0 MPa,is the best balance.Part two:The threshold flux and the limit flux of the extract of Radish Seed in the VMD process were determined by TMP stepping experiments.The flux decay,the total filtration resistance,the TPC value and the SEM image of the membrane surface under different flux behaviors were analyzed.The pemeate flux was reduced by 15.4%after 180 min when at limiting flux,and the flux had a very slight decline(only 1.63%)at threshold flux operation,and fluxes became almost stable within 10 min,indicating that the reversible fouling layer(i.e.concentration polarization and particle deposit)forms very quickly,and the total filtration resistance under limiting flux is 2.5 times the threshold flux which increased energy consumption.It was evidently that operation in threshold flux could avoid serious flux decline and was more appropriate for long-term running.Therefore,running under threshold fluxes avoids severe flux attenuation,is also more energy efficient,and is more suitable for long runs.It is proved that the threshold flux has an important effect on the better design of the membrane process and the extension of membrane life.To achieve in a certain operating condition which is the minimization of irreversible fouling although reversible fouling may not be avoided.Part three:Based on the study of the extract of Raphani Semen,effect of feed concentration and different TCM extracts on the threshold fluxes were studied in the vacuum membrane distillation process.A series of experiments were designed in order to identify which of the physical and chemical parameters play a major role in the threshold line(K value)and the threshold point(vacuum,threshold flux)and the results were analyzed statistically.As the feed concentration increases,concentration polarization improved and more solute particles deposited on the membrane surface,thus reversible fouling enhanced,irreversible fouling appeared in advance and the rate of permeability loss increased.The Pearson correlation coefficient and cluster analysis showed that the density,viscosity and particle size distribution of the feed had a great influence on the threshold line and the threshold point,and the density was positively correlated,and the viscosity and particle size were negatively correlated.Part four:The aim of this study was to evaluate the possibility to concentrate aqueous extracts of traditional Chinese medicine using an integrated membrane process involving ultrafiltration,reverse osmosis and vacuum membrane distillation.The physicochemical properties of different Chinese herbal decoctions before and after concentration were tested.It was found that the change range of pH value was small,and the conductivity,turbidity,viscosity and content of solid content increased significantly,as the concentration of the decoctions increased.It is well observed that all the biochemical properties possessed around 99%of retention during RO process.However,during VMD process the retention of effective components were higher than 93%.Samples before and after membrane process are detected by HPLC,then analysis the similarity of chromatogram.The results show that similarity among those samples from the same Chinese medicine decotion is more than 0.93.It demonstrates that RO-VMD membrane integrated process can primely maintain the integrity of all the liquid system.In this paper,the concept of threshold flux is introduced in the study of VMD from the practical application,and the basic research data are provided to explore suitable membrane process design to reduce the membrane fouling and improve the membrane separation and concentration efficiency.The reverse osmosis and membrane distillation technology are integrated to investigate adaptability for TCM extract,with originality.