| In some degree, reverse osmosis membrane has been applicated in concentration of Chinese traditional medicine decotion. However, this techonolgy can’t be used to the liquid with high concentration. In order to overcome the difficulty,20 single Chinese herbs and 5 compound systems are selected as experimental subjects in experiment to study how liquid properties have effects on reverse osmosis membrane process and the differences of different liquid systems on membrane process to verify the feasibility of enriching Chinese traditional medicine decotion.The results and conclusions are as follows:First and foremost, pretreatment is very important to reverse osmosis membrane, which can cut down membrane fouling and increase efficiency of enrichment. Ultrafiltration techonolgy is a good way of pretreatment, because of high removal rate of macromolecular substances. The results show that the best choice is the ultrafiltration membrane, which is made of PES and molecular weight cut-off is 20-50 KDa.Secondly, the effect of various operating conditions, including feed concentration, temperature and operating pressure, on reverse osmosis membrane performance was evaluated and optimized. It was found that the flux and the rejection of index components in Chinese medicine decotion throughout the membrane are dependent on the operating conditions in the following sequence:concentration> pressure> temperature. The best operation conditon were as follows:concentration 25 g·L-1, operating pressure 0.45 MPa, and temperature 30 ℃.Thirdly, the physical and chemical properties of decotion have a significant impact on the membrane process, such as pH, viscosity, density, turbidity, conductivity, and osmotic pressure. In order to study the most important property, which has a profound effect on membrane process, the data from experiments is analysised by SPASS. It is found that osmotic pressure plays an important role in influencing the flux of membrane process, and there is a good linear relationship between osmotic pressure and decline rate of flux. Therefore, detecting osmotic pressure on line is helpful to improve the efficiency of enrichment on reverse osmosis membrane.In addition, experiments was divided into two groups (salt solution and organic molecular solution with series of different concentrations) to study the material foundation of osmotic pressure. The results show that inorganic salt, saccharides and other small organic molecules are mainly causing osmotic pressure.It is found that osmostic pressure increases to a certain value, then it tends to be stable, which is called critical osmotic pressure. Otherwise, when trans-membrane pressure becomes zero, osmotic pressure at the moment is also called critical somotic pressure. All this results obtained by analysising the changing rule of osmotic pressure and trans-membrane pressure in the membrane process. And it is time to stop membrane process when the critical osmotic pressure comes up.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 91%. It demonstrates that reverse osmosis membrane can primely maintain the integrity of all the liquid system.Finally, concentration polarization coefficient and total membrane pollution resistance can be calculated to judge the membrane fouling. Further more, membrane fouling characteristic is described by classic block model. The experimental results show that concentration polarization coefficient decreases due to increasing of the osmotic pressure. The change of membrane fouling resistance is interesting. It increases at the first stage because of the decline of the flux in membrane process, and then it decreases owing to the increasing of osmotic pressure. At last, resistance increases again, which is caused by interaction of increasing osmotic pressure and decreasing flux. Membrane fouling analysis results show that standard blocking model, intermediate blocking model and complete blocking model are interactive to explain reverse osmosis memrane fouling. |
