1. Basic principle of ultrafiltration Ultrafiltration is between nanofiltration and microfiltration. The molecular weight of the trappable molecules ranges from 5×103 to 5×105um. There is a very thin dense layer on the working surface of the ultrafiltration membrane. The pore size of the micropores in the layer is about 2-15 nm, and the lower layer of the membrane is a loosely supported support layer with a void of >15 nm. The membrane structure allows the macromolecular solute particles to flow through the membrane surface in the liquid separation process. Due to the rapid flow of the liquid, the substances can neither enter the dense pores and cause internal clogging of the membrane, and will not stay. Surface clogging is formed on the membrane surface; while the small molecular material and solvent are driven by pressure through the micropores on the dense layer, they can smoothly pass through the lower loose support layer and enter the other side of the membrane. The membrane materials of the ultrafiltration membrane are mainly cellulose and its derivatives, polycarbonate (PC), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polysulfone (PS), polyethersulfone (PES), Polyacrylonitrile (PAN), polyamide (PA), and the like.
The molecular weight of the ultrafiltration membrane is 5×103～5×105um, and the relative molecular weight of the active ingredients of most Chinese medicines does not exceed 1000um. The relative molecular weights of ineffective components such as starch, protein, resin and pectin are above 5×104um. . Therefore, the selection of an ultrafiltration membrane with a suitable molecular weight cutoff range can achieve the separation of active ingredients and impurities, and can retain the original compound characteristics of traditional Chinese medicine, and maximize the efficacy.
2. Ultrafiltration operation mode and its application Unlike ordinary filtration, ultrafiltration uses a porous asymmetric ultrafiltration membrane to achieve liquid-liquid separation on the surface of the membrane. The filtration method is cross-flow, that is, the feed liquid flows parallel to the membrane surface. Ultrafiltration can be divided into batch operation and continuous operation according to the operation mode.
2.1 Intermittent operation Intermittent operation is divided into two modes of operation: the full circulation of the retentate and the partial circulation of the retentate according to the circulation mode of the retentate. In the ultrafiltration process, in order to reduce the effects of concentration polarization and membrane fouling, a high feed liquid flow rate must be maintained in the membrane cell. Therefore, a large circulation of the retentate must be used to maintain a high flow rate, and in addition, the membrane permeation flux Smaller, the feed liquid also needs to be circulated multiple times on the membrane to meet the concentration requirements.
Intermittent ultrafiltration has large transmission rate, high separation efficiency, simple operation, small equipment and membrane area, and can realize rapid concentration of a small amount of raw liquid, so it is suitable for laboratory and small-scale product processing. The disadvantage of intermittent ultrafiltration is that the amount of treatment is small, while the throughput of the continuous ultrafiltration operation is large, and the residence time of the feed liquid on the membrane is short, so the concentration ratio is low, so a large membrane area is required.
2.2 Continuous operation Liang Wanqiu et al. compared the effects of continuous plate ultrafiltration and intermittent plate ultrafiltration in the filtration and purification of cephalosporin C fermentation broth, and found that continuous plate ultrafiltration has a small degree of membrane fouling, easy recovery of membrane flux after washing, and filtrate quality. Good, the filtrate unit is equal.
Continuous ultrafiltration is divided into single-stage and multi-stage according to equipment technology. According to the circulation mode of the retentate, it can be divided into two types: no cycle and partial cycle. Among them, single-stage partial cycle and multi-stage partial cycle are widely used in the process. . The characteristic of single-stage continuous ultrafiltration is that the ultrafiltration process is always carried out at a high concentration, so the permeation amount and the rejection rate are both low. To overcome this disadvantage, multi-stage continuous operation is generally employed. The concentration of the circulating liquid in each stage of the multi-stage ultrafiltration is sequentially increased, and the last stage leads to the concentrated liquid, so that the liquid in the previous stages can be operated at a lower concentration.
3, the application of ultrafiltration in the purification of traditional Chinese medicine Pretreatment of liquid medicine is an indispensable process before the separation of traditional Chinese medicine membrane. Since the extract of traditional Chinese medicine generally contains more solids and impurities with higher relative molecular weight, and colloids which are easy to cause membrane fouling, the direct use of ultrafiltration separation of the chemical solution may cause membrane fouling and reduce the service life of the membrane. Therefore, the stock solution must be pretreated before ultrafiltration. Commonly used pretreatment methods are: first, centrifugal separation and flocculation precipitation are used to remove suspended solids such as large solid impurities, and then microfiltration further removes bacteria, colloids and the like. Due to the high content of viscous substances such as colloids in traditional Chinese medicine ingredients, the contamination phenomenon of the membrane is serious. Therefore, it is preferable to use a membrane material with better stain resistance, such as polyacrylonitrile, sulfonated polysulfone membrane and the like.
3.1 Extraction of effective part (part) of traditional Chinese medicine The composition of traditional Chinese medicine is complex, and there are some differences in molecular weight of each component. Ultrafiltration membranes with appropriate pore size can be used to separate these components by molecular size by membrane screening. Guo Lijun considered the scientific and technical problems of membrane separation of complex systems of traditional Chinese medicine from the aspects of separation of material basis, separation target and properties that can be used for separation, and proposed the process design principle of membrane separation technology of Chinese medicine and the prevention and treatment of membrane pollution.
In recent years, there have been many reports on the use of ultrafiltration technology to treat common Chinese medicine extracts. Combining the new technology of ultrafiltration with traditional Chinese medicine treatment is conducive to improving the quality of traditional Chinese medicine preparations and promoting the modernization of traditional Chinese medicine. Specific research work can be divided into specific research work can be divided into specific research work can be divided into three aspects:
(1) To explore the application of ultrafiltration in the extraction of active ingredients from traditional Chinese medicine;
(2) Studying the process conditions of ultrafiltration in the treatment of traditional Chinese medicine extracts;
(3) Industrialization of the ultrafiltration process and related problems. Li Shuli et al. used a polyacrylonitrile film with a cut-off value of 10000um for seven representative Chinese medicines (danshen drink, Si Miao Yong An Tang, Huanglian Jiedu Decoction, Ginseng Shengmaiyin, Lizhong Decoction, Astragalus extract, and leech). The preliminary study of the ultrafiltration process of the boiled liquid system was carried out. It was found that the relative fluxes of the seven systems were almost the same, and Danshen, Si Miao Yong An Tang, Huanglian Jiedu Decoction and Lizhong Decoction The recovery rate of the active ingredients in the system is above 60%, which is significantly higher than the recovery after alcohol precipitation. Li Yanni used an ultrafiltration membrane with a molecular weight cutoff of 8000um to purify the acid mucopolysaccharide of sea cucumber, and the rejection rate reached 97.2%. Xu Zhihong et al. purified the ginkgo flavonoid extract (GBE) crude raw material by using sulfonated polyethersulfone (SPES) plate ultrafiltration membrane with molecular weight cut off of 10000um, and increased the content of ginkgo flavonoids from 21.3% to 39.2%.
3.2 Application of ultrafiltration technology in the preparation of traditional Chinese medicine liquid preparations The new liquid traditional Chinese medicine preparations mainly include traditional Chinese medicine injection, Chinese medicine oral liquid and traditional Chinese medicine eye drops.
Ultrafiltration technology can filter out unstable micelles, macromolecules and other impurities in the liquid, improve the clarity of the liquid Chinese medicine preparation, remove the heat source and tannin, and improve the safety of the injection.
Ultrafiltration is an effective means of preparing Chinese herbal medicine injections. The ultrafiltration process is adopted to obtain a stable clearness of the injection, which is suitable for intravenous administration. In recent years, ultrafiltration has been widely used in the preparation of traditional Chinese medicine injections.
Traditional Chinese medicine oral liquid has good curative effect, quick effect and convenient drinking. However, the extract of traditional Chinese medicine has a large viscosity, and a large amount of impurities such as submicron particles and flocs are difficult to be refined by sedimentation, filtration, leaching, etc., and the ultrafiltration method can effectively remove these impurities and improve the quality of the Chinese medicine oral liquid and Exterior. It should be pointed out that due to the complexity of traditional Chinese medicine, the use of ultrafiltration and the selection of ultrafiltration membranes should be selected according to the nature of the drug and the composition of the drug.
4. Problems in the treatment of traditional Chinese medicine by ultrafiltration technology
Compared with the traditional treatment methods, ultrafiltration has the advantages of mild operating conditions, low energy consumption, simple operation and short process flow. However, due to the complexity and diversity of traditional Chinese medicine, it is easy to cause membrane fouling and clogging. Membrane fouling refers to the adsorption or deposition of various particles on the surface of the membrane or pores of the membrane due to the physicochemical action of particles, colloidal ions or solute molecules in the filtered liquid and the membrane, causing the membrane pores to become clogged or smaller and The permeation flux and separation characteristics of the membrane cause irreversible changes. Membrane fouling affects membrane flux and transmission while also reducing membrane life. The degree of membrane fouling is related to the membrane material, the pore size, the operating pressure of the membrane process, the concentration and nature of the macromolecular solute in the system to be separated, the pH of the solution, the ionic strength, and the charge composition. The control of membrane fouling is an urgent problem that ultrafiltration technology needs to solve in the process of treating Chinese medicine.
At present, the prevention and control of membrane pollution is mainly considered from three aspects:
(1) pre-treatment of the extract by flocculation, microfiltration, etc. before ultrafiltration to remove major membrane contaminants;
(2) During the ultrafiltration process, comprehensive adjustment of flow rate, temperature, electric field, pH and other factors to reduce the adsorption of the membrane surface, such as increasing the flow rate of the raw liquid on the membrane surface, strengthening the scouring effect;
(3) Cleaning and regeneration of the membrane.
Since the mechanism of membrane fouling is still unclear, on the one hand, the research on membrane fouling theory should be strengthened. On the other hand, experimental data and practical experience should be accumulated for different systems, and membrane equipment and membrane materials suitable for Chinese medicine separation should be developed to solve the membrane. The problems caused by contamination in membrane separation applications.
5. Conclusion In summary, in view of the complex composition of traditional Chinese medicine and the characteristics of the "group" of active ingredients, ultrafiltration technology has gradually replaced the traditional Chinese medicine extract in the separation and purification of the active ingredients (effective parts) of traditional Chinese medicine due to its many advantages. The method will play an increasingly important role in the modernization of traditional Chinese medicine. Of course, modern analytical techniques and modern Chinese medicine theory also require ultrafiltration, a new method applied to traditional Chinese medicine treatment to prepare new preparations such as traditional Chinese medicine injection and Chinese medicine oral liquid. The composition and pharmacology of traditional Chinese medicine is very complicated. With the deepening of people's understanding of traditional Chinese medicine ingredients and the development of membrane technology, ultrafiltration technology will play a greater role in the modernization of traditional Chinese medicine.
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