Current status of plant extraction equipment At present, the mainstream equipment for traditional Chinese medicine extraction includes soaking tank, multi-functional extraction tank, dynamic extraction tank and thermal reflux extraction and concentration unit. The structure and operation method of the equipment are basically the same as the single-tank equipment for oil extraction. The supercritical fluid extraction, ultrasonic enhanced extraction, microwave extraction and other process equipment launched in recent years are not mature enough, and the design idea has not jumped out of the single-tank extraction mode.
1. Dipping tank Typical dipping and extraction equipment. The solvent is added from the top of the tank, and the medicinal materials in the tank are extracted and discharged from the bottom. The advantages are that the extraction liquid contains good quality, less impurities and high extraction yield; the equipment is simple and easy to manufacture and maintain. The disadvantage is that the extraction speed is slow, the amount of solvent is large, the production efficiency is low, the energy consumption is large, and a large number of extraction tanks are required for large-scale production, which occupies a large area and requires high investment.
2. Multifunctional extraction tank The most used extraction equipment. The medicinal materials immersed in the solvent are heated with jacketed steam and extracted by soaking. In addition to being suitable for heating extraction, a closed condensing system can also be used to recover volatile oil in medicinal materials; the extraction yield can be improved when a two-stage or three-stage cross-flow extraction process is used. The disadvantage is that when the diameter of the tank is too large, the solid material hinders the heat transfer efficiency, and the material is difficult to be fully boiled, so that the extraction efficiency decreases, and a large number of extraction tanks are required for large-scale production.
3. Dynamic extraction tank (intensive extraction with stirring) It is a multi-functional extraction tank with stirring device. The advantage is that the medicinal powder can be suspended in the solvent under stirring, the heat transfer speed is fast, and the diffusion speed is also fast, so the extraction speed is fast and the extraction rate is high. The disadvantage is that the power consumption of the medicinal materials to be processed into fine powder is very large. Separation of dregs and extraction liquid needs to pass through a centrifuge or a plate and frame filter, which consumes more manpower and power.
4. Soxhlet extraction and concentration unit It is a unit that combines multi-functional extraction tank and concentrator according to the principle of Soxhlet extractor. The extract from the multi-functional extraction tank is filtered and then enters the concentrator. The solvent evaporated during concentration is condensed and returned to the multi-functional extractor. The whole process is a differential multi-stage cross-flow extraction. High extraction rate, production efficiency and extraction rate are better than the previous equipment. But the problem of the multi-function extraction tank is also inevitable.
5. Other extraction processes Supercritical extraction, ultrasonic enhanced extraction, and microwave extraction are newly developed extraction processes in recent years. The advantages of carbon dioxide supercritical extraction are strong selectivity and high purity of the extract, which is suitable for extracting lipophilic substances with known chemical structure and small molecular weight from solid materials. The disadvantages are high operating pressure, high energy consumption, and high manufacturing costs when the equipment is scaled up. It is not suitable for extracting mixtures of unknown composition and substances with low solubility in carbon dioxide. Ultrasonic enhanced extraction can use the energy of ultrasonic vibration to enhance the diffusion process, so that the solvent can be easily immersed in the solid, and the solid solute can easily diffuse from the inside of the solid to the solid-liquid interface, thereby accelerating the extraction process. The disadvantage is that due to the limitation of ultrasonic power, the economy of mass production is not good, and the safety of high-power ultrasonic waves has yet to be verified. Microwave extraction utilizes the action of microwaves on polar molecules to heat solvents and medicinal materials to rupture the cell walls to accelerate extraction. Microwave extraction is also limited by the power of microwave generation, and there are some engineering problems when scaling up the production scale. The above process equipments are all single-tank, intermittent extraction equipment, which has the advantage of flexible production arrangement, suitable for small batch and multi-variety plant extraction, and low investment in small-scale production. The disadvantage is that the overall efficiency is low, the production cost is high, and the large-scale production investment is high. Some newly developed extraction processes have technical difficulties when scaling up.