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The industrialization road of supercritical CO2 extraction of Chinese herbal medicine

Supercritical fluid technology is a new chemical technology that has generated great interest in the past 30 years. It has carried out extensive and in-depth research in the fields of chemical reaction and separation and purification, and has made great progress. Internationally, a supercritical fluid academic conference is held every three years. In October 1996, China held the "First National Symposium on Supercritical Fluid Technology Academics and Applications". The second seminar will be held in November 1998. As a new generation of chemical separation technology, supercritical CO2 extraction has been included in the "8 * 5" national scientific and technological research plan. Through the efforts of scientific and technological personnel, a number of valuable issues have been completed in the fields of medicine, chemicals, food, light industry and environmental protection, and a new industry has been initially formed.

In the past 10 years, we have researched and developed four sets of industrial-scale supercritical CO2 extraction devices of different scales. The products we have developed include Artemisinin Extract, Cnidium Extract, Turmeric Extract, Algae Extract, and Pepper Essential Oil. Patchouli oil, nutmeg oil, pepper essential oil, ginger essential oil, jasmine essential oil, wheat germ oil, and deep-sea fish oil refining. Summarize the practical experience of industrialization and put forward the following questions with peers.


1, The design and scale of the device

The overall requirements for the design of the supercritical fluid extraction device are: 1) Safe and reliable under working conditions, able to withstand frequent opening and closing of the lid (extraction kettle), and good anti-fatigue performance; 2) Generally requiring one person to operate within 10 minutes The completion of the extraction kettle is completed and closed one cycle, the sealing performance is good; 3) The structure is simple, easy to manufacture, can be used continuously for a long time (that is, can run three shifts); 4) set up safety interlocking device. The high-pressure pump has a variety of specifications to choose from. It is gratifying that the domestic three-piston high-pressure pump can better meet the requirements of the industrialization of supercritical CO2 extraction, but its flow needs to be improved, and it is necessary to trial-produce more than 40 MPa working pressure. The new high-pressure pump should be serialized and standardized. At the same time, domestically produced high pressure valves for CO2 fluids (both manual and automatic) need further study and improvement. Accelerate software development, use PLC to achieve program control, PC online detection, and improve device automation and security.

According to practical experience and in light of China's national conditions, we believe that the supercritical CO2 extraction device should be more practical in small and medium-sized enterprises. Large-scale installations such as single-kettles larger than 1 000 L should not be blindly launched. Each device configuration 2 ~ 3 extraction pot efficiency will be higher. According to data, most of the companies in Japan that have supercritical CO2 extraction devices are small and medium-sized devices. Only one of them is larger than 1000 L. See Table 1 for details.

In the selection of device size, it is recommended to note the following two points:

1.1 Selection according to the production object: The supercritical extraction device is a general-purpose device for separation technology. As an enterprise, the scale should be determined according to the business objectives and business scope. For example, we worked in a food company and realized in practice that the medium-sized supercritical extraction device can basically meet production needs. For some products, such as decaffeinated tea or extracted hop extracts, a large device is required. I have visited a 3×3000 L device owned by a company in Switzerland.


Table 1 Setting of Supercritical CO2 Extraction Device in Japan

Company Name

Equipment manufacturer

Extraction kettle

Extraction object

Volume (L)

Design Pressure (MPa)

Fuji Spice

Wood Company (Germany)

200×1

300×1

29.4

29.4

Cigarettes with spices

Food spices

YASUMA

Mitsubishi Chemical Machinery

100×1

34.3

Chili oleoresin

Gaosha Spice

Mitsubishi Chemical Machinery

300×1

34.3

Natural spices

Hasegawa spices

Wood Company (Germany)

300×2

34.3

Spices, colors, medicine

Maoli oil

Krupp Corporation (Germany)

500×1

200×1

37.73

29.4

Food flavors

Sumitomo refine

Sumitomo refine

50×2

29.4

Essential oil

Takeda Pharmaceutical Industry

Sumitomo Heavy Machinery

1200×1

Pharmaceuticals


1.2 Determine the scale of the device: not only should it be considered technically feasible, but it must also be considered economically viable. Supercritical fluid extraction is a high-pressure equipment and the investment cost is high. The larger the scale, the higher the investment cost. This is a risk investment. Generally speaking, it is a successful project to recover investment within 3 to 5 years. Otherwise, improper choice of scale will cause a burden on the company's operations and make it a bad thing.


2, Bxtraction kettle problem

According to relevant data regulations, PN 10.0 ~ 100.0 MPa is high pressure. At present, the maximum working pressure of home-made extraction kettles is mostly 32.0 MPa, but there are exceptions. The extraction device that we are designing to work at a maximum working pressure of 50 MPa is designed to extract a certain Chinese herbal ingredient. Different types of materials need to use different extraction kettles. An important parameter of the extraction tank structure is the aspect ratio. For solid form materials, the aspect ratio is about 1:4 to 1:5. For liquid form materials, the aspect ratio is about 1:10. The former loading and unloading materials are intermittent, and the latter can be continuous feeding and unloading. Most of the Chinese herbal medicine extracts are solid (cut into pieces or broken into powder, etc.), and the materials are put into the hanging basket. If the material is liquid (for example, the traditional ginseng extract removes the solvent), stainless steel ring packing is still required in the kettle.

The intermittent loading and unloading uses the lid of the quick opening device structure. At present, there are three types commonly used in domestic quick release devices: one is the clamp type, the other is the toothed type, and the other is the split ring type. Clamp type quick opening device can be divided into three kinds, one is manual, that is, by tightening or loosening bolts and nuts one by one; Second, semi-automatic, by the handle to move the screw drive clamps; three is fully automatic, by Pneumatic/hydraulic drive clamps slide along the guide rails. There are also two types of tooth-engaging quick-opening devices, internal toothing and external toothing.

Fully automatic clamp type quick opening device completes one operation cycle (ie, opening the cover, taking out the hanging basket, placing another basket containing material, closing the lid of the kettle) takes about 5 min; the tooth-engaging quick opening device completes The cycle of one operation takes about 10 minutes.

The continuous operation of the extraction kettle can depend to a large extent on the integrity of the sealing structure. When the pressure drop through the sealing surface of the medium is less than the pressure difference on both sides of the sealing surface, the medium will leak, and the extraction kettle will not work properly. Due to the strong penetrability of CO2 to rubber, most rubber-sealed extraction devices, irrespective of the type of rubber they are used in, can usually be renewed only three to five times. For industrial extraction kettles, clamp structure lids are preferred and self-tightening seals are used. We use a new sealing material, improved O-ring sealing ring, good sealing effect, convenient assembly and disassembly, long service life, and continuous use up to 300 times.

The seal between the basket and extraction kettle is also very important, it directly affects the yield. When designing the extraction kettle, it is also necessary to consider the loading and unloading convenience and safety of the basket. Baskets can be modular.

The extraction kettle is the key equipment in the supercritical extraction device system. It is necessary to withstand high pressure, develop high-strength special steel, reduce the thickness of the kettle wall, and save materials and costs. The high-purity special steels currently being studied in various countries in the world are examples. The separation vessel research with the extraction vessel is being carried out in parallel to meet the purpose of industrial production. The separation vessel can be set to one or more stages of separation depending on the purpose of the separation. For Chinese herbal medicine, it is sometimes necessary to separate three or four levels. Separation can be combined with distillation, adsorption and other processes to achieve the purpose of extraction, separation and purification.


3, The conversion of the device

There is a conversion problem in the supercritical CO2 extraction device. In order to prevent cross-contamination, the cleaning of laboratory devices is easy to implement. However, the cleaning of industrial devices is much more difficult and requires more manpower, material resources, and financial resources. If we do not fully understand the arduousness and importance of this point, incomplete cleaning may result in greater waste and loss.

From the point of view of engineering design, in order to prevent high-pressure leakage, the connection form of pipe fittings should be fixed as far as possible, ie welded connection. However, considering the actual adjustment of the product structure in production, it may be most appropriate to use a threaded flange connection as much as possible, which is easy to take apart and wash.

The method of cleaning should be selected according to different objects, and the universal method of unifying the same is not available. Alternative methods are as follows: 1) hot alkaline water → tap water → dilute acid (such as HNO3, but can not use HCl) → deionized water; 2) detergent (such as Nine × 24 + sodium metasilicate + potassium hydroxide + water) → deionized water; 3) any of the following solvents or their several solvent mixtures (ethanol, hexane, turpentine, acetone, gasoline, carbon tetrachloride) → deionized water; 4) alcohol + amo Niya water + gasoline → deionized water; 5) CO2 with modifier added.

The inlet valve of the washing solution is set at the highest point of the device, and the outlet is the discharge valve of each kettle and the lowest point of the pipeline discharge valve. It can also be cleaned by pumping and circulating. Finally, it is purged with nitrogen and transferred to the next round of new The product's extraction.

For herbal extracts, it will inevitably encounter chlorophyll, wax and other “impurities” that stick to the inner walls of equipment and pipelines like asphalt. That is, the cleaning effect using the above methods is not very satisfactory. We use alkaline high-pressure steam washing to find the effect. Very good, but you need additional equipment.

The cleaning of industrial large-scale installations is not easy to do well. It takes some time. Taking into account the economic reasons, frequent conversions will increase costs and reduce the utilization rate of equipment. Frequent production conversions are not desirable. However, equipment and pipelines must be cleaned at least once a year, even if they are not converted.


4, CO2 recovery problem

One of the advantages of supercritical CO2 extraction technology is that CO2 can be recycled, which can not only reduce costs but also avoid environmental pollution. However, it is not possible to recycle 100% of CO2 in practice. The easiest way to recover CO2 is to use pressure equalization to transfer the high-pressure CO2 in the system to a low-pressure CO2 storage tank. If it is to be further recovered, a compressor must be added, and the CO2 tank should be filled in front of it. If a local purifier is installed, if the user's local CO2 is cheap, there is no need to recycle all of them. Generally, about 80% of the recycling is appropriate, and it is easy to do so. It is constantly supplemented with some fresh CO2, which is conducive to complete extraction and process optimization.

The CO2 emissions from the installation are concentrated in a venting pipe and led out to the outdoors (the vents are more than 1 m above the roof). The diameter of the vent pipe should be at least 2 times larger than the high pressure pipe. When CO2 transitions from a high-pressure system to a low-pressure system, its transitional form is high-low pressure different-diameter pipe. The material is generally No. 20 steel, and the high-pressure flange is No. 35 steel.


5, On the issue of energy consumption

Some monographs and articles recommend that one of the features of the supercritical CO2 extraction technology is energy conservation. Because it takes less time and less steps than conventional solvent extraction, it eliminates the refining process of certain products and saves energy. However, in the industrialization process, the ratio of energy consumption to product cost must be specifically analyzed. The cost components of a product are as follows: 5.9% for raw material costs, 22.5% for energy consumption, 8.9% for CO2 consumption, 33.6% for labor costs, 22.4% for equipment depreciation, and 6.7% for wearing parts and others. The phase change in the extraction process of this product requires a large amount of energy. We believe that in-depth research on energy conservation, consumption reduction, and cost reduction is one of the issues related to the success or failure of this new technology industrialization.

To save energy and reduce consumption, we must pay attention to the following points: 1) Optimize the process, strictly control the operating conditions in order to increase the yield; 2) Strictly select high-quality raw materials for Chinese herbal medicine; 3) Ensure the equipment is in good condition and arrange the production rationally. Class operations, do not stop open and open; 4) the introduction of energy-saving technologies, from the quality of the device to improve the energy conversion rate and utilization.



6, A few noteworthy issues

6.1 The management and operation personnel of the supercritical CO2 extraction plant should have the basic knowledge of the pressure vessel necessary to understand the difference between the working pressure and the hydraulic pressure test pressure. It is forbidden to perform the production operation exceeding the allowable pressure on the extraction kettle device with the maximum working pressure of 32 MPa. Otherwise, it is dangerous. The "Safety Management Regulations for Pressure Vessels" issued by the Ministry of Labor of China not only designers but also users. Operators should hold certificates.

6.2 Overpressure Relief Devices In addition to safety valves, bursting discs should be installed. Some viscous components of Chinese herbal medicine accumulate on the valve flaps of the safety valve or block the passage of the valve, which may affect the start-up of the pressure relief device of the safety valve. Therefore, there should be Double insurance. We have seen some industrialized devices actually ignore this point. The industrialization of supercritical CO2 extraction technology calls for standardization to be followed as soon as possible.

6.3 The use of entrainer is becoming wider and wider, and the corrosion of the device should be taken seriously. Corrosion of stainless steel equipment is often localized. When in passive and active edges, pitting corrosion may occur in entrainers containing halide ions, and entrainers containing stress-sensitive corrosion-sensitive ions (such as Cl-, OH-, etc.). In the stressed part, such as near the weld seam, stress corrosion may occur.

6.4 Industrial production Unlike laboratory tests, the actual records of the production process should be separated from the equipment operation records, and technical files and usage management files should be prepared.

6.5 During the production process, in order to prevent the high-pressure system from depressurizing, the trace amount of moisture or impurities in the CO2 will be blocked due to throttling, cooling, and freezing, and the selection of the process conditions must be fully weighed and properly set. The abnormal pressure in the production system is often caused by the blockage.

The supercritical CO2 extraction process is simple and the workers in production often simply look at the strictness of the operation, resulting in fluctuations in production levels and instability in product quality. For example, in the process of variable temperature separation, the pressure of the solute plays a dominant role in a certain pressure range. As the temperature increases, the solubility increases. Within a certain pressure range, the density of the supercritical fluid plays a dominant role, and the temperature increases, and the solubility decreases. This requires the operator to correctly grasp the process flow of a product.

Supercritical CO2 extraction has potential applications in Chinese herbal medicine. Some articles have been reviewed. The author also conducted the extraction and separation of more than 10 Chinese herbal medicines. In general, the low-polar compounds such as esters, ethers, Lactones and oxygenates are more easily extracted, especially in the following areas: 1) Certain natural compounds with chiral carbon atoms, due to their optical activity, during the extraction and separation process, acid or Isomerization tends to occur after alkali. As a result, not only its optical activity is changed, but also its physiological activity is inevitably affected. If these compounds are partial lipids, it is more suitable to use supercritical CO2 extraction. For example, many monoterpenoids in Chinese herbal medicine (and marine organisms) are Belongs to this column. 2) It is of great significance to extract the active ingredients with anti-cancer effects from natural plants. The use of supercritical CO2 extraction will be more conducive to maintaining its physiological activity, such as extracting podophyllotoxin from plants of the genus Podophylla. Elemene is extracted; new vinblastine is extracted from vinca and so on, and they all have the effect of inhibiting the proliferation of cancer cells. 3) The composition of Chinese herbal medicine is complex. The polarity, boiling point, molecular weight, solubility and other characteristics of each chemical ingredient in the same flavoring medicine are different. How to use supercritical CO2 extraction technology for fractional extraction, back extraction, and widening the range of entrainer, To make full use of Chinese herbal medicine resources is a great article to do.