What is a supercritical CO2 extraction process?
The Supercritical CO2 extraction process technology is a new-type separation technology in modern chemical separation. The Super Critical CO2 extraction takes CO2 as the solvent.
As CO2 fluid under a supercritical state has a larger density and dielectric constant, larger dissolvability against substances, which can change abruptly when pressure and temperature change therefore it has not only the selection of dissolvability against some substances, but the separation of the solvent with the extracted substances is also easy.
The supercritical CO2 extraction process is especially suitable for the extraction of fat-soluble and heat-sensitive substances with a high boiling point. It is ideal for fine separation of different components, i.e. Supercritical fine distillation
The supercritical CO2 extraction process means that the solvent in the extraction tank is contacted with the extract at a suitable temperature under high pressure, and the solute diffuses into the solvent, and then the operating conditions are changed in the separator so that the soluble substances are separated and separated.
Supercritical CO2 extraction equipment is widely used in biological, pharmaceutical, food, and other fields.
List of extractable herbal oils
Ginger powder, ginger essential oil, wood sesame oil, wuhuo oil, ganoderma lucidum oil, black (white) pepper oil, celery oil seed oil, medlar seed oil, grape seed oil, fenugreek oil, white coriander oil, Tanshinone, propolis, barley oil, egg yolk powder (oil), cumin oil, sea buckthorn oil, evening primrose oil (refined), capsicum red pigment (refined), chuanxiong oil, angelica oil, safflower oil, aroma oil, walnut Kernel oil, atractylodes, white cardamom, etc.
Design of herbal oil CO2 extraction equipment
The general requirements for the design of supercritical CO2 extraction equipment are:
- Safe and reliable under working conditions, able to withstand frequent opening and closing of lids (extraction kettle), good fatigue resistance;
- Generally, one person is required to operate, and it can complete the opening and closing of the whole chamber of the extraction kettle within 10 minutes, and the sealing performance is good;
- The structure is simple, easy to manufacture, and can be used continuously for a long time (that is, it can run in three shifts);
How to choose a right CO2 extractor
Supercritical CO2 extraction equipment is general-purpose equipment for separation technology. As an enterprise, the scale should be determined according to business objectives and business scope.
Decide on equipment size
Consider not only technical feasibility but also economic feasibility. A supercritical CO2 extraction machine is high-pressure equipment. The investment cost is high. The larger the scale, the higher the investment cost. This is a risky investment. Generally speaking, being able to recover investment within 3 to 5 years is a successful project. Otherwise, improper scale selection will cause a burden on the company’s operation and make good things bad.
Extractor of CO2 extraction equipment
Chinese herbal medicines are mostly extracted from solids (cut into flakes or mashed into powders, etc.), and the materials are loaded into a hanging basket. If the material is liquid (such as traditional ginseng extract to remove the solvent), the kettle still needs to be filled with stainless steel ring packing.
According to the relevant data, PN 10.0 ～ 100.0 MPa is the high pressure. At present, the maximum working pressure of China extraction kettles is mostly 35.0-50 MPa, but there are exceptions. We are designing an extraction device with a maximum working pressure of 105 MPa to extract certain Chinese medicine ingredients. For different forms of materials, different extraction kettles are required.
An important parameter of the structure of the extraction kettle is the aspect ratio. For solid materials, the aspect ratio is between 1: 4 and 1: 5. For liquid materials, the aspect ratio is about 1:10. The former loading and unloading are intermittent, while the latter can be continuous.
Intermittent loading and unloading
The intermittent loading and unloading adopt a kettle lid with a quick-opening lid structure. At present, there are three types of China full-bore quick-opening lid devices: One is a clamp type, the other is a toothed type, and the other is a split ring type.
The clamp-type quick opening device can be divided into three types:
- One is the manual type, that is, tightening or loosening bolts and nuts one by one;
- The second is the semi-automatic type, which drives the clamp by moving the screw with the handle; The pneumatic / hydraulic device drives the clamp to slide along the guide rail. There are also two types of toothed quick-open cover devices, internal toothed and external toothed.
- A fully automatic clamp-type quick-closing lid device completes an operation cycle (ie, opening the lid, removing the gondola, putting in another hanging basket with materials, and closing the lid of the kettle) in about 5 minutes; the toothed quick-open lid device is completed An operation cycle takes about 10 minutes.
The normal continuous operation of the extraction kettle depends largely on the integrity of the sealing structure.
When the pressure drop of the medium through the sealing surface is less than the pressure difference between the two sides of the sealing surface, the medium will leak and the extraction kettle will not work properly. Because CO2 has a strong penetrability to rubber, most rubber-based sealed extraction devices, no matter what type of rubber is used, usually can only be used 3 to 5 times before being updated.
For industrial extraction kettles, it is advisable to use a clamp structured kettle lid with a self-tight seal. We use a new sealing material and an improved O-ring sealing ring, which has a good sealing effect, is easy to assemble and disassemble, has a long service life, and can be used continuously for more than 300 times. The seal between the hanging basket and the extraction kettle is also very important, it directly affects the yield of the product. When designing the extraction kettle, consideration should also be given to the ease of loading and unloading of the gondola and safety issues. The gondola can be combined.
Separation can be combined with rectification, adsorption, and other processes to achieve the purpose of extraction, separation, and purification.
The separation kettle can be set to one-stage separation or multi-stage separation according to the purpose of separation. For Chinese herbal medicine, there are sometimes three or four separations.
Cleaning method of CO2 extractor
There is a problem with cleaning in supercritical CO2 extraction units. To prevent cross-contamination, cleaning laboratory equipment is easy to achieve. However, the cleaning of industrialized equipment is much more difficult, requiring more human, material, and financial resources. If you do not fully understand the arduousness and importance of this point, incomplete cleaning may cause greater waste and loss.
From the perspective of engineering design, in order to prevent high-pressure leakage, the connection form of the pipe fittings should be fixed as much as possible, that is, welded connection. However, considering the actual adjustment of the product structure in production, it may be most suitable to use threaded flange connections as much as possible to facilitate disassembly and washing.
The cleaning method should be selected according to different objects, and there is no uniform universal method. The alternative methods are as follows:
- Hot alkaline water → tap water → dilute acid (such as HNO3, but not HCl) → deionized water;
- Detergent (such as Nine × 24 + sodium metasilicate + potassium hydroxide + Water) → deionized water;
- Any of the following solvents or a mixture of several solvents (ethanol, hexane, turpentine, acetone, gasoline, carbon tetrachloride) → deionized water;
- Alcohol + Amore Niaral water + gasoline → deionized water;
- CO2 with the modifier.
CO2 recovery system of CO2 extraction machine
A major advantage of supercritical CO2 extraction process technology is that CO2 can be recycled, which not only reduces costs but also avoids environmental pollution. However, it is impossible to recover 100% of CO2 in practice. The easiest way to recover CO2 is to adopt the pressure balance method. The high-pressure CO2 in the system is sent to the CO2 storage tank at lower pressure.
If further recovery is needed, a compressor must be installed, and the front of the CO2 storage tank must be installed. Configure a purifier. If the local CO2 price is cheap, there is no need to recycle all of them.
Generally, about 80% is suitable. It is also easy to do. Constantly replenish some fresh CO2, which is conducive to complete extraction and process optimization.
- The CO2 emissions in the plant are concentrated in an emptying pipe and lead to outdoor emissions (the exhaust opening is more than 1 m above the roof).
- The diameter of the vent pipe should be at least 2 times larger than that of the high-pressure pipe.
- When CO2 transitions from a high-pressure system to a low-pressure system, the transition from is a high-pressure and low-pressure reducer. The material is generally No. 20 steel, and the high-pressure end flange is No. 35 steel.
Some monographs and articles have recommended that one of the characteristics of supercritical CO2 extraction technology is energy conservation.
Because it takes less time and steps than the traditional solvent extraction, the refining process of some products is omitted, thereby saving energy.
However, in the process of industrialization, the proportion of energy consumption in product costs must be analyzed in detail.
The cost composition of a product is as follows: raw material costs account for 5.9%, energy consumption accounts for 22.5%, CO2 consumption accounts for 8.9%, labor costs account for 33.6%, equipment depreciation costs account for 22.4%, wearing parts and others account for 6.7%, which shows that 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 of this new technology industrialization.
Save energy and reduce consumption
To save energy and reduce consumption, we must pay attention to the following points:
- Optimize the process and strictly control the operating conditions to improve the yield;
- Strict selection of high-quality Chinese herbal medicine raw materials;
- Make sure the equipment is in good condition, arrange production reasonably, and run continuously for three shifts, don’t stop and open;
- Introduce energy-saving technology to improve the energy conversion rate and utilization rate of the device from the quality perspective.
2 Notable Issues with herbal oil co2 extractor
Maximum working pressure
Supercritical CO2 extraction device management and operators should have the necessary basic knowledge of pressure vessels, and make clear the difference between working pressure and hydrostatic test pressure, it is strictly forbidden to perform production operations exceeding the allowable pressure on the extraction kettle device with the maximum working pressure. Otherwise, it is very dangerous.
In addition to the safety valve, an overpressure relief device should also be provided with a bursting disc. Some viscous components of Chinese herbal medicines accumulate on the valve flap of the safety valve or block the passage of the valve, which may affect the activation of the pressure relief device of the safety valve, so there should be dual Insurance.
The use of cosolvent agents is getting wider and wider, and the corrosion of the device should be paid attention to. Corrosion of stainless steel equipment is often localized. When in the passive and active edges, pitting corrosion may occur in Co-solvents containing halogen ions, and Co-solvent containing ions sensitive to stress corrosion (such as Cl-, OH-, etc.).
However, stress-stressed parts (such as near the weld) may cause stress corrosion.
Example of CO2 extraction process for 3 herbs
Extraction goal: To obtain high-purity volatile oil for injection.
CO2 extraction process
The raw material is crushed into 40 meshes, the extraction pressure is 7.8MPa (subcritical state), the temperature is 31.8°C (fluid temperature), the separation Ⅰ pressure is 6MPa, the temperature is 30°C; the separation Ⅱ pressure is 5.6MPa, the temperature is 25°C, the cycle is 2 hours, and the yield is 2.8 About% (except for moisture).
Saussurea lappa clarke herbal oil
The raw material is crushed to 60 mesh, the extraction pressure is 28MPa, the temperature is 32°C; the separation I pressure is 6MPa, the temperature is 45°C; the separation II pressure is 5MPa, the temperature is 25°C, the cycle time is 1.5-2 hours, and the yield is 3%.
Houttuynia herbal oil
Respectively steam distillation method, organic solvent extraction method, and supercritical CO2 extraction method. For the extraction experiment of Houttuynia cordata volatile oil, supercritical CO2 extraction takes the extraction pressure, temperature, and flow rate as the three parameters, and designs the three-factor four-level orthogonal test.
The raw material is crushed to 40 meshes, the extraction pressure is 20MPa, the temperature is 35°C, the CO2 flow rate is 40Kg/h, and the extraction rate is 1.76%.
Influence of different extraction methods
- Steam distillation: dark yellow color, strong smell, time 6h, extraction rate 0.042%
- Petroleum ether extraction: orange-yellow color, strong odor, time 12h, extraction rate 0.084%;
- Supercritical CO2 extraction: light yellow color, pure smell, time 1.5h, extraction rate 1.76%.
Supercritical CO2 extraction of Houttuynia cordata volatile oil is superior to the other two traditional methods in terms of color, smell, extraction rate, and time.