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Supercritical CO2 extraction of herbal oil

Forewords

Supercritical extraction 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:

Evening Primrose and Evening Primrose Oil
Evening Primrose and Evening Primrose Oil

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.

About super Critical fluid technology (SCF)

The Supercritical fluid technology is a new-type separation technology in modern chemical separation. The Super Critical extraction takes CO2 as the solvent.

As CO2 fluid under super critical state has 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, the separation of the solvent with the extracted substances is also easily.

Supercritical CO2 extraction is specially suitable for extraction of fat-soluble and heat sensitive substances with the high boiling point, and is suitable for fine separation of different components, i.e. Super critical fine distillation.

Device design and scale

The general requirements for the design of a supercritical fluid extraction device 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);

The following two points in the choice of device size:

Selection according to production object:

Supercritical extraction equipment is a general-purpose equipment for separation technology. As an enterprise, the scale should be determined according to business objectives and business scope.

Decide on device size:

Consider not only technical feasibility, but also economic feasibility.

Supercritical extraction is a 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.

Extraction kettle

According to the relevant data, PN 10.0 ~ 100.0 MPa is the high pressure.

supercritical CO2 extraction kettle
supercritical CO2 extraction kettle

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.

Aspect ratio

An important parameter of the structure of the extraction kettle is the aspect ratio.

Sealing structure of supercritical CO2 extraction machine
Sealing structure of supercritical CO2 extraction machine

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 is intermittent, while the latter can be continuous.

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.

Intermittent loading and unloading

The intermittent loading and unloading adopts 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 manual type, that is, tightening or loosening bolts and nuts one by one;

Second is 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.

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) about 5 minutes; the toothed quick-open lid device is completed An operation cycle takes about 10 minutes.

Sealing structure

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.

Pod loading and unloading of supercritical CO2 extraction machine
Pod loading and unloading of supercritical CO2 extraction machine

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.

Separator

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.

Separation can be combined with rectification, adsorption and other processes to achieve the purpose of extraction, separation and purification.

Cleaning method

There is a problem of cleaning in supercritical CO2 extraction units.

To prevent cross-contamination, cleaning of 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:

  • 1) hot alkaline water → tap water → dilute acid (such as HNO3, but not HCl) → deionized water;
  • 2) detergent (such as Nine × 24 + sodium metasilicate + potassium hydroxide + Water) → deionized water;
  • 3) any of the following solvents or a mixture of several solvents (ethanol, hexane, turpentine, acetone, gasoline, carbon tetrachloride) → deionized water;
  • 4) alcohol + Amore Niaral water + gasoline → deionized water;
  • 5) CO2 with modifier.

CO2 recovery

A major advantage of supercritical CO2 extraction 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 pressure balance method.

The high-pressure CO2 in the system is sent to the CO2 storage tank with 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.

CO2 emissions

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 form 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.

Energy consumption

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.

Several noteworthy issues

Maximum working pressure

Supercritical CO2 extraction device management and operators should have the necessary basic knowledge of pressure vessels, make clear the difference between working pressure and hydrostatic test pressure, it is strictly forbidden to perform production operation exceeding the allowable pressure on the extraction kettle device with the maximum working pressure.Otherwise it is very dangerous.

The “Regulations on the Safety Management of Pressure Vessels” issued by the Ministry of Labor of China not only needs to be learned by designers, but also by users. Operators should be certified to work.

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 a dual Insurance.

Cosolvent

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 entrainers containing halogen ions, and entrainers containing ions sensitive to stress corrosion (such as Cl-, OH-, etc.).

However, stress-stressed parts (such as near the weld) may cause stress corrosion.

Archives

Industrial production is different from laboratory tests.

The actual records of the production process and the equipment operation records should be separated, and the technical archives and use management archives should be done well.

During the production process, in order to prevent the trace moisture or impurities in CO2 from being blocked due to throttling and freezing when the high-pressure system is depressurized, the selection of process conditions must be fully weighed and reasonably set.

Abnormal system pressure in production is often caused by blockages.

Technological process of a product

The supercritical CO2 extraction method has a simple process, and workers often simply look at the strictness of the operation during production, which results in fluctuations in production levels and unstable product quality.

For example, in the process of temperature swing separation, in a certain pressure range, the air pressure of the solute plays a leading role, and the temperature increases, and the solubility increases;

Within a certain pressure range, the density of the supercritical fluid plays a leading role, and the temperature increases, and the solubility decreases.

This requires the operator to correctly grasp the technological process of a product.

Final words

Supercritical CO2 extraction has potential applications in Chinese herbal medicine.

In general, low-polar compounds such as esters, ethers, lactones and oxygenates in Chinese herbal medicine components are easier to extract, especially Several aspects should be strengthened:

Certain natural compounds with chiral carbon atoms, because of their optical activity, are easily prone to isomerization when they encounter acids or bases during extraction and separation.

The result not only changes its optical rotation, but also its physiological activity is unavoidably affected. If these compounds are partial lipids, they are more suitable for extraction with supercritical CO2.

For example, many monoterpenoids in Chinese herbal medicine (and marine life) Belongs to this column.

It is of great significance to extract active ingredients with anti-cancer effects from plants in nature.

The use of supercritical CO2 extraction will be more conducive to maintaining its physiological activity, such as the extraction of podophyllotoxin from plants of Podophyllum; Extraction of elemene; extraction of vinblastine from vinca, etc., they all have the effect of inhibiting the proliferation of cancer cells.

The composition of Chinese herbal medicines is complex, and the characteristics of the chemical constituents in the same flavor are different, such as the polarity, boiling point, molecular weight, solubility and other characteristics.

There is much to be done to make full use of Chinese herbal medicine resources….

Photos of Herbal Oil Supercritical CO2 Extraction Machine