Extraction process technology of traditional Chinese medicine

Different leaching methods can be used based on production scale, solvent type, medicinal properties, and dosage form.

According to the method of adding medicinal herbs into the equipment, it can be divided into intermittent, semi continuous, and continuous types.

According to the different processing methods of medicinal materials in the equipment, the extraction of medicinal materials in pharmaceutical factories is often referred to as extraction, immersion (for static extraction), decoction (for water extraction and reflux), etc.

Extraction: water extraction, alcohol extraction; Dynamic and static extraction; Multi energy extraction, Soxhlet extraction, etc.

Separation: sieve separation; Centrifugal separation; Membrane separation, etc.

Concentration: Triple effect concentration; Spherical vacuum concentration; Evaporation concentration; Membrane concentration, etc.

Drying: spray drying; Vacuum drying; dry; Freeze drying, etc.

The commonly used leaching methods are summarized as follows:

(1) Boiling method:

The water decoction method using water as the leaching solvent is the most commonly used method.

The decoction method is suitable for medicinal herbs whose active ingredients are dissolved in water and are relatively stable to both moisture and heat. This method is simple and easy to implement, and can extract most of the effective ingredients. It can be used not only as a decoction, but also as a semi-finished product for further processing into various dosage forms.

Disadvantages: There are many impurities in the decoction, which are prone to mold and decay. Some heat-resistant and volatile components are easily destroyed or lost during the decoction process.

Boil the medicinal residue 2-3 times according to the law.

When using alcohol as the leaching solvent, the reflux extraction method should be employed.

(2) Immersion method:

It refers to the method of adding an appropriate amount of solvent to the extracted medicinal materials in the extractor, and using a certain temperature and time for extraction, so as to extract the effective ingredients and separate the solid and liquid.

According to different extraction temperatures, it can be divided into room temperature immersion method and warm immersion method.

The room temperature immersion method is traditionally used for the extraction of medicinal wine and tinctures, and its clarity has long-lasting stability.

② Warm soaking method refers to the heating soaking method below the boiling point, which is a simple and enhanced extraction method, generally using a jacket or a snake tube for heating.

The soaking time of medicinal wine is relatively long, and its room temperature soaking is mostly more than 14 days; But the time for hot impregnation (40-60 ℃) is generally 3-7 days. In order to reduce the loss of components caused by the absorption of drug residue, multiple impregnation methods can be used.

The immersion method is suitable for the extraction of viscous, unorganized, fresh, and easily swollen medicinal materials, especially for medicinal materials where the active ingredients are easily volatile or destroyed when exposed to heat.

Disadvantages: Long operation time, large solvent consumption, and often poor leaching efficiency, making it difficult to completely leach. Therefore, it is not suitable for the extraction of valuable medicinal materials and medicinal materials with low content of active ingredients.

(3) Percolation method:

• Refers to the method of extracting effective ingredients from moderately crushed medicinal herbs in a percolator, where the solvent continuously added from the upper part permeates through the layer of medicinal herbs and flows out from the bottom to extract the percolate.

During percolation, the solvent infiltrates into the cells of the medicinal material and dissolves a large amount of soluble substances, resulting in an increase in concentration and relative density, and then moves downwards. The upper layer is replaced with leaching solvent or diluted leaching solution to create a good concentration difference inside and outside the cell wall, allowing diffusion to occur naturally.

Therefore, the percolation method belongs to the dynamic extraction method, and the extraction efficiency is higher than that of the immersion method.

The percolation method has high requirements for the particle size and process conditions of medicinal materials. Improper operation can affect the percolation efficiency and even affect normal operation.

The general outflow rate of percolate is1000gCalculation of medicinal herbs.

Slow leaching at a rate of 1-3ml/min is recommended.

The rapid leaching rate is usually 3-5ml/min.

During the percolation process, it is necessary to replenish the solvent at any time, and the amount of solvent used is generally 1: (4-8) (medicinal powder: leaching solvent).

Strengthening measures: such as using a vibrating percolation tank or adding an ultrasonic device on the tank side (the tank body is supported by a spring around the tank with legs, and a vibrator is fixed at the bottom of the tank), or using a tank group counter current percolation method to enhance the relative motion between the solid and liquid phases and improve the percolation effect. This method uses liquid column static pressure to make the solvent flow upward from the bottom and the percolation liquid flows out from the upper opening.

(4) Reflux method:

The method of heating extraction involves evaporating the solvent, condensing it, and then flowing back to the extractor, repeating this process until the extraction is complete.

The solvent can be recycled and is suitable for extracting volatile (low boiling point) solvents.

The continuous circulation reflux cold soaking method involves the solvent evaporating, condensing and flowing into the storage tank, and then entering the extractor through a valve for cold soaking.

(5) Steam distillation method:

This method is applicable for the extraction and separation of chemical components that are volatile, can be distilled with water vapor without being destroyed, and are difficult to dissolve or insoluble in water, such as the extraction of volatile oils.

(6) Supercritical fluid extraction method:

Supercritical fluid (SF) refers to a fluid in which a certain gas (or liquid) or gas (or liquid) mixture has a density close to that of a liquid and a diffusion coefficient and viscosity close to that of a gas when the operating pressure and temperature are both above the critical point. Its properties are between gas and liquid. SFE technology is a technique that uses supercritical fluid as a solvent to extract certain effective components from solids or liquids and separate them.

Gases that can be used as supercritical fluids include carbon dioxide, ethylene, ammonia, nitrous oxide, monochlorotrifluoromethane, dichlorodifluoromethane, etc.

Carbon dioxide is chemically inert, non-toxic, non explosive, with a low critical pressure (7.374MPa) and a critical temperature close to room temperature（31.05℃）Due to its low cost and easy availability, carbon dioxide is commonly used as a supercritical extractant.

(7) Ion exchange and macroporous resin adsorption:

Purification and extraction method for concentrating and separating effective components from dilute solutions obtained by other extraction methods through ion exchange and adsorption selectivity of macroporous resin (referred to as macroporous resin)

Generally, ion exchange resins have small voids, less than 5nm, and low adsorption capacity. The pore size of macroporous resin network pores is relatively large, generally ranging from tens to thousands of nanometers, thus having a large adsorption surface area and adsorption capacity.