What are the characteristics of solvent extraction, steam distillation and sublimation? use

Solvent extraction generally refers to the method of extracting effective components from Chinese herbal medicines. According to the solubility of various components in Chinese medicinal materials in solvents, the solvent with high solubility for active components and low solubility for components that do not need to be dissolved is selected, and the method of dissolving effective components in medicinal tissues is called solvent extraction. When solvents are added to Chinese herbal medicines, the solvents will diffuse. Infiltration penetrates into cells through cell walls, dissolving soluble substances, resulting in concentration difference inside and outside cells. The concentrated solution in the cell keeps spreading outward, and the solvent keeps entering the drug tissue cells many times. When the concentration of solution inside and outside the cell reaches a dynamic balance, the saturated solution is filtered out, and then a new solvent is added to make most of the required components dissolve out.

Selection of solvents

Common solvents can be divided into three categories:

① Water is a strong polar solvent.

② hydrophilic organic solvent.

③ lipophilic organic solvent.

The lipophilic order of common solvents is (opposite hydrophilicity): petroleum ether >; Benzene >; Chloroform > ether > ethyl acetate >: acetone >: ethanol > methanol.

Choosing the right solvent is the key to solvent extraction.

(1) solvent has high solubility for active components and low solubility for impurities.

(2) The solvent can't change chemically with the components of traditional Chinese medicine.

③ The solvent should be economical, easily available and safe to use. Commonly used extraction methods include impregnation, percolation, decocting method, reflux extraction and continuous extraction.

Classification of solvent extraction methods:

Solvent extraction can be divided into cold extraction and hot extraction.

1. Cold formula

(1) impregnation method

This method is simple and feasible, but the leaching rate is low. If water is used, pay attention to anticorrosion.

(2) percolation method

The concentration difference is formed between the upper and lower parts, and the leaching effect is better than that of impregnation method.

2. Thermal method

(1) decocting method

The earliest traditional leaching method used in China is suitable for water extraction.

(2) Reflux method

Suitable for organic solvent extraction, filtration and solvent recovery.

(3) continuous extraction method

There is no need for filtration in the middle, and the amount of solvent is small.

Steam distillation refers to the extraction method of distilling medicinal materials containing volatile components with water, so that the volatile components are distilled with steam and separated by condensation. This method is suitable for the extraction of volatile medicinal materials, which can be distilled by steam without being destroyed, stable in water and insoluble or insoluble in water. Steam distillation can be divided into water distillation, steam distillation and water distillation. In order to increase the concentration of distillate, it is usually necessary to redistille the distillate or redistille it with salt. Common equipment is multifunctional extraction tank and volatile oil extraction tank, which are widely used in production activities.

Steam distillation refers to soaking crude powder or decoction pieces of medicinal materials containing volatile components, directly heating distillation or introducing steam distillation, or decocting and distilling medicinal materials in a multifunctional Chinese medicine extraction tank. The volatile components in the medicinal materials are distilled by steam, and the distillate is collected after condensation, which generally needs to be distilled 1 time to improve the purity and concentration of the distillate, and finally a certain volume of distillate is collected; However, the distillation times should not be too many to avoid oxidation or decomposition of some components in the volatile oil. The basic principle of this method is that, according to Dalton's law, the total vapor pressure of immiscible and chemically inert liquid mixtures is equal to the sum of saturated vapor pressures of each component at this temperature (that is, partial pressure). Therefore, although the boiling point of each component itself is higher than that of the mixed liquid, when the total pressure is equal to atmospheric pressure, the liquid mixture begins to boil and be distilled out.

Steam distillation is only suitable for extracting volatile components that can be distilled by steam without being destroyed, not reacting with water, and insoluble or insoluble in water. Most of these components have boiling points above 100℃, are immiscible or slightly soluble in water, and have a certain vapor pressure around 100℃. Heated with water, when the sum of its vapor pressure and the vapor pressure of water is one atmosphere, the liquid begins to boil, and the vapor takes away the volatile substances. For example, volatile oil in Chinese herbal medicine, some small molecular alkaloids-ephedrine, alkaloids, arecoline, and some small molecular phenols. Paeonol and so on. It can be extracted in this way. Some volatile components are slightly soluble in water, so the distillate is often redistilled to separate the volatile oil layer in the initial distillation part, or the components are extracted from the distillate water layer by salting-out method and low boiling point solvent.

1, principle of steam distillation.

Perfume and water constitute an immiscible system of essential oil and water. When heating, with the increase of temperature, essential oil and water will evaporate rapidly to produce mixed steam, which will be introduced into the condenser through the gooseneck at the top of the pot to obtain a liquid mixture of water and essential oil, and the essential oil product can be obtained after oil-water separation.

2. Distillation.

Distillation in water: put the raw materials in a sieve plate or directly into a distillation pot. Soak the material layer in the pot with water and heat the bottom of the pot.

Water distillation: (waterproof distillation) Raw materials are placed in sieve plates, and the amount of water added to the pot should meet the distillation requirements, but the water surface should not be higher than the sieve plates, so as to ensure that the material layer is not wet when water boils and evaporates. Generally, reflux water is used to keep the water in the pot constant to meet the sufficient saturated steam required for steam operation, so a mirror can be installed at the bottom of the pot to observe the water level.

Direct steam distillation: a circular tube with holes is installed under the sieve plate, and external steam is directly ejected into the sieve hole to heat raw materials, but the water dispersion effect is not sufficient, so it is necessary to disperse water outside the pot in advance, and the distillation speed in the pot is fast, so it is easy to change to pressurized distillation.

Water diffusion steam distillation: this is a new distillation technology applied abroad. Water vapor enters from the top of the pot, gradually permeates into the material layer from top to bottom, and pushes out the air in the material layer at the same time, so that the dispersed and mass-transferred essential oil can enter the bottom condenser of the pot without being completely gasified. The steam is percolation type, and the distillation is uniform, consistent and complete. The water-oil condensate quickly enters the condenser, and the obtained essential oil has better quality, higher yield, lower energy consumption, short distillation time and simple equipment.

Distillation is a common method for separating and purifying liquid mixtures, and it can also determine the boiling point of liquid compounds, so it is of certain significance for the identification of pure liquid compounds.

Substances that are azeotropic with water should be distilled by steam.

Sublimation means that a solid substance becomes a gas directly without passing through a liquid phase. Camphor, iodine, naphthalene, etc. It's easy to sublimate.

At room temperature, the intersection of Clapeyron curve and the melting point and boiling point of iodine is closer to the origin, in other words, under the same pressure, temperature has a rapid influence on its material state.

If it is ultra-low temperature, such as industrial dry ice purification, it is obtained by heating and sublimation with solid air.

Attention should be paid to proper temperature control during sublimation, and the receiving device should have a certain condensation effect and can discharge condensate in time.

If it is a laboratory method, it is only necessary to collect it at the bottom of the round-bottomed flask with cold water, and it is also necessary to pay attention to the moderate opening of the sublimation container, and it is best to heat it in a water bath for the experiment.