The reason why the end of the conduit should be placed near the bottom of the container is that water vapor can enter the lowest part of the liquid surface, which can fully heat the liquid and bring out the product, thus improving the distillation efficiency and yield.
If the conduit is only inserted in the upper or middle part, the heating effect on the liquid is much worse, and the product cannot be distilled completely, resulting in a decrease in output.
Steam distillation is the most commonly used method to extract natural plant spices, with mature technology, equipment and operation, low cost, large output and relatively simple equipment and operation.
Generally speaking, steam distillation is divided into three forms; Water distillation, water distillation and steam distillation. When dealing with various aromatic plants, it is often necessary to pretreat the plant raw materials before distilling the essential oil.
If it is a grass plant or the oil-producing part is flowers, leaves, buds, spikes, etc. Generally, it can be directly put into the distiller for processing; However, if the oil-producing part is rhizome, it usually needs cleaning, drying in the sun or drying in the shade, crushing and other steps.
Even after dilute acid soaking and alkali neutralization; In addition, some aromatic plants need to be fermented first. The steam distillation method is to soak the crude powder or decoction pieces containing volatile components, and then directly heat distillation or introduce steam distillation.
You can also put the medicinal materials into a multifunctional traditional Chinese medicine extraction tank for decoction and distillation, and bring out the volatile components in the medicinal materials by steam distillation. Distillate collected after condensation generally needs to be distilled again 1 time to improve the purity and concentration of distillate.
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 based on Dalton's law, that is, the total vapor pressure of an insoluble liquid mixture with no chemical effect.
It is equal to the sum of the saturated vapor pressures (i.e. partial pressures) of each component at this temperature. 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 more soluble in water, and the distillate is often distilled again.
In the first distillation section, the volatile oil layer is separated, or the components are extracted from the distilled water layer by salting-out method and low boiling point solvent. Such as rose oil, protoanemonin, etc., are often prepared by this method.
Steam distillation requires heating raw materials, so it is not suitable for extracting components with unstable chemical properties.