Solvent extraction for essential oils from flowers

What is extraction?
Solvent extraction in principle is the separation (separation) that exploit the differences in solubility properties of the individual components of a mixtures in certain types of solvents.
Examples are: a mixture of A and B would be separated using the X solvent. From the data of solubility properties, component of A is very soluble in X, while component of B is slightly soluble or even insoluble. If the X is added to the mixture of A and B which are different in nature of polarity, then the component of A will dissolve in the X, while B does not. So it will get a new mixture of A and X. The next stage is how to separate the A and X? One method is evaporation.
Extraction techniques are typically used to produce essential oils that are easily damaged by heat, in this case is the volatile oil of flowers such as jasmine, or rose. To dissolve the essential oils, then a chemical compound is required which is typically and non-polar. Why do non-polar? Fresh flowers naturally contain water. In the concept of chemical bonding, the water is polar. Well, if you use a polar compound such as alcohol, of course, water also contained in the raw materials will dissolve into the alcohol and thus require a more complex separation process. But if used non-polar compound so water will not dissolve into it.
There are many types of non-polar organic compounds, but the most commonly used is hexane (C6H14) although you can also use benzene (C6H6) or also petrol / gasoline. There are several criteria in choosing a solvent for extraction of flowers in addition to its non-polar. Among them are its ability to dissolve fragrant substances in the raw material perfectly, has a low boiling point and uniform, are "inert" or do not react with aromatic substances that will be extracted, the lowest price possible and easy to obtain.
The final product using the this type of extraction are of two kinds, namely concrete and absolute. Concrete is an essential oil which is mixed with a wax / resin and the residual solvent. When the extraction process takes place, not only essential oils are dissolved, but also wax / resin come into it. Concrete shaped like a semi-solid fat or butter. While the absolute is a pure essential oil without impurities such as wax / resin and the residual. Absolute is the most expensive price.
There are also other concepts that are not less important, ie vacuum evaporation. Vacuum conditions are defined as conditions under atmospheric pressure (below 1 atm / normal pressure). So the combined meaning is the process of solvent evaporation on the conditions under normal pressure.
Why should a vacuum?
The ultimate goal is to reduce the boiling point of the solvent so that the overall process temperature become low. The lower pressure, so the temperature of process is also lower. For example; hexane at normal pressure (1 atm) has boiling point at 68 Celcius degree, at a pressure of 0.7 atm, its boiling point is 58 Celcius degree, and at a pressure of 0.2 atm, its boiling point 25 Celcius degree. These conditions are expected in the extraction of essential oils from flowers in order to obtain good quality oil. It means the damage caused by essential oils of high temperatures can be avoided. While other purpose vacuum conditions is to assure that the solvent can be separated as much as possible. To maintain the vacuum needed a tool to support the vacuum pump. The most common problem emerging from this method is the stability of vacuum pump performance.

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