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Supercritical fluid extraction technology, referred to as SFE, is a relatively advanced and commonly used physical extraction technology. The principle is that when the temperature is controlled in a lower range, the gas is converted into liquid by increasing the pressure of the gas. In this process, as the pressure increases, the volume of the liquid gradually increases.But for some specific substances, when the temperature and pressure reach a certain point, no matter how high it is, the substance will not continue to transform into liquid or gas. This point is the critical point. The temperature and pressure at this time It becomes the critical temperature and critical pressure.In the range above the critical point, the state of matter between gas and liquid is a fluid, that is, a supercritical fluid.Compared with the initial state of the substance, supercritical fluid not only has the permeability of gas, but also has the high density and solubility of liquid. It has a larger diffusion coefficient and strong dissolving ability. It can dissolve and separate many substances. As a good solvent for extraction and separation.The supercritical fluid extraction is to use its strong solvency to contact the substance to be separated, and extract the components in the order of polarity, boiling point, and molecular mass.
As a high-tech, supercritical fluid extraction combines traditional distillation and organic solvent extraction, which is highly efficient and natural. There are many substances that can be used as supercritical fluids, such as carbon dioxide, ethane, ammonia, etc., but carbon dioxide is the most common.On the one hand, the critical temperature and critical pressure of carbon dioxide are relatively low. It is relatively stable during use, is non-toxic, does not cause combustion, and will not produce chemical substances to pollute the environment. It can be described as 100% pure natural and can avoid products Oxidation occurs.On the other hand, carbon dioxide can be regarded as an organic solvent similar to water, which requires milder operating conditions and will not cause serious damage to the active ingredients.In addition, when using carbon dioxide for extraction, the extracted substances can be extracted by simply changing the pressure and temperature, without repeated extraction operations, and the extracted extract does not contain nitrates or other The harmful heavy metals are suitable for extracting and fractionating heavy oil.In addition, relatively speaking, the price of carbon dioxide gas is relatively cheap, but it can achieve high purity, is easy to prepare, can be recycled, and saves a lot of cost.
Of course, the extraction operation using carbon dioxide as a supercritical fluid is not effective for all substances.In the field of petroleum processing, considering that the chemical components contained in petroleum are relatively complex, supercritical fluids with stronger dissolving power are required as solvents.Studies have shown that the critical pressure point of light hydrocarbons such as ethane and propane is significantly lower than that of carbon dioxide, which helps to save costs. Therefore, workers usually choose light hydrocarbons as supercritical fluid solvents to separate oil products.If the relative molecular mass and boiling point of the heavy petroleum oil to be separated are low, propane can be used as the supercritical solvent. If the component of the heavy oil contains greater polarity and higher boiling point, then butane or pentane Is the best choice.