I have done so much supercritical carbon dioxide extraction before, but I haven't explained the supercritical fluid I know clearly ~ ~
What is supercritical fluid ~ ~
Simply put, it is a fluid that exceeds the critical point ~
The following figure is a three-phase diagram of a substance, which has three states (solid, liquid and gaseous). The critical point is the point where the critical temperature and pressure of the substance exist (the point where liquid and gaseous exist), while the state exceeding the critical temperature and pressure is called supercritical state, which has the properties of liquid and gaseous at the same time, that is to say, supercritical teta will have high diffusivity of gas and high solubility of liquid, so,
Every fluid will have a critical point ~ ~
However, not all fluids are used for extraction ~ ~
Fluid may be safe in normal state, but it may not be safe in supercritical state ~ ~
For example: water ~ ~
Under normal conditions, it is very safe to use it in solid, liquid or gas, but when it reaches supercritical water, it is a highly oxidizing fluid, and it is often found to be used to treat waste (soil metal or waste liquid). So no matter what kind of fluid is used, it is necessary to know whether its characteristics are appropriate.
Supercritical carbon dioxide is widely used in extraction. Carbon dioxide is a nonpolar substance, so most of it is used to extract essential oil. In historical data, it is the first time to use microextraction to remove caffeine from coffee beans. Caffeine is a polar substance (water soluble). Traditional extraction methods use solvents to remove caffeine, and organic solvents were listed as prohibited objects in the early stage of the European Union. So supercritical carbon dioxide was developed to extract caffeine, but the problem came ~
The aroma in coffee beans will be lost with carbon dioxide (dissolved in carbon dioxide), and caffeine is unlikely to be dissolved in carbon dioxide. How to remove coffee without retaining aroma?
Scientists add water (cosolvent * * * solvent) in the extraction process, but the aroma will also dissolve in carbon dioxide. Therefore, a separation procedure is carried out, in which the water dissolved with caffeine is separated from the carbon dioxide dissolved with aroma for the first time, then the carbon dioxide with aroma is re-injected into the coffee beans, then the carbon dioxide and coffee beans are separated from the aroma for the second time, and then the carbon dioxide is recycled.
In the above process, we will find that supercritical fluid is not difficult, and everything is just a phase change. As long as we understand the basic physical characteristics of supercritical fluid, we can use it in many technical applications.
I knew there was nothing in supercritical technology. There is only one way, that is, to do the experiment by yourself and stick to it. There is no other way to learn more than to find out what I have learned. Of course, I also thank my colleagues, because I only have the opportunity to do it if they are unwilling to do it ~
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