1.The effect of extraction pressure
Extraction pressure is one of the important parameters affecting supercritical CO2 extraction, and its influence on supercritical CO2 extraction is mainly achieved by changing the density of CO2. Because the dissolving ability of supercritical CO2 is proportional to its density. As the extraction pressure increases, the density of supercritical CO2 increases, its solubility for solutes also increases significantly, and the extraction rate increases significantly. In the vicinity of the critical pressure, a small change in pressure will cause a sharp change in density. However, with the increase of extraction pressure, equipment costs and operating costs also increase accordingly. Therefore, the selection of extraction pressure should comprehensively consider these factors.
2.The effect of extraction temperature
Extraction temperature is another important influencing factor of supercritical CO2 extraction, and its influence is more complicated. On the one hand, when the temperature is increased under a certain pressure, the molecular spacing of supercritical CO2 as the extraction solvent increases, the intermolecular force decreases, the density decreases, and its solubility decreases accordingly, which is not conducive to extraction; on the other hand, increasing the The temperature will increase the volatility of the solute, increase the vapor pressure, increase the diffusion coefficient, accelerate the thermal motion of the molecules, and increase the chance of intermolecular association. thereby speeding up mass transfer. good for extraction. Therefore, the effect of temperature on supercritical CO2. extraction depends on which of these two aspects is dominant at the current extraction pressure. When the pressure is high, the density of supercritical CO2 is very large, and the compressibility is very small, and the positive and negative effects on the extraction effect caused by heating can be basically offset. When the pressure is low, the increase of solute vapor pressure and the increase of extraction diffusion coefficient caused by temperature rise, the progress of the process is not enough to compensate for the decrease of supercritical CO2 dissolving ability, so it is not conducive to the extraction process.
3.The effect of carbon dioxide flow
CO2 flow is a parameter that must be paid attention to in actual extraction production. On the one hand, with CO2 When the flow rate increases, the residence time of CO2 becomes shorter, the contact time with the material will decrease, and the extraction effect will be reduced. Achieving, at this time, the use of excessive traffic flow does not make much sense. On the other hand, with the increase of CO2 flow, mass transfer is accelerated, which is beneficial to extraction. In practical applications, the flow rate of an extraction process can be determined according to the principles of cost and efficiency.
4. the effect of extraction time
The extraction yield and extraction time curve of supercritical carbon dioxide extraction of different samples is different, which is related to factors such as the form of the raw material, the content of the solute in the raw material and the solubility of the solute in supercritical CO2. Generally, with the increase of extraction time, the extraction yield increases, but with the extension of time, the increase of extraction yield becomes slower and slower, and at the same time, it consumes a lot of energy and is uneconomical. Therefore, it is necessary to choose a suitable extraction time.
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