The supercritical CO2 fluid extraction process can be divided into three types of processes: isobaric changes in temperature, isothermal changes in pressure, and isobaric with isothermal.
The comparison of the three type co2 extraction processes is shown in the following table:
|Isobaric changes in temperature||CO2 extraction and separation are carried out under the same CO2 fluid pressure. After the extraction is completed, the temperature is increased by heat exchange. The CO2 fluid is under stable pressure, and the solubility of the fluid decreases with the increase of temperature. The solute in the CO2 fluid is separated, thereby get the CO2 extract.||The CO2 extraction pump (compressor) consumes relatively little energy||Affects heat-sensitive materials|
|Isothermal changes in pressure||The CO2 extraction and separation are carried out at the same temperature. After the CO2 extraction is completed, it enters the CO2 extraction and separation vessel by adjusting the flow rate of the CO2 fluid and reducing the pressure of the CO2 fluid. As the pressure of the CO2 fluid decreases, the solubility of the CO2 fluid to the extract gradually decreases, the solute is precipitated, and the CO2 extract is obtained.||Since there is no temperature change, the operation is simple, and the extraction of high-boiling, heat-sensitive, and easily oxidizable substances close to room temperature can be realized.||High pressure, high investment, high energy consumption|
|Isobaric with isothermal||The CO2 extraction is operated at constant temperature and pressure. The operation of the co2 extraction equipment requires special adsorbents for co2 extracting separation, such as ion exchange resin, activated carbon, etc., for exchange adsorption, which is generally used to remove harmful substances.||During operation, it is always in a critical state, so it is very energy-saving||Requires special adsorbent|
Isobaric changes in temperature method of the supercritical CO2 extraction process
The propane with CO2 dissolved in the propane storage tank is pressurized into a supercritical CO2 fluid and then enters the asphalt settler, and the raw oil also enters the asphalt settler. The temperature in the asphalt settler reaches 50 °C, and the liquid propane is at this time. It can dissolve all components in all raw oil except bitumen.
Because the viscosity of propane in this state is very small, it is easy to separate the bitumen, and the separated bitumen is discharged from the bottom of the settler.
In order to separate the wax component in the raw oil, it is necessary to use the characteristics of supercritical fluid to add CO2 to the asphalt settler, so that impurities such as wax are dissolved in CO2 in the supercritical state of CO2, and then the temperature is lowered to make the Impurities such as wax are separated out, CO2 is discharged after dewaxing, and recycled after being stored separately.
In order to separate the resin in the crude oil, the propane fluid can be heated up again through the heat exchanger to about 100°C. At this time, the dissolving ability of the propane to the resin will further decrease, and it will be separated in the resin settler and discharged from the bottom.
The oil from which the asphalt, wax and its resin are separated enters the rectification tower. After rectification, the propane discharged from the top of the tower is cooled by the condenser and then flows into the propane storage tank, and the deasphalted oil is discharged from the bottom.
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Isothermal changes in pressure method of the supercritical CO2 extraction process
Biomass and carbon dioxide gas enter into the CO2 extraction vessel together. CO2 can fully dissolve the effective components in the biomass into the supercritical CO2 fluid in its supercritical state. In the separation container, due to the sharp drop in the solubility of CO2, the effective components in the biomass are separated and discharged from the bottom of the CO2 extraction separation vessel. The CO2 gas enters the condenser and condenses into a liquid, and then is boosted to the extraction pressure (supercritical CO2 fluid) by the CO2 extraction pump, and then enters the CO2 extraction vessel for recycling.
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Isobaric with isothermal method of the supercritical CO2 extraction process
The caffeine supercritical extraction process is that the raw material of coffee beans is loaded into the extractor, and CO2 gas is introduced at the same time. In the CO2 supercritical state, the caffeine is dissolved in the supercritical CO2 fluid, and the caffeine is extracted, which will contain coffee. The extracted phase fluid of caffeine is discharged from the bottom of the CO2 extraction container and directly enters the absorption tower, and is contacted with water in a countercurrent manner to realize the mass transfer process of caffeine to water. Most of the caffeine in the carbon dioxide discharged from the top of the absorption tower has been separated and absorbed by water.
The carbon dioxide separated from the caffeine is returned to the extraction tower for repeated use, and the high-pressure water released from the bottom of the absorption tower is decompressed by the expansion valve and then enters the degasser to remove the dissolved carbon dioxide from the water phase. The degassed liquid aqueous solution enters the evaporative crystallizer, the caffeine is discharged from the bottom, and the water vapor is condensed and sent to the top by a CO2 extraction pump to be used as an absorption liquid.
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