When the solid-phase materials are extracted by supercritical fluid extraction process, the extraction kettle needs to repeat the operation of "loading- gas filling - boosting - running - decreasing - pressure - gas release - unloading - recharging"; while the supercritical fluid extraction of liquid-phase materials is different, it can adopt continuous extraction, and the process has obvious advantages. The process flow of supercritical CO2 extraction of liquid-phase materials has the following characteristics.
1) The extraction process is continuous
Since both the extracted material and the target product are liquid, there is no problem of solid material feeding and slagging, the extraction process can be operated continuously, which greatly improves the extraction efficiency of the device, correspondingly reduces the energy and gas consumption in the process, and reduces the production cost.
2) Extraction - distillation process integration
Liquid phase mixture extraction and separation can basically be processed by continuous countercurrent supercritical extraction device. Its technical characteristics are the coupling of CO2 extraction and distillation, effectively play the separation role of the two, realize the integration of extraction process and distillation process, and can continuously obtain high purity products.
The common supercritical CO2 extraction process for liquid-phase materials is mainly in the form of single-stage and multi-stage counter-current extraction. Since supercritical extraction of natural products, in many cases, involves a separation system that is a mixture of liquid phases, and the separation goal is to obtain high purity components, it is usually necessary to choose single-stage or multi-stage counter-current extraction to achieve this, depending on the target components to be extracted. The single-stage and multi-stage countercurrent extraction processes are mainly divided according to the mode of reflux provided in the fractionation column.
I. Single-stage extraction and separation
In the continuous supercritical fluid countercurrent extraction process, the liquid phase material to be separated is pumped into the fractionation tower, and supercritical CO2 enters the fractionation tower from the appropriate position at the bottom of the tower, and the separated material is in contact with the fluid, and the packing in the tower provides good contact conditions for the two phases of material to improve the separation effect. The process flow is similar to the traditional distillation process, that is, the top of the tower extracted part of the tower from the top back to the fractionation tower to form a reflux, repeated extraction, extraction is completed, the extracted phase and the extracted residual phase are removed from the tower, the resulting extracted phase needs to do further separation to precipitate the extracted material and recover the extractant. The single-stage extraction and separation flow chart is shown below.
II. Multi-stage extraction and separation
This process is the use of supercritical fluid solubility can be adjusted to establish a temperature gradient in the fractionation tower to achieve multi-stage extraction separation. When the fluid flows upward during extraction, the temperature gradually increases along the high direction of the tower, the fluid density becomes smaller, the solubility decreases, the components dissolved by the fluid precipitates along the high direction of the tower, forming a graded reflux in the tower, after the completion of the extraction process, the fractionation tower outflow of the liquid phase material extraction products, by lowering the pressure or heating, due to the fluid's solubility decreases and precipitates the extract, in the continuous separation by the separator, to obtain the target extraction material, multi-stage extraction and separation process is shown in the following figure.
