Physical properties of raw materials
The physical properties of raw materials mainly refer to water content and crushing particle size.
The study found that the moisture content of the material has a certain degree of influence on the extraction rate of supercritical fluid.
A certain amount of water is dissolved in the supercritical CO2 fluid and acts as an entrainer, which is beneficial to the improvement of extraction rate and extraction rate.
However, when the water content is high, it is easy to form a continuous-phase water film on the surface of the raw materials, which is not conducive to the dissolution of solutes and makes supercritical fluid extraction difficult.
In addition, when the moisture content is too high, the moisture entrained in the CO2 fluid will freeze when the CO2 is cooled, causing the pipeline to “freeze” and affect the continuous extraction.
What is the optimal moisture content of the raw material for supercritical CO2 extraction?
Studies have shown that: 5% to 7% of the water content in the raw materials has the highest extraction rate in the Supercritical CO2 extraction process.
Particle size of raw materials
Under the same conditions as other extraction conditions, the particle size of the raw materials has an important impact on the Supercritical CO2 extraction process.
Generally speaking, the smaller the particle size of the raw material, the larger the contact area between the supercritical fluid and the material, the higher the probability of breaking the wall of the raw material, and the lower the internal mass transfer resistance, which is beneficial to increase the extraction rate.
However, if the particle size of the raw material is too small, the bulk density will increase, which increases the external mass transfer resistance, and the mass transfer diffusion coefficient is small. It is also possible that the raw material will quickly become agglomerated under pressure, which will easily cause blockage of the gas path and make it impossible to continue. Extraction, thereby affecting the extraction effect.
What is the optimal granularity of the raw material for CO2 extraction?
The choice of particle size is also related to the raw material itself. For example, wheat germ may be loose in texture, and the particle size does not basically affect the extraction rate. For raw materials, the particle size is relatively small (40~60 mesh).
However, experimental studies have found that in the process of extracting vegetable oils, due to the high oil content of the raw materials, it is difficult to crush, the particle size is large, the wall breaking effect cannot be achieved, and the extraction rate is low;
If the particle size is too fine, it is easy to agglomerate during the crushing process, and cannot be sieved, which also affects the extraction effect. Therefore, the actual control of the raw material particle size is also difficult.