As a green technology, supercritical CO2 extraction has widely applied in extraction of natural materials. The annual production capacity ranges from hundreds of tons to tens of thousands of. However, the separation efficiency of supercritical CO2 extraction is very low, especially for mixtures with small different properties of composition, because it is only one stage separation. Continuous countercurrent supercritical CO2 extraction (CC–SCE) is a multistage separation process, which enables isolation and purification of components with very similar properties. But, CC-SCE is far behind the development of supercritical CO2 extraction technology.
This paper introduced CC-SCE’s process and its application in concentrating paprika pigment in terms of industrial scale. The prospect of CC-SCE was also made in other applications, like purification of ginger oil, tocopherol and citrus oil etc.Key words: supercritical CO2; countercurrent extraction; natural material.
• Oleoresin capsicum: (3.0- 8.0 % capsaicin w/w) obtained from the longer, moderately pungent Capsicum used in the production of red pepper. Commercial red pepper oleoresins are mainly used as a spice supplied in pungency ratings between 80 000 and 500 000 Scoville units. In the market place practice has shown that 1 kg of 200 000 Scoville units oleoresin replaces 10 kg of good quality red pepper.
• Paprika extract: (equivalent to 10.8% total carotenoids) obtained from varieties of C. annuum from which paprika powder is produced. It has a high colour value, but little or no pungency. Commercial paprika oleoresin is available in different colour strengths up to 150 000 colour units. In the market place practice has shown that 1 kg of paprika extract replaces 12-15 kg of paprika powder with respect to colour intensity.
The countercurrent extraction process in the tower equipment is a differential contact extraction process, and the CO2 phase fills the entire column.
Continuous phase, the raw materials are distributed in the continuous phase in the form of droplets, which is a dispersed phase.
The CO2 phase is added from the bottom of the tower and led out from the top of the tower; the raw materials enter from the top of the tower or the side of the tower, and the raffinate is collected from the bottom of the tower.
At the same time, in the presence of a temperature gradient, the solute can form an internal reflux, like distillation.
After multi-stage equilibrium of dissolution-precipitation-dissolution, the solute comes out of the column with CO2 into the separator and is collected separately.
Feeding and discharging are realized by high-pressure pump and valve automatic control. Due to the continuous operation of the extraction process, the equipment processing capacity is greatly increased, the process energy and gas consumption are reduced, and the production cost is reduced.
In addition, the materials and supercritical CO2 pass through the packing in the tower. Or the plate is used for mass transfer, and the number of theoretical plates is high, which can achieve effective separation and purification of the mixed solution with small separation factor and difficult to separate.
RESEARCH ON COUNTERCURRENT EXTRACTION PROCESS
Shi Bingjie used methylated soybean oil deodorized distillate as raw material, studied the process route of CC-SCE concentration of natural vitamin E, and discussed the effects of temperature, pressure, filler height and other factors on the extraction process.
When the raw material feed rate is 0.02 kg / h, the extraction pressure is 20 MPa, the extraction temperature gradient is 40-45-50-60-70 ℃, and the gas-liquid ratio is 80 kg / kg under the experimental conditions, the mass fraction of vitamin E And the yield reached 24.3% and 81.5%, respectively. When using double-column continuous countercurrent operation, the natural vitamin E mass fraction increased to about 54%, and the yield reached 95%.
The color price of raw material for capsicum pigment is 24000. Under the CO2 flow rate of 30000M3 / h M2 and the pressure is 36MPa, the color value of capsicum pigment increases by more than 6 times, up to 150,000. Compared with the results of supercritical CO2 extraction, under the same volume of autoclave and processing capacity, the countercurrent treatment time is only half of the traditional processing time, and the color value concentration multiple of the countercurrent extraction product is much larger than that of the first-stage extraction.
It can be seen that the countercurrent extraction process greatly improves the production efficiency of the equipment, reduces the production cost, and has high practical value.
Quote: Tan Huijun, Liu Wenqi, Zhao Yaping，School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China.
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