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1. Extractor 2. Pressure control 3.Separator A.Condenser 5.Temperature control P1. CO2 diaphragm pump P2,P3. EntraƮner pumps

Figure 1. Schematic diagram of a supercritical fluid extraction unit

In the extractor, solid as well as liquid materials may be treated. The solid material is introduced in a basket with two filter elements at both ends. The liquid material may be pumped through the valve V-7. Stirring of the material may be done through a magnetic stirrer or a stirrer with double mechanical seal.

The pressure control of the extractor is achieved by a pressure controller. The gas from the extractor contains the extracted solute. The extract is separated in the separator either by reducing the pressure or by increasing the temperature. Two hand valves V-18 and V-19 are installed for the removal of the extract in case of batch extraction of solid materials.

The evaporated carbon dioxide from the separator is condensed in the precondenser and stored at low temperature in the condenser vessel. The pressure in the condenser is kept constant by a refrigerator.

Process conditions most widely recommended for supercritical extraction with respect to the extracting fluid are:

Extraction

Separation

T = (1.3 to 1.5)TC P = P separation or P = (0.5 to 2)PC

The separation process is essentially determined by the capacity and selectivity of the extracting supercritical fluid and their dependence on temperature and pressure. The superficial velocity of the extracting agent, the pressure and temperature in the separator and the time of extraction are the other variables which affect the extraction process.

Figure 2 presents a flow sheet for a multiextractor unit with parallel feed of supercritical carbon dioxide. The separation is done in two stages by using two separators in series. Thus, the components which have lower solubility at intermediate pressure are separated and the remaining solute is separated in the second separator. The fractionation of volatile oil from oleoresin can be obtained in this manner for spice extraction.

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