It is well known that supercritical fluids have been widely used to extract some substances or analytes from various solid materials, including oils. Even, supercritical fluids can be used to extract unknown natural products from various matrices. Supercritical carbon dioxide (SCO2) is the most commonly used medium because it can be carried out at low temperatures with a critical point of about 311 °C (TC, critical temperature) and 74 MPa (P C, critical pressure). This makes SCCO 2 a suitable medium for the extraction of natural substances, which are often thermally unstable compounds.
Carbon dioxide is the first choice for medium, which is safe, safe, tasteless, colorless, non-flammable and non-toxic. Similar to other fluids, under supercritical conditions, CO2 has a gas-liquid viscosity, gas-like diffusivity, and liquid-like density. As a result, SCC2 can be used as a liquid or gas and is a good medium for the extraction of a wide range of substances from a variety of solid matrices.
In addition, CO2 is gaseous under ambient conditions;Therefore, once the extraction process is complete, CO2 can be easily and completely separated from the product by decompression. Due to these characteristics, in this work, SCCO 2 is used as a medium for extracting oil from waste white clay (SBE), which is the waste of vegetable oil refineries.
White clay is known as a clay that is rich in minerals that can be used in filtration, adsorption, or bleaching processes. As one of the steps in the vegetable oil refining process, in the bleaching process, raw bleached earth is added to edible crude oil as the most commonly used adsorbent to eliminate unwanted substances. It can adsorb heavy metals, chlorophyll, carotene, hydroperoxides, free fatty acids and non-glyceride substances in gross edible oil. Therefore, the addition of bleached earth can improve the appearance of the final oil product. It also improves the stability, taste, and flavor of the final oil product. However, after the bleaching process, the spent bleached soil is often disposed of directly to landfills without any proper treatment, leading to many environmental problems such as pollution hazards and disasters. Therefore, one of the challenges after the bleaching process is that the SBE must be disposed of again so that it can be safely landfilled.
There are several techniques for extracting oil from solid substrates, namely mechanical, biological, and chemical, and each has advantages and disadvantages in the oil extraction process. Mechanical technology is considered to be the most traditional technique for extracting oil from a solid matrix, in which the oil is extracted with force, usually under the application of high pressure. This extraction technique is simple, relatively inexpensive, and does not pose the possibility of contamination by chemical solvents. However, oil production is relatively low, and the extraction process requires a lot of time and labor. In biotechnology, active substances (enzymes) are used to release oil from a solid matrix. It is known to be eco-friendly.
However, this extraction technique is costly and observed to be more time-consuming. Other techniques are chemical techniques (solvent extraction). While chemical extraction techniques are mostly widely adopted and the operating conditions are simple and gentle, contaminating residues or harmful substances may be produced due to the use of toxic solvents. In addition, solvent extraction techniques often have the limitations of long extraction times and high solvent requirements. To overcome these limitations, SCCO 2 extraction technology is used as an alternative innovation to extract oil from the SBE solid matrix. However, CO2 is less polar]. When SCCo2 is used to extract more polar substances, the extraction process will be ineffective. Therefore, a small amount of organic solvent is added as a co-solvent to improve the CO2 solubility. In this work, ethanol was chosen as the co-solvent. This organic solvent is often used as a co-solvent due to its low toxicity and can improve the extraction capacity of polar substances.
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