Segregation of fish oils with liquid propane and butane.

Abstract

F ISH OIL REFINING has been studied for a long time because of the characteristics of the raw material which limit its utilization. The oil consists of a complex mixture of triglyeerides with a variety of saturated and unsaturated compounds. The high iodine value (170-200) suggests the possibility of obtaining an appropriate drying oil that could compete with those of vegetable origin. Compared with the latter, fish oils contain higher percentages of saturated (2535%) and monounsaturated (23-30%) fat ty acids. It is thus important to eliminate all or part of these components which will not allow an appropriate drying of the coating. In addition, fat ty acids are present with more than 22 carbons and up to six double bonds which oxidize easily, impairing the odor and color of the product. Fractional crystallization, remodelling, and extraction with solvents can be used for modifying the oil composition. Solvent extraction is widely applied in the petroleum industry for segregating and purifying lubricants. Among the solvents used for selective fractionation are liquid hydrocarbons, furfural, and methyl ethyl ketone. With liquid propane, the solubility of triglycerides decreases with temperature. A lower critical solubility temperature (CST) exists, above which there are two phases in equilibrium. The solubility of the components is determined by the degree of unsaturation and chain length. Hixson and others (1,2) have studied the solubility of pure triglycerides and fatty acids in liquid propane by using vegetable oils. They determined CST for different components and studied the separation of such systems as propane-abietic acidsunflower oil. Commercial separation of fish oils with liquid propane has been applied in South Africa to obtain Vitamin A concentrates (3). This study reports on the possibility of using liquid propane near its critical temperature for separating fish oils in two fractions of different iodine value. Fractionation studies were performed in a Magne-