Transesterification of sunflower oil in a sub- and supercritical dimethyl carbonate medium

At present, the development of environmentally friendly methods for producing biodiesel and the development of new renewable energy sources appears to be an urgent task. The present article reports on a study aimed at assessing the effect of the duration and temperature of sunflower oil processing in sub- and supercritical dimethyl carbonate media on the yield and composition of methyl esters of carboxylic acids. The experiment was carried out using a batch type autoclave in the temperature range of 150-325 degrees C and an oil: dimethyl carbonate molar ratio equal to 1 : 9. The chemical composition of transesterification products was studied using the GC-MS method. Under subcritical conditions in the range of 150-225 degrees C, no transesterification of oils practically is detected. An increase in the yield of methyl esters is observed at temperatures above 225 degrees C with a maximum value of 90.6 % mass identified in the supercritical region at 280 degrees C. When processed under subcritical conditions for 9 min, the yield of methyl esters does not exceed 80 % of the mass. Along with methyl esters, transesterification products were represented by mono- and diglycerides of fatty acids, methanol, glycerine and the products of glycerine transformations. The content of these products decreased under an increase in temperature. The transesterification product of oil under supercritical conditions is represented by the composition of methyl esters of carboxylic acids. The content of impurities is not more than 1 %. The effect of the treatment duration on the yield of methyl esters is shown to be most pronounced in the subcritical conditions of the process. Under supercritical conditions, more than 80 % of the oil triglycerides are converted to carboxylic acid methyl esters within 3-5 minutes of treatment. Based on the conducted studies, the choice of temperature conditions for the transesterification of oil in dimethyl carbonate medium was substantiated and additional information on the composition of the products was obtained.