The glycerolysis reaction of soybean oil was evaluated using crude glycerol obtained from the transesterification of soybean oil with methanol, catalyzed by sodium methoxide and sodium hydroxide, without any purification step other than the methanol removal. Crude glycerol with the lower content of remaining inorganic catalyst produced the highest concentration of monoglycerides (about 42%). The effect of the addition of water on the glycerolysis reaction was analyzed, evidencing a low formation rate of products in the first stages of the reaction due to the transformation of the inorganic catalyst to soaps, which are weaker bases. The sample of crude glycerol that led to the best results was evaluated at several temperatures. It was observed that the reaction with crude glycerol exhibits a lower formation rate of monoglycerides at low temperatures (160 and 180°C) compared with the reaction with pure glycerol and catalyzed with NaOH. This behavior was explained by the lower activity of the soaps present in the crude glycerol respect to the inorganic base. Above 200°C the reaction is very fast and the monoglycerides formed are consumed to produce diglycerides.
Glycerolysis of crude fatty acid methyl esters (FAME) with crude glycerol derived from biodiesel production was performed. The reaction was accomplished at temperatures ranging between 160 and 200 °C and molar ratios of FAME to glycerol ranging between 1.5 and 3.0. Increasing the temperature improved the formation rate of monoglycerides (MG) and diglycerides (DG). However, increasing both the temperature and the molar ratio of glycerol to FAME diminished the formation of MG. Best results (43 % MG and 26 % DG in 10 min) were obtained at 200 °C using the lowest concentration of glycerol. The effects of soap and NaOH present in crude glycerol were controlled by carrying out the reaction with pure glycerol. In comparison with NaOH‐catalyzed reactions, soap‐catalyzed reactions resulted in a slower formation rate of products. However, soap‐catalyzed reactions were less prone to secondary reactions, affording maximum yields of MG and DG, which were higher than those obtained with NaOH‐catalyzed reactions at 180 and 200 °C.
ResumenSe estudió un método de purificación para la glicerina procedente de la producción de biodiesel de aceite de palma, para alcanzar los estándares requeridos para su uso en aplicaciones que no requieran el grado USP (United States Pharmacopoeia), definidos por las normas técnicas colombianas. Se usó diseño factorial 2 3 con tres variables: tipo de ácido (fosfórico o sulfúrico), cantidad de metanol y pH. Se encontró que el tratamiento con ácido sulfúrico, con 50% de metanol y pH de 6, es el que da mejores resultados y que se requiere una decoloración con carbón activado para cumplir con la exigencia de color. La glicerina refinada y decolorada obtenida cumple con los requerimientos de la glicerina tipo 2 grado 1 y 2 según la Norma Técnica colombiana NTC1274.
AbstractA method is proposed for the purification of glycerin from palm oil biodiesel production to achieve the required standards, for use in applications non-requiring USP grade (United States Pharmacopoeia), particularly those defined by Colombian standards. A factorial design 2 3 was used with the three variables: type of acid (phosphoric or sulfuric acid), quantity of methanol and pH. It was found that the treatment with sulfuric acid, 50% methanol and pH of 6 gave the best results, and requires an activated carbon bleaching to meet the required color. Refined and bleached glycerin obtained meets the requirements of glycerin type 2 grades 1 and 2 according to the Colombian standard NTC1274.
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