ACETYLATION OF GLYCEROL OVER SULPHATED ALUMINA CATALYSTS: OPTIMIZATION OF REACTION PARAMETERS AND KINETIC STUDY

Abstract

Growing population, depleting fossil fuel reserves, hiking oil prices and environmental and health concerns are demanding for alternative sources of energy. In this quest, biodiesel has gained a lot of interest all over the world as a potential alternative for petroleum fuels. 1-lowever, the expected pace in biodiesel synthesis was decelerated due to the high production cost. Biodiesel production can be economically viable by the value addition of surplus glycerol obtained as byproduct. Among the different processes of glycerol value addition. esterification of glycerol with acetic acid is a promising route. In this work, esterification of glycerol was - performed using 2M S0427 y-A1203 catalyst developed through impregnation of sulphuric acid on '-Al2O3. The physic-chemical properties of the catalysts were characterized by various methods such as N2-adsorption, X-ray diffraction (XRD) and ammonia temperature programiiied desorption (Nlh-TPD). Catalyst performance was evaluated at atmospheric pressure and in the temperature range of 95-125°C. Different reaction parameters such as catalyst amount, glycerol to acetic acid mole ratio, reaction time was varied to maximize the glycerol conversion and yieds of the higher esters. Results demonstrated that. 2M S042 / y-Al203 catalyst was very active and complete glycerol conversion with 77.4 % selectivity of higher esters (diacetylglycerol (DAG) + iriacetylglycerol (TAG)) was obtained at 95°C. aller 5 h of reaction. Effi.ct of parameter study suggested that acetic acid to glycerol mole ratio and reaction temperature were more significant reaction parameters which influenced the glycerol conversion and products selectivity. Response surface methodology (RSM) was used for the development of empirical process model followed by optimization of reaction parameters. Optimum reaction condition was found to be acid to glycerol mole ratio of 12:1, 108.8 °C and 0.36 g catalyst at which 99.1 % glycerol conversion and 76.1 % combined selectivity to DAG and 'FAG was achieved. The interaction effect of temperature and mole ratio was explained using response surface plots. Results suggested that the glycerol acetylation reaction mechanism followed consecutive series pathway. Finally. reaction kinetic models were developed and the values of apparent reaction rate constant and corresponding activation energy were evaluated.