Heterogeneous Catalysis for Biodiesel Synthesis and Valorization of Glycerol Dheerendra Kumar Singh, M.Sc.Ph.D.DD, 14, 168 pp. Department of Energy Systems Engineering Indian Institute of Technology Bombay, Powai, Mumbai 400 076. Supervisor(s): Sanjay M. Mahajani External Supervisor(s):
Abstract Heterogeneous catalyst is an important component in chemical processes, making them costeffective and environment friendly. Metal oxides are a group of heterogeneous catalysts that can be used in several reactions. One can conveniently play with various attributes of these catalysts (e.g. acidity/basicity, porosity, particle size etc.) to achieve the desired performance.
In this work, we evaluate their applicability for biodiesel synthesis,
esterification of oleic acid, glycerol carbonate synthesis and for di-methyl carbonate synthesis. The processes involve relatively cheap raw materials such as methanol, vegetable oil, urea, fatty acid etc. They are used to produce high value products such as glycerol carbonate, mono-glycerides, di-methyl carbonate etc. In catalysis, support is used to increase the dispersion of active species due to its high surface area. The interaction between metal and support enhances the catalytic activity and improves catalyst stability. We use ZnO/zeolite, PbO/zeolite catalysts for biodiesel synthesis and for esterification of oleic acid with glycerol. The leaching of metal oxide is minimized when zeolite is used as a support. Catalysts are characterized by XRD, BET, TEM, SEM and TPD/TPR. TPR results show the shifting of reduction peak of PbO to higher temperature in PbO/zeolite due to metal support interaction between lead and zeolite. Esterification of glycerol with oleic acid can also be catalyzed by acid catalyst and ZnO/zeolite gave promising results. The effects of different parameters such as catalyst loading, mole ratio and temperature are studied. Higher temperatures and simultaneous water removal increase the reaction rate significantly. It is interesting to note that the selectivity towards mono-glyceride for a given conversion remains unaffected with respect to temperature and mole ratio. A
simplified kinetic model that considers mono and di-esterification as a combination of series and parallel irreversible reactions is proposed to explain the kinetic data. The reaction of glycerol with either urea or DMC to synthesize glycerol carbonate is base catalyzed. La2O3 is a promising basic catalyst but it has low surface area. The surface area of La2O3 can be increased by co-precipitating it with other oxide(s) of high surface area. ZnO and MgO are comparatively less basic than La2O3 but they have high surface area. Thus the mixed metal oxide synthesized by co-precipitation method results in formation of lanthanum oxide particles with small particle size, high surface and moderate basicity, thereby imparting the desired catalytic attributes to Zn-La mixed metal oxide. Mixed oxides of zinc and lanthanum are prepared at three different molar ratios (2:1, 4:1 and 6:1). Zn4La1 and Zn2La1 showed the highest catalytic activity in term of glycerol conversion and also offered high selectivity for GC. Parametric studies are performed to examine the effects of temperature, catalyst loading and the glycerol to DMC mole ratio, and a suitable kinetic model is proposed to explain the data. Zn-La mixed oxide can also be used for the synthesis of di-methyl carbonate from urea and methanol by continuous removal of ammonia. A maximum of 35.46 \% yield of DMC is realized with Zn6La1 (Zn: La mole ratio 6:1) catalyst. Ammonia is formed as a co-product in the syntheses of glycerol carbonate and DMC. It can be used, along with CO2, in the production of one of the reactants i.e. urea, thus providing an opportunity to reduce the carbon foot print.
