Calcium and Zirconium Oxide Based Solid Catalysts for the Transesterification of Low Quality Triglycerides

Abstract

In present thesis five different series of catalysts viz., Ce/ZrO2-TiO2/SO4 2-, Zr/CaO, Mo/CaO, Li/ZrO2 and Sr:Zr were prepared by wet chemical route and/or co-precipitation method to catalyze the esterification and/or transesterification of free fatty acid containing VOs in heterogeneous mode. The structure of catalysts was established by powder XRD study, while the surface morphology and particle size by SEM and TEM studies. The acidic/basic active sites present in catalysts were quantified by Hammett indicator test method. For the esterification of fatty acids, in presence of triglycerides, sulfated Ce/ZrO2‒TiO2 was employed as solid catalyst. The catalyst activity was found to be a function of its Bronsted acidic sites which in turn depends on the cerium concentration in catalyst. The catalyst was able to catalyze the fatty acid esterification even in presence of up to 12 wt% moisture contents (with respect to fatty acids). The catalyst has shown excellent stability as negligible sulfate leaching was observed and recovered catalyst was reused in five successive runs without significant loss in activity. However, the catalyst was not found to be active to carry out the transesterification of triglycerides. In order to replace highly toxic and non renewable methanol with nontoxic as well as renewable ethanol for biodiesel production, Zr/CaO catalyst was employed as heterogeneous catalyst for the transesterification of jatropha oil which contain up to 15.6 wt% FFA content. The catalytic activity was found to be a function of basic sites which in turn depend on calcination temperature and zirconium concentration. The activity of the catalyst was lost after two successive runs mainly due to the leaching of active metal. To further improve the reusability and stability of CaO based catalyst, Mo impregnated CaO catalyst was prepared (Mo/CaO) and employed as reusable catalyst for the ethanolysis of non edible oils (having up to 18 wt% FFA content), to obtain > 99% fatty acid ethyl ester (FAEE) yield. The catalyst was recovered and reused five times without significant loss in activity. In order to develop a catalyst for simultaneous esterification as well as transesterification, Li/ZrO2 was prepared and successfully employed for one-pot production of biodiesel via esterification and transesterification from vegetable oil having FFA content as high as 18.1 wt%. No significant loss in catalyst activity was observed even during 9 consecutive runs as > 90 % fatty acid alkyl ester yield was maintained. Another catalyst, Sr:Zr was also found to catalyze simultaneous esterification and transesterification of high free fatty acid containing vegetable oils with ethanol. The catalyst has been recovered and recycled without any significant loss in activity during four successive catalytic cycles. xiii Besides catalytic activity, kinetics and thermodynamic parameters of the reactions catalyzed by prepared catalyst, were also evaluated. The transesterification reaction catalyzed by all catalysts has followed (pseudo) first order kinetic equation. For all catalysts, the heterogeneous mode of action has been proved by performing hot filtration test. Koros- Nowak test was performed to demonstrate that catalytic activity was free from internal mass diffusion limitations. Few physicochemical properties of the prepared FAME and FAEE have also been studied and compared with EN 14214 and ASTM standard values.