Acid catalysed glycerol transformation to fuel additives over different metal phosphate solid acid catalysts

Investigations on the metal phosphate (MP: M = Al, Ti, Zr and Nb) solid acid catalysts are carried out in the liquid phase through the acetylation of glycerol in acetic acid and acetalization in acetone. Hydrothermal procedure was employed in the preparation of these catalysts. The physico-chemical properties, viz; amorphous or crystalline nature is determined by using X-ray diffraction, pore size distribution is measured from their respective N-2 adsorption-desorption isotherms, stretching and bending modes of various molecules is found using FT-IR and charge transfer transitions are determined using UV-DRS of these catalysts. Studies of adsorbed pyridine using ex situ FT-IR analysis and NH3-temperature programmed desorption are also carried out on these catalysts to get an insight into the structural and acidic properties by varying the metal component. The functionality of glycerol acetylation and acetalization is explained in terms of the acidity and structural properties of these MP catalysts. From the results, it was observed that the NbP was the most active catalyst, and it was achieved the highest conversion of glycerol in both acylation and acetalization reactions with 89% and 92% respectively. However, in acylation and acetylation reactions, we observed 21%, 54% and 25% selectivities for mono, di and triacetin respectively and 100% selectivity of solketal respectively for NbP catalyst. It was also observed that NbP was found to the best catalyst for activity and selectivity in both reactions as compared to TiP, ZrP and AlP. It is noteworthy to mention here is that both catalytic reactions were significantly affected by the material properties such as total acidity and textural properties. However, the various reaction parameters such as reaction temperature, mole ratio of glycerol to acetic acid, reaction time, and catalyst loadings also have some influence on the catalytic activity results.

Automated summary

Investigations on metal phosphate solid acid catalysts showed that NbP catalyst exhibited the highest activity and selectivity in glycerol acetylation and acetalization reactions. The material properties and reaction parameters also influenced the catalytic activity.