A facile approach for the synthesis of solketal, a fuel additive, from biowaste glycerol using transition metal-based solid acid catalysts

The rise in global biodiesel production leads to the surplus of glycerol as a byproduct, necessitating its industrial application in various chemicals to sustain the biodiesel industry economically. Solketal is one of the value-added chemicals in the biodiesel industry with numerous applications in the food, polymer, and chemical industries and as a fuel additive. Nowadays, researchers mainly focus on synthesizing solketal using biowaste glycerol obtained from the biodiesel industry due to its immense applications. In this work, the experimental data demonstrated that the incorporation of ZnAl2O4 plays a key role in establishing the surface sulfate groups and structural composites of the solid acid catalysts. Highly efficient heterogeneous acid SO42-/ZnAl2O4-ZrO2 and SO42-/ZnAl2O4-TiO2 catalysts were synthesized and applied for solketal synthesis. It was found that SZZ proved to be highly efficient and active towards 99.3% glycerol conversion with 98% solketal yield. In contrast, SZT showed 83% glycerol conversion with 81% solketal yield at optimized reaction conditions. SZZ showed excellent catalytic activity compared to SZT due to its better reusability, higher acidity, and good structural stability. Green metric parameters, like E-factor, PMI, and AE were studied, and it was found that SZZ is more efficient and the acetalization reaction of glycerol is environmentally friendly in nature.