Synthesis of oxygenated fuel additive solketal through catalytic acetalization of glycerol with acetone using HPMo/AlTUD-1

Abstract

The increase in global energy demand and environmental concerns have positioned biodiesel as a sustainable alternative to fossil fuels. However, biodiesel production generates glycerol as a byproduct, which cannot be used as fuel due to its high viscosity, density, and immiscibility with diesel. Thus, glycerol valorisation into high-value derivatives, such as solketal, as a fuel additive offers a promising solution to enhance the economic sustainability of biodiesel production and meet the biofuel blending mandates. Therefore, this approach addresses waste management challenges and sustainability of the biodiesel industry. In the present study, phosphomolybdic acid (HPMo) dispersed on aluminum (Al) incorporated mesoporous silica (AlTUD-1) catalyst was synthesized through the sol-gel technique and tested the catalytic performance for the acetalization of glycerol to the solketal. Characterization studies revealed that molybdenum was successfully loaded onto the mesoporous silica framework without noticeable modification of the silica mesoporous structure. Furthermore, after incorporation of HPMo on AlTUD-1, the structural properties such as surface area, pore diameter, and acid sites was altered from 421 m2/g, 8.84 nm, and 0.245 mmol/g to 241 m2/g, 12.39 nm, and 0.570 mmol/g, respectively. The synthesized catalyst facilitated the catalytic acetalization of glycerol to solketal. The 5 wt% HPMo/AlTUD-1 catalyst showed potential catalytic activity for the acetalization of glycerol to solketal, and achieved a maximum glycerol conversion of 78 %, with a solketal yield of 72 %, and selectivity of 94 % under optimized reaction conditions such as catalyst dose 10 wt% of glycerol, glycerol to acetone molar ratio 1:6, reaction temperature 333 K, and reaction time 3 h. A feasibility study designated that more than 60 % conversion was maintained over four regeneration cycles. The kinetic study revealed that the acetalization of glycerol to solketal requires an activation energy of 51.7 kJ/mol.