Increasing solketal production from the solventless ketalization of glycerol catalyzed by nanodispersed phosphotungstic acid in poly(N-methyl-4-vinylpyridinium) grafted on silica nanoparticles

Abstract

Solketal, a fuel additive, was synthesized from the solvent-free ketalization reaction of glycerol and acetone using phosphotungstic acid (PTA) catalysts. Due to strong acidity, PTA is expected to serve as an efficient acid catalyst, however low specific surface area of bulk PTA and the deactivation, by water, denounces its acid activity leading to low solketal production. The present study demonstrates a success in increasing the solketal yield in the ketalization catalyzed by PTA immobilized in the layer of poly(N-methyl-4-vinylpyridinium) grafted on silica nanoparticles (SNSs-g-PMVP/PTA). PTA with the size of 1–2 nm were dispersed in the grafted-layer of PMVP under strong binding to positively charged pyridinium while the grafted-PMVP provided the hydrophobic environment improving the water-tolerance of PTA. In addition, acid-base interactions between PTA and the pyridine group in the grafted-PMVP transformed PTA hexahydrate to PTA trihydrate. Using SNSs-g-PMVP/PTA catalyst resulted in increasing of the solketal yield above 90% within an hour of the glycerol ketalization compared with 17% yield of solketal in the ketalization catalyzed by unsupported PTA.