Engineering Surface Hydrophobicity in Zeolites for Efficient Biphasic Glycerol–Acetone Acetalization

The acetalization of glycerol with acetone encounters inefficiencies due to their low miscibility. This research presents an optimal approach for engineering hydrophobicity in organosilane-grafted zeolites. We develop organosilane-grafted HY-zeolite catalysts with tailored hydrophobicity to overcome mass transfer limitations and enhance catalytic performance. Three organosilanes, ethyltrichlorosilane (ETS), octyltrichlorosilane (OTS), and octadecyltrichlorosilane (ODTS), are grafted onto zeolite surfaces at various temperatures (100–180 °C) to systematically investigate the effects of the carbon chain length and grafting temperature. A critical hydrophobicity threshold of 128° (contact angle) is identified, which significantly improves the miscibility of glycerol and acetone, resulting in >80% glycerol conversion and >95% selectivity to solketal. Although the type of organosilane did not affect the catalytic activity, longer carbon chains (ODTS) enhanced the water resistance and catalyst recyclability. Higher grafting temperatures facilitate the multibonded functionalization with surface silanol groups but reduce the total acidity, impacting the overall reactivity. These findings provide a strategic framework for designing robust, efficient, and recyclable acid catalysts for the biphasic upgrading of glycerol and other biobased feedstocks.