Selective Dehydration of 1,2-Propanediol to Propanal over Boron Phosphate Catalyst in the Presence of Steam

Catalytic properties of metal phosphates were investigated for gas-phase dehydration of 1,2-propanediol to propanal in the presence and absence of steam in the temperature range of 150–340 °C. Boron, aluminum, and nickel phosphates showed promising catalytic activity for the dehydration reaction. Especially, boron phosphate showed outstanding catalytic activity at a low reaction temperature and high selectivity to propanal without formation of competitive dehydration products such as acetone and allyl alcohol. The catalytic activity of boron phosphate was remarkably enhanced in the presence of steam cofed with 1,2-propanediol. The additional steam was also favorable for promoting hydrolysis of dioxolane, which is a byproduct formed through acetalization of propanal, resulting in the high yield of propanal over 95%. Boron phosphate showed more durable catalytic activity and much higher yield of propanal than conventional solid acid catalysts such as ZSM-5, silica–alumina and niobium oxide that have been reported to be active for the dehydration of 1,2-propanediol.