Acid site requirement and reaction pathway for selective bio-butadiene synthesis by 1,3-butanediol dehydration

Abstract

Gas phase dehydration of 1,3-butanediol was studied at 523 K on solid catalysts with different acidic and physicochemical properties: Al2O3, SiO2/Al2O3, NaZSM5, HZSM5 and TPA (tungstophosphoric acid)/SiO2. The solids were characterized by N2 physisorption, DRX and FTIR spectroscopy of pyridine. The main products were butadiene and 3-buten-1-ol via dehydration route, in addition to propene plus formaldehyde and 4-methyl-1,3-dioxane by reverse or direct Prins condensation, respectively. The effect of reaction temperature (473–573 K) on 1,3-butanediol conversion and products distribution was evaluated. The relationship between the nature of catalytic sites and the main reaction pathway was analyzed. Catalysts with Brønsted acid sites promoted the dehydration reaching the highest yield of butadiene (75 %) on TPA/SiO2 while Lewis acid sites favored the inverse Prins reaction route to propene and formaldehyde. Further studies using the possible intermediates of 1,3-butanediol dehydration were performed and probable mechanisms of formation of the different products were proposed.