Dehydration of 1,2-propanediol to propionaldehyde over zeolite catalysts

Dehydration of 1,2-propanediol has been investigated over a range of zeolite catalysts with different pore structures and acidity. The reaction forms part of a two-step process for the conversion of glycerol to propionaldehyde. The effects of reaction temperature, concentration, space velocity, and SiO2/Al2O3 ratio have been studied. The medium pore size, unidirectional channel zeolites ZSM-23 and Theta-1 showed high activity and selectivity to propionaldehyde (exceeding 90 wt% at 300–350 °C). Selectivity to the intermolecular dehydration product 2-ethyl-4-methyl-1,3-dioxolane was high at lower temperatures for all the zeolites, but decreased to a low value at higher temperatures and lower GHSV. The results are discussed in relation to the reaction mechanism and zeolite structures. Significant deactivation was observed for higher 1,2-propanediol partial pressures, which was partially mitigated by the addition of steam.

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► 1,2-propanediol is a potential intermediate in a two-step process for conversion of glycerol to propionaldehyde.
► Zeolites show high activity for 1,2-propanediol dehydration.
► Medium pore size, unidirectional channel zeolites are very selective to propionaldehyde.
► Selectivity to propionaldehyde over ZSM-23 and Theta-1 was >90% at 300–350 °C.
► Catalyst deactivation was partially mitigated by steam addition.