Sustainable short-chain olefin production through simultaneous dehydration of mixtures of 1-butanol and ethanol over HZSM-5 and γ-Al2O3

Abstract Dehydration reactions of alcohols are of prime importance in biomass conversions. Although bio-alcohols are generally obtained as mixtures, the dehydration of alcohol mixtures is barely reported. In this work the ability of HZSM-5 and γ-Al2O3 to dehydrate a 1-butanol/ethanol mixture in a 6/1 mass-ratio was studied, corresponding to the butanol/ethanol ratio in typical ABE mixtures, at temperatures from 513 to 613 K. For HZSM-5 the difference in reactivity of the alcohols is too high to fully convert both alcohols to their respective alkenes without catalyzing secondary reactions. For dehydration over γ-Al2O3, the reactivity of ethanol and 1-butanol is more similar, which can be attributed to the lower acid strength and larger pore size, causing lower fractional coverages and diminished competition for adsorption sites, allowing both alcohols to react more simultaneously. Above conversions of 0.6, the difference in reactivity of both alcohols increases due to a shift in dominant reaction pathways towards ether decomposition and the intramolecular dehydration on γ-Al2O3. Approaching full conversion, the selectivity towards olefins is high (>0.95) for both HZSM-5 and γ-Al2O3. Since no secondary reactions occur when using γ-Al2O3, it is deemed the best of both catalysts to dehydrate mixtures of alcohols simultaneously to their corresponding alkenes.