Direct Synthesis of <i>n</i>-Butanol from Ethanol over Nonstoichiometric Hydroxyapatite

Abstract

n -Butanol is an important industrial chemical usually produced by the oxo process, an expensive, energy-consuming set of reactions over metal catalysts, using petrochemical raw materials at high pressure. We developed nonstoichiometric hydroxyapatite (HAP), a highly active calcium phosphate compound and found it catalyzed selective conversion of ethanol to n -butanol in a single reaction at atmospheric pressure and low temperature, with maximum selectivity of 76%. Higher alcohols were also formed. We postulate that ethanol is adsorbed and activated on HAP as CH 3 CH 2 OH(a) and that a C−C bond was formed between β-C in the CH 3 CH 2 OH(a) and α-C in n -C n H 2 n +1 OH to produce n -C n H 2 n +1 CH 2 CH 2 OH. We further postulate that, by successive propagation, part of this n -C n H 2 n +1 CH 2 CH 2 OH is then adsorbed and activated on HAP as n -C n H 2 n +1 CH 2 CH 2 OH(a) and that C−C bond was formed between β-C in the n -C n H 2 n +1 CHCH 2 OH(a) and α-C in n -alcohol to produce branched alcohols. Reaction simulation supported this hypothesis, suggesting that efficient, environmentally friendly production of n -butanol might be possible in future using bioethanol as raw material.