Upgrading bio-butanol in the presence of copper-hydrotalcite derived mixed oxides: From batch to continuous flow catalytic process highly selective to butyl butyrate

The conversion of bio-alcohols to chemicals and fuels can play a determinant role in the transition towards bio-economy. Different hydrotalcite derived Cu/Mg/Al mixed oxides, having a Cu atomic content in the range 1.0–7.6 %, have been employed for the first time in batch and continuous flow reactors for the conversion of n-BuOH. The catalytic performances resulted strongly tunable, being influenced by the composition of the catalytic systems and by the type of adopted reactor. The catalysts with lower Cu content resulted active both in the Guerbet condensation to 2-ethyl-1-hexanol (2EH) and in the dehydrogenative coupling (DHC) of the substrate to butyl butyrate (BB) ester, while the catalyst with the highest Cu content showed very high selectivity towards BB formation. The batch reaction evidenced a progressive deactivation of the catalytic systems with the reconstruction of the hydrotalcite precursor. On the other hand, the study in flow reactor revealed good activity and excellent stability of the catalytic system Cu7.6, a selectivity to BB > 98 mol% being maintained after 216 h of time-on-stream.