Upgraded biofuel from alcohol–acetone feedstocks over a two-stage flow-through catalytic system

Abstract

Consecutive alkylation of acetone (A) with ethanol (E) in a ratio of 1 : 2 and hydrodeoxygenation (HDO) of the obtained Guerbet products were studied. A fixed bed flow-through reactor system was applied at total pressure of 21 bar and in the temperature range of 175–350 °C using inert He or/and reducing H₂ carrier gases. In the alkylation process catalysts based on a hydrogen borrowing strategy were applied using neutral activated carbon (AC) or alkaline hydrotalcite (HT) supports, namely 5 wt% Pd/AC in presence of a 30 wt% KOH alkaline additive or 5 wt% Pd/HT. After self- and cross-condensation of the reactants the effluent product mixture was treated in a H₂ stream over a second commercial hydrodeoxygenating (HDO) catalyst (NiMo/alumina) layer. All the catalysts were activated in H₂ flow at 350 °C. In inert helium carrier gas over Pd-catalysts C5–C7 mono- or dialkylated ketones were obtained as main products however different C7–C11 mono- or dialkylated ketones were also formed due to Guerbet coupling of ethanol to butanol mimicking the acetone–butanol–ethanol (ABE) fermentation mixture as reactant. By replacing helium with hydrogen medium over Pd-catalyst systems the produced ketones could be reduced to alcohols. Finally, for hydrocarbon fuel production, the oxygen content of the alcohol–ketone mixture can be eliminated completely, by applying a second reactor section filled up with an industrial NiMo/alumina catalyst producing the parallel alkanes.