Efficient direct synthesis of 2-ethylhexanal from n-butyraldehyde and hydrogen using palladium modified base catalysts

Abstract One-step synthesis of 2-ethylhexanal (2EH) from n -butyraldehyde and hydrogen gas has been studied over palladium modified base catalysts at 1 atm and 130–200°C by using a fixed-bed, integral-flow reactor. The catalysts were characterized with various techniques: AA, XRD, BET, FT-IR and TPD of carbon dioxide. The factors affecting the catalytic results were investigated; these included the catalyst support, the reaction temperature, the palladium content, n -butyraldehyde to hydrogen molar ratio (B/H), time-on-stream and the contact time. The optimum conditions for the synthesis of 2EH were 0.5% Pd/KXU, 150°C, B/H 1 and W / F B 22.2 g·h/mol. The catalytic results were correlated to the catalyst properties; the conversion of n -butyraldehyde increases with increasing the catalyst base amount. The main reaction path started from self-condensation of n -butyraldehyde to 2-ethyl-3-hydroxyhexanal, followed by dehydration to 2-ethyl-2-hexenal which was then hydrogenated to 2EH. The minor path was direct hydrogenation on the CO double bond of n -butyraldehyde to produce 1-butanol.