Ni/γ‐Al 2 O 3 catalyzed hydrogenation sequence of conjugated double bonds in 2‐ethyl‐2‐hexenal and reaction kinetics

Abstract BACKGROUND 2‐ethylhexanol (2EHO) is an important organic chemical, which is mainly used in the manufacture of plasticizers. At present, the industrial manufacture of 2EHO is generally carried out by gas‐phase hydrogenation of 2‐ethyl‐2‐hexenal, which has high energy consumption. So it is of significance to study liquid‐phase hydrogenation of 2‐ethyl‐2‐hexenal. RESULTS Several byproducts were found such as 3‐methylheptane, 2‐ethylhexyl butyrate, 2,4‐diethyloctanol, 2,4‐diethyloctanal, 5,7‐diethylundecane and 2‐ethylhexyl‐2‐ethylhexanoate in the reaction system of 2‐ethyl‐2‐hexenal liquid‐phase hydrogenation catalyzed by Ni/γ‐Al 2 O 3 and a reaction network was proposed. The CC bond of 2‐ethyl‐2‐hexenal molecule was hydrogenated prior to the CO bond hydrogenation and furthermore the CO bond was hardly hydrogenated until the CC bond hydrogenation finished. The kinetics of liquid‐phase hydrogenation of 2‐ethyl‐2‐hexenal catalyzed by Ni/γ‐Al 2 O 3 was studied and the result demonstrated that both 2‐ethyl‐2‐hexenal hydrogenation to 2‐ethylhexanal (CC bond hydrogenation) and 2‐ethylhexanal hydrogenation to 2‐ethylhexanol (CO bond hydrogenation) were first‐order irreversible reactions. CONCLUSIONS It is made clear by means of online infrared analysis that the hydrogenation of CO bond is difficult to achieve before completion of the hydrogenation of CC bond. The 2‐ethylhexanal hydrogenation reaction, whose activation energy is higher, is the rate‐determining step in the entire hydrogenation process. © 2017 Society of Chemical Industry