Ni/γ-Al2O3 catalyzed hydrogenation sequence of conjugated double bonds in 2-ethyl-2-hexenal and reaction kinetics: 2-ethyl-2-hexenal hydrogenation sequence and kinetics

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‐Al₂O₃ and a reaction network was proposed. The CC bond of 2‐ethyl‐2‐hexenal molecule was hydrogenated prior to the CO bond hydrogenation and furthermore the CO bond was hardly hydrogenated until the CC bond hydrogenation finished. The kinetics of liquid‐phase hydrogenation of 2‐ethyl‐2‐hexenal catalyzed by Ni/γ‐Al₂O₃ was studied and the result demonstrated that both 2‐ethyl‐2‐hexenal hydrogenation to 2‐ethylhexanal (CC bond hydrogenation) and 2‐ethylhexanal hydrogenation to 2‐ethylhexanol (CO bond hydrogenation) were first‐order irreversible reactions. CONCLUSIONS: It is made clear by means of online infrared analysis that the hydrogenation of CO bond is difficult to achieve before completion of the hydrogenation of CC 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