Liquid-phase selective hydrogenation of acetylene with the feed composition of front-end process

The selective hydrogenation process is industrially used to remove trace acetylene from ethylene-rich streams. In this work, N-methyl-2-pyrrolidone (NMP) was introduced as a liquid phase to the front-end hydrogenation process, with using Pd/SiO₂ as a model catalyst, to improve the selectivity to ethylene. In the liquid-phase hydrogenation, a high ethylene selectivity of ~ 80% was obtained at an acetylene conversion of 99.69% by using two reactors in series. In contrast, the ethylene selectivity was only ~ 40% in the gas phase at a similar acetylene conversion of 99.76%. The superiority of the liquid-phase hydrogenation was attributed to the extremely low ratios of C₂H₄/C₂H₂ (β) and H₂/C₂H₂ (γ) and low concentration of C₂H₄ in NMP. In addition, the liquid phase can prevent ethylene loss even at higher reaction temperatures. Catalyst stability in the liquid-phase hydrogenation was studied to identify optimal operating conditions. Lower acetylene concentration and higher hydrogen concentration, which can be adjusted by varying temperature and pressure, were found to favor catalyst stability.