KINETICS OF FRONT-END ACETYLENE HYDROGENATION IN ETHYLENE PRODUCTION

The kinetics of acetylene hydrogenation in the presence of a large exc ess of ethylene was studied in a laboratory flow reactor. Experiments were carried out using a Pd/alpha-Al2O3 commercial catalyst-and a simu lated cracker gas mixture (H-2/C2H2 = 50; 60% C2H4; 30% H-2, and trace s of CO), at varying temperature (293-393 K) and pressure (2-35 atm). Competing mechanisms for acetylene and ethylene hydrogenation were for mulated and the corresponding kinetic equations derived by rate-determ ining step methods. A criterion based upon statistical analysis was us ed to discriminate between rival kinetic models. The selected equation s are consistent with the adsorption of C2H2 and C2H4 in the same acti ve sites followed by reaction with adsorbed hydrogen atoms to form C2H 4 and C2H6 in a one-step process. Good agreement between computed and experimental results was obtained using a nonisothermal reactor model that takes into account the existence of external temperature and conc entration gradients. The derived kinetic equations together with a pse udohomogeneous model of an integral adiabatic now reactor were employe d to simulate the conversion and the temperature profiles for a commer cial hydrogenation unit.