Kinetics of Front-End Acetylene Hydrogenation in Ethylene Production

The kinetics of acetylene hydrogenation in the presence of a large excess of ethylene was studied in a laboratory flow reactor. Experiments were carried out using a Pd/α-Al 2 O 3 commercial catalyst and a simulated cracker gas mixture (H 2 /C 2 H 2 = 50; 60% C 2 H 4; 30% H 2, and traces of CO), at varying temperature (293−393 K) and pressure (2−35 atm). Competing mechanisms for acetylene and ethylene hydrogenation were formulated and the corresponding kinetic equations derived by rate-determining step methods. A criterion based upon statistical analysis was used to discriminate between rival kinetic models. The selected equations are consistent with the adsorption of C 2 H 2 and C 2 H 4 in the same active sites followed by reaction with adsorbed hydrogen atoms to form C 2 H 4 and C 2 H 6 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 concentration gradients. The derived kinetic equations together with a pseudohomogeneous model of an integral adiabatic flow reactor were employed to simulate the conversion and the temperature profiles for a commercial hydrogenation unit.