Methane Conversion to Ethylene and Acetylene: Optimal Control with Chlorine, Oxygen, and Heat Flux

Abstract

In this paper, an optimal control strategy is applied to the problem of finding the flux profiles for the conversion of methane to ethylene and acetylene in a plug flow reactor. A chlorine-catalyzed oxidative pyrolysis mechanism is used in the calculations, in which two mechanistic pathways to the C2 products were examined. One involves CH3Cl and/or CH2Cl, and the other involves C2H6 and/or C2H5 as reaction intermediates. Optimal control designs were performed with respect to the final mass fractions of ethylene and acetylene in a plug flow reactor using heat, oxygen, and chlorine fluxes as controls. The simulation results show that for the temperatures (1200 K < T < 1900 K) and pressure (P = 1 atm) considered, C2H4 is formed initially, which is subsequently converted to C2H2. Because of the abundant supply of H2 formed during the reaction, it is possible to reform C2H4 from C2H2 by controlled extraction of energy. The heat flux plays the most important role in determining the final concentration of the desired C2 products by controlling the temperature and the rate of H-atom radical generation, and thus, the interconversion between C2H2 and C2H4 through the C2H3 radical. The solutions obtained, although not proven to be globally optimal, are of very high quality. More than 40% yield of the desired C2 products, either ethylene or acetylene, can be obtained in all cases.