Numerical simulation of fixed bed reactor for oxidative coupling of methane over monolithic catalyst

Abstract

A three-dimensional geometric model was set up for the oxidative coupling of methane (OCM) fixed bed reactor loaded with Na3PO4–Mn/SiO2/cordierite monolithic catalyst, and an improved Stansch kinetic model was established to calculate the OCM reactions using the computational fluid dynamics method and Fluent software. The simulation conditions were completely the same with the experimental conditions that the volume velocity of the reactant is 80ml·min−1 under standard state, the CH4/O2 ratio is 3 and the temperature and pressure is 800°C and 1atm, respectively. The contour of the characteristic parameters in the catalyst bed was analyzed, such as the species mass fractions, temperature, the heat flux on side wall surface, pressure, fluid density and velocity. The results showed that the calculated values matched well with the experimental values on the conversion of CH4 and the selectivity of products (C2H6, C2H4, CO, CO2 and H2) in the reactor outlet with an error range of ±4%. The mass fractions of CH4 and O2 decreased from 0.600 and 0.400 at the catalyst bed inlet to 0.445 and 0.120 at the outlet, where the mass fractions of C2H6, C2H4, CO and CO2 were 0.0245, 0.0460, 0.0537 and 0.116, respectively. Due to the existence of laminar boundary layer, the mass fraction contours of each species bent upwards in the vicinity of the boundary layer. The volume of OCM reaction was changing with the proceeding of reaction, and the total moles of products were greater than reactants. The flow field in the catalyst bed maintained constant temperature and pressure. The fluid density decreased gradually from 2.28kg·m−3 at the inlet of the catalyst bed to 2.18kg·m−3 at the outlet of the catalyst bed, while the average velocity magnitude increased from 0.108m·s−1 to 0.120m·s−1.