Scale-up analysis of autothermal operation of methane oxidative coupling with La2O3/CaO catalyst

The exothermicity of oxidative coupling of methane (OCM) renders a cooled packed-bed reactor impractical or impossible. Recently, we proposed an adiabatic autothermal reactor as a solution to this problem and reported the first results for stable autothermal operation (AO) with feed at ambient temperature. AO on the ignited branch is possible only in the region of steady-state multiplicity. High per-pass conversion and productivity requirements demand a stable ignited branch at the lowest possible feed temperature and high flow rate. To achieve OCM scale-up, many conditions must be satisfied simultaneously. Using a kinetic model for La₂O₃/CaO catalyst, we examine the impact of space time, feed methane to oxygen ratio, feed temperature, particle size, inter-phase heat and mass transfer gradients, pore-diffusion, bed scale heat/mass dispersion on the region of AO for large scale adiabatic packed-bed reactors. We show that while it is possible to achieve CH₄ conversion of about 20% and C₂ selectivity of about 80% in scaled-up reactors, these values are sensitive to the design and operating parameters.