Autothermal reactor design for catalytic partial oxidations

Abstract

A comprehensive analysis of the impact of various design and operating variables on the boundary of the region of autothermal operation of type III is presented. It is shown that for a fixed adiabatic temperature rise and space time, the largest region of autothermal operation is obtained in the homogeneous limit (small particles or high cell density monoliths) when the bed scale heat Peclet number approaches zero, mass Peclet number approaches infinity, and with smaller bed aspect ratios (height to diameter). For competing multiple oxidation reactions, while thin (shallow) beds could lead to larger region of autothermal operation, better selectivity of intermediate product may be attained using very thin beds. The impact of heat loss on the region of autothermal operation is also analyzed. When inter and intra-phase heat and mass transfer gradients are significant so that particle (channel) level ignition could occur, autothermal operation is feasible for any bed level heat Peclet number with reactor operated in the mass transfer controlled regime. The results of the analysis are applied to two processes of interest, namely, oxidative coupling of methane (OCM) with adiabatic temperature rise in the range 600–1200 K and catalytic partial oxidations (CPO) with adiabatic temperature rise in the range 200–500 K. For OCM, some feasible autothermal reactor designs that are suitable for different catalyst activity levels are proposed. For CPO, an autothermal reactor design is compared favorably to the traditional cooled multi-tubular reactor.