n‐butane partial oxidation in a fixed bed: A resolved particle computational fluid dynamics simulation

Abstract

Maleic anhydride (MA) is an important chemical intermediate, which is mainly produced by the highly exothermic partial oxidation of n-butane in fixed bed reactors. Production of maleic anhydride is limited by problems of temperature control and loss of selectivity. Here we present threedimensional resolved-particle computational fluid dynamics (CFD) simulations of n-butane partial oxidation in a randomly packed bed of 807 spherical catalyst particles. We used a semi-empirical two-site surface mechanism from the literature and obtained distributions of temperature, gas phase species, and surface species in the bed. The local selectivity patterns are strongly controlled by the changes in the gas phase flow field, the temperature in the fixed bed, and the weakly adsorbed oxygen surface coverage fraction (l O ) profiles inside the particles. Most of the selectivity loss due to product combustion happens in the interior of the catalyst particles, as opposed to the production of MA, which is mainly in the near-surface layers. We observed loss of selectivity and yield in the centre of the bed at increased bed depths, because of the temperature increase and decrease in gas phase oxygen there. The simulations show sharp l O gradients inside the particles. Near the cooled tube wall l O is strongly affected by the temperature, while at the bed centre gas phase oxygen diffusion limitations contribute to a depleted oxygen surface resulting in lower selectivity.

A conjugated heat and mass transfer model to implement reaction in particle-resolved CFD simulations of catalytic fixed bed reactors

“…Similar to the observations made for the flow around a single VPO particle described in section 5.2 and in line with the results of Partopour and Dixon (2018) for a fixed bed containing spherical catalysts, the mass fraction gradients inside the particles are steep due to the limitation by pore diffusion. However, a gradient of the n-butane and CO 2 mass fraction towards the tube wall cannot be found different to the study of Partopour and Dixon (2018) because in the presented work a shorter fixed bed with smaller tube-to-particle diameter-ratio ( Dt /dp,outer = 3.75) is investigated. Due to the exothermic reaction, the temperature increases along the packed bed length and decreases towards the cooling tube wall.…”

Experimental methods in chemical engineering: Computational fluid dynamics/finite volume method—CFD/FVM

“…Finally, the scale at which the simulation is performed is crucial in any FVM–CFD study but is especially important for chemical engineering applications, for example, the mass and heat transfer between a catalyst particle and the surrounding reacting gas. [ 73 ] These effects are local and thus need small cells to simulate them accurately. For small‐scale reactors, this can be achieved, but for larger reactors, the mean cell size would have to stay the same, so the absolute number of cells would be a lot higher.…”

Development of Solid–Fluid Reaction Models—A Literature Review

“…Both 1D plug flow and 2D continuum models have been used [4,37,[79][80][81][82][83]. If computational power permits, a 3D discrete particle model can be applied [84][85][86][87]. Dixon and Medeiros [88] compare a 3D discrete particle model to 1D/2D continuum models for the steam methane reforming process.…”