Multiscale characterization, modeling and simulation of packed bed reactor for direct conversion of syngas to dimethyl ether†

Abstract

This work presents a multiscale Computational Fluid Dynamics (CFD) analysis of direct DME synthesis in a packed bed reactor with physically mixed Cu/ZnO/Al₂O₃ and γ-Al₂O₃ catalysts. The model accounts for hierarchical transport behavior by coupling a one-dimensional intraparticle subgrid model to a two-dimensional (axial and radial) model for heat and mass transport along the catalyst bed, with fully integrated chemical reaction kinetics. To enhance the predictive accuracy, the model incorporates directly measured critical bed properties. X-ray computed tomography was performed at the scale of the packed bed reactor and the scale of individual catalyst particles to obtain bed properties such as bed porosity, particle diameter and permeability, as well as catalyst characteristics including intraparticle porosity and pore size. Experiments were conducted in a lab-scale reactor to validate the model, and the model predictions show good agreement with experimental data for the investigated process conditions. The validated model is further exercised to study the influence of process variables such as feed temperature, feed rate, and wall temperature. The results indicate that the pattern of hot spot formation and magnitude of hot spot temperature are sensitive to processing conditions, mainly the feed rate and reactor wall temperature. It has also been found that internal mass transport limitations exist even in smaller particles (∼215 μm), particularly in the hot spot region.