Physical modeling of the laboratory-scale packed bed reactor for partial gas-phase oxidation of alcohol using gold nanoparticles as the heterogeneous catalyst

Abstract

Packed bed reactors are often used for catalyst screening studies due to their simple construction and ease of operation. The use of gold nanoparticles for partial oxidation reactions of alcohols has arisen interest of the scientific community. A model was generated to explain the experimentally observed reactor behavior (conversion of alcohol, yields of products) in the alcohol oxidation over gold nanoparticles. The model for this gas-phase heterogeneously catalyzed multi-reaction system consisted of the dynamic mass and energy balances and Langmuir–Hinshelwood–Hougen–Watson, Mars van Krevelen or Power law expressions for the reaction kinetics. Fluid flow was described with convection and dispersion terms. A semi-empirical pressure drop correlation was used. This resulted in a rapidly running model by reducing the problem size significantly. Powerful gPROMS Modelbuilder software was used as the model development, simulation and parameter estimation platform. The primary task was to punctually define and solve the complete set of equations (Partial Differential Equations (PDEs) together with algebraic equations). The modeling effort focused on the selection of the complete set of equations to adjust the degrees of freedom 0 and on the simultaneous solution of the whole set. Numerical method of lines was applied to convert the partial differential equations to ordinary ones. All reactions were assumed to take place on evenly distributed active sites of the porous catalyst particles. The dynamic mass balances consisting of internal diffusion and surface reaction within the porous particles were solved simultaneously with the mass and energy balances of the whole reactor. The axial and radial concentration and temperature profiles inside the reactor and the concentration profiles within the particles were then obtained results. Starting from experiments performed at T=125–250°C, p=1atm and superficial gas velocity of 0.03m/s, a parameter estimation analysis was conducted. After the parameter estimation, the calculated alcohol conversion and yields of the main products (acetaldehyde and acetic acid) followed relatively closely the experimentally observed ones. The estimated parameters were the rate constants and the activation energies and the adsorption parameters (with LHHW kinetics, Mars van Krevelen kinetics) and reaction orders of oxygen (Power law kinetics). Simulation studies were done to show how feed temperature and catalyst loading influenced the results and how the Peclet number reflected on obtained results.