Methanol synthesis in a simulated countercurrent moving-bed adsorptive catalytic reactor

Abstract

The continuous chromatographic reactor is a device for carrying out chemical reactions and separations simultaneously in a fixed bed to improve product conversions beyond those predicted by thermodynamic equilibrium. In the simulated countercurrent moving-bed chromatographic reactor a countercurrent moving-bed operation is mimicked by periodically changing feed and product locations sequentially along a fixed bed. In the present work the synthesis of methanol from syngas in a simulated countercurrent moving-bed adsorptive catalytic reactor (SCCMBR) is studied by means of numerical modeling. Two different reactor configurations are considered. In the first, operating under adiabatic conditions, the fixed bed consists of a catalyst and a selective product adsorbent, mixed together. In the other one, operating isothermally, the catalyst and adsorbent are alternately packed in beds containing catalyst or adsorbent, and only adsorber sections participate in a discrete countercurrent movement. The present paper analyzes and compares the performance of these two reactors. In addition, a stripping section is introduced to increase the process conversion by blowing unconverted reactants back to the reaction zone before the product removal step. It is shown that there is a range of operating conditions for which very high carbon monoxide conversions (96–99%) are attainable in a single-pass operation due to adsorption of methanol and its continuous withdrawal with solid adsorbent from reaction zone. The reactors have been simulated for conditions that may be used in a commercial operation. Experimental data from the literature have been used for the calculations to describe reaction kinetics over low-pressure catalyst Cu/ZnO/Al 2O 3 and adsorption of methanol onto silica-alumina adsorbent.