Analysis of a 2-D model of a packed bed reactor for methanol production by means of CO2 hydrogenation

In recent years, methanol received the attention of many researchers as a building block of the circular economy, because of its diversified applications in different areas. Generally, methanol is produced by syngas, however recent studies are dealing with its production via carbon dioxide hydrogenation. With the aim to predict conversions, efficiencies as well as concentration, pressure and temperature profiles inside the packed bed methanol reactor, mathematical models are developed in one- (1-D) and two- (2-D) dimensions. However, a deep study about a 2-D mathematical model and conditions where its use is advisable to get reliable predictions is missing in the literature. In this research, a two dimensional model for methanol reactor via carbon dioxide hydrogenation is suggested, comparing a structured catalytic packing with a more common packed bed of catalyst pellets, which differ mainly for the respective thermal conductivity. The system of partial differential equations is solved in MATLAB® and the same operating conditions set in a previous work about a one dimensional model are considered. Results show that the 2-D model is useful for both reactor typologies under the examined operating conditions, although definitely more important for the non-structured reactor, where higher temperature and concentration differences on tube cross sections are calculated because of a stronger resistance to radial heat transfer. In addition, a higher efficiency is predicted for a structured reactor in terms of carbon dioxide selectivity to methanol and methanol yield, then a lower recycle flow rate is required in this case. A sensitivity analysis is also developed for the two reactor typologies, changing feed inlet temperature, wall heat transfer coefficient and tube diameter. Conditions are investigated, for which 2-D model results tend to corresponding outputs of a 1-D model.