Kinetic modeling and reactor design of the direct synthesis of dimethyl ether for CO2 valorization. A review

The direct synthesis of dimethyl ether (DME) is considered one of the most attractive routes for valorizing CO2 and syngas on a large scale. DME has a high cetane number and its properties are similar to those of liquefied petroleum gases (LPG). It can be used directly as fuel, selectively converted into hydrocarbons (olefins, aro-matics) or used as H-2 vector. This review explains briefly the advances in the study of the thermodynamics of DME synthesis and in the preparation of suitable catalysts. Subsequently, analyzes in detail the studies regarding the kinetic modeling, reactors design and reaction strategies. Extensive information is given on the kinetic models described in the literature, indicating the catalysts and reaction condition ranges for which the models were proposed. These kinetic models were whether based on those previously proposed separately for methanol synthesis and methanol dehydration stages on monofunctional catalysts, or models specifically proposed for bifunctional catalysts and conditions of the integrated process. Coke deposition is considered the main cause for catalyst deactivation and is quantified with different kinetic models. The presence of H2O in the reaction medium is a limiting factor for the thermodynamics and for the extent of the reactions. This problem is overcome using hydrophilic membrane reactors, whose behavior has been studied by simulation and recently with an experimental system (with an LTA zeolite membrane). Finally, an analysis of the advantages and limitations of the different reactors and the challenges to progress towards the implementation of the direct CO2 to DME synthesis process have been addressed.