Modeling and simulation of CO2-rich synthesis gas to dimethyl ether conversion in microchannel reactors

Abstract

Dimethyl ether (DME) is considered as a strong counterpart of oil derivative fuels, such as liquid petroleum gas (LPG) and diesel fuel, due to its environmentally friendly combustion characteristics and compatibility with existing infrastructure. This study aims model based comparison of two wall{coated microchannel reactors on the basis of conversion of syngas composed of H2, CO and CO2, and yield of DME. In the rst con guration,namely the mixed bed, 1:1 (by mass) physically mixed, porous layers of Cu{ZnO/Al2O3 and {Al2O3, synthesis and dehydration catalysts, respectively, are considered to be washcoated to the opposing faces of the rectangular shaped microchannel, whereas separate layers of Cu{ZnO/Al2O3 and {Al2O3 face each other in the second con guration, namely the opposing bed. Comparisons are carried out at inlet pressure, temperature, molar H2/CO and H2/CO2 ratio ranges of 20{60 bar, 493{508 K, 2.5{4.0 and 5{12, respectively, under identical contact times. On both con gurations, fast temperature rise ( <8 K) at the channel entrance is observed, subsequently decreases along the reactor owing to in situ heat removal of integrated air cooling. Higher DME yield ( 3.2%) and CO2 ( 10.5%) conversion are obtained on the opposing bed, whereas elevated CO conversion ( 60%), is observed on the mixed bed. Negative CO2 conversions dictated by excess methanol produced by faster CO hydrogenation, observed on the mixed bed, is hampered on the opposing bed. Two dimensional steady{state modeling of the reactors is based on conservation of momentum and species mass together reactive transport within the wash-coated porous catalyst layer, all of which are solved by the nite volume method run under ANSYS-Fluent software.