Optimal conditions for hydrogen production from coupling of dimethyl ether and benzene synthesis

Coupling energy intensive endothermic reaction systems with suitable exothermic reactions followed by hydrogen permeation through the Pd/Ag membrane improves the thermal efficiency of processes, achieving the autothermality within the reactor, reduces the size of reactors, produces the pure hydrogen, and achieving a multiple reactants multiple products configuration. This paper focuses on optimization of hydrogen, dimethyl ether (DME) and benzene production in a membrane thermally coupled reactor. A steady-state heterogeneous mathematical model that is composed of three sides is developed to predict the performance of this novel configuration reactor. The catalytic methanol dehydration to DME takes place in the exothermic side that supplies the necessary heat for the catalytic dehydrogenation of cyclohexane to benzene reaction in the endothermic side. Selective permeation of hydrogen through the Pd/Ag membrane is achieved by co-current flow of sweep gas through the permeation side. This novel configuration can decrease the temperature of methanol dehydration reaction in the second half of the reactor and shift the thermodynamic equilibrium. The differential evolution (DE), an exceptionally simple evolution strategy, is applied to optimize membrane thermally recuperative coupled reactor considering the summation of methanol and cyclohexane conversions and dimensionless hydrogen recovery yield as the main objectives. The simulation results have been shown that there are optimum values of initial molar flow rate of exothermic and endothermic sides and inlet temperature of exothermic, endothermic and permeation sides to maximize the objective function. The optimization method has enhanced the methanol conversion by 2.76%. The optimization results are compared with corresponding predictions for a conventional (industrial) methanol dehydration adiabatic reactor operated at the same feed conditions. The results suggest that coupling of these reactions could be feasible and beneficial. An experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.

Research highlights
► This paper focuses on optimization of hydrogen, dimethyl ether (DME) and benzene production in a membrane thermally coupled reactor.
► The catalytic methanol dehydration to DME takes place in the exothermic side that supplies the necessary heat for the catalytic dehydrogenation of cyclohexane to benzene reaction in the endothermic side.
► This novel configuration can decrease the temperature of methanol dehydration reaction in the second half of the reactor and shift the thermodynamic equilibrium.
► The results suggest that coupling of these reactions could be feasible and beneficial.