| dc.description.abstract | Around 3 billion tons of carbon dioxide is emitted every year through the chemical and petrochemical industries. To reduce these emissions and utilize the natural resources better, new sustainable routes are needed to replace the highly optimized and cost-competitive methane conversion to chemicals via the indirect syngas route. Of the proposed directed routes are the oxidative and non-oxidative coupling of methane, which have not yet been commercialized. Among other challenges, these routes require high operating temperatures (600 – 1000 oC) and strict heat management. An idea to address these challenges is to consider both chemistry routes in the same chemical plant as this can have many potential advantages. One of these potential advantages is reaching autothermal operation which reduces the energy demands and carbon emissions. This work aims to explore options for thermal coupling of exothermic and endothermic reactions in a single reactor but without any mass integration. The first reaction is the oxidative coupling of methane (OCM) which is highly exothermic (ΔHorxn= -141 kJ/mol.CH4) and produces C2+ products like ethane and ethylene. The second reaction is methane dehydroaromtization (MDA) which is endothermic (ΔHorxn= +88.4 kJ/mol.CH4) and yields C6+ products like benzene, toluene, and naphthalene.
Available kinetic models for OCM and MDA are studied from the literature and an separate ideal packed bed reactor was modeled using relatively simple kinetics. Multiple optimization studies via single-variable-at-a-time were performed and an operating window for thermal coupling is identified in between 700 – 850 oC temperature, 1 – 5 atm pressure, GHSV 830 – 14,000 h-1, and heat duties of 1–13 MW. Owing to many input and output variables, several design options can be proposed. Therefore, we developed a methodology with visual representation to help navigate between different optimization options for thermal coupling. A study was carried out by having each reaction in a separate reaction channel divided by a channel wall using heat transfer and pressure drop correlations from literature assess the temperature profile. As a starting point, both reaction channels are considered straight, having identical channel length, and filled with spherical catalyst particles in an ideal packed bed reactor. Parameters affecting such a reactor design were studied, which include heat transfer coefficient, diluents, catalyst profiling and flow direction. Using the proposed methodology, further work can mainly be carried out for achieving a global optimum via multi-objective optimization. This would allow for quick decision making between different kinetic models and reactor designs with the given targets and constraints. | en |
