Low CO2 methanol by methane pyrolysis in catalytic liquid metal bubble reactor
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Methanol production based on methane pyrolysis presents an opportunity for CO2 utilization and lower CO2 emissions than traditional methanol production processes that are based on methane reforming. This research employs a coupled hydrodynamic and kinetic pyrolysis reactor model in the design and simulation of a methanol plant that produces 2000 t/d of grade A methanol by direct hydrogenation of CO2. The methane pyrolysis occurs in a catalytic liquid metal bubble reactor where natural gas is injected at the bottom of the liquid metal bath and forms bubbles that rise through the molten metal. Methane pyrolysis occurs non catalytically inside the bubbles and catalytically at the gas-liquid interface. Solid carbon separates from the molten metal and forms a layer on top of the molten salt cap that is on top of the molten metal and is used to limit molten metal losses. The solid carbon can be continuously removed via skimming. A fired heater and heat recovery section are used to satisfy the energy demands of the process. Because the advantage of methanol synthesis based on methane pyrolysis lies in its low CO2 emissions, a comprehensive CO2 accounting is performed which accounts for the plant direct CO2 emissions as well as the indirect CO2 emissions associated with the natural gas supply chain and the capture of the process CO2 feed. The calculated CO2 emissions are compared to literature values for other methanol production processes based on methane reforming or methane pyrolysis. The plant economics are assessed to determine the levelized cost of carbon and evaluate the economic viability of the novel process. The proposed process has cradle-to-gate and cradle-to-grave emissions of 0.074 and 1.448 t CO2-eq/t MeOH, respectively, when a CH4 conversion of 80% in the pyrolysis reactor is used and when the indirect CO2 emissions are calculated at their base values. The corresponding volume of Cu0.45Bi0.55 catalytic liquid metal is 98.0 m3 . These operating conditions result in a levelized cost of carbon of $270/t. It was found that the levelized cost of carbon is most sensitive to the fixed capital investment of the plant and the purchase price of CO2. This work shows that the source of CO2 is a critical variable for this process, as it affects both the purchase price and the emissions associated with its capture.