(269a) Methanol Synthesis Processes

Hydrogenation of carbon dioxide may contribute to the reduction of industrial carbon dioxide emissions. The bulk chemical methanol is a suitable hydrogenation product. It is used for paints, plastics, and adhesives, as feedstock for the production of chemicals such as formaldehyde, ethylene, propylene, methyl tertiary-butyl ether, and acetic acid, and as fuel additive or alternative fuel. It provides promising properties for energy storage, as it can raise the energy density of hydrogen-based energy carriers by one order of magnitude. Low temperature level in reforming also suggests methanol for fuel cell applications. State-of-the-art methanol production is based on syngas, a mixture of carbon monoxide, carbon dioxide, and hydrogen, and preferably Cu/ZnO/Al₂O₃ catalysts. State of the art reactor- and process design suggest looping systems with sophisticated internal heat energy management. Huge efforts have meanwhile been made to directly process carbon dioxide instead of syngas. To our knowledge neither of the carbon dioxide based processes has established on the market, mainly because of catalyst life time limitations. To sum up the present status, the establishment of direct methanol synthesis from carbon dioxide suffers from limitations in feed gas preparation and/or appropriate catalysts. Appropriate high carbon dioxide concentration sources are available in huge quantities in the iron and steel industry or cement industry, but appropriate solutions are still missing.

When processing carbonate based iron ores (siderite) in hydrogen atmosphere our group registered that within a temperature window of 600 to 800 °C and ambient pressure it is possible to alter the carbon monoxide/carbon dioxide ratio of the exiting gas. The final solid product from ore reduction still maintains this “catalytic” property, suggesting it for syngas preparation from carbon dioxide with a cheap and robust catalyst which can easily be processed after deactivation. The process was tested and validated in a lab size plug flow reactor setup.

For experimental simulation/validation of the methanol synthesis in lab scale a CSTR loop reactor system with external cooling loop for condensing the gaseous products and pressure drop controlled gas feed was constructed. The operation window of the setup is 500 °C at maximum and 10 MPa. At present the reactor setup is equipped with two gas supply lines equipped with mass flow controllers, limiting operation flexibility to fixed stoichiometry of the carbon dioxide/carbon monoxide source. The methanol synthesis process was validated with a Cu/ZnO/MgO catalyst prepared by wet incipient impregnation and stoichiometric CO₂/H₂ feed at 250 °C and 5 MPa. Whether this catalyst can withstand long term operation with CO₂/H₂ feed with acceptable loss of activity, or whether an upgrade of the feed gas by pretreatment in the syngas reactor is needed, cannot be concluded from present experience. However, either route, dual step synthesis with feed gas pretreatment or direct synthesis shows promising features, since catalyst life span is not a crucial issue.