Using the analytical heirarchy process to select specific methanation catalysts based on their extraction impacts

Summary Methanation is an exothermic process that utilizes catalysts to convert the carbon dioxide and carbon monoxide in biogas to methane, forming synthetic natural gas. The criteria for determining a suitable catalyst should not only be its effectiveness, but also the environmental impact of extracting and refining the metal. The authors examine the environmental impacts of implementing a select group of methanation catalysts in the field for industrial scale synthetic natural gas production using the analytical hierarchy process (AHP). Catalysts containing a combination of rare earth metals are investigated separately and AHP is used to rank the catalysts based on their environmental impact per kg of CO2 converted. It is determined that catalysts containing common metals, such as nickel, have the lowest environmental impact per conversion rate across a number of metrics and represented the catalysts with the second and third highest conversion rates analyzed. Catalysts containing ruthenium are found to be the most detrimental to the environment, in spite of the favorable conversion rate offered by a ruthenium‐cesium catalyst in methanation reactors. In this analysis, the authors illustrate that the environmental impacts created by certain catalysts for the production of renewable natural gas significantly exceed the benefit they provide by having a high conversion rate of CO2. Specific, catalysts that do not utilize platinum group metals have a lower environmental impact when compared on a per conversion scale. This work connects important laboratory research on catalysis with their life cycle environmental costs.