Biogas catalytic methanation for biomethane production as fuel in freight transport - A carbon footprint assessment

The use of biomethane can help reduce greenhouse gas emissions (GHG) from road transport in trucks. To assess its potential contribution, two biomethane production pathways were analysed: conventional biogas upgrading and catalytic methanation of carbon dioxide from biogas, contained in biogas or separated via biogas upgrading. Pig manure was used as feedstock for biogas production. Throughout a life cycle assessment methodological approach, the total GHG equivalent emissions were calculated for each production pathway, considering the chemical absorption, pressure swing adoption and membrane separation technologies for biogas upgrading, and renewable sources of electricity (wind and photovoltaic) for hydrogen production further processed in methanation. Catalytic methanation via micro-structured reactors was selected as a reference process. The assessments show that emissions vary from 0.28 to 0.72 kg CO2-eq./m3 in biomethane production via biogas upgrading and from 0.36 to 1.04 kg CO2-eq./m3 via catalytic methanation. These values are comparable to those of natural gas conditioned as fuel for transportation, which lie between 0.038 and 0.55 kg CO2-eq./m3. Due to its emission neutrality, in the use phase of biomethane in trucks total emissions are substantially lower than those associated with fossil fuels (natural gas and diesel). For the investigated use cases, they range from 0.03 to 0.07 kg CO2 -eq./t km for biomethane, whereas for natural gas or diesel from 0.16 to 0.18 kg CO2 -eq./t km and 0.17–0.19 kg CO2-eq./t km. These results demonstrate the environmental benefits of biomethane in freight transport in terms of reduction in GHG emissions.