Comparing Life-Cycle Emissions of Biofuels for Marine Applications: Hydrothermal Liquefaction of Wet Wastes, Pyrolysis of Wood, Fischer-Tropsch Synthesis of Landfill Gas, and Solvolysis of Wood

Recent restrictions on marine fuel sulfur content anda heightenedregulatory focus on maritime decarbonization are driving the deploymentof low-carbon and low-sulfur alternative fuels for maritime transport.In this study, we quantified the life-cycle greenhouse gas and sulfuroxide emissions of several novel marine biofuel candidates and benchmarkedthe results against the emissions reduction targets set by the InternationalMaritime Organization. A total of 11 biofuel pathways via four conversionprocesses are considered, including (1) biocrudes derived from hydrothermalliquefaction of wastewater sludge and manure, (2) bio-oils from catalyticfast pyrolysis of woody biomass, (3) diesel via Fischer-Tropschsynthesis of landfill gas, and (4) lignin ethanol oil from reductivecatalytic fractionation of poplar. Our analysis reveals that marinebiofuels' life-cycle greenhouse gas emissions range from -60to 56 gCO(2)e MJ(-1), representing a 41-163%reduction compared with conventional low-sulfur fuel oil, thus demonstratinga considerable potential for decarbonizing the maritime sector. Dueto the net-negative carbon emissions from their life cycles, all waste-basedpathways showed over 100% greenhouse gas reduction potential withrespect to low-sulfur fuel oil. However, while most biofuel feedstockshave a naturally occurring low-sulfur content, the waste feedstocksconsidered here have higher sulfur content, requiring hydrotreatingprior to use as a marine fuel. Combining the break-even price estimatesfrom a published techno-economic analysis, which was performed concurrentlywith this study, the marginal greenhouse gas abatement cost was estimatedto range from -$120 to $370 tCO(2)e(-1) across the pathways considered. Lower marginal greenhouse gas abatementcosts were associated with waste-based pathways, while higher marginalgreenhouse gas abatement costs were associated with the other biomass-basedpathways. Except for lignin ethanol oil, all candidates show the potentialto be competitive with a carbon credit of $200 tCO(2)e(-1) in 2016 dollars, which is within the range of pricesrecently received in connection with California's low-carbonfuel standard. Biofuels could replace conventionalfossil marine fuel toreduce life-cycle greenhouse gas emissions from the shipping industryand could be made competitive with fossil fuels with recently availablecompliance credits.

Automated summary

Recent restrictions on marine fuel sulfur content and a heightened regulatory focus on maritime decarbonization are driving the deployment of low-carbon and low-sulfur alternative fuels for maritime transport. This study quantified the life-cycle greenhouse gas and sulfur oxide emissions of several marine biofuel candidates and compared them with the emissions reduction targets set by the International Maritime Organization. The results show that marine biofuels have significant potential for decarbonizing the maritime sector, with a range of 41-163% reduction in greenhouse gas emissions compared to conventional low-sulfur fuel oil.