Decarbonisation Technology August 2022 issue

America and China, the use of 85% ethanol as an alternative to gasoline is an established practice. If in the future we are faced with a scenario where liquid fuels demand falls as electric mobility becomes dominant, there will still be many valuable outlets for bioethanol. These will include reforming to hydrogen to support hydrogen fuel cell mobility or hydrogen-fired internal combustion engines, which would also be zero CO₂ emissions vehicles. Ethanol to aviation fuel or jet fuel using ethanol to jet (ETJ) technology is also a viable option. According to a report from the US Department of Energy, a life cycle analysis was conducted using the Argonne National Laboratory’s Greenhouse Gases, Regulated Emissions, and Energy Use in Technologies (GREET) Model of corn to jet fuel using the ETJ process, and it confirmed that the life cycle could indeed be carbon negative. Gevo, a leading American renewable chemicals and advanced biofuels company, and Axens, a well-established French company in the energy and petrochemical sector, have recently announced a partnership in the US to commercialise this ETJ pathway. Gevo will be the operator, and Axens will bring proprietary technology to the table. The technology pathway is achieved through dehydration, oligomerisation, and hydrogenation. The core technologies for these process steps can be leveraged from decades of experience in the refining and petrochemical sectors. Penetration of e-fuels and biofuels vs green hydrogen Currently, green ammonia or green hydrogen from renewable power or blue and turquoise hydrogen with carbon capture in various forms are in the spotlight and regarded as scalable solutions for clean energy vectors. Utilisation equipment such as fuel cells and hydrogen or ammonia-fired gas turbines are rapidly emerging to use hydrogen and ammonia directly. Even aviation is considering the use of hydrogen or ammonia as a fuel. Synthetic e-fuels and bio-based liquid fuels will need to compete for attention, funding, and project capital. There are some key points for synthetic e-fuels that utilise captured CO₂ and biofuels to focus on to compete with hydrogen and ammonia. These include:

• Use of renewable or low-climate impact electrical power to provide energy for e-fuels production • Continued development and capital cost reduction of solid oxide electrolysis, which is an ideal-fit technology for CO₂ utilisation to make syngas in the e-fuels value chain • Use of agricultural waste as a feedstock, including rice husks, coconut husks, nut shells, and pruning clippings • Avoidance of deforestation to make space for energy crops • Consideration of urea fertilizer use and the CO₂, methane, and nitrous oxide emissions from crop cultivation. There are agricultural practices that can reduce these emissions significantly • The use of managed woodlands with certified wood if wood is the biomass in question • Use of fast-growing seasonal crops that rapidly remove CO₂ from the atmosphere whilst yielding energy vectors at low cost. Grasses and food crop wastes are good examples • Careful consideration of land use or land re- use with respect to local food requirements or the regional impact on food pricing. As an example, Germany was criticised for converting many acres of food-crop land to biogas production. Whilst the German public could tolerate the small consequent increase in food prices, other regional countries with lower per-capita incomes said their people were being hit with unaffordable higher food prices due to regional supply issues • Finally, a responsible approach to communication with consideration of full life cycle analysis. In any claims of ‘climate neutrality’ or ‘carbon negative’ processes, it is essential to build trust and avoid the accusation of ‘green washing’. Conclusion Synthetic e-fuels, biofuels, and BECCS can play a significant role in the energy transition towards net zero. They might not be in the spotlight to the same extent as hydrogen, but that is by no means a reflection of their potential as part of the solution to our current dependence on fossil fuel supply chains. In some cases, they can be ‘carbon- negative’ and therefore play a valuable role in a ‘net-zero’ energy system to balance out difficult-to- decarbonise processes in other sectors. Stephen B. Harrison


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