Electricity and Control May 2021

ENGINEERING THE FUTURE

The potential of e-fuels

G rowth in global energy consumption has caused CO 2 and greenhouse gas (GHG) emissions to rise, in turn causing an increase in average global temperatures. The combustion of fossil fuels including coal, oil and natural gas, has been one of the main drivers behind this, presenting the underlying rationale for the production and use of non- fossil alternative fuels that can help reduce emissions. While progress is being made in the power sector with the integration of renewable power sources, and in light- duty on-road transport with battery electric vehicles, other sectors have been slower to adopt low-carbon technologies. IDTechEx’s latest research on electric vehicles is detailed in its report titled: Electric Vehicles: Land, Sea and Air 2021- 2041 . Electrification is key to any low-carbon strategy, providing the most efficient means to use renewable power sources. However, complete electrification is unlikely to be feasible for applications such as heating, shipping, or aviation. Taking aviation as an example, this can be easily understood given the much lower energy density of battery technology compared to kerosene (a major component of jet-fuel). Instead, sustainable gaseous and liquid fuels are going to be needed, with two main routes available: biofuels and synthetic electro-fuels (e-fuels), including green hydrogen. Biofuels are widely used today, primarily in blending bioethanol and biodiesel for on-road transport fuels. To date, food crops have been the major feedstock. Sugars can be fermented to produce ethanol and transesterification of vegetable oils produces biodiesel. Longer-term, more advanced feedstocks from cellulosic or woody feedstocks,

or from waste materials, can help limit the impact on land use, competition with food production, and minimise lifecycle emissions from biofuel production. Nevertheless, concerns remain over the true sustainability biofuels offer and limits on feedstock availability. An alternative to biofuels may therefore be needed and electro-fuels (e-fuels or synthetic e-fuels) could provide an alternative means to produce ‘drop-in’ liquid and gaseous fuels. Electro-fuels, or e-fuels, consist of fuels produced using hydrogen from water electrolysis, with the name referring to the process rather than the fuel itself and incorporating the terms power-to-X, X being a gaseous or liquid product. Hydrogen itself can be considered an e-fuel, together with methane and ammonia as other power- to-gas fuels. However, H 2 in particular is difficult to store and transport and even liquid H 2 has a comparatively low volumetric energy density. Nonetheless, liquid fuels are likely to be preferred for hard-to-abate transport sectors. Drop-in liquid fuels, such as gasoline, diesel, or jet fuel (power-to-liquid), can be obtained by combining hydrogen with a carbon source, such as from direct-air-capture (DAC). While there are various routes to produce a final e-fuel, many will rely on syngas, a combination of H 2 + CO, as an intermediate. Syngas can be produced through the combination of H 2 and CO 2 in a water gas shift reactor and further processed into drop-in fuels. It is also possible to produce syngas directly, for example, through co-electrolysis of CO 2 and steam. Methanol may be another important intermediate, produced either from syngas or again, directly via electrochemical or

Process overview for e-fuel production. [Source: IDTechEx]

30 Electricity + Control MAY 2021