E-fuels are fuels made from ‘green’ hydrogen — i.e. produced by a process using the electrolysis of water — which is then combined with CO2 captured either at plant outlets or in the air, to produce methane, methanol or synthetic paraffinic fuels such as e-gasoline, e-gasoil or e-kerosene. Ammonia can also be produced, but by reacting hydrogen with nitrogen instead of CO2.
The problem is that this type of production consumes a huge amount of energy: the renewable electricity needed to produce hydrogen by electrolysis, the energy needed to capture the CO2, then the energy needed either for the methanation or hydrogenation reaction of the CO2 to obtain e-methane, or for the other synthesis reactions, often catalytic, to obtain e-fuels (petrol, diesel or paraffin).[1] The report by the energy industry states that most energy consumption is linked to hydrogen production: the efficiency of converting electricity into fuel is between 40% and 60%, depending on the electrolyser used.[2] So while the synthesis routes for reacting carbon dioxide with hydrogen are mature and well known, they still consume energy during the process. Above all, the production of these fuels relies on a hydrogen production and CO2 capture process which is not yet mature.
The major advantage of these liquid fuels is that they can replace conventional fossil fuels without any change in use. Their properties are similar to those of fossil fuels, but they have the advantage of being purer, i.e. containing less sulphur or aromatic particles (PAHs), which generate pollution. Although these fuels require CO2 for their manufacture, thus they do not eliminate it and simply recycle it. But, like fossil fuels, they emit nitrogen oxides and particles during combustion.
