How are they produced?
It all depends on whether the desired end product is in gas or liquid form:
- gas e-fuels: renewable hydrogen and e-methane, which can both be liquefied later, to produce liquid H2 and e-GNL respectively.
- liquid e-fuels: like e-methanol and e-crude, also known as synthetic crude oil, which make e-kerosene and e-diesel.
- gas or liquid form: synthetic ammonia.
Depending on the form or the e-fuel required, either a Power-to-Gas or Power-to-Liquid process is used. Both of these production processes involve two or three phases, with first of all hydrogen (H2) production by water electrolysis from renewable electricity, associated with another molecule - CO2 for e-crude and synthetic methane or methanol, or nitrogen (N2) for synthetic ammonia. Synthetic crude oil must be refined (like fossil oil) to produce synthetic kerosene or diesel.
E-methane, e-methanol, e-diesel and e-kerosene are synthetic hydrocarbons, so their production processes require CO2. This vital element can either be captured directly from the atmosphere or taken from industrial plants that use fossil fuels. Different sources of CO2 (biomass, industry, air) have an impact on the synthetic fuel's lifecycle analysis, environmental benefits and production cost.
An alternative method of synthetic crude oil production is high temperature H2O/CO2 co-electrolysis. As it does not require the input of renewable hydrogen, CO2 being introduced at the beginning, the process is a stage shorter. This is an advantage as it improves productivity (by up to 30%) and, in theory, reduces investment costs. However, the technology is not yet very mature and most initial production projects opt for hydrogen production by low temperature electrolysis in their first phase.
What are the applications of e-fuels and in what time frame?
Heavy mobility accounts for about a quarter of global CO2 emissions. With this in mind, and at a time when electricity would appear to be the future of road transport, e-fuels have a key role to play, particularly in the maritime and air transport sectors for which decarbonisation cannot be achieved solely through electrification.
E-fuels have the advantage of using the same infrastructure as their fossil equivalents (petrol, diesel, kerosene, methanol or natural gas). Putting them in competition with biofuels, which offer the same advantage.
It is estimated that by 2070 e-kerosene will meet 40% of aviation energy demand. And what about other sectors - maritime, rail and road? Hydrogen will be part of the solution. One lead involves producing a synthetic fuel from green hydrogen and CO2 captured from industrial emitters. There are many initiatives underway worldwide, all trying to produce green e-fuels at an increasingly competitive price. In the North Sea for example, two projects are being developed to produce synthetic methanol to fuel ships. One of these projects, based in the Port of Antwerp, will meet part of the local demand for methanol.t.
"E-fuels can be used not only to transport and store hydrogen, but for many other uses, from heavy transport decarbonisation to green chemistry. They are also a way of recycling and recovering CO2, from which most e-fuels are made."
Laurence Boisramé, Hydrogen and E-fuels Programme Director
Two key families of e-fuel
E-fuels are separated into two main categories, depending on the final product, whether gas or liquid: