Tech Talk: How to make fuel out of fresh air

Innovative direct air capture technology combines CO2 with green hydrogen to make methanol for e-fuels.

By Jesse Crosse, Autocar UK calendar 06 Oct 2023 Views icon3863 Views Share - Share to Facebook Share to Twitter Share to LinkedIn Share to Whatsapp

Porsche and partners are on track with the production of e-fuel at the Haru Oni demonstration plant in Chile.

The next step is to develop the direct air capture technology (DAC) from the atmosphere to make production as sustainable as possible.

DAC captures CO2 from the atmosphere to combine with green hydrogen made at the plant using electrolysis powered by wind-generated energy. The hydrogen and CO2 are combined in a synthesis process to make methanol, which is further processed to produce the e-fuel.

The e-fuel we’re interested in is a synthetic petrol that is chemically equivalent to fossil-fuel petrol, but it can also be formulated as aviation jet fuel. The fuel can be used with existing engines and, if it were to make large-scale production in the future, could be supplied using the existing infrastructure and filling station forecourts.

Model of a Direct Air Capture unit at the VW Group stand at the IAA Summit. 

Initially, the Haru Oni plant, which started production earlier this year, used CO2 produced from biomass, so the process is still CO2-neutral because the plant matter used absorbed CO2 while growing.

Getting CO2 from DAC is more straightforward because the processing of biomass is removed from the equation. It’s also flexible because DAC plants can be set up anywhere and it can be scaled up to make the large volumes of gas needed for mass production of the green fuel.

DAC captures CO2 from the atmosphere to combine with green hydrogen using electrolysis powered by wind-generated energy. The hydrogen and CO2 are combined in a synthesis process to make methanol, which is further processed to produce the e-fuel.

The first stage in extracting CO2 from the atmosphere is to clean the air to remove large particles of dirt, before passing it through a filter material, which traps (adsorbs) the CO2. Once that’s done, the CO2 is extracted by heating the material, leaving just water as a by-product.

Electricity for the entire process is produced by a 3.4GW Siemens Gamesa wind turbine. A Siemens Energy electrolyser (working like a hydrogen fuel cell in reverse) produces pure hydrogen by splitting water into hydrogen and oxygen, and the same wind-generated electricity will also drive the DAC plant. Waste heat from the electrolysis is captured and used in the CO2 extraction process.

The finished synthetic fuel still contains carbon, which is released when the fuel is used, but the carbon isn’t fossil-based so the process is circular and sustainable. CO2 emitted into the atmosphere came from the atmosphere, but synthetic fuel doesn’t remove existing CO2 from the equation altogether.

There are already a number of DAC projects in operation around the world, and apart from making synthetic fuel, it can also be used as a raw material to make non-fossil-based plastics.

Although the project shows huge potential, it’s likely to remain a rarity, according to a report by the Potsdam Institute for Climate Impact Research released earlier this year.

It estimates the production cost of fuel produced initially at the £60 million (Rs 611 crore) pilot plant to be around £43 (Rs 4,383) per litre but at industrial scale sees that dropping to as little as 86p (Rs 87) per litre. However, that’s still twice the wholesale cost of petrol. 

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