Technical Review - The process of finding new alternative fuels
The AFS Process - turning air into a sustainable fuel
i) Air is blown up into a tower and meets a mist of a sodium hydroxide solution. The carbon dioxide in the air is absorbed by reaction with some of the sodium hydroxide to form sodium carbonate. Whilst there are advances in CO2 capture technology, sodium hydroxide has been chosen as it is proven and market ready.
ii) The sodium hydroxide/carbonate solution that results from Step 1 is pumped into an electrolysis cell through which an electric current is passed. The electricity results in the release of the carbon dioxide which is collected and stored for subsequent reaction.
iii) Optionally, a dehumidifier condenses the water out of the air that is being passed into the sodium hydroxide spray tower. The condensed water is passed into an electrolyser where an electric current splits the water into hydrogen and oxygen. Water might be obtained from any source so long as it is or can be made pure enough to be placed in the electrolyser.
iv) The carbon dioxide and hydrogen are reacted together to make a hydrocarbon mixture, the reaction conditions being varied depending on the type of fuel that is required.
v) There are a number of reaction paths already in existence and well known in industrial chemistry that may be used to make the fuels.
(1) Thus a reverse-water-gas shift reaction may be used to convert a carbon dioxide/water mixture to a carbon monoxide/hydrogen mixture called Syn Gas. The Syn Gas mixture can then be further reacted to form the desired fuels using the Fisher-Tropsch (FT) reaction.
(2) Alternatively, the Syn Gas may be reacted to form methanol and the methanol used to make fuels via the Mobil methanol-to gasoline reaction (MTG).
(3) For the future, it is highly likely that reactions can be developed whereby carbon dioxide and hydrogen can be directly reacted to fuels.
vi) The AFD product will require the addition of the same additives used in current fuels to ease starting, burn cleanly and avoid corrosion problems, to turn the raw fuel into a full marketable product. However as a product it can be blended directly with gasoline, diesel and aviation fuel.