A CLIMIT supported project has yielded such promising results that Hydro will invest in the technology

Text and photo: Hydro

In launching its new sustainability ambitions, Hydro has announced its intention to deliver its first commercial volumes of near-zero carbon aluminium in 2022. Hydro is also continuing its technology efforts toward an industrial scale pilot producing carbon-free aluminium by 2030.

Without CO₂ emissions

 In Norway, more than two million tonnes of CO₂ per year are emitted from the electrolysis plants. Globally, more than hundred million tonnes are emitted. CO₂ stems from the reaction between aluminium oxide and carbon anodes. During the electrolysis process, aluminum oxide is split into liquid aluminium metal on the cathode and CO₂ is on the anode. In the alternative process, aluminium oxide is first converted to anhydrous aluminum chloride, AlCl₃, which is then electrolysed. In this electrolysis process, aluminium chloride is split into liquid metal on the cathode and chlorine gas on the anode. The electrolysis process itself takes place without CO₂ emissions. Anhydrous aluminum chloride does not exist naturally and must be made as an integral part of the process.

On a large scale, the only proven method is so-called carbochlorination of aluminium oxide at around 700°C: Al₂O₃(s) + 1.5C(s) + 3Cl₂(g) = 2AlCl₃(g) + 1.5CO₂(g). Chlorine for this reaction will come from the electrolysis of AlCl₃. Even if CO₂ is not formed in the electrolysis process itself, CO₂ will form during carbochlorination. But this CO₂ can be captured far more easily than the one from the current electrolysis process since it is almost concentrated. It is also possible to recycle it in this process.  It is known that CO gas can be used instead of carbon to produce AlCl_3. CO₂ from the carbochlorination can therefore be converted to CO and thus recycled. For example, conversion of CO₂ to CO can occur using hydrogen or electrolysis. Alternatively, CO can be made from natural gas with hydrogen as a by-product. Then CO₂ from production of AlCl₃ must be sent to storage (CCU). An additional option is to use biomass to make CO. Then produced CO₂ could be released to the atmosphere climate neutral or, if stored, give net capture of CO₂. All these options will be evaluated in the project. In addition, the carbochlorination process will be studied in depth and a techno-economic model will be developed for the whole process.