Industry standard: Indirect
Unconverted CO
Unconverted syngas
After treatment
RWGS
F-T
Separator
Separator
CO + H
CO + H O
CO + 2H -(CH )- + H O
SA F
CO H
Unconverted syngas
After treatment
OXCCU
Separator
Proprietary catalyst
CO + 3H -(CH )- + 2H O
OXCCU: Direct
Figure 2 Indirect and direct hydrogenation of CO₂
temperature heat from the F-T reaction. RWGS also requires either a new, complex and difficult- to-scale electrically heated reactor design, or an autothermal reforming (ATR)-like reactor that burns hydrogen, resulting in significant energy loss and high operational cost. The F-T reaction itself can also require expensive reactor designs as it is very exothermic and, as mentioned earlier, needs to be kept down at 280°C. The solution is a multifunctional heterogeneous catalyst with a surface on which both reactions, RWGS and F-T, can take place (see Figure 3 ). A metal surface can bind CO₂ and then encourage the F-T chain growth reactions, which form the long-chain hydrocarbons, to occur by lowering their activation energies while suppressing methane, light gas, and oxygenate formation. The key was to go back to the iron F-T catalysts, and this is what OXCCU did. It is now scaling its patented, highly selective iron F-T catalysts for the direct hydrogenation of CO₂. Based on more than a decade of research within the University
of Oxford chemistry department and then spun out into OXCCU ( Yao, et al. 2020 ), novel catalysts with high conversion and selectivity have been developed, which result in a more efficient process with lower costs to convert CO₂ and H₂ directly to long-chain hydrocarbons. With fewer steps involved, there is a reduction in Capex and Opex, ultimately leading to lower fuel costs. This emphasis on cost reduction is supported by independent researchers from Imperial College London, who demonstrated that OXCCU’s one-step technology has a 50% lower capital cost, lower operation costs, and a reduced environmental impact compared to other methods that utilise multi-step processes to create jet fuel. Before selling as jet fuel, OXCCU will need confirmation that it is within the ASTM D7566 route for F-T SPK. Currently, the F-T SPK annex 1 refers to ‘syngas’ as the feedstock. While syngas is not specifically defined, it is generally understood that it consists mainly of CO and H₂, not CO₂ and H₂. The OXCCU process, while having only CO₂ and H₂ as the feedstock, still involves CO and H₂ on the surface. Sometimes CO₂ turns to CO on the surface and immediately undergoes a chain growth reaction. Other times, CO formed leaves the surface but is recycled, rebinds, and then undergoes F-T chain growth. Hence, all the CO₂ in the OXCCU process goes via ‘syngas’ and fits the standards. The only difference between the two-step F-T, which has already been confirmed as acceptable, and the OXCCU one-step F-T process is that the RWGS step happens on the same catalyst surface as the F-T. The intermediate is CO and H₂ (syngas) in both cases, as per annex 1.
E-Hydrocarbons
CO
H
H O
Figure 3 Dual-function catalyst for CO₂ conversion
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