solutions for syngas production. Mitsubishi Heavy Industries is reported to have successfully conducted demonstration of an integrated production process for synthesising eSAF from CO 2 , steam and renewable power via SOEC co- electrolysis coupled with FT synthesis.8 As opposed to SOEC electrolysers used for high-temperature co-electrolysis, a pioneering start-up, Twelve, has developed an efficient proton exchange membrane (PEM) CO 2 electrolyser with a polymer electrolyte that uses proprietary CO 2 -reducing catalysts to split CO 2 with just water and renewable electricity as inputs. Syngas (CO and H 2 ) is the output, and pure O 2 is the only byproduct. Also, Liquid Sun offers low-temperature co- electrolysis technology for syngas production, based on its proprietary design of low- temperature electrolysers. Meanwhile, instead of SOEC and PEM electrolysers, Sora Fuel, a venture-backed start-up, offers a liquid bicarbonate electrolyser operating in a fully closed-loop system that uses only water and renewable electricity to produce syngas. All these electrolyser set-ups use steam (or water) and CO 2 as feedstock to produce renewable syngas in a single process step, and are typically modular, enabling the system to expand as feedstock volumes and output demand increase. Smart integration of waste heat and CO 2 sources reduces electricity demand. The integrated process can also be configured to utilise process heat from the FT reactor to create the steam needed for the electrolysis process. Extensive research is ongoing in the field of co- electrolysis to generate various products via the electrochemical reduction of CO 2, depending on factors such as the types of cell and electrodes, the catalyst used, and the reaction conditions (such as voltage, temperature, and pressure). These reactions are performed in an electrolyser, which is a cell designed for CO 2 RR. Many different designs are being researched, including H-type cells, gas diffusion electrodes (GDE) cells, membrane electrode assembly (MEA) cells and solid-state electrolyte cells.5 , 6 , 7 CO 2 RR is performed using an electrolyser in which CO 2 is reduced at the cathode. Water is oxidised to O 2 gas, protons (H + ), and electrons at the anode. This typically also contains a catalyst, the choice of which heavily influences
Electrochemical reactions
Half-cell reaction 2H + + 2e − → H₂
E o /(V/SHE, pH=7)
-0.42 -0.53 -0.61 -0.38 -0.24
CO₂ + 2H + + 2e − → CO + H₂O CO₂ + 2H + + 2e − → HCOOH CO₂ + 6H + + 6e − → CH₃OH + H₂O CO₂ + 8H + + 8e − → CH₄ + 2H₂O 2CO₂ + 12H + + 12e − → C₂H₄ + 4H₂O
0.06
Table 1
the product. For example, gold and silver tend to produce CO, while copper produces compounds like ethylene or ethanol. Although the most common product is syngas (CO and H₂), other useful products are formic acid, alcohols like methanol and ethanol, and hydrocarbons such as methane and ethylene. The corresponding electrochemical reactions, along with the standard electrode potentials versus the standard hydrogen electrode (SHE), are shown in Table 1 .9 Although CO 2 RR is a promising technology, there are challenges of catalytic efficiency, selectivity, and stability that need to be overcome for it to become a viable solution. Dry reforming of methane Reforming of hydrocarbon feeds (typically methane) with steam and CO 2 , hereinafter referred to as CO 2 reforming or dry reforming of methane (DRM), offers another pathway to use CO 2 as feedstock for production of valuable syngas. DRM Reaction ( Equation 5 ), a potential syngas production technology based on CO 2 and methane, has drawn a lot of attention, especially considering the availability of biogas/biomethane and the demand for technologies with the potential of utilising waste or captured CO 2.9 CH₄ + CO₂ → 2CO + 2H₂ ΔH = +247 kJ/mole (Eq. 5) The term ‘dry’ in dry reforming originates from the substitution of water in steam reforming with CO 2 . The idea of producing synthesis gas from CO 2 and CH 4 dates back to the 19th century. Compared to SMR, DRM offers several advantages, especially in terms of energy efficiency, since little or no steam is needed, implying lower investments in terms of energy.
Refining India
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