Sora Fuel, an American cleantech company founded in 2024, has developed a novel integrated system for atmospheric carbon dioxide (CO₂) capture and conversion into syngas via electrochemical processes. This syngas serves as a key component in producing sustainable aviation fuel (SAF), supporting the aviation industry's efforts to decrease its carbon emissions.
(This article contains 7 diagrams and 1723 words.)
Challenges: carbon-neutral fuel
Carbon dioxide (CO₂), a heat-trapping greenhouse gas, contributes to climate change. Human activities, particularly fossil fuel burning and deforestation, have elevated atmospheric CO₂ levels. In 2023, CO₂ concentrations exceeded 420 parts per million (ppm), highlighting the urgent need for carbon capture technologies and sustainable energy solutions to address excess atmospheric CO₂ and curb emissions.
Carbon capture technologies like Direct Air Capture (DAC) can capture and remove CO₂ from the atmosphere. DAC systems typically use either solid sorbents or liquid solvents to capture CO₂ through a three-step process:
- Drawing in ambient air,
- Binding CO₂ to the capture agents, and
- Separating the concentrated CO₂ for storage or utilization.
This technology can be deployed anywhere with access to low-carbon energy and CO₂ storage infrastructure.
The captured CO₂ can be combined with clean hydrogen (H₂) to produce synthetic hydrocarbons, also called carbon-neutral fuels, e-fuels, or synthetic fuels. These synthetic fuels can serve as drop-in replacements for existing fossil fuels, requiring no modifications to current engines or infrastructure. Importantly, when burned, e-fuels release only as much CO₂ as was captured during their production, making them potentially carbon neutral over their lifecycle.
Sora Fuel Technology
The economics of carbon-neutral fuel production are heavily influenced by two key factors: CO₂ capture and clean hydrogen generation. For example, DAC currently comes with a hefty price tag of $600 to $1,000 per ton of CO₂. However, projections suggest a potential cost reduction to $100-$300 per metric ton by 2050, signaling a more economically viable future for this technology. The high costs associated with DAC are largely attributed to its energy-intensive processes, particularly calcination for CO₂ recovery and the regeneration of capture agents.
On the hydrogen front, green hydrogen production through renewable energy-powered electrolysis currently ranges from $4 to $12 per kilogram. This wide price range reflects variations in technology, geographical location, and the specific renewable energy source utilized. The industry is actively working towards reducing these costs, with ambitious targets set to bring the price below $2 per kilogram in the near future. This potential price reduction could significantly enhance the economic feasibility of carbon-neutral fuel production.
Sora Fuel has created an innovative integrated system combining DAC with a bicarbonate electrolyzer to convert atmospheric CO₂ into syngas. This syngas serves as a feedstock for sustainable aviation fuel (SAF) production, eliminating the need for clean hydrogen input. By avoiding high-temperature calcination typically used to produce pure CO₂, Sora Fuel's process reduces energy consumption by up to 90% compared to standard DAC methods. This efficiency enables the company to produce SAF at costs competitive with conventional jet fuel.
Sora Fuel's DAC process employs an alkaline solution to capture atmospheric CO₂, producing a bicarbonate (HCO₃⁻) solution that serves as the electrolyte feedstock for a bicarbonate electrolyzer. The bicarbonate electrolyzer converts HCO₃⁻ ions into valuable products like carbon monoxide (CO).
The key components of a typical bicarbonate electrolyzer is depicted in the diagram below:
- Catholyte: Typically 2-3 M KHCO₃ solution. It flows through the channel of the flow field plate at the cathode side.
- Anolyte: Typically alkaline solution. It is separated from the catholyte by a membrane and flows through the channel of the flow field plate at the anode side.
- Membrane: a Bipolar Membrane (BPM) or a Cation Exchange Membrane (CEM). BPM allows for water dissociation to supply protons to the cathode side. CEM permits the passage of cations while blocking anions.
- Cathode: The cathode in the catholyte chamber allows the reduction reactions to occur. Cathode materials include silver (Ag) used for highly-efficient CO production, bismuth (Bi) for efficient formate production, or copper (Cu) for multi-carbon product formation. Cathodes are often designed as gas diffusion electrodes (GDEs) to facilitate gas transport.
- Anode: Anode is electrically insulated from the cathode by the membrane. It allows oxidation reactions to occur, typically oxygen evolution. Anode materials include Ni, FeNiOₓ, iridium oxide (IrO₂), and precious metals such as platinum (Pt).
The diagram below illustrates several key electrochemical chemical reactions in a typical bicarbonate electrolyzer.
Water dissociation at BPM: H₂O → H⁺ + OH⁻
CO₂ formation near the cathode: HCO₃⁻ + H⁺ → H₂O + CO₂
CO production at the cathode: CO₂ + H₂O + 2e⁻ → CO + 2OH⁻
H₂ production at the cathode: 2H⁺ + 2e⁻ → H₂
O₂ production at the anode: 4OH⁻ → O₂ + 2H₂O + 4e⁻
The H₂/CO ratio can be adjusted by modifying operating conditions and cathode materials. A recent study has achieved a H₂/CO ratio of 1.16 at 200 mA cm⁻², suitable for industrial use.
Bicarbonate electrolyzers can achieve high faradaic efficiencies for CO production (up to 95%) and significant current densities over 100 mA cm⁻². This performance is attributed to the high concentration of bicarbonate ions in the catholyte (up to 3.3 M for KHCO₃), overcoming the limitations of traditional CO₂ electrolysis, where CO₂'s low solubility in aqueous solutions restricts maximum current density.
How Sora Fuel integrates DAC and syngas production
The diagram below depicts Sora Fuel's integrated system that combines DAC with a bicarbonate electrolyzer to produce syngas. Syngas serves as a feedstock for sustainable aviation fuel production.