Direct Air Capture to Biofuels: Closing the Carbon Loop with Engineered Biology

Introduction

Direct Air Capture (DAC) is a technology that captures carbon dioxide (CO₂) directly from the atmosphere, addressing diffuse emissions that traditional capture systems can’t reach. When combined with biofuel production, DAC enables a circular carbon cycle—turning atmospheric CO₂ into renewable fuels, effectively “recycling” emissions.

This integration creates a novel pathway for carbon-neutral or even carbon-negative fuels, especially when using engineered microbes, algae, or catalysts to convert CO₂ into hydrocarbons. It bridges two critical domains: climate mitigation and energy transition, transforming a climate liability into a renewable asset.

What Products Are Produced?

• Biofuels: Ethanol, isobutanol, biodiesel-equivalent lipids, or sustainable aviation fuels (SAF)
• Biogas & syngas: Via engineered methanogens or gas fermentation
• Hydrocarbons: Alkanes and alkenes from synthetic biology platforms
• Platform Chemicals: Acetate, formate, succinate, lactate—building blocks for green chemistry

Pathways and Conversion Strategies

1. CO₂ to Biomass (Algal or Cyanobacterial Fixation)
• Cyanobacteria and algae fix CO₂ through photosynthesis and produce lipids or sugars convertible to fuels.
2. Gas Fermentation using Acetogens
• Clostridium ljungdahlii and others use the Wood–Ljungdahl pathway to convert CO₂ + H₂ into ethanol or acetic acid.
3. Formate-Mediated Conversion
• Electrochemical DAC reduces CO₂ to formate, which engineered microbes convert to fuels.
4. Synthetic Carbon Fixation Cycles
• Engineered pathways like CETCH and crotonyl-CoA cycles enhance carbon assimilation into fuels.
5. Photobioreactor Integration
• Closed-loop systems coupling DAC units with phototrophic or chemoautotrophic microbes in bioreactors.

Catalysts and Key Tools Used

• Direct Air Capture Materials: Solid sorbents (amine-functionalized silica), hydroxides
• Electrochemical Converters: CO₂ → formate, CO, or syngas intermediates
• Engineered Organisms: Cupriavidus necator, Clostridium autoethanogenum, algae, cyanobacteria
• Key Enzymes: Formate dehydrogenase, hydrogenase, carbonic anhydrase, acetyl-CoA synthase
• Reactor Systems: Coupled DAC-bioreactors, photobioreactors, and microbial electrolysis cells

Case Study: Twelve & LanzaTech – CO₂ to Jet Fuel

Highlights

• Captures CO₂ using DAC and converts it into syngas, which is fermented by microbes into ethanol.
• Ethanol is upgraded to jet fuel using alcohol-to-jet (ATJ) technology.
• Entire system powered by renewable electricity, creating drop-in aviation fuel with net-zero emissions.
• Demonstrated scalable production of synthetic SAF from thin air.

Timeline

• 2018 – Twelve (formerly Opus 12) develops CO₂ electrolyzer to produce syngas.
• 2020 – Partnership with LanzaTech to integrate microbial fermentation of CO₂-derived syngas.
• 2022 – Produced jet fuel from air and water, flight-tested with U.S. Air Force.
• 2024 – Plans announced for commercial-scale DAC-to-fuel plant using only CO₂, H₂O, and sunlight.

Global and Indian Startups Working in This Area

Global

• Twelve (USA) – Electrochemical DAC to CO for jet fuel, plastics, and chemicals.
• LanzaTech (USA) – Gas fermentation of CO₂ into ethanol and jet fuel.
• Climeworks (Switzerland) – DAC provider partnering with fuel and chemical companies.
• CarbonCapture Inc. (USA) – DAC systems integrated with synthetic fuel platforms.

India

• Carbon Clean (Chennai/London) – Industrial CO₂ capture with future plans for synthetic fuels.
• Ossus Biorenewables (Bengaluru) – Converting captured carbon and wastewater into biohydrogen.
• Thermax & IIT Collaborations – Exploring integration of CO₂ capture and bio-based valorization.

Market and Demand

The global DAC market is projected to grow from USD 0.5 billion in 2023 to over USD 5.5 billion by 2030 (CAGR ~40%), driven by net-zero targets. When linked with synthetic and biofuels, the combined CO₂-to-fuels market is expected to exceed USD 15 billion by 2030.

Major End-Use Segments:

• Sustainable Aviation Fuel (SAF)
• Carbon-neutral diesel and gasoline
• Specialty chemicals from CO₂
• Industrial hydrogen carriers
• Grid storage fuels and e-fuels

Key Growth Drivers

• Global push for carbon-neutral aviation and shipping fuels
• Advances in electrochemical and biological CO₂ conversion
• Policy incentives like 45Q tax credit (US) and EU ETS inclusion
• Corporate net-zero pledges driving demand for synthetic fuels
• Scalability of DAC modules for distributed fuel production

Challenges to Address

• High energy demand: DAC requires significant electricity or heat input.
• CO₂ purity and concentration: Air has only 0.04% CO₂, requiring efficient sorbents.
• Conversion efficiency: Biological and electrochemical pathways still below theoretical yields.
• Cost: Current DAC-to-fuel cost is 3–6× fossil alternatives.
• Integration complexity: Combining DAC, electrolysis, and bioconversion at scale.

Progress Indicators

• 2018 – First microbial ethanol from DAC-CO₂ demonstrated
• 2020 – SAF from CO₂ flight-tested (Twelve + USAF)
• 2022 – Climeworks launches commercial DAC + storage plant (Orca)
• 2023 – DAC integrated with microbial electrolysis (lab-scale in US, UK, EU)
• 2024 – India announces roadmap for DAC-to-bioenergy under Mission Innovation 2.0

Integrated DAC-to-biofuel systems are at TRL 5–6, with individual components like DAC, electrolysis, and gas fermentation at TRL 7–9 depending on maturity.

Conclusion

Direct Air Capture to Biofuels represents a frontier solution in the climate-tech and energy space. By combining atmospheric CO₂ capture with biological or electrochemical fuel synthesis, it offers a pathway to truly carbon-neutral or carbon-negative fuels.

While cost and energy input remain barriers, rapid innovation and supportive policy frameworks are accelerating progress. In countries like India—with growing renewable capacity and carbon offset goals—DAC-to-biofuel integration could enable decentralized, clean, and circular energy systems of the future.

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