Cycle0 (Develop bioreactor to convert CO2 and green hydrogen to renewable natural gas)

Cycle0, a UK cleantech company founded in 2022, specializes in converting agricultural waste and methane emissions into biomethane. The company's 2024 acquisition of Biogasclean, a Danish firm expert in biological methanation and desulphurization systems, has propelled Cycle0 to the forefront of synthetic green gas innovation. This strategic move enhances Cycle0's capabilities in carbon capture and utilization, solidifying its position as a leader in sustainable energy solutions.

(This article contains 3 diagrams and 1440 words.)

Challenges: synthetic fuels

Carbon dioxide (CO₂), a potent greenhouse gas, is primarily generated through human activities such as fossil fuel combustion and deforestation. This gas plays a critical role in climate change by trapping heat and elevating ocean and atmospheric temperatures. In 2023, a significant milestone was reached when atmospheric CO₂ concentrations exceeded 420 parts per million (ppm) for the first time in recorded human history, highlighting the urgent need for revolutionary solutions in clean energy and carbon capture technologies.

Hydrogen (H₂) has emerged as a promising and versatile clean energy carrier with the potential to transform multiple sectors. Green hydrogen, produced by splitting water molecules using renewable electricity, offers a zero-emission alternative to fossil fuels. This innovative energy source has the capacity to decarbonize challenging industries such as steel and ammonia production, long-haul aviation, and heavy transportation.

Complementing hydrogen's rise, carbon-neutral fuels like e-methanol are gaining prominence. These synthetic fuels are produced through cutting-edge processes that combine hydrogen with captured CO₂, attracting significant interest from carbon-intensive industries, particularly shipping and manufacturing. As the world seeks sustainable alternatives to traditional fossil fuels, these innovative energy solutions are paving the way for a cleaner, more sustainable future.

Cycle0 Technology

Biogas represents a significant renewable alternative to fossil fuels, offering a promising path towards a more sustainable energy future. This versatile biofuel is produced through the anaerobic digestion of organic matter, including agricultural waste, sewage, and food scraps. Typically, biogas consists of 50-70% methane (CH₄), 30-50% CO₂, and 0.1-5.0% hydrogen sulfide (H₂S).

To harness biogas as a viable energy source, it must undergo a crucial purification process to eliminate unwanted compounds. This cleaning step is essential for ensuring the efficiency, safety, and longevity of biogas utilization systems.

One of the primary contaminants that must be addressed is H₂S, a corrosive and toxic compound that poses significant challenges. Removing H₂S is paramount before biogas can be used in boilers and engines, as it can severely damage equipment and presents serious health risks to humans.

The necessity of CO₂ removal from biogas depends on its intended application.

For biogas used directly in combustion engines or boilers for power generation, CO₂ removal is typically not required, as its presence does not significantly impact the combustion process or equipment integrity. However, when biogas is intended to replace natural gas in existing infrastructure, CO₂ removal becomes crucial. This process, known as biogas upgrading, involves reducing the CO₂ content from 30-50% to less than 2-3%, thereby increasing the methane concentration to align with natural gas specifications. The resulting product is Renewable Natural Gas (RNG), a purified form of biogas that can seamlessly integrate into existing natural gas infrastructure.

The CO₂ extracted during biogas upgrading offers a valuable opportunity for enhancing renewable energy production. Through biomethanation, this captured CO₂ can be converted into additional methane. This innovative approach not only maximizes the utilization of biogas components but also contributes to reducing overall carbon emissions. By recycling the CO₂ that would otherwise be released into the atmosphere, biomethanation effectively closes the loop in biogas production, further improving its sustainability credentials and economic viability.

Bubble column bioreactors for biomethanation offer a simple and scalable design, consisting of a vertical cylindrical vessel filled with liquid. Gas is introduced at the bottom through a distributor, forming bubbles of CO₂ and H₂ that rise through the liquid column. This creates a gas-liquid interface for mass transfer and reactions. The liquid medium can contain microorganisms, enzymes, or chemical catalysts to facilitate biological reactions. While gas is typically fed continuously, the liquid can be operated in batch mode or with continuous flow.

However, the poor solubility of H₂ in the liquid medium presents a significant challenge. This leads to poor distribution of CO₂ and H₂ throughout the liquid, limiting conversion efficiency. Additionally, the free-flowing microorganisms in the liquid face less than ideal growth conditions.

To address these limitations, Cycle0 has developed an innovative biomethanation bioreactor featuring a detachable packing material. This novel design offers several advantages:

1. Improved gas distribution
2. Enhanced growth conditions for microorganisms
3. Ability to occasionally clean the packing materials

As a result, this advanced bioreactor significantly improves the conversion of CO₂ and H₂ into methane. By overcoming the traditional constraints of bubble column reactors, Cycle0's technology promises to enhance the efficiency and productivity of biomethanation processes, potentially revolutionizing renewable energy production from biogas.

How Cycle0 converts CO₂ and H₂ into methane

The diagram below illustrates Cycle0’s biomethanation bioreactor, which converts CO₂ and H₂ into methane and water.