Mission Zero ($9M for direct air capture technology)

Mission Zero develops a low-cost Direct Air Capture (DAC) technology to capture carbon dioxide (CO₂) directly from the air by leveraging the existing, scaled and mature technologies of cooling towers and electrochemical water purification. The Mission Zero’s DAC consumes less than 800 kWh per ton of separated CO₂, which is much lower than other DAC technologies based on amine sorbent or carbonate calciner, which consume between 1,500-2,000 kWh per ton of CO₂.

Challenges: carbon emissions and Direct Air Capture

Carbon emissions

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Since the early 1900s, carbon dioxide (CO₂) levels in the atmosphere have increased by 50% due to human activities. When fossil fuels (such as coal, oil, and natural gas) are burned for energy production, transportation, and industrial processes, CO₂ is released into the atmosphere. This excess CO₂ acts as a greenhouse gas, trapping heat and causing the air and ocean temperatures to rise. CO₂ emissions play a crucial role in driving climate change.

This warming effect has caused the global average temperature to rise by about 1.1 ºC since the pre-industrial period. This has led to rising in the frequency and intensity of extreme weather events, melting of polar ice caps and glaciers and rising sea levels, shifts in species ranges and increased risk of species extinction, agriculture and food security, and ocean acidification.

To mitigate these impacts, the Paris Agreement aims to limit global warming to well below 2 ºC above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) estimates that a “carbon budget” of about 500 GtCO₂, which corresponds to about ten years at current emission rates, provides a 66% chance of limiting global warming to 1.5 ºC.

What is Direct Air Capture?

Direct Air Capture (DAC) is a process that extracts diluted carbon dioxide (CO₂) directly from the atmosphere, as opposed to industrial emissions with a high CO₂ content. The captured CO₂ can then be either utilized in various industrial applications or buried to prevent its release back into the atmosphere.

The basic principle of DAC involves using large-scale machines or facilities equipped with specialized filters or sorbents which are designed to attract and bind with CO₂ molecules from the air while allowing other gasses, such as nitrogen and oxygen, to pass through. After the CO₂ is captured, it is separated from the sorbent through a regeneration process, resulting in the release of CO₂.

DAC technology employs a variety of methods, but chemical sorbents or solvents are typically used to capture CO₂. These sorbents can chemically react with CO₂ to form solid compounds or dissolve the CO₂ in a solvent. The captured CO₂ is then released from the sorbent or solvent via heating or other processes, allowing for its storage or utilization.

Direct air capture technology challenges

DAC has seen a surge in interest and investment over the past few years, and a growing number of companies are entering the market due to the realization that carbon removal will increasingly be needed to meet national and global climate goals, as well as the advantages of DAC relative to other carbon removal technologies. However, this technology is still in its infancy and faces several challenges that are stunting its global adoption and deployment.

One of the main challenges is that CO₂ is present in the air at a much lower concentration than other commonly targeted sources, such as flue gasses resulting from energy generation and industrial processes. This makes it technically challenging and requires a lot of energy.

As carbon dioxide removal from ambient air is an energy-intensive process, DAC technology is more expensive per ton of CO₂ removed than many mitigation strategies and natural climate solutions. Today, the price range for DAC ranges between $250 and $600. By the end of this decade, however, the cost of DAC technology is projected to fall to $250-$300/mtCO₂e (million tons of CO₂ equivalent) for a multi-megaton capacity range. If further industrialization is accomplished within the ecosystem of this emerging industry, prices may fall to between $100 and $200/t.

The sociopolitical acceptance of DAC is also a challenge. Some advocates worry the carbon capture process may not be scaled up fast enough to make an impact. To implement DAC on a large scale, governments and other stakeholders must provide substantial funding and support.

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Direct air capture companies

Several companies, such as Carbon Engineering, Climeworks, Heirloom. and Noya, are developing DAC technology.

Carbon Engineering DAC technology is an engineered mechanical system that extracts CO₂ from the air using a combination of fans, filters, and chemical reactions. The captured CO₂ is then compressed and stored underground or reused. Carbon Engineering’s DAC technology is capable of capturing millions of tons of CO₂ annually, and individual DAC facilities can be built to capture one million tons of CO₂ annually.

Climeworks specializes in DAC technology that extracts CO₂ from the air using a solid sorbent. The captured CO₂ is then released through a regeneration process, while the sorbent material is reused. Climeworks has developed several DAC plants worldwide and is working to scale up its technology to capture millions of tons of CO₂ annually. The company operates the largest operating DAC plant, Orca, in the world. The plant is located in Iceland and is capable of drawing down the volume of carbon dioxide emissions equivalent to approximately 870 cars annually.

Heirloom uses limestone (CaCO₃) instead of synthetic sorbents to capture CO₂ from the air and store it safely and permanently. Limestone is heated in renewable-energy powered calciners to remove CO₂ and produce Ca(OH)₂ sorbents from the hydration of CaO powders. Ca(OH)₂ sorbents are placed on vertically stacked trays, and algorithms are used to optimize their capacity to absorb CO₂ in different environmental conditions. Heirloom’s DAC technology accelerates the natural property of limestone, reducing the time it takes to absorb CO₂ from years to just three days. The company claims that its technology has the lowest peer-reviewed, at-scale cost of any direct air capture technology on the market.

Noya has developed a unique DAC technology that combines the existing pieces of industrial cooling towers with solid CO₂ sorbents. This transforms industrial cooling towers into CO₂ capture machines, which radically reduces the upfront capital costs and installation time required to perform direct air capture. Therefore, Noya’s approach to DAC will enable them to scale quickly and provide low-priced carbon removal in the near-term.

Mission Zero Technology

Mission Zero has developed a DAC technology that continuously captures CO₂ from the air with low energy consumption. The technology utilizes the existing, scaled and mature technologies of cooling towers and electrochemical water purification.

Mission Zero uses a first absorbent solution to absorb CO₂ from the air and turns CO₂ into carbonic acid (H₂CO₃), which dissociates into HCO₃⁻ and proton (H⁺). The CO₂-captured absorbent solution is circulated through an electrodialysis cell, which separates HCO₃⁻ from the first absorbent solution by passing it through an anion-exchange membrane into a second absorbent solution. HCO₃⁻ anions recombine with protons in the second absorbent solution to form carbonic acid, which readily decomposes into CO₂ in the release vessel where CO₂ is collected and stored.

The most significant benefit of Mission Zero’s DAC technology is that the release of the captured CO₂ requires minimal energy due to the fact that carbonic acid is unstable at room temperature. Other DAC technologies based on an amine sorbent or carbonate calciner sorbent, on the other hand, require between 1,500-2,000 kWh per ton of captured CO₂.

Mission Zero direct air capture

The diagram below depicts the system of Direct Air Capture of Mission Zero.

The overall system comprises a gas-liquid contactor, an electrodialysis cell, and a CO₂ release vessel.

Gas-liquid contactor

The gas-liquid contactor receives air flow and brings it into contact with a stream of a first absorbent solution, which absorbs some CO₂ gas from the air. Mission Zero, like the DAC company Noya, employs an existing cooling tower to drive the air flow through the first absorbent solution.

Electrodialysis cell

Electrodialysis is a mature water purification technology. An electrodialysis cell comprises a cathode and an anode. Ion-exchange membranes separate the electrodes, the first absorbent chamber, and the second absorbent channel.

The first absorbent chamber contains absorbent aqueous solution, which contains CO₂ capture species of polyethyleneimine (PEI) with a molecular weight of more than 800 and CO₂ hydration catalyst. Due to the large hydrodynamic radius and high molecular weight of the capture species of PEI, neither the anion-exchange membrane nor the cation-exchange membrane is permeable to PEI; therefore, the PEI capture species remains in the first absorbent solution. The absorbent solution is circulated between the first absorbent chamber and the gas-liquid contactor .

The second absorbent channel contains absorbent aqueous solution that comprises 0.18% poly-4-styrene sulfonic acid. The second absorbent solution is circulated between the second absorbent channel and release vessel.

CO₂ release vessel

To accelerate the decomposition of carbonic acid into CO₂, the release vessel operates at temperatures and pressures below 40 ºC and below atmospheric. CO₂ is collected and stored.

How does the Mission Zero carbon removal work?

The air flow and the first absorbent solution are introduced into the gas-liquid contactor. As the air comes into contact with the first absorbent solution, CO₂ is dissolved in the first absorbent solution, aided by the presence of a hydration catalyst, and forms HCO₃⁻ anions and a hydrogen cation (H⁺), according to the chemical reactions:

CO₂ + H₂O ⇄ H₂CO₃

H₂CO₃ ⇄ H⁺ + HCO₃⁻

HCO₃⁻ anions and protons associate with and are stabilized by the PEI in the first absorbent solution, according to the chemical reaction:

H⁺ + HCO₃⁻ + R₂NH → HCO₃⁻ + R₂NH₂⁺

The figure below shows the molecular structure of PEI.

Carbon capture species of polyethylenimine (PEI).

After dissolving CO₂, the first absorbent solution containing HCO₃⁻ and R₂NH₂⁺ circulates between the gas-liquid contactor and the first absorbent chamber of the electrodialysis cell.

During operation, a potential difference is applied between the positive (anode) and the negative (cathode) electrode of the electrodialysis cell. Under the influence of an electric field, negatively-charged HCO₃⁻ ions are dissociated from the positively-charged R₂NH₂⁺ polymers and are attracted towards the positive electrode (anode). HCO₃⁻ anions migrate to the second absorbent channel through the anion-exchange membrane.

The positively-charged R₂NH₂⁺ polymers are attracted towards the negative electrode (cathode). The cation-exchange membrane is however impermeable to the large R₂NH₂⁺. Therefore, proton (H⁺) disassociates from the R₂NH₂⁺ and migrates through the cation-exchange membrane towards the cathode, leaving PEI as the CO₂ capture agent in the solution of the first absorbent chamber.

By the time the first absorbent solution reaches the outlet of the separation chamber, at least a portion of HCO₃⁻ anions have been separated from the first absorbent solution. The first absorbent solution is recirculated to the gas-liquid contactor to capture CO₂.

Protons accumulated in the solution near the cathode are circulated to the anode and migrate through another cation-exchange membrane to the second absorbent channel, which contains a slurry of poly-4-styrene sulfonic acid. Meanwhile, HCO₃⁻ anions from the first absorbent chamber recombine with protons in the second absorbent channel, resulting in the formation of carbonic acids according to the reaction:

H⁺ + HCO₃⁻ ⇄ H₂CO₃

As they flow to the CO₂ release vessel, CO₂ is released according to the decomposition reaction:

H₂CO₃ ⇄ CO₂ + H₂O

The decomposition reaction can occur at room temperature. To accelerate the decomposition, the release vessel is heated to temperatures below 40 ºC and/or pressure is reduced. The stream of the second absorbent solution is then recirculated back into the second absorbent channel in a continuous process.

The performance Mission Zero direct air capture

For practical applications, typical electrodialysis modules contain a larger number of membrane pairs to increase the energy efficiency of separation. For example, a lab-scale electrodialysis cell contains 40 membrane pairs. The electrodialysis cell operates under conditions of constant current of -0.5 mA/cm² and an applied voltage of 21.5 V. The electrodialysis cell produces up to 0.7 g of CO₂ per hour, resulting in specific energy consumption of 510 kWh/tCO₂ with a current efficiency of 69%.

Mission Zero Patent

WO2022195299A1 Method of capturing a target species from a gas
GB202219726D0 Method of capturing co2 from a gas mixture

Mission Zero Products

Mission Zero participated in Project Hajar. The project employs Mission Zero’s modular, heat-free, and electrochemical DAC technology together with 44.01’s accelerated mineralization. Project Hajar aims to unlock gigatons of CO₂ removal in the Al Hajar mountains of the Sultanate of Oman. The project is to be fully powered by renewables. Project Hajar was recognized among the top fifteen $1M Milestone Award winners revealed for the XPRIZE Carbon Removal competition.