Sustaera, an American startup founded in 2021, develops direct air capture (DAC) technology to remove carbon dioxide (CO₂) directly from the air. Sustaera is a spin-out of Susteon, a climate tech company focused on hydrogen, carbon capture, and carbon utilization. Sustaera uses renewable electricity to quickly liberate captured CO₂ in the sorbents under a mild temperature via heating underneath conductive desorption materials that are coated on the channel walls of monolithic substrate, which significantly minimizes energy input compared to conventional DAC technologies. Sustaera’s DAC system can capture 1,000+ tons/year of carbon dioxide, and the company was selected as one of the top 15 teams to receive a $1M Milestone Prize in the XPRIZE Carbon Removal competition.
Challenges: carbon emissions and Direct Air Capture
In this urgent, authoritative book How to Avoid a Climate Disaster, Bill Gates sets out a wide-ranging, practical—and accessible—plan for how the world can get to zero greenhouse gas emissions in time to avoid a climate catastrophe. (see on Amazon)
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.
Direct Air Capture
Direct Air Capture (DAC) is a process that extracts CO₂ directly from the atmosphere, as opposed to industrial emissions with a high CO₂ content. The captured CO₂ can then be either permanently stored in deep geological formations, thereby achieving CO₂ removal (CDR), or used as a climate-neutral feedstock for a range of products that require a source of carbon.
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 plays an important and growing role in net-zero pathways. Capturing CO₂ directly from the air and permanently storing it removes the CO₂ from the atmosphere, providing a way to balance emissions that are difficult to avoid, including from long-distance transport and heavy industry. 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. Currently, there is no established market for carbon removal, and the demand for carbon removal is not yet sufficient to support the large-scale deployment of DAC. Some advocates worry the carbon capture process may not be scaled up fast enough to make an impact. However, the demand for carbon removal is expected to increase as more countries and companies set net-zero targets and seek to offset their emissions. In addition, governments and other stakeholders must provide substantial funding and support.
The book Carbon Capture, written by Herzog, a pioneer in carbon capture research, begins by discussing the fundamentals of climate change and how carbon capture can be one of the solutions. (see on Amazon)
Direct air capture companies
Several companies, such as Carbon Engineering, Climeworks, Heirloom, Noya, Mission Zero, and Carbyon, are developing DAC technologies.
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 has developed a DAC technology that continuously captures CO₂ from the air with low energy consumption. Mission Zero uses a well-established electrodialysis technology to capture CO₂ from the air and turns CO₂ into carbonic acid (H₂CO₃), which dissociates into HCO₃⁻ and proton (H⁺). The H₂CO₃ solution is circulated through an electrodialysis cell, which separates HCO₃⁻ from the absorbent solution by passing it through an anion-exchange membrane into a second absorbent solution, where 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.
Carbyon develops a low-cost, energy-efficient DAC technology that uses a fast swing process by means of a continuously rotating drum. The rotating drum comprises activated carbon fiber membranes. The surface of fibers are functionalized with a monolayer of amines that are used as CO₂ adsorbents. Such a thin surface sorbent allows a rapid CO₂ absorption at ambient temperature and fast regeneration below 100 ºC. Thereby, one cycle of absorption and regeneration occurs in less than 5 seconds. The fast swing CO₂ capture process is the key to lower the energy consumption as well as the cost of the machine.
Sustaera’s DAC technology removes CO₂ directly from the air using renewable electricity and monolithic structured material assemblies. In a monolithic structured material assembly, a monolithic substrate with a honeycomb-like structure is positioned between two mesh electrodes. The monolithic substrate’s channel walls are coated with layers of conductive desorption, sorbent support, and sodium carbonate (Na₂CO₃) sorbent.
The Na₂CO₃ sorbent absorbs CO₂ from the airflow within the channels until they become saturated. To regenerate sorbent, the conductive desorption layer receives renewable electricity input via the mesh electrodes and in-situ heats the sorbent layer to quickly liberate CO₂ at temperatures below 120 ºC in a few minutes. In contrast to conventional DAC technologies, which require high temperatures to regenerate sorbents, Sustaera’s technology minimizes energy input and reduces costs significantly.
Sustaera direct air capture technology
The diagram below depicts the system of the Sustaera DAC technology.
The system consists primarily of renewable energy sources, an air contactor for CO₂ capture, a vacuum pump, and a CO₂ compression and conditioning component.
As depicted in the diagram below, the air contactor consists of stacked modules for CO₂ capture. A module can be sealed for CO₂ extraction. Each module consists of many monolithic structured materials assemblies. The module has enclosure housing structures (not shown). These modules are separated by electrically insulating spacers that prevent electrical current from short-circuiting between modules and provide a gap between modules to form airflow channels.
As depicted in the diagram below, the core technology of Sustaera is the monolithic structured material assembly.
Sustaera structured material assembly for CO₂ capture (ref. WO2022192408A2).
The monolithic structured material assembly consists of a monolithic substrate that is positioned between two electrode meshes. Highly conductive coatings connect the electrode meshes and the monolithic substrate.
The monolithic substrate is self-supporting and has a honeycomb-like structure. The monolithic substrate comprises cordierite. The chemical formular for cordierite is (Mg,Fe)₂Al₄Si₅O₁₈. This cordierite is suitably tailored to have different molar ratios and starting raw material properties of magnesia, iron, alumina, and silica to meet the performance targets for the substrate. The image below depicts a cordierite substrate.
The monolithic cordierite substrate has multiple parallel open airflow channels. The monolithic substrate channel walls provide a relatively large surface that is coated with desorption material, sorbent support material, and sorbent material.
- Desorption layer
The desorption material is electrically conductive. It comprises carbon, such as graphite, activated carbon, carbon black, hard carbon, amorphous carbon, and carbon nanotubes.
The desorption material can create a percolation network layer on the channel walls within the monolithic substrate. The overall electrical resistivity of the desorption layer ranges from 0.03 to 300 Ω∙m. When responsive to renewable electricity input via mesh electrodes, the desorption layer generates in-situ joule heat to desorb CO₂ from the sorbent at temperatures below 120 ºC.
- Support layer
Typically, the monolithic cordierite substrate has a low surface area. It is advantageous to provide a sorbent support component with a higher surface area than the substrate’s cordierite, such as alumina.
- Sorbent layer
The sorbent layer coated on or combined with support material absorbs CO₂. The sorbent material comprises sodium carbonate (Na₂CO₃). Other suitable sorbent materials include polyamines and alkali metal oxides, hydroxides, carbonates, carbonate hydrates, and bicarbonates, are also suitable sorbent materials. The sorbent layer may comprise additives or promoters, such as lithium salts, piperazine, and amino acid.
How does Sustaera direct air capture technology work?
Each CO₂ capture cycle consists of the following steps:
(1) Adsorption: Airflow passes through the channels of monolithic substrates, and Na₂CO₃ absorbs CO₂,
(2) Purge: Modules containing structured material assemblies are sealed, and undesirable air components are removed from the module void spaces, and
(3) Desorption: The conductive desorption layer responds to the input of renewable electricity and generates in-situ joule heat to desorb CO₂, which is then recovered as a product.
The operation process can be carried out in a wide range of temperatures and relative humidities, ranging from -20 ºC to 50 ºC and 10% to 100%, respectively, allowing for global deployment of the system.
During adsorption, a fan in the air contactor forces ambient air through the structured material assemblies of the modules. The Na₂CO₃ sorbents absorb CO₂ from the airflow until they are saturated with CO₂ according to the following chemical reactions:
Na₂CO₃(s) + H₂O(g) → Na₂CO₃∙H₂O(s)
Na₂CO₃∙H₂O(s) + CO₂(g) → 2NaHCO₃(s)
After CO₂ absorption is complete, the structured material assemblies are purged with a gas to remove the undesirable air components such as nitrogen and oxygen to a level that meets a final CO₂ product specification.
To regenerate sorbents, renewable electrical energy is applied to the desorption layer of the structured material assemblies of modules to in-situ heat the sorbent, which liberates the captured CO₂ at temperatures below 120 ºC in less than 5 minutes. The released CO₂ is evacuated from the module using a vacuum, gathered in tubing, and combined with CO₂ from other modules operating in similar sequencing steps.
The captured CO₂ can be either sequestered in suitable geological storage facilities or utilized in a process to produce sustainable fuels, chemicals, or other products with added value.
- WO2022192408A2 Direct air capture co2 removal system and process
Carbon offset credit market
The market value of carbon offset credits varies widely. In current carbon markets, the price of one carbon credit can range from a few cents per metric ton of CO₂ emissions to $15/mtCO₂e (metric tons of CO₂ equivalent) or even $20/mtCO₂e. However, the voluntary carbon offset market, which was worth about $2 billion in 2021, is projected to grow to $10-40 billion by 2030, transacting 0.5-1.5 billion tons of CO₂ equivalent, as opposed to the current 500 million tons. The total value of carbon credits produced and sold to help companies and individuals meet their de-carbonization goals could approach $1 trillion as soon as 2037.
The Sustaera’s unique DAC system is modular and can be entirely powered by renewable electricity. The company is building a pilot unit that can remove 1-ton CO₂ per day. Sustaera aims to capture 1 million tons per year at a cost of less than $100 per ton by2027, utilizing multiple facilities around the world. It aims to capture 500 million tons of CO₂ by 2024.
Sustaera has raised a total of $11M in funding over 2 rounds:
Their latest funding was raised on Apr 22, 2022 from a Grant round.
Sustaera is funded by 4 investors, including
Mary K Haas is CEO.