A Deep Dive into the World of CO2 Capture and Removal
For a shorter introductory article about Direct Air Capture refer to our Pace Ventures article here.
For extensive information on the Carbon Dioxide Removal (CDR) space, visit cdrprimer.org.
Introduction
One of the most fundamental questions in the climate tech space is: “How can we reduce greenhouse gas emissions (GHGs)”?
There are many ways and angles from which to approach this problem. In order to reduce greenhouse gas emissions, different streams and approaches can be considered. In this deep dive, we will provide an overview of the various technologies that can decrease our current GHG emission levels.
Let’s start with what kinds of emissions there are in the first place:
Direct Emissions:
Direct emissions refer to greenhouse gas emissions that occur directly from human activities. These emissions are released into the atmosphere as a result of specific activities and are relatively easier to measure and quantify. Examples include carbon dioxide (CO2) emissions from burning coal, oil, and natural gas, as well as methane (CH4) emissions from livestock and landfill waste.
Indirect Emissions:
Indirect emissions or embodied emissions, are associated with activities that are not the direct source of emissions but contribute to greenhouse gas emissions indirectly. These emissions occur throughout the entire lifecycle of a product or service (along the value chain or supply chain of products and services). These emissions include those resulting from manufacturing processes, transportation of goods, and energy consumed during production.
What kinds of solutions are available to tackle these emissions?
Nature-Based Approaches:
Nature-based approaches to reducing greenhouse gas emissions involve utilizing natural ecosystems and processes to absorb and store carbon dioxide. These approaches often focus on enhancing the capacity of forests, wetlands, and other natural habitats to act as carbon sinks. Afforestation (planting new forests) and reforestation (restoring degraded forests) can help sequester CO2 from the atmosphere. Additionally, the protection and restoration of wetlands and mangroves can contribute to carbon storage. Nature-based approaches also involve sustainable land management practices that promote soil carbon sequestration, such as agroforestry and regenerative agriculture.
Chemical Approaches:
Chemical approaches encompass various technologies and methods that aim to capture and remove greenhouse gases from the atmosphere or prevent their release. Carbon capture and storage (CCS) technologies capture CO2 emissions from industrial processes and power plants, storing them underground or utilizing them for other purposes. Carbon capture, utilization, and storage (CCUS) involves capturing CO2 and using it in industrial processes or converting it into products such as chemicals or building materials. Additionally, carbon removal technologies, including direct air capture (DAC), remove CO2 directly from the atmosphere using chemical processes.
An Overview of Direct Air Capture (DAC) vs. CCS
Over the last few years, a wave of innovation has been taking place in the last segment, the “chemical approach” avenue. New technologies that suck CO2 out of the air (“Direct Air Capture”), or prevent it from leaving smokestacks (“Carbon Capture and Storage”) can help reduce greenhouse gas emissions.
So let’s get into the details of Direct Air Capture (DAC) and Carbon Capture and Storage (CCS), how they are different, what good looks like, and how this tech can be implemented to have a significant impact on climate change adaptation.
DAC is a technology that aims to remove carbon dioxide (CO2) directly from ambient air, as opposed to capturing it at the point of emission. The primary goal of DAC is to mitigate climate change by reducing the concentration of CO2 in the atmosphere, which is a significant driver of global warming. DAC+S (Direct Air Capture with Carbon Storage) not only captures CO2 but also focuses on storing it permanently to mitigate climate change. CCS, in contrast, captures CO₂ from point sources of carbon dioxide, such as the smokestacks of iron and steel factories. It then transports the captured CO₂ to a storage site, where it is sequestered.
Let’s take a closer look at how the two technologies differ (Climeworks):
Distinguishing carbon removal (DAC) from carbon capture (CCS)
How the technology works
- DAC+S: Removes CO₂ from ambient air, even historic CO₂ released during the industrial revolution, reducing overall levels in our atmosphere.
- CCS: Maintains the current level of CO₂ in our atmosphere by preventing further emissions, e.g., those emitted by factories.
Where the technology can be used
- DAC+S: Can be used anywhere as CO₂ is distributed equally across the atmosphere.
- CCS: Can be used at stationary sources of CO₂ such as power plants, ethanol production plants, or other industrial facilities.
How do they address climate change?
- DAC+S: Removes carbon dioxide from the air, allowing the removal of unavoidable or historic emissions already in the atmosphere.
- CCS: Prevents new quantities of CO₂ from entering the atmosphere.
Spotlight on DAC: Removing CO2 Directly from the Atmosphere
DAC technologies are designed to remove carbon dioxide (CO2) directly from the ambient air. There are different approaches to DAC, including adsorption-based and absorption-based systems. Let’s delve into these approaches and their processes:
Adsorption-based Systems:
Adsorption-based DAC systems utilize solid materials, such as metal-organic frameworks (MOFs), zeolites, or activated carbon, which selectively adsorb CO2 from the air. The process involves several steps:
→ Adsorption: Air is passed through a filter or contactor containing the solid adsorbent material. As the air comes into contact with the adsorbent, CO2 molecules are attracted to the surface of the material and adhere to it. The adsorbent has a high affinity for CO2, allowing it to selectively capture the greenhouse gas while allowing other components of the air to pass through.
→ Saturation: Over time, the adsorbent becomes saturated with captured CO2 as more molecules adhere to its surface. The capacity of the adsorbent determines the amount of CO2 that can be captured. Once the adsorbent reaches its saturation point, it needs regeneration to release the captured CO2 and prepare it for subsequent capture cycles.
→ Desorption: To regenerate the adsorbent, it undergoes a desorption process. Typically, the adsorbent is heated, which causes the CO2 molecules to detach from its surface and be released as a concentrated CO2 stream. The released CO2 can be collected, compressed, and further processed for storage or utilization.
Climeworks, a notable player in the DAC field, operates DAC plants using solid sorbents to capture CO2. They have successfully deployed their technology in various locations, including Switzerland, Iceland, and Italy. Climeworks’ approach falls within the adsorption-based systems, utilizing solid materials for CO2 capture.
Microsoft has partnered with Climeworks and has purchased carbon credits from the DAC+S tech company. This collaboration supports Microsoft’s carbon offset strategy and helps advance DAC technology.
Absorption-based Systems:
Absorption-based DAC systems employ liquid solvents, such as aqueous alkali solutions or amine-based solvents, to chemically bind with CO2 in the air. The process involves the following steps:
→ Absorption: Air is brought into contact with the liquid solvent, which reacts chemically with the CO2 molecules, forming a stable compound. Common solvents used include sodium or potassium hydroxide solutions or amine-based solvents. The CO2 is absorbed into the solvent, effectively removing it from the air.
→ Separation: Once the CO2 is absorbed, the solvent containing the CO2 compound is separated from the air stream. Various separation methods, such as gravity settling or membrane separation, can be used to achieve this.
→ Regeneration: To release the captured CO2 from the solvent, the solvent undergoes a regeneration process. Typically, the solvent is heated, causing the CO2 to be released as a concentrated stream. The regenerated solvent can then be reused in subsequent capture cycles, allowing for the continuous capture of CO2.
Energy Requirements for DAC Systems:
DAC processes are energy-intensive, particularly during the regeneration or desorption stage where captured CO2 is released from the capture medium. The energy demand can be in the form of heat, electricity, or mechanical energy. The efficient use of energy is crucial to minimize the carbon footprint and maximize the net CO2 removal and economic viability of DAC systems. Utilizing low-carbon or renewable energy sources to power DAC systems is a key consideration for reducing their overall environmental impact.
Spotlight on Carbon Utilization Pathways: What Happens after DAC?
Once CO2 is captured through DAC, it can be utilized through various carbon valorization pathways. These pathways involve converting captured CO2 into valuable products, materials, or energy carriers. Some key carbon utilization pathways include:
Enhanced Oil Recovery (EOR):
CO2 can be injected into oil reservoirs to increase pressure and facilitate the extraction of additional oil. This process not only helps recover more oil but also securely stores the CO2 underground, contributing to emissions reduction.
Production of Synthetic Fuels:
Captured CO2 can be combined with hydrogen, obtained from water electrolysis or other methods, to produce synthetic fuels. These synthetic fuels, such as methanol, dimethyl ether, or synthetic diesel, can be used as alternatives to conventional fossil fuels in transportation and other sectors.
Chemical Manufacturing:
CO2 can be used as a building block in the production of various chemicals, including plastics, polymers, and fertilizers. By utilizing captured CO2 as a raw material, these industries can reduce their reliance on fossil fuel-based feedstocks, resulting in lower emissions.
Carbon Mineralization:
Carbon mineralization involves the conversion of CO2 into stable, solid mineral forms by reacting it with metal oxide-rich materials. These mineralized forms of CO2 can be used in various applications, such as construction materials, soil amendments, or stored to prevent CO2 from re-entering the atmosphere.
Algae Cultivation:
CO2 can be used to promote the growth of algae, which can be processed into biofuels, animal feed, or other valuable products. Algae-based systems have the potential to capture and utilize CO2 while providing additional benefits such as wastewater treatment and nutrient recycling.
Carbon valorization and mineralization play an essential role within the DAC space by offering potential revenue streams and adding value to captured CO2. This, in turn, helps offset the costs of DAC and increases its economic viability. Various pathways exist for converting captured CO2 into valuable products or materials, providing environmental benefits such as long-term carbon storage and reduced demand for natural resources.
Spotlight on CCS: Removing CO2 Directly from the Point of Source
Carbon Capture and Storage (CCS) involves the separation and capture of CO2 from emissions of industrial processes prior to atmospheric release. CCS involves storing the captured CO2 in deep geological formations to prevent it from re-entering the atmosphere. Suitable storage sites include depleted oil and gas reservoirs, deep saline aquifers, and unmineable coal seams. CO2 is typically compressed into a dense, liquid-like state and injected into these formations, where it can be trapped for long periods, potentially thousands of years or more. The storage sites are carefully monitored to ensure the integrity of the containment and minimize the risk of CO2 leakage.
CCS projects can generate carbon credits by capturing and storing CO2 that would otherwise be released into the atmosphere. These credits can be sold or traded on carbon markets. The revenue from selling carbon credits can help support the implementation and operation of CCS projects, making them economically viable.
Technologies and Startups
DAC — Capturing CO2 directly out of ambient air is prohibitively expensive (who’s willing to pay $500+/ ton?). But predictions say tech improvements over the next decade will reduce the cost of DAC by a factor of 5–10x. How do we get there?
DAC technologies still need to improve in three areas:
1) Contactor;
2) Sorbent; and
3) Regeneration to drive down the costs.
Technology-based economic development in all three areas are required to achieve <$100/ton of CO2 which makes DAC economically viable. Current DAC cost is about 2–6 times higher than the desired cost and depends highly on the source of energy used.
- Air Contactors: Massive CO2 sucking fans don’t come cheap (Carbon Engineering’s air contactor costs $200–400m for a 1 Mt/yr plant)! New innovations like passive air contactors that rely on wind & natural airflow and computational optimization are bringing down capex and opex.
→ Innovators include Noya: Their technology leverages readily available materials and a novel process for getting captured CO2 out of their material using only electricity. One of Noya’s key differentiators is that they eliminate the need for big heating equipment to remove captured CO2 from their material — they apply electricity directly to their CO2 capture material to release captured CO2 (Source: USV).
2. Solvents and Sorbents: Liquid solvents and solid sorbents can capture CO2, but require large amounts of energy to regenerate the material with a temperature and/or pressure swing. Novel sorbents like metal-organic frameworks and zeolites can solve for higher capacity and selectivity to reduce energy needs.
→ Innovators include AirHive and Ucaneo: Ucaneo specializes in adsorption-based systems, utilizing proprietary adsorbents for CO2 capture. Their technology aims to improve the efficiency and scalability of DAC systems, making them more economically viable and commercially competitive. AirHive focuses on the development of absorption-based DAC systems. Their technology relies on liquid solvents, such as aqueous alkali solutions or amine-based solvents, for CO2 absorption. By employing these liquid solvents, AirHive aims to optimize the capture process and enhance the efficiency of CO2 removal from the air.
3. Regeneration: Energy costs dominate DAC’s opex. A number of innovators are leveraging electrochemistry to unlock better energy efficiency for CO2 capture and regeneration.
→ Innovators include: Greenlyte operates in the field of carbon utilization, specifically in carbon mineralization. They work on converting captured CO2 into stable mineral forms through chemical reactions with metal oxide-rich materials. This process offers potential environmental benefits and provides opportunities for carbon storage and the development of sustainable materials.
To provide a better illustration of the importance of energy usage, in 2020 the US consumed 0.98 × 1020 J of energy; therefore, to meet the expectation of 30 GtCO2/year, DAC would require 1.97 × 1020 J of energy (U.S. Energy Information Administration, 2021). That is approximately twice that of the energy of the US in one year. This is also provided that the energy requirement meets the low range as seen in Figure 8. Essentially, the current energy demand calls for concern with regard to the hope of rapid DAC deployment and scale-up; however, researchers believe deployment remains a necessity (Realmonte et al., 2020).
Looking to other carbon capture technology, a large energy demand is not seen. The several other technologies, however, do require more in other areas. For example, more land and water would be required for BECCS and afforestation and reforestation along with the latter seeing a potential loss of nutrients in soils (Courvoisier, 2018). In addition, BECCS would also require 1018 J, a large amount of energy (Courvoisier, 2018). Energy is an issue that requires continued R&D and global support. Having examined these requirements, it is also crucial to discuss the amount of carbon that is generated as a result of energy sources. (Source: ClimateTechVC).
Analysis and Financial Considerations: What Would It Take to Deploy CDR at Gigatonne Scale?
When assessing technologies for gigatonne-scale carbon dioxide removal (CDR), it is crucial to consider scalability, cost-effectiveness, and market demand.
The cost of implementing direct air capture with carbon storage (DACCS) technologies, including adsorption and absorption approaches, has been a major hurdle for widespread deployment. Historically, DACCS installations have been expensive, ranging from $100 to $600 per metric ton of CO2 removed. Factors such as the energy-intensive nature of the technology, specialized materials requirement, and limited deployment have contributed to high costs.
While DAC alone faces challenges in meeting the carbon capture rates outlined in the Paris Agreement, it can partially offset emissions from concrete, transportation, iron-steel industry, and wildfires. Land requirements for DAC plants depend on factors like thermal energy sources and fresh water availability. Utilizing existing energy sources and investing in renewable technologies can help reduce the carbon footprint. Passive Direct Air Capture technologies like MechanicalTree, which reduce the need for thermal energy and freshwater, may offer a solution. Sequestration, on the other hand, poses no significant issues, as properly maintained storage sites can store CO2 for millions of years with minimal risk.
Simplified and modular DAC technical approaches are expected to reduce costs, as mass production and deployment of standard parts accelerate DAC’s adoption. Current trends include passive air contact, modular design, and the use of natural sorbents. It is anticipated that carbon removal costs could drop to <$100/ton by the mid-2030s. However, as research, development, and economies of scale progress, the cost of DACCS is expected to decrease significantly. Increased investment in DAC, along with supportive policies and financial incentives like carbon pricing and tax credits, will be crucial for widespread deployment and cost reduction.
Assuming that all existing (19 as of November 2022) DAC plants operate at 100% efficiency and maintain the same capacity over the years, it is estimated that a total of 2.4 million Climeworks plants and 9,980 Carbon Engineering plants with a capacity of 4,000 and one million metric tons per year, respectively, would be needed to meet the Paris agreement’s goal. It is even harder to revert earth’s climate to preindustrial revolution phase (CO2 concentration — 280 ppm), which requires a removal of 135 ppm (1,053 Gt) of CO2 from the atmosphere (Source).
To put things into perspective, capturing gigatonnes of CO2 per year is a monumental task. One gigatonne of carbon dioxide (GtCO2) is equivalent to a billion metric tonnes of CO2. Achieving gigatonne-scale CDR would require significant energy, land, water, and material resources.
Definition: A Gigatonne of carbon dioxide (GtCO2) refers to a billion metric tonnes of CO2, which is equivalent to 10¹⁵g. It is also helpful to know that 1 GtCO2 is equivalent to 0.273 gigatonnes of carbon (GtC). This unit of measurement is used most frequently when discussing the scale of CDR required to prevent the worst impacts of climate change and to keep warming below 1.5° C (i.e., gigatonne-scale CDR) (Source: CDR Primer).
In the below table, highly simplified assumptions are used to get a rough sense of approximately how much energy, land, water, and material resources are needed to achieve 1 GtCO2/yr of removal. To demonstrate the difference in the type and magnitude of underlying biophysical constraints, biological CDR methods of afforestation and reforestation (AR) are compared to a technological method, direct air capture with carbon storage (DACCS).
For context, the biggest Climeworks plant to-date is capturing only 4,000 tonnes a year (DACCS via mineralisation). The first large-scale DAC plant of up to 1 MtCO2/year is in advanced development and is expected to be operating in the United States by the mid-2020s.
The infosheet outlines the actions needed to scale CDR in the 2020s to hit 2030 climate goals. An important note is that, with the signing of the Paris Agreement, a goal of reaching a global warming of below 2°C was determined. To do so, around 30 GtCO2/year would need to be removed (Chatterjee and Huang, 2020).
Conclusion: The Way Forward
Combating climate change and greenhouse gas emissions requires a comprehensive approach that includes reducing emissions in high-emitting sectors, investing in natural climate solutions, and innovating engineered chemical solutions like DACCS.
Moving forward, attention and effort are needed for CDR innovation to ensure cost-efficient large-scale deployment, including sorbent development, political support, cost reduction, and energy efficiency.
Utilizing captured CO2 through various pathways can generate additional revenue streams and enhance the economic viability of DAC technologies, but it does not sequester CO2 permanently. As such, collaborative efforts between companies, startups, research institutions, and policymakers are essential for realizing the full potential of DACCS and accelerating the transition to a sustainable, low-carbon future.
