The Challenges of Capturing CO₂ from Low-Concentration Emissions

One of the key challenges in carbon capture is dealing with diluted CO₂ streams, where the concentration of carbon dioxide is below 10%.

 

Industrial Sources of Low-Concentration CO₂

 

These low-concentration streams are common in several industrial processes and present unique difficulties for efficient carbon capture. Some typical examples include: 

 

• Gas Turbines: Common in power generation, especially in natural gas combined cycle (NGCC) plants, gas turbines emit flue gases with CO₂ concentrations of about 3-4%. These turbines also produce large volumes of air mixed with other gases, which requires significant energy for cooling and combustion.

 

• Fired Boilers: Found in power plants and industrial heat generation systems, fired boilers, especially those using fossil fuels like oil or natural gas, emit CO₂ concentrations of about 7-10%. These emissions are also mixed with impurities like SOx and NOx, which further complicates the capture process. 

 

• Aluminum smelters: In industries such as aluminum production, smelters emit CO₂ concentrations as low as 1-2%. These emissions are diluted due to the electrolysis process, which involves large volumes of air and additional gases like fluorides.

 

These low CO₂ levels, combined with the presence of other impurities, make efficient capture difficult, as the process requires handling large volumes of gas to extract relatively small amounts of CO₂. 

 

 

Direct Air Capture (DAC) Technology and Its Limitations

 

In addition to industrial sources, Direct Air Capture (DAC) faces even greater challenges due to the extremely low concentration of CO₂ in ambient air—approximately 0.04%. While DAC technology holds great potential for capturing CO₂ directly from the atmosphere, the low concentration of CO₂ in air means that vast quantities of air need to be processed, leading to high energy demands and operational costs. 

Several carbon capture technologies are currently being used or developed to address CO₂ emissions, but they face significant limitations, especially when dealing with diluted gas streams.

 

Amine-Based Solvents for CO₂ Capture  

 

Amine scrubbing is the most established and widely used CO₂ capture technology for post-combustion flue gases. It works by using liquid solvents, such as monoethanolamine (MEA), to absorb CO₂ from exhaust gases. However, this method faces challenges, particularly in low-concentration streams: 

 

• Energy-Intensive: Amine regeneration requires substantial heat, making the process energy-intensive.

 

• Degradation: Amine solvents degrade when exposed to impurities like SOx and NOx, reducing efficiency and increasing operating costs. 

 

• Cost: The high energy requirements and frequent solvent replacement make this approach costly, especially for diluted CO₂ streams. 

 

Calcium Looping for Carbon Capture 

 

This solid-based process uses calcium oxide (CaO) to capture CO₂ by forming calcium carbonate (CaCO3). It is relatively cost-effective but presents several drawbacks: 

 

• High Temperatures: The process operates at very high temperatures (600–900°C) for both capture and regeneration, leading to high energy costs.

 

• Limited Efficiency in Low CO₂ Concentrations: This method is less efficient for diluted CO₂ streams, as the reaction kinetics slow down significantly at lower CO₂ concentrations.

 

Physical Adsorption Methods

 

Physical adsorption technologies rely on porous materials, like activated carbon or zeolites, to trap CO₂. These methods are typically more energy-efficient than chemical absorption but face limitations:

 

• Low Selectivity: These materials can adsorb other gases (e.g., nitrogen or oxygen) in addition to CO₂, leading to lower capture efficiency.

 

• High Pressure: These systems generally require high pressure to increase adsorption capacity, which makes them less practical for large-scale applications.

 

While these technologies are effective in specific cases, they struggle to perform efficiently when capturing CO₂ from diluted streams. The high energy costs, material degradation, and reduced capture efficiency create barriers to large-scale deployment, especially in industries with low CO₂ emissions or in ambient air capture (DAC) applications. 

 

MOF-based carbon capture represents a breakthrough in the efficiency of carbon capture technology. MOFs are highly porous materials with a large surface area, enabling them to adsorb significant amounts of CO₂ even from low-concentration streams. This makes MOFs particularly effective in PCC and DAC applications, where the need to capture CO₂ from diluted sources is critical. 

 

Similarly, COF carbon capture leverages covalent bonding structures that provide high stability and selectivity in CO₂ adsorption. COFs, like MOFs, are built using molecular building blocks that can be tailored at the molecular level to enhance their interaction with CO₂ molecules, ensuring efficient capture while minimizing energy requirements during regeneration. These crystalline materials with strong bonds stand out for their ability to maintain performance even in the presence of impurities, such as NOx and SOx, which are common in industrial emissions. 

 

Energy Efficiency and Cost-Effectiveness 

 

One of the primary advantages of using reticular materials such as MOF and COF carbon capture technologies is their ability to achieve a great balance between CO₂ selectivity and the energy required for regeneration. These advanced materials are designed to bind CO₂ molecules just strongly enough to capture them effectively, but not so tightly that excessive energy is needed to release the CO₂ during the regeneration process. 

 

This characteristic significantly reduces the operational costs associated with CO₂ capture technology, making it more viable for widespread deployment in both industrial settings and large-scale DAC systems. 

 

Scalability and Integration into Industrial Processes

 

For carbon capture technology to meet global climate goals, it must be scalable and easily integrated into existing infrastructure. MOF and COF carbon capture technologies are designed with scalability in mind. These modular systems can be deployed across a wide range of applications, from large industrial plants to smaller, decentralized systems, without requiring significant modifications to existing setups. 

 

The durability and longevity of these advanced adsorbent materials ensure that they can operate effectively over long periods, reducing maintenance costs and ensuring consistent performance. As climate tech companies focus on solutions that address the impacts of climate change, scalable and efficient carbon capture technologies will be essential in reducing global emissions. 

 

The challenges of carbon capture in diluted gas streams, such as those in post-combustion and direct air capture applications, require innovative solutions that can reduce energy consumption and operational costs. MOF and COF carbon capture technologies offer a path forward by improving the efficiency and scalability of carbon capture adsorbent materials. With these advancements, the future of CO₂ capture technology looks promising, providing a crucial tool in the fight against the climate crisis. 

Atoco is a leader in climate technology, founded by Professor Omar Yaghi, the pioneer of Reticular Chemistry. Atoco leverages reticular materials such as Metal Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs) to develop breakthrough solutions for carbon capture and atmospheric water harvesting. These technologies, designed with atomic precision, are engineered to tackle global and most pressing challenges: climate change and water scarcity. 

 

Atoco’s solid-state carbon capture technology, including solid-state PCC (Post-Combustion Carbon Capture) and solid-state DAC (Direct Air Capture) modules, tackles the challenges of post-combustion and DAC by using highly efficient reticular materials. This approach allows for reduced energy consumption and scalable deployment across industries, making it a vital tool in addressing global carbon emissions and the fight against climate change.