Solid Adsorbents for CO2 Capture and Utilisation

CO2 is the most significant anthropogenic greenhouse gas in the atmosphere. Its atmospheric concentration climbed to 384 ppm in 2007 from a pre-industrial level of around 280 parts per million, and it is still rising. One of the negative effects on the environment is the increase of CO2 in the atmosphere, which causes global warming.  There is no doubt that there has been a linear warming trend over the last 50 years that has almost doubled compared to 1906 to 2005. The combustion of fossil fuels, carbon emissions from industrial and energy and related chemical processes are the primary sources of CO2 emissions connected with human activities. For this problem, Carbon capture and utilisation research initiatives have been taken.

Types of Solid Adsorbents for CO2 Capture : 

Many types of solid adsorbents for CO2 Capture and Utilisation are as follows-

• Carbon-based adsorbents(carbon capture)
• Zeolite based adsorbents
•  Metal-organic framework based adsorbents
• Alkali metal carbonate-based adsorbent
• Amine-based solid adsorbents 
• Intermediate-temperature solid adsorbents(200 – 400 C)
• High-temperature solid adsorbents (> 400 C)
• Alkali ceramic-based adsorbents

Carbon capture:

Carbon capture, utilisation, and sequestration is a method that absorbs carbon dioxide emissions from sources such as coal-fired power plants and either reuses or stores the carbon dioxide from entering the environment. Power and industry are responsible for over half of greenhouse gas emissions worldwide. With the discussion over Net Zero Emissions heating up and objectives being established, it’s more important than ever to identify and implement the correct mix of emission-reduction technology. Carbon Capture and Utilisation (CCU) is one of the most important avenues for reducing carbon emissions from industrial and energy plants while developing at an unprecedented sustainability rate. Climate action; clean energy, industry, innovation, and infrastructure;  consumption and production; and partnerships to accomplish the objectives are five of the 17 Sustainable Development Goals (SDGs) that CCU supports.

The capture of CO2: 

There are three main technologies in the carbon capture technique for capturing CO2: post-combustion, pre-combustion, and oxyfuel combustion.

• Post combination: The CO2 is extracted after the fossil fuel is burned in post-combustion capture, which is the strategy that would apply to fossil-fuel power plants. At power plants and other point sources, CO2 is extracted from flue gases. The technique is well-understood and is now used in various industrial applications, but at a much lesser scale than that required in a commercial scale station
• Pre combination: Pre-combustion technique is widely used in the fertiliser, chemical, gaseous fuel (H2, CH4), and power industries. The fossil fuel is partially oxidised in these circumstances, such as a gasifier. The CO in the resultant syngas (CO and H2) combines with the additional steam (H2O) to form CO2 and H2. A sufficiently clean emission stream can be used to collect the CO2
•  Oxyfuel combustion: Instead of air, oxy-fuel is burnt in pure oxygen. Cooled flue gas is recirculated and pumped into the combustion process to keep the flame temperatures down to those seen in traditional ignition. CO2 and water vapour make up the majority of the flue gas, with the latter condensing as it cools. As a result, the CO2 stream is nearly pure. Because the CO2 stored is not a percentage removed from the flue gas stream (as in the case of pre-and post-combustion capture), power plant operations based on oxyfuel combustion are often referred to as “zero-emission” cycles

Separation technologies:

The following are the primary carbon capture methods that have been proposed

• Membrane
• Combustion of oxyfuel
• Absorption
• Absorption in many phases
• Adsorption
• Looping chemical combustion
• Calcium recirculation
• Cryogenic

Depending on the MOF’s permeability and selectivity, CO2 adsorbs to a MOF (Metal-organic framework) by physisorption or chemisorption, leaving a CO2-poor gas stream behind. The CO2 is subsequently removed from the MOF by temperature swing adsorption (TSA) or pressure swing adsorption (PSA), reusing it. For adsorbate and absorbents to be reused, CO2 must be removed from the sorbent or solution collected from the exhaust gas. Because they are mainly water, monoethanolamine (MEA) solutions, the most common amine for CO2 capture, have a heat capacity of 3–4 J/g K. 

Low heat capacities and adsorption temperatures are desired to improve a MOF capable of carbon capture. To capture as much CO2 as feasible, great operating capacity and selectivity are also needed. Selectivity and energy consumption are, however, complicated by an energy trade-off.   The energy, and hence the cost, required to regenerate increases as the amount of CO2 collected increases. MOF/CCS are the chemical and thermal stability constraints they impose.

Conclusion

To summarise, carbon capture is a vast and vital topic. It’s critical in the fight against climate change’s consequences. One of the most effective and often debated solutions to this problem is carbon capture and storage. However, there is no one-size-fits-all answer to this issue. We can’t keep pumping carbon into the ground indefinitely. Carbon capture and storage must be combined with innovative clean energy generation technologies to counteract the consequences of climate change to ensure that no more carbon is emitted into the atmosphere. Furthermore, cleaner agricultural practices, reforestation, and afforestation are excellent ways to restore natural sequestration processes before people mess with the ecosystem.