Analysis of the CO2 adsorption on AC: experimentation and statistical studies | Scientific Reports – Nature

Report on the Analysis of CO₂ Adsorption on Activated Carbon for Climate Action

Executive Summary

In response to the urgent need for climate change mitigation as outlined in the Sustainable Development Goals (SDGs), particularly SDG 13 (Climate Action), this report details a quantitative investigation into the efficiency of activated carbon (AC) for carbon dioxide (CO₂) capture. Utilizing a probabilistic modeling framework and adsorption experiments, the study analyzes the surface buildup and multilayer adsorption of CO₂ on AC. Key findings indicate that CO₂ forms three to four distinct layers on the AC surface under optimal conditions, a mechanism that significantly enhances capture efficiency. The process is identified as exothermic physisorption, suggesting potential for energy-efficient regeneration in line with SDG 7 (Affordable and Clean Energy). These insights provide a critical scientific foundation for designing advanced, thermally stable carbon capture materials, thereby supporting industrial innovation and sustainable infrastructure as targeted by SDG 9 (Industry, Innovation, and Infrastructure).

1.0 Introduction: The Role of Carbon Capture in Sustainable Development

The acceleration of global warming, driven by rising atmospheric CO₂ concentrations from anthropogenic activities, presents a direct threat to global sustainability. This challenge underscores the critical importance of SDG 13 (Climate Action), which calls for urgent measures to combat climate change and its impacts. Developing efficient carbon capture technologies is a cornerstone of this effort, providing a vital tool for decarbonizing industrial processes and energy production. This report focuses on the potential of activated carbon (AC) as a high-performance adsorbent for CO₂.

The use of AC aligns with multiple SDGs:

• SDG 9 (Industry, Innovation, and Infrastructure): The optimization of AC for CO₂ capture represents a key innovation for creating sustainable industrial systems that minimize environmental impact.
• SDG 12 (Responsible Consumption and Production): AC can be produced from various forms of biomass and agricultural waste, promoting a circular economy and sustainable management of resources.
• SDG 7 (Affordable and Clean Energy): Effective carbon capture technologies can reduce the carbon footprint of existing energy systems, serving as a transitional technology towards a fully renewable energy future.

This study provides a detailed analysis of the microscopic adsorption mechanisms of CO₂ on AC, employing a statistical physics framework to interpret experimental data. The objective is to advance the scientific understanding required to engineer more effective carbon capture solutions that contribute directly to the 2030 Agenda for Sustainable Development.

2.0 Methodology and Materials

2.1 Adsorbent Material Characterization

The adsorbent used was powdered activated carbon (AC) derived from bituminous coal. The material’s properties are crucial for its performance and its potential contribution to sustainable technology.

1. Physical Properties: The AC exhibited a high specific surface area of 879 m²/g and a total pore volume of 0.540 cm³/g. Its microporous structure is essential for the efficient capture of gas molecules like CO₂.
2. Chemical Composition: X-ray fluorescence analysis determined the elemental composition to be approximately 56.00% Carbon (C), 35.9% Oxygen (O), 7.6% Hydrogen (H), 0.35% Nitrogen (N), and 0.1% Sulfur (S).
3. Surface Morphology: Scanning Electron Microscopy (SEM) revealed a heterogeneous and highly porous surface structure, which provides numerous active sites for CO₂ adsorption. This complex structure is a key factor in its high adsorption capacity.

2.2 Experimental Procedure for Adsorption Analysis

The CO₂ adsorption isotherms were measured using Inverse Gas Chromatography (IGC). This analytical technique allows for precise characterization of the interactions between the gas (CO₂) and the solid adsorbent (AC) under various thermodynamic conditions. Experiments were conducted at four different temperatures (26, 43, 51, and 62.5 °C) to evaluate the thermal stability and performance of the material, providing data essential for designing industrial applications aligned with SDG 9.

2.3 Statistical Physics Modeling

To interpret the experimental data at a molecular level, a statistical physics approach based on the grand canonical ensemble was employed. Three theoretical models were tested to describe the adsorption isotherms:

• Model 1: A single-layer model where each adsorption site binds one layer of CO₂.
• Model 2: A two-layer model with two distinct adsorption energies.
• Model 3: A multilayer model with saturation, which accounts for the formation of multiple CO₂ layers.

Model validation was performed using the coefficient of determination (R²) and the residual root mean square error (RMSE). Model 3 demonstrated the best fit with the experimental data, indicating that a multilayer adsorption mechanism is dominant in this system.

3.0 Results and Discussion: Advancing Carbon Capture Efficiency

3.1 Adsorption Mechanism and Energetics

The analysis, based on the validated multilayer model (Model 3), revealed key insights into the CO₂ capture process, which are critical for advancing technologies for SDG 13.

• Multilayer Formation: The model indicated that between three and four distinct layers of CO₂ molecules form on the AC surface. This multilayer buildup effectively compensates for the high density of active sites, significantly enhancing the total CO₂ capture capacity of the material.
• Adhesion Energy: The calculated adhesion energies ranged from 23.08 to 23.78 kJ/mol. These values are characteristic of physisorption, a process driven by weak van der Waals forces. This is highly relevant to SDG 7, as physisorption typically requires less energy for adsorbent regeneration compared to chemisorption, leading to more energy-efficient and cost-effective carbon capture cycles.
• Exothermic Process: The negative values for adhesion energy and internal energy (E_int) confirmed that the adsorption process is exothermic. Consequently, lower temperatures favor higher adsorption capacity, a critical consideration for process optimization.

3.2 Influence of Temperature on Adsorption Parameters

Temperature was found to be a critical parameter influencing the adsorption efficiency, with direct implications for the design of robust industrial systems under SDG 9.

1. Number of Adsorption Layers (N_C): The total number of layers decreased as temperature increased, from approximately four layers at 26 °C to three layers at 62.5 °C. This is due to increased thermal agitation disrupting the weaker intermolecular forces that hold the upper layers together.
2. Density of Adsorption Sites (D_M): The density of available receptor sites on the AC surface increased with temperature. This suggests that thermal energy may activate additional sites or alter the surface configuration to make more sites accessible.
3. Saturation Capacity (Q_sat): Despite the reduction in layers at higher temperatures, the overall CO₂ uptake capacity at saturation (Q_sat) increased. This trend was primarily driven by the significant increase in the density of active sites (D_M), which outweighed the effect of forming fewer layers.

4.0 Conclusion and Implications for Sustainable Development Goals

This study successfully elucidated the molecular mechanisms of CO₂ adsorption on activated carbon using a combination of experimental analysis and statistical physics modeling. The findings confirm that AC is a highly effective adsorbent, with its performance enhanced by a multilayer adsorption process. The characterization of the process as low-energy physisorption highlights its potential for developing economically viable and energy-efficient carbon capture systems.

The implications of this research for the Sustainable Development Goals are significant:

1. SDG 13 (Climate Action): By providing a deeper understanding of CO₂ sorption mechanisms, this work directly supports the development of more efficient technologies to capture and sequester greenhouse gases, a critical strategy for mitigating climate change.
2. SDG 9 (Industry, Innovation, and Infrastructure): The detailed thermodynamic and parametric analysis offers a robust scientific basis for designing and optimizing industrial-scale carbon capture units. This innovation is essential for building resilient and sustainable infrastructure and retrofitting industries to reduce their carbon footprint.
3. SDG 7 (Affordable and Clean Energy): The confirmation of a physisorption mechanism with modest energy requirements paves the way for carbon capture technologies with lower operational costs and energy penalties. This makes the integration of carbon capture with energy production more feasible, contributing to cleaner and more affordable energy.
4. SDG 12 (Responsible Consumption and Production): The principles and models developed in this study can be applied to AC derived from sustainable biomass sources. This would create a fully circular carbon capture solution, turning waste into a valuable tool for environmental protection.

Future research should focus on applying these findings to the development of scalable, next-generation adsorbents and integrated capture systems to accelerate the global transition to a low-carbon economy.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article addresses several Sustainable Development Goals (SDGs) due to its focus on mitigating climate change through technological innovation, sustainable industrial processes, and resource management.

• SDG 13: Climate Action

  This is the most central SDG to the article. The text’s primary motivation is to combat climate change driven by greenhouse gases. The introduction explicitly states, “One of the main causes of the observed acceleration in global warming is the significant increase in greenhouse gas concentrations over the past century, especially carbon dioxide (CO₂).” The entire study is dedicated to developing “efficient carbon capture technologies” as a direct response to this challenge.

• SDG 9: Industry, Innovation, and Infrastructure

  The research directly contributes to this goal by focusing on developing and optimizing an innovative technology for industrial application. The article mentions the need to “regulating CO₂ industry emissions” and highlights that industrial activities are a major source of CO₂. The development of “more thermally stable and efficient carbon capture materials” is a key aspect of building resilient infrastructure and promoting clean, sustainable industrialization.

• SDG 7: Affordable and Clean Energy

  The article links the rise in CO₂ to energy production, stating that emissions are intensified by “the burning of fossil fuels, and the combustion of organic matter to generate energy.” Carbon capture technologies are often considered a method to make fossil fuel energy “cleaner,” thereby contributing to the transition towards more sustainable energy systems. The research supports the development of advanced and cleaner fossil-fuel technology.

• SDG 12: Responsible Consumption and Production

  The article connects to this SDG by discussing the sustainable production of activated carbon (AC). It notes that “Agricultural waste, such as coconut husks and olive leftovers, can be utilized to make ACs.” This practice aligns with sustainable production patterns by turning waste streams into valuable materials, thus reducing waste and promoting a circular economy.

• SDG 6: Clean Water and Sanitation

  Although a secondary point, the article explicitly mentions the role of activated carbon in water purification. It states there are “important uses of activated carbon (AC) in water and wastewater treatment too, such as eliminating heavy metals, pesticides, and groundwater remediation.” This directly relates to improving water quality by treating pollutants.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the issues discussed, several specific SDG targets can be identified:

1. Target 9.4: Upgrade infrastructure and retrofit industries for sustainability

   The article’s core objective is to “guide the design of more thermally stable and efficient carbon capture materials.” This directly supports Target 9.4, which calls for upgrading industries with “greater adoption of clean and environmentally sound technologies and industrial processes” to make them sustainable. Carbon capture is a key technology for retrofitting industries, such as those involved in energy generation from fossil fuels, to reduce their environmental impact.

2. Target 13.2: Integrate climate change measures into policies and planning

   The research provides a scientific basis for climate change mitigation strategies. Developing and understanding technologies like CO₂ adsorption on activated carbon is a crucial step for integrating effective climate change measures into national and industrial planning, as called for by this target.

3. Target 7.a: Facilitate access to clean energy research and technology

   This target aims to enhance cooperation and access to “advanced and cleaner fossil-fuel technology.” The scientific study on CO₂ adsorption is a form of clean energy research that contributes to the global knowledge base on carbon capture, a technology designed to mitigate the impact of fossil fuel use.

4. Target 12.5: Substantially reduce waste generation

   The article’s mention of producing activated carbon from “biomass” and “Agricultural waste, such as coconut husks and olive leftovers” directly relates to this target. By creating a high-value product for environmental remediation from waste materials, this approach supports the reduction, recycling, and reuse of waste, moving towards a more circular economy.

5. Target 6.3: Improve water quality by reducing pollution

   The article’s reference to AC’s use in “water and wastewater treatment… eliminating heavy metals, pesticides, and groundwater remediation” clearly aligns with this target, which focuses on improving water quality by reducing pollution and minimizing the release of hazardous materials.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

The article, being a quantitative scientific study, mentions or implies several indicators that can measure progress towards the identified targets.

• Atmospheric CO₂ Concentration

  The article provides a direct indicator of the scale of the climate problem by citing the rise in atmospheric CO₂ “from roughly 280 parts per million (ppm) before the industrial period to above 420 ppm in recent years.” This metric is fundamental for tracking the overall progress of climate action (SDG 13).

• CO₂ Adsorption Capacity

  The study focuses on measuring the efficiency of activated carbon for CO₂ capture. Key parameters analyzed, such as “CO₂ uptake capacity at saturation (Q_sat),” “adhesion energy (ΔEa),” and the “number of adsorption layers,” serve as direct performance indicators for the effectiveness of this clean technology. These metrics can be used to evaluate progress towards developing and adopting environmentally sound technologies as per Target 9.4.

• Industrial Emissions Rate

  The article implies the importance of this indicator by referencing the need for “regulating CO₂ industry emissions” and noting that industrial activities are a primary source of greenhouse gases. Measuring CO₂ emissions per unit of industrial output (related to official indicator 9.4.1) is crucial for tracking the decarbonization of industries.

• Waste Valorization Rate

  By mentioning that AC can be produced from “Agricultural waste,” the article implies an indicator related to the amount or percentage of waste that is repurposed into valuable products. This would measure progress towards Target 12.5 on waste reduction and reuse.

• Concentration of Water Pollutants

  The reference to AC “eliminating heavy metals, pesticides” from water implies the use of indicators that measure the concentration of these specific pollutants in water bodies. Tracking the reduction of these pollutants would measure progress towards improving water quality under Target 6.3.

4. Summary Table of SDGs, Targets, and Indicators

Source: nature.com