Recibido: 20/11/2024 Aceptado: 02/03/2025

shape, indicating significantly improved efficiency and lower energy input. DACC systems based on advanced MOFs

hold great promise for minimizing non-point source emissions and should thus be considered essential components of

a climate change mitigation strategy. This study contributes to direct future research and development toward more

efficient and cost-effective MOFs in DACC applications.

atmospheric greenhouse gases and the resulting global warming. While the exact causal relationship is still under

discussion, it is now widely accepted that human activities have significantly increased these gases in the atmosphere

which is one of the most pressing environmental threats facing humanity today. Among these GHGs, CO2 has the

largest impact, accounting for about 55% of the observed greenhouse effect and global warming. The emissions from

thermal power plants (TPPs) are a major source of CO2, as approximately 30% of the world's fossil fuel consumption

fossil fuels [5]. The International Energy Agency reports that more than two-thirds of greenhouse gas emissions and

over 80% of carbon dioxide emissions stem from energy-related activities. The global CO2 emissions grew by an

average of 2.6% annually. Many studies have documented the statistics and detrimental effects of global warming,

revealing that around 60% of the planet is now facing unprecedented high temperatures each year [6].

Currently, the most prevalent techniques for capturing CO2 from gas mixtures include absorption, membrane

separation, and low-temperature CO2 capture. Absorption typically involves using solvents that selectively absorb CO2

from flue gases, making it effective for large-scale industrial applications. Membrane separation utilizes selective

permeability to separate CO2 from other gases, offering a more energy-efficient and compact alternative. Low-

temperature CO2 capture, on the other hand, leverages cryogenic processes to condense and separate CO2 from gas

various DAC methods, including using solutions like sodium hydroxide [8]. However, these can be expensive and

energy intensive.

More recent studies have focused on using solid materials called Metal-Organic Frameworks (MOFs), which are more

efficient in capturing CO2. Metal-organic frameworks (MOFs) offer numerous significant benefits that make them

highly attractive for a range of applications, particularly in gas separation, storage, and catalysis. One of their standout

features is their exceptionally high surface area, which enhances their capacity for gas adsorption and storage, making

them efficient materials for capturing gases like CO2 and hydrogen. Additionally, the tunability of MOFs allows for

easy modification of their structural and chemical properties by altering the metal ions or organic linkers used in

synthesis, enabling the design of materials tailored to specific applications, such as selective gas separation. Their

have shown that these materials can be effective and potentially less costly than liquid solutions [10]. The research

also explores different designs to improve efficiency, such as using monolith structures, which reduce pressure drops

and increase mass transfer rates. Steam can be used as a stripping agent to regenerate the adsorbents, and some

experiments have shown that certain adsorbents can withstand repeated cycles of adsorption and desorption using

steam [11].

This paper evaluates the economic and energy performance of DAC using MIL-101(Cr)-PEI-800 and mmen-

Mg2(dobpdc) in a temperature vacuum swing adsorption (TVSA) process. The study aims to optimize the conditions

for DAC and guide future materials development to improve performance. Numerical models are used to analyze the

effect of air and steam velocity on the system's CO2 capture efficiency.

emphasizes the importance of material selection in its performance and cost-effectiveness, as illustrated in Figure I.

Two metal-organic frameworks (MOFs), MIL-101(Cr)-PEI-800 and mmen-Mg2(dobpdc), are evaluated for their CO2

capture capabilities. These MOFs are crucial because they offer high surface areas and tunable pore structures that

enhance CO2 adsorption, making them suitable for DACC applications. The study explores how these materials are

used in monolithic contactors, structures designed to maximize the contact surface between the adsorbent and air.

These contactors play a vital role in improving CO2 capture efficiency by reducing pressure drops and increasing the

adsorption rate, which leads to better overall performance in capturing atmospheric CO2.

making them a viable option for large-scale DACC operations. In terms of cost evaluation, the study examines the

energy demands and overall expenses of implementing these MOFs in a DACC system. mmen-Mg2(dobpdc) emerges

as the more effective and cost-efficient material due to its higher CO2 adsorption capacity and favorable non-linear

isotherm behavior, which allows it to perform better under varying conditions. This material also requires less energy

for regeneration compared to MIL-101(Cr)-PEI-800, making it a superior option for reducing CO2 emissions. Overall,

for future DACC applications.

400 cpsi

Figure II. Monolith channel [12]

The process (as illustrated in Figure 3) consists of the following five steps.

the air is assumed to be 400 ppm. Adsorption of CO2 by the film begins in this step.

in the MOFs from being oxidized at high temperatures. The channel at the front end is closed and is evacuated by

the use of a vacuum pump. The step continues until the oxygen concentration falls below 4%.

is done by closing the rear end and passing saturated steam at 1 atm through the front end.

pressure is dropped at the rear.

requires less water compared to the NaOH spray method, which involves significant water use and potential chemical

handling issues. This makes the process more sustainable and environmentally friendly. TVSA is more cost-effective,

especially for large-scale applications, due to its lower energy requirements and efficient operation. While initial capital

costs for vacuum equipment may be higher, the long-term savings in operational costs make it a better economic

choice.

Temperature Swing Adsorption (TSA) is a cyclic process used for the capture of CO2 and other gases; details are given

in Table 5. It leverages temperature changes to adsorb and desorb gases from solid adsorbents.

using steam or other heat sources, to increase the temperature. This heat causes the CO2 molecules to desorb from the

adsorbent surface. The efficiency of this step depends on the thermal properties of the adsorbent and the design of the

heating system. Effective heat integration can significantly lower the energy penalty associated with this step [23],

[24].

a concentrated CO2 stream, which can be captured and stored. The purity and recovery rate of CO2 depend on the

adsorbent material and the operational parameters of the TSA cycle. MOFs, for example, have shown promising results

due to their tunable properties and high selectivity for CO2 [23], [24].

performance, including a high working capacity of 17.6 wt% at 200°C. The presence of strong CO2 adsorption sites

in Mg-MOF-74 was crucial for its effectiveness in TSA processes [26].

chemical reactions that transform CO2 into valuable products such as hydrocarbons, alcohols, and other chemicals.

This process typically takes place in an electrochemical cell consisting of a cathode, an anode, and an electrolyte [22],

[27].

(CO), formate, methanol, methane, ethylene, and other hydrocarbons. The specific product depends on the catalyst

The reduction of CO2 involves multiple electron and proton transfer steps, making it a complex process. Effective

catalysts are crucial to enhance selectivity and efficiency towards desired products [22], [27].

The overall efficiency of the process depends on the ability of the anode to facilitate the oxygen evolution reaction

(OER) efficiently [22], [27].

Alloying and modifying these metals with other elements can enhance their catalytic properties and product

selectivity [22], [27].

catalysts for CO2 electroreduction. Their high surface area and tunable chemical environment make them suitable for

desorbed CO2 from the MOF pores in the opposing direction. Thus, heat is conducted into the MOF and wall and

is not transferred by diffusion of steam within the MOF phase following steam condensation [32], [33].

The pressure drop across the channel is given by the Hagen Poiseuille equation:

(1)

The other source of pressure drop is due to drag on the system, which is assumed to be negligible as compared to

pressure drop by Hagen- Poiseuille Equation [eqn. (1)].

The CO2 absorption rate is approximated by the linear driving force model as given by:

The concentration at the interface is assumed to be in equilibrium with pure liquid water and thus estimated using the

Antoine equation [eqn. (6)]:

The heat of absorption of CO2 is determined using the Clausius−Clapeyron equation.

The heat of absorption of CO2 is calculated at 25°C, 50°C and 75°C

The system design specifications and mass and heat transfer properties are tabulated in Table VI and Table VII,

[17] M. Mahmoudkhani and D. W. Keith, “Low-energy sodium hydroxide recovery for CO2 capture from atmospheric

10.1016/j.ijggc.2009.02.003.

[18] W. R. Lee et al., “Exceptional CO 2 working capacity in a heterodiamine-grafted metal–organic framework,”

Chem. Sci., vol. 6, no. 7, pp. 3697–3705, 2015, doi: 10.1039/C5SC01191D.

[19] L. A. Darunte, K. S. Walton, D. S. Sholl, and C. W. Jones, “CO2 capture via adsorption in amine-functionalized

Capture and Conversion Processes,” Ind. Eng. Chem. Res., vol. 55, no. 12, pp. 3383–3419, Mar. 2016, doi:

10.1021/acs.iecr.5b03277.

[22] “Maximum and Comparative Efficiency Calculations for Integrated Capture and Electrochemical Conversion of

https://pubs.acs.org/doi/10.1021/acsenergylett.3c02489

[23] L. Joss, M. Hefti, Z. Bjelobrk, and M. Mazzotti, “On the Potential of Phase-change Adsorbents for CO2 Capture

by Temperature Swing Adsorption,” Energy Procedia, vol. 114, pp. 2271–2278, Jul. 2017, doi:

10.1016/j.egypro.2017.03.1375.

Chem. Rev., vol. 116, no. 19, pp. 11840–11876, Oct. 2016, doi: 10.1021/acs.chemrev.6b00173.

[26] J. A. Mason, K. Sumida, Z. R. Herm, R. Krishna, and Jeffrey. R. Long, “Evaluating metal–organic frameworks

for post-combustion carbon dioxide capture via temperature swing adsorption,” Energy Environ. Sci., vol. 4, no. 8, p.

3030, 2011, doi: 10.1039/c1ee01720a.

[27] “Electrochemical Approaches for CO2 Conversion to Chemicals: A Journey toward Practical Applications |

https://pubs.acs.org/doi/10.1021/acs.accounts.1c00674

[30] M. S. Shafeeyan, W. M. A. Wan Daud, and A. Shamiri, “A review of mathematical modeling of fixed-bed columns

for carbon dioxide adsorption,” Chem. Eng. Res. Des., vol. 92, no. 5, pp. 961–988, May 2014, doi:

10.1016/j.cherd.2013.08.018.

[31] J. L. Plawsky, M. Ojha, A. Chatterjee, and P. Wayner, “Review of the effects of surface topography, surface

chemistry, and fluid physics on evaporation at the contact line,” Chem. Eng. Commun., vol. 196, pp. 658–696, May

2009, doi: 10.1080/00986440802569679.

[32] “Water and Metal–Organic Frameworks: From Interaction toward Utilization | Chemical Reviews.” Accessed:

Sep. 25, 2024. [Online]. Available: https://pubs.acs.org/doi/10.1021/acs.chemrev.9b00746

[33] “CO2 capture materials: a review of current trends and future challenges - ScienceDirect.” Accessed: Sep. 25,

2024. [Online]. Available: https://www.sciencedirect.com/science/article/pii/S2589234723001690

[34] J. L. Woodliffe et al., “Continuous flow synthesis of MOF UTSA-16(Zn), mixed-metal and magnetic composites

for CO2 capture – toward scalable manufacture,” J. Environ. Chem. Eng., vol. 12, no. 6, p. 114167, Dec. 2024, doi: