# Dynamic separation of CO2 from N2 in humid streams using nano-sized zeolites

Sajjad Ghojavand, Edwin Clatworthy, Izabel Medeiris-Costa, Véronique

Pugnet, Parveen Kumar-Gandhi, Marie Desmurs, Valérie Ruaux, Svetlana

Mintova

► To cite this version:

Sajjad Ghojavand, Edwin Clatworthy, Izabel Medeiris-Costa, Véronique Pugnet, Parveen Kumar-Gandhi, et al.. Dynamic separation of CO2 from N2 in humid streams using nano-sized zeolites. Chemical Engineering Journal, 2025, 521, pp.167113. 10.1016/j.cej.2025.167113. hal-05368760

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# Dynamic separation of CO₂ from N₂ in humid streams using nano-sized zeolites

Sajjad Ghojavand<sup>a, *,</sup>, Edwin B. Clatworthy<sup>a</sup>, Izabel C. Medeiris-Costa<sup>b</sup>, Veronique Pugnet<sup>b</sup>, Parveen Kumar-Gandhi<sup>b</sup>, Marie Desmurs<sup>a</sup>, Valérie Ruaux<sup>a</sup>, Svetlana Mintova<sup>a, *</sup>

## ARTICLE INFO

### Keywords:

- Nanozeolite
- Chabazite
- CO₂ adsorption
- Wet stream
- Gas separation

## ABSTRACT

Water is constantly encountered in untreated CO₂-containing gas streams, making their separation between CO₂ and the other components challenging. Here, the CO₂ adsorption capability of nano-sized potassium-exchanged chabazite (K-CHA45) was evaluated and compared to the industrial benchmark for CO₂ and water capture, zeolite 13X used as a reference, using equilibrium adsorption measurements and breakthrough curve analysis in the presence of humidity. K-CHA45, with its smaller crystalline domains (~45 nm), exhibited a lower isosteric heat of adsorption, indicative of more facile regeneration, compared to sodium-form 13X (~5 µm). Breakthrough experiments revealed that both adsorbents effectively adsorb CO₂ and H₂O, but purging the adsorbent bed with He alone was insufficient to regenerate the adsorbents after several cycles, necessitating additional energy input. By leveraging the different diffusion kinetics of CO₂ and H₂O, the different molecules were separated. Single-step dynamic cycling experiments demonstrated that K-CHA45 significantly outperforms 13X, achieving CO₂ removal efficiencies up to 2.2 times higher. Specifically, K-CHA45 removed 1842 and 1756 mmol g⁻¹ of CO₂ per month from gas streams containing 1.5 vol% and 3.0 vol% H₂O, respectively. These findings suggest that K-CHA45 zeolite is a highly efficient and promising adsorbent for CO₂ capture in the presence of humidity, suitable for industrial applications.

## 1. Introduction

The rising concentration of atmospheric CO₂ due to anthropogenic emissions is a pressing global problem due to its various environmental impacts, particularly regarding climate change. [1,2] A major source of CO₂ emissions is flue gas originating from fossil fuel power plants and various industries such as steel and cement production, necessitating efficient CO₂ capture technologies. Adsorption-based CO₂ capture has shown promise as an alternative to traditional solvent-based capture due to lower emissions, fewer operational problems (corrosion, solvent management, etc.) and potentially lower energy demand for regeneration. [1,3–6] However, one of the primary challenges in adsorption-based separation of CO₂ from N₂ in flue gas is the presence of humidity. While CO₂ possesses a strong quadrupole, the strong dipole moment of H₂O makes it more competitive at adsorption sites, e.g. extra-framework cations, which significantly impacts the CO₂ separation performance of physical adsorbents. [7–9]

There are many types of adsorbents applicable for CO₂ capture, however three of the most promising and investigated include zeolites, activated carbons, and metal-organic frameworks (MOFs). [10–14] Zeolites are particularly attractive candidates for CO₂ capture because they are inexpensive, environmentally friendly with respect to their synthesis, stable under humid conditions, and can adsorb significant quantities of CO₂ under ambient conditions. [1] Zeolites such as sodium faujasite (13X) and chabazite (CHA) have demonstrated excellent potential for dry CO₂ capture and separation, but their performance under humid conditions remains under-developed. For instance, Li et al. studied CO₂ capture on 13X from humid flue gas containing 3.4 vol% water at 303 K using vacuum swing adsorption and found a relatively low CO₂ purity (59 %) and recovery (68 %). [9]

Currently, the strategy for separating CO₂ from a humid stream using an aluminosilicate zeolite involves first drying the stream in a separate step before CO₂ separation, which significantly increases operational (energy consumption) and capital (guard beds) expenditures. Therefore,

<footnote><sup>a</sup> Université de Caen Normandie, ENSICAEN, CNRS, LCS, Laboratoire Catalyse et Spectrochimie, 14000 Caen, France</footnote>

<footnote><sup>b</sup> TotalEnergies, OneTech, Sustainability R&D, CSTJF, 64018 Pau, Cedex, France</footnote>

<footnote>* Corresponding authors.</footnote>

<footnote>E-mail addresses: sajjad.ghojavand@ensicaen.fr (S. Ghojavand), svetlana.mintova@ensicaen.fr (S. Mintova).</footnote>
it is desirable to develop a method for separating CO₂ under humid conditions in a single step. [15] Two strategies are being explored: developing chemical adsorbents modified with functional groups to involve H₂O molecules in the adsorption process [16–19] and hydrophobization of existing adsorbents to disfavour H₂O adsorption. [20–22] However, these materials require careful design and introduce additional fabrication steps, increasing the difficulty and cost of large-scale production and industrial application. Moreover, while hydrophobization of adsorbents can impede the adsorption of water, this can also reduce the CO₂ adsorption capacity since the adsorption of CO₂ primarily involves interactions with hydrophilic sites. [1]

As an alternative, we propose the use of existing zeolite adsorbents (such as 13X and CHA) known for their excellent CO₂ adsorption abilities under dry conditions. This approach involves dynamically separating CO₂ in the presence of H₂O, leveraging the slower kinetics of H₂O adsorption compared to CO₂. Wilkins et al. conducted breakthrough analysis on 13X with a multicomponent mixture containing CO₂ and H₂O (38 to 88 % RH) at 295 K and found that CO₂ breakthrough time remains constant regardless of water content, while water breakthrough time is proportional to its content. [23] They also observed that the adsorption bed saturates with CO₂ before H₂O, indicating that the CO₂ adsorption kinetics are faster than that of H₂O adsorption. [23,24]

Herein, we focus on two zeolites with exceptional CO₂ adsorption properties: 13X (reference) and nano-sized K-CHA. [1,3,10] Based on our previous investigations, nano-sized K-CHA zeolite is amongst the best small-pore zeolites for CO₂ capture and separation, and zeolite 13X is the industrial benchmark for CO₂ and water capture. [25] We studied the equilibrium and dynamic adsorption of CO₂, N₂, and H₂O on these zeolites by performing various equilibrium adsorption measurements and breakthrough curve analyses. Using this information, we developed a method to dynamically separate CO₂ from N₂ under different levels of humidity in a single adsorption step by designing cycling experiments.

## 2. Experimental and modeling section

### 2.1. Materials and synthesis

All reagents were used as received unless explicitly stated otherwise. Sodium hydroxide pellets (98 wt%), potassium hydroxide (85 wt%), potassium chloride (99.5 wt%), colloidal silica (LUDOX AS-40), and sodium aluminate (NaAlO₂, with 40–45 % Na₂O and 50–56 % Al₂O₃) were obtained from Sigma-Aldrich. Cesium hydroxide hydrate (15–20 wt% H₂O, 98 %) was obtained from Alfa Aesar. Ultrapure Milli-Q water was employed for all synthesis steps. Quartz fine granular washed and calcined (1173 K, 0.2–0.8 mm, Merck) was used for blank breakthrough curve measurements. Helium (helium 4.5, ≥99.995 %), carbon dioxide (dioxyde de carbone 4.5, ≥99.995 %) and nitrogen (azote 5.0, ≥99.999 %) were purchased from Linde.

Zeolite 13X powder (denoted as 13X) was purchased from Alfa Aesar. Nano-sized CHA zeolite with ~45 nm particle size (denoted as K-CHA45) was synthesized by upscaling our previously published protocol. [1] 10.80 g of NaAlO₂ was mixed with 84.00 g of water under rapid stirring (350 rpm). Upon dissolution, 34.34 g of NaOH, 16.48 g of KOH, and 8.84 g of CsOH (50 wt% Cs in water) were added and stirred for 2 h to achieve a homogenous clear suspension. 200 g of LUDOX AS-40 then was added dropwise under vigorous stirring (500 rpm) to obtain the suspension with a composition of 0.2 Cs₂O: 1.5 K₂O: 6.0 Na₂O: 16.0 SiO₂: 0.7 Al₂O₃: 141.7 H₂O. The alkali metal aluminosilicate colloidal suspension underwent an aging process under vigorous stirring at room temperature for 17 days, followed by hydrothermal treatment in a static oven at 363 K for 7 h. The resulting CHA nanocrystals were recovered by centrifugation, washed with hot water (363 K) until the decanted supernatant achieved a neutral pH (7–8), and subsequently dried in air in an oven at 333 K overnight. The zeolite nanocrystals were subjected to ion exchange with 1 M solutions of KCl with a liquid/solid ratio (ml/g) of 40 for 2 h with rapid stirring. Following ion exchange, the CHA

nanocrystals were recovered by centrifugation and washed with water. The resulting nano-sized K-CHA45 was dried in air in an oven at 333 K overnight.

The chemical composition of samples K-CHA45 and 13X were determined using ICP-MS (Table 1) and their specific surface areas using the Rouquerol BET method are 146 and 862 m² g⁻¹ (Fig. S1), respectively. [1]

### 2.2. Characterization

Powder X-ray diffraction (PXRD) patterns were acquired using an Anton Paar XRDynamic 500 diffractometer with a graphite monochromator in Bragg–Brentano configuration, Cu Kα1 and Kα2 radiation (λ = 1.5406, 1.5444 Å, 40 kV, 50 mA), and Pixos2000 detector. The patterns were collected between 2θ of 5° and 50° with a step size of 0.03° and time per step of 492.606 s. Inductively coupled plasma mass spectrometry (ICP-MS) analyses were performed with an Agilent Technologies 7900 ICP-MS system. Scanning electron microscopy (SEM) of samples was performed using a Tescan Mira I LMH operating at 30 kV.

Adsorption isotherms for CO₂ and N₂ were recorded at temperatures of 273 K, 298 K, and 313 K, and cryogenic N₂ isotherms were recorded at 77 K, using a Micromeritics 3Flex Surface Characterization unit. Prior to measurement, the samples were outgassed under vacuum at 623 K for a minimum of 7 h. The isosteric heat of adsorption for CO₂ was calculated using the Clausius–Clapeyron equation applied to CO₂ adsorption isotherms in the temperature range of 273 K to 313 K, utilizing VersaWin software by Anton Paar.

Gravimetric water adsorption analysis was conducted at 313 K using a Surface Measurements Systems Dynamic Vapor Sorption unit. The samples were degassed under vacuum at 623 K for 7 h before the analysis.

Breakthrough curve experiments were conducted using a 3P Instruments mixSorb SHP eco system combined with a Cirrus-3 Quadrupole Mass Spectrometer. Zeolite powder samples (0.633 g and 0.769 g for K-CHA45 and 13X, respectively) were first pelletized by placing the powder between two core dies in a 20 mm die sleeve, along with a base plate and plunger, and applying pressure up to approximately 1.5 tones. The pellets were then crushed with a pestle and sieved to obtain particles sized between 60 and 35 mesh (250–500 µm), which were subsequently loaded into the column, weighed, and covered with a thin layer of glass wool. To eliminate inter-particle voids, the column, with an inner diameter of 6 mm and an adsorbent bed height of 6 cm (maintaining a column inner diameter to meshed particle diameter ratio of 12–24), was tapped 100 times after loading the meshed samples. The samples underwent pre-treatment under helium flow (20 mL min⁻¹) while being heated from room temperature to 573 K at a rate of 10 K min⁻¹, as measured by an internal temperature probe. They were held at 573 K for 7 h using a heating mantle.

Thermogravimetric analysis (TG) of the zeolite samples was performed using a Setsys Evolution (SETARAM) under air, heating from room temperature to 573 K at a rate of 10 K min⁻¹ and maintaining this temperature for 7 h to determine the water content evaporated during the activation step. The water content of the meshed K-CHA45 and 13X was found to be 16.2 wt% and 23.9 wt%, respectively. Following pretreatment, the samples were exposed to a flow of He (20 mL min⁻¹) at room temperature before initiating the breakthrough curve experiments.

Breakthrough curve experiments were conducted using gas mixtures

<table><caption>**Table 1**

Chemical composition of nano-sized K-CHA45 and 13X zeolites from ICP-MS analysis.</caption><thead><tr><td>Sample</td><td>Chemical formula (ICP-MS)</td><td>Si/Al</td></tr></thead><tbody><tr><td>K-CHA45</td><td>K<sub>11.0</sub>Cs<sub>0.8</sub>Al<sub>11.7</sub>Si<sub>24.2</sub>O<sub>72</sub></td><td>2.1</td></tr><tr><td>13X</td><td>Na<sub>86</sub>Al<sub>86</sub>Si<sub>106</sub>O<sub>384</sub></td><td>1.2</td></tr></tbody></table>
of 5% CO₂, 25% N₂, x% H₂O, and He (as the carrier gas) at 1 bar, with a total flow rate of 40 mL min⁻¹ (where x corresponds to water content ranging from 0 to 3%; all percentages are vol%). Prior to the experiments, the mass spectrometer was calibrated by passing the gas mixture through a bypass line to the mass spectrometer. Before contacting the adsorbent column with the analytical mixture, the sample was subjected to a flow of He. The adsorption feed mixture was then directed through the adsorbent column once the temperature and spectrometer signals had stabilized, as determined using the bypass line.

Upon reaching equilibrium, desorption was initiated by switching the feed to 100% He at a flow rate of 40 mL min⁻¹. Both adsorption (until H₂O breaks through) and desorption (until H₂O concentration is below C/C₀ < 0.05) steps were carried out at 313 K. The pressure drops across the column loaded with the sample were measured using a pressure sensor located immediately before the column and a pressure controller located immediately after the column. In all experiments, the pressure drop was less than 0.07 bar, or 6% of the column pressure. Helium was treated as a non-adsorbing gas within the system. The dead-time of the system was approximated to be around 2 s, determined by considering the activation time of the mass-flow controllers and recording the flow composition via the mass spectrometer through the bypass line. Cycling breakthrough experiments conducted on nano-sized K-CHA45 and 13X were performed under the same gas mixtures and conditions. For 13X five cycles of adsorption (15 mins) and desorption (60 mins), and for nano-sized K-CHA45 ten cycles of adsorption (5 mins) and desorption (20 mins) were performed.

All breakthrough curve data was processed using the mixSorb Manager software. The loadings of the adsorbates (CO₂, N₂, and H₂O) were calculated from the integrated areas exemplified in Fig. S2. To obtain equilibrium H₂O loadings, the adsorption branch of the breakthrough curves was used (Fig. S2a). To avoid the uncertainties on estimating the CO₂ and N₂ loadings based on the adsorption branch of the breakthrough curves due to the roll-up effect, the desorption branch of the breakthrough was used to estimate these loadings (Fig. S2b,c).

$$n_{\text{adsorbed}} = \int V_{\text{in}}(t)c_{\text{in}}(t)dt - \int V_{\text{out}}(t)c_{\text{out}}(t)dt \quad (1)$$

where nadsorbed is the amount of molecule adsorbed, Vin is the volume of the column inlet, Vout is the volume of the column outlet, cin is the concentration at column inlet, and cout is the concentration at column outlet.

$$V_{\text{out}}(t) = \frac{V_{\text{He}}(t)}{1 - \sum_{i=1}^{n} y_{\text{adsorptive.i}}(t)} \quad (2)$$

where VHe is the volume of He and yadsorptive is the adsorptive volume fraction.

To determine the loading of molecules in the free space between adsorbent particles, blank experiments were conducted using granular quartz under identical conditions of feed composition, temperature, flow rate, and pressure. These values were then directly subtracted from the loading values of the zeolite samples (Fig. S3).

### 3. Results and discussion

This study utilized two zeolite adsorbents: a commercial zeolite molecular sieve, 13X, and a nano-sized K-exchanged CHA developed by our group, K-CHA45. [25] The chemical compositions of the zeolite samples are presented in Table 1. PXRD analysis of K-CHA45 and 13X confirmed they possess the CHA- and FAU- type framework structures, consistent with previous studies and literature references (Fig. S4). [1,26] The K-CHA45 zeolite consists of discrete single crystals approximately 45 nm in size, based on prior published results. [1,10,25–27] In comparison, the 13X zeolite contains particles between 3 and 6 µm composed of intergrown octahedral crystals (see Fig. S4).

CO₂ and N₂ adsorption isotherms of K-CHA45 and 13X were

measured at 273, 298, and 313 K, and are presented in Fig. 1 and Fig. S5. Additionally, water adsorption isotherms at 313 K were obtained for both samples, shown in Fig. 1c. The equilibrium adsorption isotherms for K-CHA45 and 13X, as depicted in Fig. 1 and Fig. S5, align with previous studies. [1,28,29] Table 2 summarizes the equilibrium loadings of CO₂ (at 5 kPa), N₂ (at 25 kPa), and H₂O (at 1.5 and 3.0 kPa) at 313 K corresponding to the composition of the multi-component gas mixtures used in subsequent breakthrough measurements (vide infra). The CO₂ isosteric heat of adsorption (HOA) was estimated from the isotherms at different temperatures (Fig. 1a and Fig. S5a) and is presented in Fig. S5c. The data indicates that the CO₂ HOA for K-CHA45 is lower than that for 13X up to a coverage of 2 mmol g⁻¹ of adsorbed CO₂, suggesting that the adsorption of CO₂ on 13X is stronger and requires more energy for regeneration, compared to K-CHA45.

Breakthrough curves for single-cycle adsorption and desorption of

<figure><img src="image_4.png" /><figcaption>Fig. 1. (a) CO₂, (b) N₂, and (c) H₂O adsorption isotherms of nano-sized K-CHA45 and 13X zeolites at 313 K.</figcaption></figure>
<table><caption>**Table 2**
Equilibrium loadings of CO₂ (5 kPa), N₂ (25 kPa), and H₂O (1.5 and 3.0 kPa) based on single-component adsorption isotherms at 313 K for K-CHA45 and 13X zeolites.</caption><thead><tr><th rowspan="2">Sample</th><th colspan="4">Equilibrium loading at 313 K/mmol g<sup>-1</sup></th></tr><tr><th>CO<sub>2</sub> (@5 kPa)</th><th>N<sub>2</sub> (@25 kPa)</th><th>H<sub>2</sub>O (@1.5 kPa)</th><th>H<sub>2</sub>O (@3.0 kPa)</th></tr></thead><tbody><tr><td>K-CHA45</td><td>1.41</td><td>0.08</td><td>5.90</td><td>7.10</td></tr><tr><td>13X</td><td>3.23</td><td>0.11</td><td>13.55</td><td>14.99</td></tr></tbody></table>

<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Adsorption branches of breakthrough curves for gas mixtures of CO₂/N₂/He (5/25/70), CO₂/N₂/H₂O/He (5/25/1.5/68.5), and CO₂/N₂/H₂O/He (5/25/3/67) at 313 K for (a) K-CHA45 and (b) 13X zeolites.</figcaption></figure>
three multi-component gas mixtures CO₂/N₂/He (5/25/70), CO₂/N₂/H₂O/He (5/25/1.5/68.5), and CO₂/N₂/H₂O/He (5/25/3/67) at 313 K for both adsorbents are shown in Fig. 2 and Fig. S6. The results indicate that N₂ breaks through almost immediately after the experiment begins for both K-CHA45 and 13X, regardless of the gas mixture composition. For K-CHA45, CO₂ breakthrough occurs after 14 min g⁻¹ of zeolite and is largely unaffected by the water content in the gas mixture (Fig. 2b). Similarly, for 13X, CO₂ breaks through after 20 min g⁻¹ of zeolite of adsorption, with the water content in the stream having minimal effect on CO₂ breakthrough time (Fig. 2b). This observation is consistent with that of Wilkins et al., whereby H₂O diffuses much more slowly through the adsorbent bed than CO₂ and thus the CO₂ breakthrough time is unchanged. [30]

The competitive equilibrium loadings obtained from breakthrough curve analysis of K-CHA45 and 13X zeolites at 313 K using the three gas mixtures: CO₂/N₂/He (5/25/70), CO₂/N₂/H₂O/He (5/25/1.5/68.5), and CO₂/N₂/H₂O/He (5/25/3/67) are summarized in Table 3. A comparison of the competitive equilibrium loadings from breakthrough curve and single-component equilibrium adsorption analyses for K-CHA45 show good agreement for CO₂ under dry conditions and under humid conditions. For 13X, the competitive equilibrium loading of CO₂ from breakthrough curve analysis under dry conditions is slightly lower than that of the equilibrium adsorption analysis. This is likely due to the incomplete removal of pre-adsorbed water by He flow and heating by the pretreatment, compared to vacuum and heating pretreatment for equilibrium adsorption analysis. During breakthrough curve analysis, the competitive equilibrium loadings of water on 13X in multi-component gas mixtures (Table 3) were higher than those in single-component adsorption measurements (Table 2).

As shown in Table 3, the presence of water in the gas mixture results in significant reductions in the equilibrium CO₂ competitive loadings. Nevertheless, according to Fig. 2, the CO₂ breakthrough times for both K-CHA45 and 13X zeolites in the presence of H₂O are similar. As mentioned earlier, this is in line with the findings of Wilkins et al. studying 13X. [23] They performed breakthrough measurements on a mixture of CO₂ and H₂O under three different humidity levels (i.e. 38, 70, and 88 % RH) at 295 K and they observed that the CO₂ breakthrough time is not affected by the H₂O level. [23,24] This is due to the considerably slower diffusion kinetics of H₂O molecules compared to the CO₂ molecules. [9,23] As a consequence, at the beginning of the breakthrough experiment in the presence of water, CO₂ will experience diffusion through an empty bed; similar to the conditions in the absence of water. [9] Over time as water diffuses through the bed, water will displace most of the adsorbed CO₂ due to competitive adsorption, reflected by a higher concentration of CO₂ at the outlet compared to the inlet (roll-up effect). When water breaks through, the CO₂ roll-up ends, equilibrium has been reached, and very little CO₂ remains in the adsorbent (Table 3). [9] Typically this behavior is considered as a disadvantage for CO₂ separation from humid streams using zeolites. However, the faster CO₂ diffusion kinetics compared to H₂O provides an opportunity to separate CO₂ molecules under dynamic conditions by performing cycling experiments when the adsorption bed becomes saturated with CO₂, which is the CO₂ breakthrough time (vide infra).

Based on these findings, we designed a cycling experiment to dynamically separate CO₂ in the presence of water, taking advantage of the faster CO₂ adsorption kinetics. The duration of the adsorption step was set to the CO₂ breakthrough time (C/C₀ > 0.05; 15 min for 13X and

5 min for K-CHA45), and the desorption step (purge by pure He flow) was set to four times the adsorption step duration (60 min for 13X and 20 min for K-CHA45).

Fig. 3 shows five consecutive cycling breakthrough measurements for two gas mixtures, CO₂/N₂/H₂O/He (5/25/1/68) and CO₂/N₂/H₂O/He (5/25/3/67), at 313 K for 13X zeolite. The adsorption step (15 min) is highlighted in green, and the desorption step (60 min) is highlighted in blue. The concentrations of CO₂, N₂, and H₂O in the effluent stream after each adsorption cycle for 13X at 313 K with two different water levels in the inlet feed (1.5 and 3.0 vol%) are presented in Table S1. The effective loadings (defined as the guest molecule captured between each step measured during the desorption step) of CO₂, N₂, and H₂O after each adsorption step for 13X at 313 K under these conditions are summarized in Table 4.

According to Fig. 3a and Table S1, when 1.5 vol% water is present in the inlet gas stream at 313 K (equivalent to 20 % RH), neither water nor CO₂ signals are observed in the outlet stream during the adsorption cycles on 13X, indicating adsorption of both molecules. The maximum CO₂ concentration in the effluent stream should be 5 % of the inlet CO₂ concentration (5 vol%), setting the detection limit for CO₂ in the effluent stream after each adsorption cycle to 0.25 vol%. Comparing the results presented in Table 4 and Table S1, the CO₂ effluent concentration after each adsorption step remained below 0.25 vol% during the five cycling adsorption steps. Table 4 indicates that, on average, 1.42 mmol g⁻¹ of zeolite CO₂ was separated dynamically in each adsorption cycle. However, based on the results presented in Table 3, the competitive equilibrium CO₂ loading at 313 K with 1.5 vol% water in the inlet feed is only

<figure><img src="image_6.png" /><figcaption>Fig. 3. Cycling breakthrough measurements for two gas mixtures of CO₂/N₂/H₂O/He (5/25/1.5/68.5) and CO₂/N₂/H₂O/He (5/25/3/67) at 313 K for 13X zeolite; five consecutive adsorption steps of 15 mins (highlighted in green) followed by desorption steps of 60 mins (highlighted in blue) are shown.</figcaption></figure>

<caption>**Table 3**</caption>

Competitive equilibrium loadings of CO₂, N₂, and H₂O based on multi-component breakthrough measurements of gas mixtures of CO₂/N₂/He (5/25/70), CO₂/N₂/H₂O/He (5/25/1.5/68.5), and CO₂/N₂/H₂O/He (5/25/3/67) at 313 K for K-CHA45 and 13X zeolites.

<table><thead><tr><th rowspan="2">Sample</th><th colspan="2">Competitive equilibrium loading at 313 K/mmol g<sup>-1</sup></th><th colspan="3">Competitive equilibrium loading at 313 K/mmol g<sup>-1</sup></th><th colspan="3">Competitive equilibrium loading at 313 K/mmol g<sup>-1</sup></th></tr><tr><th>CO<sub>2</sub> (5 %)</th><th>N<sub>2</sub> (25 %)</th><th>CO<sub>2</sub> (5 %)</th><th>N<sub>2</sub> (25 %)</th><th>H<sub>2</sub>O (1.5 %)</th><th>CO<sub>2</sub> (5 %)</th><th>N<sub>2</sub> (25 %)</th><th>H<sub>2</sub>O (3.0 %)</th></tr></thead><tbody><tr><td>K-CHA45</td><td>1.42</td><td>0.12</td><td>0.14</td><td>0.14</td><td>5.70</td><td>0.35</td><td>0.42</td><td>7.40</td></tr><tr><td>13X</td><td>2.81</td><td>0.23</td><td>0.06</td><td>0.10</td><td>15.91</td><td>0.05</td><td>0.11</td><td>16.67</td></tr></tbody></table>
<caption>**Table 4**</caption>

Effective loadings of CO₂, N₂, and H₂O based on five consecutive breakthrough adsorption and desorption cycles of 15 and 60 min, respectively for two gas mixtures of CO₂/N₂/H₂O/He (5/25/1.5/68.5) and CO₂/N₂/H₂O/He (5/25/3/67) at 313 K on 13X zeolite.

<table><thead><tr><th rowspan="2">Number of cycles</th><th colspan="3">Effective loading at 313 K/<br>mmol g<sup>-1</sup><br>CO<sub>2</sub>/N<sub>2</sub>/H<sub>2</sub>O/He (5/25/1.5/<br>68.5)</th><th colspan="3">Effective loading at 313 K/<br>mmol g<sup>-1</sup><br>CO<sub>2</sub>/N<sub>2</sub>/H<sub>2</sub>O/He (5/25/3/<br>67)</th></tr><tr><th>CO<sub>2</sub></th><th>N<sub>2</sub></th><th>H<sub>2</sub>O</th><th>CO<sub>2</sub></th><th>N<sub>2</sub></th><th>H<sub>2</sub>O</th></tr></thead><tbody><tr><td>1</td><td>1.47</td><td>0.17</td><td>0.16</td><td>1.41</td><td>0.17</td><td>0.46</td></tr><tr><td>2</td><td>1.43</td><td>0.19</td><td>0.22</td><td>1.33</td><td>0.19</td><td>0.56</td></tr><tr><td>3</td><td>1.40</td><td>0.21</td><td>0.23</td><td>1.36</td><td>0.20</td><td>0.53</td></tr><tr><td>4</td><td>1.40</td><td>0.20</td><td>0.20</td><td>1.34</td><td>0.19</td><td>0.40</td></tr><tr><td>5</td><td>1.38</td><td>0.20</td><td>0.22</td><td>1.22</td><td>0.19</td><td>0.43</td></tr></tbody></table>

0.06 mmol g⁻¹ of zeolite.

According to Fig. 3b and Table S1, when 3.0 vol% water is present in the inlet gas stream at 313 K (equivalent to 40 % RH), no water is observed in the outlet stream during the adsorption cycles. Comparing Table 4 and Table S1, the CO₂ effluent concentration after each adsorption step was around 0.25 vol% during the first three cycling adsorption steps. On average, 1.37 mmol g⁻¹ of zeolite CO₂ was separated dynamically in each adsorption cycle (Table 4). The competitive equilibrium CO₂ loading at 313 K with 3.0 vol% water in the inlet feed is only 0.05 mmol g⁻¹ of zeolite (Table 3). After the third cycle, the CO₂ effluent concentration increased to 2.89 and 5.28 vol%, with corresponding reductions in CO₂ effective loadings to 1.34 and 1.22 mmol g⁻¹ for the fourth and fifth steps, respectively (Table S1 and Table 4). This suggests that water molecules are displacing CO₂, possibly forming carbonate species, and that He purging is insufficient for complete regeneration. Therefore, increased temperature may be necessary for regeneration. Nonetheless, significant effective CO₂ loadings (1.42 and 1.37 mmol g⁻¹ with 1.5 and 3.0 vol% water, respectively, at 313 K) can be achieved for dynamic CO₂ separation from N₂ and H₂O using commercial 13X.

Fig. 4 illustrates five consecutive cycling breakthrough measurements for two gas mixtures, CO₂/N₂/H₂O/He (5/25/1.5/68.5) and CO₂/N₂/H₂O/He (5/25/3/67), at 313 K for K-CHA45 zeolite (Fig. S7 shows extended ten adsorption/desorption cycles). The adsorption step (5 min) is highlighted in green, and the desorption step (20 min) is highlighted in blue. The concentrations of CO₂, N₂, and H₂O in the effluent stream after each adsorption cycle for nano-sized K-CHA45 zeolite at 313 K under two different water levels in the inlet feed (1.5 and 3.0 vol%) are summarized in Table S3. The effective loadings of CO₂, N₂, and H₂O after each adsorption step for K-CHA45 at 313 K under these conditions are presented in Table 5 and Table S2.

When 1.5 vol% water is present in the inlet gas stream at 313 K (equivalent to 20 % RH), neither water nor CO₂ signals are detected in the outlet stream during the first five consecutive adsorption cycles of K-CHA45 (Fig. 4a and Table S3). This indicates that both water and CO₂ molecules are being adsorbed. Based on the data presented in Table 5 and Table S3, the CO₂ effluent concentration after each adsorption step was consistently below 0.25 vol% during these five cycling adsorption steps. On average, 1.07 mmol g⁻¹ of CO₂ could be dynamically separated per cycle (Table 5). However, the competitive equilibrium CO₂ loading at 313 K with 1.5 vol% water in the inlet feed is only 0.14 mmol g⁻¹ (Table 3). An extended cycling experiment up to ten cycles on K-CHA45 zeolite revealed that, from the sixth to the ninth cycles, the CO₂ concentration in the outlet stream increased from 0.06 vol% to 0.85 vol %, with a corresponding reduction in effective CO₂ loadings from 0.96 to 0.79 mmol g⁻¹. This indicates that after the eighth adsorption cycle, He purging is insufficient, necessitating additional energy, such as thermal treatment, for regeneration.

Similarly, at 3.0 vol% water in the inlet gas stream at 313 K (equivalent to 40 % RH), neither water nor CO₂ signals are observed in

<figure><img src="image_7.png" /><figcaption>**Fig. 4.** Cycling breakthrough measurements for two gas mixtures of CO₂/N₂/H₂O/He (5/25/1.5/68.5) and CO₂/N₂/H₂O/He (5/25/3/67) at 313 K for K-CHA45 zeolite; five consecutive adsorption steps of 5 mins (highlighted in green) followed by desorption steps of 20 mins (highlighted in blue) are shown.</figcaption></figure>

<caption>**Table 5**</caption>

Effective loadings of CO₂, N₂, and H₂O based on five consecutive breakthrough adsorption and desorption cycles (5 and 20 min, respectively) for two gas mixtures of CO₂/N₂/H₂O/He (5/25/1.5/68.5) and CO₂/N₂/H₂O/He (5/25/3/67) at 313 K on K-CHA45 zeolite.

<table><thead><tr><th rowspan="2">Number of cycles</th><th colspan="3">Effective loading at 313 K/<br>mmol g<sup>-1</sup><br>CO<sub>2</sub>/N<sub>2</sub>/H<sub>2</sub>O/He (5.0/25.0/<br>1.5/68.5)</th><th colspan="3">Effective loading at 313 K/<br>mmol g<sup>-1</sup><br>CO<sub>2</sub>/N<sub>2</sub>/H<sub>2</sub>O/He (5.0/25.0/<br>3.0/67.0)</th></tr><tr><th>CO<sub>2</sub></th><th>N<sub>2</sub></th><th>H<sub>2</sub>O</th><th>CO<sub>2</sub></th><th>N<sub>2</sub></th><th>H<sub>2</sub>O</th></tr></thead><tbody><tr><td>1</td><td>1.09</td><td>0.14</td><td>0.12</td><td>1.14</td><td>0.16</td><td>0.25</td></tr><tr><td>2</td><td>1.09</td><td>0.16</td><td>0.15</td><td>1.07</td><td>0.13</td><td>0.28</td></tr><tr><td>3</td><td>1.07</td><td>0.23</td><td>0.18</td><td>1.02</td><td>0.23</td><td>0.26</td></tr><tr><td>4</td><td>1.06</td><td>0.16</td><td>0.13</td><td>0.97</td><td>0.13</td><td>0.13</td></tr><tr><td>5</td><td>1.02</td><td>0.18</td><td>0.11</td><td>0.88</td><td>0.15</td><td>0.21</td></tr></tbody></table>

the outlet stream during the first five consecutive adsorption cycles on K-CHA45 (Fig. 4b and Table S3). This also indicates adsorption of both molecules. During these five cycling adsorption steps, the CO₂ effluent concentration remained below 0.25 vol% (Table 5 and Table S3). On average, 1.02 mmol g⁻¹ of CO₂ could be dynamically separated per cycle (Table 5). However, the competitive equilibrium CO₂ loading at 313 K with 3.0 vol% water in the inlet feed is only 0.35 mmol g⁻¹ (Table 3). An extended cycling experiment up to ten cycles showed that, from the sixth to the tenth cycles, the CO₂ concentration in the outlet stream increased from 0.52 vol% to 6.53 vol%, with a corresponding reduction in effective CO₂ loadings from 0.80 to 0.42 mmol g⁻¹. This suggests that after the fifth adsorption cycle, He purging is insufficient, requiring additional energy such as thermal treatment, for effective regeneration.

The adsorption behavior of CO₂, N₂, and H₂O on two zeolites with high CO₂ capture potentials (13X and K-CHA45) was studied using both equilibrium adsorption measurements (Fig. 1 and Fig. S5) and breakthrough experiments (Fig. 2 and Fig. S6). This information enabled the
formulation of a method for dynamically capturing CO₂ in wet streams through cycling experiments. For 13X, under an inlet gas mixture of CO₂/N₂/H₂O/He (5/25/1.5/68.5), five consecutive cycles of adsorption (15 min) and desorption by He purging (60 min) were sufficient, with an average of 1.42 mmol g⁻¹ CO₂ removal per cycle. After these cycles, regeneration by heating is necessary to remove the adsorbed H₂O. Using this method, it is possible to capture 816 mmol g⁻¹ of CO₂ per month. A similar method can be applied to separate CO₂ from a wet stream containing 3.0 vol% H₂O (CO₂/N₂/H₂O/He of 5/25/3/67), with three consecutive cycles of adsorption (15 min) and desorption by He purging (60 min), followed by temperature regeneration of 13X, yielding an average of 1.37 mmol g⁻¹ CO₂ removal per cycle. This method allows for the capture of 787 mmol g⁻¹ of CO₂ per month.

The nanosized K-CHA45 zeolite was also used to dynamically separate CO₂ from wet streams. Considering five consecutive cycles of adsorption (5 min) and desorption by He purging (20 min), followed by temperature regeneration to remove accumulated water molecules, it is possible to remove 1842 and 1756 mmol g⁻¹ of CO₂ per month from inlet gas streams containing CO₂/N₂/H₂O/He of 5/25/1.5/68.5 and 5/25/3/67, respectively. This demonstrates that using K-CHA45, the CO₂ removal efficiency can be increased by 2.2 times compared to zeolite 13X.

While it is true that the proposed cycling experiments still require energy-intensive regeneration by heating between cycles (depending on the water level in the inlet stream and the adsorbent type) to dry the adsorption bed and maintain dynamic CO₂ capture, this approach significantly reduces the energy needed compared to current industrial practices. Currently, the industry relies on a two-step separation process involving drying followed by CO₂ capture. In this conventional method, energy-intensive regeneration by heating is required after each cycle, just for the drying step. In contrast, the proposed single-step cycling method with K-CHA45 shows promise for CO₂ separation under humid conditions, as it simplifies the process and reduces energy consumption.

## 4. Conclusions

In this study, we investigated the performance of two zeolite adsorbents, industrial zeolite 13X and nano-sized K-form CHA (K-CHA45), for CO₂ capture from gas mixtures under varying conditions. Our analysis included equilibrium adsorption measurements and breakthrough experiments with K-CHA45 zeolite containing small crystals (~45 nm) and 13X zeolite with micron-sized particles (~5 µm). CO₂ adsorption isotherms indicated that K-CHA45 zeolite has a lower isosteric heat of adsorption than 13X, suggesting easier regeneration.

Breakthrough experiments demonstrated that the presence of water significantly impacts competitive adsorption. For zeolite 13X, both CO₂ and H₂O are effectively adsorbed, with negligible CO₂ detected in the effluent stream during initial cycles. However, He purging proved insufficient for complete regeneration after several cycles, necessitating additional energy input, such as temperature treatment. Nano-sized K-CHA45 zeolite similarly adsorbed both CO₂ and H₂O, but also required additional regeneration energy after extended cycling.

Dynamic cycling experiments showed that K-CHA45 zeolite achieved significantly higher CO₂ removal efficiency (up to 2.2 times) compared to zeolite 13X. Specifically, K-CHA45 zeolite removed 1842 and 1756 mmol g⁻¹ of CO₂ per month from gas streams with 1.5 vol% and 3.0 vol % H₂O, respectively, compared to 816 and 787 mmol g⁻¹ for zeolite 13X. This indicates that K-CHA45 is a highly efficient adsorbent for CO₂ capture in wet conditions, providing a promising solution for industrial applications requiring effective and sustainable CO₂ removal.

### CRediT authorship contribution statement

**Sajjad Ghojavand:** Writing – review & editing, Writing – original draft, Visualization, Validation, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
**Edwin**

**B. Clatworthy:** Writing – review & editing, Validation.
**Izabel C. Medeiris-Costa:** Validation.
**Veronique Pugnet:** Writing – review & editing, Validation.
**Parveen Kumar-Gandhi:** Validation.
**Marie Desmurs:** Formal analysis.
**Valérie Ruaux:** Formal analysis.
**Svetlana Mintova:** Writing – review & editing, Writing – original draft, Validation, Resources, Funding acquisition, Conceptualization.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgement

The support of the Centre for Zeolites and Nanoporous Materials, Label of Excellence, Normandy Region (CLEAR, 239216) and Eco-Gas Industrial Chair TotalEnergies is acknowledged. Co-funded by the European Union (ERC, ZEOLiGhT, 101054004). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cej.2025.167113.

### Data availability

No data was used for the research described in the article.

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