(569f) Kinetics of CO2 Sorption on Binderless Pellets of Different Cationic Forms of Y-Type Zeolites

Adsorption-based technologies hold great promise in the large-scale deployment of carbon capture and storage (CCS) to fast-track the decarbonisation of the global energy system¹. These technologies can be applied to the production of blue hydrogen², and post-combustion carbon capture from low/moderate (i.e. natural gas, coal)³ to high CO₂ concentration streams (i.e. cement, steel)⁴. Zeolites are commonly used adsorbents in these applications owing to their molecular sieving properties and excellent thermodynamic and physicochemical characteristics, such as high selectivity towards CO₂, thermal and mechanical stability, and the ability to be shaped into technical bodies without the use of a binder⁵. This last factor allows the adsorbent to retain much of the adsorption capacity of the crystalline form and be packed easily in a separation unit. Y-type zeolites show promise for pre-combustion capture of CO₂ in the production of blue hydrogen owing to their low affinity for CO₂ at low pressures, which can reduce vacuum work, and the high feed pressure in this application, thereby leading to a high working capacity.

The technoeconomic feasibility of using such materials for adsorption-based carbon capture processes is typically assessed by optimizing detailed numerical process models⁶ for which the key properties that need to be parametrized are the adsorption equilibria and kinetics. While experimental techniques for measuring adsorption equilibrium are widely available, accurate kinetic measurements remain challenging to perform and their outcomes can significantly impact the overall separation performance. Therefore, the aims of this work were three-fold: (1) To characterize the textural (porosity) and CO₂ adsorption equilibrium properties, (2) to accurately quantify the kinetics and determine the mass-transfer mechanisms involved in the sorption of CO₂, and (3) to relate these mechanisms to the textural and equilibrium properties of three different cationic forms of Y.type zeolites (Si/Al = 2.6), namely hydrogen (H-Y), sodium (Na-Y), and tetramethylammonium (TMA-Y).

To this end, we produced binderless pellets for each cationic form using a manual hydraulic press. We used nitrogen sorption isotherms at 77 K to determine their micro- and mesoporosity and mercury intrusion porosimetry to evaluate the macroporosity. The results from the combined pore size distribution obtained from these measurements indicate the samples are microporous with additional macroporosity introduced during the pelletization process. For the equilibrium sorption measurements, we obtained CO₂ sorption isotherms at 288, 298, and 308 K up to a pressure of 101 kPa. The isotherms exhibit an increase in both CO₂ capacity and concave non-linearity in the order H-Y < TMA-Y < Na-Y, which suggests an increase in strength of attraction between the zeolite and the CO­­₂ molecules due to increasing basicity of the zeolite framework⁷. We used the parameters (i.e. skeletal density, porosity, and equilibrium isotherm models) resulting from these characterization steps as model inputs to extract kinetic parameters for CO­₂ sorption from the subsequent dynamic desorption experiments.

We carried out dynamic sorption experiments on individual zeolite pellets using the experimental technique described in our previous works^8,9. The experiments were carried out at 288, 298, and 308 K by saturating the adsorbent to a CO₂ partial pressure of up to 95 kPa, followed by desorption at two different flowrates of carrier gas. Helium and argon were used separately as carrier gases to elucidate the impact of macropore resistance to mass transfer within the adsorbent pellets which can be introduced due to the packing of the zeolite crystals during the shaping process¹⁰. We then fit the time-resolved desorption profiles obtained from the experiments using a parameter estimation routine with the isotherm models fitted to the volumetric CO₂ sorption isotherms as inputs. We used the resulting two-parameter rate expressions obtained for the two cases with different carrier gases, along with the findings from textural characterization to determine the controlling resistance to mass transfer for each zeolite pellet¹¹. Ultimately, the rate expression obtained can be readily adapted in numerical models for adsorption-based processes and used for design and optimization of these separations.

References

(1) The Future of Hydrogen. Futur. Hydrog. 2019, No. June. https://doi.org/10.1787/1e0514c4-en.

(2) Streb, A.; Mazzotti, M. Novel Adsorption Process for Co-Production of Hydrogen and CO₂ from a Multicomponent Stream-Part 2: Application to Steam Methane Reforming and Autothermal Reforming Gases †. Ind. Eng. Chem. Res. 2020, 59 (21), 10093–10109. https://doi.org/10.1021/acs.iecr.9b06953.

(3) Haghpanah, R.; Majumder, A.; Nilam, R.; Rajendran, A.; Farooq, S.; Karimi, I. A.; Amanullah, M. Multiobjective Optimization of a Four-Step Adsorption Process for Postcombustion CO₂ Capture Via Finite Volume Simulation. Ind. Eng. Chem. Res. 2013, 52 (11), 4249–4265. https://doi.org/10.1021/ie302658y.

(4) Danaci, D.; Bui, M.; Mac Dowell, N.; Petit, C. Exploring the Limits of Adsorption-Based CO₂ Capture Using MOFs with PVSA-from Molecular Design to Process Economics. Mol. Syst. Des. Eng. 2020, 5 (1), 212–231. https://doi.org/10.1039/c9me00102f.

(5) Silva, J. A. C.; Schumann, K.; Rodrigues, A. E. Sorption and Kinetics of CO₂ and CH₄ in Binderless Beads of 13X Zeolite. Microporous Mesoporous Mater. 2012, 158, 219–228. https://doi.org/10.1016/j.micromeso.2012.03.042.

(6) Ward, A.; Pini, R. Efficient Bayesian Optimization of Industrial-Scale Pressure-Vacuum Swing Adsorption Processes for CO₂ Capture. Ind. Eng. Chem. Res. 2022, 61 (36), 13650–13668. https://doi.org/10.1021/acs.iecr.2c02313.

(7) Walton, K. S.; Abney, M. B.; Douglas LeVan, M. CO₂ Adsorption in Y and X Zeolites Modified by Alkali Metal Cation Exchange. Microporous Mesoporous Mater. 2006, 91 (1–3), 78–84. https://doi.org/10.1016/j.micromeso.2005.11.023.

(8) Azzan, H.; Rajagopalan, A. K.; L’Hermitte, A.; Pini, R.; Petit, C. Simultaneous Estimation of Gas Adsorption Equilibria and Kinetics of Individual Shaped Adsorbents. Chem. Mater. 2022, 34 (15), 6671–6686. https://doi.org/10.1021/acs.chemmater.2c01567.

(9) L’Hermitte, A.; Azzan, H.; Yio, M. H. N.; Rajagopalan, A. K.; Danaci, D.; Hirosawa, T.; Isobe, T.; Petit, C. Effect of Surface Functionalization on the Moisture Stability and Sorption Properties of Porous Boron Nitride. Microporous Mesoporous Mater. 2023, 352 (February), 112478. https://doi.org/10.1016/j.micromeso.2023.112478.

(10) Brandani, S.; Mangano, E. The Zero Length Column Technique to Measure Adsorption Equilibrium and Kinetics: Lessons Learnt from 30 Years of Experience. Adsorption 2021, 27 (3), 319–351. https://doi.org/10.1007/s10450-020-00273-w.

(11) Glueckauf, E. Theory of Chromatography. Part 10.—Formulæ for Diffusion into Spheres and Their Application to Chromatography. In Transactions of the Faraday Society; 1955; Vol. 51, pp A1–A68. https://doi.org/10.1016/S0301-4770(08)61562-6.