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Changes in Porous Parameters of the Ion Exchanged X Zeolite and Their Effect on CO₂ Adsorption.

ABSTRACT: Zeolite 13X (NaX) was modified through ion-exchange with alkali and alkaline earth metal cations. The degree of ion exchange was thoroughly characterized with ICP, EDS and XRF methods. The new method of EDS data evaluation for zeolites was presented. It delivers the same reliable results as more complicated, expensive, time consuming and hazardous ICP approach. The highest adsorption capacities at 273 K and 0.95 bar were achieved for materials containing the alkali metals in the following order K < Na < Li, respectively, 4.54, 5.55 and 5.94 mmol/g. It was found that it is associated with the porous parameters of the ion-exchanged samples. The Li_0.61Na_0.39X form of zeolite exhibited the highest specific surface area of 624 m²/g and micropore volume of 0.35 cm³/g compared to sodium form 569 m²/g and 0.30 cm³/g, respectively. The increase of CO₂ uptake is not related with deterioration of CO₂ selectivity. At room temperature, the CO₂ vs. N₂ selectivity remains at a very high stable level prior and after ion exchange in co-adsorption process (X_CO2 during adsorption 0.15; X_CO2 during desorption 0.95) within measurement uncertainty. Additionally, the Li_0.61Na_0.39X sample was proven to be stable in the aging adsorption-desorption tests (200 sorption-desorption cycles; circa 11 days of continuous process) exhibiting the CO₂ uptake decrease of about 6%. The exchange with alkaline earth metals (Mg, Ca) led to a significant decrease of SSA and micropore volume which correlated with lower CO₂ adsorption capacities. Interestingly, the divalent cations cause formation of mesopores, due to the relaxation of lattice strains.

SUBMITTER: Gesikiewicz-Puchalska A

PROVIDER: S-EPMC8707879 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The mechanisms of CO2/CH4 adsorption in coal are the theoretical foundation for CO2 sequestration in coal seams targeted for enhanced coalbed methane recovery. Herein, by changing the model (low rank coal: WMC, middle rank coal: XM and high rank coal: CZ) with plenty of side aliphatic chains and functional groups established in the literature, the influence and mechanism of pore parameters and functional groups(-CH3, -OH, -C2O, -C=O) on the adsorption of CO2 and CH4 in different rank coals are systematically studied. Using the Connolly surface algorithm to calculate the pore volume (V F) and the specific surface area (S SA) of coal with different functional groups, it can be seen that the influence of the functional group change on the pore structure is related to the coal rank. Changing the various functional groups in the original coal structure to a unified functional group (-CH3, -OH, -C2O, or -C=O) will increase the accessible pore volume (V F) and the specific surface area (S SA), except in low-rank and middle-rank coal, where the ordered arrangement of -C=O will decrease V F and S SA. The adsorption capacities of different pore parameters and functional groups were calculated by Grand Canonical Monte Carlo simulation and density functional theory. On pure adsorption, the pore parameters exert greater influence than the functional groups. By comparing the adsorption energy of the original pore structure containing functional groups and that of modified pores without functional groups, the contributions of the pore structure and original functional groups on CO2/CH4 adsorption are 71 and 29% and 83 and 17%, respectively. Small-diameter pores and -C2O have a strong adsorption capacity. In terms of competitive adsorption, the -C=O functional groups and pore diameters ranging from 1.0 to 2.0 nm can significantly enhance the selectivity of CO2 over CH4. The CH4 and CO2 adsorption does not occur via rigorous monolayer adsorption; multilayer adsorption can occur for CH4 and CO2 with pore diameters of 1.0-2.0 and 1.0-2.2 nm, respectively, thus causing micropore filling. These quantitative results establish a foundation for the development of adsorption theory for CO2/CH4 in coal.

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Changes in Porous Parameters of the Ion Exchanged X Zeolite and Their Effect on CO₂ Adsorption.

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Changes in Porous Parameters of the Ion Exchanged X Zeolite and Their Effect on CO2 Adsorption.

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OmicsDI is part of the ELIXIR infrastructure

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Changes in Porous Parameters of the Ion Exchanged X Zeolite and Their Effect on CO₂ Adsorption.