Optimizing Lithium-Ion-Exchanged Zeolite 13X for Enhanced CO2 Adsorption: A Systematic Analysis

The lithium modification of zeolite 13X is systematically performed with lithium ion solutions of various concentrations with a view to using it as an adsorbent for carbon dioxide (CO2) to maintain a safe atmosphere in the crew cabin of human spaceflight missions. The effect of lithium ion solution concentration on the elemental composition, crystal structure, morphology and textural properties of the lithium modified zeolite is characterized by Inductively Coupled Plasma-Atomic Emission Spectrometry, X-Ray Diffraction, Scanning Electron Microscope, and N2 adsorption-desorption analysis, respectively. Treatment with lithium ion solution does not alter the Si/Al ratio, crystal structure, and morphology of the zeolite; however, it results in partial substitution of Na with Li leading to an improvement in surface area from 557 to 640 m2/g, pore volume from 0.298 to 0.350 cm3/g, and an increase in basic character. This eventually resulted in a considerable improvement in CO2 adsorption capacity from 4.7 to 5.9 mmol/g at 298 K. The maximum surface area, pore volume, and CO2 adsorption capacity are observed at a minimum Li ion solution concentration of 0.1 M in a single treatment step. The lithium modified zeolite 13X retains majority of the CO2 adsorption capacity over a large number of adsorption-desorption cycle indicating its potential as a CO2 capture material. The CO2 adsorption capacity of 5.9 mmol/g obtained at 0.1 M lithium ion solution in a single step treatment is significantly higher than the adsorption capacity of 5.71 mmol/g reported in the literature by three cycles of treatment with 1 M lithium ion solution demonstrating a considerable saving of costly and scarce lithium resource, time, and energy.