Zeolitic sorbents for CO 2 adsorption were prepared from waste coal fl y ash (FA) through hydrothermal treatment at various ratios of NaOH/FA and NaAlO 2 /FA, including an initial alkali fusion step. The fusion step decomposed the fl y ash into very small amorphous particulate zeolite forms. The fl y ash was converted to Na-P1 type with a NaOH/FA ratio of 0.5 and Na-A type with a NaAlO 2 / FA ratio of 0.53. The product properties were affected by the reaction temperature: Na-P1 and Na-A types were formed at 100°C. Temperatures above 140°C led to the formation of more sodalite because of the redissolving and recrystallization of zeolite crystals. Alkali metal and alkaline earth metal cations were impregnated in the synthesized Na-P1 and Na-A zeolite through an ion-exchange method. The completed zeolitic sorbents were applied to the adsorption of low-level CO 2 . As a result of the experiments, calcium ions were found to be the best for CO 2 adsorption owing to their electrostatic behavior and acidbase interaction.

Detailed assessments of adsorption properties (isotherm, thermodynamics and kinetics) were carried out on chemically modified activated carbon (AC). Some pretreatment methods prior amination have been used to improve the CO 2 selective capture of AC in our previous works. Here, the inter-relationships among the adsorption properties were further investigated and reported. It was found that CO 2 molecules bind onto the heterogeneous surfaces of AC in a monolayer pattern as experimental data fit Freundlich isotherm rather than Langmuir. However, Redlich-Peterson, a 3-parameter model provided the best fit. The highest degree of precision of Chi-square analysis professed it as the most efficient error function for the isotherm study. Values of standard entropy showed to be the most significant thermodynamic limiting parameter in the adsorption process, as physisorption was found predominant for CO 2 collection at the interface. This observation was corroborated with temperature programmed desorption (TPD) analysis where ca. 86% of adsorbed CO 2 were desorbed below 500°C. The kinetic study indicated that CO 2 -AC interaction follows pseudo-second order while the higher R 2 of intraparticle diffusion over Elovich equation confirmed the deduction made from the thermodynamic study. Conclusively, the study of adsorption properties in this work provides useful information for designing proper adsorption reactor and subsequent regeneration of CO 2 -laden adsorbents at environmental levels.

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To control the levels of indoor CO2 in public spaces, we investigated adsorption at room temperature onto zeolites and activated carbon (AC) modified by alkali and alkaline earth metals. A fixed-bed adsorption apparatus was used to obtain more information about the effects of impregnated cations. Cations impregnated into the supports had a significant influence on the adsorption of CO2. In particular, sorbents impregnated with Ca had the highest adsorption capacity. Moreover, modified zeolites (for all cations) had greater adsorption capacities than ACs, despite their smaller surface areas, because of the electrostatic interforces between zeolites. The presence of moisture in the mixed gas flow caused decreases in adsorption capacity. The results of the equations of Sips and Toth matched well with the CO2 adsorptions of the present test sorbents. The presence of cations induced heterogeneous interactions between CO2 and the sorbents.

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