Carbon dioxide capture by adsorption on a biomass based activated carbon
Saeidi Harzand, Sahand (2018) Carbon dioxide capture by adsorption on a biomass based activated carbon. [Thesis]
Adsorption of carbon dioxide has been examined on activated carbons produced from sunflower’s stem pith. Interesting structure and abundance of this agricultural residue make it a good candidate for the AC’s precursor role. The AC samples are produced with a combination of physical and chemical activation methods. Two alkali hydroxides of KOH and NaOH are selected as the activation agents. FTIR, TGA and BET tests are done on the bio-chars and activated carbon produced to study the structure of them. Higher temperatures and longer carbonization, cause the elimination of more functional groups from the raw material and a bring a higher surface area to the synthesized bio-chars and ACs. The highest surface area for NaOH and KOH activated samples are measured as 2948.43 and 2267.52 m2/g, respectively. In this study, NaOH, as the activation agent, provides higher surface area but KOH produces higher micropore to total volume ratio of 0.78 and 2.08 nm average pore diameter. This pore size distribution is more favorable for carbon dioxide adsorption than of NaOH which are measured as 0.68 micropore to total volume ratio and average pore diameter of 2.63 nm. Therefore, in the adsorption pressure range of 0 to 8 bars, KOH activated samples demonstrate higher adsorption capacity than AC activated by NaOH. For NaOH activated samples, shorter carbonization time does not cause any significant difference in the CO2 uptake. In case of KOH, in the pressure range of 0 to 2 bars, the uptake difference is negligible, but for higher pressures, carbon dioxide adsorption capacity increases by increasing the carbonization time. Moreover, thermodynamic analysis about the isosteric heat of adsorption and Gibbs free energy of the samples activated by KOH, indicates that the CO2 adsorption on AC is exothermic and a physisorption process.
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