Abstract
Hydrogen sorption characteristics of activated carbons (ACs) produced by physical and chemical activations from two coal mines (Kilimli and Armutcuk) in the Zonguldak region, Turkey were investigated by a volumetric technique at 77 K. H2 adsorption isotherms were obtained on the samples exposed to pyrolytic thermal treatments in a temperature range of 600–900 °C under N2 flow and chemical activation using different chemical agents such as KOH, NH4Cl, ZnCl2 from the two mines. Experimental hydrogen adsorption isotherm data at 77 K were used for the evaluation of the adsorption isotherm constants of the Brunauer-Emmett-Teller (BET) and the Langmuir models, and also the amount of hydrogen adsorbed on the various samples was evaluated by using the adsorption isotherm data. Higher hydrogen adsorption capacity values were obtained for all the heat and the chemically treated activated carbon samples from the Kilimli coal samples than Armutcuk. The amount of H2 adsorbed on the original Kilimli coal samples was 0.020 wt%, and it was increased to 0.89 wt% on the samples pyrolyzed at 800 °C. The highest value of hydrogen adsorption obtained was 1.2 wt% for the samples treated with KOH+NH4Cl mixture at 750 °C followed by oxidation with ZnCl2. It was shown that chemical activations were much more effective than physical activations in increasing the surface area, pore volume and the hydrogen sorption capacities of the samples.
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