Hydrogen Recovery from CH₄-H₂ Gas Mixture by Adsorption Using Coconut Shell-Based Activated Carbon

In this study, attempts have been made to utilize biomass residue to recover hydrogen from CH₄-H₂ gas mixture, which might be applied for hydrocracking process in oil refineries. Part of this attempt is to produce an activated carbon based on coconut shell, which is processed through chemical and physical activation using 25% ZnCl₂ followed by activation at 800°C with N₂ flow for an hour to increase its surface area. The resulted BET surface area and iodine number are 432.26 m²/g and 644.80 mg/g, respectively. A detailed experimental study has been made for the adsorption of pure methane and hydrogen at 20°C, as well as CH₄-H₂ mixture at 10, 20 and 30°C; each isotherm condition undergoes a variety of pressure ranging from 1-6 bars. Measurements were made using volumetric technique and gas chromatograph analysis. The highest adsorption is obtained for pure methane followed by CH₄-H₂ mixture with 1:9 ratio and pure H₂. For gas mixture, the total adsorption increases with the increase of pressure in each isotherm; in which the higher temperature has lower adsorption ability. The adsorption result shows that methane has 2.7 times higher adsorption capacity than hydrogen and almost all methane in the mixtures is adsorbed by the activated carbon, therefore, the coconut shell based activated carbon produced from this research can be applied as the adsorbent in the separation process of CH₄/H₂ mixture.