Adsorption of sulfur compounds from natural gas by different adsorbents and desorption using supercritical CO2

Abstract

Natural gas is extensively used in industries as well as in other sectors as an energy resource and, sometimes, it needs to undergo processes for the removal of sulfur compounds, impurities present in its composition, which can cause damages to pipes and catalysts, making it necessary to develop and/or improve deep desulfurization methods In this work, granular activated carbon was modified through two methods, oxidation using nitric acid, and impregnation using a ferric chloride solution. The resulting adsorbents were evaluated for their capacity of adsorbing seven sulfur compounds present in the synthetic natural gas sample, through their breakthrough curves. Afterward, the adsorbents desorption was performed by using supercritical carbon dioxide under the conditions of 333.15K at 100bar, 150bar and 200bar. The results indicate an average increase of 46.4% for the samples of impregnated activated carbon and 25.1% for the oxidized ones, when compared to the virgin activated carbon. Nonetheless, the supercritical conditions studied in the desorption stage were efficient only for the unmodified activated carbon samples, reaching a maximum regeneration percentage of approximately 96%, while the impregnated and oxidized ones reached only 57.4% and 72.9%, respectively. The adsorption capacities of both modified adsorbents after the regeneration were inferior to those capacities obtained in the first adsorption, then two hypotheses were investigated: (1) destruction of the newly created sites after regeneration; and (2) incomplete desorption in the studied supercritical conditions. Through other experiments it was proved that, after the regeneration, there was no destruction of the newly created sites; therefore, further studies on the operating conditions are required in order for the modified adsorbents to achieve high regeneration capacities.