A Study on the Adsorptive Removal of Organic Sulfur Compounds in Fuel Gas Using Modified Activated Carbons

Abstract

The influence of surface modification of activated carbon on the adsorptive behavior of tertiary butyl mercaptan (TBM) and tetrahydrothiophene (THT) in methane gas was studied under mild conditions. The commercially available activated carbon was modified by oxidation using HNO3 or H2O2, and an impregnation method using KOH. The pore structure and surface properties of adsorbents were characterized using nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface pH measurements. It was found that the amount of TBM and THT adsorbed on the adsorbents that were oxidized by HNO3 or H2O2 afforded similar sulfur adsorption capacities for each adsorbent, and resulted in an adsorption capacity of ca. 2.5 times greater than that of parent activated carbon. In addition, the modifications caused by oxidizing agents HNO3 or H2O2 enhanced the selective adsorption for THT over TBM, while the presence of KOH as the impregnant directed the selectivity towards TBM over THT. Moreover, an investigation of the effect of KOH loading on the TBM adsorption capacity was also carried out by carbon modification upon oxidation with a solution of HNO3 followed by KOH impregnation. The maximum adsorption capacity for TBM was found to be 0.69 mmol/g with respect to 10 wt.% potassium loading. The desorption activation energies of TBM and THT on the modified activated carbons were also estimated through temperature-programmed desorption (TPD) experiments, which were ranked in order of value as follows: AC (20.8 kJ.mol-1) < AC-HNO3 (30.8 kJ.mol-1) < AC-H2O2 (34.6 kJ.mol-1) < AC-HNO3-KOH (124.2 kJ.mol-1) for TBM and AC-HNO3-KOH (35.7 kJ.mol-1) < AC (36.0 kJ.mol-1) < AC-H2O2 (38.8 kJ.mol-1) < AC-HNO3 (44.6 kJ.mol-1) for THT.