Deep desulfurization of fuel gas by adsorption on Cu-impregnated activated carbons in practical conditions

Deep desulfurization properties and characteristics of activated carbon (AC) modified by impregnation of CuCl₂ were studied using simulated hydrocarbon fuels containing dimethyl sulfide (DMS), tert-butylmercaptan (TBM), and tetrahydrothiophene (THT), the typical organosulfur compounds representing sulfides, thiols, and thiophenes that exist in fuel gases. The pristine AC had limited adsorptive desulfurization performance for a ternary DMS-THT-TBM mixture feed with an early breakthrough of DMS and TBM due to its preferential adsorption of THT. The adsorption of these organosulfur species on the AC surface was intrinsically weak and competing, as indicated by their low desorption activation energies (37-39 kJ mol⁻¹). However, relatively stronger adsorption of THT than the others led to the AC surface gradually being covered by THT through replacement of the initially adsorbed TBM and DMS. The impregnation of CuCl₂ on the AC (3.4 atomic % Cu) additionally formed strong and selective adsorption sites for TBM (activation energy=58.6 kJ mol⁻¹) on the AC surface, which gave rise to about three-fold increase in the total breakthrough adsorption capacity for these sulfur species. The structure and physicochemical properties of the adsorbents were characterized by N₂ adsorption, x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and surface pH measurement. The results suggested that the modulation of adsorption selectivity of the AC surface by CuCl₂ impregnation had significant effects on the overall deep desulfurization performance for fuel gases containing multiple organosulfur species in practical conditions.