Comparative Study on Adsorptive Desulfurization of Thiophenic Compounds over Terephthalic Acid-Based and Trimesic Acid-Based Metal–Organic Frameworks

Aromatic sulfur compounds present in liquid fuels in the form of thiophenes are converted into sulfur oxides (SOx) during the combustion of fuels and cause major environmental problems such as acid rain, global warming, and air pollution. The adsorptive desulfurization of four aromatic sulfur compounds─thiophene, benzothiophene, dibenzothiophene, and 4,6-dimethyl dibenzothiophene─from n-octane was investigated in the current study over five typical metal–organic frameworks (MOFs), namely MIL-53(Cr, Al, Fe), Cu-BDC, and HKUST-1, which were successfully synthesized and characterized using XRD, FT-IR, SEM, and N2 adsorption–desorption. The results indicate that for ADS of thiophene and BT, the adsorption capacity of MOFs increases in the order MIL – 53(Fe) < Cu – BDC < HKUST – 1 < MIL – 53(Al) < MIL – 53(Cr), for DBT, it increases in the order Cu – BDC < MIL – 53(Fe) < HKUST – 1 < MIL – 53(Al) < MIL – 53(Cr), and for DMDBT, it increases in the order HKUST – 1 < Cu – BDC < MIL – 53(Fe) < MIL – 53(Al) < MIL – 53(Cr). It is evident that among the synthesized MOFs, MIL-53(Cr) demonstrated the highest adsorptive desulfurization capacity upon removing sulfur compounds from model oil due to its high surface area and suitable pore diameter, with sulfur removal performance of 29, 39, 61, and 88% for the adsorption of thiophene, benzothiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene, respectively. Adsorption data were checked through kinetic models and isotherms, and it has been shown that the adsorption kinetics follow the pseudo-second-order kinetic model, and the adsorption isotherm is better described by the Langmuir equation.