Effect Of Various Modifications Of Activated Carbons On Their Desulfurization Performance For Fuel Oils

Combustion of thiophenic compounds in fuel oils can cause air pollution by SOx emission and deactivation of catalysts in off-gas converter. Deep desulfurization of fuel oils is a hot research area in upgrading quality of fuel oils.Activated carbons from different sources and with different activation methods were modified by oxidation with nitric acid, heat treatment at 600?, boron doping via hydroboration and metal loading with an incipient wetness impregnation method. Microstructure changes and adsorptive desulfurization performance of the activated carbons before and after the modifications were investigated under static and dynamic conditions for model fuels with and without a competing benzene (20wt%). In addition, a simultaneous analysis method for thiophenic compounds in ppm levels and hydrocarbons in percentage levels was established with capillary gas chromatography using one column and two detectors, FID and FPD. Results indicate that the heat treatment leads to a decrease of oxygen containing functional groups, a collapse of a part of pores smaller than 1nm, and an increase of pore volume of pores between 1.1nm to 1.6nm. There is a good correlation between the reduction of pore volume of pore less than 1nm and the reduction of content of the C-O group. The adsorption capacities for thiophenic compounds under static and dynamic condition are reduced by the heat treatment. The optimum pore size ranges for adsorption of thiophene, dibenzothiophene and 4,6-dimethyl dibenzothiophene are 0.536-1.090nm,0.536-1.179nm and 0.679-1.268nm, respectively for the activated carbons with or without heat treatment, indicating that micropore filling is the dominant mechanism for thiophenic adsorption. The adsorption isotherms of the activated carbons for dibenzothiophene are better fitted by Freundlich than Langmuir equation, implying that the active adsorption sites for thiophenic compounds are inhomogeneous. Oxidative modification of activated carbons with nitric acid leads to an increase of oxygen-containing functional groups and thiophenic adsorption capacity for the model fuels with or without a competing benzene. Boron doping of activated carbons with hydroboration causes a blocking of a part of pores, but the adsorption capacities per surface area of the activated carbons for thiophenic compounds increase after the modification. Loading metallic species such as Cu, Ni and Ni/ZnO also give rise to pore blocking effect and a decrease of thiophenic adsorption capacity for the model fuel without benzene, but the selectivity for thiophenic compounds increases after the metal loading, owing to an increase interaction between S and metals. A simultaneous analysis of thiophenic compounds in ppm levels and hydrocarbons in percentage levels is possible with capillary gas chromatography using one column and two detectors, FID and FPD.