Ultra-deep desulphurization of both model and commercial diesel fuels by adsorption method

Selective adsorption for removing sulfur from diesel fuel has emerged as a potential economically viable and effective alternative method to achieve the stringent environmental regulations for sulfur levels in diesel. In this paper, the sulfur removing activity of three different types of activated charcoal (AC, T103 and T104) and two molecular sieves (MS)- 13X and 5 A- were investigated, using both model diesel and commercial diesel. It was observed that AC, T103 and T104 displayed similar good sulfur removing activity and stability with both the model diesel (initial sulfur content: 1000 ppm) and commercial diesel (initial sulfur content: 43 ppm), with the sulfur removal efficiency varying from 60% up to 90% under the reaction conditions used in this work. These results also suggested that the adsorbents were better suited to polishing low sulfur diesel, to achieve ultra-low sulfur content. The experimental data for the adsorption of DBT fitted the pseudo-second-order kinetic equation more closely, which suggests chemical adsorption activity between DBT and the adsorbents AC, T103, T104 and MS 13X. Further experimental work, using commercial diesel with 43 ppm sulfur content, revealed that the adsorption affinity for different sulfur compounds in conventional diesel decreases in the following order: 4-MDBT >> 4,6-DMDBT(similar to)4 E, 6-MDBT(similar to)2,4,6-TMDBT(similar to)1,4,6-TMDBT. It is believed this is due to steric hindrance. The decrease in activity with molecular weight epitomizes the limitations of the adsorbents in removing refractory organic sulfur. In conclusion, activated charcoals are much more suitable for the task of deep desulphurization of diesel fuels than are molecular sieves.