Enhancement in Dibenzothiophene Reactive Adsorption from Liquid Fuel via Incorporation of Sulfur Heteroatoms into the Nanoporous Carbon Matrix

Abstract

Adsorption of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from simulated diesel fuel was investigated with polymer-derived carbon matrices. Sulfur was incorporated to the carbon surface via a high-temperature hydrogen sulfide reduction of oxygen-containing groups. The resultant carbons were characterized by nitrogen adsorption, thermal analysis, potentiometric titration, and elemental analysis. The selectivities for DBT and DMDBT adsorption were calculated with reference to naphthalene. The carbon matrices studied had comparable structures, hence, the effects of the sulfur functionalities were evident in an increase in dibenzothiophenes selectivity and the breakthrough capacity; this was especially visible at a breakthrough point where small pores are expected to be active in the adsorption process. Incorporation of sulfur atoms into the aromatic rings of the carbon matrix increases the ability of the surface to attract dibenzothiophenes via dispersive interactions (sulfur-sulfur bridges). Sulfur and sulfur-oxygen groups present in larger pores enhance the amount of adsorbed dibenzothiophenes via specific acid-base and polar interactions. They also contribute to the reactive adsorption of DBT and DMDBT (oxidized) and their chemisorption on the carbon surface.

Role of phosphorus in carbon matrix in desulfurization of diesel fuel using adsorption process

“…Scientific efforts focus on oxidation [1,2], photoxidation [3,4] or adsorption . The adsorption based methods applied activated alumina [7,8], zeolites [9], and activated carbons [7,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] as adsorbents. The results obtained on the latter materials seem promising [12,22,[26][27][28].…”

“…Presence of copper [16,24], iron [24] or silver [29] compounds on the carbons was also shown as beneficial for the selectivity of separation. In such cases the reactive adsorption involving the oxidation of DBT and DMDBT to sulfoxides and sulfones was proposed [26][27][28]. These species, owing to higher polarity than that of DBT or DMDBT interact stronger with polar groups of the carbon surface [22,23,27] and thus enhance the efficiency of the separation process.…”

“…Our recent studies demonstrated that sulfur heteroatoms in the carbon matrix enhance the performance of activated carbons as adsorbents of DBT and DMDBT from model diesel fuel [27,28,30]. Specifically thiophenic groups which can exists in small pores [27,28,30] increase the adsorption capacity while selectivity is positively affected when sulfonic acid is present in larger pores.…”

“…Specifically thiophenic groups which can exists in small pores [27,28,30] increase the adsorption capacity while selectivity is positively affected when sulfonic acid is present in larger pores. It contributes to the separation process imposing acid-base interactions with DBT and DMDBT and also to the oxidation of dibenzothiophenes in reactive adsorption [26][27][28].…”

“…Since the roles of oxygen and sulfur have been analyzed in detail elsewhere [18,22,23,[26][27][28] the main emphasis here is on the role of phosphorus. This heteroatom is usually bonded in the forms of phosphates.…”