Influence of nitrogen on deep hydrodesulfurization of 4,6-dimethyldibenzothiophene

Several researchers have clearly established the inhibiting effect of basic nitrogen compounds on the HDS of thiophene and dibenzothiophene. At very low sulfur levels, refractory nitrogen compounds could sinificantly influence the deep HDS of polyaromatic sulfur compounds (PASC). The effect of two nitrogen compounds, one basic and the other non-basic, on the deep HDS of the most refractory PASC 4,6-dimethyldibenzothiophene (4,6-DMDBT) was presented. Quinoline severely inhibited the activity of the catalyst for the HDS of 4,6-DMDBT especially when co-existing with the model sulfur compound. Different from quinoline, net charge on N in carbazole was similar to net charge on S atom in 4,6-DMDBT. The bond order in carbazole was more uniform and less than that in quinoline. The catalyst did not regain its original activity following removal of quinoline from the feedstock. No such effects were observed with the addition of carbazole to the HDS feed.