Deep HDS of Diesel Fuel: Inhibiting Effect of Nitrogen Compounds on the Transformation of the Refractory 4,6-Dimethyldibenzothiophene Over a NiMoP/Al2O3 Catalyst

Abstract

The effect of nitrogen-containing compounds (acridine and 1,4-dimethylcarbazole: 14DMCARB) on the hydrodesulfurization of 4,6-dimethyldibenzothiophene (46DMDBT) was studied on a sulfided NiMoP/Al 2 O 3 catalyst in a fixed bed microreactor (340°C, 40 bar). Both nitrogen-containing compounds inhibited the hydrodesulfurization of 46DMDBT. However, the effect of acridine (a basic compound) and mainly its hydrogenated product (presumably 1,2,3,4,5,6,7,8-octahydroacridine: OHA1) was much more significant than the effect of 14DMCARB (a non-basic compound). In the presence of acridine, the socalled direct desulfurization pathway (DDS) of the HDS of 46DMDBT was less affected than the hydrogenation pathway (HYD) and was even slightly promoted when the partial pressure of acridine increased (after a strong initial inhibition). This was ascribed to a cocatalytic contribution of the nitrogen-containing compound to the C-S bond cleavage. 14DMCARB had the same inhibiting effect on both pathways (DDS and HYD). We also demonstrated that acridine inhibited the transformation of 14DMCARB and can explain why carbazoles are generally the main nitrogen impurities present in gasole after hydrotreatment.

Recent Insights in Transition Metal Sulfide Hydrodesulfurization Catalysts for the Production of Ultra Low Sulfur Diesel: A Short Review

“…Sulfur removal from sterically hindered compounds presents a strong inhibition effect of polyaromatics and nitrogen-containing compounds, which must be solved at the same time [15]. To overcome these problems, the HDS units need to increase their working pressure and temperature conditions; however, this carries along another series of problems [16].…”

Aromaticity of five- and six-membered heterocycles present in crude oils – An electronic description for hydrotreatment process

“…In this context, our calculations also corroborate the maintenance of pyridine and pyridineAH + compounds and their implications in HDT catalyst poisoning. Pyridine ring has been detected in pyridine-containing compounds after hydrogenation of adjacent benzene rings, HDN selectivity of acridine have shown that pyridine ring is maintained in octahydroacridine as principal hydrogenated product, which is the main inhibitor of HDS catalysts [37][38][39]. It contains a pyridine ring, basic and aromatic, while carbazole hydrogenated products are tetrahydrocarbazole or hexahydrocarbazole, pyrrole ring is hydrogenated before last benzene ring.…”

Towards a New Pseudo-quantitative Approach to Evaluate the Ionization Response of Nitrogen Compounds in Complex Matrices

“…As these are getting more and more stringent, the hydrotreatment process needs to be more and more efficient and despite their relatively low amount among the gas oils, the nitrogen compounds are of high concern for refiners [13][14][15][16]. Neutral nitrogen compounds are refractory while the basic ones deactivate the catalysts used and compete with sulfur compounds for their removal [17,18]. The total nitrogen content remaining in the hydrotreated samples is a key information for assessing the efficiency of the hydrotreatment.…”