A Review on the Reaction Mechanism of Hydrodesulfurization and Hydrodenitrogenation in Heavy Oil Upgrading

Abstract

The future of fuel supply will undoubtedly involve the utilization of heavy crude oils, including those from nonconventional sources, such as bitumen and oil shale. Because of their dense nature and poor compositional characteristics, heavy oils cannot be admitted straightly as refinery feeds, since the direct processing of such oils hardly produces engine fuels of commercial standard. The currently available refinery setups also require substantial retrofitting in order to process such heavy feeds. Thus, heavy oils must undergo an initial upgrading called hydrotreatment (HDT) by which the feeds are converted to qualified fuel oils or synthetic crude (syncrude) for easy handling. Removing the considerable amount of sulfur (S) and nitrogen (N) compounds present in the heavy crude oils selectively by hydrodesulfurization (HDS) and hydrodenitrogenation (HDN), respectively, is among the most critical and challenging aspects of the upgrading. However, the mechanism of these two reactions, in relation to different catalytic sites, temperature, pressure, and other operation variables, is not fully understood or well-documented. By analyzing the possible reaction routes involved in S and N removal by HDT, this review sets to bridge the gap that has been left void for a long period of time, to serve as a guide for innovative heavy crude oil upgrading technologies. It finally reports the current challenges impeding the speedy inclusion of heavy crude oils into the global oil supply stream, and proffer perspective solutions together with future research trends.

Bimetallic CoCu-ZIF material for efficient visible light photocatalytic fuel denitrification

“…9,10 Currently, NCCs in fuel are usually removed by hydro-denitrication (HDN), which consumes expensive hydrogen and requires high temperature (range from 300 to 400 C) and high-pressure conditions (range from 30 to 130 atmospheres). 11,12 The process is not economical. Photocatalysis technology is a kind of technology with low energy consumption and mild conditions, which has attracted signicant attention.…”

Investigating the Effects of Organonitrogen Types on Hydrodearomatization Reactions over Commercial NiMoS Catalyst

“…For N removal (C-N cleavage) from carbazole and acridine, the nitrogen atom requires sp 3 -hybridization. Moreover, the C-N cleavage occurs mainly through elimination or substitution reactions [20][21][22]. Therefore, it is relevant to describe the HDN networks of carbazole and acridine, as this reveals that several of the conversion steps are hydrogenation reactions taking place prior to the C-N bond cleavage reactions.…”

Extraction of molybdenum from a spent HDS catalyst using alkali leaching reagent

“…Precipitation of ammonium molybdates ((NH4)2MoO4) then resulted, according to the following equations [19]. Na2MoO4 (aq) + 8HCl(aq) → 2NaCl(aq) + MoCl6 (aq) + 4H2O(aq) (3) MoCl6 (aq) + 3NH4OH(aq) → (NH4)2MoO4 (ammonium molybdates) + NH4Cl(aq) (4) After desorption of molybdenum from activated carbon using ammonium hydroxide, the solution reached the pH of around 9.30. Subsequently, HCl was added to the solution till the pH reduced to 2.0 with the controlled temperature at 90℃.…”

“…Nominal composition for the Ni/Mo HDS catalyst is typically 4% to 13% Mo, 1% to 5% Ni, 8% to 10% S, and 15% to 30% Al for example [2]. It was shown from ex-situ microscopic data [3] that MoS2 nanoislands comprise one or more layers of S-Mo-S sandwich in the truncated triangle shape where their active edges serve as active sites during catalytic reactions [4].…”