This paper is a selective review on design approaches and associated catalysis and chemistry for deep desulfurization and deep dearomatization (hydrogenation) of hydrocarbon fuels, particularly diesel fuels. The challenge for deep desulfurization of diesel fuels is the difficulty of removing the refractory sulfur compounds, particularly 4,6-dimethyldibenzothiophene, with conventional hydrodesulfurization processes. The problem is exacerbated by the inhibiting effect of polyaromatics and nitrogen compounds, which exist in some diesel blend stocks on deep HDS. With the new Environmental Protection Agency (EPA) Tier II regulations to cut the diesel sulfur from current 500 ppmw down to 15 ppmw by June 2006, refineries are facing major challenges to meet the fuel sulfur specification along with the required reduction of aromatics contents. The principles and problems for the existing hydrodesulfurization processes, and the concepts, advantages and disadvantages of various new approaches will be discussed. Specifically, the following new design approaches for sulfur removal will be discussed: (1) novel catalysts for ultra-deep hydrodesulfurization under conventional HDS process conditions; (2) new design concept for sulfur-tolerant noble metal catalysts for low-temperature hydrogenation; (3) new desulfurization process by sulfur adsorption and capture under H2; (4) new desulfurization process by selective adsorption at ambient temperature without H2 and a related integrated process concept; (5) oxidative desulfurization in liquid-phase; and (6) biodesulfurization.

New design approaches to ultra-clean diesel fuels by deep desulfurization and deep dearomatization

High aromatic content in diesel fuel has been recognized both to lower the fuel quality and to contribute significantly to the formation of undesired emissions in exhaust gases [1, 2]. Because of the health hazards associated with these emissions, environmental regulations governing the composition of diesel fuels are being tightened in both Europe and the United States, leading to limitations on aromatics [3, 4].

Aromatic Hydrogenation Catalysis: A Review

Heterogeneous Catalysts for the One-Pot Synthesis of Chemicals and Fine Chemicals

Dehydration of fructose to 5-hydroxymethylfurfural was performed in a batch mode in the presence of a series of dealuminated H-form mordenites as catalysts, at 165°C, and in a solvent mixture consisting of water and methyl isobutyl ketone (1:5 by volume). Under the operating conditions used, the reaction was not controlled by external or internal diffusional limitations. Fructose conversion and selectivity to 5-hydroxymethylfurfural were found to depend on acidic and structural properties of the catalysts used as well as on the micropore vs. mesopore volume distribution of those catalysts. A maximum in the rate of conversion of fructose was observed for the H-mordenite with a Si/Al ratio of 11. A maximum in the selectivity to 5-hydroxymethylfurfural was observed only for H-mordenites with a low mesoporous volume. The high selectivity obtained (>90%) was correlated with the shape selectivity properties of H-mordenites (bidimensional structure), and particularly with the absence of cavities within the structure allowing further formation of secondary products. The influence of the microporosity vs. mesoporosity on the selectivity to 5-hydroxymethylfurfural was also studied, the formation of mesopores upon dealumination procedures being damaging to obtain a high selectivity. A significant increase in the selectivity (10%) was also obtained by simultaneous extraction of 5-hydroxymethylfurfural with methyl isobutyl ketone circulating in a countercurrent manner in a continuous catalytic heterogeneous pulsed column reactor. Finally, taking into account the most recent results reported in the literature and our own results, it is possible to revise the mechanism of the dehydration of fructose.

Dehydration of fructose to 5-hydroxymethylfurfural over H-mordenites

Present State of the Art and Future Challenges in the Hydrodesulfurization of Polyaromatic Sulfur Compounds

Structure-activity relationships in hydroprocessing of aromatic and heteroaromatic model compounds over sulphided NiO-MoO3/γ-Al2O3 and Nio-WO3/ γ -Al2O3 catalysts; chemical evidence for the existence of two types of catalytic sites

The initial rate of hydrogen dissociation was studied as a function of irreversible CO coverage at 353 K on 30 wt.% Pt/carbon catalysts (Pt/C) prepared according to different processes. The Pt/C catalysts exhibit similar Pt dispersion ( D  ∼ 0.07) and mean Pt particles size (dp ∼ 16 nm). The turnover frequency (number of hydrogen molecules dissociated per CO-free surface Pt atom) was determined as a function of CO coverage from 0.0 to 0.8. The evolution of TOF as a function of CO coverage is in agreement with the model of CO adsorbing on low coordination sites (edges, corners) and then spreading across the faces to grow islands as Brandt suggested in the past (R.K. Brandt, M.R. Hughes, L.P. Bourget, K. Truszkowska, R.G. Greenler, Surf. Sci. 286 (1993) 15–25). At high CO coverage (∼0.8), TOF depends on the process by which the Pt/C catalyst was prepared. In particular, a Pt/C elaborated according to a colloidal process exhibits a low sensitivity to CO poisoning with an increase of TOF by one order of magnitude.

Robert Durand

Papers

Structure-activity relationships in hydroprocessing of aromatic and heteroaromatic model compounds over sulphided NiO-MoO3/γ-Al2O3 and Nio-WO3/ γ -Al2O3 catalysts; chemical evidence for the existence of two types of catalytic sites

Poisoning of Pt/C catalysts by CO and its consequences over the kinetics of hydrogen chemisorption

Condensation of aldehydes for environmentally friendly synthesis of 2-methyl-3-phenyl-propanal by heterogeneous catalysis

Factors affecting the hydrogenation of substituted benzenes and phenols over a sulfided NiOMoO3γ-Al2O3 catalyst

Heterogeneous hydrodeoxygenation of ketones and alcohols on sulfided NiOMoO3γ−Al2O3 catalyst