C. Moreau

DEHYDRATION OF FRUCTOSE INTO 5-HYDROXYMETHYLFURFURAL IN THE PRESENCE OF IONIC LIQUIDS

Abstract The acid-catalyzed dehydration of fructose was performed in a microbatch reactor at 80 °C using two commercially available ionic liquids, a hydrophilic one, 1-butyl 3-methyl imidazolium tetrafluoroborate (BMIM+BF4−), and a hydrophobic one, 1-butyl 3-methyl imidazolium hexafluorophosphate (BMIM+PF6−). When the reaction is carried out in 1-butyl 3-methyl imidazolium tetrafluoroborate as solvent and Amberlyst-15 as catalyst, a yield up to 50% in 5-hydroxymethylfurfural (HMF) is obtained within around 3 h. When the reaction is carried out now in 1-butyl 3-methyl imidazolium tetrafluoroborate and in 1-butyl 3-methyl imidazolium hexafluorophosphate as solvents and Amberlyst-15 as catalyst, DMSO is used as a co-solvent, in order, in particular, to solubilize fructose in the hydrophobic ionic liquid. Under these conditions, both ionic liquids allow the reaction to work more rapidly than in DMSO alone and with yields in HMF close to 80% within 24 h.

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

Abstract The hydroprocessing of nitrogen-containing model compounds such as pyridine, quinoline, acridine, pyrrole and carbazole was studied using a batch method at 340°C and 70 bar H 2 over sulphided NiO-MoO 3 /Al 2 O 3 and NiO-WO 3 /Al 2 O 3 catalysts, where it was found that saturation of the heteroaromatic rings always occurs prior to any cleavage of C-N bonds, generally C sp3 -N bonds. The rates of hydrogenation of the heteroaromatic rings were shown to be mostly influenced by the aromaticity of these rings (π-electron delocalization) and not by the basicity of the nitrogen atom. On the other hand, the basicity of nitrogen atoms considerably influences the cleavage of C sp3 -N bonds in the absence of steric effects. The hydroprocessing of substrates of general formula C 6 H 5 X, where X is an electronegative atom (OR, NHR, SR, Br, Cl, F) was also studied under the same experimental conditions. The rates of hydrogenation of the phenyl moiety and the rates of hydrogenolysis of the C sp2 -X bond are both correlated with the same substituent constant, σ o R , which represents the delocalization of π-electrons in the molecule by resonance. Hydrogenation is favoured over hydrogenolysis for highly electron-donating substituents such as NHR and OR (R=H, C 6 H 5 ); conversely, hydrogenolysis is favoured over hydrogenation for slightly electron-donating substituents such as SR (R=H, C 6 H 5 ) or halogens (Cl, Br). The presence of such correlations constitutes chemical evidence for the existence of two distinct catalytic sites, one responsible for hydrogenation associated with an electron-withdrawing character and the other responsible for the hydrogenolysis of C sp2 -X bonds associated with an electron-donating character.

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

Abstract The hydrogenation of substituted benzenes ( R = Et, Ph, c -C 6 H 11 , PhCH 2 , c -C 6 H 11 CH 2 ), of ortho - and para -substituted phenols ( R = Et, Ph, c -C 6 H 11 , PhCH 2 ) was studied by a batch method at 340 °C and 70 bar H 2 over a sulfided NiOue5f8MoO 3 / γ -Al 2 O 3 catalyst. The rates of hydrogenation are always higher for phenols than for benzenes and can be related to differences in the π-electron delocalization between the two series of organic compounds. The rates of hydrogenation of ortho - and para -substituted phenols are similar to one another and generally lower than those for phenol alone, thus suggesting a predominant role of electronic factors over steric ones.

Hydroprocessing of dibenzothiophene, phenothiazine, phenoxathiin, thianthrene, and thioxanthene on a sulfided NiOMoO3γ-Al2O3 catalyst

Abstract The hydroprocessing of phenothiazine, phenoxathiin, thianthrene, and thioxanthene was studied by a batch method at 340°C and 70 bar H2 over a sulfided NiOue5f8MoO 3 γ-Al 2 O 3 catalyst. The hydrodesulfurization (HDS) rate constants are similar to one another and about tenfold higher than that of dibenzothiophene. The presence of a second heteroatom or a methylene group does not play an important role on the removal of sulfur. The differences of reactivity could rather result from geometrical considerations in relation with the ease of adsorption on the catalyst surface. The cleavage patterns and reaction networks for the hydroprocessing of compounds dibenzothiophene, phenothiazine, phenoxathiin, thianthrene, and thioxanthene are discussed. The product distribution allows, in particular, an estimate to be made of the rates of hydrogenation and hydrogenolysis in HDS, hydrodenitrogenation (HDN), and hydrodeoxygenation (HDO) processes.

Upgrading of distillate fractions of Timahdit Moroccan shale oil over a sulphided NiOMoO3γAl2O3 catalyst

Abstract Hydrotreating of distillate fractions of Timahdit Moroccan shale oils was studied by a batch method at 340 °C and 70 bar hydrogen pressure over a conventional sulphided NiOue5f8MoO 3 γue5f8Al 2 O 3 catalyst. The removal of heteroatoms is easier for the light fractions containing paraffins than for the heavier ones containing aromatics. These results were obtained by direct hydrotreating of distillates resulting from the distillation of the crude oil and by hydrotreating of the most representative fractions (paraffins, aromatics) obtained after deasphalting and chromatography operations of the preceding distillates. The Timahdit pyrolysis oil consists of about 50% liquids where removal of heteroatoms is relatively easy. Upgrading of this oil is thus interesting for Morocco to meet the local demand for light hydrocarbons.

Influence of the source of sulfur on the hydroconversion of 1-methylnaphthalene over a Pt–Pd/USY catalyst

Abstract Hydroconversion of 1-methylnaphthalene was performed over a Pt–Pd/USY catalyst in a batch reactor at 310 °C and 5 MPa of hydrogen pressure in cyclohexane as the solvent and in the presence of 800 ppm of sulfur resulting from different sources, hydrogen sulfide, thiophene and dibenzothiophene. In a general manner, hydrogenation of 1-methylnaphthalene into the corresponding mixture of methyltetralines is not significantly affected by the nature of the sulfur species present in the starting feed. On the contrary, going from hydrogen sulfide to thiophene and finally to dibenzothiophene, hydrogenation of methyltetralines into methyldecalines is lowered and ring-opening of methyltetralines to alkylbenzenes is enhanced. This would agree with the expected sequence of appearance of hydrogen sulfide in the feed. These results are in agreement with dissociation of hydrogen into protonic and hydride species, as already proposed in the presence of sulfided catalysts, i.e., protonic species would be involved for the hydrogenation steps and hydride species for the ring-opening steps. Hydrogen sulfide present as such or resulting from the transformation of thiophene or dibenzothiophene would then reduce the hydrogenation route, and, as a consequence, increase the hydrogenolysis route.

Hydrodenitrogenation of benzo(f)quinoline and benzo(h)quinoline over a sulfided NiOMoO3γ-Al2O3 catalyst

The hydroprocessing of benzo(f)quinoline and benzo(h)quinoline was studied by a batch method at 340{degree}C and 70 bar H{sub 2} over a commercial sulfide NiO-MoO{sub 3}/{gamma}-Al{sub 2}O{sub 3} catalyst. The hydrogenation of the N ring occurs at similar rates for the two isomeric benzoquinolines but is slower than the hydrogenation of the N ring of quinoline. On the other hand, an important and unusual percentage of C{sub sp{sup 2}}-N bond cleavage is observed from the two intermediates 1,2,3,4-tetrahydrobenzo(f)quinoline and 1,2,3,4-tetrahydrobenzo(h)quinoline. These two main reactions, hydrogenation of N rings and cleavage of C-N bonds, are then discussed in terms of aromaticity; a decrease in aromaticity favors both the hydrogenation of N rings and the cleavage of C{sub sp{sup 2}}-N bonds.

Hydrodenitrogenation of benzo(f)quinoline and benzo(h)quinoline over a sulfided NiO-MoO sub 3 /. gamma. -Al sub 2 O sub 3 catalyst

The hydroprocessing of benzo(f)quinoline and benzo(h)quinoline was studied by a batch method at 340{degree}C and 70 bar H{sub 2} over a commercial sulfide NiO-MoO{sub 3}/{gamma}-Al{sub 2}O{sub 3} catalyst. The hydrogenation of the N ring occurs at similar rates for the two isomeric benzoquinolines but is slower than the hydrogenation of the N ring of quinoline. On the other hand, an important and unusual percentage of C{sub sp{sup 2}}-N bond cleavage is observed from the two intermediates 1,2,3,4-tetrahydrobenzo(f)quinoline and 1,2,3,4-tetrahydrobenzo(h)quinoline. These two main reactions, hydrogenation of N rings and cleavage of C-N bonds, are then discussed in terms of aromaticity; a decrease in aromaticity favors both the hydrogenation of N rings and the cleavage of C{sub sp{sup 2}}-N bonds.

Mechanism of carbon sp2-heteroatom bond cleavage in hydroprocessing of substituted benzenes over unsupported transition metal sulfides

Abstract Hydroprocessing of substituted benzenes like aniline, phenol, diphenylsulfide and chlorobenzene was performed in a batch reactor over unsupported transition metal sulfides, namely Co, Ni, Nb, Mo, Ru, Rh, Pd and W sulfides at 280°C and 70 bar of hydrogen pressure. Under these experimental conditions, diphenylsulfide and chlorobenzene mainly react through initial hydrogenolysis of the carbon-substituent bond whereas aniline and phenol react through initial hydrogenation of the aromatic ring. Such a behavior was already reported for conventional sulfided cobalt- and nickel-molybdenum alumina supported catalysts. Nevertheless, these new results confirm the preponderant influence of mesomeric effects on the reactivity of organic models toward sulfided catalysts. In addition to the results obtained over the supported bimetallic sulfides, it was found from quantum chemical calculations that the hydrogenolysis rate constants correlate with the π-electron density on the carbon bearing the substituent and with the overall calculated π-electron transfer between the substituents and the benzene ring. It is thus assumed that hydrogenolysis of carbon sp 2 -substituent bonds results from the attack, by a soft nucleophilic species like a hydride ion, on the carbon bearing the substituent.

Search for Simple Model Compounds to Simulate the Inhibition of Hydrodenitrogenation Reactions by Asphaltenes

Abstract The hydrodenitrogenation of 2,6-diethylaniline was performed over an industrial sulphided NiMo/Al 2 O 3 catalyst at 340°C and 70 bar H 2 in the presence of heavier N-containing compounds such as quinoline, acridine, carbazole and phenanthridine. These compounds have been found to inhibit the hydrodenitrogenation of 2,6-diethylaniline by factors of 5–25. The inhibiting effect has been shown to result from the presence of aromatic or saturated polycyclic systems.