Un procédé d'étude de l'hydrocraquage des huiles végétales en autoclave est décrit. Les principaux objectifs de cette étude sont relatifs à la transformation de l'huile de soja (composé modèle) en essence et gazole, en limitant la formation de polymères et de coke. L'analyse des gaz et la chromatographie haute résolution de deux fractions résultant de la distillation sous vide de la phase liquide ont permis de mettre en évidence les principales étapes de l'hydrocraquage. Pour cette première approche du processus général, trois types d'hydrocraquages ont été utilisés : thermique et en présence d'un oxyde ou d'un catalyseur bifonctionnel performant (hydrogénant/craquant). Dans ce dernier cas, l'hydrogénation des doubles liaisons des chaînes latérales des triglycérides a été mise en évidence pendant le chauffage du réacteur jusqu'à environ 673 K, température à laquelle s'initie le véritable hydrocraquage. A cette température sont observées la décarbonylation/décarboxylation des acides gras (précédemment issus de la coupure des liaisons ester des triglycérides) et une hydrogénolyse marquée en présence d'un catalyseur métallique. Il en résulte principalement des alcanes dont la structure linéaire est celle des acides gras initiaux. Le rendement global brut peut atteindre 83 % dans les conditions de température et de pression choisies, y inclus le pourcentage en fraction gazeuse (CO, CO2, C1-C4) A laboratory process for studying the hydrocracking of vegetable oils in a high-pressure batch reactor is described. The main goals of this study concern the transformation of soybean oil (used as a model) into gasoline and diesel fuel fractions while limiting polymerization and coking. Gas analysis and high-resolution chromatography of two liquid fractions resulting from vacuum distillation were used to determine the main steps in the hydrocracking process. For this initial study of the general process, the three types of hydrocracking used were thermal hydrocracking and hydrocracking in the presence of an oxide or of a dualfunction catalyst (hydrogenating/cracking). In the latter case, hydrogenation of the double bonds of the lateral chains of triglycerides was observed during the heating of the reactor to about 673 K, at which temperature actual hydrocracking begins. At this temperature, the decarbonylation/decarboxylation of fatty acids (coming from the cleavage of the ester bonds of the triglycerides) is observed together with a marked hydrogenolysis in the presence of a metal catalyst. The main result of this is the production of alkanes having the same linear structure as that of the initial fatty acids. The overall weight percent of conversion may reach 83% under the right temperature and pressure conditions, including the percent of gas fraction (CO, CO2, C1-C4).

Two series of chlorided-alumina-supported Sn catalysts were synthesized with different precursors, SnCl2 or SnBu4, and with various contents of Sn. The acidity of the catalysts including 0.2 wt% Sn was characterized by FTIR adsorption-desorption of 2,6-dimethylpyridine (Bronsted acidity) and pyridine (Lewis acidity) and compared with that of Al2O3-Cl. The catalytic activity of the synthesized materials was investigated for the transformation of n-propylbenzene under reforming conditions. The results show that the incorporation of Sn into Al2O3-Cl is not harmless. Neither the nature of the Sn precursor nor the content of Sn evenly affects the acidity and the distribution of the isomerized and cracked products. The correlation between the product distribution obtained for the transformation of n-propylbenzene and the acidity of the Al2O3-Cl and the 0.2Sn(SnCl2)/Al2O3-Cl catalysts supports the formation of isopropylbenzene and benzene catalyzed by Bronsted acid sites via carbenium ion chemistry. In contrast, the production of toluene and ethylbenzene occurs via radical chemistry. The formation of these products is assumed to be catalyzed by Lewis acid sites with different strengths. The stability of the proposed radical intermediate species is consistent with the involvement of stronger Lewis acid sites in the production of toluene compared with those involved in that of ethylbenzene. The catalytic cycles responsible for the formation of toluene and ethylbenzene via radical pathways over an Al-O pair are reported. Finally, it is worth noting that benzene is always the major product of the cracked compounds. (c) 2004 Elsevier Inc. All rights reserved.

The effect of moderate sintering of the platinum particles of a precoked Pt/SiO2 catalyst on the transformation of n-PB was investigated under reforming conditions (773 K, 5 bar, and H2/HC = 5). The results showed that the larger the platinum particles, the greater the formation of cyclic compounds. Furthermore, a concentration balance between the ethylbenzene and the cyclic compounds was revealed, suggesting a common reactive adsorbate for both reaction products. According to a previously proposed reactive adsorbate for ethylbenzene and the results of studies of Pt/SiO2 and PtSn/SiO2 catalysts, a reactive adsorbate was proposed for the formation of the cyclic compounds. This latter reactive adsorbate, which results from the reactive adsorbate leading to ethylbenzene, is consistent with either a decrease in the size of the Pt ensembles or an increase in the electron density of the platinum particles of the Pt/SiO2 catalyst sample with the smaller particles after coke deposition. It is still uncertain as to whether the concentration balance phenomenon is due to a geometric ensemble effect, a change in the electronic density of the platinum clusters, or both. The studies with a tin-promoted catalyst were discussed in relation to this new finding and a detailed reaction network for the transformation of n-PB over metallic sites is proposed.

Kinetics of n-propylbenzene hydrodealkylation (HDA) was investigated over model catalysts under reforming operating conditions (773 K, 5 bars, and H2/HC=5). Silica-supported platinum catalysts (Pt/SiO2 and PtSn/SiO2) and alumina materials (Al2O3 and 1 wt% Cl–Al2O3) were chosen to evaluate the influence of the metallic and acidic phases on the HDA reactions, respectively. The kinetic study showed (i) that the HDA processes occurred to a significant extent over both catalytic phases under identical operating conditions and (ii) that hydrodealkylated products (benzene, toluene, and ethylbenzene) were formed through concurrent pathways whatever the nature of the catalytic phase. In addition, product intermediates were identified and mechanisms were suggested to explain the HDA reactions over either different patches of metallic sites or different acid sites (Brønsted and Lewis). Finally, as compared to toluene and ethylbenzene, the formation rate of benzene was the highest over the acidic function and the lowest over Pt/SiO2.

Oxynitrides of early transition metals are bifunctional catalysts (metallic and acidic sites) active in hydrodenitrogenation (HDN). The HDN of indole was used as a molecular probe reaction to study the metallic and acidic properties of the dual sites on oxynitrides. The behavior of those sites was found to be different from that of supported and sulfided NiMo. The reaction was conducted at low partial pressure of H2S over both a bulk MoOxNyand a supported NiMo catalyst, nitrided before the reaction. Under high hydrogen pressure, HDN of indole was shown to occur with or without prior hydrogenation of the aromatic ring of orthoethylaniline, leading to either ethylbenzene or ethylcyclohexane. Secondary reactions, such as the joining of heterocyclic rings (leading to 1-4 tetrahydroquinoline) and dimerization, were found to occur as a result of the presence of acidic sites. Hydrogenolysis of the lateral chain of orthoethylaniline was also observed.

A molybdenum carbide supported on active carbon for catalytic hydrotreating was prepared by temperature-programmed reaction (TPR) in flowing H2of an active carbon impregnated by an heptamolybdate. TPR led at 973 K to the formation of supported Mo2C. This new method of preparation avoids the use of methane as carburizing reactant and allowsin situpreparation of supported molybdenum carbide without any contact of this pyrrophoric material with air between preparation and catalytic run. The various steps of the carburization process were studied by trapping the solid intermediates at different temperatures during TPR. Two successive reactions were evidenced: the partial reduction by H2of the initial molybdenum precursor to MoO2, and its subsequent carburization to Mo2C. This last step is mainly due to the reduction of MoO2and carburization with native methane evolved from the reaction of the carbon support with dihydrogen. Solid materials were characterized by elemental analysis, X-Ray diffraction, transmission electron microscopy and specific surface area measurements.

The reactivity of Kansk-Achinsk brown coal in thermochemical conversion with tetralin is a linear function of the network flexibility, which is primarily controlled by ionic cross-linking with carboxylate bridges via polyvalent cations such as Ca2+.

A series of chemically altered coals was investigated in the reaction with methanol and hydrogen in the presence of ZnCl2 as a catalyst. Significant beneficial effects were observed when high-rank coals were altered by reductive and reductively methylating pretreatments. The behaviour of altered low-rank brown and subbituminous coals was affected by both the mode of chemical pretreatment and the reaction conditions.

Differences between the compositions of partly hydrocracked hexane-soluble extract fractions from the liquefaction of maceral concentrates were investigated by gas chromatography-mass spectrometry. The technique identifies components within only a relatively narrow range of molecular masses, but some systematic differences were nevertheless observed. Dibenzofuran derivatives were significantly more abundant in extracts derived from inertinite concentrate than in liptinite or vitrinite extracts. Within the retention time interval where dibenzofuran and its derivatives were identified in inertinite extracts, products prepared from liptinite and vitrinite concentrates were found primarily to contain biphenyls and acenaphthene derivatives. Extract fractions from inertinite were also characterized by almost negligible contents of phenol derivatives, a class of compounds much in evidence in the liptinite and vitrinite extract fractions. These findings have suggested some differences between oxygen functionalities in, and types of chemical bonds connecting, basic structural units in different coal macerals. Basic structural units in inertinites appear to be joined more frequently by alkyl or other bridges than by linear ether bonds, in comparison with other maceral groups. This provides one likely structural explanation for the relatively low yields obtained during the liquefaction of the inertinite concentrate.

Products from the thermal reactions of tetralin in a stirred micro-autoclave and a flowing-solvent reactor were compared by gas chromatography-mass spectrometry, to study the effect on product composition of residence time in the reaction zone: of the order of seconds in the flowing-solvent reactor and normally 1 h in the stirred micro-autoclave. Significant differences were found between the products obtained in the two reactors; greater quantities of by-products from thermally induced reactions of tetralin — mainly naphthalene, butylbenzene and 1-methylindane — were found in the heated tetralin from the autoclave. A number of compounds, mainly of mass 262 and 258 u (apparently tetralin-tetralin dimers and tetralin-naphthalene adducts), were also identified in the products from both reactors; many of these products have not previously been reported in connection with the thermal reactions of tetralin. The total concentration of this class of compounds did not exceed ~ 1 wt% of the total solvent. Greater concentrations of the relatively stable dimers and adducts were identified in products from the autoclave than in those from the flowing-solvent reactor. These findings have immediate implications for the evaluation by g.c.-m.s. of coal liquefaction products prepared using tetralin as vehicle, since compounds similar to tetralin-derived by-products have also been found in product solutions from actual coal solubilization experiments.

The effect was studied of pretreatment techniques, including O-methylation with (CH3)2SO4, reduction with both K-isopropanol in THF and LiAlH4, reductive methylation with KCH3I in THF and combination thereof, on the extractability in THF of coals of different rank and on their reactivity in non-catalytic hydroliquefaction in methanol and tetralin at 380 °C. Dramatic changes in composition of the treated coals and products were found. Chemical pretreatment had a beneficial effect on coal solubility in THF and on hydroliquefaction in tetralin. O-methylation was the most effective for lignite, but reductive methylation had the most beneficial effect for high-rank coal. With methanol as solvent, reduction and O-methylation had a small effect on coal reactivity for liquefaction. The role of cross-links is discussed in order to explain the liquefaction behaviour of coals in solvents.

Compositions of lighter liquefaction product fractions from a stirred micro-autoclave and a flowing-solvent reactor were compared by gas chromatography-mass spectrometry (g.c.-m.s.). Tetralin was used as vehicle for liquefaction of a set of coals and maceral concentrates; high-pressure hydrogen and a mixture of finely powdered Fe2O3 catalyst precursor and elemental sulfur were used in the micro-autoclave. Similar conversions (sample weight loss) were observed in the two reactors when relatively long hold times (400 s) were used in the flowing-solvent reactor. Compared with products prepared in the micro-autoclave, only a negligible proportion of material released from the coal in the flowing-solvent reactor could be detected within the molecular mass interval between tetralin itself and the upper detection limit of the Chromatographic column: most aromatic constituents observed by g.c.-m.s. in products from the flowing-solvent reactor were identified as resulting from the thermal reactions of tetralin. This result suggests that nearly all components identified in products from the stirred micro-autoclave were formed from larger and/or more polar species released from the coal during secondary reactions of primary coal solubilization products. The concentrations of a limited number of alkylaromatic homologous series identified in the oil fraction of the stirred autoclave products were quantitatively determined by g.c.-m.s.. Analysis of successive product fractions from the flowing-solvent reactor, collected during time-temperature-resolved experiments, indicated that the greater part of the C20–C36 straight-chain aliphatic hydrocarbons identified in the product mixture was released from the coal between 340 and 390 °C.

Catalytic hydroliquefactions (HL) of two coals (Freyming, France and Point of Ayr, United Kingdom) and their macerals were studied in a microautoclave in the presence of an H-donor solvent (tetralin). The main results of the study were related to (i) a comparison between the behaviours of such coals or macerals in the HL process; the two raw coals showed the same total conversion, and similar wt% of oil, asphaltene and preasphaltene fractions, (ii) the contribution of each maceral to the global coal liquid; the additive effect was checked, but no synergetic effect was found (using HL and the present type of liquid phase analysis) for a 'synthetic coal'. Raw coals, vitrite and exinite had the same total conversion, whereas that for fusite was much lower, and (iii) a detailed identification of some individual compounds or of series of homologous compounds; this was made for oil fractions. 25% of these fractions were able to be investigated by GC/MS, i.e. 5-10 wt% of the initial coal. Concentrations of a large number of compounds were determined and compared from one maceral to another, and general tendencies could be deduced.

Catalytic hydrocracking of vegetable oils was performed in the presence of an NiMoγ-Al2O3 catalyst sulfided in situ with elemental sulfur under hydrogen pressure. Various vegetable oils were selected to study the effect of the degree of saturation and lateral chain length: Passiflora edulis (maracuja), Astrocaryum vulgare (tucuma), Mauritia flexuosa (buriti), Orbygnya martiana (babassu), and soybean. The effects of reaction temperature and hydrogen pressure in cyclization were studied. Carboxylic acids were used as model compounds.

Catalytic hydrocracking ofHevea brasiliensis (Seringa) andVirola sebifera (Ucuuba) oils was carried out in the presence of a NiMo/Al2O3 catalyst sulfidizedin situ with elemental sulfur at 360°C. The initial pressure of hydrogen was 140 bars. Conversions of nearly 100% of the vegetable oils were achieved. The compositions of the liquid fuels were studied in detail by gas chromatography/mass spectrometry. The main products were found to be alkanes, cycloalkanes, aromatics and carboxylic acids.

Vegetable oil hydrocracking was studied in a batch reactor under high hydrogen partial pressure (10–200 bars) at 623–673 K, catalyzed by either reduced Ni/SiO2 or sulphided Ni-Mo/γ-Al2O3. We have established the sequence of reactions which transform a vegetable oil into a diesel-type fuel. We have demonstrated the role of the catalyst in each of these reactions, and the occurrence of thermodynamic equilibria restricting the completion of the transformation. The displacement of these equilibria was achieved by an increase in hydrogen pressure, where molar yields close to 100% were attained. The corresponding product is a mixture of hydrocarbons (essentially normal alkanes in the diesel fraction).

Mössbauer Spectroscopy, X-Ray Diffraction and Electron Microscopy were applied to the study of solid residues of coal hydroliquefaction, for which tin-based catalysts were used. In the general case hydroliquefaction runs were performed in the presence of added sulphur and of finely dispersed SnO2 as a catalyst precursor. The only observed tin species were SnO2 and SnS, the former with percentages higher than expected from XRD, due to its large f factor, the latter as a symmetric doublet, which suggests that any asymmetry should be ascribed to small particle sizes rather than to structure. When the S content was only that of coal and the catalyst precursor β-Sn, FeSn2 occurred together with Sn sulfides and oxides, while no β-Sn was detected. The main catalytic role is ascribed to SnS.

Abstract Catalysis of coal hydroliquefaction (HL) was studied over highly dispersed and non porous iron sulfide catalysts (non stoichiometric pyrrhotites). The active interface between the bulk catalyst and the reactional mixture was built during liquefaction and a coke layer was deposited on the Fe 1-x S surface. During HL the first role of this coke was to prevent the sintering of the catalyst particles. Two kinds of coke were identified according to the mode of sulfidation and introduction of the catalyst into the autoclave. The catalytic roles of the interface were discussed in terms of solvent rehydrogenation, pool of active hydrogen (spillover effect) and stabilization of radicals.