Bernard Fixari

THERMOCATALYTIC HYDROCONVERSION OF HEAVY PETROLEUM CUTS WITH DISPERSED CATALYST

Abstract This report concerns the use of unsupported dispersed catalysts in upgrading heavy feeds. The conversion of heavy crudes and resids into valuable products requires an efficient hydrogen activation. A method recently investigated deals with the use of metallic or organometallic (water- or oil-soluble) compounds, which under a thermal treatment decompose and give rise to a slurry of fine solid particles. This active form of catalyst promotes locally the spill-over of the hydrogen and therefore enhances the conversion of resids to distillate, reducing the coke formation. The primary objective of this report is to assess the current state of knowledge on this field, in order to identify new directions and strategies for Research.

Visbreaking of Safaniya vacuum residue in the presence of additives

Visbreaking and hydrovisbreaking of an heavy oil (Safaniya VR) are optimized in term of conversion into light fractions (500+) using additives. H-donor diluents inhibit coke formation and reduce conversion. Addition of a small amount of thiol or disulphide allowed the transformation of the heavy oil at low temperature. Under more severe conditions, the association of H-donor diluents and sulphide additives gives high conversion yields (⩾50%) with moderate gas and coke production. This paper attempts to explain the synergism observed.

Thermal coupling of methane, experimental investigations on coke deposits

Abstract We have studied the formation of coke during the thermal coupling of an equimolecular methanehydrogen mixture at 1230 °C and under a one-atmosphere pressure. Coke samples are recovered in rectangular boats placed along the pyrolysis reactor. The deposits show a non-homogeneousness of coke along the reactor in terms of deposition rate and in terms of structure. We observed at least two kinds of coke that settle at different rates along the pyrolysis reactor: (a) a silver-grey, uniform film and (b) a black powder. Transmission electron microscopy and oxidative pyroanalysis showed that the former is a well crystallized graphite-type coke with a highly refractory character, while the latter corresponds to amorphous powder carbon.

CATALYTIC DECOMPOSITION OF ALKYL CHLOROFORMATES BY HEXABUTYLGUANIDINIUM CHLORIDE

Abstract Hexabutylguanidinium chloride (0.5 molar %) efficiently decomposes alkyl chloroformates into chlorides, with low alkenes formation, via a SN2 mechanism as demonstrated from substituents effects and asymmetric chloride synthesis.

Oxidative pyroanalysis: elemental analysis in volatile and non-volatile fractions of coals and related materials

Abstract Oxidative pyroanalysis affords accurate and quantitative analysis of coals under various temperature programmes and gas flow conditions. When applied to coals of diverse origins, this technique allows samples and products to be classified from standard proximate and ultimate analyses and from the elemental composition of any fraction. Detection of thermally evolved products from coal (water, carbon dioxide, sulphur dioxide), produced in the absence of oxidation, is also possible. Comparison with other methods shows good agreement between measured values. Characterization of coal products exemplifies the possibilities of this technique.

Hydrogenation of polyaromatics in the presence of hydrogen-hydrogen sulphide system

Abstract Thermal production of hydroaromatics by addition of molecular hydrogen to polyaromatics was studied in the presence of hydrogen sulphide or tetralin. The results indicate the importance of wall catalytic effects related to H 2 H 2 S activity during fossil fuel treatment. Yields of partly hydrogenated polyaromatic structures, potential H-donor sources for fossil fuel, treatment were improved by H 2 H 2 S pressure under batch reactor conditions, with selectivity maintained in production of dihydro aromatic forms. The reduction mechanism is shown to be related to wall effect with probable formation of H ∗ and SH ∗ reactive species. This effect is an important parameter for the use of stainless-steel reactors.

FRACTIONS DISTRIBUTION AND ELEMENTAL COMPOSITION OF HEAVY OILS BY PYROANALYSIS

ABSTRACT Oxidative pyroanalysis apparatus was settled to fully characterize heavy oils. Fractions distribution, and elemental composition were obtained in one single run on both volatile and non volatile fractions. Correlation between experimental Carbon residue values and Conradson carbon residue data is possible and a crackability index of the heaviest part of heavy oil is determined. From all gathered data, quality of products can be appreciated in these circumstances as well as thermal sensitivity resulting in accurate determination of conversion indices.

14C polyaromatics as radio isotope tracers for grafting analysis during heavy oil pyrolysis

Abstract Labelled polyaromatics, such as 14 C chrysene and 14 C acenaphthylene, have been used as tracers during pyrolysis of a heavy oil residue. Prior to this approach the thermal behaviour of 1:1 mixtures of chrysene and Safaniya vacuum residue (VR) were examined using mass spectrometry and ultraviolet (u.v.) analysis. Chrysene was found to be highly reactive, producing dimers and alkylated chrysene materials. From feedstocks with 14 C chrysene and 14 C acenaphthylene as radio tracers, the distribution of polyaromatics in the pyrolysed heavy oil fractions were determined. In this series, acenaphthylene was found to be more reactive than chrysene in grafting reactions on heavy oil components. The radical quenching propensity of polyaromatic additives towards small radicals has been confirmed, supporting their anticoke effect when used at high concentration. Interestingly, the diluted polyaromatic tracers did not accumulate in the coke fractions. This result points to weak and reversible bonding reactions of the polyaromatic additives onto the heavy oil components.

Thermal behaviour of oxidized Boscan atmospheric residue

Abstract Controlled and progressive chemical oxidation was performed on Boscan atmospheric residue, then the thermal behaviour of the samples was examined. Hydrogen peroxide-methanol gave specific sulphoxidation, while stronger oxidation of sulphur and large viscosity and solubility changes were observed with hydrogen peroxide-acetic acid and m-chloroperbenzoic acid. Thermal cracking sensitivity was reduced and coke production increased steadily with the strength of oxidation. Efficient visbreaking only occurred with H2O2-methanol from low temperature decomposition of sulphoxides to active radicals. In no case was the sulphur elimination at the level expected from model compound pyrolysis. Except with H2O2-methanol, carbonization of the oxidized residues followed by transmission electron microscopy showed deep degradation of the microstructural organization (decrease in the extent of the local molecular orientation). This altered the graphitization capacity, as confirmed by the sulphur concentration in the pre-graphites. All the results suggest that sulphone entities are mainly responsible for profound physical and thermochemical changes, with rapid destruction of the microstructural organization.

Long chain n-alkyl and n-alkylthio radicals: Reactivities towards hydrogen donor additives under gas phase condition

Abstract Fossil fuel model compounds such as didodecylsulphide 1 , 1-dodecanethiol 2 and didodecylsulphone 3 were thermally decomposed under gas phase and short contact time reaction conditions with defined medium composition. Intermolecular H-transfer occurs with sulphided species while intramolecular β-scissions and H-transfers are probably involved during decomposition of the dodecyl radical. The appearance of light alkyl radicals and the presence of thiyl and mercapto radicals clearly activate thermal conversion of the starting material. H-donor additives have a weak effect on the various intramolecular mode of fragmentation of the n-alkyl chains but they are able to inhibit the activity of light and thiyl radicals improving the yield of liquid n-olefins. In all cases only traces of n-alkanes are formed by intermolecular H-transfer.