I. Ignatiadis

Identification of carbazoles and benzocarbazoles in a coker gas oil and influence of catalytic hydrotreatment on their distribution

Abstract Fractions highly enriched in pyrrole benzologues have been extracted from a coker gas oil before and after hydrotreatment under selected operating conditions. Carbazole, methyl- and dimethylcarbazoles and benzocarbazoles have been identified by means of g.c. coelutions with standards. The study of these compounds after catalytic hydrotreatment has shown that benzocarbazoles are more effectively removed than carbazoles in highly hydrogenating conditions (partial pressure of hydrogen, 10 MPa; temperature, 360 °C) whereas alkyl carbazoles and more particularly 1-methyl derivatives are more altered at a high temperature (380 °C, partial pressure of hydrogen, 5 MPa).

Distribution of carbazole derivatives in petroleum

Abstract Carbazole, its alkyl derivatives and higher benzologs have been selectively isolated from six different crude oils. In all samples, benzocarbazoles are major constituents of a series which may extend up to dibenzocarbazole derivatives. The distribution includes unsubstituted parent compounds and shows a maximum content of methyl and dimethyl substituted species. Sixteen individual constituents have been identified by means of comparison with reference compounds using gas chromatography, mass spectrometry and high resolution spectrofluorimetry. So far, no generally acceptable explanation has been given for the origin of these compounds, which presumably are the most stable ones in their respective series of aromaticity. Thus, carbazole derivatives may result from a complex sequence of reactions during kerogen formation, not allowing the recognition of precursing molecules. The geochemical significance of this series of nitrogen compounds needs to be clarified, requiring further studies.

Identification of nitrogen bases in a coker gas oil and influence of catalytic hydrotreat ment on their composition

Abstract The investigation of nitrogen bases occurring in a coker gas oil before and after catalytic hydrotreatment has shown important differences in reactivity of azaarenes. Compounds with a low degree of aromaticity are relatively resistant compared with higher benzologues. Particularly stable are α-methylated azaarenes, which are also major nitrogen bases found in crude oils. Alkyl anilines, the last intermediates before denitrogenation, are the most abundant bases in hydrotreated samples.

Sulphur-containing polynuclear aromatic hydrocarbons from petroleum. Examination of their possible statistical formation in sediments

Abstract Two procedures are described for the determination of sulphur-containing polynuclear aromatic hydrocarbons (SPAHs) in petroleum and in its derived industrial products. As a general clean-up procedure, the total aromatic fractions were obtained after partition of the sample between dimethyl sulphoxide (DMSO) and pentane, followed by liquid—liquid extraction of the DMSO layer. In the first method, SPAHs were oxidized to sulphones, isolated selectively and back-reduced to SPAHs. The second approach was the direct determination of SPAHs in the aromatic fractions from the clean-up, by gas chromatography with selective detection using a flame photometric detector and gas chromatography—mass spectrometry with selected ion monitoring. The determination of SPAHs in four crude oils and a coker gas oil is reported. The various isomers are assumed to have been formed in sediments by random alkylation and degradation mechanisms, although specific substances with an increased stability compared with that of other isomers accumulated preferentially. For dibenzothiophene congeners, the number of GC peaks observed in a capillary column chromatogram is close to the maximum number of peaks that could be observed, as predicted by the statistical theory of Giddings. For benzothiophene congeners, the observed number is smaller. SPAHs are concluded to result from severe transformation mechanisms of the organic precursors occurring in sediments.

Distribution of diaromatic nitrogen bases in crude oils

Abstract Azanaphthalene derivatives were identified in 9 petroleum samples. In all investigated crude oils; the number of alkyl substituents was found to extend up to C 9 with a maximum most often for C 6 ; unsubstituted parent compounds are absent. Two distinct types of azanaphthalenes occur: solely methylated derivatives which are abundant in most crude oils of Cretaceous or Miocene ages, and compounds bearing alkyl chains of up to 4 carbon atoms, with a majority of 8-isopropyl quinoline derivatives, which dominate in a California crude oil of Pliocene age.

Capillary gas chromatography of azaarenes: II. Application to petroleum nitrogen bases

Abstract The retention behaviour of azaarenes on several stationary phases was investigated. Retention indices were measured with a reference system constituted by quinoline benzologues. Steric hindrance in the vicinity of the nitrogen atom was found to influence drastically the retention of azaarenes. Further important parameters are the selectivity of the stationary phase towards the location of the heteroatom and the degree of alkyl substitution of the solutes. The most useful and complementary selection of stationary phases was OV-73, OV-61 and SP-2340. Examples of separations of complex azaarene mixtures extracted from crude oils are discussed.

Capillary gas chromatography of azaarenes : I. Preparation of columns

Abstract Reproducible methods for the preparation of non-polar, medium-polar and polar capillary columns with suitable wall surface deactivation for the analysis of nitrogen bases are described. Parameters affecting deactivation, efficiency and thermal stability are discussed.

Separation et identification par chromatographie en phase gazeuse et chromatographie en phase gazeuse—spectrometrie de masse de composes azotes d'une huile lourde desasphaltee

Abstract Separation and identification by gas chromatography and gas chromatography—mass spectrometry of the nitrogen compounds from a deasphalted heavy oil. Evolution of their distribution after a catalytic hydrotreatment Basic and neutral nitrogen fractions were selectivity isolated from a deasphalted heavy crude oil and were characterized by gas chromatography and gas chromatography—mass spectrometry. Most chromatographic peaks were identified. Basic substances included C 5−10 -alkylpyridines, C 1−9 -alkylquinolines and C 1−4 -alkylbenzoquinolines; neutral fractions comprized C 0−4 -alkylcarbazoles and C 0−4 -alkylbenzocarbazoles. Only a few specific structures were isolated compared to the large total number of possible isomers. Pseudo-homologous series were recognized, a noticeable example is that of 8-isopropylalkylquinoline. These results were compared to the distribution of nitrogen substances from this sample after a catalytic hydrotreatment. Alkylpyridines totally disaapeared, whereas C 1−7 -alkylanilines were found. Identification of specific pseudo-homologous series of nitrogen substances in the hydrotreated sample confirm previous results on the resistance to hydrogenation of carbazoles and azaarenes bearing a methyl substituent in α position to the nitrogen atom.

Identification of carbazole derivatives in a hydrotreated coker gas oil by gas chromatography and gas chromatography—mass spectrometry

Abstract Non-basic nitrogen-containing polyaromatic hydrocarbons (NPAHs) were determined in a hydrotreated coker gas oil using gas chromatography and combined gas chromatography—mass spectrometry. The abundant NPAHs are alkylated benzologues of carbazole. The relative distribution of the carbazole derivatives in the sample is characterized by the presence of alkylcarbazoles with up to four carbon atoms in the substituents and alkylbenzocarbazoles branched by chains with two carbon atoms or less. Substances with polymethyl structures are the most abundant. Although severe hydrotreating conditions were applied to the feedstock, the observed NPAHs could not be eliminated. Their resistance is probably a function of the position of the alkyl groups on the aromatic nuclei.

Characterization of peak asymmetry with overloaded capillary columns

Abstract A theoretical model for elution peaks (based on the solution of the mass-balance equations with a parabolic expansion of the isotherm equation) is in good agreement with the experimental peak profiles observed in capillary gas chromatography. It depends on four parameters: the peak area, the limiting retention time at zero concentrationm, the global apparent diffusion coefficient, and the peak slant coefficient. The sorption effect, which is a flow-rate increase inside the solute band, has a back-leaning, asymmetrical effect. It is a major contribution to the peak distortions observed in capillary gas chromatography. It is shown that one of the parameters of the theoretical model, the proportionality factor μ O , is characteristic of peak asymmetry and is easily measured from the variation of peak maximum with the amount injected. The asymmetry depends greatly on the magnitude of the second derivative of the isotherm at the origin. It is due to column overloading and is independent of column length and flow-rate. It increases with decreasing column diameter and with decreasing film thickness. This proportionality factor is useful for characterizing the degree of asymmetry of capillary columns, especially for comparing the stationary phases and the coating procedures.