Didier Espinat

École Supérieure de Physique et de Chimie Industrielles, Lutetia Parisorum, Île-de-France, France

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Publications (12)20.15 Total impact

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    ABSTRACT: Refining processes produce varieties of petroleum streams which have to be characterized in order to evaluate their quality, to monitor the process or to ensure that the products meet the required specifications. For middle distillates, global properties (density, refractive index) are thus routinely measured in refining products. The cetane number (CN), which characterizes the combustion behaviour of middle distillates in diesel engines, is one of the most stringent specifications for the European market (EN 590). The reference method (ASTM D613), which consists in the measurement of the fuel auto-ignition delay, is time consuming and requires a large amount of sample (ca. 1L). Several predictive models for cetane number have been developed based on correlations with fuel global properties (density, simulated distillation). The main drawback of these global models is the lack of explicit link between the molecular composition of fuels and the cetane index which can be explained by the poor separation power of conventional analytical techniques. Comprehensive two-dimensional gas chromatography (GCGC) enables within one single injection the characterisation of diesel components by families (paraffins, naphthenes, mono-, di- and tri-aromatics) and within each class of components by groups of isomers. The integration of 2D-Chromatograms by means of a dedicated software (2DChromTM, developed by IFP and commercialised by Thermo Scientific) yielded approximately 150 groups of compounds. An average cetane number was then attributed to each group, based on experimental cetane numbers of model compounds obtained from literature. A linear regression was carried out in order to optimize this cetane number for each group of compounds taking into account chemical constraints (cetane number must be positive, normal paraffins have greater cetane numbers than iso-paraffins...) The cetane number of each diesel could thus be obtained from the molecular composition provided by GCGC analysis, using a simple linear correlation. For most of the diesels investigated, excellent agreement was reached between the cetane numbers calculated from GCGC and the reference engine values, which validates the strategy followed. However, significant differences were observed for diesels enriched in polynaphthenes (3- and 4-ring naphthenes) and olefins. These differences can be attributed to an incomplete separation in GCGC, due to co-elutions between polynaphthenes/mono-aromatics on one hand, and olefins/naphthenes on the other hand. To solve this problem, the analysis of such diesels was performed using Supercritical Fluid Chromatography (SFC) hyphenated on-line to GCGC. Using this powerful technique, saturated and unsaturated compounds were separated and recovered in two different fractions, each of which could be analysed on-line by GCGC. Therefore, polynaphthenes and olefins could be quantified by families (3- and 4-ring naphthenes, n-, iso and cyclo-olefins) and within each class of components by groups of isomers. A cetane number was attributed to each group following the same strategy as described for GCGC. The cetane index obtained from SFC-twinGCGC analysis of these diesels was found to be in excellent agreement with the engine ASTM method. Therefore, SFC hyphenated on-line to GCGC enables to predict the cetane number of olefinic and naphthenic diesels, unlike single GCGC. In conclusion, a simple composition-based model was successfully developed for predicting the cetane number of diesel fuels. Due to the explicit link between the cetane number and the detailed composition obtained from GCGC or SFC-twinGCGC, cetane numbers can also be estimated for narrow cuts of diesel samples. This is very useful for blending studies. To our knowledge, this is the first cetane number predictive model based on the molecular composition of middle distillates obtained through a single analysis. This strategy is currently being applied to the prediction of various diesel fuel properties (aromatic carbon content, cold flow properties...).
    No preview · Conference Paper · Apr 2009
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    ABSTRACT: In the current energetic context (increasing consumption of vehicle fuels, greenhouse gas emission etc.) government policies lead to mandatory introduction in fossil fuels of fuels resulting from renewable sources of energy such as biomass. Blending of fatty acid alkyl esters from vegetable oils (also known as biodiesel) with conventional diesel fuel is one of the solutions technologically available; B5 blends (up to 5%w/w esters in fossil fuel) are marketed over Europe. Therefore, for quality control as well as for forensic reasons, it is of major importance to monitor the biodiesel origin (i.e. the fatty acid ester distribution) and its content when it is blend with petroleum diesel. This paper reports a comprehensive two-dimensional gas chromatography (GC x GC) method that was developed for the individual quantitation of fatty acid esters in middle distillates matrices. Several first and the second dimension columns have been investigated and their performances to achieve (i) a group type separation of hydrocarbons and (ii) individual identification and quantitation of fatty acid ester blend with diesel are reported and discussed. Finally, comparison of quantitative GC x GC results with reference methods demonstrates the benefits of GC x GC approach which enables fast and reliable individual quantitation of fatty acid esters in one single run. Results show that under developed chromatographic conditions, quantitative group type analysis of hydrocarbons is also possible, meaning that simultaneous quantification of hydrocarbons and fatty acid esters can be achieved in one single run.
    Full-text · Article · May 2008 · Journal of Chromatography A
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    ABSTRACT: A new column association using comprehensive two-dimensional gas chromatography for the detailed molecular analysis of hydrocarbon mixtures is reported in this paper. In order to compare the impact of two different secondary columns, a novel column combination relying on a GC x 2GC system was used. This system is based on a non-polar first column (PONA) combined with both a permethylated beta-cyclodextrin (beta-Dex 120) stationary phase and a polysilphenylensiloxane (BPX 50) in the second dimension. Compared to BPX 50 stationary phase, the implementation of beta-cyclodextrin columns as the second dimension was found to improve the resolution between paraffins and naphthenes in the naphtha range but not in the middle distillate range. Attempts to improve the results and to understand the interaction mechanism remained unsuccessful. Therefore, the benefits of the beta-Dex 120-column are only demonstrated on heavy naphtha cut for the quantitation of hydrocarbons.
    Preview · Article · Feb 2008 · Journal of Chromatography A
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    ABSTRACT: The detailed characterization of middle distillates is essential for a better understanding of reactions involved in refining processes. Owing to a higher resolution power and an enhanced sensitivity, but especially to a group-type ordering in the chromatographic plane, comprehensive two-dimensional gas chromatography (GCxGC) offers unsurpassed characterization possibilities for petroleum samples. However, GCxGC fails to totally discriminate naphthenes from unsaturates occurring in hydrotreated diesel samples. This article aims at promoting the implementation of LC-GCxGC for the quantitative determination of hydrocarbon distribution in middle distillates, including naphthenes. In this configuration, liquid chromatography (LC) enables the separation of hydrocarbons into two fractions (viz., saturated and unsaturated) before the subsequent analysis of each fraction by GCxGC. In this paper, the choice of GCxGC conditions in order to achieve the separation and identification of hydrocarbons by chemical class is discussed; under these conditions, naphthenes are separated according to the number of saturated rings. For the first time, the presence of di-, tri-, and tetra-naphthenes resulting from the hydroconversion of aromatics can clearly be evidenced. A quantitative procedure for the determination of the distribution of hydrocarbons, including the distribution of naphthenes according to the number of saturated rings, is also proposed and discussed in detail. LC-GCxGC is found to provide an unequalled degree of information that will widely contribute to a better understanding of hydroconversion processes.
    Preview · Article · Nov 2007 · Journal of chromatographic science
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    ABSTRACT: This paper reports an analytical method for the comprehensive two-dimensional gas chromatography (GC x GC) separation and identification of nitrogen compounds (N-compounds) in middle distillates according to their types (basicity). For the evaluation of the best chromatographic conditions, a non-polar x polar approach was chosen. The impact of the second dimension (stationary phase and column length) on the separation of basic and neutral N-compounds was evaluated by mean of two-dimensional resolution. This study revealed that the implementation of polar secondary column having free electron pairs improves drastically the separation of N-compounds. Indeed, the presence of permanent dipole-permanent dipole interactions between neutral N-compounds and the stationary phase was enlightened. The comparison of two different nitrogen chemiluminescence detectors (NCD) was also evaluated for GC x GC selective monitoring of N-compounds. Owing to higher resolution power and enhanced sensitivity achieved using developed chromatographic and detection conditions, it was possible to identify univocally and to quantitate N-compounds (i) by class of compounds and (ii), within a class, by carbon number. Finally, quantitative comparison of GC x GC-NCD with conventional gas chromatography illustrates the benefits of GC x GC leading to an excellent correlation with results obtained by American Society for Testing Materials (ASTM) methods for the determination of basic/neutral nitrogen ratio in diesel samples.
    No preview · Article · May 2007 · Journal of Chromatography A
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    ABSTRACT: Simulated distillation (simdist) based on separation using gas chromatography (GC) is widely spread in the petroleum industry for evaluation of fossil fuels as well as petroleum feeds and cuts produced by refining and conversion processes. Through a calibration curve relating the boiling point Of normal paraffins to their elution temperature or retention time, simdist provides the hydrocarbon distribution of the sample (in weight percent) versus the boiling range of the fraction. The operating conditions used for simdist are tuned to be in agreement with preparative distillation that gives the True Boiling Point (TBP) curve. However, this technique is not compatible to heavy ends (FBP higher than 700 degrees C) due to the limitation of volatility of the products and the lack of resistance of high molecular-weight hydrocarbons to cracking reactions. The interest of supercritical-fluid chromatography (SFC) is that high temperatures are not needed to elute heavy ends and that the mechanism for extending the upper limit of simdist depends only on sample solubility into the supercritical mobile phase. This paper presents recent advances in Simdist using SFC of heavy fractions. Compared to GC, SFC extends the range of this application up to nC(126) hydrocarbons and makes possible to calibrate up to nC(200). Thus, SFC could be the tool of choice for better determination of conversion in heavy petroleum-fraction processing.
    No preview · Article · Jan 2007 · Oil & Gas Science and Technology
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    ABSTRACT: The monitoring of total sulfur content and speciation of individual sulfur-containing compounds in middle distillates is required for efficient catalyst selection and for a better understanding of the kinetics of the reactions involved in hydrotreament processes. Owing to higher resolution power and enhanced sensitivity, comprehensive two-dimensional gas chromatography (GC×GC) hyphenated to sulfur chemiluminescence detection (SCD) has recently evolved as a powerful tool for improving characterization and identification of sulfur compounds. The aim of this paper is to compare quantitatively GC×GC-SCD and various other methods commonly employed in the petroleum industry, such as X-ray fluorescence, conventional GC-SCD, and high-resolution mass spectrometry, for total sulfur content determination and speciation analysis. Different samples of middle distillates have been analyzed to demonstrate the high potential and important advantages of GC×GC-SCD for innovative and quantitative analysis of sulfur containing compounds. More accurate and detailed results for benzothiophenes and dibenzothiophenes are presented, showing that GC×GC-SCD should become, in the future, an essential tool for sulfur speciation analysis.
    Preview · Article · Nov 2006 · Journal of chromatographic science
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    ABSTRACT: A multidimensional method providing the composition of a heavy naphtha in paraffins, isoparaffins, olefins, naphthenes, and aromatics (PIONA) in the C8-C14 range is presented. The analytical set-up consists in a silver modified silica olefin trap on-line coupled to comprehensive two-dimensional gas chromatography (GC x GC). In this configuration, hydrocarbons are separated, in gaseous state, in two fractions, saturate and unsaturate, each fraction being subsequently analysed by GC or by GC x GC. The resolution between saturates and olefins was found to be improved compared to a single GC x GC run. The characterisation of the olefin trap highlights the benefits and the limits related to the use of that stationary phase as a double bond selective fractionation medium.
    No preview · Article · Nov 2005 · Journal of Chromatography A
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    ABSTRACT: The detailed analysis of petroleum cuts is required for refinery processes monitoring and for product specifications. To improve the detailed paraffin, isoparaffin, olefin, naphthene, aromatic analysis of a heavy naphtha, a multidimensional approach was proposed, which is based on the fractionation by an olefin trap of the saturate and unsaturated fractions of a heavy naphtha followed by the GC×GC analysis of each fraction. The ability of the olefin trap to separate olefins from paraffins in the C8-C14 range that provided suitable desorption conditions of heavy olefins from the trap could be found. At low concentrations, the relationship between the area and the injected quantity of olefin was linear. This is an abstract of a paper presented at the ACS Fuel Chemistry Meeting (Washington, DC Fall 2005).
    No preview · Article · Jan 2005
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    ABSTRACT: Simulated distillation (Simdis) based on GC is widely used in the petroleum industry for evaluation of fossil fuels as well as petroleum feeds and cuts treated in refining and conversion processes. Simdis gives the hydrocarbon distribution of the sample vs. the boiling range of the fraction. The conditions used for Simdis are tuned to provide results in agreement with preparative distillation that gives the True Boiling Point curve (described in ASTM D2892). Recent advances in Simdis of heavy fractions using supercritical-fluid chromatography (SFC) were presented. Compared to GC, SFC calibration range is extended up to C120 hydrocarbons and can be extrapolated to nC162. Good agreement between GC and SFC data at 450°-731°C was observed. As in GC, using element selective detectors SFC could be the tool of choice for better quantitation of conversion in heavy petroleum-fraction processing.
    Full-text · Article · Mar 2004

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    ABSTRACT: Simulated distillation (simdist) based on separation using gas chromatography (GC) is widely spread in the petroleum industry for evaluation of fossil fuels as well as petroleum feeds and cuts produced by refining and conversion processes. Through a calibration curve relating the boiling point of normal paraffins to their elution temperature or retention time, simdist provides the hydrocarbon distribution of the sample (in weight percent) versus the boiling range of the fraction. The operating conditions used for simdist are tuned to be in agreement with preparative distillation that gives the True Boiling Point (TBP) curve. However, this technique is not compatible to heavy ends (FBP higher than 700$^{\circ}$C) due to the limitation of volatility of the products and the lack of resistance of high molecular-weight hydrocarbons to cracking reactions. The interest of supercritical-fluid chromatography (SFC) is that high temperatures are not needed to elute heavy ends and that the mechanism for extending the upper limit of simdist depends only on sample solubility into the supercritical mobile phase. This paper presents recent advances in Simdist using SFC of heavy fractions. Compared to GC, SFC extends the range of this application up to nC$_{126}$ hydrocarbons and makes possible to calibrate up to nC$_{200}$. Thus, SFC could be the tool of choice for better determination of conversion in heavy petroleum-fraction processing. La distillation simulée (simdist) fondée sur une séparation par chromatographie en phase gazeuse (CPG) est largement répandue dans l'industrie pétrolière afin d'évaluer les huiles comme les charges et recettes des procédés de raffinage et de conversion du pétrole brut. Grâce à une courbe de calibration reliant le temps de rétention à la température d'ébullition de paraffines normales, la distillation simulée fournit la distribution des hydrocarbures d'un échantillon (en % poids) en fonction du point d'ébullition de cette fraction. Les conditions expérimentales de la distillation simulée sont ajustées pour obtenir des résultats en accord avec les méthodes de distillation physiques qui fournissent la température d'ébullition vraie. Cependant, cette technique n'est pas compatible avec les fractions lourdes (point final supérieur à 700$^{\circ}$C) en raison de la limitation de la volatilité et du manque de résistance des composés de haut poids moléculaire envers les réactions de craquage. L'intérêt de la chromatographie en phase supercritique (CPS) réside dans le fait que les hautes températures ne sont pas requises et que le mécanisme pour étendre la limite supérieure de la courbe de distillation dépend de la solubilité de l'échantillon dans la phase supercritique. Cet article présente des avancées récentes en distillation simulée basée sur la CPS. Comparativement à la CPG, la CPS étend la gamme de cette application jusqu'au nC$_{126}$ et rend possible une extrapolation jusqu'au nC$_{200}$. Par conséquent, la CPS est un outil de choix pour obtenir une meilleure quantification de la conversion des fractions pétrolières lourdes.
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