Didier Thiébaut

Global approach for the selection of high temperature comprehensive two-dimensional gas chromatography experimental conditions and quantitative analysis in regards to sulfur-containing compounds in heavy petroleum cuts.

Extending the knowledge on sulfur-containing compounds is crucial for the petroleum industry because they contribute to atmospheric pollution by combustion. Most of them are concentrated in heavy petroleum cuts, such as vacuum gas oils (VGOs). However, the resolution of the existing analytical methods does not allow a quantitative speciation of S-compounds contained in VGOs. Therefore, a high temperature GC×GC chromatograph hyphenated to a SCD was implemented in this study to obtain a quantitative S-compounds speciation. Firstly, various thermally stable stationary phases, in particular the new ionic liquid IL59 and Mega Wax-HT, were investigated in 1D-GC as a way to reduce the number of columns sets to be used in GC×GC. Consequently, several normal and reversed configurations of these columns were selected and tested in GC×GC. Then, a decision method was applied to facilitate the choice of the best combination of columns. Finally, the most adapted methods led to an innovative group type quantification and to a quantitative distribution of heavy sulfur species contained in a VGO sample. These results represent a major step towards the study of S-compounds in heavy petroleum cuts.

Challenge in the speciation of nitrogen-containing compounds in heavy petroleum fractions by high temperature comprehensive two-dimensional gas chromatography

Extending the knowledge related to nitrogen-containing compounds presents an important interest for the petroleum industry due to their implication in atmosphere pollution as well as their inhibitive or refractive behaviour towards hydroprocessing. Most of the nitrogenated species are concentrated in heavy petroleum cuts. As no analytical method is resolutive enough for these heavy cuts, particularly regarding nitrogen-containing compounds, a new approach is needed. For this reason, this study focuses on the development of a GC×GC technique, through the hyphenation of a specific NCD detector with a GC×GC system at high temperature. The performances of highly polar thermally stable stationary phases, in particular those composed of promising ionic liquids, were monitored in normal and reversed configurations. Subsequently, after the extraction of neutral or basic compounds by adsorption on an ion-exchange resin, a first quantitative determination was attempted for a straight-run and a direct coal liquefaction vacuum gas oils. This study led to a better understanding of the behaviour of highly aromatic N-compounds by 2D-GC including an ionic liquid phase as well as a deeper N-characterization of heavy petroleum fractions.

Investigating comprehensive two-dimensional gas chromatography conditions to optimize the separation of oxygenated compounds in a direct coal liquefaction middle distillate.

Considering the global energetic context, diversifying fuels is of growing importance and many new alternatives are promising. Coal liquefaction products definitely appear among the new generation substitutes. These products characteristics are very far from fuel specifications as they are mainly composed of naphthenes, aromatics, polycondensed naphthenic and aromatic structures and heteroatomic compounds (nitrogen and oxygen), with a very low paraffin content. Identification and quantification of oxygen-containing species in coal-derived liquids are of considerable importance to understand their behaviors in further processing. However, these species have not been characterized as fully as the predominant hydrocarbon components. Literature shows that these compounds consist mainly in alkylated phenolic and furanic structures. Therefore, comprehensive two-dimensional gas chromatography has been investigated to provide enhanced molecular characterization of these complex samples. Several different configurations involving innovative column configurations were tested. Each of them was optimized by testing different column lengths, modulation periods, and oven conditions. A comparison of the contribution of each column configuration was carried out regarding four main criteria: individual separation of oxygenates, group type separation, resolution, and space occupation. One of them enabled an outstanding separation of paraffins, naphthenes, monoaromatics, diaromatics and targeted O-compounds in a direct coal liquefaction product. It was therefore subjected to further experimentations using a time-of-flight mass spectrometer to validate the identification and unravel more than fifty oxygenated molecular structures. A group-type quantification was also established for four column arrangements and gives the distribution of paraffins, naphthenes and aromatics. It can be concluded from this study that a non-orthogonal arrangement involving a highly polar column in the first dimension was the most adapted one.

Using gas chromatography to characterize a direct coal liquefaction naphtha.

Speciation of oxygenated compounds in direct coal liquefaction naphthas is essential considering their important roles in coal conversion reactions. This study attempts to characterize them as fully as possible using gas chromatographic systems. Firstly, GC-MS was deployed allowing the identification of a few ketones, alcohols, and phenols. This conventional analysis was complemented by the application of GC-GC-FID aiming to overcome the coelutions highlighted when using one-dimensional gas chromatography. Heart-cutting and comprehensive two-dimensional gas chromatography were used and the comprehensive system led to better performances as expected considering the complexity of the matrix. In fact, it allowed the identification of more than a hundred of oxygenated compounds belonging to five chemical families: alcohols, ketones, furans, acids and phenols. Average response factors of each of these families were determined by GC×GC-FID using calibration curves and vary from 1 (hydrocarbons) to 2.50 (carboxylic acids). Thanks to a breakthrough columns set involving a trifluoropropyl stationary phase, alcohols and phenols which represent around 14% of the sample were fully identified. A detailed quantification of these species was carried out for the first time in such matrices using the determined response factors. It was concluded that 90% (w/w) of the alcohols are aromatic (phenols), 5% (w/w) are cyclic and 5% (w/w) are linear. A quantification of hydrocarbon families was also achieved and shows that the matrix is mostly naphthenic (56%, w/w), but also contains aromatics (22%, w/w) and paraffins (8%, w/w). This detailed characterization leads to a better understanding of coal conversion processes and is essential to convert them into synthetic fuels.

Extended characterization of a vacuum gas oil by offline LC‐high‐temperature comprehensive two‐dimensional gas chromatography

In a context of environmental preservation, purification and conversion of heavy petroleum cuts into high-quality fuel becomes essential. The interest for the characterization of those very complex matrices becomes a trendy analytical challenge, when it comes to get molecular information for the optimization of industrial processes. Among new analytical techniques, high-temperature 2-D GC has recently proved its applicability to heavy petroleum matrices, but lacks in selectivity to separate all chemical groups. To gain resolution, heart cutting is demonstrated for LC separation of saturated, aromatic and polar compounds prior to high-temperature 2-D GC. Therefore, an extended global resolution was obtained, especially by a better distinction of saturated compounds. This includes iso-paraffins and biomarker polynaphthenic structures, which are impossible to quantify with MS methods. This new way to analyze heavy petroleum fractions gives innovative opportunities for the construction of global weight distributions by carbon atoms number and by chemical families. This can right now be employed for quantitative analysis of heavy petroleum fractions and for studying conversion processes.

Complete elution of vacuum gas oil resins by comprehensive high-temperature two-dimensional gas chromatography ☆

The development of efficient conversion processes requires extended knowledge on vacuum gas oils (VGOs). Among these processes, hydrocracking is certainly one of the best suited to meet the increasing demand on high quality diesel fuels. Most of refractory and inhibiting compounds towards hydrocracking and especially nitrogen containing compounds are contained in a fraction of the VGO called the resin fraction, which corresponds to the most polar fraction of a VGO obtained by liquid chromatography (LC) fractionation on a silica column. However, the lack of resolution observed through existing analytical methods does not allow a detailed characterization of these fractions. A recent study showed that comprehensive high temperature two-dimensional gas chromatography (HT-GC×GC) methods could be optimized in order to elute heavy compounds. This method was implemented for the analysis of VGO resin fractions and complete elution was reached. Firstly, the method was validated through repeatability, accuracy, linearity and response factors calculations. Four VGO resin fractions were analyzed and their HT-GC×GC simulated distillation curves were compared to their GC simulated distillation (GC-SimDist) curves. This comparison showed that the method allows complete elution of most of the analyzed VGO resin fractions. However, a detailed characterization of these fractions is not yet obtained due to the very large number of heteroatomic and aromatic species that a flame ionization detector can detect. Current work aims at increasing the selectivity of GC×GC by using heteroatom selective detectors in order to improve the characterization of such products.

Determination of ethylenediaminetetraacetic acid in nuclear waste by high-performance liquid chromatography coupled with electrospray mass spectrometry.

EDTA is a chelating agent that has been used in decontamination processes. Its quantification is required for nuclear waste management because it affects the mobility of radionuclides and metals in environment and, thus, can harm the safety of the storage. Ion-pair chromatography coupled with electrospray mass spectrometry detection is a convenient method for quantitative analysis of EDTA but EDTA should be present as a single anionic chelate form. However, radioactive liquid wastes contain high concentrations of heavy metals and salts and consequently, EDTA is present as several chelates. Speciation studies were carried out to choose a metal cation to be added in excess to the solution to obtain a major chelate form. Fe is the predominant cation and Fe(III)-EDTA is thermodynamically favored but these speciation studies showed that ferric hydroxide precipitated above pH 2. Consequently, it was not possible to quantify EDTA as Fe(III)-EDTA complex. Therefore, Ni(2+) was chosen but its use implied pretreatment with a base of the solution to eliminate Fe. Deuterated EDTA was used as tracer in order to validate the whole procedure, from the treatment with a base to the final analysis by HPLC-ESI-MS. This analytical method was successfully applied for EDTA quantification in two real effluents resulting from a nuclear liquid waste process. A recovery rate between 60 and 80% was obtained. The limit of detection of this method was determined at 34×10(-9)mol L(-1).

Hypernated supercritical fluid chromatography: Potential application for car lubricant analysis

Car lubricant additives are added to mineral or synthetic base stocks to improve viscosity and resistance to oxidation of the lubricant and to limit wear of engines. In previous papers related to this purpose, it was demonstrated that SFC allows the elution of common low molecular weight additives. Since their total resolution could not be achieved owing to the limited peak capacity of packed columns, the hyphenation of selective and informative detectors, atomic emission and mass spectrometry, were also carried out for identification. This paper describes the final implementation of a packed column SFC/FID-UV-AED-FTIR-MS system to contribute to the characterisation of both the base stock, mineral or semi-synthetic, and the low molecular weight additives. SFC/FID-UV-FTIR ensures the easy confirmation of the presence of esters in the base stock. Reference additives are used to demonstrate the performances of the multi hyphenated system prior to its implementation for their identification in packages and in formulated lubricants. Identification and partial structure elucidation of additives and families of additives in package and formulated car lubricants are presented: using combined information obtained from AED traces and FTIR chemigrams, chemical families of additives can be deduced. Then, the mass spectra can be interpreted in the elution zone of interest in order to go further in the determination of the additive molecular structure. The hypernated SFC system was also employed to follow the ageing of car lubricants.

Reversal of elution order in a single second dimension by changing the first column nature in comprehensive two-dimensional gas chromatography.

This paper explains how one single stationary phase can involve two different elution orders for linear alkanes, cyclic alkanes, aromatics and phenols using comprehensive two-dimensional gas chromatography. For this purpose, a coal-derived middle distillate was injected in nonpolar×semipolar and polar×semipolar configurations implying the same second dimension stationary phase (trifluoropropyl). Results show that even if the same column is utilised as a second dimension, the group-type elution order is reversed from one combination to the other. This can be explained as follows:for the polar×semipolar combination, each fraction eluting from the first dimension contains species that differ so much in terms of boiling points, that volatility plays a key role in the second isothermal separation. This is exemplified by the separation of a phenol and demonstrated using the proportional relationship between retention times, vapour pressures and activity coefficients. Moreover, vant Hoff plots (plots of ln k vs. 1/T) demonstrated the influence of the elution temperature from the first dimension on the second dimension separation. Therefore, available choice of stationary phases combinations is much higher considering that one single column leads to very different retentions for similar compounds. Finally, this can explain why a reverse orthogonality approach is usually proficient for the separation of polar compounds.

Supercritical fluid chromatography hyphenated to bidimensional gas chromatography in comprehensive and heart-cutting mode: design of the instrumentation.

A new multidimensional chromatographic instrument has been developed to perform both SFC-GC×GC and SFC×GC×GC, in response to the challenge of complex matrices characterization. The design of this online system is fully described and enriched by theoretical and practical discussions. A new interface has been investigated: this interface allows the temporary storage of SFC fractions inside sampling loops before their quantitative transfer toward the GC×GC. This innovative design allows flexible and automatic hyphenated approaches such as single, multiple, total heart-cutting and comprehensive modes. An overview of the interfacing experimental conditions is also presented. Thanks to all the hyphenation possibilities of the three dimensions, this instrument opens up new prospects for the quantitative analysis of very complex matrices.