International audience; The oligomerization of glycerol to di- and triglycerol is an attractive reaction because these products find many applications in cosmetics, food industry and polymer ...industry. To control the oligomerization degree, it is necessary to develop a selective catalyst. In this work, two cesium mesoporous silica (MCM-41 and SBA-15) are compared in the selective oligomerization of glycerol into di- and triglycerol. The catalysts were prepared by incipient-wetness impregnation. The results showed that the stability and the activity of catalysts depend on the support nature. The use of SBA-15 support instead of MCM-41 leads to a more stable catalyst without changing polyglycerols selectivity. Different characterizations showed that it is due to the larger wall thickness of SBA-15. This study also showed that the nature of catalyst could influence the diglycerol isomers distribution. In fact the glycerol activation inside or outside the pores can strongly modify the selectivity to linear or branched diglycerol isomers.
Oxidation of finely divided molybdenum sulfide in ambient air has been studied for air exposure times from 10 min to 1 year to clarify the nature of the reaction products and the mechanistic steps. ...At the initial steps, for air exposure times from several minutes to several hours, rapid oxidation of MoS2 edges occurs with simultaneous formation of hydroxyl species and surface disulfide S2 2– moieties as attested by 1H NMR, X-ray photoelectron spectra, and temperature-programmed reduction. Prolonged air exposure of MoS2 nanodispersions leads to deep oxidation. According to the results of X-ray absorption spectroscopy, UV–visible, and electron paramagnetic resonance spectroscopies, the main oxidation products are soluble paramagnetic molybdenum blue species and sulfuric acid. As shown by EXAS fitting, the major product is oxo-bridged dimolybdenyl Mo(V, VI) species. Ambient moisture plays an important role in the oxidation process as it contributes to the formation of sulfuric acid which leads to liquescence of the material and to deep oxidation without formation of a protective passivation layer.
•Quantitative performance of forward fill/flush modulation is investigated in detail.•Parameters influencing efficiency of the modulation are delineated.•Relation between modulated peak shape and ...analyte quantitation is explored.•Role of the modulation fill and flush distances is explored through appropriate calculations.
GC × GC is an advanced separation technique allowing to achieve quantitative and qualitative characterization of complex samples. In order to perform two-dimensional separation, the system must provide suitable peak modulation which will direct short impulses of first column flow towards the second column. Forward fill/ flush differential flow modulation is a cost effective and no cryogen requiring approach which allows modulation over a wide range of analytes with very different boiling points. However, optimization of the flow modulation process can be difficult to understand and quantification performance might be compromised if the parameters of the modulation process are not properly set. Modulated peak shape can be a good indication of the efficiency of the modulation process, however it is not sufficient to guarantee good quantification. Different average velocities in the beginning and the end of the thermally programmed GC run may cause different efficiency of the modulation process in various parts of the chromatogram. The purpose of this work is to investigate quantitative performance of the forward/fill flush modulation and delineate parameters that determine the effectiveness of the modulation process and its ability to properly reflect the quantitative composition of the investigated sample.
Insight into the composition of middle distillates is essential to meet the requirements for product quality but also in terms of complying with ever more stringent environmental regulations. A newly ...introduced vacuum ultraviolet absorbance detector (VUV) possesses both quantitative and qualitative abilities and is amenable to hyphenation with comprehensive two-dimensional gas chromatography (GC×GC). It has good selectivity for hydrocarbon species and permits their differentiation even if they are not chromatographically separated. In this study, quantification of hydrocarbons in 14 gas oils coming from different origins was performed to evaluate the benefits of GC×GC-VUV for the analysis of middle distillates. Coelutions between hydrocarbon families were investigated and spectral decomposition was carried out for quantification of coeluted hydrocarbon families. Quantification obtained with GC×GC-VUV was compared with conventional techniques such as GC×GC-FID with prefractionation, MS method based on ASTM D2425, UV spectroscopic analysis, and bromine number. In general, good comparability was obtained between GC×GC-VUV and all the different techniques for major hydrocarbon families, however with a gain in time and/or information when using GC×GC-VUV. This demonstrates that GC×GC-VUV can be considered as a relevant tool for the detailed analysis of middle distillates, regardless of their origin.
Gas chromatography vacuum ultraviolet spectroscopy: A review Lelevic, Aleksandra; Souchon, Vincent; Moreaud, Maxime ...
Journal of separation science,
January 2020, 2020-Jan, 2020-01-00, 20200101, 2020-01, 2020-01-01, Letnik:
43, Številka:
1
Journal Article, Publication
Recenzirano
Odprti dostop
Accelerated technological progress and increased complexity of interrogated matrices imposes a demand for fast, powerful, and resolutive analysis techniques. Gas chromatography has been for a long ...time a ‘go‐to’ technique for the analysis of mixtures of volatile and semi‐volatile compounds. Coupling of the several dimensions of gas chromatography separation has allowed to access a realm of improved separations in the terms of increased separation power and detection sensitivity. Especially comprehensive separations offer an insight into detailed sample composition for complex samples. Combining these advanced separation techniques with an informative detection system such as vacuum ultraviolet spectroscopy is therefore of great interest. Almost all molecules absorb the vacuum ultraviolet radiation and have distinct spectral features with compound classes exhibiting spectral signature similarities. Spectral information can be ‘filtered’ to extract the response in the most informative spectral ranges. Developed algorithms allow spectral mixture estimation of coeluting species. Vacuum ultraviolet detector follows Beer–Lambert law, with the possibility of calibrationless quantitation. The purpose of this article is to provide an overview of the features and specificities of gas chromatography–vacuum ultraviolet spectroscopy coupling which has gained interest since the recent introduction of a commercial vacuum ultraviolet detector. Potentials and limitations, relevant theoretical considerations, recent advances and applications are explored.
Gas oils (GOs) analysis is essential for production process control, in order to meet quality standards, to render these products safer for the environment, and to support research for alternative ...fuels. GOs quantitative analysis can be commonly achieved by employing two-dimensional comprehensive gas chromatography with flame ionization detection (GC × GC-FID) in combination with identification templates. However, in order to perform quantification for families which coelute in GC × GC analysis (e.g., naphthenes/olefins or polynaphthenes/monoaromatics), prefractionation of gas oil before GC × GC analysis is necessary. Recent introduction of the vacuum ultraviolet (VUV) detector has offered new possibilities in GOs analysis, as this detector can discern between the majority of hydrocarbon families thus possibly rendering the gas oil prefractionation unnecessary. Additionally, it can perform quantification according to Beer–Lambert’s law provided that VUV relative response factors (RRFs) are known. The purpose of this work is to report, for the first time, VUV RRFs for numerous hydrocarbons in GOs (∼160) according to their family and their carbon number, permitting to perform their direct quantification without the necessity of GO prefractionation. VUV RRFs were measured by using a GC × GC-VUV/FID dual detection setup in which FID was employed as a quantitative reference. In order to obtain VUV RRFs representative for any gas oil, a set of 14 GOs with different origins was employed. Both VUV RRFs averaged in the 125–240 nm range and spectral VUV RRFs (reference spectra) were obtained. It was demonstrated that VUV RRFs were similar between employed GOs allowing their universal use. Obtained RRFs were used to perform hydrocarbons quantification for a light cycle oil (LCO) by GC × GC-VUV, with olefins and naphthenes being quantified through spectral decomposition. Good comparability with results obtained by prefractionation was observed demonstrating the great interest of the GC × GC-VUV approach for the detailed and rapid analysis of hydrocarbons in gas oils.
Comprehensive two−dimensional Gas Chromatography with Vacuum Ultraviolet detection (GC×GC/VUV) results in sizable data for which noise and baseline drift ought to be corrected. As GC×GC/VUV signal is ...acquired from multiple channels, these pre−processing steps have to be applied to data from all channels while being robust and rather fast with respect to significant size of the GC×GC/VUV data. In this study, we describe advanced GC×GC/VUV data pre−processing techniques for noise and baseline correction that are not available in commercial softwares. Noise reduction was performed on both the spectral and the time dimension. For baseline correction, a morphological approach based on iterated convolutions and rectifier operations is proposed. On the spectral dimension, much less noisy and reliable spectra are obtained. From a quantitative point of view, mentioned pre−processing steps significantly improve signal to noise ratio for analyte detection and hence improve their limit of detection (circa 6 times in this study). These pre−processing methods were integrated into plug im! platform (https://www.plugim.fr/).
PDF
