Kinetic Modeling of Vacuum Gas Oil Hydrotreatment using a Molecular Reconstruction Approach

International audienceVacuum Gas Oils (VGO) are heavy petroleum cuts (boiling points ranging from 350 to 550 ˚C) that can be transformed into valuable fuels (gasolines, diesels) by fluid catalytic cracking or hydrocracking. Prior to these conversion processes, hydrotreating is required in order to eliminate the impurities in VGOs. The hydrotreatment process enables to meet the environmental specifications (total sulfur contents) and to prevent nitrogen poisoning of conversion catalysts. In order to develop a kinetic model based on an accurate VGOs molecular description, innovative analytical tools and molecular reconstruction techniques were used in this work. A lumped model using a Langmuir-Hinshelwood representation was developed for hydrodearomatization, hydrodesulfurization and hydrodenitrogenation of the VGO. This lumped model was successfully applied to the experimental feed pretreatment data and was able to predict evolution of concentration of the aromatics, nitrogen and sulfur species

Development of Supercritical Fluid Chromatography Methods with Mass Spectrometry and U.V. Detection for the Characterization of Fast Pyrolysis Bio Oils

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A three-dimensional semi-quantitative method to monitor the evolution of polycyclic aromatic hydrocarbons from vacuum gas oil feedstocks to lighter products

International audienceFormation and accumulation of polycyclic aromatic hydrocarbons (PAHs) are responsible of major topical issues related to the conversion of petroleum vacuum gas oils (VGOs) in transportation fuels through hydrocracking process. To achieve an efficient management of these hydrocarbons, a detailed semi-quantitative description of PAHs contained in VGOs was provided by a threedimensional off-line analytical approach based on centrifugal partition chromatography (CPC), supercritical fluid chromatography (SFC) and high-resolution mass spectrometry (HRMS). As a result, well-organised CPCxSFC chromatograms provided a relevant separation of PAHs according to both unsaturation level (DBE) and alkylation degree. This dedicated methodology allowed the semiquantification of PAHs having a DBE superior to 12. For the first time, PAHs were quantified in six VGOs allowing to highlight differences in composition depending on the origin of the samples. Then, the evolution of PAH concentration was monitored during hydrotreating and hydrocracking processes. For the hydrotreated/hydrocracked (HDT/HCK) products, their sulphur and nitrogen contents were low enough to make possible semi-quantification of PAHs directly by SFC/HRMS. An accumulation of PAHs was observed when a recycle stream from the unconverted oil to HDT reactor was applied. This work demonstrates that valuable analytical data could be obtained leading a step 2 forward in the overall understanding of a process from native VGO feedstocks to the HDT/HCK products

A rational strategy based on experimental designs to optimize parameters of a liquid chromatography-mass spectrometry analysis of complex matrices

International audienceA high number of factors controlled by the experimenter has to be optimized to successfully separate, ionize and detect compounds when analyzing complex matrices by liquid chromatography hyphenated to high resolution mass spectrometry (LC-UV/MS). Key steps to manage such hyphenation are focused on desolvation and ionization processes. In this study, a design of experiments approach was used to optimize decisive parameters (i.e. nebulising, drying and sweep gas flow rates, ion transfer capillary voltage and temperature) for electrospray ionization and atmospheric pressure chemical ionization sources both in positive and negative modes. Central composite designs including 131 experiments each were built to cover rationally a sufficiently wide range of operating conditions. Each run was repeated three times to insure stable conditions of ionization and thus a satisfactory repeatability. Extracted ion chromatograms of twelve model oxygenated compounds were integrated and used as responses for experiment designs. Quadratic models for each standard allowed to take into account interactions between factors. Then responses were simultaneously maximized to achieve optimized factors. To illustrate the methodology relevance, optimal conditions were applied to a lignocellulosic biomass fast pyrolysis oil. Thanks to our high sensitivity method, a large number of molecular formulae was identified, as for instance in negative-ion mode electrospray with more than 5500 identified molecular formulae whereas analysis of the same sample by mass spectrometry without any prior chromatographic separation provided less than 2000 molecular formulae. In short, this study proposed a rational methodology to optimize ionization efficiency for LC-UV/MS analysis of complex mixtures

Hyphenation of SFC and HRMS for the analysis of bio-oils

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Input of an off-line comprehensive three-dimensional method (CPCxSFC/HRMS) to quantify polycyclic aromatic hydrocarbons in vacuum gas oils

International audienceHeavy polycyclic aromatic hydrocarbons (HPAH) are known to cause undesirable effects in petroleum hydrocracking processes by deactivating the catalysts and accumulating themselves in the downstream of reactors. Polycyclic aromatic hydrocarbons with less than 7 rings (PAH) naturally contained in vacuum gas oils (VGO) act as precursors in the HPAH formation. However, getting a detailed quantitative characterisation of such polycyclic hydrocarbons has never been done until now because of the high chemical complexity of VGO. Thus an off-line comprehensive three-dimensional methodology was required to achieve a quantitative analysis: centrifugal partition chromatography (CPC) as the first dimension of separation, supercritical fluid chromatography (SFC) as the second dimension hyphenated to Fourier transform ion cyclotron resonance mass spectrometry as the third dimension. In this study, we demonstrated that the developed CPC method fractionated samples according to hydrocarbons alkylation degree, whereas our SFC method provided an elution order according to their double bond equivalent. Finally, high-resolution mass spectrometry (HRMS) brought crucial information on the identity of analytes and proved to be essential in the event of unresolved peaks from CPC and SFC chromatograms. To assess the ability of the three-dimensional method for quantification purposes, matrix effects were evaluated by spiking VGO samples with deuterated pyrene. A strong ion suppression phenomenon was highlighted when using only SFC/HRMS whereas no significant matrix effect was observed with CPC×SFC/HRMS approach. These experiments revealed the high potential of this innovative methodology to quantify both PAH and HPAH in VGO for the first time

On-line two-dimensional liquid chromatography hyphenated to mass spectrometry and ion mobility-mass spectrometry for the separation of carbohydrates from lignocellulosic biomass

International audienceLignocellulosic biomass is a promising resource of renewable energy. Its transformation to ethanol requires efficient pretreatment leading to complex liquid mixtures made of hundreds of oxygenated analytes. A large part of the released compounds belong to the carbohydrates family. To overcome the complexity of such samples, a comprehensive on-line two-dimensional reversed-phase liquid chromatography hyphenated to high-resolution mass spectrometry (RPLC × RPLC-HRMS) was dedicated to the separation of carbohydrates and more specifically oligomers coming from pretreated lignocellulosic biomass. The first part of this study consisted in the optimization of such hyphenation (i.e. selection of stationary phases, mobile phases, sampling time, etc.). Then, the analytical method was applied to an industrial aqueous biomass product coming from the sulfuric acid-based pretreatment of a wheat straw. Around 70 well-resolved chromatographic peaks corresponding to oligomers were obtained. Occupation of the separation space between each chromatographic dimension was estimated to 75%. In the last part of this study, the interest of ion mobility-mass spectrometry in addition to RPLC × RPLC was discussed. Some examples highlighted the additional separation that can bring ion mobility to RPLC × RPLC-IMS-HRMS method. Using this four-dimensional hyphenation method, each analyte was described by two retention times, the collisional cross section and the molecular formula allowing to reach a level of detail never seen for biomass sample compositions

Membrane fractionation of biomass fast pyrolysis oil and impact of its presence on a petroleum gas oil hydrotreatment.

International audienceIn order to limit the greenhouse effect causing climate change and reduce the needs of the transport sector for petroleum oils, transformation of lignocellulosic biomass is a promising alternative route to produce automotive fuels, chemical intermediates and energy. Gasification and liquefaction of biomass resources are the two main routes that are under investigation to convert biomass into biofuels. In the case of the liquefaction, due to the unstability of the liquefied products, one solution can be to perform a specific hydrotreatment of fast pyrolysis bio-oils with petroleum cuts in existing petroleum refinery system. With this objective, previous studies [Pinheiro et al., 2009], [Pinheiro et al., 2011] have been carried out to investigate the impact of oxygenated model compounds on a straight run gas oil (SRGO) hydrotreatment using a CoMo catalyst. The authors have demonstrated that the main inhibiting effects are induced from CO and CO2 produced during hydrodeoxygenation of esters and carboxylic acids. To go further, cotreatment of a fast pyrolysis oil with the same SRGO as used in the previous studies was investigated in this present work. Firstly the bio-oil was separated into four fractions by membrane fractionation using 400 and 220 Da molecular weight cut-off membranes. The bio-oil and its fractions were analyzed by spectroscopic and chromatographic techniques. Then, one fraction (i.e. fraction enriched in compounds with molecular weight from 220 to 400 Da) was mixed with the SRGO and co-treated. Despite some experimental difficulties mainly due to the emulsion instability, the hydrotreatment was successful. An inhibition has been observed on the HDS, HDN and HDCa reactions of the SRGO in presence of the bio-oil fraction. The measurement of the CO/CO2/CH4 molar flowrate at the reactor outlet showed that the inhibition was due to the presence of CO and CO2 coming from HDO rather than to the oxygen compounds themselves

Hyphenation of supercritical fluid chromatography and high resolution mass spectrometry for the characterization of a fast pyrolysis oil

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Off-line comprehensive size exclusion chromatography × reversed-phase liquid chromatography coupled to high resolution mass spectrometry for the analysis of lignocellulosic biomass products

International audienceBiochemical and thermochemical processes are two pathways to convert lignocellulosic biomass into fuels and chemicals. Both conversion types produce aqueous complex samples containing many oxygenated chemical functions over a wide range of masses. Nowadays, composition of these biomass products is still largely unknown, especially their nonvolatile part (300–1000 Da) mostly made of carbohydrates and their derivatives. In the present study, size exclusion chromatography (SEC) was investigated and applied on water soluble phase of a fast pyrolysis bio-oil (thermochemical conversion) and on aqueous phase of pretreated wheat straw (biochemical conversion). An optimization of mobile phase composition using model molecules was necessary to limit non-steric interactions and elute all chemical families. At the end, separation of carbohydrates, heterosides and aromatic species was performed. The chemical organization of SEC chromatograms was confirmed by coupling SEC with a Fourier transform-ion cyclotron resonance mass spectrometer (FT-ICR MS) using electrospray ionization (ESI) in the negative mode. On-line SEC-UV/FT-ICR MS hyphenation was a powerful tool to provide exact mass distribution of samples and get molecular formulae classed by chemical family. To go further, the complementarity of SEC with reversed-phase liquid chromatography (RPLC) was established with an off-line comprehensive 2D-LC analysis of the two samples. First, 140 fractions were collected physically from SEC separation for each sample, then each fraction was analyzed by RPLC hyphenated to an Ion Trap - Time of Flight mass spectrometer (SEC × RPLC-UV/IT-TOF MS) using ESI in both positive and negative modes. This comprehensive approach combining 2D-LC and high resolution mass spectrometry nearly doubled the number of peaks detected in comparison with 1D RPLC analysis and thus offered well resolved 2D contour plots, considered as relevant analytical fingerprints of the aqueous phase of biomass samples