Reconstruction moléculaire de coupes pétrolières

La reconstruction des coupes pétrolières comprend l'ensemble des méthodes permettant de créer des mélanges de molécules à partir de données analytiques partielles. Dans le cadre de cette thèse, deux approches différentes ont été mises en place. La méthode de reconstruction stochastique suppose que les mélanges pétroliers peuvent être décrits par des distributions de blocs structuraux. Le choix des blocs et des distributions se fait en intégrant des expertises, le passage d'un jeu distributions à un mélange de molécules s'obtient par une méthode déchantillonnage Monte Carlo et l'optimisation des distributions est effectuée par un recuit simulé. Cette approche est adaptée aux coupes pétrolières les plus lourdes. La méthode de reconstruction par maximisation d'entropie est basée sur une bibliothèque prédéfinie de molécules dont les fractions molaires sont ajustées de manière à obtenir un mélange pétrolier cohérent avec les analyses. L'optimisation des fractions se fait en maximisant un critère entropique en présence de contraintes linéaires. Cette méthode est adaptée aux coupes pétrolières légères et moyennes. En dehors du développement et de l'amélioration de ces deux méthodes, plusieurs cas d'application ont été fournis. Pour les essences de FCC, l'utilisation de la reconstruction par maximisation d'entropie permet de retrouver la composition moléculaire d'une essence à partir de son analyse PIONA et de sa distillation simulée. pour les gazoles LCO, le couplage reconstruction stochastique / maximisation d'entropie permet d'estimer des analyses manquantes à partir de la spéctrométrie de masse et de la distillation. Pour les résidus sous vide, la reconstruction stochastique est comparée aux travaux de Trauth. Dans tous ces cas, les applications valident les mélanges pétroliers en terme de propriétés physico-chimiques. L'étape suivante pourrait consister à tutiliser des études cinétiques moléculaires afin d'effectuer une validation en terme de propriétés réactives.LYON-ENS Sciences (693872304) / SudocSudocFranceF

Mechanistic modeling of enzymatic hydrolysis of cellulose integrating substrate morphology and cocktail composition.

International audienceA complete mechanistic model of enzymatic hydrolysis taking into account the morphology of the cellulosic particles and its evolution with time was developed. The individual behavior of the main enzymes involved in the reaction (cellobiohydrolases, endoglucanases and β-glucosidases), as well as synergy effects, were also included. A large panel of experimental tests was done to fit and validate the model. This database included different enzymes mixtures and operating conditions and allowed to determine and compare with accuracy the adsorption and kinetic parameters of the different enzymes. Model predictions on short hydrolysis times were very satisfactory. On longer times, a deactivation constant was added to represent the hydrolysis slowdown. The model also allowed to predict the impact of enzymes ratios and of initial substrate parameters (chain length distribution, polymerization degree) on hydrolysis, and to follow the evolution of these parameters with time. This model revealed general trends on the impact of cellulose morphology on hydrolysis. It is a useful tool to better understand the mechanisms involved in enzymatic hydrolysis of cellulose and to determine optimal cellulolytic cocktails for process design

Kinetic modeling of the enzymatic hydrolysis of cellulose integrating the evolution of the substrate morphology.

http://www.etaflorence.it/proceedings/International audienceThe biological production of ethanol from lignocellulose has been widely investigated for decades. During the SHF process (Separate Hydrolysis and Fermentation), the biomass, which is composed of cellulose, hemicelluloses and lignin, is converted into bioethanol following four main steps. After an appropriate pretreatment (step 1), the cellulose is hydrolyzed into glucose in the presence of three types of cellulolytic enzymes acting in synergy (step 2): endoglucanases (EG) which attack randomly the cellulose molecules and create new chain ends, cellobiohydrolases (CBH) which hydrolyse chain ends into cellobiose and β-glucosidases (BG) which convert cellobiose into glucose. The glucose is then converted into ethanol during a fermentation step (step 3). The alcohol is recovered by distillation (step 4) and incorporated into fossil fuel. Currently, the enzymatic hydrolysis of biomass is one of the main bottlenecks of the process, as it implies very complex mechanisms: long hydrolysis times (until 1 week) with enzyme deactivation, heterogeneity and modification of the substrate during the reaction, production of inhibitive coproducts, presence of lignin... In order to optimize the process at the industrial scale and reduce the enzyme loading, a model must be developed to predict the behaviour of the lignocellulosic substrate during enzymatic hydrolysis. However, even if a plethora of models has already been published, only few of them take into account the morphology of the cellulosic substrate and its evolution during the saccharification step. The morphological aspect of the cellulosic matrix is yet strongly linked to the global performances of the enzymes. As it is drastically changed during the reaction, it has to be integrated into an heterogeneous predictive model. The model should also distinguish the action of the different types of enzymes, although several authors consider only a global effect of the cocktail on the cellulose hydrolysis. In the model proposed in this article, the substrate is only composed of many chains of cellulose gathered into fibers. The fibers have a cylindrical shape and comprise both external and internal areas. The endoglucanases and the cellobiohydrolases are adsorbed onto the accessible area and produce cellobiose by shrinking the fiber, while the b-glucosidases form a complex with the soluble cellobiose to produce glucose. The individual action of each enzyme, the synergy between the enzymes and the product inhibitions are also taken into account. The evolution of the concentrations of glucose, cellobiose and free enzymes calculated with the model agree well with the experimental data on short times (30 min). It has still to be validated on much longer periods. In this case the deactivation of the enzymes with time will be added. This model can help to understand the mechanisms implied in enzymatic hydrolysis of cellulose, and will be next extended to real lignocellulosic substrates containing lignin. Lignin has indeed two main impacts on the hydrolysis: its presence decreases the accessibility of cellulases to cellulose and reduces the quantity of efficient enzymes because a part of them is adsorbed on lignin in a non productive way. These influences will be further studied

Impact of delignification on the morphology and the reactivity of steam exploded wheat straw.

International audienceThe purpose of this article was to better understand the role of lignin in the recalcitrance of lignocellulosicbiomass during enzymatic hydrolysis. Steam exploded wheat straw was partially delignified with sodiumchlorite to six different grades of delignification. Delignification did not have a significant impact on theenzymatic hydrolysis of the studied wheat straw in the experimental conditions tested. Inhibitive impactof lignin in terms of non-productive adsorption was then explored using soda lignin from wheat straw andkraft lignin from softwood. The addition of both lignins had a strong negative influence on the hydrolysis of highly crystalline cellulose (Avicel), whereas it impacted only slightly the hydrolysis of delignifiedwheat straw. These results are probably linked to the greater accessibility and surface area of steamexploded wheat straw cellulose, which are much higher than those of the crystalline cellulose Avicel

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

A Review of Kinetic Modeling Methodologies for Complex Processes

In this paper, kinetic modeling techniques for complex chemical processes are reviewed. After a brief historical overview of chemical kinetics, an overview is given of the theoretical background of kinetic modeling of elementary steps and of multistep reactions. Classic lumping techniques are introduced and analyzed. Two examples of lumped kinetic models (atmospheric gasoil hydrotreating and residue hydroprocessing) developed at IFP Energies nouvelles (IFPEN) are presented. The largest part of this review describes advanced kinetic modeling strategies, in which the molecular detail is retained, i.e. the reactions are represented between molecules or even subdivided into elementary steps. To be able to retain this molecular level throughout the kinetic model and the reactor simulations, several hurdles have to be cleared first: (i) the feedstock needs to be described in terms of molecules, (ii) large reaction networks need to be automatically generated, and (iii) a large number of rate equations with their rate parameters need to be derived. For these three obstacles, molecular reconstruction techniques, deterministic or stochastic network generation programs, and single-event micro-kinetics and/or linear free energy relationships have been applied at IFPEN, as illustrated by several examples of kinetic models for industrial refining processes

A Review of Kinetic Modeling Methodologies for Complex Processes

In this paper, kinetic modeling techniques for complex chemical processes are reviewed. After a brief historical overview of chemical kinetics, an overview is given of the theoretical background of kinetic modeling of elementary steps and of multistep reactions. Classic lumping techniques are introduced and analyzed. Two examples of lumped kinetic models (atmospheric gasoil hydrotreating and residue hydroprocessing) developed at IFP Energies nouvelles (IFPEN) are presented. The largest part of this review describes advanced kinetic modeling strategies, in which the molecular detail is retained, i.e. the reactions are represented between molecules or even subdivided into elementary steps. To be able to retain this molecular level throughout the kinetic model and the reactor simulations, several hurdles have to be cleared first: (i) the feedstock needs to be described in terms of molecules, (ii) large reaction networks need to be automatically generated, and (iii) a large number of rate equations with their rate parameters need to be derived. For these three obstacles, molecular reconstruction techniques, deterministic or stochastic network generation programs, and single-event micro-kinetics and/or linear free energy relationships have been applied at IFPEN, as illustrated by several examples of kinetic models for industrial refining processes

Deep hydrodesulfurization of FCC gasoline and gas oil cuts: Comparison of CO effect, a by-product from biomass

International audienceRegarding the composition of the various feedstocks which should be hydrotreated inorder to obtain fuels with amount of sulfur less than 10 wt ppm, we have shown that thepresence of traces of CO, a by-product from lignocellulosic biomass feedstock conversion,inhibited the transformation of model compounds representative of FCC gasolines and gasoils over CoMo-based sulfide catalysts. Thus, this effect is more significant in the presenceof 2-methylthiophene and 2,3-dimethylbut-2-ene representative of a FCC gasoline than inthe presence of dibenzothiophene and 4,6-dimethyldibenzothiophene representative of astraight run gas oil, even if the operating conditions are not the same. This effect isattributed to phenomena of competitive adsorption between sulfur compounds, alkenesand CO on the catalyst surface