Degradation of 22 compounds was evaluated in stainless steel batch reactors at 140 °C for 14 days under a pressure of 0.5 MPa (mixture of 75% CO2, 20% N2, and 5% O2). For each run, two corrosion coupons, one carbon steel (XC38) and one stainless steel (304Ti), were immersed in aqueous solutions of amines to determine corrosion due to degraded solutions. Two additional coupons were put in the vapor phase above solutions. At the end of the run, corrosion rates were evaluated through weight-loss measurements. The amounts of remaining starting material were determined with a quantitative gas chromatography method. Corrosion and degradation data were compared with those of a benchmark molecule (MEA, monoethanolamine), tested under the same conditions. Results indicate that some molecules are less corrosive and have a better chemical stability than MEA. In addition, a quantitative structure property relationship (QSPR) model was built that can be applied to predict compound degradation.
Re´sume´-Cine´tique du dioxyde de carbone avec les amines -I. É tude par stopped-flow en solution aqueuse. Une revue -Il est possible de trouver de nombreuses informations sur la cine´tique de re´action amine-CO 2 dans la litte´rature. Toutefois, comme il existe plusieurs techniques expe´rimentales et plusieurs me´canismes re´actionnels possibles, on observe parfois une grande dispersion des re´sultats expe´rimentaux avec diverses interpre´tations. Dans cet article, une me´thode qui permet de comparer les constantes cine´tiques obtenues par diffe´rents auteurs est propose´e. D'abord nous pre´sentons les diffe´rentes techniques expe´rimentales et justifions de comparer les donne´es obtenues par la technique d'e´coulement a`flux bloque´. Ensuite nous repre´sentons les donne´es cine´tiques des diffe´rentes amines e´tudie´es dans la litte´rature a`partir d'une de´pendance en loi puissance en fonction de la concentration. Cette repre´sentation illustre certaines relations structure-proprie´te´et permet de confronter les donne´es expe´rimentales aux diffe´rents me´canismes propose´s. Les avantages et limites de chaque me´canisme sont discute´s. Finalement nous justifions l'utilisation d'un mode`le termole´culaire pour comparer les donne´es obtenues par diffe´rents auteurs. Ce mode`le conduit a`l'observation d'un phe´nome`ne de compensation qui est un argument en faveur du me´canisme correspondant.Abstract -Kinetics of Carbon Dioxide with Amines. I. Stopped-Flow Studies in Aqueous Solutions. A Review -It is possible to find plenty of information about kinetics of reaction between amine and carbone dioxide in the literature. However, there are several experimental techniques and several possible mechanisms which lead to observe sometimes high dispersion of experimental results with various interpretations. A method which enables to compare kinetic constant got by different authors is proposed in this work. First, we present experimental techniques and justify comparison of data obtained by stopped-flow technique. Then, we plot kinetic data for all amines studied in the literature by a power law dependency with the concentration. This representation illustrates some structureactivity relationships and enables to confront experimental results with the different mechanisms. Advantages and limits of each mechanism are discussed. Finally, we justify the choice of the termolecular model to compare data got by different authors. This model leads to a compensation effect which is an argument in favour of this mechanism.
BackgroundAn efficient hydrolysis of lignocellulosic substrates to soluble sugars for biofuel production necessitates the interplay and synergistic interaction of multiple enzymes. An optimized enzyme mixture is crucial for reduced cost of the enzymatic hydrolysis step in a bioethanol production process and its composition will depend on the substrate and type of pretreatment used. In the present study, an experimental design was used to determine the optimal composition of a Trichoderma reesei enzyme mixture, comprising the main cellulase and hemicellulase activities, for the hydrolysis of steam-exploded wheat straw.MethodsSix enzymes, CBH1 (Cel7a), CBH2 (Cel6a), EG1 (Cel7b), EG2 (Cel5a), as well as the xyloglucanase Cel74a and the xylanase XYN1 (Xyl11a) were purified from a T. reesei culture under lactose/xylose-induced conditions. Sugar release was followed in milliliter-scale hydrolysis assays for 48 hours and the influence of the mixture on initial conversion rates and final yields is assessed.ResultsThe developed model could show that both responses were strongly correlated. Model predictions suggest that optimal hydrolysis yields can be obtained over a wide range of CBH1 to CBH2 ratios, but necessitates a high proportion of EG1 (13% to 25%) which cannot be replaced by EG2. Whereas 5% to 10% of the latter enzyme and a xylanase content above 6% are required for highest yields, these enzymes are predicted to be less important in the initial stage of hydrolysis.ConclusionsThe developed model could reliably predict hydrolysis yields of enzyme mixtures in the studied domain and highlighted the importance of the respective enzyme components in both the initial and the final hydrolysis phase of steam-exploded wheat straw.
Background: An efficient hydrolysis of lignocellulosic substrates to soluble sugars for biofuel production necessitates the interplay and synergistic interaction of multiple enzymes. An optimized enzyme mixture is crucial for reduced cost of the enzymatic hydrolysis step in a bioethanol production process and its composition will depend on the substrate and type of pretreatment used. In the present study, an experimental design was used to determine the optimal composition of a Trichoderma reesei enzyme mixture, comprising the main cellulase and hemicellulase activities, for the hydrolysis of steam-exploded wheat straw. Methods: Six enzymes, CBH1 (Cel7a), CBH2 (Cel6a), EG1 (Cel7b), EG2 (Cel5a), as well as the xyloglucanase Cel74a and the xylanase XYN1 (Xyl11a) were purified from a T. reesei culture under lactose/xylose-induced conditions. Sugar release was followed in milliliter-scale hydrolysis assays for 48 hours and the influence of the mixture on initial conversion rates and final yields is assessed.Results: The developed model could show that both responses were strongly correlated. Model predictions suggest that optimal hydrolysis yields can be obtained over a wide range of CBH1 to CBH2 ratios, but necessitates a high proportion of EG1 (13% to 25%) which cannot be replaced by EG2. Whereas 5% to 10% of the latter enzyme and a xylanase content above 6% are required for highest yields, these enzymes are predicted to be less important in the initial stage of hydrolysis.
-Approche QSAR Graph Machines pour la modélisation des propriétés thermodynamiques des amines : application au captage du CO 2 en postcombustion-Le procédé d'absorption aux amines est considéré comme la technologie la plus efficace pour limiter les rejets de CO 2 dans le cadre du captage en postcombustion puis du stockage du CO 2. Cependant, l'optimisation des propriétés du solvant nécessite d'évaluer un grand nombre de candidats potentiels et donc de collecter une quantité importante de propriétés expérimentales. Dans ce contexte, l'utilisation de méthodes de modélisation statistique de type QSAR (Quantitative Structure Activity Relationship) s'avère être un outil très précieux puisqu'elles permettent d'établir une relation entre un ensemble de vecteurs d'entrées (i.e. les caractéristiques ou les propriétés des molécules étudiées) et un ensemble de vecteurs de sorties (i.e. les propriétés ciblées). Dans ce travail, nous avons utilisé un équipement d'expérimentation à haut débit pour mesurer la solubilité du CO 2 dans un ensemble de 46 solutions aqueuses d'amines. Les isothermes d'absorption sont modélisées en utilisant une approche thermodynamique basée sur l'évaluation de deux constantes d'équilibres, pKa * et pKc * caractéristiques des principales réactions chimiques intervenant dans la phase liquide. Nous avons ensuite utilisé une approche statistique baptisée graph machines à la fois pour classifier les molécules et modéliser la variation de la constante d'acidité pKa * en fonction de la structure moléculaire. L'originalité de notre approche réside dans l'utilisation des graphes associés aux molécules afin de les représenter dans des espaces multidimensionnels et construire, en même temps, un modèle prédictif de leurs propriétés physico-chimiques. Cette approche est appliquée dans cet article pour prédire les propriétés thermodynamiques d'un ensemble de 5 nouvelles molécules.
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