Absorption-désorption des gaz acides par des solutions aqueuses d'amines

A constant interfacial area gas-liquid reactor was designed to measure CO2 desorption rates from alkanolamines aqueous solutions. Experiments were achieved in an extended range of temperatures, 40°C - 110°C, with CO2 loadings in the range 0.05 - 0.85 molCO2/molamines, and with 25 and 50 wt % MDEA aqueous solutions, 45-5 and 30-20 wt % MDEA-DEA aqueous blends. An analytical method using thermodynamic and kinetic approximations represents the CO2 desorption rates from MDEA aqueous solutions, with loadings lower than 0.50 molCO2/molMDEA. It has been shown that it is necessary to use a general mass transfer model taking into account chemical reactions, coupled to a thermodynamic model representing CO2-H2O-Amines physical and chemical equilibria. A numerical tool was developed to represent the mass transfer phenomenon with chemical reactions. The liquid phase concentration profiles and flux rates for transferred species at the gas-liquid interface are obtained from the resolution of the material balance equations for each species. This kinetic model, combined with appropriate parameters, was successfully applied to the CO2 absorption into MDEA aqueous solutions, MDEA-MEA and MDEA-DEA aqueous blends. By coupling consistent kinetic and thermodynamic parameters, this tool gives a good representation of the desorption rates measured in the constant interfacial reactor.Une cellule à interface gaz-liquide fixe a été conçue pour la mesure de flux de désorption de dioxyde de carbone à partir de solutions aqueuses d'amines. Les expériences ont été réalisées pour des températures comprises entre 40°C et 110°C, pour des taux de charge en gaz acide compris entre 0,05 et 0,85 molCO2/molamines, à partir de solutions aqueuses de MDEA 25 % et 50 % massiques et de mélanges MDEA-DEA de composition 45-5 et 30-20 % massiques. L'utilisation d'une méthode analytique faisant intervenir des approximations thermodynamiques et cinétiques permet de représenter les flux de désorption expérimentaux obtenus avec les solutions aqueuses de MDEA pour des taux de charge inférieurs à 0,50 molCO2/molMDEA. Il est apparu nécessaire de coupler un modèle de transfert prenant en compte les réactions chimiques avec un modèle thermodynamique représentant les équilibres physiques et chimiques des systèmes CO2-H2O-Amines. Un outil numérique a alors été développé pour représenter les phénomènes de transfert en présence de réactions chimiques. Les profils de concentration de chaque espèce et le flux de transfert de l'espèce transférée à l'interface gaz-liquide sont obtenus à partir de la résolution des équations de bilan de masses. Ce modèle cinétique, combiné avec un jeu de paramètres adéquats, a été appliqué avec succès à la représentation de l'absorption de CO2 par des solutions aqueuses de MDEA et des mélanges aqueux de MDEA-DEA et MDEAMEA. En couplant des paramètres cinétiques et thermodynamiques cohérents, cet outil permet de représenter les flux de désorption mesurés dans la cellule à interface constante

Absorption-désorption des gaz acides par des solutions aqueuses d'amines

A constant interfacial area gas-liquid reactor was designed to measure CO2 desorption rates from alkanolamines aqueous solutions. Experiments were achieved in an extended range of temperatures, 40°C - 110°C, with CO2 loadings in the range 0.05 - 0.85 molCO2/molamines, and with 25 and 50 wt % MDEA aqueous solutions, 45-5 and 30-20 wt % MDEA-DEA aqueous blends. An analytical method using thermodynamic and kinetic approximations represents the CO2 desorption rates from MDEA aqueous solutions, with loadings lower than 0.50 molCO2/molMDEA. It has been shown that it is necessary to use a general mass transfer model taking into account chemical reactions, coupled to a thermodynamic model representing CO2-H2O-Amines physical and chemical equilibria. A numerical tool was developed to represent the mass transfer phenomenon with chemical reactions. The liquid phase concentration profiles and flux rates for transferred species at the gas-liquid interface are obtained from the resolution of the material balance equations for each species. This kinetic model, combined with appropriate parameters, was successfully applied to the CO2 absorption into MDEA aqueous solutions, MDEA-MEA and MDEA-DEA aqueous blends. By coupling consistent kinetic and thermodynamic parameters, this tool gives a good representation of the desorption rates measured in the constant interfacial reactor.Une cellule à interface gaz-liquide fixe a été conçue pour la mesure de flux de désorption de dioxyde de carbone à partir de solutions aqueuses d'amines. Les expériences ont été réalisées pour des températures comprises entre 40°C et 110°C, pour des taux de charge en gaz acide compris entre 0,05 et 0,85 molCO2/molamines, à partir de solutions aqueuses de MDEA 25 % et 50 % massiques et de mélanges MDEA-DEA de composition 45-5 et 30-20 % massiques. L'utilisation d'une méthode analytique faisant intervenir des approximations thermodynamiques et cinétiques permet de représenter les flux de désorption expérimentaux obtenus avec les solutions aqueuses de MDEA pour des taux de charge inférieurs à 0,50 molCO2/molMDEA. Il est apparu nécessaire de coupler un modèle de transfert prenant en compte les réactions chimiques avec un modèle thermodynamique représentant les équilibres physiques et chimiques des systèmes CO2-H2O-Amines. Un outil numérique a alors été développé pour représenter les phénomènes de transfert en présence de réactions chimiques. Les profils de concentration de chaque espèce et le flux de transfert de l'espèce transférée à l'interface gaz-liquide sont obtenus à partir de la résolution des équations de bilan de masses. Ce modèle cinétique, combiné avec un jeu de paramètres adéquats, a été appliqué avec succès à la représentation de l'absorption de CO2 par des solutions aqueuses de MDEA et des mélanges aqueux de MDEA-DEA et MDEAMEA. En couplant des paramètres cinétiques et thermodynamiques cohérents, cet outil permet de représenter les flux de désorption mesurés dans la cellule à interface constante

A New Reactive Absorption Model Using Extents of Reaction and Activities. I. Application to Alkaline-salts-CO2 Systems

International audienceCO2 absorption into basic aqueous solutions is widely used for CO2 separation from gas streams (e.g., for natural gas purification). CO2 loading and ionic strength increase significantly along industrial columns. In absorption modelling, deviation from ideality should then be considered.This study implements a general steady-state model for reactive gas-liquid absorption. Firstly, equilibrium relations, Nernst-Planck diffusion fluxes and reaction rates are written based on activities. Secondly, local fluxes are related by stochiometric constraints through extents of reaction. In a first case study, the model, together with an appropriate thermodynamic representation, was applied with the stagnant film theory (Whitman, 1923) to alkaline salts-water-CO2 systems. The following Arrhenius expression was found for the direct kinetic constant of reaction CO2 + HO- ↔ HCO3-: lnk (m3.mol-1.s-1) = 19.84 - 5248.8/T (K) – 12% overall AAD. This kinetic law can be used in any system involving this reaction (e.g., aqueous amine solutions). This part I paves the way to the further study of CO2 absorption into aqueous amine solutions

A new reactive absorption model using extents of reaction and activities. II. Application to CO 2 absorption into aqueous MDEA solutions

International audienceAbsorption into basic aqueous solutions is widely used for CO 2 separation from raw natural gas or from flue gases. This study implements a general steady-state model for reactive gas-liquid absorption. This work expands upon a first case study where the model was applied with the stagnant film theory (Whitman, 1923) to alkaline salts-water-CO 2 systems. This second case study uses the resulting Arrhenius expression to examine published CO 2 absorption and desorption flux data in MDEA-water-CO 2 system. Arrhenius parameters are optimised for the reaction CO 2 + MDEA + H 2 O ↔ HCO 3-+ MDEAH + with lnk (m 3 .mol-1 .s-1) = 16.69-6385/T (K). Results emphasise the role of CO 2 physical solubility representation in reactive absorption model overall performance. Global modelling is needed: kinetic parameters should be used together with all underlying parameters with which they were obtained. The relevance of activity-based modelling is shown, especially at high CO 2 absorption/desorption driving force

Absorption de gaz par des solutions réactives : adaptation de l’instrumentation d’une cellule agitée d’étude cinétique et application à des systèmes CO2/amines

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Selective transformation of methyl and ethyl mercaptans mixture tohydrocarbons and H2S on solid acid catalysts

International audienceThe catalytic conversion of C2H5SH on protonic molecular sieves, i.e. ZSM-5 with various Si/Al ratios,Ferrierite, Y, SAPO-34, was studied in a gas flow reactor. Ethylene and H2S are the main products, butsmall amounts of C1-C4 alkanes, C6-C8 aromatics, coke, CS2and thiophenes are formed. The catalyticbehavior strongly depended on both acidic and textural properties of solids. Assuming a pseudo first orderkinetic model, the rate constant and the activation energy have been evaluated for all catalysts. Over thebest catalytic material, H-ZSM-5 (Si/Al = 15), full conversion of C2H5SH was achieved at temperaturehigher than 673 K. Additionally, the catalyst lifetime measured at 823 K was more than 70 h of time-on-stream. With C2H5SH/CH3SH mixture, over H-ZSM-5, the conversion of thiols was total at 823 K for atleast 11 h. In that case, significant amounts of coke and aromatics were formed, but after the thermalregeneration with air, the spent catalyst recovered the properties of the fresh zeolite

A highly efficient process for transforming methyl mercaptan into hydrocarbons and H2S on solid acid catalysts

International audienceThe catalytic conversion of CH3SH and CH3SCH3 (DMS) on protonic zeolites H-ZSM-5, H-Y and H-ferrierite was studied in a gas flow reactor from 423 to 823 K. Below 700 K, CH3SH is converted at equilibrium into DMS and H2S. Above 700 K, light alkanes (C1-C3), benzene, toluene and xylene appear alongside H2S in the gas phase, and a carbonaceous deposit builds up on the catalyst. DMS is assumed to be the intermediate in the CH3SH transformation into H2S and hydrocarbon species. At 823 K, the CH3SH conversion is total on H-ZSM-5, and only partial on H-Y and H-ferrierite. These are selective to alkanes, and produce large quantities of coke. In contrast, much less coke builds up on H-ZSM-5, which is also more selective to aromatics. After calcination in air flow at 823 K, the spent H-ZSM-5 sample recovers the properties of the fresh catalyst. Similarities and differences with the methanol-to-hydrocarbons process are discussed

Conversion of methyl mercaptan and methanol to hydrocarbons over zeolites - a comparative study

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