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International audience; Ammonia has a potential as carbon-free and high-energy density compound for chemical storage of renewable energies and its synthesis from green H2 requires to be as energetically efficient as possible. In this work, a superstructure optimization methodology for process synthesis is proposed and applied to an ammonia production process. The approach covers three different scales: process, equipment, and molecules. Process scale refers to finding the optimal process structure, while the equipment scale is related to the best set of operating conditions, and the molecular scale studies two catalysts (Fe and Ru) with their respective kinetic rates. The optimization intends to minimize the Levelized Cost of Ammonia (LCOA) and maximize the energy efficiency. The best trade-off is found with the Ru catalyst, with an LCOA of 766 €/tNH3 and 57.2 % of energy efficiency. In comparison with reference cases, the LCOA decreases 0.6 % and the energy efficiency increases 1.5%. The main improvement is found in the pressure, 75 bar, reduced in 25 %. The production of 11.6 tNH3/day equals to 2.5 MW of stored power from 3 MW supplied as H2 to the process, with a total energy consumption of 10.67 kW h/kgNH3, including prior H2 and N2 production processes.

International audience; The influence of the mixer shape on the stereoselectivity was measured for lithium–bromine exchange on a gem-dibromoalkene followed by proton trapping. Sixteen passive mixers with eight different angles (135, 120, and 105° (Y mixers); 90° (T mixer); 75, 60, 45, and 30° (W mixers)) and two internal diameters (500 and 250 μm) associated with a tubular microflow reactor having an internal diameter of 500 μm were used. The 45° W-shaped mixer with a smaller internal diameter gave the best selectivity for the monobrominated E product over a range of flow rates without the usual cryogenic conditions (20 °C). With methyl benzoylformate as the electrophile, the corresponding polyfunctionalized product was obtained in a space-time yield of 81 kg L–1 h–1.

L’intensification des procedes est un concept applicable a de nombreuses industries de transformation de la matiere et de l’energie. De nombreuses operations unitaires sont toutefois limitees par les caracteristiques geometriques des equipements (reacteurs, echangeurs de chaleurs, melangeurs…) qui leur sont associees. Les procedes de fabrication de ces equipements peuvent etre une limite au developpement d’appareillages plus complexes, pour atteindre des niveaux de compacite et d’efficacite superieurs aux solutions existantes. Cet article a pour objectif de presenter et d’exemplifier les nouvelles opportunites offertes par la fabrication additive pour la conception et la realisation d’equipements permettant l’intensification des procedes.

International audience; This paper focuses on the best way to produce methanol by Coke Oven Gas (COG) conversion and by carbon dioxide capture. The COG, produced in steelworks and coking plants, is an interesting source of hydrogen that can be used to hydrogenate carbon dioxide, recovered from flue gases, into methanol. The architecture of the reuse process is developed and the different process units are compared by considering a hierarchical decomposition. Two case studies are selected, process units are modelled, and flowsheets are simulated using computer-aided design software. A factorial techno-economic analysis is performed together with a preliminary carbon balance to evaluate the economic reliability and the environmental sustainability of the proposed solutions. The production costs of methanol are equal to 228 and 268 €/ton for process configurations involving, respectively, a combined methane reforming of COG and a direct COG separation to recover hydrogen. This cost is slightly higher than the current price of methanol on the market (about 204 €/ton for a process located in the USA in 2013). Besides, the second case study shows an interesting reduction of the carbon footprint with respect to reference scenarios. The carbon dioxide capture from flue gases together with COG utilization can lead to a competitive and sustainable methanol production process depending partly on a carbon tax.

International audience; The design of sustainable energy systems requires to enlarge the analysis beyond the traditional boundaries for including the economic, environmental, and societal needs and constraints in the decision-making process. In this regard, this work investigates the conceptual design of distributed energy systems by means of a multi-objective optimization strategy to simultaneously address the economic, environmental, and social aspects in the energy system design. Initially, the water consumption and the inherent safety indicators were introduced and evaluated through two single-objective optimization problems to enhance the analysis of the environmental and social dimensions of sustainability. Then, a framework including the total annualized cost, CO2 emissions, water consumption, grid dependence, and inherent safety index was used to perform the multi-objective analysis. To carry out a thorough and comprehensive analysis, four optimization problems including different combinations of the sustainability indicators were proposed and solved. The compromise among the objective functions was identified, and the obtained Pareto sets were explored for elucidating the changes in the design and operating conditions across the non-dominated solutions. According to results, the cost of energy can range between 0.37 and 0.63 €/kWh, the CO2 emissions can vary between 10.6 and 68.5 kgCO2/MWh, and the water consumption can be between 27.8 and 70.2 m3H2O/GWh depending on the evaluated objective. Moreover, it was determined that the safety of the energy system can be improved by increasing the use of the water electrolysis pathway to produce hydrogen and by reducing the capacity of the hydrogen storage unit.

International audience; The growing concerns about climate change and energy security have led to a shift in the paradigm of the energy framework. In this regard, distributed generation offers the possibility to deal with inefficiencies in energy delivering, and the fossil fuel dependence of conventional and centralized power plants. This work presents a modeling and multi-criteria optimization strategy for designing and operating decentralized power plants including different energy vectors. The modeling approach considers the time-varying operation of the energy conversion units for responding to electricity and hydrogen demands, along with the seasonal behavior of the storage system. A multi-criteria evaluation addressing economic, environmental and social aspects was implemented. The objective functions are the total annualized cost, the CO2 emissions and the grid dependence. According to optimization results, it is highlighted the influence of the assessed criteria upon the structure and the operating policy of the power plant. Additionally, by comparing the performance of the distributed energy system with respect to a centralized scenario, it is noted the significant potential of the decentralized generation. Indeed, depending on the optimization goal, CO2 emission reduction up to 89%, and self-sufficiency up to 81% can be achieved.

A one-dimensional model of catalyst-coated fin in plate-fin heat exchanger reactors was developed in this study to consider the effects of heat of reaction on the fin efficiency. The results of the model showed that the occurrence of a surface reaction must be treated carefully since it drastically changes fin behaviour compared to conventional thermal fins. The impact of dimensionless numbers representing the coupling between fin geometry, surface reaction and heat and mass transfer was investigated, and limit conditions where a reactive fin behaves as a conventional thermal fin was circumscribed according to these parameters. The results of the developed reactive fin model were also compared to computational fluid dynamics simulations and showed very good representativeness for all heat transfer, reaction and by-pass effects. The comparison demonstrated that this simplified model is strong enough to represent reactive fins on the surface of which a catalytic surface reaction occurs, for both laminar and turbulent flows in square millichannels.

Adequate and accurate models describing quantitatively the syntheses of fine and pharmaceutical chemicals are essential to optimize the performances of chemical processes. However, it is difficult, time consuming and experimentally expensive to develop such models. Appropriate, efficient and systematic strategies for model development are therefore required. In this context, the aims of this work consist in methodological development, numerical implementation and experimental validation of a systematic model-development strategy. In the first stage of this work, a methodologically systematic model-development strategy, consisting of initial data acquisition, model development, model identification, model validation and model refining modules, is developed. In the initial data acquisition module, preliminary experiments are designed and performed to provide the basic information for the initial model development. Module development module is composed of three steps: model structure development, model structure analysis and model parameter development. Model structure development is based on the reaction network proposed within the reaction supernetwork containing all feasible chemical reactions and mass transfers. For model identification, validation and refining, the model-based experimental design is performed by taking into consideration several reactors, which enlarges the explored experimental windows. In the second stage of this work, in order to facilitate the application of the strategy, a software, integrating model parameter estimation, model evaluation, model-based experimental design for model refining and performance optimization, is developed using MATLAB R2014a. The initial version of the software is suitable for the liquid-phase reaction systems, 4 ideal reactors are taken into consideration: batch stirred-tank reactor, semi-batch stirred-tank reactor, continuous stirred-tank reactor and continuous tubular reactor. In the third stage of this work, the feasibilities and generalities of the developed strategy and strategy-based software are demonstrated with two experimental case studies, relating to the valorization of sunflower oil, namely, NaOH-catalyzed ethanolysis of sunflower oil and epoxidation of sunflower oil by performic acid generated in situ.

La chimie en flux est une methode de synthese proposee depuis quelques annees dans le domaine de la chimie organique pour ameliorer le controle des conditions de reaction afin de maximiser les conversions et les rendements, mais dont les avantages sont souvent plus nombreux. Le present article vise a introduire et expliquer les principaux concepts theoriques utiles a l’experimentateur qui souhaite mettre en œuvre les dispositifs de la chimie en flux et comprendre les resultats obtenus. Il presente les principales limitations a la reaction que sont les transferts de matiere et de chaleur et leur impact sur la selectivite des reactions.

International audience; A continuous pilot-scale tubular reactor is designed for the polymerization of acrylic acid in aqueous solution. The reactor is equipped with CSE-X static mixers from Fluitec which strongly increase heat and mass transfer despite laminar flow. A mathematical model of the reactor is proposed assuming that it is a perfect plug-flow reactor and using kinetic and rheological equations previously established using a lab-scale rheo-Raman device. Calculated values of temperature and polymer concentration profile along the reactor as well as outlet average molar masses and viscosity are in good agreement with experimental results. Provided that the outlet viscosity of reaction medium does not exceed 0.5 Pa s, no reactor fouling occurred. On the contrary, fouling is detected after 6 to 8 h running with higher viscosities. This work is the first demonstration of applicability of CSE-X static mixer elements in a continuous polymerization process producing high molar mass water-soluble polymer. In addition, successful scale-up of polymerization reactor is reported up to pilot-scale as well as batch to continuous transposition, only on the basis of lab-scale rheo-Raman data. The interest of rheo-Raman device for the acquisition of primary data is established.

International audience; Currently, a significant transformation for energy systems has emerged as a result of the trend to develop an energy framework without fossil fuel reliance, the concerns about climate change and air quality, and the need to provide electricity to around of 17% of world population who lacks the service. Accordingly, the deployment of power plants located close to end-users and including multiple energy sources and carriers, along with the growing share of renewable energies, have suggested changes in the energy sector. Despite their potential capabilities, the design of distributed energy systems (DES) is a complex problem due to the simultaneous goals and constraints that need to be considered, as well as to the high context dependence of this kind of projects. For these reasons, in this work a systematic literature review of DES including hydrogen as energy vector, was made analyzing 106 research papers published between the years 2000–2018, and extracted from Scopus® and Web of Science databases. The aim was to identify how hydrogen is employed (technologies, uses) and the criteria that are evaluated (economic, technical, social and environmental) when these systems are designed, planned and/or operated. The results constitute a baseline information covering the type of technologies, equipment sizes and hydrogen applications, that could be valuable for the preliminary stages of research or project planning of DES involving hydrogen. Furthermore, other factors have also been identified, such as the focus on techno-economic issues, and the lack of considering socio/political aspects and the uncertainty about input data like weather conditions, energy prices and demands. Additionally, a more integrated approach is needed including all the hydrogen supply chain stages and project stakeholders, to tackle issues like safety of the energy systems that could produce consumer rejections.

International audience; This work studies how deeply the reagents choice influences micromixing characterisation by the Villermaux-Dushman method, when applying it to a 1 litre stainless steel standard vessel with two baffles, stirred by an inclined blade turbine. For the first time, borate and phosphate buffer are compared on their use in the method. It is observed that triiodide production is higher when borate buffer is used. Moreover, perchloric acid leads to higher triiodide production than sulphuric acid, when injecting the same concentration of both acids. Finally, the influence of the ionic strength is also studied, since there has been a great deal of controversy about it over the last years. The results show that the ionic strength affects triiodide production, although relatively slightly. Advice concerning the choice of the reagents is given in conclusion.

Kinetics of methanol synthesis from carbon dioxide hydrogenation is studied on two noncommercial catalysts: a copper–zinc oxide catalyst on alumina (CuZA) and a copper–zinc oxide catalyst on zirconia (CuZZ). The experiments have been performed in an isothermal fixed bed reactor with a temperature range between 200 and 230 °C, a total pressure comprised between 50 and 80 bar, a gas hourly space velocity (GSHV) between 7800 and 23 400 h–1 and for different hydrogen:carbon dioxide molar ratios (between 2 and 6). Unlike other works in the literature, no carbon monoxide is contained in the feed which corresponds to the conditions of some recent industrial applications, the influence of the catalyst support has been tested to improve the methanol selectivity. The experimental data were modeled using the kinetic laws and adsorption coefficients determined by Graaf et al. based on a Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism. The reactor model was based on an isothermal pseudo-homogeneous plug flow model...

International audience; The objective of this article is to find the optimal dimensions of rectangular plate-type micro-separators in order to enhance the continuous separation of immiscible liquids. The main structure of the separators contains two plates: a hydrophobic (PTFE) upper plate and a hydrophilic (stainless steel) bottom plate which formed the contact surfaces for the fluids in the channel. The devices have two outlets, one for the aqueous phase and the other for the organic phase enabling the continuous separation and withdrawal of the separated phases. Demulsification has been carried out using Shellsol/water emulsion in the presence of a non-ionic surfactant (Teen 80). The separation efficiency is investigated as a function of micro-separator sizes, channel depths, flow rates and plate configurations. The major parameter that controls the destabilization mechanism is the ratio between the droplet size and the channel depth. When the size of the dispersed droplets remains smaller than the height of the separator (channel depths: 25-100 mu m), creaming is the main demulsification mechanism. Creaming refers to the migration of the dispersed phase of an emulsion, under the influence of buoyancy. The particles float upwards and rise to the top due to the difference in the densities of the particles and the medium. The separation efficiency depends mainly on the residence time of the liquid/liquid mixture in the device regardless of the separator dimensions and channel heights. The separation rate is limited by the removal of the cream layer, formed at the top of the upper plate, from the separator. When the size of the dispersed droplets is larger than the depth of the separator (channel height of 9 pm), the separation performance and mechanism become different. The coalescence of the dispersed droplets occurs by passing through the device. The comparison of the data corresponding to creaming and coalescence phenomena emphasizes that the coalescence greatly enhance and accelerate the separation action. The phase separation in the micro-coalescer takes place considerably faster than in the micro-separators.

International audience; Process intensification is recognized as a promising strategy to satisfy the objectives of sustainable development and economic competitiveness. Unfortunately, no general methodology still enables to choose the best available technologies from the many potential solutions. This work describes a step-by-step methodology that guides engineers from a given problem to a list of existing appropriate intensified devices. The first step of the methodology consists in identifying the process limitation among a list of 16 possibilities that cover a large spectrum of cases. Then, the methodology relates, through a prefilled connection matrix, the identified limitations to a set of intensification strategies such as geometric (micro)structuring, periodic operation or multi-scale design. The third step relates these strategies to a list of technologies that apply these strategies or in which they can be applied. The matrices enable to sort these technologies by relevance with respect to the initial problem. The final step provides quantitative charts to compare the characteristics of these potential solutions with the specifications of the problem. The methodology not only yields to a short list of appropriate solutions to be technically designed and economically assessed, but also to a list of innovation strategies.

International audience; A pilot-scale tubular reactor containing static mixers is equipped with several Raman probes in order to perform online monitoring of radical copolymerization of acrylic acid in aqueous solution. This setup allows determination of residence time distribution while polymerization reaction occurs, using sodium nitrate as a tracer. These results prove that the use of convenient static mixers allows obtaining a nearly perfect plug-flow reactor in all explored conditions (reactive and nonreactive medium, between 0.001 and 1 Pa s viscosity). Furthermore, the dynamics of the pilot-scale reactor is characterized. Experimental transient and steady-state values are compared to predictions based both on residence time distribution and model of polymerization kinetics. The applicability of Raman spectroscopy to online monitoring of pilot-scale reactors is demonstrated.

International audience; A complete mathematical model of the free-radical copolymerization of acrylic acid in an aqueous solution, taking place in a pilot-scale tubular reactor equipped with static mixers, is presented. The developed kinetic/reactor model is numerically integrated in terms of a coupled deterministic-stochastic numerical approach that combines the advantages of speed, efficiency, and increased predictive capabilities. A series of experimental measurements on the monomer conversion and the molecular weight characteristics of the produced copolymer, under a wide range of process conditions, are used for the identification of the kinetic model parameters while a thorough analysis of the compositional characteristics of the produced copolymers is also carried out in terms of a series of bivariate distributed properties

Process intensification and micro-structured reactor design can be relevant means to improve the safety of a process involving hazardous substances. This work deals with the intensification of a chlorination reaction usually performed in batch mode, using thionyl chloride (SOCl2) to chlorinate a sterically hindered carboxylic acid dissolved in dimethylacetamide (DMAC). This chlorination reaction involves the exothermic formation of a species called Vilsmeier reagent, resulting from a reaction between SOCl2 and DMAC. In order to intensify this process, a reaction scheme with kinetic and thermal data is identified in the first place. This model is then used to suggest how the chlorination reaction could be carried out in a continuous mode and under which optimal operating conditions it should be operated. Tests are then conducted using a lab-scale microreactor providing good mixing and heat exchange, resulting in better performances than the batch process, within seconds of residence time. Further tests are performed at larger scale using a pilot-scale microreactor, designed to achieve the same yield and quality performances as the lab-scale microreactor with a higher throughput, as long as residence time, ratio between reactants and temperature remain constant.

International audience

International audience; A laboratory pilot unit has been developed to solve the issues of thermodynamic equilibrium shift for the transesterification of vegetable oil into biodiesel. It consists in a two stages continuous heterogeneous catalytic reactor operating at 50 bar and 175 degrees C. Under the working conditions, only one homogeneous phase can be assumed. The reactions of transesterification need a large excess of methanol implying an additional energy consumption and higher capital expenditure because of larger size of equipments, and operating pressure. In this work, a numerical model has been developed in order to better understand the different coupled phenomena (thermodynamic equilibrium, kinetics, mass transfer limitations, etc.) governing biodiesel production. The model is based on a heterogeneous plug flow reactor with axial dispersion taking into account mass transfer in the catalyst and dynamic aspects. The reactor is supposed isothermal since transesterification reactions are almost athermic. Kinetic parameters have been optimized by comparison with experimental results previously obtained by IFPEn. Simulation results are used to establish the future experimental conditions that will be used on the pilot unit. Mass transfer limitations are characterized by changing the diameter of catalyst particle. Concentration and reaction rate profiles are depicted in the fluid phase and in the catalyst. The simulations indicate that a conversion of triolein of 87% can be reached with a methanol to triolein molar ratio of 36 at reactor inlet and with a mean residence time of 1 h.

A falling film micro-absorber (FFM) is used to treat gas effluents containing a chlorinated VOC. In such operation, mass transfer can be enhanced by optimizing micro-absorber geometry and operating conditions. Firstly, the influence of gas cavity thickness and gas flow rate on absorption performances, were investigated. Experimental study is performed for a range of cavity thickness between 2 and 6 mm and gas flow rate between 45 and 390 N mL/min. Results showed a significant improvement of absorption rate when cavity thickness is reduced, especially for low gas velocities. Indeed the global mass transfer coefficient K G a can be multiplied by 7 when cavity thickness is divided by a factor of 3. The mass transfer is then intensified and apparatus compactness is enhanced. The modeling of gas/liquid mass transfer ( Monnier and Falk, 2011 ) indicated that mass transport is performed mainly by diffusion. A new simulations showed an important axial dispersion in gas concentrations profile when gas flow rate and gas cavity thickness are relatively high ( t G =5–6 mm, G V >400 N mL/min). Then, to optimize micro-absorber performances, the integration of gas turbulence promoters must be considered. The second part of this paper concerns the characterization of gas-side mass transfer in the FFM. A dimensionless correlation is developed: S h G = 2.04 R e G 0.23 S c G 0.5 ( t G / Z ) 0.17 When compared to other relations found in literature, this correlation characterizes gas laminar flow in this kind of micro-structured device.

International audience; The falling film microabsorber developed by the Institut für Mikrotechnik Mainz is used to study its performance for the treatment of VOC-containing gases. The technique used is the gas/liquid absorption. The gas (mixture of air and tetrachloroethylene) and the solvent (Di(ethyl-2-hexyl) adipate, DEHA) flow counter-currently in the microabsorber. The solvent streams by gravity on a plate structured by microchannels. This technique makes it possible to miniaturize the process by increasing the mass transfer flow per volume unit as explained in Part I. Experiments are presented and a model is developed from equations of mass and momentum transfers. Results show a competition between two transport phenomena: diffusion and convection. The mass transfer rate is also studied with respect to the structure of microabsorber. It is also shown that it is possible "to optimize" the geometry of the apparatus in order to intensify the transfer so as to miniaturize the process. In the case of physical absorption, mass transfer intensification ( Murphree Efficiency) increases when the number of transfer unit NTU G (= τ/ t transfer) increases too. It is mainly due to the small volume of the apparatus where the gas phase residence time must be taken into account in the study of the mass transport towards the gas/liquid interface: the radial and the axial distances for the mass transfer and the mass transport have the same order of magnitude.

International audience; The present study investigates evaporation and separation of a binary mixture of ethanol and n-propanol in a microstructured falling film contactor made from two electrically heated vertical plates grooved with straight microchannels and forming the sides of a common gas chamber. Experiments were performed at atmospheric pressure (101.3 kPa) and various wall temperatures above the saturation temperature of the inlet binary mixture. Electrical heating fluxes ranged from 2 to 4 kW/m2 and feed flowrate between 1 and 8 g/min. The feed concentration was fixed around 46 mol.% of ethanol. The results indicate that the microcontactor performances depend essentially on heat flux and feed flowrate and provide fundamental insight on critical values of these two factors. Analysis of the results point out that intermittent local dry-zone can occur at high heat flux or at low feed flow rate. This occurrence influences microcontactor performances which can be evaluated in terms of stripping efficiency and power of separation.

The absorption of tetrachloroethylene – the VOC – in di-ethyl-hexyl-adipate – the solvent – was carried out as an example of gaseous waste treatment. Two gas–liquid contactors were used: a column provided with as structured Sulzer EX ® packing and a microstructured falling-film absorber provided with thin vertical channels, manufactured by the Institut fur Mikrotechnik Mainz (IMM). The overall transfer coefficient of VOC, K G a , was calculated from the absorption efficiency of the various runs carried out, allowing comparison of the two gas–liquid contactors. Due to the high solubility of the considered VOC, mass transfer was shown to be mainly controlled by gas-side transfer rates. Transfer coefficient K G a of the two absorbers were found to be comparable, but with gas and liquid velocity in the microstructured absorber from one to two orders of magnitude below those in the column, expressing the high transfer performance offered by the microsystem. Moreover, the thickness of the liquid film in the channels was below 100 μm, much lower than that in a structured packing near 500 μm. This shows that lower liquid flow rates can be used for efficient absorption in the microsystem. It is shown that contrary to conventional structured packing, the designed contact specific area in the microabsorber strictly corresponds to the interfacial G / L surface. This enables more compact and to miniaturize G / L contactors to be designed.

International audience

International audience; The benefits and drawbacks of micro-monoliths with respect to conventional monoliths, for heterogeneous reactions in a gaseous phase, have been described experimentally in numerous studies. In this work, the interest of using a micro-monolith is demonstrated by achieving a preliminary analysis and by solving an isothermal model of the monolith. Ethanol steam reforming to produce hydrogen is considered as a case study to evaluate the performances of three different devices (having different channel diameters) used in an experimental study of Casanovas et al. [1]. To get a better understanding of the experimental results, simulations are performed in a new way, more suitable for a clearer comparison between the different devices. In kinetic regime, the better performance of a micro-monolith with respect to other devices is due to a higher catalyst amount per unit of reactor volume. The main interest of using a micro-monolith is a high compactness for a quite slow chemical reaction, while for a very fast one, the main interest is to avoid mass transfer limitations. Finally, a map representing the Damkholer number for a first order chemical reaction provides information to wisely choose the channel diameter of a monolith.

International audience; The transesterification of vegetable oils by methanol implies a set of three parallel–series reversible reactions. Over a heterogeneous catalyst, reactions are limited by molecular diffusion, resulting in the use of a large excess of methanol to achieve a high conversion. This excess is detrimental to process efficiency because it involves large energy requirement for downstream separation. In order to identify the coupled physico-chemical phenomena and to optimize the process, a pilot unit was developed to perform transesterification of triglycerides with methanol over a solid ZnAl2O4 catalyst in a tubular fixed bed reactor under high pressure and temperature. The effects of different parameters such as particle diameter, temperature, residence time and molar feed ratio of methanol to triglyceride on fatty acid methyl ester (FAME) yield and triglyceride (TG) conversion were studied. A pseudo-homogeneous reactor model has been developed to identify rate laws and kinetic parameters by exploiting the experimental data in stationary regime. A set of kinetic constants was also determined for the given catalyst considering two kinetic models: an Eley–Rideal model with the reaction between TG and methanol as the rate determining step and a classical second order model taking into account thermodynamic equilibrium without adsorption. A heterogeneous model has also been established to determine molecular diffusion coefficients for each species in the mixture, through the use of experimental results in the transient regime. These molecular diffusion coefficients are dependent on the mixture viscosity and temperature. As a result, it was determined that diffusion of triglycerides and the first reaction kinetic rates are limiting the global conversion of the system.

On the basis of the experimental works of Krummradt et al. (1999), this paper shows how it is possible, for certain systems of reactions, to reduce considerably the operations times from a semi-batch stirred tanks to a continuous microreactor, in which mixing and heat transfer are intensified. In the case of the Grignard reaction, we demonstrate that it is so possible to reduce the operation time from 5 h to less than 10 s. However, to reach the productivity of the industrial 6 m 3 stirred tank, it is necessary to use five minireactors in parallel. For such exothermic reactional systems, the field of interest for an intensified reactor use as an industrial production tool is specified.

Resume A partir d'une representation analytique simple d'un procede comportant des operations de transfert et/ou de reaction, on relie l'efficacite du procede au rapport de 2 constantes de temps : le temps de passage du fluide et le temps caracteristique d'operation. L'analyse de l'evolution du temps caracteristique d'operation en fonction des dimensions caracteristiques du systeme montre, en fonction de la nature de l'operation, comment la microstructuration permet d'ameliorer les performances et/ou de miniaturiser le procede etudie. Pour citer cet article : J.-M. Commenge et al., C. R. Physique 5 (2004).

Heat transfer performances for non-boiling and boiling flow of a micro-vaporizer have been measured by standard methods (temperatures, flow rates, effective power input). The study was carried out for laminar flow (Re

Velocity and residence time distributions play a crucial role in the performance of microreactors for chemical synthesis. The specific features of fluid flow through multiplate microchannel reactors are examined by an approximate pressure drop model whose validity is confirmed through comparison with more detailed finite-volume calculations. The model results allow for determination of the influence of the geometrical characteristics of the microchannel structures on the flow distributions and are used to optimize the reactor design for maximum flow uniformity.

International audience; This paper presents the results of the characterization of a new method for quantification of the micromixing efficiency in a viscous medium in stirred tank reactors. The used method is inspired by a chemical system based on two competitive reactions, the iodide-iodate reaction system (Villermaux-Dushrnan method), whose products selectivity is a measure of the mixing efficiency. The approach proposes a new protocol based on a phosphate buffer and the use of HydroxyEthylCellulose (NEC, 720, 000 g/mol) as an inert viscosifying agent, exhibiting various interesting properties (no disturbance of the spectrophotometric measure, low cost, low required amount, eco-friendly product). This agent is almost Newtonian up to 0.25 wt% in water and becomes non-Newtonian above 0.5 wt%. By means of its use, the viscosity of the reactive medium can be raised by around two orders of magnitude while adding less than 1 wt% HEC to the water solution. Preliminary micromixing results of moderate viscous solutions (50 mP as with NEC 0.5 wt%) in a stirred tank reactor are presented.

International audience; The present paper aims at proposing a complementary view of process intensification (PI) based on the concepts of local intensification and global intensification. Local intensification is defined here as the classical approach of PI based on the use of techniques and methods for the drastic improvement of the efficiency of a single unit or device. Some examples are given to illustrate that local process intensification presents several limitations when compared to holistic overall process-based intensification, named global intensification. Indeed, when PI focuses on single units (reactors, separators, hybrid separators, etc.), the strong interactions among all units within the process are ignored and the impact of local intensification of a single unit can be very limited, resulting in weak improvement of the whole process. This paper identifies that process intensification is broader than technical improvement of devices or processes and has to consider several drivers such as economics, safety, eco-efficiency and sustainability to fulfill the key objectives in designing new plants and retrofitting existing units.

This paper focuses on the impact of reactant staging on conversion for one single reversible reaction in a two-stage, isothermal, continuous reactor. The analytical expression of global conversion has been derived for a series of two continuously stirred-tank reactors. Improvements in the overall conversion and yield by staging can be obtained for low Damköhler number systems leading to low conversions, when the volumetric flow rate of the staged reactant has a higher value than that of the other one. The example of triolein transesterification involving three reversible reactions in a two-stage plug flow reactor is also studied as a concrete example of a consecutive/parallel reversible reactions system. Results are obtained by using a pseudo-homogeneous model and are compared with those obtained with a heterogeneous model from a previous study.

International audience; A high-impact polystyrene (HIPS) process has been studied using Raman spectroscopy as a monitoring technique for the first time. Thermal polymerization of styrene was carried out in the presence of polybutadiene. A Raman probe with a short focal distance, immersed into the reaction medium, allowed in situ monitoring of styrene consumption over the whole reaction progress. A Raman probe with a long focal distance set outside the glass reactor was applied to detect phase separation and phase inversion. Finally, coupling Raman spectroscopy and flow rheometry into a single experimental setup allowed in situ monitoring of both phase behavior and viscosity variation during the HIPS process. Results obtained from Raman spectroscopy were correlated to those from laser granulometry and gravimetric analysis.

International audience; Acrylic acid free radical polymerization in aqueous solution was studied using a new experimental setup coupling Raman spectroscopy and flow rheology in a Couette-like geometry. In situ monitoring of polymer concentration and viscosity of reaction medium versus time was carried out, for different reactant concentrations (acrylic acid and initiator) and process conditions (temperature and shear rate). Experimental variations of polymer concentration and reaction medium viscosity before the occurrence of gel effect as a function of reactant concentration and process conditions were obtained. An overall model combining kinetic scheme and rheological equation was proposed. Kinetic and rheological parameters of the model were identified and found consistent with literature. Gel effect was detected as a sharp increase of polymer concentration much faster than the calculated trend. The occurrence of gel effect was mapped as a function of monomer feed concentration and shear rate. These lab-scale data provided experimental and theoretical bases for process scale up to pilot-scale plant.

Two chemical test methods used for micromixing characterization, the iodide-iodate test and the diazo coupling between naphthol and diazotized sulphanilic acid, have been compared. Experiments were carried out in a one litre stirred tank yielding segregation index as a function of stirring speed. It has been observed that the principal asset of the diazo coupling is to present a good sensitivity to micromixing effects and that the iodide-iodate test offers the advantages of being cheap and easy to handle. A simple phenomenological model, the incorporation model, has been used for the interpretation of experimental data. Micromixing times obtained are in good agreement with the turbulence theory and are independent of the chemical test chosen.

Efforts to model precipitation processes in chemical reactors need to combine fluid mechanics with precipitation processes description. The main difficulty is to consider together micromixing phenomena, which are known to play an important role, with complex reactions kinetics and particles size distribution in the flow. In the present study, a probability density function (PDF) method is presented to calculate the evolution of the particles size distribution. The main advantage of the method is to include a micromixing model based on a Lagrangian frame where chemical reactions are treated without modelling and which requires minimal computational resources. The micromixing model considered is the interaction and exchange with the mean (IEM). Precipitation reactions are nucleation, growth and aggregation. Because of the nature of the powerful numerical technique used, based on Monte-Carlo simulations, the method is able to produce, at any point in the flow, reactants concentration and supersaturation fields, and the particles size distribution field, by simple moments method. The main advantage of the method over traditional population balance solvers is its capability to treat multi-dimensional (e.g. size, crystal morphology, chemical properties, etc.) population balances just as efficiently as it treats high-dimensional PDF. The PDF code is coupled with the commercial CFD package FLUENT which is used for the turbulent calculation of the flow (classical k–e turbulence model), where the presence of the solid phase is assumed not to affect the flow field. An example is presented in the case of silica particles aggregation. The influence of initial reactants concentration and hydrodynamics parameter are investigated.

The present paper comprises direct numerical simulation of the mixing of passive and reactive scalars in two-dimensional flows dominated by coherent vortices. By means of highly accurate pseudo-spectral methods the instationary Navier–Stokes and convection–diffusion–reaction equations are numerically integrated on the torus. We present the evolution of typical vortex arrangements and analyze their ability to mix scalars. Furthermore, we attribute the influence of vortices on the mixing to the formation of spirals and to the merging of vortices. As a way of quantifying the mixing, we consider global and local mixing time scales which describe the overall and the early variance decay, respectively. Moreover, the influence of the Schmidt number and of a chemical reaction on mixing processes are investigated.

In a previous paper (Part I), the operating conditions of the iodide–iodate reaction system used to quantify micromixing phenomena in chemical reactors and mixers has been presented. In order to determine the micromixing time through models, the complete kinetics of the reactions must be known. This paper presents the kinetics of the Dushman reaction obtained in operating conditions close to the micromixing test conditions. The results confirm the single fifth-order process widely reported in published work and establish the rate constant as a function of ionic strength ranging between 0 and 2 M.

This paper describes in a very practicable way the operating conditions of the iodide–iodate reaction system used to quantify micromixing phenomena in chemical reactors and mixers. Several operating procedures are given for batch and continuous mixers. Recommendations to adapt these procedures to any specific mixers and complete analysis procedures are also provided. Finally, a simple micromixing model is used to calculate micromixing time tm. It is checked that tm is non-dependent on the reactant concentrations at constant hydrodynamic conditions. In a second following paper (Part II), the reactions kinetics, essential for a knowledge of micromixing time tm, are presented.

A new mixing device, suitable to achieve the mixing of reactants undergoing fast chemical reactions, is studied. In the sliding-surface mixing device, the chemical reagents are introduced in a confined mixing zone (CMZ), in which high shearing stresses are created in a very small volume to realize rapid micromixing. A system of parallel competing test reactions was used to characterize the micromixing level in the CMZ as a function of feed flow rate, rotation speed, feed pipe position, and a geometric parameter characterizing the CMZ. The influence of these parameters on micromixing efficiency was studied, and a hydrodynamic model was developed. This model successfully predicts micromixing times that were measured at two different flow regimes, two feed points, four recirculation flow rates, three geometric configurations, and various stirrer speeds.

A particle trajectory in a turbulent flow is measured by a 3-dimensional tracking technique and compared with the pattern calculated by a Lagrangian model. The geometry chosen is a standard vessel provided with a Rushton turbine. First, the flow field is simulated using the commercial Fluent package. The impeller global performance is determined. The dimensionless numbers are calculated: t c , N QP , N P . These results are validated by LDV data. The numerical particle trajectory is compared to the experimental trajectory, and the reliability of the numerical trajectory is proved. Finally, some news tools for analyzing the flow are presented. Useful information is included in the long particle trajectory, which enables one to compute a probability of presence. The fluid dynamic behavior is visualized by Poincare sections.

A simple method has been developed to track the three-dimensional motion of a small particle convected in a stirred tank for about 1 h. Different flow patterns induced by a Rushton or a pitched blade turbine have been studied. The results have been compared with known results obtained by conventional techniques. Several tools which have been proposed for this purpose give rise to new insights and interpretation of transport and mixing processes in stirred tanks for engineering applications. On a mis au point une methode simple pour suivre le deplacement tridimensionnel d'une petite particule dans un reservoir agite pendant environ 1 heure. Differents profils d'ecoulement induits par une turbine Rushton ou a pales inclinees sont etudies. Les resultats sont compares avec des resultats connus obtenus par des techniques traditionnelles. Plusieurs outils proposes a cette fin permettent de mieux comprendre et interpreter les procedes de transport et de melange dans les reservoirs agites pour des applications d'ingenierie.

The use of the iodide-iodate test reaction was extended to study micromixing in glycerin-water mixtures with viscosities up to 170 mPa s. The properties of the mixtures and the kinetics of the test reaction were determined as a function of viscosity. Experiments were carried out in a stirred tank yielding the micromixedness ratio α = (1−X s ) X s as a function of stirring speed for different viscosities. A micromixing model involving two steps (incorporation of bulk fluid and exchange between smaller eddies) has been used for the interpretation of the experimental data. Further work is required to interpret experiments at higher viscosities where hydrodynamic data are still lacking.

This paper presents the main challenges of controlling and optimising mixing operations in the chemical industry. Several typical results obtained during a JOULE European project involving 13 partners are presented to show how computational and experimental techniques are helpful to understand and to improve mixing of reactive species in chemical reactors.

International audience; Studies show that oxidation resistant pollutants are present after conventional water treatment systems. Nowadays a new class of oxidation processes is studied: advanced oxidation processes. Our process is based on the use of an electrical discharge (Glidarc and DBD) to produce HO center dot, which is generated on the surface of a thin film of water. The first results show that the DBD is more efficient than the Glidarc with a degradation efficiency of the target pollutant (4-chlorobenzoic acid (pCBA)) of about 0.87 g kWh(-1) for DBD and 0.16 g kWh(-1) for gliding arc discharge. However, it appears that secondary reactions due to corrosion of the metallic micro-structured plate cause slower degradation of the pollutant. Moreover, the presence of nitrates in solution after treatment indicates the formation of NOx in the discharge and the possible formation of nitrogenous oxidation by-products.