Showing papers by "Laurent E. Prat published in 2006"

Experimental and numerical study of droplets hydrodynamics in microchannels

Abstract: This article reports on numerical simulations and experimental determination of the hydrodynamics of liquid–liquid flow in rectangular microchannels. The numerical method is an interface-capturing technique without any interface reconstruction. Microparticle image velocimetry (micro-PIV) measurements are used to obtain experimental velocity fields inside droplets that are compared to simulations. Finally, injecting a passive tracer in the simulated droplets also helps to obtain a better understanding of the mixing phenomenon. These results allow interpreting mixing defaults during bleaching experiments inside microdroplets. Furthermore, this study leads to important results about interface deformation and velocity fields inside the droplets and in the continuous phase for mass- and heat-transfer studies. 2006 American Institute of Chemical Engineers AIChE J, 52: 4061–4070, 2006

Increasing and decreasing droplets velocity in microchannels

Abstract: This paper deals with a specific aspect of non-miscible liquid–liquid systems in microfluidic. For Chemical Engineering applications, the main constraints of functioning lie in the droplets velocity and frequency. Furthermore, the material used and the composition of the fluids is often imposed by the chemistry of the system (material resistance and fluids composition) and there is no possibility of adding other compounds (e.g., surfactants). A technique under evaluation is presented: by using secondary channels and pumps, it is possible to increase or decrease, at will, the droplets velocity after they have been generated. Some experimental results are presented and discussed, including the possible limits of such an approach.

Fast Batch to Continuous Transposition: Application to the Extraction of Andrographolide from Plants

Abstract: The objective of this study is to propose a fast development method for batch to continuous processes transposition. This method is based on transient regime experiments analysis and is applied to a solid liquid extraction. The application under consideration is the extraction of an active principle from plant in a non-sinusoidal pulsed column. Typically, the proposed signal is composed of two different periods: in one hand, a classical sinusoidal pulsation step used to mix the liquid and solid phases in the active part of the column and allow an optimal mass transfer and, in a second hand, an impulsion phase, used generally for the transport of solid. The extraction is carried out in a disc and doughnut column of 54 mm in diameter, and 3.5 m in height. Liquid and solid are flowing cocurrently and downwardly. This technological improvement has been implemented to solve the difficulties due to the important heterogeneity of the matter: part tends to float and other to sink, which always leads to a definitive flooding in classical operations. The effects of the solid flow rate and of the solvent characteristics on the hydrodynamic behavior of the column are studied. The mean residence time and the total solid holdup are calculated by using transient regime mass balance on experiments. These experiments allow pointing out and quantifying opposite effects of the operating parameters. Mass transfer experiments have been performed and the results fit calculated values obtained by coupling the hydrodynamic with batch extraction results. Despite of the simplification made, this validates the fast development method proposed to help the batch to continuous transposition.

Optimisation of solvent replacement procedures according to economic and environmental criteria in pharmaceutical industry

Abstract: During pharmaceutical syntheses, the reaction solvent has often to be switched off from one reaction step to the following one. Because of the standard industrial practices, solvent replacement generally constitutes a slow and high solvent-consuming operation. In this paper, a specific methodology, based on a batch processes optimisation framework, is proposed for the optimisation of solvent replacement procedures. Optimisation may be performed at different levels according to economic and environmental criteria and satisfying safety and waste treatment constraints. In fact, the proposed methodology allows both to design new procedures of solvent replacement and to improve existing industrial processes. Two industrial applications are detailed to emphasize the benefits related to this methodology. In each case, the proposed methodology leads to the suitable recipe from comparison of traditional and empirical replacement procedures generally used in the pharmaceutical industry.

Procede de preparation d'une composition humique artificielle, et applications

Abstract: L'invention concerne un procede de preparation d'une composition humique artificielle dans lequel on fait subir a une composition de matiere ligno-cellulosique fraiche un traitement thermique et mecanique, dit traitement mixte, dans lequel: - on place ladite composition de matiere ligno-cellulosique fraiche dans une enceinte (3) portee a une temperature comprise entre 1000C et 2800C, - on soumet ladite composition de matiere ligno-cellulosique fraiche a un traitement mecanique a sec comprenant au moins un deplacement entretenu d'au moins un organe mecanique rigide (2a ; 2b) au sein et au contact de ladite composition de matiere ligno-cellulosique fraiche. Ce traitement mixte permet de preparer un produit solide traite, d'un brun plus ou moins intense, riche en substances humiques artificielles. Ces substances humiques artificielles, faciles a extraire, notamment par extraction alcaline, montrent des proprietes remarquables sur la croissance et le developpement des plantes, et peuvent etre utilisees comme fertilisant.

Optimisation of a chemical reaction in an open plate-type reactor

Abstract: The invention relates to a method of optimising a chemical reaction in an open plate-type reactor, consisting in: establishing a dynamic model of the reactor for said reaction; applying an integration software tool to said dynamic model in order to solve the equations thereof; determining and optimising a set of reactor parameters from assessments of the objectives to be achieved, the constraints to be respected and the variable reactor and reaction data; constructing a reactor that complies with the optimised parameter set; and measuring physical parameters as the reaction is being performed in the reactor thus constructed in order to validate the operation thereof.

Mise en œuvre de micro-réacteurs à l’échelle de micro-gouttes : caractérisation du mélange

Abstract: L’emergence actuelle des micro-reacteurs offre des perspectives interessantes pour l'acquisition rapide de donnees physico-chimiques, et notamment les parametres de cinetique reactionnelle. L'appro...

An Innovative Pulsed Column Applied to Solid‐Liquid Contacting the BPC Column

Abstract: The innovative process presented is a novel type of pulsed column (BPC column) used as a solid/liquid contactor. An evolution in the design of the internals and in the shape of the pulsation has been set up. The initial objectives were to achieve a reactor of greatly longer solid residence time, independently of the liquid phase. Phase contacting is carried out in a 1.5 m height column. Liquid and solid are flowing countercurrently. Solid is fed in at the bottom of the column and flows upwardly, whatever the density difference between both phases. The behaviour of solid and liquid phases was investigated through the analysis of residence time distributions. The working conditions range has been determined and it was found that an optimal tuning of the operating conditions (pulsation parameters, flows control…) could minimize the influence of the size and the density of particles and uncouple residence times of both phases. The column has been manufactured, in order to handle a large range of solid-liquid systems (solid treatment, purification or reaction, raw materials, floating or dense particles, polydispersed particles). On the basis of the model calculations and design considerations, preliminary data can be given on the technical and economical feasibility of the various applications quoted above. The final aim of this study is to prove that, for a fixed production rate and a product quality, the new column can satisfy the specifications required and even exceed them.

Method for preparing a synthetic humic composition, and uses thereof

Abstract: The invention concerns a method for preparing a synthetic humic composition which consists in subjecting a fresh lignocellulosic material composition to a thermal and mechanical treatment, called mixed treatment, consisting in: placing said fresh lignocellulosic material composition in a chamber (3) brought to a temperature ranging between 1000C and 2800C; subjecting said fresh lignocellulosic material composition to a dry process mechanical treatment including at least one maintained displacement of a rigid mechanical member (2a; 2b) inside and in contact with said fresh lignocellulosic material composition. Said mixed treatment enables a treated solid product to be prepared, more ore less intensely brown, rich in synthetic humic substances. Said synthetic humic substances, easily extracted, in particular via alkaline extraction, exhibit remarkable properties for the growth and development of plants, and can be used as fertilizer.

Application to the Extraction of Andrographolide from Plants

Abstract: A fast development method for batch to continuous process transposition is proposed. This method is based on transient regime experiment analyses and is applied to a solid-liquid extraction. The application under consideration is the extraction of an active principle from a plant in a non-sinusoidal pulsed column. Typically, the proposed signal is composed of two different periods: firstly, a classical sinusoidal pulsation step is used to mix the liquid and solid phases in the active part of the column and allow an optimal mass transfer and, secondly, an impulsion phase, used generally for the transport of solids. The extraction is carried out in a disc and doughnut column of 54 mm diameter and 3.5 m height. Liquid and solid are flowing co-currently and downwardly. This technological improvement has been implemented to solve the difficulties due to the significant heterogeneity of the matter: one part tends to float and other to sink, which always leads to a definitive flooding in classical operations. The effects of the solid flow rate and the solvent characteristics on the hydrodynamic behavior of the column are studied. The mean residence time and the total solid holdup are calculated by using a transient regime mass balance on the experimental results. These experiments allow the identification and quantification of opposite effects of the operating parameters. Mass transfer experiments have been performed and the results fit calculated values obtained by coupling the hydrodynamic and batch extraction results. Despite the simplifications made, this validates the fast development method proposed to help batch to continuous transposition.

Colonne pulsee pour systeme solide/liquide

Abstract: L'invention concerne une colonne pulsee permettant de realiser un traitement d'un systeme comprenant une phase liquide et une phase solide.Elle concerne plus particulierement une colonne pulsee permettant de controler et regler le temps de sejour de la phase solide dans la colonne independamment du temps de sejour et du debit de la phase liquide. Cette colonne comprend des moyens d'application de pulsions d'amplitude faible et de frequence eleve et des moyens d'application de frequence d'amplitude forte et de frequence elevee. Les plateaux comprennent un orifice pour permettre la circulation de l'ensemble des phases entre les etages ou volumes de la colonne. Ces orifices comprennent des moyens d'obturation actionnes en position ouverte pendant l'application des impulsions de forte amplitude. la colonne de l'invention permet de controler le temps de sejour de la phase solide independamment du temps de sejour de la phase solde.

Method for preparing a synthetic humic composition

Abstract: The invention concerns a method for preparing a synthetic humic composition which consists in subjecting a fresh lignocellulosic material composition to a thermal and mechanical treatment, called mixed treatment, consisting in: placing said fresh lignocellulosic material composition in a chamber (3) brought to a temperature ranging between 1000C and 2800C; subjecting said fresh lignocellulosic material composition to a dry process mechanical treatment including at least one maintained displacement of a rigid mechanical member (2a; 2b) inside and in contact with said fresh lignocellulosic material composition. Said mixed treatment enables a treated solid product to be prepared, more ore less intensely brown, rich in synthetic humic substances. Said synthetic humic substances, easily extracted, in particular via alkaline extraction, exhibit remarkable properties for the growth and development of plants, and can be used as fertilizer.