How the experimental knowledge of the irreversible fouling distribution can contribute to understand the fluid circulation in a spiral ultrafiltration membrane.

International audienceIt is commonly thought that in a spiral membrane the fouling is high at the module inlet and progressively decreases toward the outlet. Thanks to an exptl. mapping of the irreversible fouling existing in a spiral membrane of 6.5 m2 area, this paper shows that it is not systematically true and that the fouling distribution can be much more complex. This paper shows also in what extent the mapping of the irreversible fouling existing in a spiral membrane is a powerful approach to deal with the role of the velocity/turbulences gradient that can be exptl. studied independently of the transmembrane pressure gradient in appropriate filtering conditions. The fouling distribution suggests that the velocity/turbulences are roughly const. on 50% of the membrane area located in its center when dealing with a radial dimension, whereas part of this mean position, velocity/turbulences can increase or decrease. [on SciFinder(R)

Le nettoyage (une étape-clef pour une production durable par procédé à membrane)

Le nettoyage en place des membranes en industrie agro-alimentaire est une opération cruciale qui, outre les exigences de sécurité sanitaire des installations et des produits traités doit permettre de restaurer les performances de la filtration (sélectivité, flux) en éliminant le colmatage formé pendant l'étape de production. Malheureusement cette étape repose encore sur des bases empiriques et non optimisées. A cause d'un manque de notions fondamentales, elle est encore pressentie comme un frein à l'utilisation massive des procédés membranaires. Une démarche originale a été menée dans le cadre de cette thèse incluant la réflexion sur l'incidence des paramètres hydrodynamiques des conditions de production sur la cohésion du dépôt colmatant et plus particulièrement de sa fraction irréversible, dont la nettoyabilité est étudiée. Pour fonder cette démarche, une étude comparée du colmatage et du nettoyage au flux limite et au flux critique a été réalisée en intégrant le rôle de la physico-chimie et de l'hydrodynamique pendant la phase de production. cette étude s'inscrit dans un cadre d'éco-conception de procédé, avec une analyse de cycle de vie réalisée afin d'estimer l'impact environnemental de l'étape de nettoyage via divers scénarii simplifiés.The cleaning in place of membranes in food-processing industry is crucial operation which, besides the requirements of sanitary safety of the installations and the treated products allows to restore the performances of the filtration (flux, selectivity) by removing the fouling formed during the production step. Unfortunately, this cleaning step still rests on empirical and not optimized bases. Because of a lack of fundamental notions, it is still anticipated as a brake in the massive use of the membrane processes. An original approach is led within the framework of this thesis including the reflexion on the incidence of the hydrodynamics parameters of the conditions of production on the cohesion of the fouling deposit and more particularly its irreversible fraction which this cleanability is studied. To establish this approach, a study compared by the fouling and by the cleaning with the limiting flux and with the critical flux is realized by integrating the role of the physic-chemistry and the hydrodynamics during the production step. This study joins in a frame of eco-design of process, with an analysis of life cycle realized to estimate the environmental impact of the cleaning step by diverse scenarios.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF

Evidencing the chemical degradation of a hydrophilized pes ultrafiltration membrane despite protein fouling

International audienceHydrophilisation of polyethersulfone (PES) based membrane is often achieved by addition of polyvinylpyrrolidone (PVP) leading to a physical blend of the two polymers. This paper shows that the most commonly used membrane for UF in dairy industry is a PES/PVP based one. Nevertheless if hydrophilisation limits the organic fouling, PVP is also the Achilles heel of these membranes. It is particularly true when membranes are exposed to hypochlorite as it is the case for cleaning/disinfection steps. Evidencing the disappearance of PVP from a pristine PES/PVP membrane can be easily achieved by FTIR-ATR analyses. But when one wants to study the ageing of a membrane used in UF it gets more complicated: regardless of the cleaning efficiency the membrane always remains fouled by some proteins. As both PVP and proteins own chemical bounds leading to absorption at the same wavenumber in FTIR-ATR, it thereby prevents the easy highlighting of the PVP degradation. The aim of this paper is to propose a simple treatment of raw FTIR-ATR spectra to dissociate these two contributions, allowing consequently the study of the degradation of a fouled membrane. Then the procedure is applied to a real case study on a spiral membrane

Comparison of two nanofiltration membrane reactors for a model reaction of olefin metathesis achieved in toluene

International audienceThe recent commercialisation of nanofiltration membranes resistant toward organic solvents is a real opportunity for fine chemistry. This study deals with different ways of integration of organic solvent nanofiltration for a specific type of reactions known as olefin metathesis and shows the use of two nanofiltration membrane reactors both running in cross-flow filtration mode (0.1 m s- 1). They are used either in semi-continuous or continuous mode. A model ring closing metathesis reaction is chosen for the demonstration. A commercially available pre-catalyst, namely Grubbs-Hoveyda II, as well as a commercial polyimide membrane (Starmem 122, MWCO 220 g mol- 1) are used. Firstly, nanofiltration of the single pre-catalyst allows establishing that the highest retention is obtained with a 40 bar pressure. Secondly, this pressure is used with the two membrane reactors before testing other conditions. Finally, interests and limitations of the two reactors are discussed

Filterability of exopolysaccharides solutions from the red microalga Porphyridium cruentum by tangential filtration on a polymeric membrane

International audienceThe red microalga Porphyridium cruentum is exploited industrially for its exopolysaccharides (EPS) and pigments production. EPS produced by P. cruentum are partially released and dissolved into the surrounding environment, they can be recovered from the culture medium after removing the cells. This paper presents a parametric study of the ultrafiltration of EPS solutions on organic membrane. The EPS solutions were produced in conditions representative of an industrial production. They were filtered at lab-scale on a flat, PES 50 kDa MWCO membrane in a complete recirculation mode of permeate and retentate. Permeate flux-transmembrane pressure (TMP) curves were established up to the limiting flux for the filtration of solutions with various values of concentration in EPS (0.10 to 1.06 kg GlcEq.m), fluid tangential velocity (0.3 to 1.2 m.s) and temperature (20 and 40 °C). The reversible and irreversible parts of fouling were evaluated for each experiment and the critical flux was determined for an intermediate EPS concentration (0.16 kg GlcEq.m). The results showed that EPS solutions had a strong fouling capacity. When filtering the lowest concentrated solution (0.10 kg GlcEq.m) with moderate fouling conditions, the overall fouling resistance was approximately half of the membrane and the share of irreversible/reversible fouling was 88 and 12%. However, the part of reversible fouling becomes predominant when approaching the limiting flux. Permeate fluxes which were obtained allow to estimate that a VRR of approximately 10 could be obtained when concentrating EPS solutions using PES membranes in flat or tubular modules but not in spiral-wound

Synthese d'une phase de Chevrel supportee sur #chi#-alumine en vue de l'application catalytique a l'oxychloration de l'ethylene

SIGLEINIST T 74330 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Intérêts et limitations d'un réacteur à membrane de nanofiltration appliqué à une réaction de métathèse des oléfines en milieu organique

La métathèse des oléfines peut être considérée comme une réaction majeure de la chimie fine. Elle est encore peu appliquée à l'échelle industrielle car la gestion de la séparation du catalyseur organo-métallique soluble et des produits de la réaction est mal maitrisée. L'objectif de cette thèse est d'explorer comment l'intégration de la nanofiltration organique peut permettre de répondre à cette problématique. Différentes approches ont été testées et sont discutées selon que la nanofiltration est une opération unitaire réalisée en cascade après un réacteur de synthèse ou qu'elle est couplée à la synthèse en une seule opération au sein d'un réacteur à membrane, qui fonctionne en discontinu ou en continu. Pour cette étude, des catalyseurs homogènes de type Hoveyda II ont été utilisés dans une réaction modèle de métathèse cyclisante.Olefin metathesis can be considered as a major reaction in fine chemistry. But nowadays, it is not largely applied at industrial scale because of the lack of mastering of the separation between the soluble organo-metallic catalyst and the reaction products. The aim of this study is to explore how the integration of organic solvent nanofiltration (OSN), can allow to answer this question. Several approaches can be a unit operation in cascade with a synthesis reactor. Secondly OSN can be coupled with the reactor in a single operation to obtain a membrane reactor, that can be used either in a discontinuous or a continuous mode. In this study, several homogeneous catalysts of Hoveyda II type are used in a model reaction of ring closing metathesis.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Rôle de la physico-chimie sur les flux limites et critiques en ultrafiltration, nanofiltration et osmose inverse (application à des effluents laitiers modèles)

Les caséines, principales protéines du lait, sont reconnues comme responsables de la limitation des flux en filtration tangentielle de lait écrémé. La versatilité de ces protéines vis-à-vis du pH est connue et peut être montrée à partir des mesures de taille et de potentiel zéta (charges). Cette thèse traite de la détermination des flux critiques (durables) et des flux limites (maximum) en ultrafiltration, nanofiltration et osmose inverse lors de la filtration de laits écre més, modifiés ou non, dans une gamme de pH allant de 3,7 à 11,5 dans le but de modéliser des effluents de laiterie concentrés, acides ou basiques. Les flux critiques et les flux limites varient de manière similaire et complexe avec le pH pour l UF, la NF, et l OI, en décrivant 4 régions distinctes qui peuvent être corrélées aux variations de taille et de charge des caséines. Les rétentions du lactose (principale molécule neutre du lait) ainsi que des protéines, qui sont les principale responsable de la teneur en DCO des effluents, sont mesurées et discutées en fonction des différents paramètres étudiés.Caseins, the main proteins of milk, are known to be responsible of flux limitations in tangential filtration of skim milk. These proteins are well-known to be versatile with the pH that can be shown from measurements of theirs size and zeta potential (charges). This thesis deals with the determination of both critical (sustainable) and limiting (maximum) fluxes during ultrafiltration, nanofiltration and reverse osmoses of natural and modified skim milks in the pH range 3.7 to 11.5 in order to model concentrated effluents from dairy industry, either acid or alkaline. The critical and limiting fluxes varied similarly but in a quite complicated way with the pH, for UF, NF and RO leading to 4 different regions that can be correlate to variations of size and zeta potential of caseins. Retentions of lactose (main neutral solute of milk) and whole proteins, main responsible of COD, were measured and discussed in relationship with above-mentioned parameters.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Nettoyage éco-efficace de membranes planes et spirales d ultrafiltration de lait écrémé (approches physico-chimiques et hydrodynamiques concertées)

Le nettoyage est une étape clé indispensable, des procédés à membrane installés dans les industries agroalimentaires, permettant de restaurer les performances membranaires en éliminant le colmatage, mais actuellement mal maitrisée, ainsi que coûteuse et polluante, faute de connaissance des mécanismes fondamentaux. Nos travaux s insèrent dans une démarche d éco-conception visant à installer les procédés à membrane comme procédé de production durable. Ils se sont déroulés selon 3 axes, pour l ultrafiltration spirale de lait écrémé: i) analyse critique selon une démarche d éco-conception de la pratique industrielle empirique, ii) étude des mécanismes d adsorption/désorption des protéines en dynamique pour intégrer les rôles de la physico-chimie et de l hydrodynamique, iii) recherche de détergents éco-efficaces. L efficacité du nettoyage est déterminée selon la récupération de la perméabilité membranaire (traditionnelle) et la quantification par FTIR-ATR du colmatage protéique résiduel (originale), qui s avère être le meilleur outil pour évaluer l efficacité du nettoyage alors que le flux peut être trompeur.Cleaning is a key step of membrane processes used in the food industry. It allows to restore the membrane flux and selectivity by eliminating irreversible fouling. Currently, cleaning hasn't been mastered, expensive and polluting, due to a lack of knowledge of the fundamental mechanisms of cleaning. This study follows an EcoDesign approach that aims to install membrane processes as sustainable production processes for the skim milk ultrafiltration with spiral wound module. 3 axis were followed: critical analysis with an EcoDesign approach of empiric cleaning processes in the industry, a study of dynamic protein adsorption/desorption mechanisms to understand the respective part of physicochemistry and hydrodynamic, a search for ecologically and economically efficient detergents. The efficiency of cleaning was measured with a traditional method, namely recovery of the membrane permeability, and with an original FTIR-ATR method, quantifying the concentration of residual proteins on the membrane surface. The latter turned out to be the best tool in order to evaluate the efficiency of membrane cleaning, whereas the flux can be misleading.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF