Caractérisation de filtrabilité par la filtration centrifuge – CEFU

Il existe une grande diversité des techniques pour la mesure de la filtrabilité de suspensions. Cependant, les techniques existantes ne sont pas adaptées à la caractérisation rapide d’un grand nombre de petits échantillons (surtout, des échantillons liquides).Depuis quelques années l’Université Technologique de Compiègne et la société LUM GmbH travaillent sur le développement de la centrifugation analytique pour la caractérisation accélérée de la filtrabilité des suspensions et dispersions. La méthode consiste à réaliser des essais de filtration à l’aide de la centrifugation analytique puis à analyser les courbes de la filtration centrifuge obtenues pour en extraire des propriétés des solutions.La comparaison simple des courbes de filtration obtenues permet de classifier les échantillons selon leur filtrabilité. De plus, l’analyse des courbes de filtration permet la caractérisation quantitative de la filtrabilité : détermination de la résistance de la membrane colmatée, de la résistance spécifique du gâteau et des propriétés de réversibilité de la compression du gâteau. La méthode d’analyse des données dépend de la nature des échantillons : deux méthodes adaptées pour des suspensions concentrées et des solutions des colloïdes sont validées actuellement .Le congrès MemPro6 sera l’occasion de présenter les résultats les plus récents sur l’ultra- et la microfiltration centrifuge pour la caractérisation de la filtrabilité des solution

Centrifugal ultrafiltration for determination of filter cake properties of colloids

The article is devoted to the application of analytical centrifugation for the measurement and analysis ofcentrifugal ultrafiltration kinetics. The model of centrifugal ultrafiltration of colloids accounting for the cakeformation, compression and possible decompression is proposed. The method for the determination of filter cakeproperties (pressure dependency of specific cake resistance) from the results of batch centrifugal ultrafiltrationexperiment is presented.The method was tested for the determination of filterability of model samples: aqueous solutions of protein(bovine serum albumin) and nanoparticle suspension (Laponite RD). The pressure dependency of specific cakeresistance was determined in the range of 10−500 kPa from the results of centrifugal ultrafiltration experimentsat different centrifugal rotation speeds. The obtained values of specific resistance were in good correspondencewith those measured in a series of reference constant pressure dead-end filtration test

Characterization of membrane fouling via single centrifugal ultrafiltration

International audienceThe article introduces a novel method for accelerated analysis of membrane fouling during ultrafiltration of colloids: centrifugal ultrafiltration with a stepwise change of centrifugal rotation speed. The method allows simultaneous analysis of membrane fouling for different colloidal samples in a single analytical centrifugation experiment. The analysis for determination of fouled membrane resistance, specific cake resistance and reversibility of the filter cake compression is provided. The method applicability was tested with bovine serum albumin solutions at different protein concentrations. Fouled membrane resistance as well as pressure dependency of specific cake resistance was determined in a wide pressure range of 10…450 kPa. Results obtained with the help of the proposed method were in a good agreement with those obtained using the conventional method of constant pressure dead-end ultrafiltration

Caractérisation de la filtrabilité de dispersions colloïdales par filtration centrifuge

Notre travail est dédié à l’application de la filtration centrifuge (développement de la théorie, équipement, protocoles expérimentaux et méthodes d’analyse des données) pour la caractérisation automatisée de la filtrabilité de dispersions colloïdales. La filtration est réalisée grâce à un équipement de centrifugation analytique fabriquée par LUM GmbH, Allemagne (Figure 1). L’utilisation de cet équipement permet l’analyse simultanée de 12 combinaisons échantillon/membrane différentes.Les courbes de filtration (volume du filtrat en fonction du temps de la filtration) sont obtenues à partir de la mesure automatique du niveau de filtrat par le système optique de la centrifugeuse analytique. La filtration est générée par la pression hydrostatique créée par la force centrifuge. Par ajustement de l’accélération centrifuge, la pression appliquée à l’échantillon peut varier de 10 à 500 kPa.L’analyse du colmatage de la membrane et la mesure des propriétés de filtrabilité des dispersions sont basées sur l’analyse de la variation de la résistance de la membrane au cours de la filtration (en fonction du volume de filtrat et de la pression).Les expériences systématiques réalisées avec des solutions aqueuses de l’albumine de sérum bovin valident la possibilité de caractériser la filtrabilité des dispersions colloïdales stables (mesurer la résistance spécifique du gâteau en fonction du temps) par l’ultrafiltration centrifuge.Les résultats préliminaires d’expériences réalisées avec des solutions aqueuses de β-lactoglobuline démontrent la possibilité de caractériser le colmatage interne de la membrane par la microfiltration centrifuge

Multistep centrifugal consolidation method for characterization of filterability of aggregated concentrated suspensions

Current development of analytical centrifugation methods facilitates the experimental characterizationof dispersion stability and optimization of separation processes (such as centrifugation and filtration).Nevertheless, theoretical analysis of the centrifugal data remains rather complex. In addition, differentside effects can influence the centrifugal process and complicate data interpretation.The present paper proposes a simple method for characterization of filterability of concentrated aggregatedsuspensions by centrifugal consolidation. Different experimental protocols were tested in order toreduce the influence of side effects. Selection of the optimal protocol was based on X-ray analysis of local(spatially resolved) consolidated sample structure. The multistep centrifugal consolidation with constantcentrifugal acceleration ratio is suggested. Data analysis based on a single numerical solution of a basicconsolidation equation yields the pressure dependency of specific cake resistance. A satisfactory correspondence(15% difference) was observed between the pressure dependency of specific cake resistancedetermined from the proposed multistep centrifugal consolidation, and conventional constant pressuredead-end filtration experiments for the studied concentrated aggregated kaolin suspension in the pressurerange of 7.5. . .170 kPa

Analytical centrifugation for characterization of sludge filterability: centrifugal consolidation kinetics supported by x-ray analysis of sediment structure

The knowledge of pressure dependency of filterability (particle volume fraction φ and specific cake resistance α) is essential for optimization of sludge dewatering operations (settling, centrifugation, dead-end filtration-consolidation). The analytical centrifugation is a promising alternative to the classical laboratory methods of the filterability measurement (constant pressure dead-end filtration, compression permeability experiments) due to the possibility of automated many samples characterization. A number of methods are available for the analysis of centrifugal consolidation data (i.e.,dependency of centrifugal consolidation kinetics and sediment height on centrifugal acceleration) and characterization of sludge filterability, which are based on the idealized representation of a sample (usually, concentrated and aggregated suspension) behaviour in the centrifugal field [1-4]. However, recent works suggest that centrifugal consolidation can be influenced by side different effects (as wall friction [5] and particles segregation [6]) that must be taken into account (or eliminated by appropriate choice of the experimental protocol) for the correct characterization of filterability. Objective: Our current work is devoted to the development of a new method and protocols for the determination of pressure dependency of filterability of concentrated aggregated suspensions (pressure dependency of particle volume fraction φ and specific cake resistance α) from the centrifugal consolidation data (two-stage and multistage centrifugal consolidation kinetics).Methods: The method is based on the comparison of experimental characteristic consolidation time with the values tabulated for samples with different filterability. The tabulated values of characteristic consolidation time are obtained by the numerical solution of basic consolidation equation [7] for moderately compressible samples. The method was tested on the aqueous kaolin suspensions. Different experimental protocols were studied (Lumisizer): a) single stage centrifugation different constant centrifugal accelerations; b) two-stage centrifugation (centrifugal pre-consolidation at low centrifugal acceleration followed by centrifugation at different higher accelerations); c) multistage centrifugal consolidation (pre-consolidation followed by centrifugal acceleration ramping); Results: The x-ray transmission analysis (Lumireader x-ray) revealed that the single stage centrifugation can result in formation of nonhomogeneous sediment (probably, due to the particles segregation at high centrifugal acceleration), while two-stage and multistage experiments yields sediments with homogeneous solid pressure distribution. Conclusions: Sample pre-consolidation at low centrifugal acceleration is necessary for the correct analysis of the filterability be the method of centrifugal consolidation. The kinetics of two- and multistage centrifugal consolidation can be analyzed with the help of the developed method in order to determine the pressure dependency of the specific cake resistance in the wide solid pressure range