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Poster De Conférence Année : 2011

On the determination of a "critical osmotic pressure" from the filtration of compressible soft colloids

Résumé

In colloidal filtration, severe fouling occurs when a critical concentration for phase transition is reached at the membrane surface. At this concentration, an irreversible deposit is formed, strongly affecting the performances of the filtration. Knowing the critical concentration, and/or the corresponding critical osmotic pressure, it becomes possible to control the filtration and to model the evolution of the filtration performances with time. Recently, Bessiere et al. proposed an innovative method in which the critical osmotic pressure is determined through a series of dead-end filtration steps at constant pressures, followed by gentle rinses [1]. In our study, we used this method to measure the critical osmotic pressure of casein micelles dispersions. Ultra- and microfiltration of skim milk are indeed widely used in the dairy industry as tools for the separation and the fractionation of proteins and it has been shown that the performances of these filtrations (permeability and selectivity) are directly related to the presence of the casein micelles, the major protein constituent of milk [2]. Casein micelles are protein aggregates of four different caseins together with minerals and can be viewed as very hydrated and complex colloidal entities with a mean diameter of about 150 nm. In contrast to the latex or clay particles with which Bessiere et al. developed their methodology, casein micelles are highly soft and compressible objects [3]. Filtrations of model casein dispersions were performed in dead-end mode with PES ultrafiltration membranes (10 kDa MWCO) at 20°C, and under different transmembrane pressures ranging from 50 to 400 kPa. From these experiments, two important results were obtained: - First, we show that the approach developed by Bessière and co-workers [2] is successful in observing the formation of a deposit/gel with casein micelles dispersions. In contrast, dispersions of "unstructured" caseins never formed any irreversible fouling layer on the membrane (meaning that no critical osmotic pressure could be measured). It confirms some of our previous observations suggesting that the micelles get connected through "structure-dependent" interactions [3]. - Second, we found that the critical osmotic pressures estimated for the casein micelle dispersions (i) depend very strongly on the transmembrane pressure, and (ii) are much higher that the critical osmotic pressure that we determined form osmotic stress experiments [3]. We explain these two unexpected results through the deformability and elastic characteristics of the casein micelle, two specific features that are not taken into account in the original approach proposed by Bessiere et al. [2]. We believe that our results can be generalized to any colloidal dispersion of soft and compressible objects. It clearly shows that new theoretical concepts need to be developed in order to get an accurate estimation of a "true" critical osmotic pressure for such systems
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Dates et versions

hal-01454259 , version 1 (02-02-2017)

Identifiants

  • HAL Id : hal-01454259 , version 1
  • PRODINRA : 195938

Citer

Peng Qu, Antoine Bouchoux, Geneviève Gésan-Guiziou. On the determination of a "critical osmotic pressure" from the filtration of compressible soft colloids. ICOM International Congress of Inorganic Membranes, Jul 2011, Amsterdam, Netherlands. , 2011. ⟨hal-01454259⟩
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