Stéphane Sarrade

New applications of supercritical fluids and supercritical fluids processes in separation

This presentation is a review of new ideas recently proposed in the field of supercritical fluid (SCF)-and membrane coupled processes or membranes preparation. First, few studies are presented in order to illustrate the preparation of ceramic membranes using the supercritical route. New materials obtained in supercritical conditions lead us to develop original ceramic membrane for filtration or application. The other applications concern coupled supercritical CO2 (SC CO2) extraction with nanofiltration separation to purify low molecular weight compounds. This process has been proposed as an environment safeguarding solution for coupling extraction and separation. Cross-flow filtration applied to viscous liquids fluidified with SC CO2 is also investigated. The basic idea is to reduce liquid viscosity at ordinary temperature by injecting a gas (CO2) in supercritical conditions before filtration. Finally, these works, as well as other examples involving new membrane contactor or reactor types and supercritical fluids as solvents, bear testimony of the main interest to use such hybrid techniques regarding performance and environmental constraints.

Nanofiltration membrane behavior in a supercritical medium

Abstract The permeability values of “TN” organomineral nanofiltration membranes to water, L , and to supercritical CO 2 , G , were compared. The resulting values for G were an order of magnitude higher than for L . The difference may be directly related to the viscosity difference between the two fluids. Temperature- and pressure-related variations in G were also analyzed; for this purpose, Poiseuilles model satisfactorily accounts for experimental behavior, while Knudsens model is unsuitable. A hysteresis effect was observed on the isotherms corresponding to variations in G versus pressure, suggesting partially irreversible CO 2 adsorption on the micropore walls, that would diminish the radius. This phenomenon could be enhanced by an increased fluid density and viscosity.

Dynamic characterization and transport mechanisms of two inorganic membranes for nanofiltration

Abstract This article discusses the transport mechanisms of water and uncharged solute molecules (PEG) through two new nanofiltration membranes: a pure ceramic (γ-alumina) and a Nafion layer deposited on a mesoporous tita-nium oxide substrate. It is shown that in both cases the transport mechanisms are always predominantly convective rather than diffusive, even if the difference between the two components is less important with Nafion than with alumina due to specific chemical interactions between the membrane material and the solutes. This approach was also used to characterize the two membranes morphologically, notably the pore radius of ∼0.6 nm.

Enhanced filtration of organic viscous liquids by supercritical CO2 addition and fluidification. Application to used oil regeneration

Cross-flow filtration of viscous liquids is a difficult challenge because it demands high-energy consumption for poor permeate flow rates. Moreover, the final concentration is clearly limited by the pressure drop through pipes and membrane. Usually, apparent viscosity is decreased by means of temperature, addition of organic fluidiser (organic solvent) or by means of increasing shear when a non-Newtonian fluid is concerned. Another possibility has been developed by CEA since 1998 and we propose to use a supercritical agent as a fluidiser. This process is very well adapted for the regeneration of used motor oils, as well as natural oils or polymers filtration. The experimental pressurised cross-flow filtration sets up is designed with inorganic membranes, using model compounds or real oil effluents. Model compounds (polymers, standard oils) are then tested in order to study hydrodynamic behaviours with ultrafiltration membranes whose pore sizes are much greater than compound sizes. Finally, two different used motor oils are ultrafiltred. One is a standard type used oil, while the other is a residue of a vacuum distillation column. The hydrodynamic results clearly show an increasing flow resistance for a low value of the retentate velocity. For high velocities, no polarisation is observed. Used oils ultrafiltration leads to a complete purification while the addition of supercritical CO 2 and a decrease of viscosity ranging from 5 to 500 is observed. A complete metal separation and an almost dry concentrate residue are achieved.

Improvement of the Ultrafiltration of Highly Viscous Liquids by Injection of Pressurized Carbon Dioxide

The injection of pressurized carbon dioxide (CO2) (gas or supercritical) in a liquid induces a lowering of viscosity the magnitude of which is a function of temperature and pressure. In this work, the addition of pressurized CO2 to highly viscous liquids is proposed as an ecologically viable and economically competitive technology to increase permeate flux during ultrafiltration at low temperature. Initially viscosity and phase-equilibrium data of model compounds, polyethylene glycols (PEG), in the presence of CO2 were studied at high pressure. Then tangential filtration runs with PEG-CO2 mixtures were conducted on pilot-plant units equipped with mineral membranes. Results thus obtained were analyzed using the previously measured kinetic and thermodynamic data.