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 CO2 and a decrease of viscosity ranging from 5 to 500 is observed. A complete metal separation and an almost dry concentrate residue are achieved. (C) 2001 Elsevier Science B.V. All rights reserved.