Effect of dense CO2 on polymeric reverse osmosis and nanofiltration membranes and permeation of mixtures of macauba oil (Acrocomia aculeata) and CO2

Abstract The performance of four commercial membranes upon subcritical and supercritical CO 2 treatments have been characterised by different methods. The membranes were treated up to 8 h in static process, using two different conditions (18 MPa/313.15 K – supercritical and 8 MPa/293.15 K – subcritical). The possible changes in membrane characteristics were investigated by atomic force microscopy (AFM), contact angle and surface free energy, thermogravimetric analysis (TGA), scanning electronic microscopy (SEM). Membrane performance was also evaluated by measuring CO 2 flux and macauba oil retention factors. Changes in membrane roughness and in contact angles were observed for all membranes after sub and supercritical CO 2 treatments. Moreover, the surface free energy and the polar component showed a decrease after CO 2 exposure, confirming an increase in surface hydrophobicity of membranes detected from contact angle results. This empowerment of hydrophobicity is associated mainly with the CO 2 –polymer interaction. Other intra and interchain effects should not affect the thermal stability leaving TGA results unchanged after CO 2 exposure. ORAK and NP030 membranes showed high macauba oil retentions; 95% and 85%, respectively in supercritical condition. This latter revealed to cause important changes in the membranes due to the higher solubility of CO 2 in polymeric matrix at this condition. However, the selectivity was not changed and it is possible to use commercial polymeric membranes in supercritical systems for CO 2 regeneration and partial fatty acid fractioning.