Understanding microalgae lipids recovery by membrane processes: cross flow filtration of a representative synthetic mixture

E. Clavijo Rivera (1, 2) , Villafaña Lopéz , S. Liu (3) , P. Bourseau (4) , M. Frappart (5) , C. Monteux (6) , E Couallier

1 CNRS - Centre National de la Recherche Scientifique
2 GEPEA-BAM - Bioprocédés Appliqués aux Microalgues
3 LAL - Laboratoire de l'Accélérateur Linéaire
4 LIMATB - Laboratoire d'Ingénierie des Matériaux de Bretagne
5 BIM - Biomécanique et génie biomédical
6 SIMM - Sciences et Ingénierie de la Matière Molle

Microalgae are considered as a feedstock of high-valuable products such as proteins, polysaccharides and lipids. The microalgae biorefinery concept considers the fractionation of biomass into multiple products whose integrity needs to be preserved during separation. In the context of lipids separation from aqueous microalgae, the recovery of triglycerides, suitable for biodiesel production, can be accomplished using membrane filtration techniques, but the presence of amphiphilic molecules in the feed solution deeply influences the process performances (permeate flux, selectivity and cleanability). This research focuses on the understanding of neutral lipids separation by membrane processes from a complex mixture of grinded microalgae, in presence of polar compounds stabilizing the water-oil interface. Due to the complexity and variability of grinded microalgae suspensions, a simplified synthetic solution (oil-in-water o/w emulsion) has been formulated and used for this study. Lipids used in the formulation were defined on the basis of a preliminary lipids characterization from nitrogen starving Parachlorella kessleri. The prepared emulsion was constituted by 98% w/w of water and 2% w/w of lipids. The dispersed fraction was composed of 70% w/w of a mixture of vegetable oils (as neutral lipids) and 30% of polar lipids as surfactants: 50% of phospholipid and 50% of glycolipid. An emulsification protocol, performed using a high-speed dispersing unit, was established to obtain a stable o/w emulsion with a specific droplet size distribution. The oil separation performance was assessed for five membranes, hydrophilic (PAN 500kDa, PES 300kDa and 200kDa) and hydrophobic (PVDF 1.5μm and 0.4μm) using a cross-flow filtration system. Oil concentration was evaluated in the retentate and the permeate. Results showed an oil retention rate higher than 92% and oil permeation only for PVDF membranes. These results were compared with experimental data obtained within the same context but using dynamic filtration, for which critical and transmembrane pressures were higher. The PAN 500kDa membrane exhibited the most suitable characteristics for oil concentration purposes in terms of permeate flux, retention and cleanability. Subsequently, the oil-water interface was physicochemically characterized in order to evaluate the influence of the filtration process on the emulsion stability. The response of the interfacial tension to compression/dilatation of the interface was assessed for different surfactant concentrations, suggesting possible rearrangements and adsorption/desorption of amphiphilic molecules at the L-L interfacial layer. Further experiments at the liquid-solid interface (sessile drop analysis) with clean and fouled membranes will provide fundamental information for understanding the relation between interfacial properties and the emulsion destabilization during filtration.

Domaines: Génie des procédés

E. Clavijo Rivera, Villafaña Lopéz, S. Liu, P. Bourseau, M. Frappart, et al.. Understanding microalgae lipids recovery by membrane processes: cross flow filtration of a representative synthetic mixture. 10th World Congress of Chemical Engineering, Oct 2017, Barcelone, Spain. ⟨hal-01897689⟩