Supercritical CO2 extraction of neutral lipids from microalgae: Experiments and modelling

Abstract

The aim of this work is to show that the equations developed by Sovová, based on the concept of broken and intact cells for describing the supercritical extraction curves from plants and vegetables, can be applied for the modelling of the supercritical CO2 extraction curves obtained with microalgae. Experimental and modelling results of supercritical carbon dioxide extraction of lipids from four different microalgae: Nannochloropsis oculata, Cylindrotheca closterium, Chlorella vulgaris and Spirulina platensis, are presented. The experimental setup is a laboratory scale apparatus which allows an accurate monitoring of the mass loss of the microalgae sample during the extraction. The experimental data were obtained at a pressure of 40MPa, a temperature of 333K and CO2 flow rates from 0.3 to 0.5kgh−1. The extraction experiments were performed on samples having undergone different pretreatments: (i) after harvesting and centrifugation, microalgae were dried either by freeze-drying or air flow drying) and (ii) they were ground and sieved at different particle sizes (particle diameters ranging from 160 to 1000μm). The complete extraction of neutral lipids was performed leading to mass losses up to 30% depending on the samples and on the operating conditions. Extracts were mainly composed of triglycerides (more than 90wt% of extracts). The mathematical model published in 2005 and the simplified equations of extraction curves (using the characteristic times characterizing each extraction step) published in 2012 by Sovová were chosen to fit the experimental data. Among the hypotheses proposed by Sovovà, we considered that the flow pattern of supercritical CO2 in the extraction autoclave was plug flow and the extraction process was supposed to occur with negligible solute–matrix interactions. The adjustable parameters were calculated by minimizing the sum of least squares between experimental and calculated values of the extraction yield. Good agreement between the two models and our experimental measurements was obtained. The average absolute relative deviation ranges between 0.5 and 10.2%.