SUPERCRITICAL CO_2 EXTRACTION OF OIL FROM MICROALGAE FOR BIOFUEL APPLICATION

摘要

This study is one part of the Shamash French project whose aim is to produce biofuel from microalgae. Eight academic and industrial partners work together to contribute to the future large scale production of biofuel from microalgae. The main idea is to select and produce microalgae which can accumulate large quantities of oil under nitrogen starvation. Once grown, harvested and dried, microalgae are subjected to extraction with supercritical carbon dioxide, a clean process for recovering oil. Oil can be trans-esterified in methylic or ethylic esters to be used as biodiesel. This work relates the influence of operating parameters on supercritical extraction yields from dried microalgae. Preliminary results on supercritical CO_2 extraction yields from microalgae AB1 are presented. The influence of operating parameters (pressure, temperature, CO_2 flow rate and extraction duration) upon oil extraction yields has been determined through an experimental design. The experiments were performed under pressures from 28 to 46MPa, temperatures from 318 to 338K and CO_2 flow rate from 0.3 to 0.8kg/h corresponding to CO_2/microalgae mass ratio from 80 to 200. The extraction time was set at 1h30. The studied response to the experimental design was the microalgae mass loss. Depending on experimental conditions the mass loss varied from 4 to 16%. The latter value corresponds to the total neutral lipid content in the microalgae.Secondly, the influence of microalgae particle size on extraction yields has also been studied. The experiments were performed under 40MPa, at 333K and with a CO_2 flow rate of 0.4kg.h~(-1). The microalgae tested were cylindrotheca and chlorella. Microalgae were first crushed and sieved. Two particles sizes were chosen: less than 160μm and more than 1mm. Results show the great influence of crushing. As expected, the smaller the particle size, the most rapid extraction kinetics. The influence of pre-treatment was also studied. The comparison between freeze-drying and drying is proposed for the microalgae cylindrotheca. It appears that drying provides more rapid extraction kinetics.