Mikroalg chlorella vulgaris'ten biyodizel üretimi için süperkritik karbondioksit ile yağ ekstraksiyonunun teorik ve deneysel olarak incelenmesi

Finite availability of fossil fuels and negative impacts of anthropogenic greenhouse gases emissions causing global warming have stimulated development of alternative resources for transportation fuels. Among alternatives, liquid biofuels such as biodiesel is attractive as they can be directly utilized in existing infrastructure. Recently, microalgae lipids has attracted increasing attention to be used for biodiesel resources thanks to superior properties of microalgae. They can be cultivated on non-arable land without competing with human food. Their lipid productivity is much higher than agricultural crops. Lipid extraction from microalgae is one of the steps affecting economic feasibility of biodiesel production from microalgae. Supercritical CO2 (scCO2) extraction technology is considered as a promising alternative since it is environmentally friendly and prevents solvent contamination by enabling solvent free extract. In this study, scCO2 extraction of high amount of lipid producing microalgae Chlorella vulgaris lipids was investigated in the pressure range from 200 to 400 bar and temperature range from 40 to 70 °C. Microalgae cultivation was performed with 27 liter flat panel type photobioreactor. Lipid productivity was tracked by Nile red method and it was found that highest lipid productivity was reached at early stationary phase. ScCO2 extraction was compared with conventional Soxhlet extraction with n-hexane and comparable extraction yields were obtained. Moreover, it took far less time to reach same extraction yield with scCO2. Increase in pressure at constant temperature and increase in temperature at constant pressure significantly improved scCO2 extraction yield. Effluent lipid concentration curves showed a fast extraction period followed by a much slower extraction period. Sovova's model describing these periods as external mass transfer controlled and internal diffusion controlled was used to predict experimental data. Lipid solubility in scCO2 at operating conditions was predicted from slope of the first part of the extraction curve. Predicted solubilities ranged between 2.7 and 9.0 mg lipid/g CO2. Fluid and solid phase mass transfer coefficients regressed from experimental data were the order of 10-4 m/s and 10-8 m/s, respectively. Common correlations in mass transfer for forced convection were used to predict fluid phase mass transfer coefficient. Best agreement was found with mass transfer correlation Sh=2+1.1*〖Re〗^0.6*〖Sc〗^(1/3) which was developed for evaporation from drops. Fatty acid methyl esters (FAME) profiles obtained by transesterification were considerably affected by extraction method and operating conditions of scCO2 extraction. No changes on FAME profiles were detected as a function of scCO2 extraction time.