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Experimental Study and Modeling of Lipid Extraction in Downstream Processing of Biodiesel Production from Microalgae

Abedini Najafabadi, Hamed | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47684 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Vossoughi, Manouchehr; Pazuki, Gholamreza
  7. Abstract:
  8. In this research, experimental study and modeling of biodiesel production process from microalgae has been investigated. First, to have a biomass with suitable lipid content, a novel two-step process based on cultivation under nutrient sufficient followed by cultivation under nitrogen starvation condition has been proposed. Then the effect of using different organic and inorganic carbon sources on this process has been investigated which the results indicated that sodium acetate had a better performance compare to other carbon sources. In the following, the effect of using different light regimes on growth rate, lipid content and fatty acid composition have been investigated. Experimental studies on Synechocystis sp. pcc 6803 and Chlorella vulgaris species showed that the light wavelength has a huge effect on growth rate but did not has a significant influence on lipid and fatty acid content and just changed the fatty acid composition in some circumstances. After making biomass with suitable lipid content, the extraction and purification of algal lipid has been investigated. Various mixtures of polar and non-polar organic solvents have been used for extraction and the results revealed that mixture of equivolume of hexane and methanol has quite the same efficiency as Bligh and Dyer method. In the next step, the effect of using solvent mixture with different ratios of hexane/methanol and also the biomass moisture content on crude lipid and fatty acid recovery have been investigated. The results showed that the best performance was attained by using equivolume of hexane and methanol. Washing process has been used to purify the extracted lipid. In this method, hexane and water is added to the extraction mixture to make an aqueous/organic two phase system in which the purified lipid is accumulated in organic phase. The results revealed that by adding more water and hexane, fatty acid recovery as well as fatty acid/lipid ratio in organic phase was increased. Nevertheless, the maximum fatty acid recovery yield was 87% and adding more water and hexane did not improve the results significantly. Gibbs free energy models have been employed to model the extraction and purification process. The results revealed that the proposed models can accurately estimate the fatty acid recovery yield in these processes. To sum up the extraction and transesterification steps in one process, direct conversion of algal biomass using methanol was studied. To increase the efficiency of this method in presence of water, supercritical methanol has been used. The results indicated that in this way the moisture content has no significant effect on the performance of this process. The effect of using various co-solvents in increasing the efficiency of the supercritical process was investigated. It has been shown that hexane has better performance compare to the other co-solvents
  9. Keywords:
  10. Microalgae ; Extraction ; Biodiesel ; Photo Bioreactor ; Transesterification Reaction ; Experimental Investigation

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