| With the advantages of high growth speed, utilization rate of light energy and lipid content,microalgae is an important renewable resource. But because of its minuscule cell and highmoisture content, the microalgae harvesting and lipid extraction is of great difficulty, and alsobecome the bottleneck of industrial production of the microalgae energy. At present, researchreported at home and abroad mainly focuses microalgae lipid extracted from microalgae powder,but reports about the direct use of wet paste for lipid extraction are relatively few. Marinechlorella vulgaris was taken as raw material, and experiments on technology of microalgaeflocculation and lipid extraction were carried out in order to provide important references for thebiodiesel synthetic process.Firstly, flocculation harvesting experiment of the chlorella vulgaris was conducted, theresults showed that compared with aluminum sulfate and ferric chloride, flocculation harvestwith calcium hydroxide had lower cost, higher recovery rate and the flocculant could be easilyremoved by blowing CO2into the culture water. Results of single factor experiment andoptimization of response surface analysis showed that the recovery rate of chlorella vulgarisreached to92.2%when the flocculation time, dosage of calcium hydroxide, and pH of culturefluid were respectively maintained at77min,0.7g/L and9.3, and the microalgae cells werecomplete, so it was a highly efficient and low-cost concentration method of chlorella vulgaris.Using different solvents to extract microalgae lipid, the experimental results showed that then-hexane-ethanol and ethanol extractant performed well for relatively safe and non-toxic withlighter lipid colour except for the extraction rate not the highest. In addition, experiments oneffects of different water content of microalgae paste on lipid extraction rate were carried out andit was found that when the moisture content of microalgae paste was60%, higher extraction ratestill could be reached with the extractant of ethanol, while when the moisture content ofmicroalgae paste was70%, higher extraction rate and transparency could be obtained by usingn-hexane-ethanol, but a small amount of suspended solids existed. Lipid extraction experimentresults showed that the best extraction processing parameter of the ratio of solvent to algalbiomass, the extraction temperature and the extraction time were8:1,45℃and3h by acid hotwall-breaking, respectively. For repeated freezing wall-breaking method, it was7:1,45℃and3h, respectively. Based on the results of response surface methodology, the best extractingconditions by n-hexane-ethanol were solvent to algal biomass ratio of8:1, hexane to ethanolratio of3.4:1, the extraction time of4h and the temperature of55℃，under such conditions, theextraction rate of lipid was up to95.2％.Finally gas chromatography was used to analyze the fatty acid composition of lipidextracted from marine chlorella vulgar paste. Conclusions can be draw that the main fatty acidcomposition of lipid extracted by this two kinds of solvents was so little difference, mainlycomposed by C16:0, C16:1and C20:5. But there were differences of the relative contents forC16:0and C16:1extracted by ethanol were higher and the total content could be up to59.7%, nearly9%higher than that extracted by n-hexane-ethanol. Ethanol was more conducive to enrichC20:5and the percentage could reach23.0%, nearly4%higher than that extracted byn-hexane-ethanol. The total percentage of C18:0, C18:1and C18:2was close to8%of microalgaelipid extracted by n-hexane-ethanol, while it only accounted for about3％in that extracted byethanol and it showed that n-hexane-ethanol has good selectivity with C18fatty acids, so takenthe biodiesel conversion into consideration, n-hexane-ethanol was more suitable for the synthesisof biodiesel. |
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