Lipids Enrichment In Diatoms By Growth Regulation And Characteristics Of Diatom Biodiesels

Development of bio-diesel is of great significance on the sustainable development of the economy, promoting energy alternative, reducing pressure on the environment and controlling the urban air pollution. Compared with terrestrial plants, microalgae have become the first choice for bio-fuel. Because microalgae have great biomass, short growth cycle, high lipid content and take no farmland.In order to enrich more lipids in diatoms and convert into more biodiesel fuels, the impacts of cell growth conditions (pH value, nitrogen content, silicon content and harvest time) on lipid enrichment in two diatoms (Chaetoceros gracilis and Nitzschia closterium) were studied in this paper. It is found that nitrogen deprivation, silicon deprivation and longer harvest time are beneficial to increase lipid contents in two diatoms, while C. gracilis has a higher lipid content than N. closterium. The lipid content in C. gracilis increases from 13.25% to 31.74% (2.4 times) with a lipid yield of 39.62 mg/L, when the silicon (Na2SiO3·9H2O) content decreases from 200 to 0 mg/L, nitrogen (NaNO3) content decreases from 12.0 to 0.5 mmol/L, arid harvest time increases from 8 to 32 days.Transform the bio-oil of the two diatoms into biodiesel by transesterfication and do gas chromatographic analysis of the biodiesel. Then we know the main fatty acids components of the two diatoms biodiesel are C14:0,C16:0,C16:1,C16:2,C16:3,C18:3 and C20:5。The content of each fatty acid in the two diatoms increases when the nitrogen is sufficicent, decrease when the nitrogen become lacking, and increases again when the algae adapte to nitrogen starvation. Harvest at the same time, there is a best nitrogen concentration that corresponding the highest lipid content of the two diatoms, and in this condition the contents of their short-chain fatty acids are highest and the contents of their long-chain fatty acids are lowest. Compared with the Chinese pistache tree bio-diesel and the cornus wilsoniana bio-diesel, the fatty acids compositions of the two diatoms bio-diesel are more complex, the carbon chains of the fatty acids are longer, and contains a large amount of C20:5;Thermogravimetric experiments are done to know the pyrolysis characteristics and kinetic parameters of pyrolysis of the two diatom bio-diesel, and compared these with Chinese pistache tree bio-diesel and the cornus wilsoniana bio-diesel. Then we obtain that the pyrolytic residue vol of Chaetoceros gracilis bio-diesel is lower than Nitzschia closterium, but higher than Comus wilsoniana bio-diesel and Chinese pistache bio-diesel. The pyrolysis charicteristics of the two diatoms are between Comus wilsoniana bio-diesel and Chinese pistache bio-diesel, the pyrolysis activation energy is lower, similar with the Comus wilsoniana bio-diesel, but far below the Chinese pistache bio-diesel. Among all the bio-diesel of the two diatom, the bio-diesel of the Chaetoceros gracilis cultivated under a nitrogen concentration of 0.5mmol/L, has the lowest pyrolytic residue vol, its pyrolysis starting temperature Ti is 192.58℃and its pyrolysis ending temperature Tn is 466.89℃, and its pyrolysis activation energy is the highest(46.684kJ/mol).