Biodiesel Production From Wet Microalgae Through Extraction With Hexane After The Transesterification Of Lipid

As sources of third generation biofuel, microalgae are considered as a promising alternative and a renewable feedstock source for biofuels. Instant catapult steam explosion (ICSE) was employed to disrupt wet microalgal cells for efficient lipid extraction.The structural and morphological changes of wet microalgal cells disrupted through ICSE were characterized throughvariousmeasurement.A chloroform-free novel process for the efficient production of biodiesel from wet microalgae is proposed. The yield of FAME extracted into the hexane from the wet microalgae is increased 6-fold after the transesterification of lipids. Subcritical water was employed to separate microalgal lipid from wet biomass for biodieselproduction.Instant catapult steam explosion (ICSE) was employed to disrupt wet microalgal cells for efficient lipid extraction. The exploded cells increased in fractal dimension (1.53-1.65) when preheat time was prolonged from 0 min to 5 m in and in surface pore area when steam pressure was increased. Meanwhile, the exploded cells decreased in mean size (1.69-1.44μm) when the filling ratio of wet microalgal biomass in the preheat chamber decreased (75%-12.5%). The specific energy requirement of ICSE treatment for cell disruption was only 8.15 MJ/kg. The lipid yield was increased from 56% to 93.9% after ICSE.A chloroform-free novel process for the efficient production of biodiesel from wet microalgae is proposed. Crude biodiesel is produced through extraction with hexane after microwave-assisted transesterification (EHMT) of lipids.Decreased droplet size and lipid polarity were observed after transesterification with alcohol in microalgae cells. The yield of FAME extracted into the hexane from the wet microalgae is increased 6-fold after the transesterification of lipids. Organics with apolar functional groups in the cytoplasm decreased the contact angle of methanol against triglyceride by 13.92°, which subsequently increased transesterification efficiency by 2.4 times. The microalgal biomass, given its higher hydrophilicity index of 1.96 than lipids, was more accessible to hydrophilic alcohols, which subsequently promoted transesterification. Water in the cytoplasm promoted the dielectric constant of methanol and increased the contact angle of methanol against triglyceride by 20.51°, which subsequently decreased transesterification efficiency by 72.6%. Microwave decreased the electric constants of alcohols and reduced the polarity difference between alcohols and lipids, thereby improving transesterification efficiency. Microwave-assisted transesterification with ethanol and isopropanol, which were more miscible with lipid in cells, resulted in higher fatty acid alkyl ester (FAAE) yields than that with methanol when the reaction temperature was lower than 90 ℃. The crystallization temperatures (0.19℃ and -3.15℃) of biodiesels produced from wet microalgae through lipid transesterification in cells with ethanol and isopropanol were lower than that with methanol (2.08℃).To avoid the use of organic solvents, subcritical water was employed to separate microalgal lipid from wet biomass for biodieselproduction. Subcritical waterdisruptedthe microalgal cells and subsequently disrupted the stronger interaction between lipid and other molecule. The microalgal lipid was then separated through filtration due to its high viscosity and insolubilization in water. Microalgal riglyceride was hydrolysis in subcritical water, and thus subsequentlypromoted the acid-catalyzed biodiesel production.72.3% of microalgal lipid was separated after treated withsubcritical water at 260℃.The rate of acid-catalyzed conversion formicroalgal lipid was increased from 49.6% to 98.4% after treated in subcritical water at 260℃.Thus, biodiesel production from microalgae without organic solvent was achieved.The FAME content in crude biodiesel extracted with hexane is 86.74%, while that in crude biodiesel extracted with chloroform is 75.93%. The higher heating value (41.18 MJ/kg) for the crude biodiesel extracted with hexane is greater than that of the crude biodiesel (38.45 MJ/kg) extracted with chloroform. Products of vacuum distillation at teampurature of 105-254℃, 255-259℃, and 260℃-280℃ were obtained. Theproducts of vacuum distillation at different teampurature were characterized through Gas chromatography-mass spectrometer, Nuclear and magnetic resonance spectroscopy, Fourier transform infrared spectroscopy (FTIR), and thermogravimetry (TGA). High FAME content of 94.6% was obtained after vacuum distillation at 255-259℃.A pilot-scale system with 10 tons of biodiesel production per year from microalgae was built in Inner Mongolia based on the novel EHMT process. The HHV of the biodiesel produced from pilot-scale system was 40.79MJ/kg. The biodiesel produced from pilot-scale system were shown to meet the national standards by third-party testing organizations.