Fundamental Research On Microalgae Derived Biofuels By Higher Pressure Catalytic Liquefaction

Biomass directly liquefaction has been one of the main processes of producingrenewable bio-oils. This research, taking Spirulina （one kind of microalgae rich inprotein） as raw material, aims at converting the microalgae into biofuels. Taking theautoclave as reactor, the microalgae, H-donor solvent and catalysts were added intothe reaction. The following parameters were investigated in this paper: the reactiontemperature, ratio of material to solvent, holding time, the type and dosage of solventadditives and catalysts. To study the characteristics of bio-oils thoroughly, theinstruments of elemental analyzer, Fourier transform infrared spectrophotometry（FT-IR）, gas chromatography-mass spectrometer （GC-MS） and scanning electronmicroscopy （SEM） were employed in the analysis parts.The water as solvent, the range of reaction temperature was from200to300℃,and the yield of bio-oil reached the highest point（35.4%） at the temperature of300℃.Holding time was selected from10to60min, and the yield of bio-oils was increasedwith the rise of holding time. The largest bio-oil yield was49.3%. On the contrary, theyield of crude bio-oil declined with the increment of the ratio of material weight tosolvent volume. The ratio of0.20g/mL was regarded as the better condition for higheryield and productivity. The catalysts of zeolite-Ca and zeolite-Fe had no positiveeffect on improvement of the yield of biofuel. It could be considered that these twocatalysts were helpful for producing gaseous phase products. Elemental analysis datafor the oil illustrated that C content increased and that of O reduced significantly, andthe HHV （High Heat Value） increased up to30MJ/kg. According to the FT-IRspectrograms of bio-oils, these functional groups were observed: associating N-H,-CH₂-, C=O and C-O group, which might indicate the existence of amide and esterscontent. SEM images showed that complete cellular structure has been obviouslydamaged, and adhesion phenomenon of the residual was visible. Using ethanol as solvent, almost the corresponding parameters were investigated.The yield of bio-oil had increased before declined, with the temperature increasingfrom220℃to280℃. Under the temperature of260℃, the yield arrived at thehighest point of72.8%. The ratio of solid weight to solvent volume was investigatedfrom0.20g/mL to0.50g/mL, and the author considered that the value of0.30g/mLcould not only guarantee the productivity of the bio-oil but also save energy input.The yield of bio-oil rose from68.3%to74.8%, with the increase of holding time from10to30min, and then the yield remained stable. Tetrahydrofuran and ethylene glycol,hydrogen donor, were added into the reaction. The former one almost had noimprovement impact on the yield of bio-oils, which rose slightly to75.1%eventhough with8%tetrahydrofuran additive in the solvent. However, the ethylene glycolcould enhance the productivity significantly. The yield went up gradually with the riseof quantity of ethylene glycol, while the residue yield just remained round6.0%.Moreover, the particle of the residue was homogeneous and there was no debris andadhesion phenomenon. Several types of catalysts were tested for the hydrothermalliquefaction process. Actually, only two kinds of catalysts, Na₂SiO₃·9H₂O andCa-catalyst, could promote the generation of bio-oils obviously. The highest point ofliquid products arrived at79.4%, with the dosage of Ca-catalyst being5%. The besttemperature condition for this type of experiments was260℃as well. To the resultsof liquefaction with ethylene glycol additive and Ca-catalyst, the yield of bio-oil wasextremely as high as85.2%and that of residue was relatively as low as4.5%. Themain compounds of bio-oil maybe amide and esters matter according to the FT-IRanalysis, and it was obviously that no benzene compounds existed in the oil sample.GC-MS results, combined with that of FT-IR, indicated that the bio-oils might mainlyconsist of esters matter and N heterocyclic compounds （such as pyrimidine）. TheSEM images of the residue showed that the aggregation and adhesion appearancewere more serious, which just explained the higher yield of residual when usingethanol as solvent.