Co-liquefaction Of Microalgae And Synthetic Polymer Mixture In Sub-and Supercritical Ethanol

Co-liquefaction of microalgae （Spirulina） and synthetic polymer （HDPE,high-density polyethylene） in sub-and supercritical ethanol was investigated in astainless steel autoclave （1000mL） at different reaction conditions （i.e. reactiontemperatures, feedstock/ethanol ratio, solvent filling ratio and catalysts）. Therelationship between the liquefaction conditions and liquefied products yield as wellas characterization of products was studied. Meanwhile, the optimized reactionconditions of co-liquefaction of microalgae and HDPE was established by analyzingthe total conversion of liquefaction, the yields of bio-oil and residue. The propertiesand chemical composition of bio-oils from liquefaction of different raw materials（pure microalgae, pure HDPE and microalgae/HDPE mixture （1:1）） were analysed bya series of chemical analysis methods to explore controllable liquefaction route andprovide theoretical basis for improvement of the yield and quality of bio-oil products.The bio-oil yields of the co-liquefaction were deeply affected by the reactiontemperatures. The bio-oil yields and total conversion of the co-liquefaction wereenhanced with the increment of temperature. To identify the influence of the additionof microalgae to thermal degradation of HDPE in co-liquefaction reactions, seriesexperiments of liquefaction with different composition of feedstock （pure microalgae,pure HDPE, micraogalae/HDPE mixture （1:1）） were conducted in a low temperature（340℃）. The conversion of pure HDPE in340℃was much lower （<10%），however,co-liquefaction of HDPE and microalgae could shift the thermal decomposition ofpolypropylene to a lower temperature and lowered the thermal stability of HDPE. Thevariety of feedstock/solvent ratio had a remarkable influence to the productdistribution. There existed a positive correlation between the solvent filling ratio andthe reaction pressure. When the solvent filling ratio was increased from12%to20%,the yield of liquid products was improved. However, more residues were producedwhen the solvent filling ratio exceeded20%. Alkali catalysts added in the liquefactionprocess induced the increment of residue yield, while FeSO₄and HZSM-5canpromote the gas products.Bio-oil from liquefaction of pure microalgae contained higher O content andlower concentration of C and H. Fuel properties of microalgae bio-oil （i.e. the acidvalue and caloric value） were not up to fossil fuel standards. Compared to themicroalgae liquefaction, the bio-oil from co-liquefaction of microalgae and HDPE had a higher concentration of C and H, together with a higher heating value.It was established by the FT-IR and GC-MS analyses that the bio-oil fromliquefaction of pure microalgae contained large quantities of oxygen containingcompounds, such as fatty acids, fatty acid esters and ketones. Octadecanoic acid（RT=27.39min） was the most abundant compound in microalgae bio-oil, according tothe maximum peak area （41.23%）. As regards the bio-oil derived from liquefaction ofmicroalgae and HDPE, wide spectrum of hydrocarbon was detected. The chemicalcomposition of the bio-oil derived from microalgae/HDPE co-liquefaction was similarto that from pure HDPE.