Direct Liquefaction Of Microalgae And Lignocellulosic Biomass In Ethanol-water Co-solvent For Bio-oil Production

Clean and renewable bio-fuels are considered to the most promising alternative fuels due to its low pollution and carbon neutral when compared with traditional fossil fuels.Among the biomass conversion technologies,direct liquefaction process,which can make full use of the whole biomass,is viewed as one of the best conversion methods for producing liquid bio-fuels because it is not sensitive to components in feedstocks and avoids the energy intensive drying and dewatering steps.Microalgae and lignocellulosic biomass have obvious differences in chemical compositions and cell structures.Thus,direct liquefaction of Spirulina?microalgae?and Spartina alterniflora?lignocellulosic biomass?were performed in ethanol-water co-solvent with a 50 mL autoclave reactor.The effects of operating parameters such as reaction temperature,ethanol volume fraction in co-solvent,reaction time and solvent to biomass ratio were conducted to understand its influence on direct liquefaction behavior of biomass,especially on product distribution and bio-oil properties.Various detection methods were used to analysis material characteristics,main components and energy assessment of the bio-oil.Meantime,potential reaction mechanism and simplified reaction pathways for direct liquefaction of biomass in ethanol-water co-solvent were explored preliminary.When Spirulina was used as the liquefaction material,results showed that Spirulina was a kind of low-lipid and high-protein microalgae with N content higher than that of lignocellulosic biomass.Moreover,the empirical formula and higher heating value?HHV?were CH_1.77O_0.57N_0.2 and 18.5MJ/kg,respectively.Reaction temperature,ethanol volume fraction and reaction time had significant effect on bio-oil yield which increased firstly and then declined.The optimal operating conditions for bio-oil yield and conversion rate were reaction temperature of 300 ?,reaction time of 45 min,ethanol content of 50 % and solvent to microalgae ratio of 40/4 mL/g,which gave the bio-oil yield of 59.5% and conversion rate of 94.73%.Ethanol was more easier than water to promote the conversion of large molecules to oil phase.Compared to single solvent,conversion rate in co-solvent was significantly higher,indicting the synergistic effect between ethanol and water during microalgae direct liquefaction.The results of FT-IR and GC-MS analyses revealed that composition and relative content of compound in bio-oil were affected by solvent types.The major compounds in bio-oil from water were acids and ketones,while esters were the most abundant compounds in bio-oil from both pure ethanol and co-solvent.Ethanol in co-solvent could react with acids and amides through esterification and alcoholysisreactions to obtain esters respectively,thus enhancing bio-oil quality and yield.The bio-oil obtained from 50% ethanol-water co-solvent had higher energy recover rate?80.7%?and HHV?33.9MJ/kg?than those from pure water.When Spartina alterniflora was used as the liquefaction material,results showed that Spartina alterniflora was one kinds of lignocellulosic biomass.The C and O contents in material were rich while N content was less than 1%.Additionally,the empirical formula and HHV were CH1.66O0.96N0.02 and 117.8MJ/kg,respectively.The heating rate affected the thermogravimetric characteristics of Spartina alterniflora.As the heating rate increased from 10 to 40 ?/min,TG and DTG curves were almost same but tended to shift toward to high temperature side because of the combination of time and temperature.Optimal operating conditions were reaction temperature of 340 ?,ethanol volume fraction in co-solvent of 50% and solvent to biomass ratio of 10 mL/g,resulting the highest bio-oil yield of 44.2% and minimum solid residue yield of 12%.Bio-oil was a complex and oxygen-containing organic mixture,mainly including acids,phenols,furans,esters and ketones.And the major components of bio-oil were phenols?29.62%?and esters?11.27%?.Most of the esters were from the esterification between acids and ethanol while the majority of phenols were derived from the decomposition of lignin.The energy recover rate of bio-oil obtained from direct liquefaction in ethanol-water co-solvent with 50%ethanol volume fraction reached up to 76.5%,which was significantly higher than that in single solvent?water or ethanol?.Based on synergistic effect between water and ethanol,not only bio-oil yield but also bio-oil quality were improved under 50% ethanol-water co-solvent.Therefore,direct liquefaction of different types of biomass in ethanol-water co-solvent was a potential way for bio-oil preparation.