Comparative Studies On Sub-and Supercritical Liquefaction Characteristics Of Microalgae Using Different Organic Solvents

The effect of solvent type on liquefaction characteristics of Spirulina wereinvestigated in the same autoclave at different temperatures from300to380℃usingpolar protic solvent (methanol and ethanol) and dipolar aprotic solvent (1,4-dioxane).The paper analyzed the relationship between liquefaction conditions and liquefiedproducts yield as well as characterization of products. The optimaized reactiontemperature of microalgae liquefaction was established. The yields of bio-oils,physical and chemical properties of bio-oils obtained with different solvents were alsocompared through various analyses to explore the liquefaction mechanism,controllable liquefaction route.The temperature was an important affect of liquefaction of biomass, as theconversion rate increased continuously with the increased temperature. And the typeof solvent had an obvious influence on the conversion rate. Methanol had the bestpromotion influence on the conversion rate of Spirulina following with ethanol and1,4-dioxane, respectively.Compared with using1,4-dioxane as solvent, higher conversion rates ofSpirulina using methanol or ethanol were obtained inllustrating that the alcoholicsolvents could react with the intermediates derived from microalgae. The effect ofsolvent type on the yields of bio-oil was obvious.The oxygen content of microalgae bio-oils was decreased to9.91-12.43%from39.19%, and the caloric value was also increased greatly. The bio-oil produced withmethanol contained higher carbon and hydrogen concentrations but a lower oxygencontent, resulting in a higher caloric value. The content of nitrogen and oxygen inbio-oil was high, as a result, the further refining processes to remove the nitrogen andoxygen in bio-oil product is still necessary for their application.The results of FTIR and GC-MS analyses indicated that the compositions ofbio-oil products were greatly affected by the type of solvent used for the liquefactionprocess.The major compounds of bio-oils were phenols, alkanes and alkenes, esters (longchain or aromatic esters), organic acids, nitriles and nitrogen heterocycles (indolesand pyridines). The major component of bio-oil produced with methanol washexadecanoic acid methyl ester (C17H34O2,35.53%). However, ethanol favored theformation of hexadecanoic acid ethyl ester (C18H36O2,26.27%). When Spirulina were operated with1,4-dioxane, the bio-oil was dominated by hexadecanenitrile(C16H31N,22.7%).