Liquefaction Of Macroalgae Enteromorpha Prolifera In Sub-and Supercritical Fluids

With the gradual depletion of fossil fuels and the intensification of environmental pollution, to develop and use biomass renewable energy has received worldwide concern. Sub-/supercritical fluids can covert biomass to liquid fuels in a quick and efficient way for their excellent solvent properties, which makes it a research focus in the field of bio-energy conversion.In this study, the liquefaction behaviors of macroalgae Enteromorpha prolifera in sub-critical water, sub-/supercritical methanol and ethanol in a batch reactor were investigated. Different processing conditions on the liquefaction yields were studied, and liquefaction products were analyzed using a variety of detection methods, then the mechanisms of Enteromorpha prolifera liquefaction in water and alcohols were discussed.Temperature, reaction time and solid to liquid ratio significantly affected the liquefaction yields of Enteromorpha prolifera in subcritical water. In the condition without catalyst, temperature of 300℃, the solid to liquid ratio of 1:7.5, and reaction time of 30min led to the highest bio-oil yield of 20.4%, with residue yield of 16.2%. Na2CO3, K2CO3 and KOH as catalysts showed good catalytic effect for promoting the liquefaction of Enteromorpha prolifera, and to a certain extent, improved the bio-oil yield, while, the catalytic effect of FeSO4 was poor. The liquefaction of Enteromorpha prolifera in water at 300℃, reaction time of 30min, with 5% Na2CO3 yielded a 23.0% of bio-oil, and the bio-oil yield was 24.9% when 5% K2CO3 was added.The composition of bio-oil obtained by liquefaction of Enteromorpha prolifera in water was very complex, containing ketones, aldehydes, phenols, alcohols, alkenes, aromatics, fatty acids, methyl esters and nitrogen compounds, and the heating values of bio-oils were around 30MJ/kg. Catalysts showed almost no effects for altering the composition of bio-oils. The water-soluble organics were mainly composed of acids, glycerol and nitrogen compounds, in which the highest relative content was acetic acid. The liquefaction process of Enteromorpha prolifera in subcritical water was very complex. It mainly involved hydrolysis and condensation reactions of polysaccharides, cellulose, proteins and lipids, and also interactions between the intermediate products.Under the reaction time of 15min, the suitable condition for liquefaction of Enteromorpha prolifera in sub-/supercritical methanol was at 280℃, solid to liquid ratio 1:10, which resulted 31.08% bio-oil yield,41.36% residue yield; the suitable condition for liquefaction of Enteromorpha prolifera in sub-/supercritical ethanol was at 300℃, solid to liquid ratio 1:10, and resulting 35.31% bio-oil yield,42% residue yield.The main components of bio-oil obtained by liquefaction of Enteromorpha prolifera in methanol at 280℃were methyl esters, with the highest relative content of palmitic acid methyl ester, accounting for 31.87%, and the heating value of bio-oil was 25.06MJ/kg; the bio-oil obtained by liquefaction in ethanol at 300℃was mainly composed of ethyl esters, the highest relative content of palmitic acid ethyl ester, accounting for 37.10%, and the heating value of bio-oil was 30.05MJ/kg. In addition, the two bio-oils contained a certain amount of nitrogen compounds and small quantities of hydrocarbons, carbohydrates and fatty alcohols/ketones. The liquefaction process of Enteromorpha prolifera in sub-/supercritical methanol or ethanol mainly involved decomposition of each sub-unit of Enteromorpha prolifera and reactions between the intermediate products during decomposition, then a series of esterification reaction occurred between methanol/ethanol and all these products.