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 a stainless steel autoclave (1000 mL) at different reaction temperatures (T), Spirulina/HDPE ratio (R₁), (Spirulina + HDPE)/ethanol ratio (R₂) and solvent filling ratio (R₃). Results showed that the addition of Spirulina to HDPE liquefaction could make the conversion conditions of HDPE milder. The yield of bio-oil obtained at 613 K with a 1/10 R₂ and a 2/10 R₃ was increased by 44.81 wt.% when the R₁ was raised from 0/10 to 4/6. Meanwhile, the synergetic effects (SE) between HDPE and Spirulina were increased from 0 to 30.39 wt.%. Further increasing R₁ resulted in a decrease in SE. The yields of bio-oil increased with increasing R₂ firstly and then declined. An opposite trend was observed for the yield of residue. The effect of R₃ to the yields of liquefaction products was similar to that of R₂. The content of C and H in bio-oils reduced with increasing R₁, while the content of O increased. The bio-oil from pure Spirulina liquefaction runs mainly consisted of oxygen-containing compounds, such as carboxylic acids, esters and ketones. But the major components of bio-oil from co-liquefaction of Spirulina and HDPE mixture were similar to those of pure HDPE-derived bio-oil, in which aliphatic hydrocarbons dominated.