Abstract
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 (
R
1), (
Spirulina
+
HDPE)/ethanol ratio (
R
2) and solvent filling ratio (
R
3). 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
R
2 and a 2/10
R
3 was increased by 44.81
wt.% when the
R
1 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
R
1 resulted in a decrease in
SE. The yields of bio-oil increased with increasing
R
2 firstly and then declined. An opposite trend was observed for the yield of residue. The effect of
R
3 to the yields of liquefaction products was similar to that of
R
2. The content of C and H in bio-oils reduced with increasing
R
1, 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.
► Co-liquefaction characteristics of
Spirulina and HDPE were investigated. ► The addition of
Spirulina could make the conversion conditions of HDPE milder. ► Significant synergetic effects between
Spirulina and HDPE increased bio-oil yield. ► The presence of HDPE also improved the quality of
Spirulina-derived bio-oil. ► Adhesion between
Spirulina and HDPE could impede the heat and mass transfer.