Co-pyrolysis of microalgae and waste rubber tire in supercritical ethanol

• Temperature and R/M ratio significantly affected yield and quality of the bio-oil.
• Microalgae allows the conversion of WRT under milder conditions than WRT alone.
• A positive synergistic effect was observed between the WRT and the microalgae.
• ZnO and carbon black in the WRT improved the quality of the bio-oil.
• HHVs of bio-oils were found to be in the range of 35.80–42.03 MJ/kg.

Co-pyrolysis of microalgae and waste rubber tire (WRT) in supercritical ethanol was examined to investigate the effects of reaction temperature (290–370 °C), time (10–120 min), WRT/microalgae mass ratio (R/M, 5/0–0:5), and ethanol/feedstock ratio (EtOH/(R + M), 5:5–30:5). Temperature and mass ratio are two factors that significantly affect the yield and quality of bio-oil. Under optimal reaction conditions, the highest bio-oil yield achieved was 65.4 wt%. The presence of microalgae allows the conversion of WRT to occur under milder conditions than WRT alone. The temperature needed for adequate conversion of WRT and microalgae in supercritical ethanol (330 °C) is much lower than the co-pyrolysis temperature without a solvent. ZnO and carbon black in the WRT played catalytic roles in the conversion of the WRT and microalgae as well as the in situ denitrogenation and deoxygenation of the bio-oil. A positive synergistic effect between the WRT and the microalgae was observed. The highest value for the synergistic effect (37.8%) was observed at an R/M mass ratio of 1:1. The interaction of microalgae and WRT during co-pyrolysis also favored denitrogenation and deoxygenation, thus improving the quality of the bio-oil. The heating values of the bio-oils produced from the co-pyrolysis of WRT and microalgae were found to be in the range of 35.80–42.03 MJ/kg. The main components in the gas phase are typically CO2, H2, and CH4. However, methods for improving the quality of bio-oil via co-pyrolysis will require further study.