Hydrothermal conversion of scrap tire to liquid fuel

The hydrothermal liquefaction of scrap tires (ST) using a stainless-steel batch reactor is examined in this study. The effects of reaction temperature (from 200 to 430°C), corresponding pressure (from 0 to 28MPa), time (from 20 to 120min), H₂O/ST mass ratio (from 0/3 to 12/3), and atmosphere (air, CO₂, CO, H₂, and N₂) on the yields of product fractions (liquid products, gas, and char) and the properties of the liquid products were examined. Of the variables examined, temperature was the most influential factor affecting the yield and quality of the liquid products. Under optimal conditions, the highest liquid product yield of 52.73wt.% was achieved. Thermal decomposition of the ST begins at approximately 120°C and finishes at approximately 500°C. The addition of water made the complete conversion of ST milder than that its direct pyrolysis (without water). During hydrothermal liquefaction, water was partly incorporated into the liquid products. The liquid products, which are highly viscous at room temperature and flow with difficulty, had higher heating values of approximately 44.20-45.09MJ/kg. The liquid products mainly consisted of unsaturated hydrocarbons and aromatics, and approximately 60wt.% of the chemical energy in the ST was retained in the liquid products in these conditions. The gaseous products were mainly CO₂, H₂, and CH₄. This study suggests that ST can be hydrothermally converted into a high quality liquid fuel.