Evaluation on hydrothermal gasification of waste tires based on chemical equilibrium analysis

Massive amounts of waste tires are produced globally, which brings great challenges to the disposal and recycling of used tires. Hydrothermal gasification is a promising option for recycling waste tires. The hydrothermal gasification of waste tires was evaluated based on the chemical equilibrium analysis along with the response surface methodology (RSM) in terms of subcritical temperature range (250–300 °C), transition temperature range (350–400 °C), supercritical temperature range (550–600 °C), supercritical pressure (22.5–30.5 MPa) and feedstock concentration (5–20 wt%). CH4 yield at 350 °C reached a maximum, 41.575 mmol/g. H2 yield increased from 0.0283 to 53.602 mmol/g with increasing the temperature from 250 °C to 600 °C. CH4 yield at the supercritical temperature increased with lifting the feedstock concentration, while H2 yield decreased. The optimal parameters regarding maximum H2 and CH4 yields in the subcritical temperature range were 300 °C, 22.5 MPa and 12.5 wt%, respectively, while they in the supercritical temperature range were 550 °C, 30.5 MPa and 5.4 wt%, respectively. RSM was more suitable for predicting H2 yield in the hydrothermal gasification of waste tires at subcritical and supercritical temperature ranges, but it was available for predicting CH4 yield in three temperature ranges. This study can provide basic data for the hydrothermal treatment of waste tires.