Pyrolysis Characteristics of Tire Rubber at Low Temperatures

Pyrolysis of used tires is a promising method for recovering valuable chemicals. However, the conventional high-temperature pyrolysis of natural rubber (polyisoprene)-based tires suffers from a low-selective isoprene recovery, heavy carbon black (CB) damage, and coke formation on the CB. In this paper, we report on characteristics of the low-temperature pyrolysis of CB-containing polyisoprene-based tire rubber that is vulcanized with sulfur. The low-temperature pyrolysis of the tire rubber cleaves the main chain and cross-linking bonds, which allows for the recovery of low-molecular-weight tire rubbers, tire rubber dissolution into the solvent, and CB isolation from the rubber matrix. The maximum liquid rubber recovery rate was 76.7% after 1 h of heating at 282 °C. In addition, the molecular weight of the thermally treated rubber substantially decreased from M_w 340,000 to approximately 20,000 after 1 h of heating at 282 °C. Furthermore, the maximum isoprene skeleton retention rate of the recovered rubber was 83% at 267 °C after 1 h of heating. The remaining rubber matrix on the recovered CB surface was nearly eliminated at temperatures above 320 °C. In conclusion, we believe that the low-temperature pyrolysis of tire rubber is a promising pretreatment method for recovering CB without thermal damage and reducing the molecular weight of tire rubber, which will improve the recovery of isoprene.