Valorisation of rubber granules by hydrothermal treatment

Abstract

Several treatments were tested on rubber granules to try to eliminate benzothiazole, which is the most abundant VOC detected. First, hydrothermal treatments with water as the only reagent were evaluated. They resulted in an important decrease in the amount of VOCs as more than 80% of benzothiazole was removed after only 1.5h of treatment. Good VOC removing performance were obtained by the 3h hydrothermal treatment with 0.1M in HNO3 as it managed to successfully remove benzothiazole from the granules. This highlights that hydrothermal treatment appears as a very promising method to remove VOCs from rubber. The other purpose of this work was to investigate the ability of hydrothermal treatment to valorize rubber granules for further applications. Treatments of rubber granules with nitric acid managed to greatly degrade the rubber network of the granules and to produce a carbonaceous powder. 6h hydrothermal treatments with 1.5M in HNO3 therefore greatly degrades the polymer, completely extracts zinc from the granules and yields a carbon black powder with good properties. This powder was used as an anode in a coin cell, with impedance measurement confirming the conductivity of the powder. The attempt to achieve galvanic cycling on the battery obtained failed due to a short circuit appearing during the charge of the cell. This short circuit could be explained by the persistence of polymer and/or SiO2 in the powders which would be degraded when charging the battery. Treatment of the powders under reducing atmosphere resolved this problem. Galvanostatic cycling of the reduced powders revealed a significantly greater capacity which could be explained by the presence of Si. In conclusion, the battery formed with the reduced powders as anode appears as of now to be a promising application of the powders recovered by hydrothermal degradation of rubber granules.