Valorisation of tyre waste from a vulcanisation plant by catalytic pyrolysis – Experimental investigations using pyrolysis–gas chromatography–mass spectrometry and drop-tube–fixed-bed reactor

Abstract

This study focuses on the use of car tyre waste collected at a tyre repair station in Krakow (Poland). Waste from damaged tyres is disposed of as municipal solid waste. Therefore, the management of waste tyres already shredded by pyrolysis at 500 °C has been proposed. Tyre waste was hypothesised to be converted into valuable chemical products by pyrolysis in a hybrid reactor (drop-tube–fixed-bed reactor). On a micro scale, pyrolysis–gas chromatography–mass spectrometry was used to analyse the pyrolysis process. It has been shown that the formation of aromatic hydrocarbons during pyrolysis clearly depends on whether the catalyst and tyre waste are mixed together or arranged in layers. Since the layered arrangement favoured the formation of hydrocarbons, such a system was used in the drop-tube–fixed-bed reactor. The high heating rate (500 °C/s) of tyre particles in the drop-tube–fixed-bed reactor at 500 °C allowed for the obtained a raw carbon black yield of 40.8 %. A similar yield of raw carbon black determined by thermogravimetric analysis for a heating rate of 0.17 °C/s) was observed at 800 °C. However, before commercial use, raw carbon black requires demineralisation because of its high ash content (approximately 50 %). The raw carbon black ash contained up to 90 % $SiO_{2}$, indicating that it could be a valuable catalyst material. Pyrolysis of tyre waste over the catalyst reduced the oxygen content in the oil and yield. The oil yields of tyre pyrolysis without a catalyst and over zeolite Y were 38 wt% and 35 wt%, respectively. The main components identified in the tyre pyrolysis gas were methane (27.6%), ethene (28.8%), and hydrogen (15.6%). The gas from catalytic pyrolysis was richer in CO and $CO_{2}$.