The transformation and fate of sulphur during CO2 gasification of a spent tyre pyrolysis char

The transformation and fate of sulphur (S) in a spent tyre pyrolysis char during CO2 gasification were studied by following the S species and contents using X-ray photoelectron spectroscopy (XPS). The spent tyre pyrolysis char (particle size fraction <= 150 mu m), without and with 1 M HCl acid washing to remove inorganic S, were gasified in a fixed bed reactor. The effect of temperature (850, 950, 1050 degrees C), reaction time (1, 2, 3, 6 h) and CO2 concentration (33.3, 50.0, 66.7 vol% in N 2 ) on the S species in the char samples were investigated. The main S species in the spent tyre pyrolysis char were ZnS and aliphatic sulphide. After CO2 gasification, aliphatic sulphide, thiophene, sulphoxide and sulphone became the dominant organic S while ZnS and CaSO4 were the main inorganic S. The percentage of total S increased with increasing gasification temperature, time and CO2 concentration. The content of organic S increased with increasing gasification temperature and time, while, the content of inorganic S decreased. Increasing CO2 concentration had negligible effect on the content of organic S but led to significant reduction in the content of inorganic S since ZnS reacted with CO2 to produce ZnO and SO2. Aliphatic sulphide, sulphoxide and sulphone were shown to have transformed to more stable thiophene. ZnS decomposed to release SX at > 900 degrees C while CaSO4 reacted with CO and carbon to produce COS. Both SX and COS reacted with the organic matrix in the char to form sulphoxide and sulphone. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.