Waste tyres valorization by solvent extraction pre-treatment and pyrolysis.
Russ, Kyola Ngosa.
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Solvent extraction was studied as a pre-treatment method to eliminate certain impurities such as additives, plasticizers and heteroatoms before pyrolysis of waste tyres. This approach is the starting point for the proposal of waste tyres treatment to increase the yield of the liquid fraction and the efficiency of the pyrolysis process's accuracy. Two solvents, DCM and DEE, were used during the pre-treatment process. The products from both the pre-treated and untreated waste tyres crumbs pyrolysis are compared in yield and characterized using various analysis such as TGA, FTIR, GCMS. The results show that DCM is the best solvent for waste tyres pre-treatment due to its polarity and strength in the heteroatom removal. The optimum results were found at an extraction time of 150 min, a recovery of 14.15 wt.% for oil yield using waste tyres small size (0.5-1 mm) with a selectivity of 1.35. These results make DCM a suitable solvent in the waste tyres pre-treatment. The GCMS results for TDO show the predominance of DL-Limonene and BTXE, while those from solvent extraction oil show a predominance of 4-Benzenediamine, N-1,3-dimethylbutyl-N. This compound is used during the tyres manufacturing process as a rubber accelerator. The FTIR results show a prevalence of alkane, alkene, aldehyde and halo-compound functional group. The waste tyres crumb pre-treated and untreated have conducted to the pyrolysis unit as a feedstock. The highest oil yield was 55.64 wt.% at 550 °C, with the nitrogen flow rate of 6.5 l min-1 and 15 °C min-1 heating rate using waste tyres treated with DCM, large particle size (4-5 mm). The FTIR analysis shows a predominance of carbonyls C=O, aldehyde CHO and ketone RCOR. There is also some ester RCOOR, acid RCOOH, N-H bending amine with a strong bond in the wavenumber range between 1700-400 cm-1. As can be seen from the results above-mentioned, the better way to deal with waste tyres is to pre-treat them with solvent extraction using DCM as a solvent and the particle size in the range of 1-5 mm before the pyrolysis process. This method showed an improvement in the oil yield with a significant decrease in impurities.