Kinetic study of the effect of the heating rate on the waste tyre pyrolysis to maximise limonene production

•The kinetic model of production of isoprene and dl-limonene from waste tire pyrolysis is proposed.•Increase in the heating rate increased the peak temperature of isoprene and dl-limonene.•The peak temperature increase was more significant in dl-limonene compared to isoprene.•Rapid heating resulted in the less energy allocated to the formation of products.•Increase in the heating rate favored the formation of the lower Ea compound (dl-limonene). The formation of isoprene and dl-limonene during waste tyre pyrolysis was investigated in terms of the effect of the heating rate (up to 100°C/min). Ion current signals were used to track during pyrolysis the evolution of the predominant ions of isoprene (isoprene 67) and dl-limonene (limonene 93), by using a thermogravimetric analyser coupled with mass spectrometry (TGA/MS). The combined model-free and model-based kinetics were used to estimate the activation energy (Ea) for isoprene and dl-limonene formation at 131 and 115kJ/mole, respectively, based on the Kissinger method. Reaction order (n) values were estimated at 1.2 and 1.1 for isoprene and dl-limonene, respectively. Better model fit (R2=0.998) of the experimental data to the Arrhenius equation for isoprene and dl-limonene, respectively, was observed when the Kissinger method was used compare to Friedman method. Although the Ea values for isoprene and dl-limonene were not significantly different, the combined three kinetic parameters (Ea, pre-exponential constant (A), and n) may be significantly different. Therefore, for dl-limonene formation selectivity over isoprene, the differences in the three kinetic parameters values for each compound model and heating rate on the reaction progress was significant. The reaction progress at peak isoprene and dl-limonene formation rate increased from 0.42 to 0.45 and more significantly from 0.35 to 0.44, respectively as the heating rate was increased from 15 to 100°C, confirming that the preferred strategy to maximise dl-limonene production is rapid heating to the moderate final pyrolysis temperature.