# Thermogravimetric Study of Refuse Derived Fuel Produced from Municipal Solid Waste of Kazakhstan
## 3 Results and Discussions
### Combustion Kinetics
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Sample**} & \multicolumn{3}{c}{**Paper**} & \multicolumn{3}{c}{**Plastic**} & \multicolumn{3}{c}{**Textile**} & \multicolumn{3}{c}{**RDF**} \\ \hline Heating rate (\({}^{\circ}\)C/min) & 10 & 20 & 30 & 10 & 20 & 30 & 10 & 20 & 30 & 10 & 20 & 30 \\ DTG\({}_{1}\) (\%/min) & 9.4 & 19.9 & 26.1 & 5.5 & 8.1 & 9.7 & 7.3 & 14.8 & 19.7 & 7.3 & 13.8 & 23.3 \\ Temperature and DTG\({}_{1}\) (\({}^{\circ}\)C) & 320 & 329 & 326 & 312 & 326 & 340 & 328 & 347 & 344 & 309 & 319 & 326 \\ DTG\({}_{2}\) (\%/min) & 3.9 & 5.5 & 7.1 & 3.2 & 7.8 & 16.2 & 4.1 & 7.2 & 11.4 & 3.0 & 5.8 & 7.3 \\ Temperature DTG\({}_{2}\) (\({}^{\circ}\)C) & 434 & 458 & 471 & 424 & 450 & 451 & 424 & 429 & 434 & 417 & 426 & 440 \\ DTG\({}_{3}\) (\%/min) & 0.4 & 0.5 & 0.9 & 5.1 & 6.7 & 8.5 & 3.3 & 6.4 & 7.8 & 2.6 & 4.6 & 6.7 \\ Temperature at DTG\({}_{3}\) (\({}^{\circ}\)C) & 640 & 662 & 679 & 476 & 495 & 500 & 502 & 504 & 531 & 457 & 478 & 471 \\ DTG\({}_{4}\) (\({}^{\circ}\)min) & - & - & - & 0.3 & 0.9 & 1.2 & 0.2 & 0.4 & 0.7 & 0.4 & 0.7 & 1.0 \\ Temperature at DTG\({}_{4}\) (\({}^{\circ}\)C) & - & - & - & 614 & 671 & 678 & 607 & 631 & 663 & 645 & 672 & 663 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Differential thermogravimetry (DTG) peak characteristics of paper, plastic, textile, and RDF samples during combustion. It is important to notice that the correlation coefficients significantly decreased for textile and RDF fractions during combustion. There are three combustion regimes that could occur, namely diffusion-controlled, intermediate, and kinetically controlled regimes. The results, as observed from Figure S1a-c reveals that at low temperatures, 292-370 \({}^{\circ}\)C for textile and 264-319 \({}^{\circ}\)C for RDF, kinetically controlled combustion occurred. As the temperature increases to 375 \({}^{\circ}\)C for textile and 320 \({}^{\circ}\)C for RDF, the combustion regime changed to intra-particle diffusion regime, which led to a decline of correlation coefficients. Kinetic parameters of RDF samples calculated by FWO, KAS, and Friedman methods shown in Table 4. It can be noted that the regression coefficient (R\({}^{2}\)) of RDF samples have shown higher values in most points of conversion, except one point of 0.6 (see Table 4). Lastly, as shown in Figure 6, the activation energies of RDF and its fractions, viz., paper, textile, and plastic varied significantly as conversion rate were changed. The activation energies of paper increased slightly and then decreased at higher conversion rates. This is consistent with the literature and is due to gradual degradation of cellulose that finally results in ash. In case of textile, fluctuations were observed in the activation energies, which occurred due to textile content. The reason of first increase in the activation energy can be due to decomposition of aliphatic polyester while the second increase can be due to decomposition of aromatic polyester, which is used in the textile production. Interestingly, the higher activation energies were not required for plastic combustion at lower conversion rate. However, there was a peak at 348 kJ/ mol, which can be a sign of dechlorination or the hydrocarbon decomposition. The curve of E\({}_{a}\) vs. \(\alpha\) for RDF samples gradually decreased from \(\sim\)370 to \(\sim\)140 kJ/kmol. With conversion rate up to \(\alpha<50\), the relationships were slightly above the other compounds, while \(\alpha>50\) onward, the relationship was found between the curves of plastics, paper and textile. Overall, the relationship of E\({}_{a}\) vs. \(\alpha\) of RDF samples were still closer to other compounds as shown in Figure 6.