Thermal Decomposition Kinetics of Sugarcane Mills Wastes

Silva, D. R.; Crespi, M. S.; Ribeiro, C. A.; Capela, J. M. V.

Supplementary Material

Table S1General empirical kinetic model and r, s and q for some kinetic models [51]

Model / f (α) / r / s / q
R2 / 2 (1 – α)1/2 / 0 / 0.5 / 1
R3 / 3 (1 – α)2/3 / 0 / 2/3 / 1
F1 / 1 – α / 0 / 1 / 1
F2 / (1 – α)2 / 0 / 2 / 1
A3/2 / 1.5 (1 – α) [-ln (1-α)]1/3 / 0.338 / 0.856 / 1.003
A4 / 4 (1 – α) [-ln (1-α)]3/4 / 0.775 / 0.703 / 1.004

Fig. S1lnA versus E plots of studied samples in N2 atmosphere

Fig. S2lnA versus E plots of studied samples in N2/O2 atmosphere

Fig. S3Kinetic parameters of pyrolysis of the studied samples

Fig. S4Kinetic parameters of combustion of the studied samples

Appendix 1. Sample Constitution

Table A1Element concentrations in dry samples

Element / Macronutrients
Concentration (g kg-1, dry basis)
Bagasse / Filter Cake / Vinasse
A / B / A / B / A / B
Al / 0.28 ± 0.05 / 0.23 ± 0.05 / 8.14 ± 0.08 / 6.59 ± 0.11 / 0.80 ± 0.02 / 0.12 ± 0.02
Ca / 0.42 ± 0.03 / 0.40 ± 0.03 / 15.5 ± 1.8 / 27.0 ± 2.0 / 22.9 ± 2.0 / 20.8 ± 6.0
Fe / 0.40 ± 0.02 / 0.50 ± 0.10 / 12.3 ± 0.3 / 1.10 ± 0.03 / 1.48 ± 0.01 / 0.26 ± 0.03
K / 1.00 ± 0.07 / 1.10 ± 0.11 / 4.41 ± 0.47 / 1.00 ± 0.06 / 0.11 ± 0.06a / 0.10 ± 0.04a
Mg / 0.28 ± 0.01 / 0.26 ± 0.02 / 2.20 ± 0.14 / 1.57 ± 0.02 / 8.55 ± 0.03 / 9.52 ± 3.03
Na / 0.52 ± 0.06 / 0.43 ± 0.02 / 1.27 ± 0.12 / 0.64 ± 0.08 / 21.9 ± 1.1 / 20.9 ± 1.2
P / 0.13 ± 0.00 / 0.14 ± 0.00 / 3.72 ± 0.69 / 1.76 ± 0.03 / 1.90 ± 0.09 / 1.43 ± 0.00
Element / Micronutrients
Concentration (mg kg-1, dry basis)
Bagasse / Filter Cake / Vinasse
A / B / A / B / A / B
Cr / 2.12 ± 1.13 / 32.8 ± 5.4 / 50.6 ± 12.2 / 58.5 ± 5.4 / 49.0 ± 0.8 / 10.2 ± 4.4
Cu / 1.30 ± 0.28 / 2.90 ± 0.42 / 61.0 ± 3.0 / 40.0 ± 0.9 / 18.8 ± 2.8 / 9.60 ± 1.40
Mn / 18.6 ± 2.0 / 25.0 ± 1.8 / 1.03 ± 0.05a / 847 ± 26 / 361 ± 20 / 138 ± 6
Ni / 0.33 ± 0.00 / 13.4 ± 11.0 / 19.5 ± 4.4 / 10.6 ± 0.2 / 20.4 ± 2.4 / 7.87 ± 0.67
Pb / 13.5 ± 2.8 / 6.50 ± 0.71 / 43.0 ± 9.2 / 25.5 ± 2.1 / 30.5 ± 8.7 / 6.00 ± 9.64
Zn / 2.57 ± 0.42 / 3.97 ± 0.42 / 148 ± 23 / 145 ± 13 / 52.2 ± 1.9 / 25.8 ± 1.6

a x 103

From FT-IR spectra, it could be observed that all samples presented an organic similar composition with stretchings and scissorings related to carbonyl and hydroxyl functional groups in addition to C-C and C-H stretchings associated to aromatic rings and aliphatic chains, respectively, typical of any biomass (Fig. A1) [53]. SEM images showed that, after milling, bagasse and filter cake (Fig. A2C and Fig. A2D) samples presented fibrous and spongy fragments, respectively. For both wastes, holes and fractures in their surfaces could be seen, especially for filter cake. SEM image acquired for vinasse sample (Fig. A2E) displayed crystalline forms which, because of high hygroscopicity, reached dimensions above 200 μm. In contrast to what was observedin bagasse and filter cake samples, imperfections such as holes or fractures were not observed, resulting in particles with well-defined planes.

XRD profiles obtained for bagasse and filter cake samples displayed an amorphous aspect (Fig. A3A and Fig. A3B). Bagasse and filter cake samples showed a broad band around 22° corresponding to cellulose lattice plane (002) [54]. Regarding filter cake samples, slight differences between diffractograms could be seen, especially for Filter Cake B. Small peaks emerged around 40° and 58° due to the presence of SiO2 in addition to other calcium aluminum oxides [55, 56]. An even more pronounced peak was observed near 68° probably due to CaO since such metal was detected in a great concentration in that sample. Vinasse samples showed crystalline XRD profiles (Fig. A3C). Such observation likely resulted from the drying of these samples which favored crystallization of metals and Si, mainly as oxides. Other peaks related to SiO2 and CaOwere observed for both Vinasse A and Vinasse B.

Fig. A1 FT-IR spectra of a) Bagasse A (line) and Bagasse B (dotted line); b) Filter Cake A (line) and Filter Cake B (dotted line); c) Vinasse A (line) and Vinasse B (dotted line)

Table A2 Interpretation of FTIR spectra of samples [48]

Wave Number (cm-1) / Attribution
4000-3600
3600-3400
3400-3100
3000-2900
1800-1700
1700-1600
1600-1550
1550-1500
1500-1450
1450-1400
1400-1300
1300-1200
1150-1100
1100-1000
1000-950
950-900
900-850
850-800
800-750
650-600
600-500
500-450 / O-H stretching (free phenols and alcohols)
N-H asymmetric stretching
C-H stretching of =CH2
C-H stretching of –CH (methyl and methylene)
C=O stretching (non-conjugated ketones, carbonyl, and esthers)
C=O stretching (aromatic and p-substituted ketones)
C=O stretching coupled with aromatic rings vibrations
Aromatic rings vibrations
C-H asymmetric deformation (-CH3 and –CH2)
Aromatic rings vibrations coupled with C-H scissoring
C-H stretching (aliphatic C-H of CH3 and phenolic O-H)
Condensation of S and G rings
C=O deformation (conjugated esthers)
C-O deformation (secondary alcohols and aliphaticesthers)
C-H rocking (aromatic C-H), C-O deformation (primary alcohols) and C-H stretching
C-H angular deformation (CH sp)
C-H angular deformation (aromatic rings)
C-H angular deformation (G-unit)
CH2 vibration
OH angular deformation
C-C planar deformation
C-Cl angular deformation

Fig. A2 SEM images of: a) bagasse – 100x; b) bagasse – 1000x; c) filter cake – 100x; d) filter cake – 500x; e) vinasse – 100x

Fig. A3 XRD of samples of a) bagasse; b) filter cake; c) vinasse

Appendix 2.PCA of studied samples.

It can be observed that carbon and hydrogen concentrations were directly proportional to HHV because both C and H vectors show a slight deviation from HHV vector and all of them pointed to the third quadrant (Fig B1). However, sulfur and nitrogen concentrations pointed to the opposite direction (first quadrant), being inversely proportional to HHV. Oxygen concentration exhibited a low influence over HHV because the O vector pointed to the second quadrant, with a 90º angle about HHV vector. Thus, it can be said that every vector agreed with the modified Dulong’s Equation (Eq. 9) used in this work to estimate HHV.

Bagasse A was the only sample which was located in the third quadrant and presented one of the greatest HHVs of all samples. Despite being situated in the second quadrant, Bagasse B displayed an even more negative value of PC1 (-19, about -14 of Bagasse A) and the highest HHV when every studied sample was compared. Filter Cake B was placed, considering the third quadrant, in a nearer position in comparison with Filter Cake A which resulted in a higher HHV for Filter Cake B. Finally, both vinasse samples were located in the first quadrant and presented the lowest HHVs of all samples. Since Vinasse A was situated in a nearer position from the third quadrant about Vinasse B, HHV of Vinasse A was higher.

Fig.B1 PCA of studied samples (ultimate analysis and HHV)

Figure B2 shows, by a PCA plot, how the presence of metals and phosphorous affected HHVs of every studied sample. PC1 represented 95.87% of variance while PC2 accounted for 3.42% of that parameter. Together, they are responsible for 99.29% of sample variance. According to the vectors position in the PCA, it was verified that presence of inorganic matter affected HHVs negatively. Meanwhile, HHV vector pointed to the first quadrant; every other vector was pointing to other quadrants.

Only bagasse samples were located in the first quadrant. Their low contents of metals and phosphorous contributed to elevating their HHVs to the highest values detected when all samples were compared. Besides, since the concentration of metals and P were very similar to Bagasse A and Bagasse B shared the same point in PCA plot.

Filter cake samples were situated in the fourth quadrant. However, due to their distinct contents of inorganic matter, the distance between the points representing Filter Cake A and Filter Cake B was the largest about other samples. Filter Cake A presented the greatest Fe, Al and P concentrations detected for all samples. However, total inorganic content observed for Filter Cake A was lower than the one verified for Filter Cake B, mainly due to the great Ca amount detected for this sample. That resulted in a nearer position, about the first quadrant, for Filter Cake A and, thus, a higher HHV in comparison with Filter Cake B.

Regarding vinasse samples, it was seen that both were positioned in second and third quadrants border. High K contents detected for those samples were responsible for that, and their HHVs were the lowest among all studied samples. Consequently, both presented the largest distances about the first quadrant, and their PC1 was negative, below -60. Because the total metal content of Vinasse A was higher than Vinasse B, the PCA point representing the former had the most negative value for PC1 (around -75) and, thus, HHV of Vinasse A was the lowest when every sample was compared.

Fig. B2 PCA of studied samples (inorganic matter and HHV)

1