Comparative Thermal Degradation Behaviors and Kinetic Mechanisms of Typical Hardwood and Softwood in Oxygenous Atmosphere
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Thermogravimetric Experiments
2.3. Kinetic and Thermodynamic Analyses
2.3.1. Kissinger-Akahira-Sunose Approach
2.3.2. Coats-Redfern Approach
2.4. Determination of Combustion Characteristic Parameters
3. Results and Discussions
3.1. Thermogravimetric Analyses
3.2. Kinetic and Thermodynamic Analysis
3.2.1. Activation Energy by KAS Approach
3.2.2. Kinetic Mechanisms by the CR Approach
3.2.3. Thermodynamic Analyses
3.3. Kinetic Modeling
3.4. Combustion Characteristic Parameters’ Analysis
4. Conclusions
- (1)
- Softwood decomposition began and ended at lower temperatures than hardwood in air atmosphere. Two diverse peaks and one shoulder appeared on the reaction rate curves for both hardwood and softwood. The maximal reaction rate of hardwood was larger than that of softwood.
- (2)
- The activation energy was maintained at a constant in the conversion degree range of 0.1–0.6 for hardwood, while 0.1–0.65 for softwood. The thermal degradation process can be divided into two regions by the dividing points of α = 0.6 and α = 0.65 for hardwood and softwood, respectively. The mean E value of hardwood was larger than that of softwood during the whole decomposition process.
- (3)
- The thermal degradation process occurring in region 1 was dominated by the Avrami-Erofeev model (g(α) = [−ln(1 − α)]2) and the 3D diffusional model (g(α) = [(1 − α)−1/3 − 1]2) for hardwood and softwood, respectively. The average A value of softwood was larger than that of hardwood in region 1.
- (4)
- The simulated conversion degree curves were consistent with the experimental curves at 5, 15, 20, and 40 K/min. Therein, the thermogravimetric experimental profile under 20 K/min was not used for estimating the kinetic triplet.
- (5)
- The values of ignition temperature (Ti), peak temperature (Tmax), and burnout temperature (Tb) for both hardwood and softwood exhibited an increasing trend with the increased heating rate. Under the same external conditions (heating rate and atmosphere), the combustion performance of hardwood was superior to softwood.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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No. | Kinetic Mechanism | ||
---|---|---|---|
1. Power law | |||
1 | Nucleation | ||
2 | Nucleation | ||
3 | Nucleation | ||
4 | Nucleation | ||
2. Reaction order | |||
5 | Assumed random nucleation and its subsequent growth | ||
6 | Chemical reaction | ||
7 | Chemical reaction | ||
3. Avrami-Erofeev | |||
8 | Assumed random nucleation and its subsequent growth | ||
9 | Assumed random nucleation and its subsequent growth | ||
10 | Assumed random nucleation and its subsequent growth | ||
11 | Assumed random nucleation and its subsequent growth | ||
12 | Assumed random nucleation and its subsequent growth | ||
13 | Assumed random nucleation and its subsequent growth | ||
14 | Assumed random nucleation and its subsequent growth | ||
4. Contracting | |||
15 | Contracting cylinder (cylindrical symmetry) | ||
16 | Contracting sphere (spherical symmetry) | ||
5. Diffusion | |||
17 | One-dimensional diffusion | ||
18 | Two-dimensional diffusion | ||
19 | Three-dimensional diffusion, cylindrical symmetry | ||
20 | Three-dimensional diffusion |
Sample | Heating Rate (K/min) | Decomposition Temperature Range (K) | Shoulder Temperature (K)/Reaction Rate (K−1)/Conversion Degree α | First Peak Temperature (K)/Reaction Rate (K−1)/Conversion Degree α | Second Peak Temperature (K)/Reaction Rate (K−1)/Conversion Degree α |
---|---|---|---|---|---|
Hardwood | 5 | 451–753 | 560.82/6.41 × 10−3/0.21 | 596.27/14.30 × 10−3/0.50 | 730.93/4.80 × 10−3/0.96 |
15 | 459–781 | 582.49/6.25 × 10−3/0.23 | 616.05/12.65 × 10−3/0.50 | 756.53/5.30 × 10−3/0.96 | |
40 | 469–810 | 596.61/6.23 × 10−3/0.23 | 634.01/11.69 × 10−3/0.52 | 776.22/3.63 × 10−3/0.96 | |
Softwood | 5 | 441–738 | 564.67/7.88 × 10−3/0.29 | 589.10/10.26 × 10−3/0.50 | 711.54/4.55 × 10−3/0.94 |
15 | 444–765 | 585.76/8.03 × 10−3/0.32 | 606.09/9.04 × 10−3/0.49 | 735.42/6.93 × 10−3/0.95 | |
40 | 448–795 | 606.66/8.25 × 10−3/0.37 | 618.12/8.59 × 10−3/0.47 | 752.70/4.18 × 10−3/0.94 |
α | Hardwood | Softwood | Standard Deviation of E Values | Standard Deviation of A Values | ||||
---|---|---|---|---|---|---|---|---|
E (kJ/mol) | R2 | A (min−1) | E (kJ/mol) | R2 | A (min−1) | |||
0.10 | 170.62 | 0.9985 | 29.99 | 180.31 | 0.9997 | 32.72 | 4.85 | 1.37 |
0.15 | 170.42 | 0.9984 | 30.14 | 173.60 | 0.9997 | 31.40 | 1.59 | 0.63 |
0.20 | 172.22 | 0.9982 | 30.60 | 172.01 | 0.9998 | 31.17 | 0.11 | 0.29 |
0.25 | 175.89 | 0.9981 | 31.34 | 173.03 | 0.9999 | 31.46 | 1.43 | 0.06 |
0.30 | 180.56 | 0.9975 | 32.21 | 176.30 | 1.0000 | 32.18 | 2.13 | 0.02 |
0.35 | 182.94 | 0.9968 | 32.57 | 180.53 | 1.0000 | 33.06 | 1.21 | 0.25 |
0.40 | 180.64 | 0.9961 | 32.02 | 184.21 | 1.0000 | 33.80 | 1.79 | 0.89 |
0.45 | 176.89 | 0.9964 | 31.24 | 185.83 | 0.9998 | 34.10 | 4.47 | 1.43 |
0.50 | 173.87 | 0.9967 | 30.66 | 183.91 | 0.9993 | 33.68 | 5.02 | 1.51 |
0.55 | 172.59 | 0.9969 | 30.42 | 179.80 | 0.9993 | 32.82 | 3.61 | 1.20 |
0.60 | 175.92 | 0.9962 | 31.06 | 176.45 | 0.9993 | 32.05 | 0.27 | 0.50 |
0.65 | 191.68 | 0.9940 | - | 181.35 | 0.9986 | 32.61 | 5.17 | - |
0.70 | 223.85 | 0.9753 | - | 175.02 | 0.9974 | - | 24.42 | - |
0.75 | 214.93 | 0.9706 | - | 178.48 | 0.9948 | - | 18.23 | - |
0.80 | 203.91 | 0.9815 | - | 186.50 | 0.9875 | - | 8.71 | - |
0.85 | 200.89 | 0.9858 | - | 201.42 | 0.9725 | - | 0.27 | - |
0.90 | 201.56 | 0.9888 | - | 208.64 | 0.9700 | - | 3.54 | - |
Average 1 | 175.69 | 0.9973 | 31.11 | 178.73 | 0.9997 | 32.59 | 1.52 | - |
Average 2 | 206.14 | 0.9827 | - | 188.57 | 0.9868 | - | 8.79 | 0.74 |
Average | 186.43 | 0.9921 | - | 182.20 | 0.9952 | - | 2.12 | - |
No. | g(α) | 5 K/min | 15 K/min | 40 K/min | Average Value | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
E (kJ/mol) | lnA (min−1) | R2 | E (kJ/mol) | lnA (min−1) | R2 | E (kJ/mol) | lnA (min−1) | R2 | E (kJ/mol) | lnA (min−1) | R2 | ||
1 | α3/2 | 111.54 | 19.78 | 0.9722 | 115.1 | 21.19 | 0.9769 | 116.54 | 21.56 | 0.9772 | 114.39 | 20.84 | 0.9754 |
2 | α1/2 | 30.86 | 2.92 | 0.9586 | 31.88 | 4.3 | 0.9656 | 32.2 | 4.86 | 0.9658 | 31.65 | 4.03 | 0.9633 |
3 | α1/3 | 17.41 | −0.25 | 0.9415 | 18.01 | 1.13 | 0.9512 | 18.15 | 1.72 | 0.9512 | 17.86 | 0.87 | 0.948 |
4 | α1/4 | 10.69 | −2.03 | 0.9127 | 11.08 | −0.65 | 0.927 | 11.12 | −0.05 | 0.9262 | 10.96 | −0.91 | 0.922 |
5 | −ln(1 − α) | 85.95 | 15.04 | 0.9884 | 87.18 | 16.1 | 0.9898 | 88.27 | 16.54 | 0.9907 | 87.13 | 15.89 | 0.9896 |
6 | (1 − α)−1 − 1 | 103.3 | 19.09 | 0.9936 | 102.98 | 19.7 | 0.9941 | 104.31 | 20.12 | 0.9956 | 103.53 | 19.64 | 0.9944 |
7 | (1 − α)−2 − 1 | 123.13 | 24.38 | 0.9887 | 120.82 | 24.43 | 0.9903 | 122.43 | 24.81 | 0.9923 | 122.13 | 24.54 | 0.9904 |
8 | [−ln(1 − α)]2/3 | 54.14 | 8.28 | 0.9869 | 54.88 | 9.44 | 0.9883 | 55.52 | 9.95 | 0.9893 | 54.85 | 9.22 | 0.9882 |
9 | [−ln(1 − α)]1/2 | 38.24 | 4.79 | 0.985 | 38.73 | 5.99 | 0.9866 | 39.15 | 6.54 | 0.9877 | 38.71 | 5.77 | 0.9864 |
10 | [−ln(1 − α)]1/3 | 22.33 | 1.1 | 0.9799 | 22.58 | 2.35 | 0.982 | 22.78 | 2.94 | 0.9833 | 22.56 | 2.13 | 0.9817 |
11 | [−ln(1 − α)]1/4 | 14.38 | −0.91 | 0.972 | 14.5 | 0.36 | 0.9748 | 14.59 | 0.96 | 0.9763 | 14.49 | 0.14 | 0.9744 |
12 | [−ln(1 − α)]2 | 170.83 | 32.45 | 0.9943 | 172.14 | 32.98 | 0.9953 | 175.97 | 33.55 | 0.9961 | 172.98 | 32.99 | 0.9952 |
13 | [−ln(1 − α)]3 | 276.82 | 53.96 | 0.9902 | 280.99 | 54.45 | 0.9913 | 284.74 | 54.46 | 0.9921 | 280.85 | 54.29 | 0.9912 |
14 | [−ln(1 − α)]4 | 372.26 | 73.14 | 0.9904 | 377.89 | 73.33 | 0.9915 | 382.98 | 73.13 | 0.9923 | 377.71 | 73.2 | 0.9914 |
15 | 1 − (1 − α)1/2 | 78.25 | 12.53 | 0.9808 | 80.07 | 13.77 | 0.9837 | 81.05 | 14.22 | 0.9843 | 79.79 | 13.51 | 0.9829 |
16 | 1 − (1 − α)1/3 | 80.75 | 12.71 | 0.9838 | 82.38 | 13.9 | 0.986 | 83.4 | 14.35 | 0.9867 | 82.18 | 13.65 | 0.9855 |
17 | α2 | 151.88 | 27.88 | 0.9735 | 156.7 | 29.29 | 0.978 | 158.71 | 29.58 | 0.9783 | 155.76 | 28.92 | 0.9766 |
18 | α + (1 − α)ln(1 − α) | 160.89 | 29.26 | 0.9801 | 165.16 | 30.5 | 0.9832 | 167.29 | 30.77 | 0.9837 | 164.45 | 30.18 | 0.9823 |
19 | 1 − 2/3α − (1 − α)2/3 | 164.24 | 28.53 | 0.9822 | 168.26 | 29.7 | 0.9849 | 170.44 | 29.95 | 0.9854 | 167.65 | 29.39 | 0.9842 |
20 | [(1 − α)−1/3 − 1]2 | 192.38 | 34.98 | 0.9925 | 194.15 | 35.48 | 0.9932 | 196.72 | 35.69 | 0.9942 | 194.42 | 35.38 | 0.9933 |
No. | g(α) | 5 K/min | 15 K/min | 40 K/min | Average value | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
E (kJ/mol) | lnA (min−1) | R2 | E (kJ/mol) | lnA (min−1) | R2 | E (kJ/mol) | lnA (min−1) | R2 | E (kJ/mol) | lnA (min−1) | R2 | ||
1 | α3/2 | 105.58 | 18.77 | 0.9478 | 104.48 | 18.95 | 0.9514 | 104.42 | 19.35 | 0.9589 | 104.83 | 19.02 | 0.9527 |
2 | α1/2 | 28.92 | 2.55 | 0.9218 | 28.38 | 3.29 | 0.9256 | 28.21 | 4.04 | 0.9357 | 28.5 | 3.29 | 0.9277 |
3 | α1/3 | 16.15 | −0.52 | 0.8892 | 15.7 | 0.3 | 0.8922 | 15.51 | 1.11 | 0.905 | 15.79 | 0.3 | 0.8955 |
4 | α1/4 | 9.76 | −2.27 | 0.8345 | 9.35 | −1.41 | 0.8343 | 9.15 | −0.59 | 0.8499 | 9.42 | −1.42 | 0.8396 |
5 | −ln(1 − α) | 81.7 | 14.33 | 0.9747 | 80.71 | 14.67 | 0.9771 | 80.5 | 15.15 | 0.9818 | 80.97 | 14.72 | 0.9779 |
6 | (1 − α)−1 − 1 | 98.75 | 18.37 | 0.9923 | 97.57 | 18.58 | 0.9935 | 97.24 | 18.94 | 0.9952 | 97.85 | 18.63 | 0.9937 |
7 | (1 − α)−2 − 1 | 118.3 | 23.65 | 0.998 | 116.91 | 23.69 | 0.9982 | 116.43 | 23.94 | 0.9973 | 117.21 | 23.76 | 0.9978 |
8 | [−ln(1 − α)]2/3 | 51.33 | 7.8 | 0.9711 | 50.58 | 8.37 | 0.9737 | 50.37 | 8.99 | 0.9789 | 50.76 | 8.39 | 0.9746 |
9 | [−ln(1 − α)]1/2 | 36.15 | 4.41 | 0.9668 | 35.52 | 5.09 | 0.9695 | 35.3 | 5.8 | 0.9754 | 35.66 | 5.1 | 0.9706 |
10 | [−ln(1 − α)]1/3 | 20.96 | 0.83 | 0.9551 | 20.46 | 1.62 | 0.958 | 20.23 | 2.39 | 0.9655 | 20.55 | 1.61 | 0.9595 |
11 | [−ln(1 − α)]1/4 | 13.37 | −1.14 | 0.937 | 12.93 | −0.3 | 0.9396 | 12.7 | 0.51 | 0.9494 | 13 | −0.31 | 0.942 |
12 | [−ln(1 − α)]2 | 160.56 | 30.68 | 0.9801 | 160.72 | 30.8 | 0.9781 | 162.88 | 31.35 | 0.9796 | 161.39 | 30.95 | 0.9793 |
13 | [−ln(1 − α)]3 | 263.91 | 51.91 | 0.9786 | 261.48 | 50.88 | 0.9808 | 261.3 | 50.46 | 0.9849 | 262.23 | 51.09 | 0.9814 |
14 | [−ln(1 − α)]4 | 355.02 | 70.41 | 0.979 | 351.86 | 68.7 | 0.9812 | 351.7 | 67.82 | 0.9852 | 352.86 | 68.98 | 0.9818 |
15 | 1 − (1 − α)1/2 | 74.15 | 11.83 | 0.9605 | 73.25 | 12.24 | 0.9636 | 73.09 | 12.76 | 0.9699 | 73.5 | 12.28 | 0.9647 |
16 | 1 − (1 − α)1/3 | 76.59 | 12.01 | 0.9657 | 75.67 | 12.4 | 0.9685 | 75.49 | 12.91 | 0.9743 | 75.92 | 12.44 | 0.9695 |
17 | α2 | 143.91 | 26.55 | 0.9502 | 142.53 | 26.45 | 0.9538 | 142.53 | 26.66 | 0.9609 | 142.99 | 26.55 | 0.955 |
18 | α + (1 − α)ln(1 − α) | 152.72 | 27.91 | 0.9602 | 151.23 | 27.74 | 0.9634 | 151.17 | 27.9 | 0.9696 | 151.71 | 27.85 | 0.9644 |
19 | 1 − 2/3α − (1 − α)2/3 | 156 | 27.18 | 0.9637 | 154.48 | 26.97 | 0.9667 | 154.4 | 27.11 | 0.9726 | 154.96 | 27.09 | 0.9677 |
20 | [(1 − α)−1/3 − 1]2 | 183.6 | 33.59 | 0.9841 | 181.77 | 33.16 | 0.986 | 181.5 | 33.12 | 0.9893 | 182.29 | 33.29 | 0.9865 |
Sample | β (K/min) | ɑ (s−1) | 95% CI of ɑ | b (mol/kJ) | 95% CI of b | kiso | Tiso (K) | R2 | Temperature Range of Region 1 (K) |
---|---|---|---|---|---|---|---|---|---|
Hardwood | 5 | −3.3864 | (−3.7181, −3.0547) | 0.2059 | (0.2036, 0.2082) | 0.0338 | 584.16 | 0.9977 | 400–605 |
15 | −2.0282 | (−2.3536, −1.7028) | 0.1997 | (0.1975, 0.2019) | 0.1316 | 602.30 | 0.9977 | 400–624 | |
40 | −1.3764 | (−1.7022, −1.0506) | 0.1948 | (0.1926, 0.1970) | 0.2525 | 617.45 | 0.9976 | 400–641 | |
Total heating rates | −2.2630 | (−2.4769, −2.0491) | 0.2001 | (0.1986, 0.2015) | 0.1040 | 601.09 | 0.9969 | - | |
Softwood | 5 | −3.4308 | (−3.7637, −3.0979) | 0.2084 | (0.2060, 0.2108) | 0.0324 | 577.15 | 0.9975 | 400–613 |
15 | −2.4137 | (−2.7468, −2.0805) | 0.2025 | (0.2001, 0.2050) | 0.0895 | 593.97 | 0.9973 | 400–632 | |
40 | −1.4932 | (−1.8264, −1.1599) | 0.1975 | (0.2000, 0.1951) | 0.2247 | 609.01 | 0.9971 | 400–648 | |
Total heating rates | −2.4441 | (−2.6568, −2.2314) | 0.2028 | (0.2013, 0.2044) | 0.0868 | 593.09 | 0.9966 | - |
Conversion Degree, α | Hardwood | Softwood | ||||
---|---|---|---|---|---|---|
ΔH (kJ/mol) | ΔG (kJ/mol) | ΔS (J/(mol·K)) | ΔH (kJ/mol) | ΔG (kJ/mol) | ΔS (J/(mol·K)) | |
0.1 | 165.97 | 171.63 | 16.73 | 175.72 | 152.63 | 38.10 |
0.15 | 165.69 | 170.63 | 16.26 | 168.93 | 152.82 | 26.59 |
0.2 | 167.43 | 170.11 | 19.17 | 167.27 | 152.86 | 23.78 |
0.25 | 171.03 | 169.96 | 25.19 | 168.24 | 152.83 | 25.41 |
0.3 | 175.63 | 170.17 | 32.88 | 171.45 | 152.74 | 30.88 |
0.35 | 177.94 | 170.69 | 36.74 | 175.63 | 152.62 | 37.96 |
0.4 | 175.59 | 171.23 | 32.82 | 179.26 | 152.52 | 44.12 |
0.45 | 171.81 | 171.47 | 26.50 | 180.84 | 152.47 | 46.79 |
0.5 | 168.75 | 171.44 | 21.39 | 178.87 | 152.53 | 43.46 |
0.55 | 167.43 | 171.36 | 19.20 | 174.71 | 152.64 | 36.42 |
0.6 | 170.73 | 171.44 | 24.71 | 171.30 | 152.73 | 30.63 |
0.65 | - | - | - | 176.09 | 152.60 | 38.77 |
Average value | 170.73 | 170.92 | 24.69 | 174.03 | 152.67 | 35.24 |
Biomass | β/K min−1 | Temperature/K | −Rp/% min−1 | Time/min | Combustion Parameters | |||||
---|---|---|---|---|---|---|---|---|---|---|
Ti | Tp | Tb | ti | tp | tb | C/10−4% min−1 K−2 | Cb/10−4 min−1 | |||
Hardwood | 5 | 561.19 | 596.44 | 748.24 | 6.60 | 47.61 | 54.66 | 85.02 | 0.21 | 18.19 |
15 | 578.20 | 616.05 | 770.28 | 17.51 | 17.00 | 19.56 | 29.81 | 0.52 | 52.22 | |
40 | 589.01 | 634.01 | 800.23 | 42.13 | 6.65 | 7.77 | 11.93 | 1.21 | 117.80 | |
Softwood | 5 | 541.56 | 590.13 | 733.28 | 4.79 | 43.68 | 53.40 | 82.03 | 0.16 | 12.22 |
15 | 553.18 | 606.63 | 758.98 | 12.38 | 15.34 | 18.90 | 29.06 | 0.40 | 30.07 | |
40 | 563.29 | 616.58 | 787.57 | 32.17 | 6.00 | 7.34 | 11.61 | 1.01 | 70.23 |
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Xu, X.; Pan, R.; Chen, R. Comparative Thermal Degradation Behaviors and Kinetic Mechanisms of Typical Hardwood and Softwood in Oxygenous Atmosphere. Processes 2021, 9, 1598. https://doi.org/10.3390/pr9091598
Xu X, Pan R, Chen R. Comparative Thermal Degradation Behaviors and Kinetic Mechanisms of Typical Hardwood and Softwood in Oxygenous Atmosphere. Processes. 2021; 9(9):1598. https://doi.org/10.3390/pr9091598
Chicago/Turabian StyleXu, Xiaokang, Renming Pan, and Ruiyu Chen. 2021. "Comparative Thermal Degradation Behaviors and Kinetic Mechanisms of Typical Hardwood and Softwood in Oxygenous Atmosphere" Processes 9, no. 9: 1598. https://doi.org/10.3390/pr9091598