 Glucose is used in pharmaceutical applications as a filler and binder for tablets and sweetening agents. The thermal decomposition is investigated by means of thermogravimetric analysis. |
| Conditions of Measurements |
| Instrument: |
NETZSCH TG 209 C Iris® |
| Sample mass/mg: |
2.7 .. 2.9 |
| Heating rates/(K/min): |
1, 2, 5, 10 |
| Atmosphere: |
Argon |
| Gas flow rate/(ml/min): |
20 |
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| Thermal decomposition of Glucose |
| The first decomposition step produces mainly water. The mass loss of this step is independent from the heating rate. The mass loss of the second step, however, is strongly dependent on the heating rate. This is sufficient proof that after the first step the later decomposition follows at least two competing reaction paths. |
| Already now a proposal can be given for the kinetic model of the whole process (see result of model fit). |
| It should be emphasized once again that this model has a more formal character. In particular, no information on the proceeding chemistry can be given from thermogravimetric data only. Considerably more information would be obtained by coupling thermogravimetry with mass spectroscopy. |
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| Model-free analysis according to Ozawa-Flynn-Wall |
| The energy-plot indicates for the first step an activation energy of approximately 110 kJ/mol and for the dominant path of the second step an activation energy of 180 kJ/mol. |
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| Results of model fit |
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| Model-fit of Thermal Decomposition of Glucose |
| The triple-step reaction, containing competitive reaction paths, allows a high quality fit of all TGA measurements. |
| |
| Kinetic Parameters as Result of Nonlinear Regression |
| # |
Parameter |
Value |
Standard Dev. |
| 0 |
lg A1/s-1 |
10.60 |
0.31 |
| 1 |
Act.Energy 1/(kJ/mol) |
122.83 |
2.75 |
| 2 |
React.order 1 |
1.58 |
0.16 |
| |
| 3 |
lg A2/s-1 |
14.42 |
0.74 |
| 4 |
Act.Energy 2/(kJ/mol) |
182.14 |
7.92 |
| 5 |
React.order 2 |
1.80 |
0.05 |
| |
| 6 |
lg A3/s-1 |
- 3.54 |
0.72 |
| 7 |
Act.Energy 3/(kJ/mol) |
5.44 |
7.88 |
| 8 |
React.order 3 |
1.20 |
0.68 |
| |
| 9 |
Follow.React.1 |
0.27 |
0.012 |
| 10 |
CompReact. 2 |
1.00 |
constant |
| 11 |
CompReact. 3 |
0.03 |
0.06 |
| |
| 12 |
MassLoss 1 |
84.01 |
0.35 |
| 13 |
MassLoss 2 |
84.01 |
equal 12 |
| 14 |
MassLoss 3 |
84.01 |
equal 12 |
| 15 |
MassLoss 4 |
84.01 |
equal 12 |
| |
| |
Correlation Coeff. |
0.99973 |
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| The branched reaction path results in a specific behavior: by changing of the reaction temperature the parts of product C and D are varied. |
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| At temperature of 210 °C the largest part of B is transformed to the product D. Inversely, at a temperature of 280 °C the largest part is transformed to the product C. This behavior is caused by the large difference of the activation energies for step 2 and step 3, respectively. |
Thermokinetics
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