Kinetic study of thermal processing of glycerol by thermogravimetry

Over the past years, the production of biodiesel has significantly increased in Brazil due to its obligatory use in the composition of diesel for vehicle use. As a result, in the most ordinary processes, a hundred thousand tons of glycerol is produced as by-product per 1 billion liters of biodiesel. Glycerol has already been widely studied. Nonetheless, the quantity produced today demands new proposals for uses, such as a fuel. In this aim, the authors studied the kinetics of the thermal processing of glycerol. In this research, thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA) were used to provide the experimental data. Kinetic parameters were calculated by Kissinger method for the global process observed during the heating of the samples from the room temperature up to 600 °C, both in open and in sealed crucibles (with a little hole). Kinetic data were also determined at different isoconversion conditions during heating, by applying Ozawa–Flynn–Wall and Blazejowski methods to TG data. Results show that glycerol heated from 30 to 600 °C, under normal pressure, does not experience simple volatilization. The activation energies calculated at different conversion degrees by these methods show that only volatilization occurs when the mass loss of glycerol is lower than 40% and that for higher conversion degrees, partial thermal decomposition and/or dissociation of glycerol are occurring as well. These facts are also confirmed by the volatilization enthalpies estimated using another method developed by Blazejowski based on Van’t Hoff equation.     

Thermal degradation of fluorocarbon elastomers by thermogravimetry

The thermal degradation of fluorocarbon and fluorochlorocarbon polymers has been studied using dynamic thermogravimetry. The effects of silicate fillers, carbon black and the cross-linking reaction on the degradation parameters (temperatures, rates) and activation energies were found. Kinetic values were determined with the procedure of Freeman and Carroll via graphical and computer techniques.     

Thermal degradation and oxidation of polystyrene studied by factor-jump thermogravimetry

Factor-jump thermogravimetry has been used to study the activation energy of polystyrene degrading in a vacuum, in N₂ flowing at 4 mm/s and in $\text{N}{}_2\text{O}{}_2$ mixtures. The results show the activation energy to be 44·9 ± 0·2 kcal/mole (188 ± 0·8 kJ/mole) for degradation above 350°C in vacuum or in flowing N₂. This agrees well with work reported in 1949 by Jellinek⁷ but with few results reported subsequently.The apparent activation energy for polystyrene losing weight above 280°C in an atmosphere of abundant O₂ is 21·5 ± 0·2 kcal/mole (90·2 ± 0·8 kJ/mole). In all cases where O₂ was deliberately introduced (partial pressures >4 mm Hg), the sample degraded to a black tar and the activation energy was ≤30 kcal/mole, depending on the amount of oxygen present and on the thermal history of the sample.     

Thermal decomposition of gamma-irradiated potassium bromate by dynamic thermogravimetry

The thermal decomposition of γ-irradiated KBrO₃studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were computed by means of the Coats-Redfern, Freeman-Carroll and modified Horowitz-Metzger methods and were compared with those for the unirradiated salt. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy is decreased on irradiation. The mechanism for the decomposition of unirradiated and irradiated KBrO₃ follows the Avrami model equation, [1-(1-α)^1/3] = kt, and the rate-controlling process is a phase boundary reaction assuming spherical symmetry.     

Thermal stability of glycerol containing compounds from the biodiesel production chain

Journal of Thermal Analysis and Calorimetry - Glycerol is a by-product from transesterification for biodiesel production. Due to the presence of hydroxyl groups (–OH), glycerol is pointed as...     

Possibilities of determination of alteration degree of rocks by thermogravimetry

Rhyolite-rhyodacite tuff samples were analysed by X-ray powder diffraction, ICP-OES and thermogravimetric (TG) methods to determine mineral and major element composition as well as different types of bound water, respectively. Similarly to CIA values, some TG parameters (H₂O[I] — water released up to ca. 200–220°C; H₂O[III] — water loss above 500–550°C and H₂O[I+III]) show positive correlation to the amount of secondary minerals. Moreover, these parameters are in close positive correlation to CIA values. Our results suggest that TG determination of different types of bound water may serve as a useful tool for estimation and characterisation of alteration degree of rocks.     

Determination ofFe 2+ content of NiZnCo iron-excess ferrites by thermogravimetry

Experimental results are reported on the determination by thermogravimetry of the iron(II) content of the NiZnCo ferrite with the molar ratio Fe₂O₃NiOZnOCoO=59.019.520.51.0.     

Thermal degradation of polyisobutylene studied using factor-jump thermogravimetry

The overall activation energy of the thermal degradation of polyisobutylene has been measured using factor-jump thermogravimetry to be 206±1 kJ/mole over the range 365 to 405° in N₂ at 800 mm Hg pressure and flowing at 4 mm/s over the sample. This is consistent with some values reported for thermal degradation in vacuum and in solution. In 5 mm Hg of N₂, an apparent activation energy of 218±2 kJ/mole was found, and in vacuum the apparent activation energy is 238±13 kJ/mole. Troublesome bubbling made the vacuum values difficult to measure. Substitution of reasonable values for the activation energies of initiation,E _i , termination,E _t , and the activation energy,E _a , for vacuum degradation in the equationE _a =E _i /2E _d -E _t /2 yields an activation energy E_d=84 kJ/mole for the unzipping reaction. This equation presupposes a degradation mechanism of random initiation, unzipping, and bimolecular termination. Substitution of reasonable values for the heat of polymerization, ΔH, in the definition ΔH=E _p ?e _d suggests that the activation energy of the polymerization reaction at 375° is approximately 30 kJ/mole.     

Thermal stability of limestone with a low iron content

The thermal stability of reagent-grade calcite and limestone samples with high and low content of iron compounds was compared. The causes of the revealed differences were discussed.     

Determination of the water content of foods : Indirect determination of the water content

The indirect determination of the water content of foods is dealt witli on the basis of tlie following general considerations: A. The absolute vapour pressure of the water in the substance to be desiccated ; B. The absolute vapour pressure of the water in the surrounding air, C. Behaviour of the non-water components of the substance to be desicented , D. Special causes of errors, viz.: 1.. Retardation in the establishment of equihbrium; 2. Retardation due to title structure of the substancc to be desiccated, 3. Crust formation; 4. Analytical errors. E. Rate of desiccation: reference methods and rapid routine methods.We prefer to consider the problems relating to the indirect determination of the water content on the basis of absolute water vapour pressures. The advantages and disadvantages of this method of treatment have been indicated.     

Thermal stability of fatty acids in subcritical water

In this work, hydrolytic reaction conditions of various temperatures (300–370 °C) and times (0–30 min) at a constant pressure of 20 MPa were applied to the thermal decomposition of three kinds of fatty acids (FAs), stearic acid, oleic acid, and linoleic acid, in subcritical water. The degradation characteristics were investigated from the derived data, and the thermal stability of FAs in subcritical water was estimated. The primary reactions we observed were isomerization and pyrolysis of FAs. The main pathway of degradation was deduced by analyzing the contents of pyrolyzed products. We found that more saturated FAs have greater thermal stability in subcritical water. All FAs remained stable at 300 °C or below. Based on these results, we recommend that hydrolysis of vegetable oils and fats using subcritical water should be carried out below 300 °C (at 20 MPa) and for less than 30 min to obtain high-yield FA production.     

The determination of coal combustion kinetics with thermogravimetry

This investigation concerns the determination of the kinetics of coal combustion. It is not well possible to use an exact analytical formula for the rate equation. For that reason a stepwise method is proposed, giving the activation energy as function of the reaction parameter , without assumption of any specific rate equation.

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Zusammenfassung Diese Arbeit beschäftigt sich mit der Kinetik der Kohleverbrennung. Für die Reaktionsgeschwindigkeit ist es jedoch nicht möglich, eine exakte analytische Gleichung anzuwenden. Aus diesem Grunde wird ein schrittweises Vorgehen vorgeschlagen, das die Aktivierungsenergie ohne Voraussetzung jeglicher spezifischer Geschwindigkeitsgleichungen als Funktion des Reaktionsparameters liefert.

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The authors wish to thank Mr. L. J. M. van der Valk for doing a lot of the experiments and Mr J. J. B. van, Hoist for making the drawings.     

Thermal degradation study of isotactic polypropylene using factor-jump thermogravimetry

The degradation of isotactic polypropylene in the range 390–465°C was studied using factor-jump thermogravimetry. The degradations were carried out in vacuum and at pressures of 5 and 800 mm Hg of N₂, flowing at 100–400 standard mL/s. At 800 mm Hg this corresponds to linear rates of 1–4 mm/s. In vacuum bubbling in the sample caused problems in measuring the rate of weight loss. The apparent activation energy was estimated as 61.5 ± 0.8 kcal/mol (257 ± 3 kJ/mol). In slowly flowing N₂ at 800 mm Hg pressure the activation energy was 55.1 ± 0.2 kcal/mol (230 ± 0.8 kJ/mol) for isotactic polypropylene and 51.1 ± 0.5 kcal/mol (214 ± 2 kJ/mol) for a naturally aged sample of atactic polypropylene. For isotactic polypropylene degrading at an external N₂ pressure of 5 mm Hg the apparent activation energy was 55.9 ± 0.3 kcal/mol (234 ± 1 kJ/mol). A simplified degradation mechanism was used with estimates of the activation energies of initiation and termination to give an estimate of 29.6 kcal/mol for the ß-scission of tertiary radicals on the polypropylene backbone. Initiation was considered to be backbone scission ß to allyl groups formed in the termination reaction. For initiation by random scission of the polymer backbone, as in the early stages of thermal degradation, an overall activation energy of 72 kcal/mol is proposed. The difference between vacuum and in-N₂ activation energies is ascribed to the latent heat contributions of molecules which do not evaporate as soon as they are formed. At these imposed rates of weight loss the average molecular weights of the volatiles in vacuum and in 8 and 800 mm H_g N₂ are in the ratios 1–1/2–1/9.     

Thermal stability of limestone with a medium content of iron

The thermal stabilities of limestone with varied content of iron are compared. The nature of the differences observed is discussed.     

HPLC-ELSD法测定生物柴油中游离甘油含量

建立了高效液相色谱(HPLC)-蒸发光散射(ELSD)法测定生物柴油中游离甘油的方法。用水萃取生物柴油中的甘油,选用强酸型阳离子交换柱(Ultimate XB-SCX)分离甘油和杂质,流动相为乙腈-水(25:75,V:V),柱温35℃;ELSD漂移管温度30℃,载气压力360 kPa。结果表明:在7.12～307.31 mg/kg范围内,甘油峰面积和其浓度的对数具有良好的线性相关性,相关系数r为0.9929。甘油的回收率为96.3%～105.6%,RSD均小于2.0%(n=5)。最低检测限(LOD)和最低定量限(LOQ)分别为2.50 mg/kg、7.12 mg/kg。该研究为生物柴油中游离甘油的提取和检测提供了一种快速高效的方法。     

Variability in water sorption and in thermogravimetry of bentonite

Macroscopic and microscopic /SEM/ arrangement of bentonite grains, the average particle thickness. δ and therniogravimetry, TG were found to be dependent on sample preparation and storing conditions, i.e. drying from suspension, water sorption, WS or water retention, WR. Decreased δ, incraased TG-weight loss and compact microaggregates were observed after WR test. Increased δ, decreased TG and loose macroaggregates were the results of WR tost.     

Thermal decomposition study of chloride-containing complex ammonium nitrate-based fertilizers by thermogravimetry and differential scanning calorimetry

Thermogravimetry and differential scanning calorimetry were used to study the thermal properties of chloride-containing complex ammonium nitrate-based fertilizers produced with various degrees of phosphoric acid ammonization on the basis of ammonium nitrate. Isoconversion integral methods were used to calculate the dependence of the activation energy on the degree of exothermic decomposition. It was shown that the exothermic decomposition process occurs in several stages. A conclusion was made on the basis of the results obtained that the thermal decomposition of these types of fertilizers is affected by the degree of ammonization and by the component ratio.     

Thermal relaxation of glycerol and propylene glycol studied by photothermal spectroscopy

In this paper we report on experimental data for the frequency and temperature dependence of the thermal properties of supercooled glycerol and propylene glycol. By using a photopyroelectric method the specific heat capacity and thermal conductivity were separately determined in a bandwidth of several decades. We have recently shown that the thermal conductivity has no relaxation behavior, which simplifies the analysis of our results. The relaxation behavior of the specific heat capacity is compared with literature results for other physical quantities and a detailed analysis of the temperature dependence of the relaxation parameters is presented.     

Study on water evaporation through 1-alkanol monolayers by the thermogravimetry method

The influence of 1-alkanol monolayers on the rate of water evaporation has been studied by measuring water loss per unit time using thermogravimetry. The evaporation rate of water from the surface covered by an insoluble monolayer for each of four saturated 1-alkanols (C(13)OH, C(15)OH, C(17)OH, and C(19)OH) was measured as a function of temperature and alkyl chain length, where the monolayer was under equilibrium spreading pressure. The evaporation rate decreased with increasing alkyl chain length or increasing molecular interaction among 1-alkanol molecules in the insoluble monolayer. Using the Arrhenius equation, the activation energy for the water evaporation was calculated from the temperature dependence of the evaporation rate, which showed that the activation energy decreased with increasing temperature. On the other hand, the activation energy increased with increasing alkyl chain length, which indicates that the activation energy includes the energy to cross the insoluble monolayer at the air/water interface. This energy increased almost linearly with alkyl chain length, when the length is longer than a dodecyl group. This means that water molecules need more energy to escape from the liquid to the gaseous phase across a membrane of longer 1-alkanols, which becomes more evident at lower temperatures. The temperature dependence of the activation energy was slightly larger for longer 1-alkanols than for shorter ones.