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.     

Kinetics of evaporation of some liquids by thermogravimetry

Latent heat of evaporation is one of the decisive factors in the design and operation of chemical plants [1], Brennan et al. [2] have shown that the heat of evaporation of a liquid and the activation energy of evaporation, E^evap_act are found, as expected, to be numerically similar. We present here some results on the kinetics of evaporation of five liquids (selected at random) based on TG data.     

A kinetic analysis of the pyrolysis of some australian coals by non-isothermal thermogravimetry

The pyrolysis of a suite of brown coal samples and bituminous coal maceral concentrates is investigated by non-isothermal thermogravimetry. The TG data for these coals reveal a two-stage pyrolysis process. The activation energy for the primary pyrolysis stage is considerably higher than that for the secondary pyrolysis stage. It is evident that a particular coal may be characterised by the weighted mean apparent pyrolysis activation energy which correlates with the corresponding specific energy of the coal.

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Zusammenfassung Mittels nichtisothermer Thermogravimetrie wurde die Pyrolyse einer Reihe von Braunkohlenproben und Mazeralkonzentrate aus bituminösen Kohlen untersucht. Die TG-Daten dieser Kohlen weisen einen zweischrittigen Pyrolyseprozeß auf. Die Aktivierungsenergie für den ersten Pyrolyseschritt ist erheblich höher als die des zweiten Pyrolyseschrittes. Es ist offensichtlich, daß eine gegebene Kohle durch den gewichteten Mittelwert der scheinbaren Aktivierungsenergie der Pyrolyse charakterisiert werden kann, welcher mit der entsprechenden spezifischen Energie der Kohle korreliert.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday     

Kinetic dehydroxylation of nontronite,estimated from isothermal and nonisothermal thermogravimetry

Dehydroxylation of an American nontronite (Manito) was followed via records of isothermal and dynamic thermogravimetry. Analysis of the isothermal weight-change curves (673-753 K). was performed with the procedure suggested by Hancock and Sharp. A fourteen-kinetic equation procedure was employed for analysis of the non-isothermal weight change in the range 623–1023 K. (A second-order decomposition equation seems to fit the dehydroxylation better under these conditions). The activation energies associated with the isothermal and nonisothermal processes are 118.8 and 136.8 kJ/mol^–1, respectively.

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Zusammenfassung Anhand isothermer und herkömmlicher Thermogravimetrie wurde die Dehydroxylierung eines amerikanischen Nontronites (Manito) verfolgt. Die isothermen TG-Kurven (673–753 K) wurden mittels der von Hancock und Sharp (1972). Ein kinetisches Vierzehngleichungsverfahren wurde zur Analyse der nichtisothermen TG-Kurven im Bereich 623–1023 K angestellt. Einer Dehydroxylierung unter diesen Bedingungen scheint eine Zersetzungsgleichung zweiter Ordnung besser zu entsprechen. Die Aktivierungsenefgie für die isothermen bzw. nichtisothermen Prozesse beträgt 118,8 bzw. 136,8 kJ/mol.

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(). (673–753 ) . , 623–1023, . . , , 118,8 136,8 /.

     

Volatility rate by thermogravimetry

ASTM Committee E37 on Thermal Measurements published a new test method 'Standard Test Method for Volatility Rate by Thermogravimetry' in June 1999 with the designation E 2008. This approach to assessing volatility utilizes an extension of the pinhole technology previously employed by E37 for vapor pressure determinations using differential scanning calorimetry (ASTM E 1782). After publication of the test method E 2008, an Interlaboratory Study was undertaken to develop a 'Precision and Bias' statement to be assigned with the test method. This paper provides some background data that supports the claim that E 2008 is generally insensitive to experimental conditions other than temperature. The Interlaboratory Study showing the statistical review is also discussed.     

Kinetic investigation of ethylene polymerization catalyzed by nickel-diimine catalysts

The effect of ethylene pressure on the activity of ethylene polymerization with the complex (1,4-bis(2,6-diisopropylphenyl))-acenaphtenediimine-dichloronickel(II) (1) and trimethylaluminum was evaluated. At low ethylene concentrations, the polymerization rate is first order with respect to monomer concentration. At higher ethylene concentrations, the polymerization rate has a negative order with respect to monomer concentration. We propose a mechanism where the active sites are in a dynamic equilibrium with latent states, the later having two monomer molecules coordinated to the metal center. In situ spectroscopic observations corroborate the proposed mechanism and show that the cocatalyst nature might affect the ion pair formation.     

Kinetic investigation of photopolymerization initiated by oligomeric photolatent base

Macrophotoinitiators often show polymer effect and photolatent bases make molecular amplification reaction. A main-chain oligomer containing α-aminoalkylphenone chromophore (OAK) had been synthesized with the characteristics of both photoinitiators and photolatent base hybrid structure. In order to determine whether such an effect or reaction exists in photopolymerization initiated by OAK, we used photo-differential scanning calorimeter to analyze the kinetic behavior. The experimental rate constants at different conversions were obtained by Arrhenius equation at different temperatures, the theoretic rate constants were simultaneously calculated with the use of phenomenological model. The results showed that the model correctly predicts the rate constant at the early stage, but underestimates it later. The comparative experiment between OAK and polymeric α-hydroxyalkylphenone photoinitiator (KIP150) shows that the molecular proliferation reaction caused by OAK significantly increases the experimental rate constant in the high-crosslinked stages of the polymerization. The photolatent base would be expected to provide one possible pathway in tackling photo-curing of opaque/thick material.     

Following photochemical reactions by thermogravimetry

A new thermal analysis system has been designed to follow the influence of light on solid reactants. This method is based upon the association of a thermogravimetric system for the kinetic measuring method, and a U. V. irradiation system for the activation method. This instrument allows comparative studies of a thermal reaction and the corresponding photochemical one under exactly the same experimental conditions. The experiments, carried out in silver carbonate, have provided new information on photochemical kinetics, but also on solid-state reactivity and even on thermal processes. More generally, this device, designed for studies on reactivity, can be applied to any other system needing the action of light. With the device, the influence of the light intensity, the wavelength and the lifetime of light effects on many reactions can be studied.

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Zusammenfassung Ein neues thermisches Analysensystem zur Untersuchung der Einwirkung von Licht auf feste Reaktanden wird beschrieben. Die Methode beruht auf einer Kombination eines thermogravimetrischen Systems für kinetische Meßmethoden mit einem UV-Bestrahlungssystem für die Aktivierungsmethode. Das Gerät ermöglicht vergleichende Untersuchungen einer thermischen und der entsprechenden photochemischen Reaktion unter gleichen Versuchsbedingungen. An Silbercarbonat ausgeführte Untersuchungen haben neue Informationen über die photochemische Kinetik, aber auch über die Festkörperreaktivität und sogar über thermische Prozesse ergeben. Allgemeiner gesagt, das für Reaktivitätsstudien konstruierte Gerät kann auch zur Untersuchung anderer die Einwirkung von Licht erfordernden Systeme benutzt werden. Mit dem Gerät können der Einfluß der Lichtintensität, der Wellenlänge und der Wirkungsdauer der Lichteffekte auf viele Reaktionen untersucht werden.

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Kinetic investigation of aquation of some Fe(II) Schiff base amino acid complexes

Kinetics of aquation of some Fe(II) Schiff base amino acid complexes was followed spectrophotometrically. The Schiff base ligands were derived from salicylaldehyde and isoleucine, leucine, serine, methionine, tryptophan, or histidine. The reaction was studied in aqueous media, aqua–propanol mixtures, and in the presence of different concentrations of KBr. Moreover, the activation parameters were calculated and discussed for structures and other physical properties observed. The reaction was acid catalyzed and the general rate equation was suggested as follows: rate = k_obs [complex], where k_obs = k₂ [H⁺]. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 372–379, 2010     

Cyclo dehydration reaction of polyhydrazides. II. Kinetic parameters obtained from isothermal thermogravimetry

The kinetics of the thermal conversion reaction of poly-(1,3-phenyl-1,4-phenyl)-hydrazide into poly-(1,3-phenyl-1,4-phenyl)-1,3,4-oxadiazole have been studied with isothermal thermogravimetry in continuation of a study with nonisothermal thermogravimetry described in a previous paper. Although the isothermal measurements are much more time-consuming, they provide some new information and insight about the cyclo dehydration reaction of the polyhydrazide. The physical state of the sample, rubbery or glassy, seems to influence the kinetics considerably. The kinetic parameters determined with the isothermal method for the polymer in its glassy state agree well with the parameters derived from the previously reported nonisothermal measurements, while the kinetic parameters for the expected rubbery state differ considerably. The morphological state or the history of the polymer has also a considerable influence on the kinetics of the isothermal conversion process. The powder form of the polymer has a much lower isothermal conversion rate than the film form.     

Cyclo dehydration reaction of polyhydrazides. I. Kinetic parameters obtained with nonisothermal thermogravimetry

The thermal conversion reaction of poly-(1,3-phenyl-1,4-phenyl)-hydrazide into poly-(1,3-phenyl-1,4-phenyl)-1,3,4-oxadiazole has been studied using thermogravimetry (TG). For the evaluation of the energie of activation and other kinetic parameters of this cyclo dehydration reaction a method developed by Ozawa was used, where polymer samples are heated with different constant heating rates. With this method the energy of activation can be determined accurately as a function of the degree of conversion. In this way a parallel reaction could be observed starting at the end of the nonisothermal conversion process. The polymer was used in two different morphological states, a powder and a film. A slightly higher energy of activation and a considerably higher pre-exponential factor were observed for the film indicating a dependency of the kinetics on the morphological state or on the history of the polymer sample.     

Kinetic investigation on alcoholysis of triethylaluminium by differential thermal analysis

The alcoholysis of triethylaluminium can be investigated by DTA in the liquid phase. The reaction enthalpy of the alcoholysis with primary alcohols is from –150 to –170 kJ mole^–1 in tetrahydrofuran/toluene as solvent. The reaction rate in pure hydrocarbons is higher than in the presence of Lewis bases. The reaction mechanism is probably ofS _E2 type and the reactivity decreases in the sequence primary, secondary, tertiary alcohol. In the second step of substitution the diethylaluminium alkoxides are less reactive than triethylaluminium because of the stronger association of the alkoxides. For the turnover of two moles of alcohol with one mole of triehylaluminium two DTA peaks appear in accordance with consecutive reactions.

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Zusammenfassung Die Reaktion zwischen einer Lösung von Alumimumtriethyl und einer Reihe von aliphatischen oder aromatischen Alkoholen kann mittels DTA quantitativ verfolgt werden. Die negative Reaktionsenthalpie der Alkoholyse mit primären Alkoholen beträgt 150 bis 170 kJ mol^–1, sofern ein Lösungsmittelgemisch aus Tetrahydrofuran/Toluen eingesetzt wird. Die Reaktionsgeschwindigkeit in unpolaren Kohlenwasserstoffen ist grösser als in Gegenwart von Lewis-Basen. Wahrscheinlich ist der Reaktionsmechanismus vom TypS _E2, wobei die Reaktivität in der Folge primäre, sekundäre, tertiäre Alkohole fällt. Der zweite Schritt der Alkoholyse, ausgehend vom Diethylaluminiumalkoxid, ist wegen der starken Selbstassoziation weniger reaktiv. Bei Umsatz von 2 Mol Alkohol treten entsprechend der Folgereaktion zwei DTA-Peaks auf.

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. –150 –170 ^–1 - . , . , S _E2 , , . , , . -, .

     

Investigations of perlites by modified differential thermogravimetry

DTA, TG and TMA were used to study wool samples of 64 quality, dyed and chromed in a dyeing bath at a low temperature (353 K), as well as by the conventional method involving boiling (369 K). The TMA data allowed establishment of the basic temperatures connected with theα-β transition of the wool keratin, the melting of the crystal regions and protein denaturation. It was shown that wool fibres chromed with 30 w.% K₂Cr₂O₇ at 353 K exhibit a decreased exothermic process in the range 700–750 K, which provides a possibility for evaluation of the effect of processing on the structural changes of the fibre keratin.     

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.     

Monitoring of calcium stearate formation by thermogravimetry

Naphthenates are produced when naphthenic acids present in crude oil are mixed with brine. They deposit at oil/water interface and are insoluble in either of the phases causing a large problem to the oil industry. Generally, naphthenates precipitate jointly with others compounds such as sulfates and carbonates. This fact makes difficult their characterization. In this study, calcium stearate formation from stearic acid was investigated, under different conditions, as a previous model to understanding of calcium naphthenate precipitation. Medium reactions distinct were studied and the results indicated that the ethanol medium was the most efficient for the formation of solids because in this only case, the stearic acid was completely converted into stearate. Monitoring of the conversion was performed by thermogravimetry in spite of this technique not be typical in salts characterization. Nevertheless, the thermogravimetric analysis showed that is possible to identify differences between an organic acid, a salt of this acid and an inorganic salt, in the same sample. Infrared spectra was used in order to confirm the results obtained by thermogravimetry. However, this technique showed less efficiency and sensibility.