Non-isothermal Thermogravimetry Research Articles

00/01745 Non-isothermal thermogravimetry and decomposition kinetics of two Jordanian oil shales under different processing conditions

00/01745 Non-isothermal thermogravimetry and decomposition kinetics of two Jordanian oil shales under different processing conditions

A new method for determining solute diffusivity in polymers from data obtained by non-isothermal thermogravimetry

A numerical method for determining solute diffusivity in polymers over wide temperature ranges was developed based on non-isothermal thermogravimetry (TG). The method combines the Fickian equations with a heat transfer equation in order to take into account temperature gradients within the polymer sample during a heating scan. The requirement of thermal equilibrium in the specimen during the heating scan need not be fulfilled, and this permits the study of desorption of solute from thick specimens at high heating rates. The numerical procedure is capable of considering concentration-dependent solute diffusivity and temperature-dependent thermal diffusivity. The method was tested on the desorption of n-hexane in polyethylene between 25 and 120°C. The results obtained agreed with experimental data obtained at heating rates from 10 to 40°C/min up to 90°C and yielded an activation energy of 46 kJ/mol, which is in agreement with earlier reported experimental data.

Effect of cleaning process on combustion characteristics of lignite

In this research, the results of a study on the combustion characteristics of Soma lignite before and after cleaning are presented. Non-isothermal thermogravimetry (TG/DTG) experiments were carried out for four different size fractions. Experiments were performed from ambient to 900°C in air atmosphere at 10°C/min heating rate. TG/DTG curves revealed three reaction regions. The first region is due to the evaporation of moisture in the coal. The second region can be called the primary reaction region, whereas third region is related to the decomposition of mineral matter in the lignite. Kinetic analysis has revealed that increase in reactivity and long-lasting combustion is the distinctive effect of cleaning on combustion characteristics of Soma lignite.

Non-isothermal thermogravimetry and decomposition kinetics of two Jordanian oil shales under different processing conditions

Two oil shale samples from two different deposits in Jordan have been non-isothermally pyrolysed using a thermogravimetric analyser (TGA). The controlling parameters studied were the final pyrolysis temperature (up to 900°C) and the influence of the heating rate (from 20 to 50 K min −1) as well as type of purge gas (N 2 or CO 2) employed on the process of thermal degradation of the shale sample. The integral method was used in the analysis of TGA data in order to determine the pyrolysis kinetics. The main region of the sample's weight loss, arising from the conversion of organic matter to oil and gas, occurred within the temperature range 200°C to 600°C. The magnitude of the total weight loss was mainly dependent on the final temperature, as well as, to a lesser extent, on the heating rate employed. The rates of decomposition of the Ellujjun and Sultani oil shales changed significantly at a critical temperature of ∼305±15°C.

Kinetic Analysis of the Decomposition of Chelates of Di-alkyldithiocarbamate of Cd(II)

The thermal decomposition kinetics of the solid complexes Cd(S2 CNR2 )2 , where R =C2 H5 , n -C3 H7 , n -C4 H9 or iso -C4 H9 , was studied by using isothermal and non-isothermal thermogravimetry. The superimposed TG/DTG/DSC curves revealed that thermal decomposition reactions occur in the liquid phase. The kinetic model that best fitted the experimental isothermal TG data was the one-dimensional phase-boundary reaction-controlled process R1 . The thermal analysis data suggested the thermal stability sequence Cd(S2 CNBun2 )2 >Cd(S2 CNPrn2 )2 >Cd(S2 CNBui2 )2 >Cd(S2 CNEt2 )2 , which accords with the sequence of stability of the apparent activation energies.

Thermal degradation and ageing of segmented polyamides

The degradation behaviour and kinetics of degradation of segmented polyamides with varying block lengths have been studied by non-isothermal thermogravimetry in air and nitrogen and by infrared spectroscopy. In air, all the polymers show two stage decomposition, whereas in nitrogen, the decomposition occurs in a single stage. In both atmospheres the degradation, however, follows first order kinetics. The infrared spectroscopic analysis of the degraded products reveals that the decomposition occurs in the polyether linkage followed by polyamide hard block. The mechanism of degradation is of course a complex one. In the case of thermooxidative degradation, a decrease in hard block molecular weight has a great influence on the activation energy values. The effect of ageing on the mechanical properties of these polymers has also been studied. On ageing, it is observed that both tensile strength and elongation at break drop sharply in the initial stage. After this initial drop, both properties show a marginal change with time and temperature of ageing. Retention of physical properties is better with high hard block molecular weight polymers.

Effect of mineral matter on the reactivity of lignite

In this study, effects of total mineral matter content and of elements Ca, Mg, Na, K, Si and Al on the combustion reactivity of 25 lignite samples, originating from different areas of Turkey, was investigated. Non-isothermal thermogravimetry, where the sample was heated in air and the temperature of which increased at a linear rate of 40 K min −1 to 1273 K, has been used to investigate the combustion reactivities of the lignite samples. The calculated combustion activation energy values were related to the mineral impurities and definite correlations were observed.

Particle size effect on the oxidation mechanism of lignites

In this research, effect of particle size on the oxidation mechanisms of Çayirhan, Tunçbilek and Soma lignites are studied. Non-isothermal thermogravimetry and derivative thermogravimetry (TG/DTG) experiments were carried out for 12 different size fractions. Data obtained from TG/DTG experiments are converted into dimensionless time (instantaneous size/original size) versus dimensionless time (time/burn-out time) to show the progress of oxidation mechanisms of lignites. It was found that lignites show linear behaviour at elevated temperatures, which justifies the assumption that chemical reaction is the controlling step.

Thermal degradation of bisphenol A polysulfone by high-resolution thermogravimetry

The thermal degradation and kinetics of bisphenol A polysulfone (PSF) have been studied by high-resolution thermogravimetry (TG). The influence of the testing atmosphere and heating rate on the thermal degradation characteristics of the PSF has been discussed. The thermal degradation temperature of the PSF increases slightly with an increase of heating rate or with the variation of testing atmosphere in the order of: in air<in nitrogen<in vacuum<in argon. The activation energy of the thermal degradation for the PSF also increase from 140, 258 to 293 kJ/mol with variation of the testing atmosphere from air, nitrogen to argon. The activation energy of thermal degradation calculated by high-resolution TG in nitrogen and air are almost the same as those by traditional isothermal or constant heating rate TG. The isothermal weight loss in a certain temperature range could be correctly predicted on the basis of the kinetic parameters determined by nonisothermal high-resolution TG.

THERMAL DEGRADATION KINETICS OF THERMOTROPIC COPOLY (P-OXYBENZOATE-ETHYLENE TEREPHTHALATE-VANILLATE) BY A HIGH-RESOLUTION THERMOGRAVIMETRY

Thermotropic liquid crystalline terpolymers consisting of three units of p-oxybenzoate (B), ethylene terephthalate (E), and vanillate (V), were studied through a high-resolution thermogravimetry to ascertain their thermostability and kinetics parameters of thermal decomposition in nitrogen and air. Overall activation energy data of the major decomposition have been calculated through four calculating techniques. The thermal degradation occurs in three steps in nitrogen, but in four steps in air due to an additional thermo-oxidative step. The thermal degradation temperatures are higher than 436°C in nitrogen and 424°C in air and increase with increasing B-unit content at a fixed V-unit content of 5 mol%. The temperatures at the first maximum weight-loss rate are higher than 444°C in nitrogen and 431°C in air and increase slightly with an increase in B-unit content. The first, second, and third maximum weight-loss rates almost maintain at 10–11, 10–11, and 3.6–5.3%/min regardless of copolymer composition and testing atmosphere. The char yields at 500°C in both nitrogen and air are larger than 40 wt% and increases with increasing B-unit content. But the char yields at 800°C in nitrogen and air are quite different, i.e., 18–25 wt% in nitrogen and 0 wt% in air. The activation energy and Ln (pre-exponential factor) for the major decomposition are higher in nitrogen than in air and decrease slightly with an increase in B-unit content at a given V-unit content 5 mol%. There is no regular variation in the decomposition order with the variation of copolymer composition and testing atmosphere. It is found that the most V-unit-containing terpolymer exhibited the lowest degradation temperature, lowest activation energy, and lowest Ln (pre-exponential factor). The activation energy, decomposition order, and Ln (pre-exponential factor) of the thermal degradation for the terpolymers, are situated in the ranges of 121–248 kJ/mol, 1.5–2.8, 19–38 min−1, respectively. These results indicate that the terpolymers exhibit high thermostability. The isothermal decomposition kinetics of the terpolymer at 450°C have also been discussed and compared with the results obtained based non-isothermal high-resolution thermogravimetry.

Nonisothermal degradation of poly(vinyl chloride)/methylmethacrylate-butadiene-styrene blends

The thermal degradation of poly(vinyl chloride)/methylmethacrylate-butadiene-styrene (PVC/MBS) blends was studied by nonisothermal thermogravimetry in nitrogen. Measurements were carried out in the temperature range 323–823K. The kinetic parameters were determined by applying Flynn–Wall–Ozawa and Kissinger’s methods. According to the compensation parameters the mechanism of degradation remains the same on adding the MBS; only the kinetics change. The thermal stability of the blends depends on the blend composition and shell/core ratio in MBS. ©

Kinetics of the thermal decomposition of bis(dialkyldithiocarbamate) of palladium(II) complexes in isothermal and nonisothermal conditions

Dialkyldithiocarbamate of palladium(II) complexes, Pd(S 2CNR 2) 2, with R=C 2H 5, n–C 3H 7, n–C 4H 9, i-C 4H 9 and C 5H 11 were synthesized from the direct reaction of PdCl 2 with corresponding amine and carbon disulphide. The complexes were characterized by the techniques of melting points, infrared absorption spectroscopy and mass spectrometry. The thermal decomposition reaction of complexes have been studied by isothermal and nonisothermal thermogravimetry. Superimposed curves of TG/DTG/DSC show that these reactions occur in the liquid phase. The kinetic isothermal model that best adjusted the experiment data were the R1 model.

Kinetic study of the thermal decomposition on bis(dialkyldithiocarbamate) Cd(II) complexes by isothermal and non-isothermal thermogravimetry

The thermal decomposition kinetics of solid Cd(S 2CNR 2) 2 complexes, where R=C 2H 5, n-C 3H 7, n-C 4H 9 and iso-C 4H 9, has been studied using isothermal and non-isothermal thermogravimetry. Superimposed TG/DTG/DSC curves show that thermal decomposition reactions occur in the liquid phase. The kinetic model that best adjusted the experimental isothermal TG data was the one-dimensional phase-boundary reaction controlling process R 1. The thermal analysis data suggest the thermal stability sequence Cd(S 2CNBu n 2) 2>Cd(S 2CNPr n 2) 2>Cd(S 2CNBu i 2) 2>Cd(S 2CNEt 2) 2, according to the order of stability of apparent activation energy.

Thermal degradation studies of electron beam cured terpolymeric fluorocarbon rubber

The thermal degradation of fluorocarbon rubber (FKM) electron beam cured in the absence and presence of crosslink promoter, trimethylolpronane triacrylate (TMPTA) and MgO has been studied by non-isothermal thermogravimetry. For comparison, control fluorocarbon rubber without any crosslinking has been taken. These studies suggest that thermal stability is improved on radiation and more so in the presence of TMPTA. MgO stabilizes the rubber matrix more against thermal attack, because of the additional crosslinks formed in its presence.

High-resolution thermogravimetry of poly(4-methyl-1-pentene)

Thermal degradation and kinetics of poly(4-methyl-1-pentene) were investigated by nonisothermal high-resolution thermogravimetry at a variable heating rate. Thermal degradation temperatures are higher, but the maximum degradation rates are lower in nitrogen than in air. The degradation process in nitrogen is quite different from that in air. The average activation energy and frequency factor of the first stage of thermal degradation for the poly(4-methyl-1-pentene) are 2.4 and 2.8 times greater in air than those in nitrogen, respectively. Poly(4-methyl-1-pentene) exhibits almost the same decomposition order of 2.0 and char yield of 14.3-14.5 wt % above 500°C in nitrogen and air. The isothermal lifetime was estimated based on the kinetic parameters of nonisothermal degradation and compared with the isothermal lifetime observed experimentally.

Thermal degradation and ageing behaviour of novel thermoplastic elastomeric nylon-6/acrylate rubber reactive blends

The thermal degradation behaviour of thermoplastic elastomeric blends of nylon-6 and an acrylate rubber (ACM) has been studied by non-isothermal thermogravimetry. The thermal stability of the blends is low compared to that of nylon-6, which is explained on the basis of ‘ester-amide interchange’ reaction at high temperature during degradation. The exchange reaction effectively degrades the nylon-6 phase in the blends. The melt reaction between nylon-6 and ACM which occurs during the blending operation, slightly improves the stability of the blends. Ageing of dynamically cured 40/60 (w/w) nylon-6/ACM blend, which is thermoplastic elastomeric (TPE) in nature, has been carried out in air at various temperatures and times. The results show excellent heat resistance of the TPE at elevated service temperature.

Thermal Decomposition of BaC2O4·0.5H2O Studied by Stepwise Isothermal Analysis and Non-Isothermal Thermogravimetry

Thermal decomposition of BaC2O4·0.5H2O in air was studied by a combination of stepwise isothermal analysis (SIA) and non-isothermal thermogravimetry. The results from both techniques show that the crystal water is released in one step and that anhydrous barium oxalate is decomposed in one step, while BaCO3 decomposes in three steps to BaO, forming two intermediate compounds with the formulas of BaCO3·(BaO)2 and (BaCO3)0.5·(BaO)2.5. Reaction mechanism analyses using the data from SIA measurements show that the controlling mechanism for all the five decomposition steps in isothermal conditions is a two-dimensional phase-boundary controlled process. Kinetic parameters are obtained for the five decomposition steps from the non-isothermal thermogravimetric data.

Modelling of volatile product evolution in coal pyrolysis. The role of aerial oxidation

Non-isothermal thermogravimetry has been applied to study the pyrolysis behaviour of coal and its changes as a consequence of aerial oxidation. A mathematical model has been developed to calculate the kinetic parameters of the coal pyrolysis process, which takes into account three different groups of thermal decomposition reactions for fresh coal, and two groups for oxidised coals. The agreement between the model predictions, for any heating rate, and the experimental values was fairly good. The volatile matter release profile of fresh coal can be described using three stages: Stage I (250–475°C), mainly light species are liberated; Stage II (475-575°C), characteristic of bituminous coals, high molecular weight species (tar) and hydrocarbons (primary gases) are evolved, which may lead to melting (metaplast); Stage III (>575°C), secondary gases are produced while undergoing ring condensation and leading to the formation of coke. The decrease in the amount of aliphatic hydrocarbons released in the pyrolysis of oxidised coals implies that stage II is not observed, `mobile' phase is insufficient to allow aromatic planar units to slide over each other, the melting cannot begin, and oxidised coals pass directly to stage III. This causes loss of plasticity and is therefore, responsible for the degradation of coking properties, as a consequence of oxidation. The aromatic fractions, that cannot rearrange, form a poor ordered structure and yield a powdered char.

Effect of the reaction temperature on the chlorination of a Fe2O3TiO2C mixture

Abstract The intrinsic kinetics of the chlorination of an hematite-titania-carbon mixture was studied by means of scanning electron microscopy and isothermal and non-isothermal thermogravimetry between 580 and 1123 K. It was observed that various reactions take place simultaneously and that a carbon surface deactivation occurs between 733 and 820 K. The latter was attributed to chemisorption of iron chlorides on the carbon surface.

Effect of particle size on the thermal and combustion properties of coal

Abstract In this research effect of particle size on the combustion properties of Cayirhan coal sample was studied. Non-isothermal thermogravimetry and derivative thermogravimetry (TG/DTG) experiment were carried out for twelve different size fractions of the Cayirhan coal sample. Thermogravimetry experiments were performed from ambient to 900°C in air atmosphere. Differential thermogravimetric data were analysed using an Arrhenius type reaction model assuming a first-order reaction. Kinetic parameters of the samples are determined and the results are discussed.