Thermal decomposition kinetics of melt-mixed ethylene-co-vinyl acetate – based bio-composites

Bio-composites of ethylene-co-vinyl acetate (EVA) with chitosan (CS) and chitosan-g-PANi (CS-PANi) have been developed by using a melt-mixing process by varying the composition of fillers. Investigations on the degradation mechanism of thermoplastics lead to insights of their performance at high temperatures. The decomposition kinetics of the bio-composites was determined by plotting thermograms at different heating rates. The model-free Flynn-Wall-Ozawa and Kissinger method has been used to estimate the energy of activation (E_a) of the developed composites. The activation energies of EVA/CS composites lie between 162 and 209 kJ/mol and EVA/chitosan-g-PANi composites within the range of 145–256 kJ/mol. The variation in activation energy across the extent of conversion levels denotes multistep kinetics of degradation. The calculated E_a has been found to be in good agreement with the literature reports.     

Evaluation of the 3-hydroxy pyridine antioxidant effect on the thermal-oxidative degradation of HTPB

The effect of the mixture of two antioxidants has been evaluated on the thermal-oxidant degradation of the hydroxyl-terminated polybutadiene (HTPB) because of its importance in the coatings and adhesives industries. 2,2-Methylene bis(4-methyl-6-tertiarybutylphenol) or A.O.2246 and 3-hydroxy pyridine have been considered as antioxidants in this study as a common HTPB antioxidant and an active antioxidant, respectively. The thermal-oxidant degradation behavior of the HTPB has been investigated in the presence of a mixture of two antioxidants by TGA and DTG tests, and, subsequently, the results of these tests have been interpreted by two model-free methods, e.g., Kissinger–Akahira–Sunose and Friedman methods. The results revealed that the mixture of two antioxidants affected the activation energy of the thermal-oxidant degradation reaction of the HTPB. The calculated activation energy value obtained from the Kissinger–Akahira–Sunose method was about 199 ± 1 kJ⋅mol⁻¹. In addition, the E_a value at various conversion rates has also been calculated by using the Friedman method. This method showed that the highest E_a value in the thermal-oxidant degradation reaction belonged to the initiation step of the reaction (about 299 kJ⋅mol⁻¹). Moreover, the lowest activation energy value was correlated to the second step of the degradation reaction at a conversion rate of 0.6 (about 184 kJ⋅mol⁻¹).     

A high yield method for the direct amidation of long-chain fatty acids

The amidation of long-chain fatty acids is the key step for preparing surfactants with excellent interfacial activity. Gas chromatography–mass spectrometry was employed to detect the reactants and products in the direct amidation reactions. The conversion and the concentration of the amides in the reaction process were also investigated to determine the best catalyst, the reaction rate constants, and activation energy. It was identified that the amidation reaction of the long-chain phenyl fatty acid was a zero-order reaction and 3,4,5-trifluorophenylboronic acid was the most effective catalyst by which the activation energy reduced to 55.79 kJ/mol from 95.44 kJ/mol. The method can be applied to other long-chain fatty acids, saturated or unsatureated. The turning-over-temperature was 156°C, over which high yields can be achieved without any catalyst. These provide a reference for the preparation of long-chain fatty acid amides.     

Organic acid catalyzed production of platform chemical 5-hydroxymethylfurfural from fructose: Process comparison and evaluation based on kinetic modeling

Fructose was converted to 5-hydroxymethylfurfural (HMF), an important biomass-derived platform chemical, under mild conditions (100–130 °C) with several organic acids including p-toluene sulfonic (pTSA), oxalic, maleic, malonic and succinic acids as the catalysts. The process kinetics was compared considering fructose dehydration to HMF as the objective reaction and condensation of fructose and HMF to humin and rehydration of HMF as the main side reactions. DMSO was found to be the most effective solvent reaction medium to obtain high fructose conversion and HMF yield. Observed kinetic modeling illustrated that the rehydration and condensation of HMF in DMSO actually could be neglected, especially for the oxalic acid catalyzed system. The determined observed activation energy for fructose conversion to HMF and humin in DMSO medium was 33.75 and 24.94 kJ/mol for pTSA catalyzed system, and 96.51 and 78.39 kJ/mol for oxalic acid-catalyzed system, respectively. HMF yields of 90.2% and 84.1% were obtained for pTSA and oxalic acid catalyzed systems, respectively.     

Kinetic of non-isothermal dehydration of equilibrium swollen poly(acrylic acid-co-methacrylic acid) hydrogel

The kinetic of non-isothermal dehydration of equilibrium swollen poly(acrylic acid-co-methacrylic acid) hydrogel (PAM) has been investigated. Thermogravimetric and conversion dehydration curves were recorded at various heating rates 5–30 K min^?1. The conversion dehydration curves at all investigated temperatures can be mathematically described using the logistic regression function in entire. It was found that activation energy complexly changes with the increasing dehydration degree. Physical meaning of the parameters of logistic function (b and w) is given. It was established that, during the dehydration, changes in the fluctuating hydrogel structure occur, and that limiting step on the kinetics of hydrogel dehydration have rate of structural rearrangement of hydrogel (actual relaxation mechanism). A procedure for determining the dependence of effective activation energy on temperature and dehydration degree, based on logistic function, is exposed. Possible explanation for the existence of negative values of activation energy in the certain range of temperature, is given.     

Dechlorination of carbon tetrachloride by Nanoscale Nickeled Zero‐Valent Iron @ Multi‐Walled Carbon Nanotubes: Impact of reaction conditions,kinetics and mechanism

The nanoscale nickeled zero‐valent iron @ multi‐walled carbon nanotubes (NF@MWCNTs) were synthesized, characterized and used to dispose carbon tetrachloride (CT) in aqueous solution. Scanning electron microscopy (SEM), X‐ray energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) gas sorptometry measurements were conducted to characterize the microstructure of the NF@MWCNTs. And batch experiments under different operation parameters were conducted to investigated the activity of NF@MWCNTs on degrading CT, including the content of NF@MWCNTs composites, temperature, catalyst dosage, initial pH and different anions. The experimental results showed that 4% nickel content of Ni/Fe bimetal and 2:1 doping ratio of Fe/MWCNTs were the wise choices in this study, which provided excellent degradation efficiency of CT when compared with nanoscale zero‐valent iron (nZVI) (97.44% and 55.28%, respectively). That was benefited from the fact that MWCNTs as an excellent support material could reduce the activation energy of 7.952 kJ/mol, and the nickel metal further reduced the reaction activation energy of 11.022 kJ/mol as presented in the conceptual model. Beyond that, NF@MWCNTs showed good reusability after five times consecutive reaction. Based on these, the reaction mechanism and degradation pathway also had been discussed.     

Effect of Sulfation of Zirconia on Catalytic Performance in the Dehydration of Aliphatic Alcohols

Catalytic dehydration of 2‐propanol and that of 1‐butanol were performed at atmospheric pressure and 150–300°C over ZrO₂ and sulfated ZrO₂ (S/ZrO₂) in a fixed‐bed, tubular reactor. The catalysts were characterized with XRD, elemental analysis, FT‐IR, N₂ physisorption, TG/DTA, TPD, and TPR. The main structures of ZrO₂ and S/ZrO₂ were monoclinic and tetragonal, respectively. As ZrO₂ was modified with sulfuric acid, its surface area and acid amount were greatly increased, whereas the pore volume, the pore diameter, and the particle size were reduced. Both samples owned weak basicity. For both reactions, only dehydration products of alkene and ether were obtained. The alcohol conversion enhanced remarkably with the catalyst acid amount and the surface area as well as the reaction temperature. In addition, the ether selectivity on S/ZrO₂ decreased with raising the reaction temperature. The activation energy was 81.0 kJ/mol in the propene formation from 2‐propanol over S/ZrO₂. The corresponding value was 94.4 kJ/mol for the dehydration of 1‐butanol.     

Kinetics of the thermal decomposition of processed poly(lactic acid)

The kinetics of the thermal decomposition of processed poly(lactic acid) has been studied and compared to that of raw material. Processing consisted of two different industrial processes: 1) Injection (with or without further annealing); 2) Extrusion followed by injection (with or without further annealing). For this study, an integral method (based on the general analytical solution), differential methods (based on the first conversion derivative and on the 2nd derivative) and special methods have been used. On the other hand, a method based on the maximum decomposition rate has been considered. By doing that, the kinetic parameters (reaction order, frequency factor and activation energy) have been determined. It has been demonstrated that there was only one first-order reaction for the entire conversion range. A new equation (based on the second conversion derivative plot as a function of temperature) was developed allowing the calculation of the reaction order. This method quantifies peak areas (and not peak heights, as reported by Kissinger). It is very useful because it considers both peak shape and width. Activation energy, as determined by using the general analytical solution, was 318 kJ/mol for unprocessed poly(lactic acid) whereas it was 280 ± 5 kJ/mol for processed materials. All the processed materials had approximately the same thermal stability (T₅ = 333.0-335.8 °C, at 95% confidence level), which was slightly lower than that of unprocessed materials (T₅ = 337.5 °C). PLA melting (during extrusion and injection) was responsible for depolymerization reactions (the small molecules formed during melting processes can volatilize readily).     

Dehydration kinetics of theophylline-7-acetic acid monohydrate

A hydrated form of theophylline-7-acetic acid obtained by recrystallization from water is described and characterized in terms of thermal properties, physical stability with respect to relative humidity and dehydration kinetics. The hydrate resulted to be stable at ambient conditions. Fitting of experimental dehydration data to solid state reaction equations suggests a three dimensional phase boundary reaction proceeding from the surface of the crystal inward along three dimensions. The relevant activation energy calculated from the Arrhenius plot is 173 kJ/mol.     

Studies on curing kinetics of a novel combined liquid crystalline epoxy containing tetramethylbiphenyl and aromatic ester‐type mesogenic group with diaminodiphenylsulfone

The curing kinetics of a novel liquid crystalline epoxy resin with combining biphenyl and aromatic ester‐type mesogenic unit, diglycidyl ether of 4,4′‐bis(4‐hydroxybenzoyloxy)‐3,3′,5,5′‐tetramethyl biphenyl (DGE‐BHBTMBP), and the curing agent diaminodiphenylsulfone (DDS) was studied using the advanced isoconvensional method (AICM). DGE‐BHBTMBP/DDS curing system was investigated the curing behavior by means of differential scanning calorimetry (DSC) during isothermal and nonisothermal processes. Only one exothermal peak appeared in isothermal DSC curves. A variation of the effective activation energy with the extent of conversion was obtained by AICM. Three different curing stages were confirmed. In the initial curing stage, the value of E_a is dramatically decreased from ～90 to ～20 kJ/mol in the conversion region 0–0.2 for the formation of LC phase. In the middle stage, the value of E_a keeps about ～80 kJ/mol for cooperative effect of reaction mechanism and diffusion control. In the final stage, a significant increase of E_a from 84 to 136 kJ/mol could be caused by the mobility of longer polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3922–3928, 2007     

Green process of fuel production under porous γ-Al2O3 catalyst: Study of activation and deactivation kinetic for MTD process

One of the methods of industrial dimethyl ether production is the catalytic dehydration of methanol. In this research work, methanol dehydration reactor has been modeled using continuous model and its results have been compared with experimental works and Voronoi pore network model. A 1D heterogeneous dispersed plug flow model was utilized to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether. The mass and heat transfer equations are numerically solved for the reactor. The concentration of the reactant and products and also the temperature varies along the reactor, therefore the effectiveness factor would also change in the reactor. We used the the effectiveness factor that was simulated according to the diffusion and reaction in the catalyst pellet as a Voronoi pore network model. Sensitivity analysis was performed to determine the influence of T, P and weight hourly space velocity on performance of the chemical reactor. Acceptable agreement was reached between the measured and the model data. The results showed that the maximum reaction conversion was obtained about 90 % at WHSV = 10 h^?1 and T = 560 K, while the inlet temperature (T_inlet) had a greater effect on methanol conversion. In addition, the effect of water in the feed on methanol conversion was quantitatively studied. Also, the deactivation kinetics of γ-Al₂O₃ heterogeneous-acidic catalyst in methanol to dimethyl ether dehydration process was studied using integral analysis method. Based on independent deactivation kinetics, a second order was found that accurately fitted the experimental conversion time data. The main reaction activation energies and catalyst deactivation energies were 143.1 and ?102.1 kJ/mol, respectively.     

New approach for the kinetic analysis of cellulose using EGA-MS

This paper describes a new approach for kinetic analysis based on evolved gas analysis-mass spectrometry (EGA-MS) using pyrolyzer-gas chromatography/MS (Py-GC/MS). The kinetic results derived by this model-free kinetic analysis using the EGA-MS thermograms of cellulose were comparable to those using thermogravimetric analysis (TGA). The activation energies were in the range of 149–194 kJ/mol (mean 169 kJ/mol) for EGA/MS and 152–181 kJ/mol (mean 165 kJ/mol) for TGA. This suggests that Py-GC/MS can be used not only for the qualitative analysis of pyrolyzates, but also for the kinetic analysis of pyrolysis.     

A systematic tandem mass spectrometric study of anion attachment for improved detection and acidity evaluation of nitrogen‐rich energetic compounds

The development of rapid, efficient, and reliable detection methods for the characterization of energetic compounds is of high importance to security forces concerned with terrorist threats. With a mass spectrometric approach, characteristic ions can be produced by attaching anions to analyte molecules in the negative ion mode of electrospray ionization mass spectrometry (ESI‐MS). Under optimized conditions, formed anionic adducts can be detected with higher sensitivities as compared with the deprotonated molecules. Fundamental aspects pertaining to the formation of anionic adducts of 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX), 1,3,5‐trinitro‐1,3,5‐triazinane (RDX), pentaerythritol tetranitrate (PETN), nitroglycerin (NG), and 1,3,5‐trinitroso‐1,3,5‐triazinane energetic (R‐salt) compounds using various anions have been systematically studied by ESI‐MS and ESI tandem mass spectrometry (collision‐induced dissociation) experiments. Bracketing method results show that the gas‐phase acidities of PETN, RDX, and HMX fall between those of HF and acetic acid. Moreover, PETN and RDX are each less acidic than HMX in the gas phase. Nitroglycerin was found to be the most acidic among the nitrogen‐rich explosives studied. The ensemble of bracketing results allows the construction of the following ranking of gas‐phase acidities: PETN (1530‐1458 kJ/mol) > RDX (approximately 1458 kJ/mol) > HMX (approximately 1433 kJ/mol) > nitroglycerin (1427‐1327.8 kJ/mol).     

Ab initio crystal structure predictions for flexible hydrogen‐bonded molecules. Part III. Effect of lattice vibrations

In crystal structure predictions possible structures are usually ranked according to static energy. Here, this criterion has been replaced by the free energy at any temperature. The effects of harmonic lattice vibrations were found by standard lattice‐dynamical calculations, including a rough estimate of the effects of thermal expansion. The procedure was tested on glycol and glycerol, for which accurate static energies had been obtained previously (Part II of this series). It was found that entropy and zero‐point energy give the largest contribution to free energy differences between hypothetical crystal structures, adding up to about 3 kJ/mol for the structures with lowest energy. The temperature‐dependent contribution to the energy and the effects of thermal expansion showed less variation among the structures. The overall accuracy in relative energies was estimated to be a few kJ/mol. The experimental crystal structure for glycol corresponded to the global free energy minimum, whereas for glycerol it ranked second at 1 kJ/mol. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 816–826, 2001     

Examining the kinetics of the thermal polymerization of commercial aromatic bis‐benzoxazines

Three commercial bis‐benzoxazine monomers based on the aniline derivatives of bisphenol A (BA‐a), bisphenol F (BF‐a), and 3,3′‐thiodiphenol (BT‐a) are examined using a variety of spectroscopic, chromatographic, and thermomechanical techniques. The kinetics of the polymerization of BA‐a were found to be well described using an autocatalytic model for which values of n = 1.39 and m = 2.49 were obtained for the early and later stages of reaction respectively (activation energy = 81–88 kJ/mol.). Following recrystallization the same monomer yielded values of n = 1.80, m = 0.92, and E_a = 94–97 kJ/mol. BF‐a and BT‐a were also found to be well described using an autocatalytic model for which values of n = m = 2.11 (BF‐a) and n = 2.10, m = 1.47 (BT‐a) were obtained for the early and later stages of reaction (activation energy = 80–84 kJ/mol. for BF‐a and 88–95 kJ/mol. for BT‐a). The kinetic data are compared with parallel studies involving chemically initiated benzoxazine monomers. Molecular simulation is used to examine the rotational freedom of the central bridging units and this is related to the degree of conversion achieved. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2068–2081     

Model-free kinetics applied to sugarcane bagasse combustion

Vyazovkin's model-free kinetic algorithms were applied to determine conversion, isoconversion and apparent activation energy to both dehydration and combustion of sugarcane bagasse. Three different steps were detected with apparent activation energies of 76.1 ± 1.7, 333.3 ± 15.0 and 220.1 ± 4.0 kJ/mol in the conversion range of 2-5%, 15-60% and 70-90%, respectively. The first step is associated with the endothermic process of drying and release of water. The others correspond to the combustion (and carbonization) of organic matter (mainly cellulose, hemicellulose and lignin) and the combustion of the products of pyrolysis.     

Hindered internal rotation of the CF<Subscript>3</Subscript> group in the 2-trifluoromethylnitrobenzene radical anion in DMF:H<Subscript>2</Subscript>O mixtures

The temperature dependences of the EPR spectrum of the 2-trifluoromethylnitrobenzene radical anion in DMF:H₂O mixtures, caused by the dynamic modulation of the fluorine isotropic hyperfine interaction by the hindered internal rotation of the CF₃ group, have been measured and reconstructed numerically. The activation energy of rotation (E _F) and the dynamic mode depended on the water content in the mixture. For mixtures with a molar fraction of water χ = 0, 0.186, 0.315, 0.409, 0.534, 0.650, 0.810, and 0.910, E _F = 34.70 kJ/mol, 41.31 kJ/mol, 42.30 kJ/mol, 38.41 kJ/mol, 37.01 kJ/mol, 34.51 kJ/mol, 24.10 kJ/mol, and 21.78 kJ/mol, respectively. For χ = 0.186 in the temperature ranges accessible for measurements, the dynamic exchange is slow; for χ = 0.315, 0.409, 0.534, and 0.650, transitions from slow to intermediate and fast exchange take place; for χ = 0.810 and 0.910 in the temperature ranges under study T ∈ [252, 309]; [254, 297] (K), the exchange is fast. In the range 0.6 < χ < 0.9, E _F decreased drastically, and the activation energy of rotational diffusion (E _r) of the radical anion became maximum, which corresponds to the range of the compositions of DMF:H₂O with maximum deviations from the ideal state.     

On the polymerisation of the epoxidised biodiesel: The importance of the epoxy rings position,the process and the products

Polyesters were prepared using epoxidised methyl esters of oleic acid (EP_OAME) and epoxidised biodiesel (mixture of methyl esters) from sunflower oil (EP_SOME) and linseed oil (EP_LOME) with cis-1,2-cyclohexanedicarboxylic anhydride and triethylamine. The kinetic of partial processes involved in the polymerisation were elucidated and related to epoxy rings position in the fatty acid chain. The activation energies (E_a) for the epoxy ring opening by the catalyst are 298, 216 and 136 kJ/mol for EP_OAME, EP_SOME and EP_LOME respectively. The reactions of the epoxy rings in the positions C9–C10, C12–C13 and C15–C16 with anhydride require average activation energies of 116, 32 and 22 kJ/mol, respectively. The compensation effect between activation energy and pre-exponential factor is observed. The polymerisation enthalpy, molecular weight, glass transition temperature and electrical properties were determined. The polyesters studied show promising properties for use in various technological applications.     

Studies on bulk polymerization of methyl methacrylate. I. Thermal polymerization

The thermal bulk polymerization of methyl methacrylate (MMA) in a wide range of temperatures has been studied using a dilatometric reactor. It is shown that, irrespective of the care taken to purify the MMA, the evolution of the time-conversion curve can be explained only if we account for the presence of an impurity associated with the monomer acting as a free radical initiator. The activation energy for the decomposition of this impurity has been estimated as 98 kJ/mol. Having accounted for this impurity, the activation energy for the real thermal polymerization of the MMA has been estimated to be 75 kJ/mol. © 1993 John Wiley & Sons, Inc.     

Kinetics and mechanism of non-isothermal dehydration of nickel acetate tetrahydrate in air

The non-isothermal decomposition of nickel acetate tetrahydrate in air was studied using thermogravimetry (TG)–DTG, differential scanning calorimetry (DSC) and XRD techniques. The decomposition occurs in two major steps and the final product is NiO. The dependence of mass loss on heating rates in TG measurements imply that the dehydration and hydrolysis concur at temperature below 240 °C; the apparent activation energies calculated by Flynn, Wall and Ozawa (FWO) isoconversional method indicate the existence of a consecutive process. The kinetics of the first major decomposition step (below 240 °C) was obtained with multivariate non-linear regression of four measurements at different heating rates. According to the kinetics results from non-linear regression, the dehydration reaction (F1 type with an activation energy E of 167.7 kJ/mol) goes first. After the loss of almost half of water, the retained water and acetate are linked to each other by hydrogen bonding, so dehydration and hydrolysis concur. The pathway with a lower E is related to the hydrolysis process and the other is corresponding to the dehydration process. The simulations of reactants at different heating rates were used to verify the correctness of the reaction model. With the kinetics results, the dehydration mechanism was discussed for the first time.