Non-isothermal Studies Research Articles

Thermokinetics and synergistic effect analysis of peat-lignite coal co-pyrolysis

ABSTRACT In this study, the synergistic effect between peat and lignite coal was investigated in terms of kinetic energy and mass loss trends using a thermogravimetric analyzer. Thermogravimetric non-isothermal studies were conducted at different heating rates under inert nitrogen atmosphere. Kinetic analysis was performed using model-free KAS, OFW, and Starink methods and the average activation energies varied between 88.62 kJ/mol and 204.28 kJ/mol. Differential mass loss trends were determined using experimental and theoretical data. An obvious deviation was obtained at a blend ratio of PT:CL40:60. Thus, results revealed that the PT and CL co-pyrolysis has synergistic effects, especially for sample PT:CL40:60. SEM and BET analyses were performed on the coke sample of peat, coal, and PT:CL40:60 blend ratio samples for further analysis. The surface area of peat and coal was determined to be 416 m2/g and 83.06 m2/g, respectively. It was concluded that the porosity and surface area of coal (187.02 m2/g) increased with the addition of peat. The results are expected to be useful in the design of peat biomass and coal co-pyrolysis systems.

Co-pyrolysis of petroleum coke and banana leaves biomass: Kinetics, reaction mechanism, and thermodynamic analysis

Insights into thermal degradation behaviour, kinetics, reaction mechanism, possible synergism, and thermodynamic analysis of co-pyrolysis of carbonaceous materials are crucial for efficient design of co-pyrolysis reactor systems. Present study deals with comprehensive kinetics and thermodynamic investigation of co-pyrolysis of petroleum coke (PC) and banana leaves biomass (BLB) for realizing the co-pyrolysis potential. Thermogravimetric non-isothermal studies have been performed at 10, 20, and 30 °C/min heating rates. Synergistic effect between PC and BLB was determined by Devolatilization index (Di) and mass loss method. Kinetic parameters were estimated using seven model-free methods. Standard activation energy for PC + BLB blend from FWO, KAS, Starink, and Vyazovkin methods was ≈165 kJ/mol and that from Friedman and Vyazovkin advanced isoconversional methods was ≈171 kJ/mol. The frequency factor calculated for the blend from Kissinger method was found to be in the range of 106-1016s−1. Devolatilization index (Di) showed synergistic effect of blending. The data pertaining to co-pyrolysis was found to fit well with R2 (second order) and D3 (three dimensional) from Z(α) master plot. Thermodynamic parameters, viz. ΔH ≈ 163 kJ/mol and ΔG ≈ 151 kJ/mol were calculated to determine the feasibility and reactivity of the co-pyrolysis process. The results are expected to be useful in the design of petcoke and banana leaves biomass co-pyrolysis systems.

Crystallisation competition between cubic and hexagonal ice structures: molecular-dynamics insight

ABSTRACT Under ambient pressure, two different ice polytypes of ice, cubic (Ic ) and hexagonal (Ih ) can be crystallised. Here, we elucidate the mechanism and kinetics of the phase transition of cubic ice with no stacking disorder to a perfect hexagonal ice at various temperatures, via molecular simulation. The study was performed through non-isothermal and isothermal molecular-dynamics simulations; these conditions were enforced on an equilibrated Ic /LDA/Ih system. Different results have been drawn from analysis in terms of local density, annealing kinetics, and phase transition. The evolution from cubic to hexagonal ice becomes prevalent at higher temperatures during the performed non-isothermal studies; to this end, a model-free kinetic study was proposed to address this phenomenon’s kinetic properties over a characteristic temperature range. Ice crystallisation is also studied in solid/liquid systems, where cubic or hexagonal ice was in contact with liquid water at sub-zero temperatures. It was revealed that water molecules have a propensity to follow and crystalise in the existing ice structure rather than forming a new interface.

Non-isothermal decomposition kinetics, X-ray diffraction, infrared spectrum and antimicrobial studies of gamma irradiated barium doped diaquamalonatozinc(II)

Abstract The present investigation probes into the effect of gamma irradiation as well as doping on non-isothermal decomposition kinetics, structural, spectral and antimicrobial studies of barium doped diaquamalonatozinc(II). The compound were prepared by reported procedures and characterized by elemental analysis and spectral studies. Pure dried samples of uniform mesh size were encapsulated in glass ampoules and irradiated to 200 kGy using 60Co gamma rays. Non-isothermal studies of barium doped [Zn(mal)(H2O)2] were done before and after gamma irradiation by Coats-Redfern method. Results revealed that activation energy and associated kinetic parameters were lowered upon irradiation as well as doping. From X-ray diffraction studies both unirradiated and irradiated samples are found to be monoclinic. Lattice parameters are changed after irradiation. Change in intensity of FTIR bands were observed after irradiation. Antimicrobial studies revealed irradiation induced activity towards Escherichia coli, Staphylococusaureus and Sacchromycescerevisiae.

Synthesis, Characterization, Thermal and Non-Isothermal Degradation Studies of Two Mononuclear Nickel and Copper Complexes Containing Schiff Base Moiety

Synthesis, Characterization, Thermal and Non-Isothermal Degradation Studies of Two Mononuclear Nickel and Copper Complexes Containing Schiff Base Moiety

Bis(isomaleimide) and diphenol blends: Non-isothermal degradation kinetics and TG-FTIR studies

Blends of 4,4′-bisisomaleimidodiphenyl methane (VS) with structurally different diphenols are made in 1:1 molar ratio and thermally polymerized. Thermogravimetric studies of the cured materials show that the thermal stability, the degradation pattern and the char yield are much dependent on the structure of the diphenol that is used for blending. The decreased thermal stability of materials from the blends is attributed to decreased cross links owing to the opening of the isomaleimide rings by diphenols during thermal polymerization. The materials with trimethylphenylindane and tetramethylspirobiindane units exhibit char residue of 21% at 800°C. This is due to the thermal stability of the indane and spirobiindane moieties present in the diphenol molecules. The apparent activation energy for thermal degradation ( Ea-D) and pre-exponential factor (ln A) are derived. The Friedman, corrected Flynn–Wall–Ozawa, corrected Kissinger–Akahira–Sunose and advanced Vyazovkin methods are used to calculate the Ea-D values for various reaction extents ( αs). The Ea-D values of poly(4,4′-bisisomaleimido-diphenyl methane) vary from 168 to 226 kJ mol−1. A slight decrease in Ea-D is noted for the initial α levels and increases constantly up to α = 0.3–0.75 and then the Ea-D values decrease with increasing α values. The highest values of Ea-D and ln A are observed for the polymer derived from the blend of VS with tetramethylspirobiindane diphenol. The volatile products obtained during the thermal degradation of these polymers are analysed using thermogravimetry–Fourier transform infrared (TG-FTIR) spectroscopy. The TG-FTIR studies showed the compounds carbon monoxide, carbon dioxide and aromatic amines are the major degradation products from the polymerized blends.

Influence of fish collagen on viscoelastic properties and sol-gel phase transition of chitosan solutions

The thermosensitive hydrogels are widely used in tissue engineering due to their non-invasive application. Special interest of researchers, due to the specific characteristics of both materials, is aimed at composites of natural origin obtained from chitosan hydrogels combined with collagen. The mechanical properties of the thermosensitive chitosan-fish collagen hydrogels and the sol-gel phase transition parameters were determined by the rotational rheometry measurement techniques. Based on comparison of the obtained storage modulus G' curves, it was found that the addition of collagen negatively affects the mechanical properties of composite scaffolds. The addition of this protein substance decreases their elasticity. Only the smallest concentration (0.25g collagen/1 g chitosan) of collagen improves the mechanical properties of composite hydrogels, from 56 kPa to 61 kPa. Conducted non-isothermal studies allowed to conclude that the addition of collagen causes an increasing temperature of sol-gel phase transition. However, the observed changes are not a monotone function of the biopolymer concentration.

Non-isothermal kinetics of spin crossover.

Non-isothermal magnetic studies can be used to estimate the activation energy of cooperative spin transition. Model-free isoconversional integral methods give reliable estimates of the activation barrier height for highly cooperative spin crossover systems with wide thermal hysteresis.

Spectroscopic, thermal, non-isothermal decomposition kinetics and quantum chemical computational studies of Ni(II)- and Cu(II)-Schiff base complexes

Herein we report spectroscopic, thermal, non-isothermal decomposition kinetics and theoretical studies of two mononuclear Ni(II)- and Cu(II)-complex of general formula [M(L)(H2O)]·xH2O; {M = Ni(II) & Cu(II)} derived from tridentate 2,4-dichloro-6-{[(5-chloro-2-sulfanylphenyl)imino]methyl}phenol ligand (H2L). These compounds were synthesized and characterized by various physicochemical and spectral techniques. Thermal decomposition of complexes was studied in four steps at different temperature regions to understand the degradation pattern of complexes under nitrogen atmosphere up to 1073 K at the 10 K min−1 heating rate. The non-isothermal kinetic parameters viz. activation energy (E*), pre-exponential factor (Z), entropy of activation (ΔS*), enthalpy of activation (ΔH*) and free energy of activation (ΔG*) of degradation process were calculated using Coats–Redfern (C–R), Piloyan–Novikova (P–N) and Horowitz–Metzger (H–M) methods assuming first order degradation and proposing a random nucleation mechanism of thermal decomposition. Quantum chemical computational investigations were carried out at the B3LYP level using 6-31G basis set. The calculated harmonic vibrations were compatible with the observed FTIR and Raman frequencies. The thermodynamic properties (C p,m °; S m ° and H m °) with varying temperatures up to 500 K and non-linear optical properties were also evaluated at the same level of theory.

Nucleating agents for high-density polyethylene-A review

A review of nucleating agent (NA) types and their effect on crystallization in high-density polyethylene (HDPE) is presented. The focus is on methods to improve the physical properties of HDPE due to its widespread use in commercial applications and high volume use in typical industrial processes including extrusion, injection molding, and blow molding. The crystallization process in HDPE significantly affects its final optical, mechanical, and thermal properties. The addition of NAs affects the physical properties of HDPE by controlling the crystallization from the melt state. Specific NAs improve properties such as clarity, cycle time, and modulus. NAs are more widely developed for polypropylene (PP) than HDPE as its slower crystallization rate allows greater control in achieving property improvements. While certain NAs are effective in improving property characteristics in HDPE, greater control over the crystallization process would achieve further improvements in specific properties. Research has progressed in identifying effective NAs for HDPE, though the magnitude of the effects remains lower than those generally observed in PP. Inorganic and organic NAs are reviewed with an emphasis on the mechanisms by which they function. Fundamentals of polymer crystallization and modeling kinetics during both isothermal and nonisothermal studies provide the necessary framework for characterizing the effects of a NA in HDPE. Finally, the interactions between HDPE, NA, and industrial processing conditions as related to practical applications are discussed. POLYM. ENG. SCI., 56:541–554, 2016. © 2016 Society of Plastics Engineers

Approximation-based integral versus differential isoconversional approaches to the evaluation of kinetic parameters from thermogravimetry

The relative accuracies of approximation-based integral versus differential isoconversional approaches for ‘actual’ E determination were investigated on experimental dehydration data of roxithromycin monohydrate from thermogravimetric (TG) analysis. The dehydration kinetic parameters and the relationship to the structural characteristics of the monohydrate and anhydrate forms from differential scanning calorimetry (DSC) and single-crystal X-ray diffractometry (SC-XRD) are also reported. Integral methods versus the differential Friedman isoconversional method evaluated E correspondences in both iso- and non-isothermal TG methods. The reliability in E from Friedman approached that of estimates from current most accepted integral isoconversional methods and was even superior to methods (for non-isothermal studies) that employ an approximation to the temperature integral (modified Kissinger–Akahira–Sunose, Senum–Yang fourth degree). Structural characterization (DSC, SC-XRD) and kinetic analysis from generalized kinetic master plots concluded that coordinated water occupied interlinked voids in crystal structure which may have facilitated the multidimensional diffusional loss of water upon heating without disruption of the crystal structure.

The effect of particle size on the kinetics of thermal decomposition of Co(C2O4)·2H2O nanopowders under non-isothermal conditions

Cobalt oxalate dihydrate nanopowders have been prepared by precipitation method. The crystal size of Co(C2O4)·2H2O obtained in the absence and presence of CTAB surfactant was 30 and 60 nm, respectively. The effect of particle size on the thermal decomposition of Co(C2O4)·2H2O powders in air was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG). Non-isothermal studies revealed that the decomposition occurred in two main stages: removal of water and next decomposition of CoC2O4 to Co3O4. Both oxalate and the final decomposition residue were characterized by means of XRD, FT-IR and TEM techniques. The kinetic parameters of the two decomposition steps were evaluated from TG to DTG data by several integral and differential calculation methods. Based on the iterative isoconversional calculation procedure, the activation energy values Eit associated with the decomposition steps were evaluated. Kinetic parameters are given, and the most probable mechanism functions are suggested. The results show that the decomposition increases with decreasing the particle size.

Dehydration Kinetics of Natural Talc

Abstract The dehydration kinetics of natural talc were studied using thermogravimetric analyses (TGA). The dehydration rate of talc increases with decreasing grain size, but there is little effect on the dehydration rate when the grain size is less than 5 μm. The dehydration reaction of talc occurs in the temperature range 1103–1323 K; the thermal decomposition of talc yields enstatite and quartz plus water. The probable reaction mechanism for the dehydration of talc is an approximately second-order reaction, whose differential and integral rate expressions are f ( α ) = ( 1 − α ) n and G ( α ) = ( 1 − ( 1 − α ) ( 1 − n ) ) / ( 1 − n ) , respectively. The value of the reaction order n is 1.7, the activation energy E is 344 kJ/mol, and the pre-exponential factor α is 4.9 E12 s −1 . This dehydration reaction is probably a one-step reaction. The dehydration reaction is controlled by a heterogeneous mechanism. The relationship between the conversion rate of talc and time at different temperatures was obtained using the parameters derived from non-isothermal studies, and was used to predict the stability of talc at different temperatures.

Effect of Misch Metal Nanoparticles on Thermal Decomposition of Ammonia Borane

Ammonia borane (NH 3BH 3) with its high hydrogen content (19.6 % per mass) and mild desorption conditions has the potential to meet the onboard hydrogen storage requirements for vehicular applications. Ammonia borane decomposes in three steps at the temperatures of about 100 °C, 140 °C and 1000 °C respectively, releasing one mole equivalent of hydrogen in each step. The major obstacle towards the use of AB as a hydrogen store is the poor kinetics and irreversibility of the reaction products. With the use of catalyst, the decomposition temperature could be reduced and the kinetics can be improved. In the current work, misch metal (Mm) nanoparticles are used as catalyst. These nanoparticles were synthesized using ball milling and characterized. Homogeneous mixture of AB and catalyst was prepared in the ratio 10:1 using ball milling. Isothermal as well as non-isothermal studies were performed on neat AB and AB with Mm nanoparticles. Samples as well as solid residues of the decomposition reaction were characterized using XRD and FTIR. It was observed that with catalyst, AB starts releasing hydrogen even at room temperature and the induction period was found to be practically absent. Misch metal is found to be a good catalyst for ammonia borane decomposition.

Thermal and spectral properties of alkali metal complexes of vitamin K3 analogue phthiocol

Hydroxynaphthoquinones, alkali, and alkali metal salts were used to synthesize several biologically important molecules. As hydroxynaphthoquinones act also as potential ligands, it is possible that alkali metal complexes may be formed as intermediates in such reactions. To ensure this, the reactions of 2-hydroxy-3-methyl-1,4-naphthoquinone (phthiocol, a vitamin K3 analogue) with sodium metal, alkali such as NaOH and KOH, and alkali metal salts such as CH3COONa, Na2CO3 and K2CO3 were studied in the present investigation. The products were characterized by various analytical techniques, namely elemental analysis, FT-IR, 1H NMR, UV–Vis, thermogravimetric (TG) analysis, GC–MS, and DSC studies. 100 % reduction of the ligand was observed in Phth-1 with sodium metal as reducing agent. The solution of CH3COONa, NaOH, KOH, and K2CO3 in methanol facilitates the reduction of phthiocol ligand. The reduction of the ligands may be probably due to disproportionate reaction of the ‘catechol’ form and the fully oxidized naphthoquinone form of the ligand. The radical signatures of the ligands in complexes were detected by EPR studies and also by carbonyl frequencies in FT-IR spectra. Non-isothermal TG studies confirm the presence of adsorbed and coordinated water molecules. Residue formed after complete decomposition was observed to be 1/2 Na2O in Phth-1 to Phth-3, K2O in Phth-4, and 1/2 K2O in Phth-5. Based on GC–MS and TG studies, three decomposition mechanisms are being proposed for all complexes.

Synergistic effects of nucleating agents and plasticizers on the crystallization behavior of poly(lactic acid).

The synergistic effect of nucleating agents and plasticizers on the thermal and mechanical performance of PLA nanocomposites was investigated with the objective of increasing the crystallinity and balancing the stiffness and toughness of PLA mechanical properties. Calcium carbonate, halloysite nanotubes, talc and LAK (sulfates) were compared with each other as heterogeneous nucleating agents. Both the DSC isothermal and non-isothermal studies indicated that talc and LAK were the more effective nucleating agents among the selected fillers. Poly(d-lactic acid) (PDLA) acted also as a nucleating agent due to the formation of the PLA stereocomplex. The half crystallization time was reduced by the addition of talc to about 2 min from 37.5 min of pure PLA by the isothermal crystallization study. The dynamic mechanical thermal study (DMTA) indicated that nanofillers acted as both reinforcement fillers and nucleating agents in relation to the higher storage modulus. The plasticized PLA studied by DMTA indicated a decreasing glass transition temperature with the increasing of the PEG content. The addition of nanofiller increased the Young’s modulus. PEG had the plasticization effect of increasing the break deformation, while sharply decreasing the stiffness and strength of PLA. The synergistic effect of nanofillers and plasticizer achieved the balance between stiffness and toughness with well-controlled crystallization.

Non-isothermal crystallization kinetics from the melt of nanocomposites based on poly(3-hydroxybutyrate) and modified clays

Poly(3-hydroxybutyrate) (PHB) films and its nanocomposites were obtained by casting. Three types of modified clays were used in order to improve the compatibility with the PHB. The films were characterized determining the thermal properties and the non-isothermal crystallization kinetic parameters from the melt. No change in the melting temperature of PHB was observed with the clay addition but the Tg diminished for the nanocomposites with the clay modified by ion exchange (MI) and by acid activation (MAI) to the PHB, due to the effect of the organic modifiers.From non-isothermal studies, it was observed a diminution of the peak of the crystallization temperature of PHB with the addition of clay at all of the cooling rates studied. The nanocomposites with MI and MAI exhibited the slowest crystallization rate among the materials, studied by the Liu–Mo model. However, the addition of the clay modified by silylation (MAGI) did not affect the crystallization rate of PHB.Effective activation energy (Eα) of the crystallization process of PHB and the nanocomposites was calculated by the isoconversional methods of Friedman and Vyazovkin. The Eα of the PHB increased with the addition of any type of the clays studied, but the rate of crystallization was reduced.

Kinetic parameters of CaCO3 decomposition in vacuum, air and CO2 calculated theoretically by means of the thermochemical approach

Fundamental advantages of the thermochemical approach compared with the activation approach were supported in this work by the results of theoretical calculations of the A and E kinetic parameters of CaCO3 decomposition in vacuum, air and CO2 and their comparison with experimental data. The temperature of the reaction in CO2 increases from 800 K (in vacuum) up to 1,200 K at equal rates of decomposition. This effect (unexplained in the framework of the activation approach) is of tremendous importance for estimating the thermal stability and lifetime of materials. It has been shown that the pre-exponential factor A in the Arrhenius equation is related to the entropy change of decomposition reaction and, in the isobaric mode, additionally, to the pressure of the external gaseous product. The mysterious effect of “variable activation energy” observed in many non-isothermal studies of solid decompositions, in particular, for CaCO3, was explained by the change of the reaction regime from the isobaric mode at low temperature (and decomposition degree) to the equimolar mode at higher temperatures (and higher decomposition degrees). This effect manifests itself for reactions related to the evolution of O2, H2O and CO2 gaseous products, which can be present in the reactor media as impurities.

Kinetics and Mechanical Studies of Melaminium bis(trichloroacetate) dihydrate

The thermal decomposition kinetics of melaminium bis(trichloroacetate) dihydrate (MTCA) has been studied by thermogravimetry and derivative thermogravimetry techniques using non-isothermal experiments at three different heating rates 10, 15, and 20 ◦C min−1. Non-isothermal studies of MTCA revealed that the decomposition occurs in three stages involving dehydration and decomposition. The apparent activation energy (Ea) and the pre-exponential factor (lnA) of each stage of thermal decomposition at various linear heating rates are calculated using Flynn Wall, Friedman, Kissinger, and Kim Park method. A signi cant variation of e ective activation energy (Ea) with conversion (α) indicates that the process is kinetically complex. The linear relationship between the A and Ea values is well established (compensation e ect). Isothermal kinetics of thermal decomposition of MTCA was found to obey Avrami Erofeev's (A4) and power law (P3) equations. In addition to the above, mechanical properties have been estimated by Vicker's microhardness test for the grown crystal.

Thermal analysis kinetics of thermal decomposition of nickel–viscose composite fiber

In this study, the thermal decompositions of nickel composite fibers (NCF) under different atmospheres of flowing nitrogen and air were investigated by XRD, SEM–EDS, and TG–DTG techniques. Non-isothermal studies indicated that only one mass loss stage occurred over the temperature regions of 298–1,073 K in nitrogen. The mass loss was from the decomposition. But after this decomposition, nickel was oxidized in air, when the temperature was high enough. In nitrogen media, the model-free kinetic analysis method was applied to calculate the apparent activation energy (E a) and pre-exponential factor (A). The method combining Satava–Sestak equation with one TG curve was used to select the suitable mechanism functions from 30 typical kinetic models. Furthermore, the Coats–Redfern method was used to study the NCF decomposition kinetics. The study results showed that the decomposition of NCF in nitrogen media was controlled by three-dimension diffusion; mechanism function was the anti-Jander equation, the apparent activation energy (E a) and the pre-exponential factor (A) were 172.3 kJ mol−1 and 2.16 × 109 s−1, respectively. The kinetic equation could be expressed as following: $$ \frac{{{\text{d}}\alpha }}{{{\text{d}}T}} = \frac{{ 2. 1 6\times 1 0^{ 9} }}{\beta }{ \exp }\left( {\frac{ - 2 0 7 2 4. 1}{T}} \right)\left\{ {\frac{ 3}{ 2}(1 + \alpha )^{2/3} [(1 + \alpha )^{1/3} - 1]^{ - 1} } \right\}. $$