Model-free Kinetic Methods Research Articles

Analysis of the pyrolysis kinetics of wastewater-fed microalgal biomass by a parallel order-based reaction model

ABSTRACT Wastewater-fed microalgal biomass has attracted a considerable interest for biofuel production via pyrolysis in recent years. In this study, thermal degradation behavior and pyrolysis kinetic parameters have been investigated by non-isothermal thermogravimetric analysis. Analysis of the reactive phase showed two partially overlapping devolatilization stages, with degradation peaks at 540–570 K, accompanied by a shoulder at around 590–615 K, and 735–785 K, respectively. Model-free kinetic methods showed a large variation in the activation energy with the conversion degree, suggesting a multi-step reaction scheme. Consequently, a parallel order-based reaction model of three pseudo-components (proteins, carbohydrates and lipids) was applied, showing a good agreement with the experimental data. Based on this approach, the average activation energies were 143, 166 and 61 kJ·mol−1 for proteins, carbohydrates and lipids, respectively, while the average orders of reaction were 2.3, 1.6 and 0.6.

Effects of Amino Acids on the Crystallization of Calcium Tartrate Tetrahydrate

This work assesses the effects of various amino acids, including serine, alanine, methionine, and proline, on calcium tartrate tetrahydrate (CTT) crystals. The crystallization experiments were performed in batch mode at 25 °C, pH 9 with three amino acid concentrations. The CTT crystals were characterized by XRD, FTIR, SEM, particle size and zeta poten-tial analysis. All of the amino acids used in this study were found to significantly affect the surface electrical charge, size, and morphology of the obtained crystals. In addition, the thermal decomposition of the produced crystals obtained in pure media was examined and the obtained data were used to investigate the decomposition kinetics of the crystals with the help of three different model-free kinetic methods, namely Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink. The average activation energy of the crystals for the first, second, third, and fourth stages using the FWO, KAS, and Starink methods was calculated to be 91.0, 158.0, 249.1, and 224.8 kJ/mol; 89.6, 155.9, 250.7, and 221.1 kJ/mol; 88.6, 156.8, 250.5, and 220.4 kJ/mol, respectively. Thus, the results of this work are useful for selecting CTT mor-phology modifiers and explaining the decomposition kinetics of CTT crystals.

Thermal degradation kinetics of a lignin particle-reinforced phenolic foam

In the present work, the thermal degradation kinetics of a phenolic (PF) and lignin particle-reinforced phenolic (LRPF) foam and the lignin used as the reinforcement (LR) were studied. The activation energies of the degradation processes were obtained using a discrete distributed activation energy model (discrete DAEM) and the Vyazovkin model-free kinetic (MFK) method. The discrete DAEM was validated by comparing the predicted values with the data obtained at 8 °C min−1. Heating ramps of 6 and 12 °C min−1were used to calculate the kinetic parameters through the model. The effect of the reinforcement on the kinetics of the LRPF was studied by comparison with the results obtained for the PF. For reactions with non-zero mass fractions, the activation energies of the PF were in the range between 79.9 and 177.6 kJ mol−1, and the activation energy for the LRPF ranged from 91 to 187 kJ mol−1. For the LR, the activation energy values were in a narrower range than for the foams: 150–187 kJ mol−1. The degradation process of the LRPF was modified due to the use of LR: the range of activation energy for LRPF was between the ranges for the PF and LR. The activation energy dependence on conversion was also calculated using the Vyazovkin method and compared with the DAEM results; no compensation effect for the kinetic parameters was found.

Combustion mechanism and model free kinetics of different origin coal samples: Thermal analysis approach

Five coal samples from different origins are characterized for their pyrolysis and combustion features using coupled thermogravimetry - mass spectrometry (TG-MS). The samples are heated at temperatures ranging from 25 to 900 °C in air atmosphere under heating rates of 10, 20, and 30 °C/min. The characteristic temperatures (initial, peak, burn out), reaction intervals, mass loss rate, ash residues, ignition and combustion performances, an ignition-combustion index and the reactivities of the coal samples are calculated and the associated heating rate effects are estimated. The less reactive coal exhibits higher peak temperature in conversion and low value of ignition index and reactivity. The reactivity of the coal samples varied in between 2.31 and 7.84 x102 (1/min). The main volatile and combustion products (H2, CH4, H2O, CO, CO2, C6H6, COS, SO2) release for the corresponding TG and temperatures are estimated using online 3D measurements of MS based on their relative intensities and relevancy. Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) type model free kinetic methods are applied to determine the activation energies of the coals which are exhibited in-between 44.6 - 75.1 kJ/mol and 50.5–96.6 kJ/mol using OFW and KAS methods respectively. The estimated kinetic constants are compared and found consistent with combustion performance parameters.

Kinetic analysis and catalytic pyrolysis of spent medicinal herb over HZSM-5 and HY

In this study, the kinetic analysis on the pyrolysis of a spent medicinal herb, namely spent Achyranthes root, is performed using a thermogravimetric analyzer and a model-free kinetic analysis method, allowing the calculation of activation energy values without the assumption of kinetic model. Owing to the structural change of lignin and elimination of hemicellulose during the decoction of raw Achyranthes root, the thermogravimetric analysis results show a large difference between the derivative thermogravimetry curves of spent and raw Achyranthes roots. The average apparent activation energy value of spent Achyranthes root, obtained from the non-isothermal thermogravimetric analysis, are found to be lower than those of raw Achyranthes root. This comes as a result of the much lower content of hemicellulose in spent Achyranthes root caused by the hemicellulose elimination from raw Achyranthes root during the decoction process. The catalytic fast pyrolysis of spent Achyranthes root over HZSM5-30 (HZSM-5 with SiO2/Al2O3 = 30) and HY30 (HY with SiO2/Al2O3 = 30) was performed using a two-stage fixed-bed reactor system. The catalytic fast pyrolysis of spent Achyranthes root over both HY30 and HZSM5-30 produced the much larger amount of aromatic hydrocarbons, compared to the non-catalytic fast pyrolysis, with a parallel decrease of oxygen-containing pyrolyzates. Owing to its robust pore structure and high acidity, it was the HZSM5-30 that produced the highest quality oil during the catalytic fast pyrolysis of spent Achyranthes root, having higher selectivity of mono-aromatic hydrocarbons compared to HY30.

Activation energy of domestic wastewater sludge in combustion process by using thermogravimetric analysis

The increasing demand of energy and environmental problem due to the consumption of fossil fuel has led the exploration of biomass fuel as an alternative energy. One of the potential biomass feedstocks that is available in Malaysia is Domestic Wastewater Sludge (DWS). In this study, DWS fuel characterization and the effect of experimental condition such as gaseous atmosphere, heating rate and particle size to the thermal behaviour of DWS has been carried out. In addition, kinetic parameter such as activation energy was determined by using the iso-conversional model free kinetic method, Flynn Wall Ozawa (FWO) model. Furthermore, lower heating rate and smaller particle size of DWS produced more volatile gas (84.51%), resulted to low ignition temperature (209°C) and low burnout temperature (515°C). Higher volatile indicates that it can accelerate the ignition process. In addition, low ignition temperature and low burnout temperature reveal that DWS can be ignited easily and shorten the time for combustion process. Based on the finding, the average activation energy for combustion of DWS which is about 143.86 kJ/mol.

Characterization of PVC/MWCNTs Nanocomposite: Solvent Blend

Abstract Polyvinyl Vinyl Chloride (PVC) multiwall carbon nanotubes (MWCNTs) nanocomposite flexible films were prepared using the solvent blend technique. Chloroform (CHCl3) and tetrahydrofuran ((CH2)4O) were used as solvents for MWCNTs and PVC, respectively. The effect of the solvents’ blend on electrical, optical and thermal properties of PVC/MWCNTs were investigated. The results of the Raman spectrum showed that all the characteristic bands of PVC polymer have a slight shift due to addition of MWCNTs. Electrical results showed that the nanocomposite samples with chloroform volume ratios of 10% and 25% had nearly the same conductivity. This is attributed to the formation of the MWCNTs network, which assisted in electrical conductivity. The I-V hysteresis curve decreases as the temperature increases and as it approaches the glass transition temperature. The non-isothermal kinetics analysis for PVC and PVC/MWCNTs were investigated by Thermogravimetry Analysis (TGA) using the model-free kinetic method. The non-isothermal measurements were carried out at five heating rates of 5 to 40∘C/min. The results show that the main decomposition process has constant apparent activation energies for all samples. The use of the bi-solvent method has improved the dispersion of untreated MWCNTs, and this has been reflected on the stability of both electrical and thermal properties.

A comparative applicability study of model-fitting and model-free kinetic analysis approaches to non-isothermal pyrolysis of coal and agricultural residues

Comparative applicability of model-fitting and model-free kinetic methods to pyrolysis of two coals and four agricultural residues was analyzed by using two models from each class of methods. The two model-fitting methods were Arrhenius and Coats-Redfern while Friedman and Vyazovkin were selected from the model-free category. According to kinetic analysis by all four models, the fuels could be arranged in following order of activation energy, CC > DC > SD > RH > FS > CH. The two model-fitting methods exhibited different kinetic parameters (E and reaction mechanism). All fuels were found to have a third order reaction mechanism (F3) by using Arrhenius model. In the case of Coats-Redfern model, the CC and RH displayed 3-dimensional diffusion mechanism (D3) whereas CH, SD and FS exhibited third order reaction mechanism (F3). DC was found to decompose according to 2-dimensional diffusion mechanism (D2). The percentage difference between the values of activation energy found from the Arrhenius and Coats-Redfern models was in the range of 6.24–21.64%. The percentage difference between the values of activation energy from two isoconversional models was not more than 3.29% for coals and 4.91% for agricultural residues in the fractional conversion range of 0.1–0.7. Isoconversional models were found to be more reliable and accurate for estimation of non-isothermal kinetics for pyrolysis of solid fuels compared with model-fitting methods.

The determination of the activation energy of diesel and biodiesel fuels and the analysis of engine performance and soot emissions

The behaviors of a biofuel and a fossil fuel were evaluated by different techniques, namely thermal analysis (Thermogravimetry-TG and Differential Thermal Analysis-DTA) and engine performance tests. From TG and DTA curves, two decomposition phases were identified for diesel fuel with ignition temperature (IT) at 250 °C and three phases for biodiesel fuel with IT at 300 °C. Combining conversion (α) versus temperature and a model-free kinetics method, the range of activation energies (Ea) values were determined for both diesel (from 48.5 kJ mol−1 up to 61.0 kJ mol−1) and biodiesel (from 58.6 kJ mol−1 up to 55.0 kJ mol−1) fuels. At the initial phase of combustion, diesel fuel presents lower Ea and IT than biodiesel fuel. At the final phase of combustion, an opposite behavior is observed. These results provide subsides to predict that the behavior of diesel-biodiesel blends is the best option due to the lowering of Ea along the entire combustion process. As regards the engine tests, the B20 blend showed improvements compared with diesel fuel. In average, B20 presented increases of 1.2% in power, 1.0% in torque and 1.2% in thermal efficiency. In terms of soot, B20 presented 8.9% lower emissions than diesel fuel. Although thermal analysis and engine performance tests are executed under very different conditions, the results from both techniques showed the same trend, i.e., the best option for the combustion performance is a diesel-biodiesel blend.

Linear baseline interpolation for single-process DSC data—Yes or no?

Theoretical simulations were used to evaluate performance of the linear baseline interpolation for the consequent kinetic analysis of single processes under different circumstances including the effects of varying height of the heat capacity step between the reactants and products, or varying asymmetry of the interpolated kinetic peak. In general, height of the Cp step was found to have larger distorting influence than the peak asymmetry. The model-free kinetic methods were found to be robust enough not to be significantly affected by the distortions caused by using linear interpolation (the performance was compared to that of the most accurate and physically meaningful tangential area-proportional interpolation) – the largest errors in activation energy did not exceed approx. 3%. On the other hand, model-based analysis has shown that usage of the linear interpolation leads to a significant distortion of the shape of the kinetic peaks and large deviations in the integrated area of the kinetic peak (corresponding e.g. to specific heat associated with the process studied by differential scanning calorimetry). Distortions of the peak shape consequently led to often largely deviated values of kinetic exponents determined for the correctly preselected known kinetic models. Model-based kinetic analysis of real-life experimental data treated via linear interpolation could in such case lead even to a selection of an incorrect kinetic model.

Studies on Crystallization and Melting Behaviors of UHMWPE/ MWNTs Nanocomposites with Reduced Chain Entanglements

The nonisothermal crystallization and melting behavior of UHMWPE (ultra-high molecular weight polyethylene)/ MWNTs (multi-walled carbon nanotubes) nanocomposites with reduced chain entanglements was studied using differential scanning calorimetry (DSC) technique. The Ozawa approach failed to describe the crystallization behavior of nanocomposites, whereas the modified Avrami analysis could explain the behavior of UHMWPE/ MWNTs nanocomposite to some extent. A novel kinetic model by Liu et al. was able to satisfactorily describe the crystallization behavior of UHMWPE/MWNTs nanocomposites. The Dobreva and Kissinger methods failed to calculate the nucleation activity and activation energy, respectively, for the UHMWPE/MWNTs systems. Also the Vyazovkin model-free kinetic method was applied to nonisothermal crystallization to evaluate the dependence of the effective activation energy on conversion and temperature.

Isothermal DSC Study of the Curing Kinetics of an Epoxy/Silica Composite for Microelectronics

Abstract Curing kinetics of an industrially important printed-circuit board (PCB) base material (epoxy–phenol/glass fillers) were studied by isothermal differential scanning calorimetry (DSC) measurements between 150 and 190°C, as relevant curing temperatures for the PCB industry. The extent of cure was calculated by integration of the exothermic peak and normalization by the total heat of reaction (obtained by nonisothermal DSC). Although the cross-linking was completed above 180°C, the kinetic profiles show two regimes: one fast and one slow. The kinetic parameters have been elucidated using an isoconversional model-free kinetic method, with the exact method of Friedman, to give to the PCB manufacturers a road map to predict curing behavior of base material. The linearity of Arrhenius plots was satisfactory. The apparent activation energy of curing reaction has been found to increase with the degree of conversion. The elucidation of the kinetic parameters allows us to propose an accurate and predictive description of the curing kinetics within the fast regimen of reaction (i.e., without vitrification). Finally, we discuss how these kinetic measurements and models can be completed and optimized.

Kinetics and evolved gas analysis for pyrolysis of food processing wastes using TGA/MS/FT-IR

The objective of this study was to identify the pyrolysis of different bio-waste produced by food processing industry in a comprehensible manner. For this purpose, pyrolysis behaviors of chestnut shells (CNS), cherry stones (CS) and grape seeds (GS) were investigated by thermogravimetric analysis (TGA) combined with a Fourier-transform infrared (FT-IR) spectrometer and a mass spectrometer (MS). In order to make available theoretical groundwork for biomass pyrolysis, activation energies were calculated with the help of four different model-free kinetic methods. The results are attributed to the complex reaction schemes which imply parallel, competitive and complex reactions during pyrolysis. During pyrolysis, the evolution of volatiles was also characterized by FT-IR and MS. The main evolved gases were determined as H2O, CO2 and hydrocarbons such as CH4 and temperature dependent profiles of the species were obtained.

Characterization of lignocellulose biomass and model compounds by thermogravimetry

ABSTRACTIn this research, combustion characteristics of lignocellulose biomass (hazelnut shell) and three main components (cellulose, hemicellulose, and lignin) were investigated using thermogravimetry (TGA-DTG) technique at different heating rates. The ignition, peak, burn-out temperatures, and the heat liberation of lignocellulose biomass and three main components were also measured. Two different model-free kinetic methods, known as Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS), were used in order to determine the activation energy values. Throughout the study, it is observed that the activation energy values of the biomass compounds varied between 83.8 and 191.7 kJ/mol for OFW and KAS methods, respectively.

Isothermal DSC study of the curing kinetics of an epoxy/silica composite for microelectronics

Abstract Curing kinetics of an industrially important printed-circuit board (PCB) base material (epoxy-phenol/glass fillers) were studied from isothermal differential scanning calorimetry (DSC) measurements between 150 and 190 °C. The extent of cure was calculated by integration of the exothermic peak and normalization by the total heat of reaction (obtained by non-isothermal DSC). The kinetic profiles show two regimes: one fast, and one slower. The completion was reached above 180 °C. The kinetic parameters have been elucidated using an isoconversional model-free kinetic method. The linearity of Arrhenius plots was satisfactory. The apparent activation energy of curing reaction has been found to increase with the degree of conversion. The elucidation of the kinetic parameters allows us to propose an accurate and predictive description of the curing kinetics of the composite until a degree of conversion of 50%. Finally, we discuss how these kinetic measurements and models can be completed and optimized.

Pseudo-component thermal decomposition kinetics of tomato peels via isoconversional methods

The kinetics of the thermal decomposition of tomato peel residues under nitrogen atmosphere was studied by non-isothermal thermogravimetric analysis in the heating rate range 2–40°C/min. Due to the complexity of the kinetic mechanism, which implies simultaneous multi-component decomposition reactions, an analytical approach involving the deconvolution of the overlapping decomposition steps from the overall differential thermogravimetric curves (DTG) and the subsequent application of model-free kinetic methods to the separated peaks was employed. Two freely available Matlab functions, which adopt a non-linear optimization algorithm to decompose a complex overlapping-peak signal into its component parts, were used. Different statistical functions (i.e., Gaussian, Voigt, Pearson, Lorentzian, equal-width Gaussian and equal-width Lorentzian) were tested for deconvolution and the best fits were obtained by using suitable combinations of Gaussian and Lorentzian functions. For the kinetic analysis of the deconvoluted DTG peaks, the Friedman's isoconversional method was adopted, which does not involve any mathematical approximation. The reliability of the derived kinetic parameters was proved by successfully reproducing two non-isothermal conversion curves, which were recorded at a heating rate of 60°C/min and 80°C/min and not included in data set used for the kinetic analysis. Seven pseudo-components were identified as a result of the deconvolution procedure and satisfactorily associated with the main constituents of the investigated tomato peels.

Thermal properties and thermal degradation kinetics of phenolic and wood flour-reinforced phenolic foams

In the present work, the thermal stability, changes in chemical structure during thermal degradation, and the kinetics of thermal degradation of a phenolic foam were studied. An 8.5 wt% of Pinus radiata wood flour reinforcement was added to the phenolic foam. A commercial phenolic resol was used as the matrix for the foam. The wood flour-reinforced foam showed a structure similar to the phenolic foam according to the Fourier transform infrared spectroscopy results. The wood flour increased the thermal stability of the phenolic foam in the first stage of thermal degradation ( T5%), decreased it in the second step ( T25%), and negligibly influenced the final stage. The activation energies of the degradation processes of the studied materials were obtained by the Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa model-free kinetic methods and a 2-Gaussian distributed activation energy model. The values of the activation energies obtained by the model-free kinetic methods for the first degradation stage of the phenolic foams were in a range between 110 and 170 kJ mol−1, whereas for the wood flour it was 162 kJ mol−1for almost all of the conversion range of its main degradation stage. The applied models showed good fits for all the materials, and the activation energies calculated were in agreement with the values found in the literature.

Chemical evaluation and kinetics of Siberian, north regions of Russia and Republic of Tatarstan crude oils

ABSTRACTIn this research, thermal characteristics and model free kinetics of five different °American Petroleum Institute gravity crude oil samples from different locations were studied using combustion calorimetry and thermogravimetry (TGA) techniques. Higher heating values of crude oils were determined from the combustion calorimetry experiments. It was shown that these values increase with an increase in saturate fraction and °API gravity of studied samples and decrease with an increase in viscosity, aromatics fraction, and resin fraction of crude oils. In thermogravimetry, experiments were performed at 10, 20, and 30°C/min heating rates under an air atmosphere. Thermal characteristics of the samples such as reaction intervals and corresponding peak temperatures, mass loss, and residue of the crude oil samples were also determined. Two different model free kinetic methods, known as Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS), were used in order to determine the activation energy values of the crude oil samples studied.

Deconvolution of calorimeter response from electrical signals for extracting kinetic data

Calorimetry is a powerful tool for the study of chemical reactions and of biological systems. Nevertheless, reaction calorimeters and calorimeters may have high time constants. In this study, the correction brought by two types of deconvolution methods using electrical signals has been compared. The distortion of the calorimetric signals has been evaluated and its effect on kinetic parameters determination has been quantified. For this purpose, relative errors on activation energy, pre-exponential factors and kinetic exponents have been computed by reference to measured signals whose thermokinetic parameters were perfectly known. 1st and 2nd order deconvolutions were found to be more suitable for kinetic analyses. Integral methods allow obtaining the most accurate results with model-fitting and model-free kinetic methods, while differential methods are more sensitive to noise and submitted to numerical instability. The correction proposed allows slightly improving the accuracy in the estimation of kinetic parameters and to adapt the correction to the kind of kinetic method used. The deconvolution method has been applied to isothermal data, but the method is easily transposable to nonisothermal measurements.

Thermal characterization and model-free kinetics of biodiesel sample

In this study, combustion and pyrolysis behaviours of methanol route biodiesel were investigated using thermal analysis techniques known as simultaneous thermogravimetry and differential scanning calorimetry (DSC) at different heating rates. Reaction regions, peak temperatures, mass loss and heat flow rates of the biodiesel sample are determined using TG-DTG and DSC data. It was found that as the heating rate of the reactions increased, peak temperatures of the reactions shifted higher temperatures, implying that as the heating rate of the reactions increased, reaction lost their sensitivity. Two different model-free kinetic methods, known as Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose, as proposed by ICTAC kinetics committee, were applied to determine the pyrolysis and combustion reaction parameters of biodiesel sample, and the results are discussed.