Parallel Independent Reactions Research Articles

Pyrolysis of household coffee vis-à-vis tea waste: A detailed insight into physicochemical properties, kinetics, and thermodynamics study

The present study compares the kinetics and thermodynamics of the pyrolysis process of coffee and tea waste with respect to their physicochemical properties to analyze their potential as an energy and carbon source. Coffee and tea waste exhibit a promising source as a biofuel that has gross calorific values of 22.7 MJ kg−1 and 20.2 MJ kg−1, with significant differences in the overall volatile conversion of 76 % and 65 %, and as final carbon with a yield of 22 % and 31 %, respectively. Kinetic analyses using isoconversional methods show a trend of activation energy and frequency factor with conversion for both samples, with a significant difference at a conversion beyond 0.6 due to the higher lignin content in coffee waste. The predicted master plots indicate complex pyrolysis kinetics for both samples. Furthermore, the reaction kinetics determined by the multivariate regression approach, assuming parallel independent reactions of the nth order applicable to all heating rates, provide the individual mass change and carbon yield of each reaction process that can be controlled using experimental conditions. Finally, the thermodynamic parameters indicate that the pyrolysis process of both coffee and tea waste is nonspontaneous and endothermic, and its reactivity increases with conversion.

Kinetic analysis of complex chemical reactions by coupling model-free and model-fitting analysis

Three different complex multi-step reaction mechanisms of parallel-competing, consecutive and parallel-independent reactions were simulated for two different sets of kinetic parameters. The two sets were chosen in such a way to represent two very different situations. An advanced non-linear isoconversional method (NLN) and a multiple heating rates model-fitting method using nonlinear optimization (NLO) were applied to the data. The errors in kinetic parameters were evaluated for each set of data and for each method. It is shown that analysis of the thermoanalytical curves and of the Eα-dependencies can be used in complementary with the model-fitting approach for the elucidation of the reaction mechanisms and estimation of the kinetic parameters of each step. In most cases, NLO improved the accuracy of the kinetic parameters obtained from NLN method, but only if the mechanism was known. However, selecting the right mechanism is an essential problem of NLO. The study showed that it was possible to accurately fit the mechanism of two consecutive steps with a model of two independent steps that resulted in evaluating invalid kinetic parameters. This example also highlights an important limitation of the so-called deconvolution kinetic analysis which consists in fitting of various multi-step reaction mechanisms with a model of independent steps.

On the applicability of model free isothermal prediction procedures for complex processes

This paper analyses the possibility of using the model free isothermal prediction procedures for the complex processes. The validity of these procedures applied for complex processes is sometimes suspected because of some depressing results. It has been shown that the obtaining of arbitrary results by these methods is due to the assumption that the characteristic apparent activation parameters of the complex process depend only on the degree of conversion and that a correct prediction is obtained for any set of heating rates at which the necessary thermoanalytical data were recorded for applying the isoconversional method used. In order to obtain a satisfactory prediction, some “modified model free isothermal prediction procedures” have been suggested, which include an initial stage of determining the range of heating rates at which the thermoanalytical data necessary for the application of these procedures must be recorded, and in which it is considered that the apparent activation parameters depend both on the degree of conversion as well as the temperature for which the prediction is made. The validity of these modified procedures has been verified for simulated data corresponding to two complex processes, namely two first order parallel independent reactions and two first order consecutive reactions.

Model-free isothermal and nonisothermal predictions using advanced isoconversional methods

Four complex mechanisms of two parallel independent reactions were simulated under various isothermal and nonisothermal conditions. Equations to perform isothermal predictions and nonisothermal simulations at a different temperature program are presented, based on the isoconversional methods of Vyazovkin and Friedman. Isoconversional kinetic parameters were used to simulate the reaction progress under different isothermal and nonisothermal conditions. It was shown that accurate simulations can be performed in a model-free way, i.e. without knowledge of the reaction mechanism. A higher accuracy was obtained for mechanism involving more separated individual steps. The methods proposed are applicable to both DSC and TG data.

Thermogravimetric Kinetics of Selected Energy Crops Pyrolysis

The main purpose of this paper was to compare the pyrolysis kinetics of three types of energy crops: Miscanthus giganteus, Sida hermaphrodita, and Sorghum Moench. Studies were conducted in thermobalance. Feedstock samples were heated up from ambient temperature to 600 °C under an inert argon atmosphere. Three heating rates of β = 5, 10, and 20 °C/min were applied. Reactions occurring in the given temperature ranges were grouped together into so-called lumps identified by the deconvolution of derivative thermogravimetry (DTG) curves that corresponded to biomass compositions (hemicellulose, cellulose, and lignin). For the estimation of the activation energy and pre-exponential factor, the Friedman and Ozawa–Flynn–Wall methods were used. The final kinetic parameters were determined by nonlinear regression assuming that thermal decomposition proceeded via three parallel independent reactions of the nth order. The activation energy of hemicellulose, cellulose and lignin was determined to be in the range of 92.9–97.7, 190.1–192.5, and 170–175.2 kJ/mol, respectively. The reaction order was in the range of 3.35–3.99 for hemicellulose, 1.38–1.93 for cellulose, and 3.97–3.99 for lignin. The obtained results allow us to estimate the pyrolytic potential of energy crops selected for this study, and can be used in designing efficient pyrolizers for these materials.

Thermal degradation of leaves from the Amazon rainforest litter considering non-structural, structural carbohydrates and lignin composition

This work investigates the thermal degradation of leaves from the Amazon Rainforest litter, which is currently unknown. It formulates innovative thermal degradation equations useful for numerical simulation of wildfires in this biome. Furthermore, this work quantifies for the first time structural and non-structural components of litter leaves, which translates into an improved representation of the thermal degradation process. The main output of this work is the reaction mechanism with six parallel independent reactions for soluble sugars, pectin, hemicellulose, cellulose, lignin, and other organic compounds, which represent the thermal degradation of the litter leaves. The average composition of the Amazonian litter leaves is soluble sugars 22.9%, pectin 9.0%, hemicellulose 18.3%, cellulose 9.1%, lignin 21.2%, and inorganic plus other organic compounds 19.5%.

Detailed kinetic analysis of slow and fast pyrolysis of poly(methyl methacrylate)-Flame retardant mixtures

In this study, thermal decomposition kinetics of poly(methylmethacrylate) (PMMA) is investigated in the presence of a phosphorus-based flame retardant (Exolit®) under slow and fast pyrolysis conditions. Multi-Gaussian distributed activation energy model (DAEM) is employed to determine the kinetic parameters at slow heating rates. The multi-Gaussian DAEM with five parallel independent reactions predicts well the experimental mass loss and differential mass loss profiles. The incorporation of 3 and 5 wt.% Exolit® in PMMA delays the decomposition temperature and slows down the rate of PMMA pyrolysis. Isothermal fast pyrolysis is carried out in the temperature range of 400−700 °C at short time intervals of 2−150 s. The rate constant of decomposition of PMMA + 5 wt.% Exolit® mixture was lower than that for pure PMMA. Through analytical pyrolysis coupled with Fourier transform infrared spectroscopy it is shown that the addition of Exolit® to PMMA significantly delays the evolution of methylmethacrylate, which is the major pyrolysate.

Coupling gas flow pattern and kinetics for tyre pyrolysis modelling

A novel strategy has been proposed for the rigorous kinetic modeling of tyre pyrolysis in a conical spouted bed reactor. A kinetic model coupled with a gas flow model was used in the fitting of experimental results obtained in a bench scale unit in the 425–610 °C range. A gas flow model should be incorporated to account for the delay and mixing phenomena observed in tracer experiments, as these phenomena cause remarkable deviations in the assessment of the kinetic parameters. The gas flow pattern from the reactor to the measuring device was modeled using two different approaches based on ideal flow reactors. Furthermore, two kinetic schemes considering lumped products have been proposed; the first one is based on four parallel independent reactions accounting for the volatile products (gas, liquid, aromatics and tar). The second one considers an additional secondary reaction of aromatic formation from the liquid. The strategy proposed for coupling the kinetics and the flow model led to a suitable fitting of the experimental results, with the performance of the model considering a secondary reaction being slightly better than the simple one.

Reaction: Exploring the Chemistry Frontier in Water-Borne Vessels

In 2007, John Warner and Jim Babcock founded the Warner Babcock Institute for Green Chemistry and, with Amy Cannon, founded the green chemistry education nonprofit organization Beyond Benign. John is the recipient of the 2004 Presidential Award for Excellence in Science Mentoring and the 2014 Perkin Medal. In addition, John is one of the founders of the field of green chemistry and is co-author of the defining textbook Green Chemistry: Theory and Practice. In 2017, the German Ministry of Economic Affairs and the Technische Universitat Berlin announced the naming of the John Warner Center for Green Chemistry Start-Ups in his honor.

Kinetic modeling of polyurethane pyrolysis using non-isothermal thermogravimetric analysis

The pyrolysis of polyurethane was studied by dynamic thermogravimetry analysis (TGA). The studied polyurethane is used as organic binder in casting process to make sand cores and molds. A semi-empirical model is presented that can be used to describe polyurethane pyrolysis occurring during TGA experiments. This model assumes that the polyurethane is pyrolysed by several parallel independent reactions. The kinetic parameters of polyurethane pyrolysis were evaluated by fitting the model to the experimental data obtained by TGA over a wide variety of heating rates. A nonlinear least-squares optimization method is employed in the fitting procedure. A hybrid objectives based simultaneously on the mass (TG) and mass loss rate (DTG) curves has been used in the least-squares method. The values of the activation energy obtained by the non-linear fitting were then recalculated by the methods of Kissinger and Friedmand. Furthermore, the parameters obtained in the present paper were then compared with those reported in the literature.

Nonisothermal Degradation of Zetaplus Impression Material: Kinetic Aspects

Kinetic analysis of the nonisothermal degradation process of Zetaplus impression material has been performed. Kinetic data for the investigated degradation process were obtained from the thermogravimetric (TG) and differential thermal analysis (DTA) measurements conducted at the three different heating rates (β = 10, 20, and 25 °C min−1) in an air atmosphere. For determination of the kinetic model function (f(α) or g(α)), the isoconversional and Master-plot methods were used. It was found that the first degradation stage of Zetaplus impression material can be described by the three-dimensional diffusion (D3) and with the following values of kinetic parameters: Ea = 99.5 kJ mol−1 and A = 1.05 × 108 min−1. Kinetic analysis shows that the first degradation stage corresponds to the bond cleavages and polydimethylsiloxane thermal volatilization, which is contolled by the rate of diffusion and evaporation of oligomers produced on decomposition. The observed second degradation step is more complex; it includes two parallel independent reactions with different values of the apparent activation energy. By applying the nonlinear regression (NLR) method, it was found that the second degradation stage can be described by two independent parallel first-order reactions (nth-order reaction model).

Curing kinetics and chemorheological analysis of polyurethane formation

AbstractThe cross‐linking kinetics and the rheological behavior of a polyurethane system during curing are investigated by DSC and small amplitude oscillatory shear rheometry. In this study, isoconversional methods are applied to understand the reaction complexity. The activation energy depends on the extent of conversion. It can be shown that three parallel reactions occur during the evolution of the global reaction in non‐isothermal conditions. An original multi‐step model can involve these three parallel independent reactions. Dynamic viscosity is measured as a function of time and is found independent of shear rate. Isothermal viscosity rise is related to reaction extent by a phenomenological model. The gelation time is determined by the tanδ crossover at different frequencies. Polym. Eng. Sci. 44:518–527, 2004. © 2004 Society of Plastics Engineers.

Combustion behavior of xylite/lignite mixtures

The behavior and the kinetics in nitrogen and air of two low-rank coals (lignite and xylite) and their blends, as well as the compatibility of the component coals in the blends were evaluated, in an effort for the rational use of poor coals. The experiments were conducted in a thermobalance system, at non-isothermal heating conditions, with heating rates of 20 and 100 °C/min, in the temperature range of 25–850 °C. Material particle size was −100 μm. A first-order parallel independent reactions model and a power law model fitted successfully the rate data of pyrolysis and combustion, respectively. Activation energy values and reaction orders ranged from 23 to 182 kJ/mol and 0.8 to 2 respectively. The heating rate did not affect the kinetic parameters considerably, however when this was increased the reactions were shifted to higher temperatures and the rates were greater. The pyrolysis kinetics of lignite/xylite blends could be sufficiently predicted, based on the data of the individual fuels. However, this was not true in the case of char combustion. Blending of lignite with xylite, in any proportion, seemed to cause some interactions between the component coals in air.

Isothermal and Non-Isothermal Kinetics When Mechanistic Information Available

In the case of a complex mechanism of two parallel independent reactions, peak maximum evolution methods and model-fitting methods give only a mean value of the kinetic parameters, while isoconversional methods are useful to describe the complexity of the mechanism. Isothermal and non-isothermal isoconversional methods can be used to elucidate the kinetics of the process. Nevertheless, isothermal isoconversional methods can be limited by restrictions on the temperature regions experimentally available because of duration times or detection limits.

An approach to the solution of the inverse kinetic problem in the case of complex processes. Part III. Parallel independent reactions

This paper is devoted to the investigation of the possibility of identifying a complex process incorporating parallel independent reactions. The identification was achieved using a previously proposed method relying on the investigation of the form of the transformation-degree dependence of the effective activation energy. Using model data, we consider three main variants of the complex process and have established the characteristic dependences of their activation energy on the transformation degree. It is shown that the shape of these dependences is determined by the ratio of the rates of individual reactions and their partial contribution to the gross transformation degree and can be used for identifying the complex process under consideration.

Potentialities of software for kinetic processing of thermoanalytical data by the isoconversion method

The potentialities of the proposed software, which is based on the isoconversion method of calculating the Arrhenius parameters, are compared with software of the Du Pont and Mettler thermoanalysers. Calculations by the model DSC curves for a process involving two parallel independent reactions have shown that the software of the thermoanalysers does not provide reliable information about the kinetics of complex processes. The proposed software makes it possible to establish the complex character of a process and its type, to evaluate the activation energies of parallel reactions and to predict the kinetics of its proceeding outside the experimental temperature range.