The Use of Nonlinearity Measures in the Estimation of Kinetic Parameters of Sugarcane Bagasse Pyrolysis

The majority of the pyrolysis kinetics models presented in the literature is nonlinear. In these models, the influence of temperature is normally described by the Arrhenius equation. In some studies related to parameter estimation of nonlinear models suggestions can be found for reparameterization of the Arrhenius‐type equation due to inadequate results on the parameter estimation. In this work, kinetic modeling is proposed in order to predict the primary biomass decomposition behavior under a dynamic regime. This model is based on the traditional model of parallel reactions and uses the Arrhenius‐type equation in the reparameterized form. Some nonlinearity measures are used as a tool to correctly estimate the kinetic parameters of the pyrolysis of sugarcane bagasse. The predictions from the proposed model properly reproduced the experimental DTG curves. The reparametrized model showed non‐significance for bias and nonlinearity measures.     

Master curve and time–temperature–transformation cure diagram of lignin–phenolic and phenolic resol resins

The aim of this work is to generate both a master curve of resol resins based on the time–temperature superposition principle and their TTT cure diagrams. The samples used for this purpose were lignin–phenolic and phenol–formaldehyde resol resins. A TMA technique was employed to study the gelation of resol resins. In addition, a DSC technique was employed to determine the kinetic parameters through the Ozawa method, which allowed us to obtain isoconversional curves from the data fit to the Arrhenius expression. Establishing the relationship between the glass‐transition temperature and curing degree allowed the determination of the vitrification lines of the resol resins. Thus, using the experimental data obtained by TMA and DSC, we generated a TTT cure diagram for each of resins studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3362–3369, 2007     

Effect of mold temperature on the long‐term viscoelastic behavior of polybutylene terepthalate

The effect of mold temperature variation during injection molding on the long‐term viscoelastic behavior of polybutylene terepthalate (PBT) was studied by dynamic mechanical thermal analysis (DMTA) and flexural creep tests. The time–temperature superposition (TTS) principle was applied to the experimental data and the master curves were created to predict their long‐term behavior. The WLF and Arrhenius models were verified for the shift data in the investigating temperature range and the activation energies for the deformation process were calculated based on the Arrhenius equation. Further a four‐element Burger model was applied to the creep results to represent the creep behavior of the PBT processed at two different mold temperatures and to better understand the deformation mechanism. Differential scanning calorimetry (DSC) and density measurements were accomplished to characterize the process‐dependent microstructures. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Characterization of temperature‐dependent moisture diffusivity in PMR‐15 resin

The temperature‐dependent moisture diffusion behavior of high‐temperature polyimide resin, PMR‐15, is presented. Adsorption and high temperature desorption tests are used to experimentally determine moisture diffusivity at several temperatures. Diffusivity is determined from the weight change based on the initial slope and using a nonlinear regression technique with Fickian diffusion assumption. The basic test procedures and diffusivity values are presented in this study. The results also include the relative humidity (RH) dependent equilibrium moisture concentration and a relationship between the RH and equilibrium moisture concentration. As direct measurement at typical operating temperature may be precluded by blistering, an Arrhenius‐type temperature‐diffusivity relationship is used to estimate the temperature‐dependent moisture diffusivity for the PMR‐15 resin. The moisture diffusivity of PMR‐15 tested is estimated to be 6.64 E ?10 m²/s at 288°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Development of a two‐stage,dual‐Arrhenius rheology model for a high‐performance phenylethynyl‐terminated poly(etherimide)

A two‐stage, dual‐Arrhenius rheology model was successfully utilized to model the isothermal complex viscosity of a phenylethynyl‐terminated poly(etherimide) as a function of time and temperature over the experimental temperature range of 325°C to 350°C. Union of the dual‐Arrhenius model with a previously developed combination reaction kinetics model provided a chemoviscosity model giving viscosity as a function of degree of cure. A two‐stage, versus a single, dual‐Arrhenius model was used to accommodate a transition in the reaction process from chain growth to branching and network forming that was found to onset around a degree of cure of 0.37. The reduction in chain mobility brought on by branching and networking was quantified by the almost order of magnitude increase in the apparent activation energy for initial viscosity from the chain growth stage to the networking stage. The calculated apparent activation energies for gelation for the first and second stages, 2.14 × 10⁵ J/mol and 2.05 × 10⁵ J/mol, respectively, agree well with results presented elsewhere from differential scanning calorimetry measurements. The experimental procedures followed to obtain the rheological data and the construction of the model from these data are described; the predictions of the model are compared with experimental results.     

Characterization of rheological and thermophysical properties of HDPE–wood composite

The objective of this study is to develop a new biocomposite material with high deformation ability. In this regard, the thermal, rheological, and thermophysical properties of this new composite were characterized as a function of temperature and filler concentration. High density polyethylene (HDPE) was the matrix of this new composite which was reinforced with six sawdust concentrations 0%, 20%, 30%, 40%, 50%, and 60%. Maleic anhydride grafted polyethylene (PE‐g‐MA) was used as coupling agent. Addition of sawdust with PE‐g‐MA increased significantly the complex viscosity, the storage modulus (G′), and loss modulus (G″) of the matrix. The superposition of the complex viscosity curves using temperature dependent shift factor, allowed the construction of a viscosity master curve covering a wide range of temperatures. Arrhenius law was used for the relationship of the shift factor to temperature. Furthermore, method of Van Gurp and Palmen (tan delta vs. G*) is also used to control the time–temperature superposition. The experimental results can be well fitted with the cross rheological model which allowed the prediction of the thermorheological properties of the composites over a broad frequency range. By increasing wood concentration, both the activation energy and relaxation time for the biocomposites determined using, respectively, the Arrhenius law and the cole–cole rule increased. By contrast, specific heat of the matrix decreased with sawdust addition while its dimensional stability improved. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40495.     

Modeling of Kinetic Expressions for the Reduction of NOx by Hydrogen in Oxygen‐Rich Exhausts Using a Gradient‐Free Loop Reactor

The reduction of NO_x by hydrogen under lean conditions is investigated in a gradient‐free loop reactor. Using this computer‐controlled reactor, the reaction rates can be measured under exact isothermal conditions. Systematic variation of the input concentrations of hydrogen, nitric oxide, oxygen as well as reaction temperature provides a complete data set of reaction rates for the given reaction system. A number of kinetic rate expressions were evaluated for their ability to fit the experimental data by using toolboxes of MATLAB. The temperature influence on reaction rate constants and adsorption equilibrium constants were correlated simultaneously using Arrhenius and van’t Hoff equations, respectively. The kinetic rate expression based on a Langmuir‐Hinshelwood‐type model describes the data and the model can be improved by introducing a correction term in square root of hydrogen partial pressure over the range of conditions investigated.     

Purification of glycerol/water solutions from biodiesel synthesis by ion exchange: sodium removal Part I

BACKGROUND: In this study, equilibrium and kinetic data of the ion exchange of sodium from glycerol–water mixtures on the strong acid resin Amberlite‐252 were obtained. Basic parameters for the design of ion exchange units for the purification of the crude glycerol phase from biodiesel production have been determined. RESULTS: Equilibrium uptake of sodium ions with the strong acid ion exchanger Amberlite‐252 was studied at three temperatures. The Langmuir equation and the mass action law model were used to fit the experimental equilibrium data. Equilibrium constants and thermodynamic parameters were obtained at each temperature. Kinetic experiments were carried out to evaluate the effective diffusion coefficients of sodium on the resin Amberlite‐252 in glycerine–water media. CONCLUSIONS: Equilibrium results indicate that this process is favourable and also that its selectivity decreases with temperature increase from 303 to 333 K. Both models were able to fit the experimental equilibrium data. Kinetic experiments showed that the rate of mass transfer in this binary system is high. An Arrhenius type equation allowed the correlation of effective diffusion coefficients and temperature. The results indicate that the macroporous resin Amberlite‐252 could be useful for removal of sodium ions from glycerine/water solutions with a high salt concentration. Copyright © 2008 Society of Chemical Industry     

Unified correlation for overall gas hold‐up in bubble column reactors for various gas–liquid systems using hybrid genetic algorithm‐support vector regression technique

The objective of this study is to collect the data on overall gas hold‐up (∈_G) for bubble column reactors handling various gas–liquid systems and further develop a unified data‐driven model for the estimation of the same. In this work, around 3300 experimental points for ∈_G have been collected from 85 open sources spanning the years 1963–2008. The data‐driven model for overall gas hold‐up has been established using hybrid Genetic Algorithm‐Support Vector Regression (GA‐SVR)‐based methodology. In the present study, GA has been used for nonlinear rescaling of the parameters. These exponentially scaled parameters are subsequently subjected for SVR training. The technique is an extension of conventional SVR technique, showing relatively enhanced results. The proposed hybrid model is based on various prominent design and operating parameters (15 in number) which includes superficial gas velocity, superficial liquid velocity, gas density, molecular weight of gas, sparger type, sparger hole diameter, number of sparger holes, liquid viscosity, liquid density, liquid surface tension, ionic strength of liquid, operating temperature, operating pressure, liquid height, and the column diameter. The estimations made by the SVR‐based unified model for ∈_G shows an excellent agreement with actual values with estimation accuracy of 98.5% and % AARE of 9.32%. For ease in applicability and ready reference of the practicing engineers, the hybrid GA‐SVR‐based model in the form of software and the entire database for ∈_G has been uploaded on the link http://www.esnips.com/web/UICT‐NCL .     

Analytical and experimental evaluation of elastic properties of vacuum assisted resin infusion molded polymer composites with eight‐harness woven fiber mats

An analytical and experimental evaluation of elastic properties of composite materials under tensile load is presented in this paper. The analysis focuses on composite materials molded by vacuum assisted resin infusion molding (VARIM). The molded composite structure consists of AS4‐8 harness carbon fiber mats and a high‐temperature polymer (5250‐4‐RTM). The analytical model presented is adapted and formulated using optical microscopy observations of cross sections of samples molded by VARIM. Effects of resin degree of cure, fiber undulation, and resin rich areas between fiber bundles are addressed in the model. An experimental case study is presented to evaluate the accuracy of the adapted analytical model. The evaluation shows a reasonable agreement between the experimental and analytical results. POLYM. COMPOS., 29:63–71, 2008. © 2007 Society of Plastics Engineers     

A reaction order functional relationship with the Williams–Landel–Ferry equation in curing kinetics

A methodology is presented to obtain a kinetic model for curing reactions, from conversion against time and the glass‐transition temperature versus conversion data. Isothermal runs for a cyanate ester resin from 140 to 190°C, reported previously, were evaluated. The approach utilizes the conversion measurement time derivatives that allow following the estimated parameters' trends: the rate constant and the reaction order, in this case. An autocatalytic model was found, and the rate constants were truly constant along the experiments; thus, their Arrhenius parameters were evaluated. The methodology allowed constructing a master curve relating the variable reaction order with a temperature difference (reaction and glass transition) explained by the Williams–Landel–Ferry (WLF) equation. Four parameters describing the reaction order variation, two related to an exponential‐like behavior and two required by the WLF equation, allowed describing the whole experimental set accurately. POLYM. ENG. SCI., 54:1900–1908, 2014. © 2013 Society of Plastics Engineers     

Modeling of dynamic mechanical properties of vulcanized fluoroelastomer

The dynamic mechanical properties of a vulcanized fluoroelastomer (FKM) were studied over a range of temperatures and shear frequencies. Dynamic mechanical analysis and differential scanning calorimetry were used for the purpose of the study. A model was developed in order to describe FKM's viscoelastic behavior at various temperatures. The model was fitted to experimental data using an algorithm, which was developed for this purpose. As a result the FKM discrete relaxation spectrum at two reference temperatures was obtained, as well as the Williams‐Landel‐Ferry (WLF) equation parameters or the activation energy equivalent. Further on, the model was applied on storage modulus and loss tangent values obtained from the experiments, during which the temperature increased linearly. It was observed that the WLF equation fits well with the results during the glass transition, while the Arrhenius‐type relationship predicted too rapid decrease of the storage modulus during the glass transition. The master curves were constructed using the previously calculated WLF parameters and the activation energy equivalent. The developed model may be readily applied for the prediction of the numerous FKM compounds' frequency–temperature behavior using the dynamic mechanical properties obtained from either isothermal or low linear heating rate program measurements. POLYM. ENG. SCI., 47:2085–2094, 2007. © 2007 Society of Plastics Engineers     

Main events occurring in styrene microemulsion polymerization

A previously presented model with four states (conversion, active and inactive particles and micelles) is further tested with conversion versus time experimental data at 50, 60, and 70°C, to recognize the main events occurring in styrene microemulsion polymerization. The S‐shaped conversion–with no overprediction‐ and the bell‐shaped active particles number concentration–evidencing diffusive effects at late stages–versus time data, are well described by the proposed model. It was found that: (i) transfer of monomer and surfactant from micelles to particles occurs, (ii) the capture of radicals by micelles is the only cause of particle nucleation, (iii) the rate coefficient of radical‐entry‐to‐micelles is much smaller than that of exit‐from‐particles, and (iv) no coagulation between particles was detected. The Arrhenius dependency on temperature of the kinetic rate parameters is also reported. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41720.     

Glass‐polymer melt hybrids. I: Viscoelastic properties of novel affordable organic‐inorganic polymer hybrids

A novel class of organic‐inorganic polymer hybrids was developed by melt‐blending up to 50 (v/v) % [about 83 (w/w) %] tin‐based polyphosphate glass (Pglass) and low‐density polyethylene (LDPE) in conventional plastics processing equipment. The liquid‐ and solid‐state rheology of the polymer hybrids was studied under oscillatory shear flow and deformation to understand the behavior of these materials and to accelerate efforts to melt process the Pglass with organic polymers. All the materials were found to be linearly viscoelastic in the range of temperature and frequencies examined and their viscoelastic functions increased with increasing Pglass concentration. The Pglass significantly enhanced the shear‐thinning characteristics of the Pglass‐LDPE hybrid, indicating the presence of nonlinear chemical and physical interactions between the hybrid components. Morphological examination of the materials by scanning electron microscopy revealed interesting evolution of microstructure of the Pglass phase from droplets (or round beads) to elongated and interpenetrating network structures as the glass concentration was increased in the Pglass‐LDPE hybrids. Melt viscosities of the materials were well described by a simple power‐law equation and a Maxwellian (Hookean) model with three relaxation times. Time‐temperature superpositioning (TTS) of the complex viscosity versus frequency data was excellent at 170°C < T < 220°C and the temperature dependencies of the shift factors conformed excellently well to predictions from an Arrhenius‐type relation, enabling calculation of the flow‐activation energies (25–285 kj/mol) for the materials. The beneficial function of the Pglass in the hybrid system was significantly enhanced by pre‐treating the glass with coupling agents prior to incorporating them into the Pglass‐LDPE hybrids.     

Investigation on Thermal Runaway in Batch Reactors by Parametric Sensitivity Analysis

A batch system is an inherently parametric sensitivity system where small changes of input parameters can induce large changes of output variables. In the present work, temperature and temperature sensitivity with respect to the initial temperature were investigated by parametric sensitivity analysis using a dimensionless batch reactor model. The influence of the Semenov number, the heat of reaction parameter and the Arrhenius‐type number on reactor temperature and temperature sensitivity were studied. It is demonstrated that batch reactors can exhibit high sensitivity when small changes in input parameters lead to large changes in temperature and temperature sensitivity trajectories. A criterion is established for thermal runaway by analyzing temperature sensitivity trajectories and applied to some experimental examples. This criterion allows runaway and safe conditions to be identified, the results being in agreement with the experimental data. The proposed criterion can satisfactorily predict the safety limits of the operating conditions.     

A numerical model for flame spread along combustible flat solid with charring material with experimental validation of ceiling flame spread and upward flame spread

This paper gives a numerical model for flame spread along combustible flat solid with charring materials. The presented model consists of a one‐dimensional flame spread model coupled with a one‐dimensional pyrolysis model. The existing experimental data (the ceiling flame spread beneath medium density fibreboard) are used for comparison to validate the model. In addition, the model can also be used to predict upward flame spread; only some expressions are changed. A comparison with full‐scale experimental data on the upward flame spread over plywoods from the literature is performed. The results obtained from numerical simulations using the model are consistent with these two kinds of experimental tests. Thus, the presented model is appropriate for modelling not only the ceiling flame spread, but also the upward flame spread. Copyright © 2007 John Wiley & Sons, Ltd.     

The Thin-Layer Drying Characterstics of White Onion Slices

ABSTRACT

A batch–type experimental dryer with a computer–aided data acquisition system was designed and built for the thin layer drying studies of onion (Allium cew L., cv. Southport White Globe) slices. Twenty seven single–layer drying curves were established for a temperature range of 42.5–90⁰C, an air velocity range of 0.6–1.4 m/s, an air humidity range of 0.0093–0.0442 kg of water/kg of dry air: and a slice thickness range of 0.002–0.005 m. The single–term exponential model adequately described the single–layer drying behaviour of the onion slices. l'he dependence of the drying rate constant on air temperature, absolute humidity, velocity and on slice thickness was best explained by an Arrhenius–type relationship. The drying rate constant in which moisture diffusion and shrinkage effects are lumped was greatly influenced by the sample thickness and drying air temperature, and to a lesser extent, by the air humidity and velocity.     

Application of time–temperature–stress superposition principle on the accelerated physical aging test of polycarbonate

The effect of physical aging on the polymer mechanical properties is very important for long‐term safety assessment of engineering application. In this paper, the physical aging tests of polycarbonate (PC) were conducted systemically under different temperature and uniaxial tensile stress level. It was shown that both temperature and stress have obvious accelerated effect on the physical aging of PC. The higher the temperature and stress level are, the faster the aging process is. To predict the long‐term behavior after physical aging using the short‐term test results of PC, the elongation‐at‐break was chosen as the index of the severity of physical aging. An Arrhenius‐type time–temperature–stress superposition principle (TTSSP) was proposed to evaluate long‐term performance using short‐term test data. Using the proposed method, time and cost can be dramatically reduced for the assessment of long‐term physical aging performance of polymeric material. POLYM. ENG. SCI., 55:2215–2221, 2015. © 2015 Society of Plastics Engineers     

Modeling the viscoelasticity of polyetherimide

Viscoelasticity is a mechanical phenomenon where the material modulus varies with time and temperature. Modern experimental methods can determine material properties within certain time and temperature ranges, but modeling the viscoelastic behavior remains challenging, mainly because the data processing is complex and different materials have distinct properties. Using polyetherimide as an example and based on the change in the secondary bonds of polyetherimide in different viscoelastic stages, we proposed a new shift factor model in Arrhenius format with alterable activation energy. We also used two methods based on nonlinear least squares to obtain the Maxwell model of the polyetherimide, and we then used a novel method integrated with Laplace transforms and partial fraction decomposition to convert the Maxwell model into the Voigt model. The results of our model are reliable and self‐consistent, showing its potential for modeling the viscoelasticity of other materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46102.     

Kinetics of reactions involved in pvrolvsis of cellulose II. The modified kilzer-bioid model

At temperatures below 300°C, it has been shown that the pyrolysis of cellulose can be modeled in terms of a modified Kilzer-Broido ((K-B) Model. According to this model, cellulose decomposes via two competitive reactions, a dehydration reaction to form anhydrocellulose and a depolymerization reaction to form levoglucosan. Anhydrocellulose later decomposes to chars and gaseous products via two competitive reactions. Arrhenius parameters and a technique of estimating empirical constants from experimental data for the K-B type reactions are presented. Comparison of the ability of the modified K-B model and the three reaction model to predict weight loss, product yields and heat pretreated results are also made.