Reliable Kinetic Models Research Articles

Influence of torrefaction on the pyrolysis of energy cane

This work aims to study the influence of torrefaction on the energetic properties and thermal decomposition kinetics of energy cane Saccharum spontaneum. An experimental planning (473–533 K, 15–45 min) was realized, and the best conditions were 503 K and 45 min with mass yield above 70%, which led to the decrease in volatile matter and oxygen contents (15%) and the increase of 14.5% in the heating value. The thermogravimetric analysis (heating rates of 5, 10 and 15 K min−1) under inert atmosphere was used for the application of the independent parallel reactions scheme in the multistep model. The activation energies found were 111, 119, 197 and 51 kJ mol−1 for both raw and torrefied biomasses related to extractive, hemicellulose, cellulose, and lignin, respectively. Then, this approach provided reliable kinetic models capable of describing the thermal decomposition for both raw and torrefied samples (deviation < 3%).

Development of a Reliable Kinetic Model for Ladle Refining

Kinetic modeling of ladle refining can be used by steel plants to improve steelmaking and to produce cleaner steels. It can also help researchers to understand the process better. There have been several recent attempts to develop a kinetic model that can predict changes in steel, slag, and inclusion compositions with time. Often the models require parameters that can be difficult to measure under plant conditions, and model limitations have not been discussed in detail. In this study, a two-parameter kinetic model has been developed to predict changes in steel, slag, and inclusion compositions during ladle refining; the two parameters are the mass-transfer coefficient in steel and the inclusion flotation rate constant. The model was based on FactSage macro-processing. Examples of results show that the model can be used to diagnose effects of steel and slag sampling practices and to estimate alloy dissolution time. The model results demonstrate that the presence of solids in slag can significantly reduce the rate of steel–slag reaction while maintaining a high inclusion flotation rate. Some limitations of the model are discussed: the overprediction of calcium transfer to alumina inclusions and the absence of information on inclusions originating from entrained slag.

Ethanol production using Zymomonas mobilis: Development of a kinetic model describing glucose and xylose co-fermentation

Reliable kinetic models are important for the design and optimisation of lignocellulosic ethanol production. A new kinetic model describing ethanol production using Zymomonas mobilis ZM4(pZB5) that is applicable to single (glucose or xylose) or mixed (glucose and xylose) substrate fermentations is developed. This work extends previous contributions through consideration of an empirical term for the preferential usage of glucose when compared to xylose as well as the prediction of the production rate of xylitol. Kinetic model parameters are obtained through kinetic fitting using experimental data available in the literature (seventeen fermentations in batch or continuous operation). The average coefficient of determination of xylose, xylitol, ethanol, glucose and biomass predictions using the kinetic model developed in this work was 0.984. Furthermore, it is demonstrated that through the inclusion of xylitol production and the inhibition of xylose consumption by xylitol in the kinetic model the productivity of ethanol may be accurately estimated.

A new model with serial hydrolysis reactions for the anaerobic digestion of waste activated sludge under thermophilic conditions

Hydrolysis is one of the rate-limiting reactions in the anaerobic digestion (AD) of wastewater sludge; thus, reliable kinetic models for hydrolysis reactions are essential in numerical simulations of AD.

Identifying unified kinetic model parameters for thermal decomposition of polymer matrix composites

Predicting thermal responses of composite materials requires accurate input parameters derived from reliable thermal property characterization and kinetic models. Composite material properties and decomposition kinetics vary with temperature and heating rate. Typically, conventional kinetic models derived from thermogravimetric analysis data result in multiple sets of kinetic model parameters, which are difficult to implement into numerical simulations under widely varying temperature and heating rate conditions. Here, a methodology was developed to reliably predict decomposition processes of composite materials with a single (i.e., unified) set of kinetic model parameters. The unified kinetic model parameters for each of four different composite materials were used to accurately predict decomposition kinetics observed over the entire range of experimental temperatures and heating rates. Furthermore, this broadly applicable methodology may predict decomposition from limited data sets, and is expected to extrapolate reliably measurable data to experimentally challenging heating rates and temperatures.

Modeling and simulations of plasma and sheath edges in warm-ion collision-free discharges

It has been shown recently by Kos et al. [Phys. Plasmas 25, 043509 (2018)] that the common plasma-sheath boundary is characterized by three well defined characteristic points, namely the plasma edge (PE), the sheath edge (SE) and the sonic point. Moreover, it has been shown that the sheath profiles, when properly normalized at the SE, as well as the potential drop in the plasma–sheath transition region (PST), (region between between PE and SE) in collision-free (CF) discharges are rather independent of discharge parameters, such as the plasma source profile, ion temperature and plasma density, providing that the sheath thickness is kept well bellow the plasma length. While these findings were obtained by theoretical means under idealized discharge conditions, the question arises whether and to which extent they are relevant under more complex physical scenarios. As a first step toward answering this question the CF discharge with warm ions is examined in this work via kinetic simulation method in which some of the model assumptions, such as independence of time and the Boltzmann distribution of electrons can hardly be ensured. Special attention is payed to effects of ion creation inside the sheath. It is found that only with considerably increased sheath thickness the sonic point always shifts from SE towards the wall. Whether the absolute value of ion directional velocity at the sonic point will increase or decrease depends on the ion temperature and the source strength inside the sheath. In addition preliminary comparison of results obtained under CF assumption with the representative ones obtained with strongly enhanced Coulomb collisions (CC), indicate the relevancy of hypothesis that the VDF of B&amp;J can be considered as a universal one in future reliable kinetic modeling and solving the plasma boundary and sheath problem in both collisional and collision-free plasmas.

Kinetics of the Bioproduction of Succinic Acid by Actinobacillus succinogenes from Oil Palm Lignocellulosic Hydrolysate in a Bioreactor

Soluble products from oil palm frond hydrolysate (OPFH) were incorporated as the fermentation substrate for succinic acid (SA) production. To construct a reliable kinetic model for the production of SA from OPFH, the inhibitory effects during fermentation involving glucose were evaluated based on the modified Gompertz model. The application of the modified Gompertz model was found to fit well with the experimental data for characterizing the SA fermentation profile and could predict the maximum potential of the metabolite formation in the form of concentrations, production rates, and initial lag times. The maximum potential of the SA production was determined to be 38.0 g/L, which was yielded from 61.3 g/L glucose in anaerobic batch cultivation after 30 h. The inhibitory effects on the cell growth and SA production became more apparent at higher substrate concentrations, which coincided with the substrate inhibition constant of 78.7 g/L. The model also helped in estimating the OPFH fermentation baseline, which consequently led to a SA concentration of 36.5 g/L and productivity of 1.95 g/Lh. The results suggested that OPFH as an inexpensive and renewable source of lignocellulosic syrup is advantageous for the economic production of SA.

Development of a relationship between kinetic triplets and heating rates to improve pyrolysis kinetic modeling of polymer

Pyrolysis kinetic modeling of polymers is important for the analyses of their combustibility and flame spread mechanism in fire safety science and engineering. The objective of this work is to improve the reliable kinetic parameter analyses for polymers by introducing a new idea of the linear dependence of kinetic triplets on the heating rates in Thermogravimetric Analysis (TGA) experiments. The virtual kinetic triplets are also introduced for the case with the infinitely slow heating rate. Pyrolysis kinetic analyses are conducted by Genetic Algorithm (GA) optimization for the TGA data based on the single-scan, multi-scan and the new method here with the modified kinetic triplet series. The results show that the fitting errors for the independent case based on the single-scan method can be as small as 0.1–0.5%. But Kinetic Compensation Effects (KCE) problem is its main restriction to hinder the determination of reliable kinetic triplets. The results also show that based on the multi-scan method, the relatively reliable kinetic parameters can be calculated but with large total fitting errors in the range of 4.7–9.8%. Finally, the total fitting error can be minimized to about 0.6–1.7% by the new method here, which illustrates its obvious improvement for the reliable pyrolysis kinetic modeling of fuels. The new method based on the kinetic triplet series here is a modified multi-scan method, in which the traditional multi-scan method is also included as the case with the linear coefficient of zeros.

Electrochemical treatment of wastewater from a bakery industry: Experimental and modeling study

Abstract The typical treatment of wastewater from the bakery industry in skimming tanks and bioreactors has some limitations, such as low removal of grease, and partial degradation of organic matter. The primary aim of this investigation was to evaluate the use of electrocoagulation as an alternative/complementary method to treat efficiently such an effluent, with focus on the determination of the best operating conditions, and on the kinetics of electrocoagulation at the optimal defined set of process variables. To search for the optimal, a 23 factorial design of electrocoagulation experiments with iron and aluminum electrodes was applied in the pH range from 4.6 to 7.0, at 6 and 12 V for 1200 s and 2400 s. A reliable statistical model revealed that the results of removal of chemical oxygen demand (6–8%) and turbidity (32–98%) by using aluminum electrodes, which were in average about twice as high as those with iron electrodes, were influenced by almost all the considered factors (p ≤ 0.05). At the best determined values of pH (7.0) and voltage (12 V), kinetic experiments of electrocoagulation with aluminum electrodes were performed by monitoring periodically the pH, turbidity, apparent color, concentration of oil/grease, chemical oxygen demand, concentration of chloride anion and electric conductivity of the wastewater for 2400 s. Almost all the examined pollutant parameters, and in particular the content of oil/grease (traditionally poorly removed in fat traps) were reduced to negligible values in a short treatment time. A reliable semi-empirical kinetic model described properly the high rates of disappearance of turbidity and apparent color.

Analysis of kinetics of thermal decomposition of melamine blended with phosphorous ionic liquid by green approach

As a common halogen-free flame retardant, melamine is vastly employed in flame-retardant fields of various polymer materials. To preferably optimize the flame retardancy of melamine, a phosphorous ionic liquid of 1-butyl-3-methylimidazolium dibutyl phosphate ([Bmim][DBP]) was introduced as a synergist. In this study, a novel synergistic flame retardant was prepared through an easy operated physical mixing. Then, pyrolysis behavior of melamine and its compounds were measured using thermogravimetric analysis. The apparent activation energy and pre-exponential factor were evaluated using Kissinger–Akahira–Sunose method and Flynn–Wall–Ozawa method, and the most probable kinetic function was also determined using double extrapolation method. Results showed that the addition of [Bmim][DBP], in general, improved thermal stability and residual capacity of melamine. It meant that melamine blended with [Bmim][DBP] possessed the synergistic flame-retarding potential from the preliminary analysis. Significantly, accurate and reliable thermal decomposition kinetic models of melamine and its compounds were established and the kinetic compensation effects were also discussed. More relevant combustion tests would be performed in the following study.

Multi-step cure kinetic model of ultra-thin glass fiber epoxy prepreg exhibiting both autocatalytic and diffusion-controlled regimes under isothermal and dynamic-heating conditions

As packaging technologies are demanded that reduce the assembly area of substrate, thin composite laminate substrates require the utmost high performance in such material properties as the coefficient of thermal expansion (CTE), and stiffness. Accordingly, thermosetting resin systems, which consist of multiple fillers, monomers and/or catalysts in thermoset-based glass fiber prepregs, are extremely complicated and closely associated with rheological properties, which depend on the temperature cycles for cure. For the process control of these complex systems, it is usually required to obtain a reliable kinetic model that could be used for the complex thermal cycles, which usually includes both the isothermal and dynamic-heating segments. In this study, an ultra-thin prepreg with highly loaded silica beads and glass fibers in the epoxy/amine resin system was investigated as a model system by isothermal/dynamic heating experiments. The maximum degree of cure was obtained as a function of temperature. The curing kinetics of the model prepreg system exhibited a multi-step reaction and a limited conversion as a function of isothermal curing temperatures, which are often observed in epoxy cure system because of the rate-determining diffusion of polymer chain growth. The modified kinetic equation accurately described the isothermal behavior and the beginning of the dynamic-heating behavior by integrating the obtained maximum degree of cure into the kinetic model development.

In vivo EPR pharmacokinetic evaluation of the redox status and the blood brain barrier permeability in the SOD1G93A ALS rat model

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder affecting the motor pathways of the central nervous system. Although a number of pathophysiological mechanisms have been described in the disease, post mortem and animal model studies indicate blood-brain barrier (BBB) disruption and elevated production of reactive oxygen species as major contributors to disease pathology. In this study, the BBB permeability and the brain tissue redox status of the SOD1G93A ALS rat model in the presymptomatic (preALS) and symptomatic (ALS) stages of the disease were investigated by in vivo EPR spectroscopy using three aminoxyl radicals with different cell membrane and BBB permeabilities, Tempol, 3-carbamoyl proxyl (3CP), and 3-carboxy proxyl (3CxP). Additionally, the redox status of the two brain regions previously implicated in disease pathology, brainstem and hippocampus, was investigated by spectrophotometric biochemical assays. The EPR results indicated that among the three spin probes, 3CP is the most suitable for reporting the intracellular redox status changes, as Tempol was reduced in vivo within minutes (t1/2 =2.0±0.5min), thus preventing reliable kinetic modeling, whereas 3CxP reduction kinetics gave divergent conclusions, most probably due to its membrane impermeability. It was observed that the reduction kinetics of 3CP in vivo, in the head of preALS and ALS SOD1G93A rats was altered compared to the controls. Pharmacokinetic modeling of 3CP reduction in vivo, revealed elevated tissue distribution and tissue reduction rate constants indicating an altered brain tissue redox status, and possibly BBB disruption in these animals. The preALS and ALS brain tissue homogenates also showed increased nitrilation, superoxide production, lipid peroxidation and manganese superoxide dismutase activity, and a decreased copper-zinc superoxide dismutase activity. The present study highlights in vivo EPR spectroscopy as a reliable tool for the investigation of changes in BBB permeability and for the unprecedented in vivo monitoring of the brain tissue redox status, as early markers of ALS.

Kinetics of Pressure Cycling Extraction of Solute from Leaves of Mate (Ilex paraguariensis) Dispersed in Water

A set of seven extraction experiments was performed to investigate the influence of pressure cycles on the kinetics of solute removal from leaves of mate dispersed in water. The mass ratio of liquid to dry solid (40), the temperature (32°C), and time of extraction (3600 s) were not varied. Five extraction runs were under cyclic pressurization (1 cycle = 300 s at 91.4 kPa + 300 s at 182.8 kPa) and stirring speeds (S) of 0, 150, 500, 1500, and 2000 rpm, while the two other ones were at constant pressure (182.8 kPa) and S close to 1500 and 2000 rpm. Based on seven pairs of parameters of a reliable second-order kinetic model (R2 ≥ 0.967), cyclic pressurization had no effect on equilibrium and kinetics of extraction (p > 0.05) when the role of convection on solute transfer was negligible (S ≥ 500 rpm). In the stirring speed range from 500 to 2000 rpm, the operation was controlled by diffusion (Bi > 1.7 × 103), so a transient two-dimensional diffusion model was able to describe correctly the changes of solute concentration with time. Below 500 rpm, solute transfer was governed by a combination of diffusion and convection with the external resistance to mass transfer as a function of S (16 ≤ Bi ≤ 28).

Multistep process kinetics of the non-isothermal pyrolysis of Moroccan Rif oil shale

The kinetic analysis of the complex process of Moroccan Rif oil shale pyrolysis was studied in detail by thermogravimetric (TG) analysis and its derivative (DTG) under non-isothermal conditions. The investigated pyrolysis region, located between 325 and 600 °C, is formed by partially overlapping peaks and it was successfully separated into three discrete processes using the mathematical Fraser-Suzuki algorithm that accommodates asymmetric functions. For each separated process, the isoconversional differential and integral Model Free methods were used to evaluate activation energy and two Master plots fitting methods were explored to get reliable kinetic models. The main pyrolysis step of Moroccan Rif oil shale involves the devolatilization of organic matter including bitumen and kerogen respectively and subsequent decomposition of pyrite mineral FeS2. The first process represents the principal pyrolysis kinetic in accordance with dominance of bitumen products in the studied oil shale. By applying the nonlinear least square analysis to kinetic data, it was found that all processes were well described by n-th order kinetic equations, with n ≈ 1, for the first and third processes and n ≈ 1.67 for the second process. Besides, the thermodynamic functions of activated complexes (ΔS*, ΔH* and ΔG*) for the pyrolysis step of studied oil shale were calculated and discussed.

Structure of premixed H2/O2/Ar flames at 1–5 atm studied by molecular beam mass spectrometry and numerical simulation

A lack of available experimental data for spatial distributions of the species mole fractions in the flames of hydrogen at the pressures higher than atmospheric, which are required for developing and validating reliable kinetic models for hydrogen combustion, motivated this study. Stoichiometric laminar premixed H2/O2/Ar flames stabilized on flat burners at pressures 1, 3 and 5atm were examined in this work by molecular beam mass spectrometry. Mole fraction profiles of all flame species (H2, O2, H2O, H2O2, H, O, OH, HO2) were measured. A decrease in the peak mole fractions of H, O, OH radicals and an increase in the peak mole fractions of HO2 and H2O2 with pressure was observed. Two detailed kinetic mechanisms proposed recently by Konnov (2008) and Burke et al. (2012) for hydrogen combustion were validated against new experimental data reported in this work. Both mechanisms reproduced well the mole fraction profiles of H2, O2, H2O and H, O, OH radicals in the flames. However, the mechanism of Burke et al. was found to be more adequate in predicting the mole fraction profiles of peroxy species in the flames. The observed changes in the flame structure with pressure were explained on the basis of a kinetic analysis of the model developed by Burke et al. The experimental data reported in this work can help in further development and improvement of the future kinetic models of hydrogen combustion at elevated pressures.

Kinetic modeling and optimization of Claus reaction furnace

Optimization of Claus sulfur recovery plants requires a reliable kinetic model to describe the reaction furnace and waste heat boiler. In order to develop a suitable kinetic model for prediction of reaction furnace and waste heat boiler effluents, several reaction schemes were tested and the best reaction set was selected. The kinetic parameters of the best reaction scheme were optimized and different reactor networks were analyzed using the optimum reaction set. The modified model results were in good agreement with the experimental measured plant data both before and after waste heat boiler (The mean absolute errors were 7.62% and 7.88% respectively). In addition, the effects of increasing ammonia and oxygen content of feed, and air to acid gas ratio on reaction furnace effluents were investigated through various case studies. An optimization study was performed to control the operating variables of an operating sulfur recovery unit in order to obtain optimum conditions (including maximum reaction furnace temperature), maintain H2S to SO2 ratio at constant 2 and lower COS emissions from waste heat boiler.

Cyclic pressurization assisted extraction of lipids from microalgae for biodiesel production: Non-equilibrium and equilibrium data

The extraction of lipids from a microalgae (Chlorella pyrenoidosa) was experimentally investigated at a constant temperature of 30°C with ethanol. The experiments involved a bed of dry solids loaded in a cylindrical vessel with approximately 23.5×10−3kg of solvent. At the top of the cylinder there was a moving piston to allow extraction at cyclic or constant pressurization. A set of 10 kinetic extraction experiments was performed by varying the solid–liquid feed ratio at 5 levels under atmospheric pressure (91.4kPa) and cyclic pressurization (300s at 91.4kPa+300s at 200kPa per cycle) for 25,200s (51×21=10). At p⩽0.1 a significant statistical effect of cyclic pressurization and solid–solvent ratio on mass fraction of extracted lipid at equilibrium (yAe) was observed, while the influence of pressure at cyclic pressurization on the same response was negligible. yAe was a parameter of a reliable first-order kinetic model tuned on different extraction curves involving a full set of almost 500 experimental kinetic data. Based on these equilibrium data, the highest yield and efficiency of lipid extraction were 11.3% d.b. and 72%, respectively. The slopes of tie lines in rectangular equilibrium diagrams of Ponchon–Savarit for extraction at atmospheric pressure and cyclic pressurization confirm that lipids in microalgae are not easily removed from the insoluble solid. The fraction of microalgae lipids converted to biodiesel by an esterification reaction based on the method of Hartman and Lago was approximately 89±7%.

High ramp rate thermogravimetric analysis of zirconium(II) hydride and titanium(II) hydride

Zirconium and titanium hydride are utilized in liquid phase metal foam processing techniques. This application results in immediate exposure to molten metal and almost immediate decomposition at high temperatures. Most decomposition characterization techniques utilize slow heating rates and are unable to capture the decomposition behavior of hydrides under foam processing conditions. In order to address this issue a specialized high ramp rate thermogravimetric analyzer was created from a xenon arc image refiner. In addition to thermogravimetry, complimentary techniques including X-ray diffraction and scanning electron microscopy were used to characterize hydride decomposition and compare the results to literature. Hydrides were partially oxidized and separated into particles size ranges to evaluate the influence of these factors on decomposition. Oxidizing treatments were found to decrease decomposition rate only at temperatures below 933K (660°C) while particle size effects appeared to be negligible. Several improvements to the unique TGA apparatus presented in the current work are suggested to allow reliable kinetic modeling and analysis.

Modeling of oxidative dehydrogenation of ethane to ethylene on a MoVTeNbO/TiO2 catalyst in an industrial-scale packed bed catalytic reactor

The oxidative dehydrogenation of ethane (ODH-Et) seems the most promising alternative to produce ethylene compared to conventional processes. Nevertheless, there is not even a pilot plant for ODH-Et worldwide nowadays. This work presents the simulation of the catalytic behavior of a highly active and selective MoVTeNbO catalyst for the ODH-Et in a wall-cooled industrial-scale packed-bed reactor with a tube to particle diameter ratio equal to 3.12. The feasibility of using this complex yet necessary reactor design, as well as the influence of operating conditions on conversion and yield along the reactor are analyzed. The simulations are carried out using a two-dimensional pseudo-heterogeneous model, which makes use of both a reliable kinetic model and reliable transport parameters. Specifically, the kinetic model, obtained from lab-scale experimental data, is coupled to the reactor model accounting for transport phenomena wherein the effect of hydrodynamics on heat transfer is assessed from independent experiments in absence of reaction in an industrial-scale reactor. The developed kinetics successfully accounts for both the inhibiting effect of adsorbed water on oxidative dehydrogenation and total oxidations and the effect of the inlet partial pressure of oxygen and ethane on conversion and selectivity. Besides, the reactor model elucidates the importance of accounting for the role of the hydrodynamics on the heat transport in order to have reliable conversion and yield predictions. From the parametric sensitivity study, the temperature of the coolant fluid and the inlet ethane concentration are variables for tuning the reactor performance.

Saponification reaction system: a detailed mass transfer coefficient determination

The saponification of an aromatic ester with an aqueous sodium hydroxide was studied within a heterogeneous reaction medium in order to determine the overall kinetics of the selected system. The extended thermo-kinetic model was developed compared to the previously used simple one. The reaction rate within a heterogeneous liquid-liquid system incorporates a chemical kinetics term as well as mass transfer between both phases. Chemical rate constant was obtained from experiments within a homogeneous medium, whilst the mass-transfer coefficient was determined separately. The measured thermal profiles were then the bases for determining the overall reaction-rate. This study presents the development of an extended kinetic model for considering mass transfer regarding the saponification of ethyl benzoate with sodium hydroxide within a heterogeneous reaction medium. The time-dependences are presented for the mass transfer coefficient and the interfacial areas at different heterogeneous stages and temperatures. The results indicated an important role of reliable kinetic model, as significant difference in k(L)a product was obtained with extended and simple approach.