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.     

Estimation of kinetic parameters associated with the curing of thermoset resins. Part II: Experimental results

This is a two-part theoretical and experimental study on the estimation of the kinetic parameters associated with the curing of a thermoset epoxy resin. In Part II, the kinetic parameters associated with the curing of the bisphenol-A-diglycidylether/meta-phenylenediamine (BADGE/mPDA) resin were estimated from both differential scanning calorimetry (DSC) and dielectric experimental data using a new estimation procedure described in Part I. The kinetic parameters estimated were the Arrhenius constants associated with a kinetic model used to describe the degree of cure. Isothermal experiments were performed using both experimental techniques at four different curing temperatures. The resulting estimates of the kinetic parameters were compared with results obtained from the same data using a linear regression method. The magnitude of the confidence intervals of the estimated parameters and the standard deviation of the model (based on the residual errors between predicted values of the degree of cure and experimental values) were used as criteria in the comparison of the results. From this comparison, it was concluded that the parameters estimated from DSC data using the new estimation procedure provided the estimates with the least variability and, consequently, the smallest errors associated with the kinetic model.     

Analysis of the heat-release mechanism during thermal stabilization of polyacrylonitrile fiber rope

Results of experimental studies of heat release during heating of polyacrylonitrile (PAN) rope are presented. The heating conditions for PAN rope samples of elemental fiber linear density 0.08, 0.10, and 0.12 tex to 330°C at rates 2, 3.5, and 5 K/min were selected to model thermal stabilization processes in an oxidation furnace. These data were used to determine the kinetic constants in the Arrhenius equation using the method proposed by L. I. Volkova. Experimental heat release in rope as a function of time at various heating rates was used to determine the kinetic reaction constants. Kinetic constants of the generalized reaction were determined for all tested ropes and conditions. A heat-release equation was formulated based on the kinetic constants for each PAN rope sample. The rope mass change as a function of time M(t) expressed in fractions and represented as a second-order polynomial was determined from the rope mass loss at heating rate 3.5 K/min.     

Measured kinetics of the acid-catalysed hydrolysis of sugar cane bagasse to produce xylose

Experimental trials of the water hydrolysis of bagasse to produce xylose, arabinose and glucose were conducted using a temperature-controlled microwave digester. The experimental variables were temperature, ratio of water mass to bagasse mass, type of bagasse material and reaction time. The pH of the liquid and concentration of dissolved xylose, arabinose and glucose were measured at the completion of each trial. Kinetic modelling of the global rates of formation of monosaccharide products was performed using schemes based on earlier researchers’ models of acid hydrolysis using mineral acids. For the most plentiful product, xylose, the most accurate kinetic model of the global reactions was determined to be two parallel pathways for hydrolysis of xylan to xylose followed by a single pathway for xylose decomposition. The calculated activation energies of the reactions were within the range reported by other researchers for the hydrolysis of a range of lignocellulosic materials using mineral acids.     

Optimized benzaldehyde production over a new Co-ZSM-11 catalyst: Reaction parameters effects and kinetics

An efficient Co-ZSM-11 catalyst has been synthesized for benzaldehyde production by the selective styrene oxidation. Reaction parameters such as catalyst mass, reaction temperature, molar ratio styrene/hydrogen peroxide and stirring speed were optimized, by performing the styrene oxidation reaction in a stirred batch system with fine particles of Co-ZSM-11 in suspension under microwave heating. A kinetic study was done by using the initial rate method and the Arrhenius parameters were estimated. This catalyst presents a higher reaction rate about 30% with respect of those found in literature and a higher selectivity towards benzaldehyde about 80% at optimal conditions.     

大庆常渣催化裂解反应动力学模型

An 8-lump kinetic model was proposed to predict the yields of propylene,ethylene and gasoline in the catalytic pyrolysis process of Daqing atmospheric residue.The model contains 21 kinetic parameters and one for catalyst deactivation.A series of experiments were carried out in a riser reactor over catalyst named LTB-2.The kinetic parameters were estimated by using sub-model method,and apparent activation energies were calculated according to the Arrhenius equation.The predicted yields coincided well with the experimental values.It shows that the kinetic parameters estimated by using the sub-model method were reliable.     

Biosorption of the Reactive Blue 5G Dye in a Fixed Bed Column Packed with Orange Bagasse: Experimental and Mathematical Modelling

The removal of reactive dye in a fixed bed column packed with orange bagasse was modelled using a model that considers the effects of axial dispersion, external and internal mass transfer limitations, and the equilibrium in the liquid-solid interface. The equilibrium and kinetic parameters were obtained through fit the model to the experimental data. In the parameters identification procedure the PSO optimization method was used. The mathematical model showed good performance when describing the dye adsorption process. Furthermore, orange bagasse is an attractive and cost-effective alternative as an adsorbent to remove reactive blue 5G dye from wastewaters.     

The characterization of thermoset cure behavior by differential scanning calorimetry. Part I: Isothermal and Dynamic Study

A study of the isothermal cure kinetics of an unsaturated polyester resin by differential scanning calorimetry is described. An autocatalyzed second order kinetic model is adopted to elucidate the cure reaction and also assess the kinetic parameters. The rate constant, the maximum cure rate, the extent of cure, and the degree of conversion at the maximum cure rate, all increase with increasing cure temperature, while the half-life and the time required to reach the maximum cure rate both decrease. Discrepancies between the experimental results and the predicted values of some of the kinetic parameters, especially at high degrees of conversion, are attributed to the highly different-controlled cure reaction following the gel point. The activation energy (E) and the pre-exponential factor (1n A) of the polyester cure reaction were estimated, using differential graphical techniques, to be 131 ± 4 kJ/mol and 39 ± 1 respectively. An ASTM method (E698) produces erroneously low values of the Arrhenius parameters, suggesting that the assumptions of the method may be overly simplified.     

C36二聚脂肪酸/聚乙二醇聚酯的制备及动力学研究

以C36二聚脂肪酸和聚乙二醇400为原料,缩聚得到一种新型高分子表面活性剂,适宜的工艺条件:在0.097 MPa下,n(二聚脂肪酸)∶n(聚乙二醇400)为1∶1.2,催化剂SnCl2(相对二聚脂肪酸质量分数为0.3%,反应温度200℃,反应时间6 h,酯化率达到98.11%。建立了SnCl2催化下,二聚脂肪酸与聚乙二醇缩聚反应的动力学模型,并采用改进的遗传算法,对动力学模型参数进行估算。结果显示,二聚脂肪酸与聚乙二醇400缩聚反应级数为0.998级,酯化反应活化能E=97.18 kJ/mol,指前因子A=1.947 9×109L/(mol.min),缩聚反应的Arrhenius方程为lnk=21.39-11.689/T。     

Estimation of kinetic parameters associated with the curing of thermoset resins. Part I: Theoretical investigation

This is a two-part theoretical and experimental study on the estimation of kinetic parameters associated with the curing of a thermoset epoxy resin. In Part I, the estimation procedure is presented. This estimation procedure is based on a method referred to as the Box-Kanemasu method, which involves the minimization of a least squares function, and it represents a new application of this method. The kinetic parameters under consideration were the Arrhenius constants associated with two rate constants in a kinetic model used to describe the curing rate of an amine epoxy resin. The use of differential scanning calorimetry (DSC) and dielectric data assuming isothermal and dynamic experimental conditions was first investigated in a sensitivity study. It was determined that the degree of cure should be treated as the dependent variable and that data from isothermal experiments should be used. The estimation procedure was then used to estimate the Arrhenius constants from simulated degree of cure data with added errors. These results compared favorably with those found using a linear regression method.     

Reaction kinetics and modelling of the gold catalysed glycerol oxidation

The kinetics of the glycerol oxidation using a carbon supported gold catalyst was studied experimentally in a batch reactor at oxygen pressures up to 10 bar and at temperatures from 25 to 100 °C. The influence of the mass transfer on the reaction was estimated and confirmed with theoretical calculations. A kinetic model has been proposed on the basis of a Langmuir-Hinshelwood mechanism for the experiments carried out in the kinetic regime and the kinetic parameters (reaction rate and adsorption constants as well as activation energies) were calculated.     

离子液体中裂解C_5馏分二烯烃聚合反应动力学

用离子液体1-丁基-3-甲基咪唑六氟磷酸盐作为裂解C5馏分中混合二烯烃的反应介质和催化剂,考察了其对混合二烯烃二聚反应的影响。在温度303.15—343.15 K、离子液体质量分数0.3—0.8范围内,采用封管实验方法测定了C5混合二烯烃的动力学数据。在相同温度范围内,测定了离子液体介质中环戊二烯无限稀释状态下的动力学数据。将催化剂影响因数引入Arrhen ius方程,确定了离子液体介质中二烯烃聚合反应动力学模型。用墨森数值积分和非线性最小二乘法拟合求取了各反应速率常数,得到了模型参数和各聚合反应对于催化剂质量分数的反应级数,动力学模型预测值与实验值吻合良好。     

Predicting Temperature Dependent Viscosity for Unaltered Waste Soybean Oil Blended with Petroleum Fuels

Using vegetable oil based alternative fuels for diesel engines has grown in interest over recent years due to the rising cost of petroleum products and instability in the energy marketplace. One of the major hurdles to overcome in using vegetable oil as a diesel fuel is high viscosity. Here, we experimentally determine the viscosity of unaltered waste soybean oil (WSO) blended with petroleum fuels. Three blend viscosity models Arrhenius, Wright, and the ASTM D7152-05 Standard were evaluated for viscosity prediction accuracy over a temperature range of −10 to 40 °C. Results indicated that the Arrhenius method using volume fractions was the most accurate predictor of viscosity for binary blends made of WSO and diesel (2.31% absolute average deviation) as well as multi-component blends made from WSO, diesel, kerosene, and gasoline (8.72% absolute average deviation). An intermolecular interaction correction factor was empirically determined for each model in an effort to improve prediction accuracy for the multi-component blends. Using the correction constants improved the absolute average deviation for the Arrhenius method to 6.85%, 5.87% for the Wright method based on mass fractions, and 9.67% for the ASTM method based on mass fractions. The use of this correlation constant for the Arrhenius method was only helpful for blends containing more that 30% WSO, indicating that molecular interaction behavior only deviates significantly from ideality at these higher WSO fractions.     

Study of the effect of BDMA catalyst in the epoxy novolac curing process by isothermal DSC

Epoxy novolac/anhydride cure kinetics has been studied by differential scanning calorimetry under isothermal conditions. The system used in this study was an epoxy novolac resin (DEN431), with nadic methyl anhydride as hardener and benzyldimethylamine as accelerator. Kinetic parameters including the reaction order, activation energy and kinetic rate constants, were investigated. The cure reaction was described with the catalyst concentration, and a normalized kinetic model developed for it. It is shown that the cure reaction is dependent on the cure temperature and catalyst concentration, and that it proceeds through an autocatalytic kinetic mechanism. The curing kinetic constants and the cure activation energies were obtained using the Arrhenius kinetic model. A suggested kinetic model with a diffusion term was successfully used to describe and predict the cure kinetics of epoxy novolac resin compositions as a function of the catalyst content and temperature. Copyright © 2003 Society of Chemical Industry     

A kinetic study of the thermal decomposition of poly(aryl-ether-ether-ketone) (PEEK) in nitrogen

The kinetic parameters of the thermal decomposition of poly(aryl-ether-ether-ketone) (PEEK) in a nitrogen atmosphere have been obtained using an isothermal weight-loss method. Several mathematical approaches have been used to obtain the Arrhenius parameters based upon the use of different reaction models. The values obtained for the activation energy (E = 198.4 to 219.7 kJ/mol) and preexponential factor (log A = 11.1 to 12.3 min^?1) fall within a narrow range, irrespective of the method of calculation. Although the kinetic data most closely fits an Avrami two-dimensional nucleating model, the data can be just as easily described by a first-order rate law.     

Lipase-catalyzed transesterification of ethyl ferulate with triolein in solvent-free medium

The lipase-catalyzed transesterification of ethyl ferulate with triolein in a solvent-free medium was investigated. Transesterification was catalyzed by immobilized lipase from Candida antarctica (Novozym 435), to form ferulyl oleins, a mixture of ferulyl diolein and ferulyl monoolein. These ferulated esters can be widely used as natural antioxidant in both lipid containing food and cosmetic applications. External mass transfer limitations were lowest, when the agitation speed was higher than 180 rpm. A linear relationship between the initial reaction rate and enzyme load up to 10% demonstrated that the internal diffusion limitations could be minimized. The effects of various parameters on yields and rates of reaction were studied in the absence of mass transfer limitations. The initial reaction rate increased when the reaction temperature was raised in the range of 45-65 °C, further increase to 70 °C decreased the final yield to 48.9%. The value of activation energy was calculated as 65.04 kJ/mol based on the Arrhenius law. Under the most favorable conditions, a kinetic model based on the ping-pong bi-bi mechanism with triolein inhibition was found to fit the initial reaction rate data very well and the kinetic parameters were evaluated by non-linear regression analysis.     

Ring-opening of decalin - Kinetic modelling

Upgrading of the low-quality feedstocks into high-quality diesel fuel fractions by hydrogenation combined with ring-opening of naphthenes offers a new possibility to improve the diesel fuel properties. Decalin was selected as a probe molecule for dinaphthenes that would be present in refinery streams after hydrogenation of aromatic refinery fractions.The experiments aimed at ring-opening of decalin were performed in a batch reactor by using a platinum-modified zeolite Beta. A wide range of reaction conditions (1-6 MPa, 476-563 K, and catalyst concentration 10-40 g/l) was covered in the experiments. It was observed that decalin was converted into three major product groups, namely skeletal isomers of decalin, as well as ring-opening and cracking products, in several consecutive reaction steps.A mechanism was proposed for the ring-opening of decalin on platinum-modified zeolite Beta. A kinetic model was derived, based on the elementary reaction steps of the mechanism and the values of the parameters of the model were estimated. A comparison of the model predictions and the experimentally obtained data showed that the model was able to describe well the experimental data in the whole range of experimental conditions. Moreover, the precision of the estimated parameters was good as most of the parameter standard errors were less than 10%. The model can be thus used to optimize the experimental conditions to maximize the yields of ring-opening products.     

Structural parameter identifiability analysis for dynamic reaction networks

A fundamental problem in model identification is to investigate whether unknown parameters in a given model structure potentially can be uniquely recovered from experimental data. This issue of global or structural identifiability is essential during nonlinear first principles model development where for a given set of measured variables it is desirable to investigate which parameters may be estimated prior to spending computational effort on the actual estimation. This contribution addresses the structural parameter identifiability problem for the typical case of reaction network models. The proposed analysis is performed in two phases. The first phase determines the structurally identifiable reaction rates based on reaction network stoichiometry. The second phase assesses the structural parameter identifiability of the specific kinetic rate expressions using a generating series expansion method based on Lie derivatives. The proposed systematic two phase methodology is illustrated on a mass action based model for an enzymatically catalyzed reaction pathway network where only a limited set of variables is measured. The methodology clearly pinpoints the structurally identifiable parameters in dependence of the given measurements and input perturbations.     

Kinetic modeling formulation of the methanol to olefin process: Parameter estimation

Detailed kinetic models at the elementary step level were developed for the methanol to olefins (MTO) process over SAPO-34 catalyst. Starting from believable mechanisms, forming primary products was modeled rigorously by the Hougen–Watson formalism. Discrimination of kinetic equations and calculation of the parameters of best fit were performed by solving the mass conservation equations of the main products of the kinetic scheme. For rate constants, preexponential factors and apparent activation energies were then calculated according to the Arrhenius equation. For thermodynamic constants, the difference between apparent activation energies of forward and reverse reaction was considered. The kinetic model fits well the experimental data, which is obtained in a fixed bed reactor. The results showed that rising space-time is favorable for olefin yields while an optimum temperature might produce the maximum olefin.     

Rheokinetic studies for the reaction injection molding of polydicyclopentadiene

Dicyclopentadiene (DCPD) based liquid engineered resins are emerging among the newest commercial reaction injection molding (RIM) systems. Since the filling stage is coupled with chemical reaction, an understanding of the chemorheological changes is critical for establishing moldability criteria. An adiabatic reactive viscometry technique which involves the simultaneous measurement of viscosity and temperature changes was used to investigate the chemorheological changes during the adiabatic copolymerization of a DCPD based RIM system. The influence of impingement mixing conditions and initial material temperature on the reaction kinetics, rheology, as well as the resulting final physical properties of the system were investigated. The “apparent gel time” under adiabatic conditions is estimated from the intersection of the tangents to the initial and final portions of the viscosity curve. An autocatalytic kinetic model with an Arrhenius rate constant was used to model the reaction kinetics.