Polyesterification reactions of adipic acid-based polyesters

A series of studies of uncatalyzed and catalyzed polyesterification experiments have been investigated using different glycols at different temperatures. The experimental results for uncatalyzed reactions agreed quite well with the kinetic equation as proposed by P. J. Flory. However, Flory proposed a second-order reaction for an externally added strong acid as a catalyst. In contrast to Flory's theory, a mixed mechanism, based on a combination of carboxylic acid groups from the raw material and an external organotin catalyst, was proposed for the catalyzed reaction. In this article, the reaction rate of catalyzed and uncatalyzed polyesterifications using different glycols was compared, and the effect of different temperatures and catalyst levels was also discussed. The reaction rate constant decreases in the following order for both catalyzed and uncatalyzed polyesterification: 1,6-HD > 1,4-BD > NPG > DEG > EG ? PG. © 1993 John Wiley & Sons, Inc.     

Kinetics,mass transfer,and thermodynamic and statistical modeling study for esterification of valeric acid with n‐butanol: Homogeneous and heterogeneous catalysis

The esterification of valeric acid with n‐butanol was studied with homogeneous and heterogeneous catalysts. The activity and performance of homogeneous p‐toluenesulfonic acid and heterogeneous cation exchange resin catalysts Amberlyst 36, Indion 190, and Amberlite IRC‐50 were evaluated. The pseudo‐homogeneous kinetic model was used to investigate the kinetic parameters of homogeneous‐ and heterogeneous‐catalyzed esterification. The UNIFAC (universal functional activity coefficient) approach was used to study the nonideality of the esterification reaction. The reaction was statistically modeled and optimized by the application of response surface methodology. The effects of independent variables such as reaction temperature, initial molar ratio, and catalyst loading on the conversion of valeric acid were investigated. The optimized conditions for the esterification reaction catalyzed by Amberlyst‐36 were found as temperature 360.4 K, initial molar ratio 3.8, and catalyst loading 6.7 wt%. The predicted conversion (89%) at these optimized conditions is in good agreement with the experimental conversion (87.3 ± 1.6%).     

稻壳炭基固体酸催化剂的制备及其催化酯化反应性能

以热解稻壳炭为原料, 浓硫酸为磺化剂制备了固体酸催化剂. 采用X射线衍射、X射线光电子能谱、元素分析、孔结构分析和热重-质谱联用等手段对其进行了表征. 以油酸和甲醇的酯化为探针反应, 考察了磺化温度和时间对催化剂活性的影响, 探讨了反应条件对油酸转化率的影响, 并对所制催化剂的稳定性进行了研究. 结果表明, 制备该催化剂的适宜磺化温度和时间分别为90℃和0.25 h, 在该条件下制得的催化剂为无定形碳结构, 磺酸基密度为0.7 mmol/g. 该催化剂表现出较高的催化酯化反应活性, 在催化剂用量为5%、甲醇/油酸摩尔比为4、酯化温度和时间分别为110℃和2 h的条件下, 油酸的酯化率可达98.7%. 该催化剂具有较好的稳定性, 经7次连续反应后, 油酸的酯化率仍可达96.0%.     

Ruthenium(III) catalyzed oxidation of paracetamol by chloramine-T in aqueous alkaline medium – A kinetic and mechanistic pathway

The kinetic study of ruthenium(III) chloride catalyzed oxidation of paracetamol by N-chloro-p-toluene sulfonamide (chloramine-T) in the alkaline medium has been performed. The reaction exhibits second order nature and the effect of the catalyst indicates the occurrence of uncatalyzed reaction simultaneously. Rate is decelerated by hydroxide ions. A plausible reaction mechanism has been suggested and the rate law is derived to account for such experiential observations. The activation parameters have been calculated. No evidence of the participation of free radicals is observed.     

Catalysis and mechanistic studies of ruthenium and osmium on synthesis of anthranilic acids

Ruthenium, osmium and ruthenium + osmium catalyzed synthetic methodology was developed for the synthesis of anthranilic acids from indoles in good to excellent yields using bromamine‐B in alkaline acetonitrile–water (1:1) at 313 K. Detailed catalysis studies of ruthenium, osmium and the mixture of both were carried out for the synthetic reactions. The positive synergistic catalytic activity of Ru(III) + Os(VIII) was observed to a large extent with the activity greater than the sum of their separate catalytic activities. Detailed kinetic and mechanistic investigations for each catalyzed reactions were carried out. The kinetic pattern and mechanistic picture of each catalyzed reaction were found to be different for each catalyst and to obey the underlying rate laws: where, x, y < 1. The reactions were studied at different temperatures and the activation parameters were evaluated for each catalyzed reaction. Under the identical set of experimental conditions, the kinetics of all the three catalyzed reactions were compared with uncatalyzed reactions, revealing that the catalyzed reactions were 6‐ to 42‐fold faster. The catalytic efficiency of aforementioned catalysts followed the order: Ru(III) + Os(VIII) > Os(VIII) > Ru(III). This trend may be attributed to the different d‐electronic configuration of the catalysts. The proposed mechanisms and the rigorous kinetic models derived give results that fit well with the experimental data in each catalyzed reaction. Copyright © 2010 John Wiley & Sons, Ltd.     

Kinetics study of propyl acetate synthesis reaction catalyzed by Amberlyst 15

The reaction kinetics of esterification of acetic acid with n‐propanol was investigated. The reaction was catalyzed by the commercial cation‐exchange resin Amberlyst 15, and the kinetic data were obtained in a batch reactor within the temperature range 338–368 K. The chemical equilibrium constant, K_eq, was first determined experimentally; the result shows that K_eq is about 20 and slightly temperature dependent. Altogether 14 sets of kinetic data were then measured. The influences of operating parameters such as temperatures, initial molar ratios, and catalyst concentrations were checked. The pseudo‐homogeneous (PH), Rideal–Eley (RE), and Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic models were developed to interpret the obtained kinetic data. The parameters of the kinetic models were identified by the software DIVA, and the confidence interval of each parameter was also estimated. Both the chemical equilibrium constant and kinetic models were formulated in terms of the liquid phase activity, which was described by the nonrandom two‐liquid (NRTL) model. The LHHW model gives the best fitting result, followed by the RE model and the PH model, whereas the confidence intervals rank in the reverse order. In addition, an effective solution was proposed to overcome a convergence problem occurring in the LHHW model parameter identification, which has been reported several times in the literature. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 245–253, 2007     

Kinetics and mechanism of indigo carmine-acidic iodate reaction. An indicator reaction for catalytic determination of Ru(III) ion

A kinetic study of uncatalyzed and Ru(III) catalyzed oxidation of indigo carmine(IC) (disodium 3,3′-dioxobi-indolin-2,2′-ylidene-5,5′-disulphonate) by iodate ion in aqueous sulphuric acid solution is reported. The uncatalyzed reaction order was found to be four; one each with respect to IC and iodate ion and second order with H⁺ ion. The Ru(III) catalyzed reaction was of fifth order, second order with respect to H⁺ and first order with respect to reductant, oxidant, and catalyst. Stoichiometric ratios of both reactions were the same with a 3:2 reductant-oxidant ratio. In both uncatalyzed and catalyzed reactions isatin-5-monosulphonic acid (2,3-dioxoindoline-5-sulphonic acid) was observed as the oxidation product. Rate constants for both the reactions are reported. Reaction mechanisms consistent with the experimental data are suggested. Further, a fixed time method is described for the determination of Ru(III), based on its ability to catalyze the oxidation of IC by acidic iodate. Using [H⁺] 2.25M, [iodate] 1.00 × 10^?3M and [IC] 5.0 × 10^?5M, in presence of Ru(III), the reaction followed first order kinetics with respect to IC. The interference of various cations, neutral salts, and potassium iodide on the determination of Ru(III) was studied using synthetic mixtures. The selectivity of the method and the recommended procedure are described.     

Kinetics of the liquid phase esterification of acrylic acid withn-octanol and 2-ethylhexanol catalyzed by sulfuric acid

Kinetics of the liquid phase esterification of acrylic acid withn-octanol and 2-ethylhexanol catalyzed by sulfuric acid has been studied in an isothermal semibatch reactor. The reaction appears to be second order. The kinetic parameters have been determined.     

A Kinetic Study for the Noncatalytic Esterification of Palm Fatty Acid Distillate

In this work, the reaction scheme for the esterification of palm fatty acid distillate performed under the noncatalytic and high‐temperature condition (230–290°C) was investigated with a rigorous mathematical modeling. The esterification reaction was assumed to be the pseudo–homogeneous second‐order reversible reaction, and the mass transfer effectiveness factor (η) was introduced in the modeling framework to systematically and collectively consider both evaporation and reaction, which are simultaneously and competitively occurred in the liquid phase. The nonlinear programming problem was constructed with the objective function consisting of the errors between experimental data and the estimated values from the reaction model. The problem was solved by using the Nelder–Mead simplex algorithm to identify kinetic parameters, reaction rate constants, and mass transfer coefficients. The values of mass transfer coefficients were found to follow the Hertz–Knudsen relation and expressed as a function of reaction temperature. From the reaction rate constants obtained from the proposed kinetic models, the apparent activation energy was estimated to be 43.98 kJ/mol, which is lower than the value obtained from the reaction using heterogeneous catalysts. This low value indicates that reactants and products behave as an acid catalyst at relatively high operating temperature and constant pressure.     

Kinetic study on the reaction of lauric acid with ethanol catalyzed by deep eutectic solvent based on cetyl trimethyl ammonium bromide

In this work, a novel type of deep eutectic solvents (DES: CTAB–DES) based on cetyl trimethyl ammonium bromide (CTAB) was successfully synthesized by mixing CTAB with p-toluenesulfonic acid monohydrate and applied as catalysts for the esterification reaction of ethanol and lauric acid. The kinetics of the reaction of ethanol and lauric acid catalyzed by CTAB–DES was investigated in the temperature range of 328.15–348.15 K. The influence of different parameters including agitation speed, temperature, catalyst loading, and the lauric acid to ethanol molar ratio on the conversion of lauric acid was discussed. The kinetic experimental data obtained were correlated by the pseudo-homogeneous model, and the results show that it can predict the reaction process well. Moreover, CTAB–DES can be reused six times without any significant decrease in catalytic activity.     

Study on the consecutive reaction kinetics of synthesis of di(2‐ethylhexyl) terephthalate under nonisothermal conditions

Since more information concerning kinetic parameters can be obtained from a nonisothermal reaction, it was selected to investigate the consecutive esterification kinetics of terephthalic acid with 2‐ethylhexanol in the presence of tetrabutyl titanate catalyst. This is an equilibrium reaction that is carried out in industry to completion by removing the water formed. It results in an automatic rise in the esterifying temperature, from 453 to 519 K. Research shows that the first step of esterification carried out in a heterogeneous system has a slow reaction rate, but the second step of esterification in a homogeneous system has a relatively fast reaction rate. Based on the quasi‐homogeneous assumption, first the differential method is presented to deal with nonisothermal reaction data. Arrhenius equations of the two steps are established by using this method. It was found that the apparent activation energy of the first step of esterification was about 55 kJ/mol higher than that of the second step. The ratio (K) of reaction rate constants of the two steps decreases gradually with the increase in the reaction temperature. An equation of K vs. temperature is also derived from Arrhenius equations. Subsequently, integral expressions of components' concentrations are used to simulate experimental results of the nonisothermal reaction as well as a three‐stage isothermal reaction. The obtained simulations show that the determined kinetic equations and the parameters are reasonable. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 577–584, 2006     

Kinetics of ruthenium(III) catalyzed and uncatalyzed oxidation of monoethanolamine by <Emphasis Type="Italic">N</Emphasis>-bromosuccinimide

Kinetics of uncatalyzed and ruthenium(III) catalyzed oxidation of monoethanolamine by N-bromosuccinimide (NBS) has been studied in an aqueous acetic acid medium in the presence of sodium acetate and perchloric acid, respectively. In the uncatalyzed oxidation the kinetic orders are: the first order in NBS, a fractional order in the substrate. The rate of the reaction increased with an increase in the sodium acetate concentration and decreased with an increase in the perchloric acid concentration. This indicates that free amine molecules are the reactive species. Addition of halide ions results in a decrease in the kinetic rate, which is noteworthy. Both in absence and presence of a catalyst, a decrease in the dielectric constant of the medium decreases the kinetic rate pointing out that these are dipole—dipole reactions. A relatively higher oxidation state of ruthenium i.e., Ru(V) was found to be the active species in Ru(III) catalyzed reactions. A suitable mechanism consistent with the observations has been proposed and a rate law has been derived to explain the kinetic orders.     

Esterification of Tertiary Amides: Remarkable Additive Effects of Potassium Alkoxides for Generating Hetero Manganese–Potassium Dinuclear Active Species

A catalyst system of mononuclear manganese precursor 3 combined with potassium alkoxide served as a superior catalyst compared with our previously reported manganese homodinuclear catalyst 2 a for esterification of not only tertiary aryl amides, but also tertiary aliphatic amides. On the basis of stoichiometric reactions of 3 and potassium alkoxide salt, kinetic studies, and density functional theory (DFT) calculations, we clarified a plausible reaction mechanism in which in situ generated manganese–potassium heterodinuclear species cooperatively activates the carbonyl moiety of the amide and the OH moiety of the alcohols. We also revealed details of the reaction mechanism of our previous manganese homodinuclear system 2 a , and we found that the activation free energy (ΔG^≠) for the manganese–potassium heterodinuclear complex catalyzed esterification of amides is lower than that for the manganese homodinuclear system, which was consistent with the experimental results. We further applied our catalyst system to deprotect the acetyl moiety of primary and secondary amines.     

Esterification of sorbitol and lauric acid with catalystp-TSA

Kinetics of the esterification of sorbitol with lauric acid in the presence ofp-TSA as a catalyst has been studied. A kinetic model of reversible second order reaction was proposed for the esterification. Parameters in the model (kinetic constants) were estimated by non-linear regression. The temperature dependence of the rate was calculated from the experimental constants estimated at various temperatures, using the Arrhenius equation. Experimental results are in good accordance with the proposed theoretical model.     

FTIR isothermal cure kinetics and morphology of dicyanate ester resin/polysulfone blends

The isothermal cure of a dicyanate ester monomer by “in situ” Fourier transform infrared spectroscopy (FTIR) has been investigated. The degree of cyanate conversion and the kinetic parameters have been determined for cobalt catalyzed and uncatalyzed resin as well as for polysulfone (PSF) modified systems at different curing temperatures. The cyanate conversion increases with the increment of temperature and with the addition of a catalyst, but it does not vary with the addition of PSF. In all the systems studied, the rate of reaction showed a second-order dependence on the cyanate concentration in the kinetically controlled stage. Moreover, the addition of PSF generates a matrix with two-phases that changes in composition and morphology depending on the percent of added thermoplastic and curing temperature as observed by scanning electron microscopy.     

Kinetic modeling of liquid-phase esterification of acetic acid with n-butanol using heterogeneous poly(o-methylene p-toluene sulfonic acid) as catalyst

Liquid-phase esterification of acetic acid with n-butanol to n-butyl acetate is studied in the presence of a polymeric catalyst, that is, poly(o-methylene p-toluene sulfonic acid). The performance of the proposed catalyst is compared with the other commercially available homogeneous and heterogeneous catalysts in terms of its activity. Experiments are conducted in an isothermal stirred batch reactor to study the effects of speed of agitation, temperature, and catalyst loading on the rate of reaction. A concentration-based pseudo-homogeneous (PH) kinetic model and activity-based kinetic models such as PH, Eley-Rideal (ER), and Langmuir-Hinselwood-Hougen-Watson (LHHW) models are developed. All the models considered in this study resulted in similar percentage deviation close to 4%. Further, kinetic models are validated through additional experiments, and it is observed that the simple concentration-based PH model is able to predict experimental data with least deviation compared to activity-based PH, ER, and LHHW models. The developed kinetic models are also tested using the Fisher-Snedecor test (F-test) and are found to be acceptable. By incorporating both modeling data and validation data, the overall absolute average deviations of different models are found to be concentration-based PH model 4.354%, activity-based PH model 5.006%, ER I model 5.189%, ER II model 5.403%, ER III model 5.437%, and LHHW model 6.104%, illustrating the superiority of the simple concentration-based PH model.     

Activity-Based Models to Predict Kinetics of Levulinic Acid Esterification

The solvent is of prime importance in biomass conversion as it influences dissolution, reaction kinetics, catalyst activity and thermodynamic equilibrium of the reaction system. So far, activity-based models were developed to predict kinetics and equilibria, but the influence of the catalyst on kinetics has not been succesfully predicted by thermodynamic models. In this work, the thermodynamic model ePC-SAFT advanced was used to predict the activities of the reactants and of the catalyst at various conditions (temperature, reactant concentrations, γ-valerolactone GVL cosolvent addition, catalyst concentration) for the homogeneously acid-catalyzed esterification of levulinic acid (LA) with ethanol. Different kinetic models were applied, and it was found that the catalyst influence on kinetics could be predicted correctly by simultaneously solving the dissociation equilibrium of H₂SO₄ catalyst along the reaction coordinate and by relating reaction kinetics to proton activity. ePC-SAFT advanced model parameters were only fitted to reaction-independent phase equilibrium data. The key reaction properties were determined by applying ePC-SAFT advanced to one experimental kinetic curve for a set of temperatures, yielding the reaction enthalpy at standard state , activation energy and the intrinsic reaction rate constant k=0.011 s⁻¹ at 323 K, which is independent of catalyst concentration. The new procedure allowed an a-priori identification of the effects of catalyst, solvent and reactant concentration on LA esterification.     

Aqueous Ti(IV)-catalyzed Diels-Alder reaction

The aqueous Diels-Alder reaction of 1,3-cyclohexadiene with 1,4-benzoquinone was compared and contrasted to the same reaction catalyzed with Flextyl P, a novel Ti(IV) performance catalyst. The catalyst improved conversion by 22% versus the uncatalyzed reaction and represents a rare example of a Ti(IV) catalyzed Diels-Alder reaction in water.     

Thermal kinetics and morphological investigation of alkaline treated rice husk biomass

Agro waste bio mass are creating challenges for environment in term of air pollution due to improper disposal. Rice milling is the process in which rice husk is produced as by-product. The agro-waste rice husk has tremendous potential to be used either in its raw form or in ash form. The inherent component of this waste cellulose provides enhanced properties in a reinforced composite when used as filler. Rice husk is the hard outer layer and covering rice seed, which makes reinforcement challenging in its original form. Fiber surface treatment significantly improves adhesion with matrix and various thermo chemical properties of filler as well as of composites. NaOH treatment is cost-effective and it ensures the adhesion with matrix by removal of hemicellulose and lignin. The chemical treatment of agro-waste (rice husk) is performed with 5% alkali solutions of NaOH in water. Results are compared with the properties of untreated rice husk for thermal and morphological characterizations. In the present work, we are trying to quantify the impact of chemical treatment on rice husk thermal decomposition and its kinetics. Thermogravimetric analysis and kinetics study of thermal degradation, provide key input towards pyrolysis pattern of rice husk, while FTIR and SEM analysis provide the prospects of this bio filler using a reinforcing agent to develop green composite and productive disposal. The FTIR data helps to find the possibilities of blending different bio fillers and natural fibers to find suitable reinforcing substances. The average activation energy of treated fiber is noted as 137.95 by KAS method and 108.08 by FWO method as compared to 55.56 by KAS method & 54.26 by FWO method for untreated rice husk.     

Efficient monooleoyl glycerol synthesis employing hybrid ultrasonic-infrared-wave promoted reactor: Concurrent catalytic and noncatalytic esterification kinetics

For the first time, intensification of monooleoyl glycerol (MOG) synthesis has been investigated in an ultrasonic-infrared-wave (USIRW) promoted batch reactor. Esterification of octadecanoic acid (ODA) with glycerol (Gl) has been conducted [using Amberlyst 36 wet catalyst] in three different reactors, namely traditional batch reactor (TBR), infrared wave promoted batch reactor (IRWPBR), and USIRW-promoted batch reactor (USIRWPBR) to assess the relative efficacy. The energy-efficient USIRWPBR remarkably intensifies the ODA-Gl esterification as manifested through superior ODA conversion (92.5 ± 1.25%) compared to that achieved in IRWPBR (79.8 ± 1.2%) and TBR (36.39 ± 1.25%). The most favorable reaction condition for optimum ODA conversion and maximum MOG yield was identified through statistical optimization over a selected parametric range, namely 3-5 Gl/ODA mole ratio, 0.004-0.006 g/mL Amberlyst 36 catalyst concentration, 300-700 rpm impeller speed, and 333-353 K reaction temperature. The present study also reports the formulation and validation of an innovative reaction kinetics, that is, concurrent noncatalytic and heterogeneously catalyzed (CNCHC) reaction mechanism in addition to the conventional heterogeneous kinetic models (LH and Eley-Rideal mechanisms). Under combined USIRW, the CNCHC esterification mechanism could best describe ODA-Gl esterification (R² = 0.98) compared to LH (R² = 0.97) and Eley-Rideal (R² = 0.88) mechanisms. The optimal product (MOG) was characterized by differential scanning calorimetry and thermogravimetric analysis to assess its crystallization property and thermal stability for possible application as plasticizer/fuel additives.