Effect of light irradiation on esterification of oleic acid with ethanol catalyzed by immobilized Pseudomonas cepacia lipase

The present study demonstrates the effect of light irradiation on the esterification of oleic acid catalyzed by immobilized Pseudomonas cepacia lipase. The reaction rates of all the experiments under light irradiation were found to be higher than dark conditions. The kinetics of reactions supported the Ping‐Pong Bi‐Bi mechanism with dead end inhibition by both the alcohol and acid substrates. Moreover, circular dichroism (CD) spectroscopy was used to analyze the effect of light on lipase enzyme. The CD spectroscopic studies confirmed that the conformational changes in the secondary structure of the lipase enzyme increased the reaction rate of light‐illuminated experiments, which might have opened up the active sites of enzymes and thus, resulted in higher reaction rates compared to dark reactions. These results have successfully demonstrated that the light illumination positively influenced the rate of P. cepacia enzyme‐catalyzed esterification reactions.     

Kinetic studies on immobilised lipase esterification of oleic acid and octanol

The present work investigates the reaction kinetics of immobilised lipase esterification of oleic acid and octanol, in a solvent-free system. Lipase from Rhizomucor miehei was immobilised on a hydrophobic support. The initial reaction rate was investigated as a function of octanol concentration and temperature, and the reaction kinetics were described in terms of the Michaelis–Menten mechanism. Evaluating K_m, V_max and k_cat/K_m as a function of temperature, it was found that K_m was minimum and k_cat/K_m was maximum at 40°C while V_max was maximum at 50°C. Furthermore, applying the Ping Pong Bi Bi mechanism yielded good results for this two-substrate system.     

Triazine reaction of cyanate ester resin systems catalyzed by organic tin compound: kinetics and mechanism

The mechanism and kinetics of the thermal cure reaction of two cyanate esters (CEs), 1,1′bis(4‐cyanatophenyl)ethane (AroCy L‐10) and bisphenol A dicyanate ester (BADCy), in the presence of dibutyl tin dilaurate (DBTDL) has been investigated using Fourier‐transform infrared spectroscopy (FTIR) and High‐performance liquid chromatography (HPLC). It was found that the organic tin compound (H₉C₄)₂Sn(NCO—R—OCN)₂, an active catalyst, has high catalytic efficiency in the polymerization of cyanate esters. The consuming rate of cyanate concentration showed a first‐order dependence on both active catalyst and the cyanate ester monomer concentration. The apparent activation energies (E_a) and frequency factors of both AroCy L‐10 and BADCy were calculated. A mechanism of cyclotrimerization was proposed, based on the kinetic data and FTIR spectra, which involves the formation of an active catalyst and the catalysis of the active catalyst. Copyright © 2004 Society of Chemical Industry     

The kinetics of epoxidation of trimethylolpropane ester

Kinetics pertaining epoxidation reaction of a palm oil‐based synthetic lubricant trimethylolpropane (TMP) ester were investigated. The epoxidation reaction of TMP ester was carried out utilizing peracetic acid generated by an in situ technique. The analysis of the reaction kinetics was performed within the low temperature (30, 50, and 60°C) and high temperature (70, 80, and 90°C) regions, owing to the nature of the reactions. The maximum conversion of the unsaturated carbon to oxirane ring was achieved in 1 h at high temperature region, while epoxidation of TMP esters took more than 4 h to reach the maximum conversion at the low temperature region. From the experimental data, the kinetics of epoxidation of TMP esters fitted well with both the second‐order and pseudo first‐order models. The rate constants for pseudo first‐order model increased from 0.0009 to 0.0055 by increasing temperature at the low temperature region, and from 0.0129 to 0.0209 within the high temperature region. The values of activation energies at low temperature and high temperature regions were found to be 69.4 and 53.3 kJ/mol, respectively.     

Kinetics of the pre-treatment of used cooking oil using Novozyme 435 for biodiesel production

The pre-treatment of used cooking oil (UCO) for the preparation of biodiesel has been investigated using Novozyme 435, Candida antarctica Lipase B immobilised on acrylic resin, as the catalyst. The reactions in UCO were carried out using a jacketed batch reactor with a reflux condenser. The liquid chromatography–mass spectrometry (LC–MS) method was developed to monitor the mono-, di- and triglyceride concentrations and it was found that the method was sensitive enough to separate isomers, including diglyceride isomers. It was found that the 1,3 diglyceride isomer reacted more readily than the 1,2 isomer indicating stereoselectivity of the catalyst. This work showed that Novozyme 435 will catalyse the esterification of free fatty acids (FFAs) and the transesterification of mono- and diglycerides typically found in UCO when Novozyme 435 is used to catalyse the pre-treatment of UCO for the formation of biodiesel. A kinetic model was used to investigate the mechanism and indicated that the reaction progressed with the sequential hydrolysis esterification reactions in parallel with transesterification.     

Effect of Yb doping concentration on crystallization kinetics in yttrium aluminum garnet nano-powders

Different ytterbium concentration–doped yttrium aluminum garnet (Yb:YAG) nanopowders were synthesized using coprecipitation with nitrate salts as the starting materials. The phase evolutions, morphologies, and microstructures of the powders synthesized from various ytterbium-doped precursors were investigated. Ytterbium doping concentration was discovered to have a crucial effect during the YAG phase formation from the precursor. Crystallized Yb:YAG powders were directly obtained at temperatures as low as 900 °C without the formation of any intermediate phase. The crystallization kinetics of the Yb:YAG precursors were analyzed using non-isothermal differential scanning calorimetry. Avarami parameters of 0.97, 1.00, 1.13, and 1.21 were obtained for Yb doping concentrations of 0, 3, 6, and 9 at% respectively, and crystallization activation energies of 1506±40, 1342±36, 1171±31, and 978.1±26 kJ/mol were calculated. The activation energy for YAG crystallization was lower when a high Yb doping concentration was used because the presence of Yb³⁺ prohibited the presence of anionic SO₄²⁻ in the precursors, thus enhancing the elemental diffusion between particles. Both the average grain size and particle size of Yb: YAG decreased when Yb doping concentration was increased, and at various calcination temperatures.     

非水相脂肪酶在维生素酯类衍生物合成中的应用

脂肪酶在非水介质中催化是目前生物技术中一个颇具基础性和应用性的研究领域。非水介质中的酶催化反应已经被成功应用到了多肽合成、聚合物合成、药物合成、立体异构体拆分及维生素改性等。介绍了脂肪酶在非水介质中的催化机理及其影响催化活性的重要因素,概述了近年来非水介质中脂肪酶催化合成几种维生素酯的研究进展。     

Bleaching kinetics of sunflowerseed oil

The bleaching process for sunflowerseed oil follows a rate formula, log (A/A ₀)=−κ , according to absorbance measurements. The dark color of crude oil converts to a light color as the absorbance value decreases. The activation energy E _a was calculated from the Arrhenius equation as 3 kJ, and other activation thermodynamic parameters were determined as ΔS ^⊄=−4.4 J K⁻¹, ΔH ^⊄=−31.2 J mol⁻¹, and ΔG ^⊄=1.6 kJ mol⁻¹. The study showed that the bleaching process was exothermic, presented a decrease of entropy, and was a nonspontaneous process during activation.     

超声酶促维生素A棕榈酸酯反应的动力学

考察超声辐照下影响合成维生素A棕榈酸酯反应的因素(溶剂、底物摩尔比、底物浓度、反应时间、酶量和超声功率),并优化了反应条件:在10 mL的正己烷溶剂中,0.164 g维生素A醋酸酯和0.32 g棕榈酸,在酶与维生素A醋酸酯的质量比为1∶4的固定化脂肪酶Novozym 435催化下,超声功率为90 W,反应6 h,酯化率可达82%。并对其动力学进行了研究,由非线性拟合得到动力学参数:最大反应初速率(rmax)为0.522 mmol/(min.g);维生素A醋酸酯的米氏常数为0.404 mmol/L;棕榈酸的米氏常数为0.034 mmol/L。     

Heterogeneous esterification kinetics of isopropyl oleate synthesis under non-ionizing excitation using nano-anatase imbued mesoporous catalyst

Performance of a green, cost-effective bio-hydroxyapatite (derived from waste Suidae bone) supported nano-anatase catalyst, has been investigated in the synthesis of isopropyl oleate (IPO) in presence of non-ionizing (NI) excitation. FTIR, XRD, SEM, TGA, BET, NH₃-TPD and TEM methods were employed to characterize the catalyst. At identical optimal operating conditions, esterification results demonstrated the energy-efficient augmentation in catalytic performance under NI excitation (OA conversion: 93?±?2%) compared to the orthodox heating system (OA conversion: 50?±?2%). This indicated intensification effects of NI excitation over orthodox heating (activation energy: 67.12?kJ/mol). Furthermore, the developed catalyst showed better performance (identified by Langmuir-Hinshelwood kinetics) in terms of lower esterification activation energy (30?kJ/mol) compared to Amberlyst 15 (48.31?kJ/mol) under NI activation. The developed catalyst also showed 2 times more recycling efficiency compared to Amberlyst 15; thus, enumerating sustainable valorization of slaughterhouse waste for preparation of supported catalysts.     

Effect of demineralization and heating rate on the pyrolysis kinetics of Jordanian oil shales

The effect of mineral matter content on the activation energy of oil shale pyrolysis has been studied. Kerogen was isolated from raw oil shale by sequential HCl and HCl/HF digestion. Oil shale and kerogen samples were pyrolyzed in a Thermogravimetric Analyzer at different heating rates (1, 3, 5, 10, 30, and 50 °C/min) up to a temperature of 1000 °C. Total mass loss of all oil shale samples remained almost constant irrespective of the heating rate employed, whereas it decreased with the increase of heating rate for kerogen (74.5 to 71.4%). From the pyrolysis profile activation energy (Ea) was found to vary between 70 and 83 kJ/mol for oil shale, while 82-112 kJ/mol has been determined for isolated kerogen. An increase of both Ea and pre-exponential factor was observed with an increasing heating rate. It is concluded that the mineral matter in oil shale enhances catalytic cracking as is evident from the reduced Ea values of oil shale compared with those for kerogen.     

Experimental study and model of reaction kinetics of heterogeneously catalyzed methylal synthesis

Reaction kinetics of the heterogeneously catalyzed formation of methylal from aqueous methanolic formaldehyde solutions are studied in a plug flow reactor at 323, 333 and 343 K using the acidic ion exchange resin Amberlyst 15 (Rohm and Haas) as catalyst. Parameters of an activity-based pseudo-homogeneous reaction kinetic model are fitted to the experimental results. The model is based on the true speciation in the reacting solution and explicitly includes the oligomerization reactions of formaldehyde in aqueous methanolic solutions. The reaction kinetic model describes the experimental data well and is suited for process simulations in which both chemical reactions and phase equilibria have to be described simultaneously.     

Isothermal and nonisothermal crystallization kinetics of bio-sourced nylon 69☆

Bio-sourced nylon 69,one of promising engineering plastics,has a great potential in developing sustainable technology and various commercial applications.Isothermal and nonisothermal crystallization kinetics of nylon 69 is a base to optimize the process conditions and establish the structure–property correlations for nylon 69,and it is also highly bene ficial for successful applications of nylon products in industry.Isothermal and nonisothermal crystallization kinetics has been investigated by differential scanning calorimetry for nylon 69,bio-sourced even–odd nylon.The isothermal crystallization kinetics has been analyzed by the Avrami equation,the calculated Avrami exponent at various crystallization temperatures falls into the range of 2.28 and 2.86.In addition,the Avrami equation modi fied by Jeziorny and the equation suggested by Mo have been adopted to study the nonisothermal crystallization.The activation energies for isothermal and nonisothermal crystallization have also been determined.The study demonstrates that the crystallization model of nylon 69 might be a twodimensional(circular)growth at both isothermal and nonisothermal crystallization conditions.Furthermore,the value of the crystallization rate parameter(K)decreases signi ficantly but the crystallization half-time(t1/2)increases with the increase of the isothermal crystallization temperature.To nonisothermal crystallization,the crystallization rate increases as the cooling rate increases according to the analysis of Jeziorny's theory.The results of Mo's theory suggest that a faster cooling rate is required to reach a higher relative degree of crystallinity in a unit of time,and crystallization rate decreases when the relative degree of crystallinity increases at nonisothermal crystallization conditions.     

明胶的酶降解反应动力学研究——Ⅱ.动力学规律和机理

根据文献[1]中的实验数据,结合化学反应动力学的基础理论,计算了明胶的酶降解反应的反应级数、表观活化能、指前因子等有关动力学参数值。得到反应的总速率方程。所求得的反应速率常数与温度的关系表明,在实验温度范围内,符合Arrhenius公式。最后提出了该反应的酶催化反应机理,实验结果与所推得的机理动力学方程相吻合。     

Mechanism and kinetics of combustion-carbothermal synthesis of AlN nanopowders

In this work, the carbothermal reduction-nitridation process of low-temperature combustion synthesis (LCS) (Al₂O₃+C) precursor was investigated in detail. Compared with conventional precursor, the LCS precursor possesses many advantages such as amorphous structure, nanosized particles, homogeneous mixing at molecular level. The experimental results indicate that the methods for preparing precursor exert great influence on phase transformation of Al₂O₃, onset temperature of nitridation and reaction activity. During the calcination, the phase transformation of Al₂O₃ is hindered by a large amount of surrounding C particles rendering Al₂O₃ maintains high reactivity. Accordingly, the nitridation reaction initiates at 1300 °C and completes at 1500 °C for 2 h. Furthermore, the reaction mechanism was also discussed on the basis of experiments. More significantly, it is established that the activation energy of carbothermal reduction-nitridation reaction using LCS precursor is Eα=336 KJ/mol.     

Influence of phenoxy addition on the curing kinetics for uncatalyzed and catalyzed cyanate ester resin

The curing behavior of the dicyanate ester of bisphenol‐A (DCBA) modified with poly(hydroxy ether of bisphenol‐A) (phenoxy) is studied by differential scanning calorimetry in dynamic and isothermal tests at temperatures between 120 and 240°C. The addition of phenoxy to DCBA produces an increase in the reaction rate and a decrease in the temperature of maximum reaction rate for the uncatalyzed resin, and also for the system catalyzed with copper (II) acetyl acetonate/nonylphenol. The exothermic heat of curing for the mixtures is also dependent on the phenoxy content. These facts evidence a catalytic effect of phenoxy on the curing of the cyanate ester resin, even though an autocatalytic behavior is observed for all uncatalyzed DCBA/phenoxy mixtures. A simplified mechanistic kinetic model is used to calculate the kinetic parameters. For the uncatalyzed systems, a decrease in the kinetic constant for the initiation reactions, and an increase in the propagation constant are measured when the cyanate content increases. The thermal activation energy for the initiation reaction of the catalyzed systems is lower than that of the uncatalyzed ones, and it depends on the weight fraction of cyanate in the mixture. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal kinetics and phase stability of 8 mol% samaria doped zirconia nanopowders prepared via reverse coprecipitation

Nanocrystalline samaria (8 mol%) doped zirconium oxide (8SmSZ) was synthesized using reverse co-precipitation technique, the calcination temperature ranging from 873 K to 1273 K for 2 h. XRD structural analysis results confirm the tetragonal(t) nature of the synthesized 8SmSZ nanocrystalline powder. The calculated crystallite size of tetragonal zirconia calcined at 873 K is around 9.0±0.5 nm and with increase in calcination temperature the size increases to 16.0±0.8 nm (1273 K). Thermogravimetric-Differential thermal analysis (TG-DTA) was carried out to study the crystallisation kinetics and growth behaviour of the 8SmSZ. The activation energy for the crystallisation of tetragonal ZrO₂ formation in the 8SmSZ powder was found to be 308.1 kJ/mol by a non-isothermal DTA method. The growth morphology parameter was found to be n=2 indicating two-dimensional growth. The phase stability of the samples after annealing at 1573 K for 100 h was investigated by Raman spectroscopy and it was found that samaria doped zirconia exhibits better phase stability. These preliminary results confirmed the higher phase stability at elevated temperature thereby confirming its suitability in thermal barrier coating (TBC) applications.     

The non-isothermal kinetics analysis of the thermal decomposition of kaolinite by Effluent Gas Analysis technique

The thermal decomposition of kaolin with high-content of the medium ordered kaolinite was studied by Effluent Gas Analysis (EGA) under non-isothermal conditions. This technique enables to distinguish two overlaying processes during the thermal decomposition of kaolin: oxidation of organic compounds and dehydroxylation. The kinetic of non-isothermal dehydroxylation of kaolinite is controlled by the rate of the third-order reaction. For the given reaction mechanism, the overall activation energy (E_A) and pre-exponential (frequency) factor (A) values are 242 kJ mol⁻¹ and 2.21 × 10⁸ s⁻¹, respectively.