Selection of the most effective kinetic model of lactase hydrolysis by immobilized Aspergillus niger and free β-galactosidase

The kinetic model of the hydrolysis of lactose by β-galactosidase from Aspergillus niger immobilized on a commercial ceramic monoliths was estimated in the attendance of lactose and its hydrolysis reaction products galactose and glucose. The aim of this work was to developing kinetic model of lactase hydrolysis by Aspergillus niger. The variables in this study are temperature, pH, enzyme concentration, substrate concentration and final product. The optimum temperature used to achieve the best hydrolysis performance in the kinetic model selection was 55 and 60 °C. The optimum pH used for enzyme activity was about 3.5 to 4. Five kinetic models were proposed to confirm experimental data the enzymatic reaction of the lactose hydrolysis by the β-galactosidase. The kinetics of lactose hydrolysis by both Immobilized and soluble lactases were scrutinized in a batch reactor system in the lack of any mass conduction restriction. In both instance the galactose inhibition kinetic models predicted the experimental data. The model is capable to fit the experimental data correctly in the extensive experimental span studied.     

乙醇的低温光催化氧化实验研究

利用傅里叶变换红外光谱仪(FT-IR)，在间歇式反应器中研究了高浓度乙醇的低温光催化氧化特性。研究结果表明，FT-IR技术能够用来研究气态有机物的光催化降解特性；在乙醇的光催化降解过程中，有乙醛等中间产物生成，乙醇先被氧化为乙醛，再被氧化为二氧化碳；在间歇式反应器中，乙醇的循环流量对乙醇的瞬时降解速率影响不大；高浓度乙醇的低温光催化氧化过程可以用单步Langmuir-Hinshelwood 方程来描述；温度对乙醇光催化氧化的初始反应速率的影响十分显著，高浓度乙醇的初始反应速率随温度的升高而迅速提高。     

Enzyme Thermistor Analysis of Kinetics and Stability of Immobilized Invertase

Abstract

The kinetic behaviour of immobilized invertase was investigated using calorimetric measurements in an enzyme thermistor device. The hydrolysis of sucrose is an exothermic process with inhibition-like kinetics above 300 mmol/1; glucose gave no measurable heat of reaction and fructose molecules are condensed in an endothermic process. The concentration dependence of the temperature signal of fructose condensation is linear up to 2 mol/1 at an optimal pH of 3.3, and the absolute value of the heat of reaction is only 25% compared with that of the hydrolytic reaction. A higher K_m-value and a lower V_max are therefore assumed. The reaction heat of hydrolysis of sucrose decreases with increasing product concentration. A shift of the equilibrium by increasing concentrations of both products is accompanied by a competitive condensation reaction in the case of fructose. The stability of invertase in aqueous ethanol solutions was also investigated. It depends on the ethanol concentration and on the time of contact with the solvent. At 30% ethanol no inactivation within 20 min. occurs, whereas at 60% ethanol a linear dependence of the inactivation on the time of contact was found. Above 80% ethanol less than 10% enzymatic activity remained after a five-minute treatment. This irreversible inactivation has to be considered if invertase is applied in water miscible organic solvents.     

Estimation of Fundamental Kinetic Parameters of Polyhydroxybutyrate Fermentation Process of Azohydromonas australica Using Statistical Approach of Media Optimization

Polyhydroxybutyrate or PHB is a biodegradable and biocompatible thermoplastic with many interesting applications in medicine, food packaging, and tissue engineering materials. The present study deals with the enhanced production of PHB by Azohydromonas australica using sucrose and the estimation of fundamental kinetic parameters of PHB fermentation process. The preliminary culture growth inhibition studies were followed by statistical optimization of medium recipe using response surface methodology to increase the PHB production. Later on batch cultivation in a 7-L bioreactor was attempted using optimum concentration of medium components (process variables) obtained from statistical design to identify the batch growth and product kinetics parameters of PHB fermentation. A. australica exhibited a maximum biomass and PHB concentration of 8.71 and 6.24?g/L, respectively in bioreactor with an overall PHB production rate of 0.75?g/h. Bioreactor cultivation studies demonstrated that the specific biomass and PHB yield on sucrose was 0.37 and 0.29?g/g, respectively. The kinetic parameters obtained in the present investigation would be used in the development of a batch kinetic mathematical model for PHB production which will serve as launching pad for further process optimization studies, e.g., design of several bioreactor cultivation strategies to further enhance the biopolymer production.     

Enzymatic synthesis of prebiotic oligosaccharides

Prebiotic oligosaccharides are nondigestible carbohydrates that can be obtained by enzymatic synthesis. Glucosyltransferases can be used to produce these carbohydrates through an acceptor reaction synthesis. When maltose is the acceptor a trisaccharide composed of one maltose unit and one glucose unit linked by an alpha-1,6-glycosidic bond (panose) is obtained as the primer product of the dextransucrase acceptor reaction. In this work, panose enzymatic synthesis was evaluated by a central composite experimental design in which maltose and sucrose concentration were varied in a wide range of maltose/sucrose ratios in a batch reactor system. A partially purified enzyme was used in order to reduce the process costs, because enzyme purification is one of the most expensive steps in enzymatic synthesis. Even using high maltose/sucrose ratios, dextran and higher-oligosaccharide formation were not avoided. The results showed that intermediate concentrations of sucrose and high maltose concentration resulted in high panose productivity with low dextran and higher-oligosaccharide productivity.     

Bifunctional Polyacrylonitrile Fiber‐Mediated Conversion of Sucrose to 5‐Hydroxymethylfurfural in Mixed‐Aqueous Systems

A highly efficient catalytic system composed of a bifunctional polyacrylonitrile fiber (PANF‐PA[BnBr]) and a metal chloride was employed to produce 5‐hydroxymethylfurfural (HMF) from sucrose in mixed‐aqueous systems. The promoter of PANF‐PA[BnBr] incorporates protonic acid groups that promote the hydrolysis of the glycosidic bond to convert sucrose into glucose and fructose, and then catalyzes fructose dehydration to HMF, while the ammonium moiety may promote synergetically with the metal chloride the isomerization of glucose to fructose and transfer HMF from the aqueous to the organic phase. The detailed characterization by elemental analysis, FTIR spectroscopy, and SEM confirmed the rangeability of the fiber promoter during the modification and utilization processes. Excellent results in terms of high yield (72.8 %) of HMF, superior recyclability (6 cycles) of the process, and effective scale‐up and simple separation procedures of the catalytic system were obtained. Moreover, the prominent features (high strength, good flexibility, etc.) of the fibers are very attractive for fix‐bed reactor.     

Development of kinetic models for acid‐catalyzed methyl acetate formation reaction: Effect of catalyst concentration and water inhibition

The reaction kinetics of reversible liquid‐phase esterification of acetic acid with methanol is investigated in the temperature range 26–50°C using sulfuric acid catalyst. The main goal of this work is to study the effect of catalyst concentration and sensitivity to the presence of water on the rate expression of this industrially important reaction. Experiments are conducted in an isothermal batch reactor and a second‐order kinetic model is used to correlate the experimental data, which are found to fit well with the assumed kinetic model in terms of the concentrations of reactants and products. Furthermore, an activity‐based kinetic model is also developed employing the UNIQUAC (universal quasi‐chemical equation) model to compute the activities. It is observed that the rate constant is influenced by the concentration of catalyst, and the reaction rate increased with an increase in the catalyst concentration. It is also observed that the catalyst activity is slightly inhibited by the water present in the reaction mixture. The performance of the proposed models is compared with that of other models reported in the literature, and it is found that the proposed models outperformed all the other models reported in the literature. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 263–277, 2011     

Kinetics of Phase Transfer Catalytic Preparation of Benzyl Benzoate

The kinetics is studied for the phase transfer catalytic preparation of benzyl benzoate from sodium benzoate and benzyl chloride with tetrabutylaramonium iodide as catalyst in a well stirred batch reactor. Benzyl chloride is dissolved in toluene as the organic phase and sodium benzoate is dissolved in water as the aqueous phase. The kinetics of the overall reaction is described by a first-order model based on the concentration of benzyl chloride in the organic phase at the later time of the batch reaction. The rate constant increases with an increase of the catalyst concentration while decreases slightly with an increase of the concentration of sodium benzoate under the experimental condition.     

The study of cyclooctene oxidation with molecular oxygen catalyzed by VSi2

The catalytic effect of VSi₂ on initial stages of the liquid-phase oxidation of cyclooctene by molecular oxygen was studied. The vanadium disilicide influences on the oxidation process in the presence of hydroperoxide. VSi₂ takes part in a radical formation stage by catalysis of hydroperoxide decomposition reaction. The catalyst was investigated before and after reaction using FTIR spectroscopy. From the data obtained, the kinetic model of the catalytic oxidation process was proposed and the equation for the reaction rate was derived. The equation has described all observed dependences of reaction rate on the concentration of reactants and content of catalyst.      

Kinetic Modeling of Fructooligosaccharide Production Using Aspergillus oryzae N74

In this study, the kinetic for the bioconversion of sucrose to fructooligosaccharides (FOS) by free cells of Aspergillus oryzae N74 was modeled. In addition, the effect of immobilized glucose isomerase (IGI) on FOS production yield was evaluated and considered in the kinetic model. The selected kinetic models were based on a proposed reaction mechanism described by elementary rate equations and modified Michaelis?CMenten kinetic equations. The use of IGI allowed to increase the FOS production yield (FOS_Yield) and to decrease the glucose/fructose (G/F) ratio. At shake flask scale, the FOS_Yield was increased in 4.7?% (final yield 58.3?%), while the G/F ratio was reduced 6.2-fold. At bench scale, the FOS_Yield was increased in 2.2?% (final yield 57.3?%), while the G/F ratio was reduced 4.5-fold. The elementary rate equation model was the one that best adjusted experimental data for FOS production using either the fungus biomass or the mixture fungus biomass?CIGI, with an overall average percentage error of 7.2. Despite that FOS production yield was not highly improved by the presence of IGI in the reaction mixture, it favored the reduction of residual glucose in the mixture, avoiding the loss of material owe to glucose transformation to fructose that can be used in situ for FOS production by the fructosyltransferase.     

Kinetic Study of Empty Fruit Bunch Using Hot Liquid Water and Dilute Acid

Empty fruit bunch (EFB), a residual product of the palm plantation, is an attractive biomass for biorefinery. As xylan is susceptible to high temperature pretreatment, it is important to setup a proper pretreatment condition to maximize the sugar recovery from EFB. Kinetic parameters of mathematical models were obtained in order to predict the concentration of xylose, glucose, furfural, and acetic acid in the hydrolysate and to find production conditions of xylose. We investigated the kinetics of hot liquid water and dilute sulfuric acid hydrolysis over a 40-min period using a self-designed setup by measuring the concentrations of released sugars (xylose, glucose) and degradation products (acetic acid and furfural). The reaction was performed within the range 160～180 °C, under reaction conditions of various concentration of sulfuric acid (0.1～0.2%) and 1:7 solid-liquid ratio in a batch reactor. The kinetic constants can be expressed by the Arrhenius equation with the activation energy for the hydrolysis of sugar and decomposition of sugar. The activation energy of xylose was determined to be 136.2187 kJ mol(-1).     

Kinetics of Enzymatic Hydrolysis of Olive Oil in Batch and Fed-batch Systems

This work reports experimental data, kinetic modeling, and simulations of enzyme-catalyzed hydrolysis of olive oil. This reaction was performed in batch system and an ordered-sequential Bi Bi model was used to model the kinetic mechanism. A fed-batch system was proposed and experimental data were obtained and compared to the simulated values. The kinetic model used was able to correlate the experimental data, in which a satisfactory agreement between the experimental data and modeling results was obtained under different enzyme concentration and initial free water content. Therefore, the modeling allowed a better understanding of the reaction kinetics and affords a fed-batch simulation for this system. From the results obtained, it was observed that the fed-batch approach showed to be more advantageous when compared to the conventional batch system.     

Kinetic study of spiramycin removal from aqueous solution using heterogeneous photocatalysis

Spiramycin macrolide antibiotic (SPM) can be photocatalytically degraded on TiO₂ (anatase variety). The experiments are done in a batch reactor and the effect of some key parameters is investigated under low energy of artificial UV light. The reaction rate is affected by varying TiO₂ dose, pH and SPM concentration. Under optimized conditions, a photodegradation efficiency of 98% is achieved and the SPM photodegradation follows pseudo-first order kinetics. The Langmuir–Hinshelwood (L–H) model is successfully used to fit the experimental data, indicating the dependence of the reaction rate on the chemical reaction step. The L–H model led to the determination of both reaction kinetic and adsorption/desorption equilibrium constants. In order to give an overall estimate of the by-products, chemical oxygen demand, total organic carbon, and calculated average oxidation state monitor the photodegradation process.     

Interaction forces between a deformable air bubble and a spherical particle of tuneable hydrophobicity and surface charge in aqueous solutions

Unsupported nanosized MoS(2) and CoMo-sulfide catalysts were synthesized, and their catalytic performances for the deep hydrodesulfurization (HDS) of treated gas oil were investigated as compared with that of a CoMo/Al(2)O(3) catalyst. The HDS reactions were carried out in a batch autoclave reactor at 340 °C and 3 MPa H(2). The CoMo-sulfide catalyst shows the highest activity and can reduce the sulfur content to less than 10 ppm. The decrease in total sulfur content as a function of reaction time was found to follow pseudo-second order kinetics (empirical form). The change in the concentration of some individual representative sulfur-containing species in gas oil as a function of time was found to follow pseudo-first-order kinetics. However, the change in combined concentration of these species in the gas oil during HDS with the reaction time was found to corroborate pseudo-second-order kinetics. A kinetic model approach was proposed from which an estimation of the intrinsic kinetic data can be achieved. The model fitted the obtained data reasonably well, suggesting its potential for better assessment of the catalytic activity in the HDS of real feedstock. The study reveals that ranking of catalyst activities using model refractory sulfur-containing compounds does not necessarily imply a typical rank in case of investigating the real feedstocks.     

Determination of reducing sugars with a 2,4-dinitrophenolate-selective membrane electrode

A 2,4-dinitrophenolate-selective liquid-membrane electrode based on tetrapentylammonium dinitrophenolate dissolved in 2-nitrotoluene is described. The electrode exhibits rapid and near- Nernstian response to the activity of 2,4-dinitrophenolate anions in the range 3×10^?5 ?1×10^?2 M. The response is unaffected by pH in the range 7.5–12.5. The electrode has been successfully applied to the kinetic potentiometric determination of fructose, glucose and galactose at 60°C and of fructose in the presence of glucose and galactose at 30°C. The electrode can be used for the potentiometric determination of glucose and fructose after completion of the reaction with excess of 2,4-dinitrophenolate ions and of sucrose after acid hydrolysis. Mixtures of glucose, fructose and sucrose in aqueous solutions or honey samples can be determined by the proposed procedures with an average error of about 2%.     

Cellulose hydrolysis under extremely low sulfuric acid and high-temperature conditions

The kinetics of cellulose hydrolysis under extremely low acid (ELA) conditions (0.07 wt%) and at temperatures >200°C was investigated using batch reactors and bed-shrinking flow-through (BSFT) reactors. The maximum yield of glucose obtained from batch reactor experiments was about 60% for α-cellulose, which occurred at 205 and 220°C. The maximum glucose yields from yellow poplar feedstockswere substantially lower, falling in the range of 26–50%. With yellow poplar feedstocks, a large amount of glucose was unaccounted for at the latter phase of the batch reactions. It appears that a substantial amount of released glucose condenses with nonglucosidic substances. in liquid. The rate of glucan hydrolysis under ELA was relatively insensitive to temperature in batch experiments for all three substrates. This contradicts the traditional concept of cellulose hydrolysis and implies that additional factors influence the hydrolysis of glucan under ELA. Inexperiments using BSFT reactors, the glucose yields of 87.5, 90,3, and 90.8% were obtained for yellow poplar feedstocks at 205, 220, and 235°C, respectively. The hydrolysis rate for glucan was about three times higher with the BSFT than with the batch reactors. The difference of observed kinetics and performance data between the BSFT and the batch reactors was far above that predicted by the reactor theory.     

Esterification of butyric acid with n-butanol: Kinetic study using experimental data and modeling

Present study involves the investigation of the esterification kinetics between butyric acid and n-butanol. This reaction was conducted in a batch reactor, utilizing homogeneous methanesulfonic acid (MSA) catalyst. Response surface methodology (RSM) was conducted prior to the kinetic study using “Design Expert; version-11.0” for finding the causal factors influencing the conversion of butyric acid. Most important factors identified with their limits against conversions (during optimization of the process using RSM) were taken up to critically analyze the effect of them on butyric acid conversion. Concentration and activity-based model of the process were proposed assuming second order reversible reaction scheme using homogeneous MSA catalyst. During the study of non-ideal behavior of the system, UNIFAC model was adapted for assessing the activity coefficients of species present in equilibrated liquid phase. Experimental data were used to evaluate kinetic and thermodynamic parameters such as rate constants, activation energy, enthalpy, and entropy of the system. The endothermic nature of esterification was confirmed by positive value of enthalpy obtained. The effect of various levels of causal variables like temperature (60–90°C), catalyst concentration (0.5–1.5 wt.%), and molar ratio of n-butanol to butyric acid (1–3) on conversion kinetics of butyric acid was investigated during transient and equilibrium phase of the reaction. It has been observed that molar ratio of butanol to butyric acid has the highest influence on the conversion. The rate equation derived offered a kinetic and thermodynamic framework to the generated data. It also exhibits a notable degree of conformity of predicted data to the experimental ones and effectively characterizes the system across different reaction temperatures, reactant molar ratio, and catalyst concentration.     

A kinetic expression for the pyrolytic decomposition of polytetrafluoroethylene

Despite the fact that the thermal decomposition of polytetrafluoroethylene has been extensively studied over the past six decades, some inconsistencies regarding the kinetic parameters, e.g. the order of the reaction, remain. Representative kinetic data are essential for practical purposes such as reactor design and scaling. In general the literature data refer to homogeneous bulk heating, whereas the case of the non-homogeneous heating of a single particle has not received attention. Data (reaction rate and pre-exponential factor) applicable to this latter case were experimentally determined from isothermal thermogravimetric analyses of the depolymerisation reaction of PTFE. The kinetic data obtained on coarse granules (800-1000 μm) are reported here. The rate law is consistent with a shrinking particle kinetic model, with chemical kinetics controlling phase-boundary movement. The mass loss rate is directly proportional to surface area. A rate law applicable to this case, and useable for geometries of arbitrary shape, is derived.     

Kinetics of dialin thermolysis

The liquid-phase thermolysis of 1,2-dihydronaphthalene was studied in a batch reactor in the range of 350–400°C. The measured product distributions were in good agreement with calculations based on a free-radical scheme with rate constants estimated by thermochemical methods. The kinetic calculations were carried out by numerical integration and by the long-chain approximation (LCA), which yielded a closed-form solution.     

以葡萄糖和蔗糖为电子给体在Pt/TiO2上光催化制氢

以Pt/TiO2为催化剂, 研究了以葡萄糖和蔗糖为电子给体的光催化制氢反应以及有机物自身的去除效果.