HYDROLYSIS OF ETHYL-2-BROMOISOBUTYRATE ESTER IN AN ALKALINE SOLUTION

The hydrolysis of ethyl-2-bromoisobutyrate in an alkaline solution/organic solvent two-phase medium as well as the effect of quaternary ammonium salt (e.g., tetrabutylammonium bromide) on the hydrolysis of ethyl-2-bromoisobutyrate were investigated in this work. The proposed mechanism for the hydrolysis of ethyl-2-bromoisobutyrate was verified based on experimental analysis. Both the bromo-alkyl (Br-C bond) and ester (-COOR) functional groups of ethyl-2-bromo-isobutyrate hydrolyze into alcohol and acid. Several reaction steps for the hydrolysis of these bromo-alkyl and ester functional groups were developed and discussed. A kinetic model of each reaction step was developed in which the rate expression was derived. The intrinsic rate constants of the reactions were determined from the experimental hydrolyzing data of ethyl-2-bromoisobutyrate using curving fitting. The effects of the reaction conditions on the conversion of reactants were investigated in detail. The results indicated that the conversion of reactants is highly dependent on the concentration of alkaline compound in the aqueous solution. An optimum value of alkaline concentration to produce a maximum conversion of reactant was obtained. Moreover, the conditions for reducing the hydrolysis of halo ester by adding sodium carbonate are recommended.     

Batch adsorptive removal of copper ions in aqueous solutions by ion exchange resins: 1200H and IRN97H

The removal of copper from aqueous solution by ion exchange resins, such as 1200H and IRN97H, is described. Effect of initial metal ion concentration, agitation time and pH on adsorption capacities of ion exchange resins was investigated in a batch mode. The adsorption process, which is pH dependent, shows maximum removal of copper in the pH range 2–7 for an initial copper concentration of 10 mg/L. The experimental data have been analyzed by using the Freundlich, Langmuir, Redlich-Peterson, Temkin and Dubinin-Radushkevich isotherm models. The batch sorption kinetics have been tested for a first-order, pseudo-first order and pseudo-second order kinetic reaction models. The rate constants of adsorption for all these kinetic models have been calculated. Results showed that the intraparticle diffusion and initial sorption into resins of Cu(II) in the ion exchange resins was the main rate limiting step. The uptake of copper by the ion exchange resins was reversible and thus has good potential for the removal/recovery of copper from aqueous solutions. We conclude that such ion exchange resins can be used for the efficient removal of copper from water and wastewater. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

The formation of feldspar strontian (SrAl2Si2O8) via ceramic route: Reaction mechanism,kinetics and thermodynamics of the process

The reaction mechanism, the equilibrium composition, the temperature range of stability of formed intermediates as well as the kinetics and thermodynamics of activated state during the formation of monoclinic strontium-aluminum-silicate feldspar stroncian (SrAl₂Si₂O₈) via the ceramic route from the mixture of SrCO₃, Al₂O₃ and SiO₂ is described in this work. Strontian does not appear up to the temperature of 1150 °C and is the only stable phase at the temperature ≥1600 °C. Three independent reactions lead to two parallel reaction pathways, i.e. the formation of strontian from single or binary oxides (1) and with Sr-gehlenite as the intermediate (2). Since the reaction rate constants ratio is higher than one (k₁/k₂>1), the first reaction route is favored according to the Wegscheider principle. The kinetics of chemical reaction of 1.5 order corresponding to the kinetic function F_2/3 ((1−α)^−1/2−1) was determined as the rate determining the mechanism of formation of strontian. The integral and differential methods show that the process requires average apparent activation energy of 229.3 kJ mol⁻¹. The determined average value of frequency factor is 2.1×10⁵ s⁻¹.     

Biolubricant Production of 2‐Ethylhexyl Palmitate by Transesterification Over Unsupported Potassium Carbonate

Owing to the decrease of global oil price, development of downstream value‐added products is important to biodiesel industry. In this study, we used palmitic acid methyl ester (PAME) as a starting material to produce 2‐ethylhexyl palmitate (2‐EHP), an environmentally friendly biolubricant product, which was derived from the transesterification of fatty acid methyl esters and long chain fatty alcohols. Conventional synthetic routes of 2‐EHP have disadvantages, including high catalyst price, low conversion efficiency, and pollution issues. To solve these problems, in situ transesterification of PAME with 2‐ethylhexanol (2‐EH) was conducted over unsupported potassium carbonate as heterogeneous catalyst. The optimal reaction temperature, 2‐EH to PAME molar ratio, and catalyst to PAME mass ratio were 180 °C, 3:1, and 3.0 wt%, respectively. The PAME conversion reached up to 100% within 1 hour under the optimal conditions. In addition, a kinetic model describing the experimental data over a temperature range of 160–180 °C was developed. The dependence of kinetic rate constant (k) on temperature was evaluated, and the activation energy (E_a) for the transesterification of PAME with 2‐EH was calculated to be 57.04 kJ mol^?1.     

Kinetic analysis of magnesium aluminate spinel formation: Effect of MgO:Al2O3 ratio and titania dopant

The mechanistic pathway of MgO-Al₂O₃ reaction in solid state to form MgAl₂O₄ spinel was investigated to correlate the kinetic parameters with ratio of reactants (MgO:Al₂O₃) and with the presence of a doping agent, TiO₂. The time-temperature-expansion data of oxide compacts was analyzed using several model free analyses and model based (linear and non-linear) kinetic algorithms. These indicated that spinel formation process can be best described by single step with n-dimensional Avrami equation for every MgO:Al₂O₃ ratio, irrespective of titania dopant. The activation energy (E_a) of the process was proportional to % spinel formed in each system and validated with quantitative XRD analysis. The higher value of Avrami coefficient (n) in 90 wt% Al₂O₃ compositions has been explained with geometric considerations of powder packing. Incorporations of 1% TiO₂ in the MgO: Al₂O₃ oxide compact did not markedly affect the reaction model, frequency factor and Activation energy.     

MODEL APPLICATION: HYDRATION AND GELATINIZATION DURING RICE PARBOILING

The rate of water absorption of a local rough rice variety at temperatures below and above the corresponding gelatinization temperature was investigated. A mathematical model that describes water diffusion and gelatinization within the grain, was used to simulate rice parboiling. The data were processed using a nonlinear regression procedure to calculate the diffusion coefficients and reaction rate constants in the temperature range 35-95°C. Both coefficients follow an Arrhenius temperature dependency with a break point at 77°C, where rapid gelatinization of rice begins. From the comparison between the activation energies for diffusion and reaction it is concluded that the parboiling process is limited by the reaction of starch with water below 77°C and by diffusion of water above 77°C.     

Theoretical Aspects Of The Kinetics Of Competitive First Reactions Of Ozone In The O3/H2O2 And O3/UV Oxidation Processes

Kinetics of competition between the ozone direct reaction with compounds in water, ozone-hydroperoxide ion reaction leading to free radicals in the O₃/H₂O₂ process, and the photolysis of ozone in the O₃/UV process are discussed in terms of diffusion and reaction times to establish conditions for these reactions to be competitive. Film theory and chemical kinetic concepts then are applied to estimate initial rates of ozone absorption and consumption, removal rates of compounds present in water, and the importance of the radical oxidation path versus direct ozone and/or photolysis reactions.     

聚丙烯与超支化聚酯共混物的非等温动力学(英文)

Polypropylene (PP) with different contents of the second generation hyperbranched polyester (HBP) is prepared by melt blending method. The non-isothermal crystallization kinetics of PP and PP/HBP blends is investigated under differential scanning calorimetry (DSC). The Mo equation is used to analyze the DSC data. The results show that the Mo theory is suitable for crystal ization kinetics of the blends. Fast cooling rate is not good for crys-tallizing and nucleating. The values of half crystal ization time (t1/2), crystal ization enthalpy (ΔHc) and temper-ature range (ΔT) of PP/HBP blends decrease when HBP is added. The required cooling rate of PP is higher than that of PP/HBP blends in order to reach the same relative crystal inity. Crystallization rate increases with the ad-dition of HBP. The crystallization rate reaches a maximum when the content of HBP is 5%. In addition, the activa-tion energies of PP and PP/HBP blends are calculated by Kissinger equation, revealing that the content of HBP has a little effect on the crystallization activation energy.     

表面活性元素影响钢液脱氮动力学

在４０ｋｇ真空感应炉上进行表面活性元素（氧、硫）影响钢液脱氮动力学的研究，实验采用真空碳脱氧工艺，研究在不同的硫含量条件下，钢中脱氧和脱氮的相互关系．研究结果表明：（１）当钢中硫含量较低时，脱氮速率很快，随着硫含量的逐步增加，脱氮速率相应降低．（２）钢中硫含量较低时，脱氮速率快于脱氧速率；而当硫含量较高时，脱氧速率大于脱氮速率．（３）真空碳脱氧过程中，脱碳、脱氧速率与硫含量关系不大．     

蔗渣酶解的动力学模型探讨

以压力为２．０ＭＰａ，时间为２０ｍｉｎ的直接加热膨化蔗渣为对象，采用日本ＹａｋｕｌｔＲＳ纤维素酶进行蔗渣酶解实验，探讨了产物抑制情况，分析和判别了反应类型，由结果可以认为该反应属于非竞争型产物抑制反应，可以用Ｍｉｃｈａｅｌｉｓ－Ｍｅｎｔｅｎ方程的修正式来进行模拟。通过蔗渣浓度为（１．９６～８．９６）×１０－２ｇ／ｍＬ，反应时间为２～９６ｈ的４８组实验数据，以最小二乘法回归出模型参数，计算结果与实验值能较好吻合