聚氨酯中异氰酸酯基测定方法述评

关于聚氨酯中异氨酸酯基的测定,国内外已进行了大量的研究工作。文中对测定聚氨酯中异氛酸酯基的一些主要方法作简要评述,包括化学分析法、分光光度法、红外光谱法、气相色谱法和高压液相色谱法。     

粘度法研究RIM聚氨酯反应动力学

本文根据粘度法测定反应级断ｎ的理论依据，利用旋转粘度计在等温、无催化剂条件下研究ＲＩＭ聚氨酯的反应动力学，发现在异氰酸酯基／羟基（浓度比）等于１．５时，其反应级数为１．３５，这与份数时间法测定的结果相一致。     

Phase diagram and supercritical deoxidation kinetics of manganese oxides in organic solvent N,N-dimethylformamide

Deoxidation of manganese oxides in supercritical N,N-dimethylformamide (SC-DMF) is revealed, contrasting to previous amounts of reports on supercritical water oxidation. Mn₃O₄ and MnO can be produced by the reaction starting from layered manganese oxides (δ-MnO₂) in a uniform supercritical process. Time effect can give rise to the transition to Mn₃O₄ under low temperature, but the prolonged time, under a temperature lower than 200 ̊C, cannot cause this transition. Phase diagram is obtained, including three regions of MnO₂, Mn₃O₄ and MnO as the main material phase. The completion of transition accompanies with an oxygen loss course. Comparison between supercritical oxidation of water and supercritical deoxidation of organic DMF demonstrates the unique mechanisms of supercritical processing. In terms of the surface contacting fluid, deoxidation kinetics has a reciprocal law of growing size for manganese oxides. The new deoxidation procedure using organic solvent is proposed for the processing of metal oxides.     

线性聚醚溴化反应的动力学研究

本文报导热催化法制备烷基直链型溴代聚醚的溴化反应动力学。研究了各因子对溴代聚醚含溴量的影响,并建立了经验方程。     

N,N-二甲基乙酰胺的合成反应动力学

为了给N,N-二甲基乙酰胺的工业生产提供动力学支持,文章研究了二甲胺和冰醋酸直接缩合反应生成N,N-二甲基乙酰胺的本征动力学。在消除外扩散的影响下,考察了质量分数40%二甲胺与醋酸的摩尔比和反应温度对缩合反应的影响。测定和分析了在389.15,397.15,403.15,407.15,418.15 K下的动力学实验数据,利用数据处理软件进行拟合,得到N,N-二甲基乙酰胺的合成反应动力学方程,并通过了实验验证,为反应精馏的优化模拟提供了重要的基础数据。     

Kinetics and mechanism of the hydrogenation process – the state of the art

It is just over a century ago that the first industrial hydrogenation plant for edible oils was commissioned. Although at that time several fatty acids had been identified, the analytical characterization of these oils was mainly by physical properties like melting point, density and refractive index and chemical properties like saponification value and iodine value. Some of these properties were used to follow a hydrogenation reaction. Early kinetic studies of the hydrogenation reaction focused on triglycerides but with the advent of GC, fatty acid compositions became so readily available, that kinetic studies switched to the ‘common fatty acid pool’ concept. According to this concept, the rate of reaction of an unsaturated fatty acid in a triglyceride molecule does not depend on the chemical nature of the other fatty acid moieties in this molecule. The concept greatly simplified the understanding of what happens during a hydrogenation reaction and thereby stimulated research. It took more than 50 years before this concept was shown to be an incorrect assumption. Kinetic studies of the hydrogenation process have also been hampered by the lack of an instrument that can measure the hydrogen concentration in oil. That may well be the reason why this concentration has received rather little attention and that its effect on the relative rates of the various, simultaneously proceeding reactions has only fairly recently become clear. Accordingly, the present review will describe the mechanism of the various reactions that occur during the hydrogenation process and highlight the effect of the hydrogen concentration and the triglyceride composition rather than that of the fatty acid composition. It will discuss industrial process conditions rather than laboratory conditions and therefore limit itself to nickel catalysts. It will also paint the most simple picture that is consistent with generally accepted observations.     

Kinetics of the water–gas shift reaction over nanostructured copper–ceria catalysts

Water–gas shift reaction was studied over two nanostructured Cu_xCe_1−xO_2−y catalysts: a Cu_0.1Ce_0.9O_2−y catalyst prepared by a sol–gel method and a Cu_0.2Ce_0.8O_2−y catalyst prepared by co-precipitation method. A commercial low temperature water–gas shift CuO–ZnO–Al₂O₃ catalyst was used as reference. The kinetics was studied in a plug flow micro reactor at an atmospheric pressure in the temperature interval between 298 and 673 K at two different space velocities: 5.000 and 30.000 h⁻¹, respectively. Experimentally estimated activation energy, E_af, of the forward water–gas shift reaction at CO/H₂O = 1/3 was 51 kJ/mol over the Cu_0.1Ce_0.9O_2−y, 34 kJ/mol over the Cu_0.2Ce_0.8O_2−y and 47 kJ/mol over the CuO–ZnO–Al₂O₃ catalyst. A simple rate expression approximating the water–gas shift process as a single reversible surface reaction was used to fit the experimental data in order to evaluate the rate constants of the forward and backward reactions and of the activation energy for the backward reaction.     

关于氟化氢铵与硅反应的动力学研究

介绍了白炭黑和废砂浆的研究现状,阐述了硅制取白炭黑的两反应两循环新的氟化法工艺路线。利用传统的排水收集气体的方法,并将气体量转化为浓度,研究了氟化氢铵与线切割废砂浆中硅反应的动力学。结果表明,该反应符合二级反应规律[-r=k(C(NH4)HF2)2],确定50℃与60℃条件下的反应速率常数:k50=3.47×10-4mol3/(L.s)和k60=5.62×10-4mol3/(L.s),以及此反应的活化能Ea=43.16 kJ/mol与指前因子A=3 288.85。     

Isocyanate reactions in and with N,N-dimethylformamide

Solutions of phenylisocyanate (I) in DMF were stored at different temperatures in the presence of both polyurethane catalysts and 1,3-diphenylurea (II) . The reaction products were determined by HPLC. Beside the hydrolysis of I to II , a significant reaction of I with II to 1,3,5-triphenylbiuret (III) was observed at 20°C. Above 60°C, I reacted with the solvent to form N,N-dimethyl-N′-phenylformamidine (V) . In DMF, III dissociated to I and II already at temperatures >40°C.     

Kinetics of the water–gas shift reaction on Pt catalysts supported on alumina and ceria

We report the kinetic parameters for the water–gas shift (WGS) reaction on Pt catalysts supported on ceria and alumina under fuel reformer conditions for fuel cell applications (6.8% CO, 8.5% CO₂, 22% H₂O, 37.3% H₂, and 25.4% Ar) at a total pressure of 1 atm and in the temperature range of 180–345 °C. When ceria was used as a support, the turnover rate (TOR) for WGS was 30 times that on alumina supported Pt catalysts. The overall WGS reaction rate (r) on Pt/alumina catalysts as a function of the forward rate (r_f) was found to be: r = r_f(1 − β), where r_f = k_f[CO]^0.1[H₂O]^1.0[CO₂]^−0.1[H₂]^−0.5, k_f is the forward rate constant, β = ([CO₂][H₂])/(K_eq[CO][H₂O]) is the approach to equilibrium, and K_eq is the equilibrium constant for the WGS reaction. The negative apparent reaction orders indicate inhibition of the forward rate by CO₂ and H₂. The surface is saturated with CO on Pt under reaction conditions as confirmed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The small positive apparent reaction order for CO, in concert with the negative order for H₂ and the high CO coverage is explained by a decrease in the heat of adsorption as the CO coverage increases. Kinetic models based on redox-type mechanisms can explain the observed reaction kinetics and can qualitatively predict the changes in CO coverage observed in the DRIFTS study.     

国内外聚氨酯工业发展近况

对近年来聚氨酯工业的发展动态、生产和市场情况进行了介绍,并就国内聚氨酯工业发展的若干问题提出了建议。     

Modeling the Kinetics of Protein Conjugation Reactions

Over the past decades, the pharmaceutical industry has shown a continuous infatuation for therapeutic proteins. In order to constantly improve their efficacy, chemical reactions involving the conjugation of the therapeutic protein with various chemical reagents have been developed. Little efforts have been put forth to simulate the kinetics of protein conjugation and the literature dealing with kinetic models is rather scarce as compared to the abundant references about conjugation reactions in general. In this work, techniques to measure the kinetics of reaction, model the conjugation between add‐on molecules and proteins, and evaluate the model parameters are discussed.     

Kinetics,Thermodynamics, and Isothermic Evaluation in Sorption Study of Hazardous Dye Using Sodium Dodecylsulfate Physically Impregnated in Polyester‐Type Polyurethane Foam

Use of polyester‐type polyurethane foam (PUF) is an effective adsorbent for the removal of hazardous dye: crystal violet (CV) from an aqueous solution. In this adsorption study, the formation of hydrophobic ion pair (opposite charge attraction) between the charged species, i.e., cationic (basic) dye CV and anionic surfactant sodium dodecylsulfate (SDS) sorbed onto PUF. Chemical calculations were performed using quantum simulation to understand ion‐pair formation for CV–SDS at the semiempirical PM6 level. Adsorption studies were performed using 200 mg cylindrical PUF with an overhead stirrer in solutions containing varying compositions of the dye–surfactant mixture. The equilibrium thermodynamics and kinetics of the adsorption process were studies by measuring CV dye removal as a function of time and temperature. Results show that the formation of the dye–surfactant ion pair is necessary for effective adsorption onto PUF. Various adsorption isotherms, viz., Langmuir, Freundlich, Temkin, Dubinin–Radushkevich (DRK), Harkin‐Jura, and several kinetic models, viz., pseudo‐first order, pseudo‐second order, Elovich, and Intraparticle diffusion were used to fit the spectrophotometric result. The equilibrium adsorption data fit to the Langmuir isotherm gives the maximum adsorption of PUF as 33.39 mg g^?1 from 200 mL 5.0 × 10^?5 mol L^?1 CV solution at 298.15 K. The kinetics study showed that the overall adsorption process follows pseudo‐second‐order kinetics. The Morris–Weber model suggests that an intraparticle diffusion process is active in controlling the adsorption rate. The Freundlich, Temkin, DRK adsorption isotherms showed that solute dye transfers from solution to the PUF adsorbent surface through physical adsorption. The Langmuir and Harkin‐Jura adsorption isotherms suggest that the adsorbent surface is homogeneous in nature. The thermodynamic data showed that the adsorption process is spontaneous and endothermic with a positive enthalpy change and a negative change in Gibb's energy.     

Kinetics of esterification of propionic acid with n-amyl alcohol in the presence of cation exchange resins

Esterifications of n-amyl alcohol with propionic acid catalyzed by macroporous (Amberlyst-15) and microporous (Dowex 50 W and Amberlite IR-120) polymeric ion-exchange resins were carried out between 333–348 K. When these catalysts were used as commercially available, Amberlyst-15 was observed to be the most effective catalyst with respect to rate constants, but after drying it became the less effective one. The reaction rate increased with increase in catalyst concentration and reaction temperature. Stirrer speed and different mesh sizes had virtually no effect on the rate under the experimental conditions. The effect of divinylbenzene content was examined for the microporous resin Dowex 50W, and the results showed that the propionic acid conversion decreased as the divinylbenzene content was increased. The rate data were correlated with a second-order homogeneous reaction model. The apparent activation energies, reaction enthalpies and entropy values were calculated for each catalyst. Reaction monitoring is simple and fast by volumetric method and the reproducibility of this method was the order of ± %2.54.     

Analytical expression for the non-isothermal effectiveness factor: the nth-order reaction in a slab geometry

The problem of calculating the effectiveness factor for a porous slab of catalyst pellet under non-isothermal conditions has been revisited. An exact formal analytical solution was obtained for a nth-order (integer n?0), exothermic and irreversible chemical reaction. Numerical calculations where performed, and an analytical formula was obtained for the very fast reaction limit. In addition, a fairly simple formula, which was called the low beta approximation, was developed and tested to be valid for low values of the thermicity group β?0.1.     

A hybrid stochastic-deterministic algorithm for lattice-gas models of catalytic reactions and the computation of TPD spectra

We present a hybrid numerical approach for modeling surface reactions in the framework of a lattice-gas model with lateral interactions between adsorbed particles. A hybrid multiscale algorithm, which we refer to as Quasi-Equilibrium Kinetic Monte Carlo (QE-KMC), comprises traditional Metropolis Monte Carlo (MMC) simulations of equilibrium systems and standard numerical methods for deterministic ordinary differential equations (ODEs). The functional dependence of these ODEs on the macroscopic state variables (adsorbate coverages) is not explicitly known, but their right-hand sides can be evaluated “on the fly” with prescribed accuracy by means of the MMC simulations. At the time scale of these ODEs it is assumed that an equilibrium statistical distribution of adsorbed particles on an infinite lattice is attained at every moment in time due to infinitely fast surface diffusion. QE-KMC and conventional KMC simulations are used to study the temperature-programmed desorption (TPD) spectra of adsorbed particles. We critically discuss results of previous studies that applied Monte Carlo simulations to describe the TPD spectra in the case of fast adsorbate diffusion and strong lateral interactions. We show that the quasi-equilibrium TPD spectra can be quickly and accurately estimated by the QE-KMC algorithm, while the KMC simulations require much more extensive computational resources to obtain the same results.     

Impact of Fluorinated Cobalt(II) Phthalocyanine Catalysts on Aerobic Thiol Oxidation Kinetics

Kinetic studies were conducted for the aerobic oxidation of 2-mercaptoethanol (2-ME) and 4-fluorobenzenethiol (4-FBT) catalyzed by cobalt(II) phthalocyanines: H₁₆PcCo, F₁₆PcCo, and F₆₄PcCo, each exhibiting a metal center subject to increasing Lewis acidity and steric hindrance. The experiments were performed in a reaction-limited, isothermal, bench-scale, batch reactor, with thiol concentrations measured using GC/FID. Conversions of 2-ME to 2-hydroxyethyl disulfide and 4-FBT to 4-fluorophenyl disulfide in excess of 90% were achieved. Kinetic analyses suggest that the substrate binding and electron transfer are directly related to the Lewis acidity and steric bulkiness of catalyst molecules. Substrate binding was found to be the slow step for thiol oxidations catalyzed by H₁₆PcCo. The rate-determining step for thiol oxidations, catalyzed by F₁₆PcCo and F₆₄PcCo, is the expulsion of the thiyl radical (RS^?) from the catalyst molecule.