The principle of critical simplification in chemical kinetics

The paper introduces the concept of critical simplification for chemical kinetics. The principle is valid in the presence of a dominant competitive reaction and critical phenomena. A justification based on singular perturbation and bifurcation analysis is provided. A simple methodology is identified by which kinetic mechanisms and reaction rate parameters may be readily identified from a mono-parametric experiment (reaction rate vs. reaction parameter).     

INVESTIGATION OF INSTABILITY OF OXIDATION OF H2 AND NH3 + H2 PLATINUM

Kinetics of oxidation reactions of H₂; and mixture H₂ + NH₃ on Pt has been studied at atmospheric pressure using a compensative electrothermography method. Existence of multiple steady states of catalyst activity and of isothermal critical phenomena is demonstrated for the system H₂ + O₂. Regions of reaction occurence are singled out and studied. Relaxation autooscillations of activity are detected. The phenomena observed are interpreted in terms of the hypothesis of branching-chain surface process. The study of critical phenomena in the mixture H₂ + NH₃; points to a common nature of active centres at oxidation of H₂ and NH₃ on Pt. A possible explanation of physical nature of active centres (a.c.) in the branching-chain surface process is proposed; the hypothesis suggests that a.c. are represented by catalyst adatoms.     

REMOVAL OF HEAVY METAL IONS FROM INDUSTRIAL WASTE WATERS

The reaction of cyclohexene over tellurium loaded NaX zeolite has been studied kinetically and new reaction pathways have been developed to explain observed phenomena. The reaction of cyclohexene is believed to involve extensive disproportionation of cyclohexene molecules and hydrogen transfer between cyclohexene and intermediate cyclohexadiene molecules. The kinetics of the system is discussed in terms of adsorption based rate models.     

KINETIC STUDY OF S-ALKYLATION OF 2-MERCAPTOBENZIMIDAZOLE CATALYZED BY TETRABUTYLAMMONIUM BROMIDE

The S-alkylation of 2-mercaptobenzimidazole (MBI) by α-bromo-m-xylene (RBr) under phase transfer catalytic reaction condition was successfully carried out in an aqueous solution of KOH/organic solvent two-phase medium. No product was obtained from N-alkylation during or after the reaction period by using a limited quantity of α-bromo-m-xylene. The reaction is greatly enhanced by adding a small amount of tetrabutylammonium bromide (TBAB) and/or potassium hydroxide. Based on the experimental evidence, a rational reaction mechanism is proposed. A kinetic model is derived, from which a pseudo steady-state hypothesis (PSSH) is applied to the reaction system. The kinetic behaviors and the characteristics of the reaction are sufficiently described by the pseudo first-order rate law. The effects of the reaction conditions, including agitation speed, amount of TBAB catalyst, amount of KOH, quaternary ammonium salts, volume of water, volume of dichloromethane, amount of 2-mercaptobenzimidazole, amount of α-bromo-m-xylene, inorganic salts, organic solvents, and temperature on the conversion of the reactant and the apparent rate constants (k_app) were investigated in detailed. Rational explanations are provided for the observed phenomena from experimental results.     

Kinetic behaviour and product formation in polymerization reactors operating at high viscosity

Reaction kinetics in bulk polymerization reactors are influenced by the presence of accumulated polymer. At high viscosity, the mobility of some polymer radicals becomes reduced. A reaction scheme which allows for this phenomena is compatible with the polymerization kinetics. Cases in which radical combination is important are examined in detail. Styrene polymerization is used as an example. Experimental results, from a continuous-flow back-mixed reactor and from batch reactors, are used to show that polymer molecular weight distributions obtained in practice are consistent with predictions from the reaction scheme. Reaction schemes which require growing radicals to be influenced equally by the presence of polymer are incompatible with the molecular weight data.     

SiO2表面上制备纳米TiO2中水量对TiO2含量和形貌的影响

利用吸附相反应技术在SiO2表面原位制备了纳米TiO2,研究水的加入量对TiO2粒子制备的影响。用分光光度法测定乙醇体相中Ti含量随反应时间的变化,发现Ti含量呈现先快后慢的变化趋势,且水量在1．0～1．1ml。时Ti含量出现急剧变大。Ti含量的这一突变区域通过电子色散能谱仪对载体SiO2表面Ti含量的测定得到了进一步地确定。由透射电子显微镜观察到SiO2表面TiO2粒子存在着两种不同的形貌：覆盖在SiO2表面黑色区域和直径在1nm左右的单一小粒子。X射线衍射分析表明：TiO2晶粒粒径随着水量的增加而变大。实验结果发现：在不同的水量下,钛酸丁酯能够与吸附层和乙醇体相中的水以及SiO2表面羟基发生水解缩合反应。3种反应的不同反应速率导致了Ti含量曲线中的不同斜率,另外钛酸丁酯在醇体相中的水解也导致体系中Ti含量的急剧变大。     

BIOLOGICAL EXTRACTION OF METALS: THE RATE-CONTROLLING STEP

Although an enormous amount of work has been done in the area of biohydrometalJurgy, the influence of the inert solid matrix on metal extraction, and consequently the rate-controlling mechanism have not been fully understood. Actually, most studies have mainly focused on the bioextraction of metals from high-grade mineral concentrates. Such an approach is important in elucidating the diffusion and reaction phenomena that are taking place on the surface of the mineral. In reality, however, the mineral is embedded within an inert solid matrix which will have significant effects on diffusion and chemical reaction rate processes. In this work, a detailed experimental kinetic study was conducted to incorporate this factor in an attempt to quantify the rate-controlling mechanism involved. The biological dissolution of pyrite in the presence of acidophilic Thiobacillus ferrooxidans was investigated in a batch experiments on three distinct mine waste rocks. The experiments were conducted on two particle sizes and at three operating temperatures. Based on particle size and activation energies results, it was found that intraparticle mass transfer resistances were solely the rate-controlling mechanism for this process This new finding is different from that reported by other investigators who underestimated the importance of intraparticle mass transfer resistances. Also, because similar processes are ubiquitous in nature, this work should have broad applications.     

TiAl对燃烧合成Ti_2AlC的影响

以单质粉末Ti,Al和炭黑为原料,添加一定量燃烧合成法自制的金属间化合物TiAl,在保持总配方中Ti2AlC化学计量比不变时,研究了TiAl对燃烧合成产物的影响。结果表明:不添加或添加质量分数为20%～35%的TiAl,燃烧合成产物的主晶相均为Ti3AlC2,只含有少量Ti2AlC。产物中Ti3AlC2量随添加TiAl量增加而增加,而Ti2AlC相的含量基本不变。生成Ti2AlC和Ti3AlC2的反应是Ti-Al-C燃烧反应体系中的平行反应,实验中生成Ti3AlC2的速率大于生成Ti2AlC的速率。金属间化合物TiAl不是控制燃烧合成Ti2AlC反应速率的物质,而是控制燃烧合成Ti3AlC2反应速率的物质之一。从化学反应动力学和热力学角度探讨了TiAl对Ti-Al-C体系燃烧合成过程的影响机理。     

INVESTIGATION OF INSTABILITY OF OXIDATION OF H2 AND NH3 + H2 PLATINUM

Abstract

Kinetics of oxidation reactions of H₂; and mixture H₂ + NH₃ on Pt has been studied at atmospheric pressure using a compensative electrothermography method. Existence of multiple steady states of catalyst activity and of isothermal critical phenomena is demonstrated for the system H₂ + O₂. Regions of reaction occurence are singled out and studied. Relaxation autooscillations of activity are detected. The phenomena observed are interpreted in terms of the hypothesis of branching-chain surface process. The study of critical phenomena in the mixture H₂ + NH₃; points to a common nature of active centres at oxidation of H₂ and NH₃ on Pt. A possible explanation of physical nature of active centres (a.c.) in the branching-chain surface process is proposed; the hypothesis suggests that a.c. are represented by catalyst adatoms.     

自由基聚合/扩散动力学模型与仿真

基于自由体积和反应动力学理论,考虑了非稳态过程“笼蔽效应”对引发效率的影响,大分子自由基质心扩散、链段重排扩散、反应扩散对速率常数的影响,聚合物系体积变化对浓度的影响,松弛效应对于自由体积的影响.建立了自由基聚合动力学模型,并就苯乙烯本体聚合作了仿真验证.     

Transient diffusion and reaction of ions in an electrostatic double-layer: Application to the response of potentiometric electrodes

The transport equations for unsteady diffusion and simultaneous chemical reaction in an electrostatic double-layer in series with a mass transfer boundary layer have been solved. The results are presented in terms of the transient response of a potentiometric electrode, and show hysteresis and non-first-order behavior associated with the transport phenomena in the double-layer. The double-layer effects can be reduced and even eliminated in the presence of chemical reaction, which provides an alternate mechanism for ion transport within the double-layer.     

持续振荡行为的动力学模拟

作者已经研究了甲醇在 KY 分子筛上催化氧化的振荡行为。本文进一步探讨反应的机理,对表面覆盖度、表面温度和产物浓度随时间变化的非线性方程组进行稳定性分析。证明了极限环和周期解的存在性。数值计算模拟了实验得到的振荡行为,结果与实验现象和分析较好吻合。     

非离子表面活性剂乳液体系抗聚并稳定性的实验与分析

实验考察了非离子表面活性剂TX和AEO乳化白油所得乳液体系抗聚并稳定性随电解质浓度和表面活性剂HLB值的变化规律 .针对上述体系建立了两液珠间的静态力学模型 .利用模型考察了界面电位和电解质浓度对两液珠间作用力的影响 .通过分析上述模型模拟结果和实验现象之间的矛盾 ,指出在液珠的碰撞过程中 ,表面活性剂分子在界面静电排斥力的作用下 ,存在着被挤入到分散相液珠内的趋势 ,从而导致了界面的变形和表面活性剂空穴区的形成 ,阐述了乳液珠滴发生聚并的一种微观机制     

Copolymerization of styrene and acrylonitrile in the presence of ethylene-propylene copolymer

Summary The degree of conversion, intrinsic viscosity, composition and particle average size distribution of styrene (S)- acrylonitrile (AN) copolymer, formed mainly under heterogeneous conditions and in the presence of EPM, were investigated as function of the reaction time. An induction period, characterized by unstable preferential solvatation phenomena, is followed by a regular copolymerization period which can be described by apparent S and AN reactivity ratios. The regular copolymerization at high conversion is ascribed to the formation of EPM-g-SAN which acts as an emulsifier in the reaction system.Dedicated to Prof. Dr. Hermann Mark on the occasion of his 85th birthday     

脱硫工艺中氧对N-甲基二乙醇胺的降解影响及对策研究

根据齐鲁石化公司炼厂用ＭＤＥＡ从酸性废气中回收Ｈ２Ｓ装置中出现的胺液降解的现象,用大量的分析和实验结果,对氧引起ＭＤＥＡ降解反应机理和对其它物质引起降解反应的影响进行了详细的分析与讨论,并提出相应的抑制措施     

钠与水反应实验的改进

针对人教版化学教材中钠与水反应实验的传统装置存在钠粒乱溅、无法检验生成的气体是氢气而缺乏实验严谨性等不足之处,利用微型化学仪器进行了改进,将研究钠与水反应的现象和产物研究一体化,保证实验的完整性,提高其可操作性。     

THE KINETIC FOUNDATIONS AND THE PRACTICAL APPLICATION OF THE TIME ON STREAM THEORY OF CATALYST DECAY

Perhaps the most difficult practical problem in the study of catalysis is presented by the loss of catalyst activity during reaction. This very complicated phenomenon is made even more confusing by the wide variety of deactivation phenomena and the lack of systematization in this field of research. Consequently little fundamental work has been done on systems in which the catalyst is subject to deactivation. This review proposes to focus on one broad type of catalyst deactivation which also happens to be the most common type of deactivation found in practice.     

环氧丙烯酸双酯树脂的合成与表征

探讨了季铵盐催化环氧树脂与丙烯酸的酯化反应过程中催化剂、反应温度、反应时间对反应过程的影响 ,对反应产物进行了化学分析和红外光谱表征。结果表明 ,反应过程中环氧基团和羧基基团的消耗速率是相当的 ,适当提高温度有利于酯化反应的进行