Optimal time-varying potential control

As an illustration of the potential utility of optimal-control theory, we determine the time-varying electrode potential which maximizes the desired product produced from a coupled, chemical-electrochemical reaction sequence occurring in a well-mixed batch reactor for a specified reaction time. The reactant is electrochemically reduced to a stable intermediate which is itself a reactant for two competing parallel reactions: a homogeneous chemical decomposition to the desired product, or a further electrochemical reduction to an undesired product. If the transfer coefficient of the first reaction is greater than that of the second, then chattering control, in which the potential switches at an infinite frequency between two limits, is optimal. If the transfer coefficients have the opposite relationship, then a continuous, time-varying potential is optimal. We compare the results of applying the optimal, chattering-potential control with those resulting from the best continuous and steady controls. Improved selectivity results from a chattering control and may be effected even in the presence of significant mass-transfer resistance. Since an infinite-frequency control cannot be actually implemented, we discuss how a high-frequency, rectangular waveform can be determined which results in essentially the same product distribution as a chattering control. A qualitative, simple-to-apply method to determine whether selectivity enhancement is attainable using chattering controls is also illustrated.     

蒎烯水合反应及其副产物分析

通过蒎烯水合反应生成主产物和副产物的分析,研究其与反应历程的关系。采用硫酸催化蒎烯的水合反应。考察了反应物配比、硫酸的浓度和反应温度等因素对反应结果的影响;同时对副产物的组成进行了GC-MS分析。结果表明,反应温度在15-20℃,硫酸浓度在27％时水合萜二醇的产率在89％以上,副产物1,4-桉叶油素等占50％以上。产物的比例是与水合反应历程有关。     

Steady-state multiplicity in the autohumidification polymer electrolyte membrane fuel cell

“Ignition/extinction” phenomena and steady-state multiplicity were discovered in an autohumidification polymer electrolyte membrane fuel cell. At steady state, the water produced by the fuel cell reaction is balanced by water removal by the flowing reactant gas streams. Ignition, corresponding to a high fuel cell current, arises from positive feedback between the water produced by the reaction and the transport of protons in the membrane. A critical level of membrane hydration is required for ignition; insufficient membrane hydration will extinguish the fuel cell current. This new autocatalytic mechanism has an interesting analogy to the autothermal reactor.     

MAXIMIZING SELECTIVITY OF LIQUID-LIQUID REACTION SYSTEMS. CONTROL OF THE DISPERSION PROCESS

Currently available information on droplet coalescence and break-up rates in turbulent flows in mixing vessels can be used to control drop sizes in dispersed phase equipment. The effect of drop size distributions on the selectivity and productivity in multi-reaction systems is examined in this paper.

The reaction system features the primary desired product (C) as resulting from reaction (in the bulk phase) between a reactant (A) in the drop phase and a second reactant (B) in the bulk phase. An adverse reaction is also envisaged which consumes (C) by further reaction with (B) to form a waste product. While small drops promote conversion because of large interfacial area, larger drops promote selectivity because of the facility of the product to re-enter the drop phase avoiding further reaction (to form waste) in the bulk phase. The effect of the bivariate distribution of drop size and reactant (A) concentration in the feed to a continuous stirred tank reactor on the selectivity and productivity of (C) is investigated within the framework of film theory while neglecting drop dynamics such as coalescence and break-up.

The results show the selectivity can be substantially improved by controlling drop size and distribution of the reactants among the differently sized droplets. Contrary to conventional wisdom which emphasizes creation of interfacial area by promoting very small droplets, it emerges that optimal distributions of drop size and reactant concentration which maximize productivity of the desired product exist. The practical implications are discussed.     

阻燃剂BDP的合成研究

提出了以双酚A、三氯氧磷和苯酚为原料合成双酚A双二苯基磷酸酯（BDP）。研究了原料配比、反应温度、反应时间等因素对产品质量和收率的影响,从而确定最佳的工艺条件：三氯氧磷、双酚A和苯酚的摩尔比为6：1：4.05,酰氯化反应温度为120℃,保温反应3.5小时,酯化反应阶段,120℃保温反应3小时,150℃保温反应3小时,产品收率为91.12%,BDP单体含量为83.68%。     

阻燃剂RDP的合成研究

提出了以间苯二酚、三氯氧磷和苯酚为原料合成四苯基间苯二酚二磷酸酯（RDP）。研究了原料配比、反应温度、反应时间等因素对产品质量和收率的影响,从而确定最佳的工艺条件：三氯氧磷、间苯二酚和苯酚的摩尔比为5：1：4.2,酰氯化反应温度为114℃,保温反应4小时,酯化反应阶段,120℃保温反应3小时,150℃保温反应3.5小时,产品收率为92.6%,RDP单体含量为72.5%。     

Impact of sand and filler materials on the hydration behavior of calcium aluminate cement

In earlier work, we have observed discrepancies relating to the early hydration of calcium aluminate cement (CAC) when comparing data from heat flow calorimetry of CAC paste with results from mortar strength tests using the crushing method. Here, we investigated on this phenomenon and found that the sand which is used as a filler exerts a major influence on CAC hydration resulting in acceleration. Furthermore, in particular fine filler materials such as, for example, microsilica, fine limestone powder, and especially α- and γ-Al₂O₃ also produced a strong hydration accelerating effect which is dependent on their specific surface area. The mechanism underlying the acceleration is that under alkaline conditions their negative surface charge attracts calcium ions as was confirmed via inductively coupled plasma atomic emission measurements. Such a layer generates favourable conditions for the nucleation of CAC hydration products (C-A-H phases). The resulting crystalline hydrates which form on the surface of the filler particles submerged in CAC cement pore solution were visualized via SEM imaging. This way, specifically selected fillers can significantly accelerate CAC hydration and save precious lithium salts which are commonly used to boost the early strength of CAC.     

A kinetic approach to the esterification of maleic anhydride with methanol on H-Y zeolite

The purpose of this work is to study the kinetics of the esterification of maleic anhydride with methanol to form dimethyl maleate in a batch reactor in the presence of H-Y zeolite as a catalyst. This is a series-parallel type multiple reaction where, the first reaction involves the formation of monomethyl maleate that further reacts with alcohol to form dimethyl maleate. Dimethyl maleate was found to be the only product in the reaction mixture. Temperature, speed of agitation, catalyst size, reactant mole ratio and catalyst loading have pronounced effect on the rate of the reaction. A homogeneous rate model and heterogeneous rate models have been derived and fitted with the experimental data. The activation energy was found to be 44.65 kJ/mol.     

锰矿粉氧化1-萘胺合成1,4-萘醌

在硫酸介质中1-萘胺先形成硫酸铵盐,再经锰矿粉氧化合成1,4-萘醌。考察了反应温度、反应时间、原料摩尔比、反应介质、硫酸质量分数等因素对产品收率的影响。得到较优的反应条件为:1-萘胺1.8 g、n(1-萘胺)∶n(MnO2)=1∶7、w(H2SO4)=40%的硫酸61 g、反应温度80℃、反应时间3 h。在该条件下,1,4-萘醌的收率59.8%。该法具有操作简单、反应时间短和产物易分离等优点。     

Stresses developed in reaction-bonded ceramics

A physical model is presented that predicts the stress distribution created in a particle during its reaction with a surrounding reactant to form a uniform layer of reaction product on its surface, when the reaction involves a volume change. The results of the model are applied specifically to the case of silicon reacting with nitrogen to form Si₃N₄. The model predicts the generation of a high, tensile hydrostatic stress in the Si core as well as high tensile radial stress and compressive tangential stress in the nitride layer. Although the model is restricted to elastic deformation only and therefore predicts unrealistically high stresses in some cases, the results are anyway of relevance in the consideration of possible non-elastic processes such as creep and fracture and also in assessing the possible effect of stress on the reaction equilibrium. It is predicted that the nitride reaction layer would fracture during the nitridation process. A second model is also presented predicting the residual stresses arising during cooling of a partially reacted particle as a result of the difference in thermal expansion of the reactant core and the reaction product layer. In the case of the reaction of silicon to silicon nitride these thermal expansion mismatch stresses are significant but small compared to the stresses due to the chemical reaction. ©     

Kinetics of Tricalcium Aluminate and Tetracalcium Aluminoferrite Hydration in the Presence of Calcium Sulfate

Hydration reactions of C₃A and C₄AF with calcium sulfate hemihydrate and gypsum were investigated and the kinetics of the reactions compared. The rates of C₃A and C₄AF hydration, as determined by heat evolution, vary depending on whether the sulfate-containing reactant is gypsum or calcium sulfate hemihydrate. The following sequence of reactions involving C₄AF occurs when hemihydrate is the reactant: gypsum formation during the first hour, ettringite formation between 20 and 36 hours, and the conversion of ettringite to monosulfate over a period of about 12 hours. Monosulfate formation initiates prior to the complete consumption of gypsum. The onset of this conversion occurs at a shorter hydration time when hemihydrate is a reactant and the total amount of heat evolved is lower. The hydration reactions in saturated calcium hydroxide solution occur more slowly than those in water. Based on heat liberation, C₄AF reacts at a much higher rate than C₃A. Ettringite formation occurs during the first 8 to 9 days of C₃A hydration. Once the gypsum is consumed, ettringite converts to monosulfate during two additional days. Compared to gypsum, hemihydrate decreases the rates of hydration of both C₃A and C₄AF. The effects on the hydration characteristics of C₄AF are significant. The hydration of C₃A with gypsum in water, in saturated Ca(OH)₂ solution, and in 0.3 M NaOH solution were compared. Heat evolution is the lowest for hydration in 0.3 M NaOH. The onset of monosulfate formation occurs prior to the complete reaction between gypsum and C₃A in the NaOH solution.     

The velocity profile and resultant mixing with chemical reaction in rotating tubular flow

The velocity profile in analytical form has been developed for the growing swirl in a rotating tube under stable laminar conditions by solving the equation of motion via perturbation treatments. The resultant mixing induced by fluid flow in the presence of molecular diffusion and chemical reactions has also been characterized. The results suggest that the rotational speed provides an additional degree of freedom with which to vary the level of reactant conversion and of product distribution for a consecutive-competitive reaction.     

硅酸盐水泥基无大孔胶凝材料中金属离子的作用

在聚丙烯酰胺和硅酸盐水泥基无大孔胶凝材料中掺入无机阳离子对聚合物链和水泥水化物的交联反应有着很大的影响，ＳＥＭ和ＥＤＸ的研究结果表明，水泥水化析出和掺入无大孔材料中的无机离子都参与形成交联的阳离子－聚合物复合结构，多价阳离子，如Ａｌ和Ｃａ，与聚丙烯酸交联后相互接触形成稳定的分子结构，对水泥的水化反应影响较小，而单价阳离子（Ｋ和Ｎａ）与聚丙烯酸反应形成不稳定的盐，加速水泥的水化，并促进水泥水析出的多     

Interactions between alite and C3A-gypsum hydrations in model cements

This paper focuses on the interactions that occur between cement phases during early hydration, especially between the hydration of alite and C₃A-gypsum. This study shows that alite reaction is accelerated in the presence of gypsum. This acceleration was attributed to the interaction of gypsum with Aluminium ions present in alite. Three exothermic peaks attributable to the aluminate reaction could be observed in model cements instead of one in C₃A-gypsum systems. The first corresponds to the C₃A dissolution when the sulfate ions run out, but the product formed is ettringite. The second corresponds to the formation of calcium monosulfoaluminate, but the third could not be assigned to any specific reaction. The effect of alite/C₃A ratio, the dispersion of the phases in the grains and the temperature were also investigated. With respect to temperature, it was found that the activation energy for the C₃A-gypsum reaction was higher than that for alite.     

Oxidation reaction kinetics of Athabasca bitumen

The oxidation reaction kinetics of bitumen from Athabasca oil sands have been investigated in a flow-through fixed bed reactor using gas mixtures of various compositions. The system was modelled as an isothermal integral plug-flow reactor. The oxidation of bitumen was found to be first order with respect to oxygen concentration. Two models were examined to describe the kinetics of bitumen oxidation. In the first, the Athabasca bitumen is considered to be a single reactant and the oxidation reaction a single irreversible reaction. The activation energy for the overall reaction was found to be 80 kJ mol^?1. This model is limited to calculating the overall conversion of oxygen. Because the fraction of oxygen reacting to form carbon monoxide and carbon dioxide increases with temperature, a more sophisticated model was proposed to take this into account. The second model assumes that the bitumen is a single reactant and that the oxidation of bitumen may be described by two simultaneous, parallel reactions, one producing oxygenated hydrocarbons and water, the other producing CO and CO₂. The activation energy for the first reaction was found to be 67 kJ mol^?1, and for the second, 145 kJ mol^?1. This more sophisticated model explains the result that at higher temperatures more oxygen is consumed in the oxidation of carbon, because this reaction has a higher activation energy than the reaction leading to the production of oxygenated hydrocarbons and water. This model can also predict the composition of the product gases at various reaction conditions.     

CL-20原料胺的工业制备方法

报道了 CL - 2 0原料胺的一种新的制备方法。在芳香醛存在下 ,苄基氯与氨水反应生成苄基胺 ,加入芳香醛可有效地抑制副产物二苄胺、三苄胺的生成 ,苄基胺的产率达到 70 %以上 ;反应物采用浓氨水可使反应体系体积缩小 ,提高生产能力 ,此方法设备简单 ,操作简便 ,采用密闭操作 ,防止空气污染 ,产率高 ,成本低 ,对降低 CL- 2 0的生产成本有重要意义     

铬铁渣水泥固化体水溶性Cr6+溶出规律及其水化产物

铬铁渣无害化处理与资源化利用主要集中在水泥建筑材料的应用上,但由于缺乏对铬铁渣水泥固化体固化、养护过程及其水化产物中水溶性Cr6+溶出规律和水化反应程度及水化产物的了解,从而限制了铬铁渣的资源化和规模化安全利用水平。以青海某厂铬铁渣为研究对象,对其水溶性Cr6+溶出规律及其水化产物做了研究。结果表明：水溶性Cr6+和Cr3+参与了水泥的水化反应,形成了稳定的水化产物,随着铬铁渣掺量的增加,水泥-铬铁渣复合胶凝材料水化过程中水溶性Cr6+量呈上升趋势,当掺量不大于15%时,水溶性Cr6+质量分数不超过0.000 19%,符合利用铬渣作水泥混合材的标准;铬铁渣作水泥混合材的最佳掺量是10%。     

环己烯水合生产精己二酸提质提量的研究

为提高己二酸生产负荷和产品质量,在对环己醇与硝酸反应机理进行研究的基础上,发现环己烯水合生成环己醇、环己醇与硝酸反应生成己二酸的氧化反应产生的热量及NOx气量较大,制约了氧化反应负荷的提升。通过调整NOx总管压力以及吸收塔吸收液输送阀自控条件,提高氧化反应的空气补入量,同时稳定输送吸收塔吸收液,实现了己二酸装置高负荷连续运行。另外,通过增加原料过滤设施,控制己二酸中丁二酸、戊二酸含量等措施,提高了己二酸产品质量。     

Microstructural development of early age hydration shells around cement grains

An important microstructural aspect of the early hydration of Portland cement (PC) is the formation of a shell of hydration products around cement grains. There is, at present, limited information on the mechanism of formation of the shell and of the chemistry of the phases that constitute the shells. Through the use of STEM imaging of early age hydrated cement pastes as early as 2 h, the present work shows that the shells correspond to the first C-S-H type product formed which has a distinct morphology compared to C-S-H formed later when the main reaction occurs (nucleation and growth stage at setting time). The shells form only around the silicate part of the grain and are not empty but filled with a fragile fibrous C-S-H which appears to have a lower (packing) density than the rest of the hydration products. The cement grains underneath the shells are seen to react unevenly and the hydration seems to follow a reaction front, leaving striations up to 1 µm deep on the grains. Over the long term, the original fragile product seems to densify and gives rise to the usual inner C-S-H. High resolution EDS chemical analysis and mappings were used to get insight into the chemistry associated with the formation of these early age products. The C/S ratio of all C-S-H (inner and outer shell) is the same (within the limits of the analysis accuracy) and evolves insignificantly over the first 24 h of hydration. High concentrations of sulfate are associated with the C-S-H formed during the early development of the microstructure, but these decrease later, the sulfate being mainly incorporated into ettringite.     

Hydration of dibarium silicate II. rate of hydration

The rate of hydration of dibarium silicate (Ba²SiO₄) in paste form at room temperature was investigated. The uncombined barium hydroxide produced in the reaction, determined by a modified Franke method, was used as a measure of the extent of hydration. The linear relationship obtained between the uncombined barium hydroxide and the chemically combined water confirms that similar hydration products are formed at all stages of hydration, and either may be used as a measure of the degree of hydration. The rate of hydration of dibarium silicate was found to be lower than that of tricalcium aluminate, but higher than those of alite, tricalcium silicate and β-dicalcium silicate. The effect of water/solid ratio on the rate of hydration was also investigated. Dibarium silicate was completely hydrated after 30 days when it was mixed with a water/solid weight ratio > 0.7:1.