绝热法研究己内酰胺阴离子聚合尼龙动力学

采用己内酰胺钠盐、N-75缩二脲作为反应催化体系, 确定反应温度在145-160 ℃之间, 通过计算得到动力学参数: 反应级数为准一级、活化能在73.2-77.1 kJ·mol-1之间、指前因子在2.9×1011-3.6×1011 mol1-n·s-1范围内. 本实验条件下测定并计算的反应热为134.5-137.3 J·g-1, 与文献值(138.6 J·g-1)吻合. 并在前人基础上修正并建构了己内酰胺阴离子绝热反应动力学模型, 对反应过程的模拟结果与实验数据基本吻合, 从而证明了本模型的正确合理.     

甲醇制汽油反应及动力学研究

采用等温流动积分反应器，在下列条件范围内：反应温度３６０℃～３９０℃，压力０．１ＭＰａ～４．０ＭＰａ，重量空速５．０ｈ￣－１～１１．Ｏｈ￣－１、对甲酵在ＺＳＭ－５分子筛催化剂上转化制汽油反应进行了研究。根据实验结果，对Ｍｔｈａｉｌ￣［１］提出的甲醇转化成烃类机理做了某些修正。建立了甲醇在ＺＳＭ－５分子筛催化剂上转化成汽油的动力学模型，该模型是一个包括２６个方程的常微分方程组。用Ｇｅａｒ法求解此方程组，用Ｐｏｗｅｌｌ法和Ｍａｒｑｔｉａｒｄｔ法相结合的方法对实验数据进行了回归，求出了每个反应的活化能和指前因子。用此模型预测反应结果，计算值与实验值相符合较好。     

正癸烷加氢裂化集总动力学研究

选用国产３８２５加氢裂化催化剂，对正癸烷加氢裂化动力学进行了研究。根据Ｗｅｅｋ－ｍａｎ集总原理，建立了正癸烷加氢裂化四集总动力学模型。利用Ｍａｒｑｕａｒｄｔ法估计了各反应速度常数，确定了完善的速度表达式。计算了两种压力（６．５和８．５ＭＰａ）下的表观活化能，预测了各反应产物分布，其计算结果与实验值吻合。同时，讨论了空速、温度、压力和反应活化能对产物分布的影响，为重油和渣油加氢裂化集总动力学研究提供     

用新型水溶性偶氮引发剂引发二甲基二烯丙基氯化铵的聚合反应

偶氮双脒式丙烷二盐酸盐在水介质中引发的二甲基二烯丙基氯化铵聚合，其引发速率较用过硫酸铵引发的快，转化率，分子量也较高。对反应助剂Ｎａ４ＥＤＴＡ和水介质的ＰＨ值对两引发体系的影响进行了研究。计算出在绝热聚合条件下三种引发体系的活化能。     

烟酸钠Na(C6H4NO2)(s)的低温热容和热化学

选择分析纯烟酸和无水醋酸钠作为反应物, 用室温固相合成方法合成了无水烟酸钠. 利用FTIR和X射线粉末衍射等方法进行了表征, 利用化学分析和元素分析确定其组成为Na(C6H4NO2). 用精密自动绝热热量计测量其在78~400 K温度区间的低温热容. 研究结果表明, 该化合物在此温度区间无热异常现象发生. 用最小二乘法将实验摩尔热容对温度进行拟合, 得到热容随温度变化的多项式方程. 用此方程进行数值积分, 得到在此温度区间每隔5 K的舒平热容值和相对于298.15 K时的热力学函数值. 在此基础上, 通过设计合理的热化学循环, 选用1 mol/L NaOH溶液作为量热溶剂, 利用等温环境溶解-反应热量计分别测得固相反应的反应物和产物在所选溶剂中的溶解焓, 得到固相反应的反应焓. 最后, 计算出无水烟酸钠的标准摩尔生成焓为: ΔfHm0[Na(C6H4NO2), s]=-(548.96±1.11) kJ/mol.     

3,6-二肼基-1,2,4,5-四嗪的热行为、比热容及绝热至爆时间

利用差示扫描量热法(DSC)、热重-微商热重法(TG-DTG)研究了3,6-二肼基-1,2,4,5-四嗪(DHT)的热行为, 其分解过程可分为两个放热的分解过程, 且热分解反应的表观活化能分别为154.8和123.4 kJ·mol-1, 指前因子分别为1016.63和109.48 s-1. DHT热爆炸的临近温度为426.10 K. 同时, 利用微量热法和理论计算方法研究了DHT的比热容, 298.15 K时的标准摩尔比热容为183.61 J·mol-1·K-1. 计算获得了DHT的绝热至爆时间为263.84-297.58 s之间的某一值.     

物理化学教学中3个易错例题的分析

分析了物理化学中学生容易混淆或犯错的3个案例。[案例1]若从同一始态出发,理想气体经过绝热可逆膨胀和绝热不可逆膨胀2条途径,分别到达相同体积时的终态,其温度、压力的大小如何比较?这个问题的解答不能用最大功原理,因为终态不同,用熵增加原理解释更为科学;[案例2]关于二级反应2A→B,其速率常数及半衰期的计算问题;[案例3]水蒸馏时存在过热现象,要蒸出某个直径的小气泡需要过热多少度?这个问题的解答要用到克劳修斯-克拉贝龙方程,探讨了方程中压力如何取值及代表的意义。     

绝热式热动力学的研究II: 一级反应的热谱解析

本文采用自制的绝热式自动量热计,对两个反应体系进行了一级反应的绝热式热动力学研究.速率常数的计算结果在误差范围内,与文献值符合均好.本文还在实验数据处理中提出了局外过程热效应的线性校正法.     

绝热式热动力学的研究 Ⅱ.一级反应的热谱解析

本文采用自制的绝热式自动量热计,对两个反应体系进行了一级反应的绝热式热动力学研究。速率常数的计算结果在误差范围内,与文献值符合均好。本文还在实验数据处理中提出了局外过程热效应的线性校正法.     

水合邻苯二甲酸钠的合成、结构表征及热化学性质

选择邻苯二甲酸和氢氧化钠作为反应物,利用液相合成方法合成了水合邻苯二甲酸钠.利用X射线粉末衍射、化学与元素分析等方法表征了它的组成和结构.利用精密自动绝热热量计测定了该化合物在78～366K温区的摩尔热容.将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp,m)对温度(T)的多项式方程,用此方程进行数值积分得到此温度区间内每隔5K的舒平热容值和相对于298.15K时的热力学函数值.另外,依据Hess定律,通过设计合理的热化学循环,利用等温环境溶解-反应热量计分别测量了固相量热反应的反应物和产物在所选溶剂中的溶解焓,从而确定反应的反应焓为:ΔrHm=29.073±1.05kJ·mol-1.最后,利用反应的反应焓和其它反应物和产物已知的热力学数据计算出水合邻苯二甲酸钠的标准摩尔生成焓为:-1493.637±1.11kJ·mol-1.     

样条函数逼近法研究环氧树脂固化动力学

采用样条函数逼近DSC曲线,分别对4,5-环氧环已烷1,2-二甲酸二缩水甘油酯、四氢邻苯二甲酸二缩水甘油酯及双酚A二缩水甘油醚与间苯二胺的固化动力学作了研究.结果表明,样条函数逼近DSC曲线有较高的精度,由模拟函数处理实验数据取得较满意的结果.     

Effects of electron correlations in a surface-molecule model for the adiabatic electrochemical electron transfer reactions with allowance for the electrostatic repulsion of electrons on an effective orbital of metal

Within the framework of a surface-molecule model for the adiabatic electrochemical electron transfer reactions, exact expressions for the adiabatic free energy surfaces are obtained and the diagrams of kinetic modes are constructed with allowance made for the electrostatic repulsion between electrons with the opposite spin projection both on the valence orbital of the reactant and on the effective electron orbital of the metal. It is shown that taking into account the electrostatic repulsion on the effective orbital of the metal and the correlation effects connected with it is very substantial for a number of electrochemical electron-transfer reactions and leads not only to an alteration of the activation free energies but also to qualitatively different forms of adiabatic free energy surfaces in some regions of values of the model’s parameters.     

两种量热模式下物质热分解的动力学补偿效应

热分析量热仪主要包括动态、等温、恒温及绝热四种操作模式。很多学者基于动态及等温模式的测试结果,采用Arrhenius速率常数进行动力学计算,进而发现了所谓的“动力学补偿效应”。为了解绝热模式下是否也存在动力学补偿效应,分别采用绝热加速量热法(ARC)及动态差示扫描量热法(DSC)研究了过氧化二异丙苯(DCP)、40%(质量分数,下同)DCP溶液、葡萄糖、45%葡萄糖溶液的热分解特性,在此基础上基于Arrhenius公式计算了对应的表观活化能E和指前因子A,并对计算结果进行了分析。结果表明:绝热模式下,不同质量的同种样品及其溶液的最佳动力学参数,或者同一组数据采用不同的反应级数获得的lnA和E之间均存在明显的线性关系。此外,尽管由动态DSC数据计算获得的E和lnA普遍小于绝热模式的结果,但两种模式下获得的lnA和E之间仍然存在动力学补偿效应。由此可以推断,具有相同或类似反应机理的反应,虽然实验模式不同,但其E和lnA之间存在明显的动力学补偿效应。     

Electron Correlation Effects for Adiabatic Electrochemical Reactions of Electron Transfer in a Model for an Electrode with an Infinitely Wide Conduction Band: Computing Adiabatic Free Energy Surfaces

The adiabatic free energy surfaces for adiabatic electrochemical reactions of electron transfer are calculated in a model for an electrode with an infinitely wide conduction band with exact allowance for electron–electron correlations. The surfaces are analyzed on the basis of a diagram of kinetic modes obtained earlier. It is shown that, as in a surface-molecule model for these reactions, the correlation effects play an essential role and lead to a considerable decrease in the activation free energies and to qualitatively different forms of adiabatic free energy surfaces in certain ranges of model parameters.     

Absolute rate calculations for atom abstractions by radicals: energetic,structural and electronic factors

We calculate transition-state energies of atom-transfer reactions from reaction energies, electrophilicity indices, bond lengths, and vibration frequencies of the reactive bonds. Our calculations do not involve adjustable parameters and uncover new patterns of reactivity. The generality of our model is demonstrated comparing the vibrationally adiabatic barriers obtained for 100 hydrogen-atom transfers with the corresponding experimental activation energies, after correction for the heat capacities of reactants and transition state. The rates of half of these reactions are calculated using the Transition-State Theory with the vibrationally adiabatic path of the Intersecting-State Model and the semiclassical correction for tunneling (ISM/scTST). The calculated rates are within an order of magnitude of the experimental ones at room temperature. The temperature dependencies and kinetic isotope effects of selected systems are also in good agreement with the available experimental data. Our model elucidates the roles of the reaction energy, electrophilicity, structural parameters, and tunneling in the reactivity of these systems and can be applied to make quantitative predictions for new systems.     

High-resolution kinetic energy release distributions and dissociation energies for fullerene ions Cn+, 42 < or = n < or = 90

We have measured the kinetic energy released in the unimolecular dissociation of fullerene ions, Cn+ --> C(n-2)+ + C2, for sizes 42 < or = n < or = 90. A three-sector-field mass spectrometer equipped with two electric sectors has been used in order to ensure that contributions from isotopomers of different masses do not distort the experimental kinetic energy release distributions. We apply the concept of microcanonical temperature to derive from these data the dissociation energies of fullerene cations. They are converted to dissociation energies of neutral fullerenes with help of published adiabatic ionization energies. The results are compared with literature values.     

Critical study of the isoconversional methods of kinetic analysis

A critical study of the use of isoconversional methods for the kinetic analysis of non-isothermal data corresponding to processes with either a real or an apparent variation of the activation energy, E, with the reacted fraction, α, has been carried out using for the first time simulated curves. It has been shown that the activation energies obtained from model-free methods are independent of the heating rate. However, the activation energy shows a very strong dependence of the range of heating rates used for simulating the curves if the apparent change of E with α is caused by overlapping processes with different individual activation energies. This criterion perhaps could be used for determining if a real dependence between E and α is really occurring.     

Compensation effect in the hydrogenation/dehydrogenation kinetics of metal hydrides

The possible existence of a compensation effect, i.e. concurrent changes in activation energy and prefactor, is investigated for the hydrogenation and dehydrogenation kinetics of metal hydrides, by analyzing a series of reported kinetic studies on Mg and LaNi(5) based hydrides. For these systems, we find a clear linear relation between apparent prefactors and apparent activation energies, as obtained from an Arrhenius analysis, indicating the existence of a compensation effect. Large changes in apparent activation energies in the case of Mg based hydrides are rationalized in terms of a dependency of observed apparent activation energy on the degree of surface oxidation, i.e., a physical effect. On the other hand, we find the large concurrent changes in apparent prefactors to be a direct result of the Arrhenius analysis. Thus, we find the observed compensation effect to be an artifact of the data analysis rather than a physical phenomenon. In the case of LaNi(5) based hydrides, observed scatter in reported apparent activation energies is less pronounced supporting the general experience that LaNi(5) is less sensitive toward surface contamination.     

Kinetic behaviour of aluminum naphthenate/benzene system in process of gelation and degradation

The kinetic behaviour of aluminum naphthenate/benzene system in the process of gelation and degradation was systematically studied. The results obtained from the kinetic experiments indicated that the gelation stage was in accordance with a kinetic model of an auto-catalytic first-order reaction, and the degradation stage was a simple first-order reaction. The rate constants in these two stages at various temperaturs were measured. And the determined apparent activation energies for the gelation stage and for the degradation stage are 27.5±2.0 and 37.7±2.3 kJ/mol, respectively.     

Derivatographic investigations of polycarbonates

Derivatographic non-isothermal investigations of the decomposition of PC in air provide useful information on the characteristic decomposition temperatures and the apparent activation energies of the observed steps of decomposition. The following sequence of apparent activation energies of the pyrolysis step was obtained: PC-M>PC-C>PC-A. The values ofE for PC-M are the highest, due to shielding of the ester linkages by the ortho-methyl substituents.This work was supported by a grant from the National Scientific research Committee.