Phase separation of the reaction system induced by CO2 and conversion enhancement for the esterification of acetic acid with ethanol in ionic liquid

The effect of CO2 on the phase behavior of the reaction system and equilibrium conversion for esterification of acetic acid and ethanol in ionic liquid (1-butyl-3-methylimidazolium hydrogen sulfate, [bmim][HSO4]) was studied at 60.0 degrees C up to 15 MPa. It was demonstrated that there was only one phase in the reaction system in the absence of CO2. The reaction system underwent two-phase-->three-phase-->two-phase transitions with increasing pressure. The pressure of CO2 or the phase behavior of the system affected the equilibrium conversion of the reaction markedly. As the pressure was less than 3.5 MPa, there were two phases in the system, and the equilibrium conversion increased as pressure was increased. In the pressure range of 3.5-9.5 MPa, there existed three phases, and the equilibrium conversion increased more rapidly with increasing pressure. As the pressure was higher than 9.5 MPa, the reaction system entered another two-phase region and the equilibrium conversion was nearly independent of pressure. The total equilibrium conversion was 64% without CO2 and could be as high as 80% as pressure was higher than 9.0 MPa. The apparent equilibrium constants (K(x)) in different phases were also determined, showing that the K(x) in the middle phase or top phase was much greater than that in the bottom phase.     

Chiral recognition of the Schiff bases by NMR spectroscopy in the presence of a chiral dirhodium complex. Deuterium isotope effect on 13C chemical shift of the optically active Schiff bases and their dirhodium adducts

The dirhodium method has been successfully applied in chiral recognition of the optically active Schiff bases, derivatives of ortho-hydroxyaldehydes existing in the NH-form. or at tautomeric equilibrium. The position of the equilibrium of Schiff bases as well as their adducts has been established on the basis of measurements of deuterium isotope effects on 13C chemical shifts. The presence of the proton transfer equilibrium or NH-tautomer has promoted the adduct formation. At the equilibrium state, formation of the adducts has shifted the proton transfer equilibrium towards the NH-form. The binding site was the oxygen atom of the proton donor group.     

Determination of polybutylene terephthalate polycondensation equilibrium constant using a batch reactor

The PBT polycondensation equilibrium constant at 255°C was determined using a batch reactor. Starting from a Polybutylene terephthalate (PBT) prepolymer having a degree of polymerisation of 12.7, equilibrium experiments were performed in the range of 1 to 50 mbar. The equilibrium degree of polymerisation (i) was determined indirectly using dilute solution viscometry of a solution of 1 weight % PBT in m - cresol. The degree of polymerisation of PBT obtained at equilibrium in the range of 1 to 50 mbar at 255°C as a function of the BDO partial pressure (mbar) could be expressed by: i = 111.47 − 86.18 exp(−1.14 equation/tex2gif-stack-1.gif). The equilibrium solubility of 1,4 butanediol (BDO) in the PBT melt was derived form the BDO partial pressure using the Flory - Huggins theory. The PBT polycondensation reaction equilibrium constant was related to the degree of polymerisation by the equation: in the range i = 26 − 100. The PBT polycondensation equilibrium constant at high degrees of polymerisation is in line with literature data and thermodynamics.     

Reaction and phase equilibria of esterification of isoamyl alcohol and acetic acid at 760 mm Hg

The thermodynamic behavior of esterification reaction equilibrium and vapor–liquid equilibrium (VLE) of acetic acid and isoamyl alcohol mixture and its products, isoamyl acetate and water were investigated in this study. The experiments of chemical and phase equilibria were conducted in an Othmer type equilibrium cell. Since this esterification reaction proceeds very slowly, thus, a commercial Y type zeolite, NaY catalyst, was added to accelerate reaction rate such that the reaction equilibrium will be reached sooner and before phase equilibrium is considered. Using experimental data and phase and reaction equilibrium equations, the reaction equilibrium constants were calculated at different temperatures. The experimental results showed that the reaction equilibrium constant was very slightly dependent on temperature. The experimental data were then correlated by the Wilson, NRTL, and UNIQUAC models with the consideration of association effect of acetic acid in vapor phase. The concept of transformation composition by Barbosa and Doherty [D. Barbosa, M.F. Doherty, 1987, Proc. R. Soc. London Ser. A 413, 443–459.] was applied to construct three-dimensional figures showing experimental data and the calculated composition surfaces. It is observed from figures that the reactive azeotropy described by Barbosa and Doherty does not exist for this quaternary mixture. This study provides the required thermodynamic information for the development and design of this esterification process.     

化学平衡的本质——浅谈混合熵对化学平衡的贡献

化学平衡是物理化学的重要内容之一。化学反应的等温方程式,给出了平衡常数与标准摩尔反应Gibbs自由能的关系。然而,仅从化学反应等温方程式还很难理解混合熵对化学平衡贡献的本质。本文建立了理想气体体系Gibbs自由能与反应进度的关系,给出了三个理想气体反应体系Gibbs自由能与反应进度的具体关系,分析了混合熵对化学平衡的本质贡献。     

支化高分子溶胶-凝胶相变的热力学

以典型的Aa-Bb型缩聚反应为例, 应用统计力学和热力学的基本原理对反应体系的一些平衡特征进行研究. 基于从两种不同角度所构造的正则配分函数, 导出反应体系的平衡自由能以及质量作用定律的解析形式, 同时指出获得数量分布函数的新方法, 并通过计算反应体系的等温压缩系数从而得到反应体系的凝胶化条件. 进一步利用数量分布函数的不变性, 给出临界点后溶胶相和凝胶相的平衡自由能, 探讨了溶胶-凝胶相变的相关问题.     

An improved model for predicting hydrate phase equilibrium in marine sediment environment

Based on the models of hydrate phase equilibrium in bulk water and porous media, an improved model was proposed to predict the methane hydrate equilibrium in marine sediment environment. In the suggested model, mechanical equilibrium of force between the interfaces in hydrate-liquid-vapor system was considered. When electrolyte was present in pore water, interfacial energy between hydrate and liquid was corrected by an equation that is expressed as the function of temperature and electrolyte concentration. The activity of water is calculated based on the Pitzer model and the interfacial energy between liquid and gas is solved using the Li method. The prediction results show good agreement with the experimental data. By comparison with other models, it is proved that this model can improve the accuracy for predicting hydrate phase equilibrium in marine sediment environment.     

基于PC-SAFT方程研究多孔介质中水合物相平衡的预测模型

对多孔介质中水合物的形成条件预测模型进行了研究.利用微扰链-统计缔合流体理论状态方程(PC-SAFT)结合van der Waals-Platteuw模型和毛细管Kelvin模型,建立了用于多孔介质水合物体系的相平衡预测模型.在此模型基础上,针对甲烷水合物和CO2水合物对界面张力作了进一步的研究.根据多孔介质水合物相平...     

Elution Behaviour of Monocarboxylic Acids on a Cation-exchange Resin Column

The retention mechanism of monocarboxylic acids on a cation-exchange resin column was investigated. It was assumed that both Donnan membrane equilibrium and adsorption equilibrium were involved in the chromatographic process. On the basis of the proposed mechanism, an equation was derived for correlating distribution coefficient, Kd, dissociation constant, Aa, and adsorption equilibrium constant, K, of the analyzed acid. By this approach, retention data for some aliphatic acids under different operating conditions were predicted. Results are reasonably in agreement with experiment.     

异丁烷脱氢反应的热力学分析

利用HSC5.0软件对异丁烷脱氢反应进行热力学分析,计算了异丁烷脱氢过程中各反应的平衡常数和不同温度、压力及氢烃比的异丁烷脱氢反应的平衡转化率.结果显示,裂解反应平衡常数比脱氢反应大约3个数量级,在热力学上裂解反应更易进行.在异丁烯异构化产物中,trans-C4 H8生成的平衡常数最大,cis-C4 H8其次,1-C4...     

Chemical equilibrium of glycerol carbonate synthesis from glycerol

In this paper, the chemical equilibrium for the glycerol carbonate preparation from glycerol was investigated. The chemical equilibrium constants were calculated for the reactions to produce glycerol carbonate from glycerol. The theoretical calculation was compared with the experimental results for the transesterification of glycerol with dimethyl carbonate. Transesterification of glycerol with cyclic carbonates or alkyl carbonates is thermodynamically favourable for producing glycerol carbonate from glycerol according to the equilibrium constant. Increasing temperature can increase the chemical equilibrium constant for the reaction of glycerol with dimethyl carbonate. For the reaction of glycerol with ethylene carbonate, increasing temperature can decrease the chemical equilibrium constant. The reaction of glycerol with carbon dioxide is thermodynamically limited. High temperature and low pressure are favourable to the reaction of glycerol and urea.     

含不同价态的多组份体系萃取平衡算法研究

基于萃取平衡计算的计算机模拟是研究稀土分离工艺的重要手段,在实践中获得了成功应用。在实际稀土萃取分离过程中,除三价稀土离子外还存在着不同价态的其他离子,如Na+,Ca2+,Mg2+,Eu2+,Fe3+,Al3+,Ce4+,Th4+等。研究不同价态离子共存条件下的萃取平衡计算方法,对于研究实际萃取分离体系中非稀土元素及变价稀土元素的行为具有重要意义。本文从酸性萃取剂体系中n价阳离子的萃取平衡关系出发,推导出萃取平衡计算的多元方程组,并将其简化为一元方程后给出了抛物线逼近的数值求解方法。通过对数据实例的计算表明,算法收敛快速稳定,适用于含不同价态多组份体系的萃取平衡计算。     

Defect disorder of titanium dioxide

The present work derived defect disorder diagram representing the effect of oxygen activity on the concentration of both ionic and electronic defects for undoped TiO2. This diagram was determined using the equilibrium constants derived in the present work, including (i) the intrinsic electronic equilibrium constant, (ii) the equilibrium constant for the formation of oxygen vacancies, and (iii) equilibrium constant for the formation of titanium vacancies. These equilibrium constants are consistent with three properties determined independently, including: electrical conductivity, thermoelectric power and change of mass determined by thermogravimetry. The derived defect disorder diagram may be used for tailoring semiconducting properties of TiO2 that are desired for specific applications through the selection of optimized processing conditions.     

采用液上色谱法测定污水中微量有机氟化合物

采用液上色谱法(缩写为HSGC)测定水中有机氯化物已有报道,但测定有机氟化合物未见报道,本文运用测定污水中有机氯化合物的原理,建立污水中有机氟化合物的测定方法,结果八氟丁烯的最小检测浓度为10^{-2ppm.经一年间断考察,方法的重现性较好。}     

Equilibrium distribution of permeants in polyelectrolyte microcapsules filled with negatively charged polyelectrolyte: the influence of ionic strength and solvent polarity

The effects of ionic strength and solvent polarity on the equilibrium distribution of fluorescein (FL) and FITC-dextran between the interior of polyelectrolyte multilayer microcapsules filled with negatively charged strong polyelectrolyte and the bulk solution were systematically investigated. A negatively charged strong polyelectrolyte, poly(styrene sulfonate) (PSS), used for CaCO3 core fabrication, was entrapped inside the capsules. Due to the semipermeability of the capsule wall, a Donnan equilibrium between the inner solution within the capsules and the bulk solution was created. The equilibrium distribution of the negatively charged permeants was investigated by means of confocal laser scanning microscopy as a function of ionic strength and solvent polarity. The equilibrium distribution of the negatively charged permeants could be tuned by increasing the bulk ionic strength to decrease the Donnan potential. Decreasing the solvent polarity also could enhance the permeation of FL, which induces a sudden increase of permeation when the ethanol volume fraction was higher than 0.7. This is mainly attributed to the precipitation of PSS. A theoretical model combining the Donnan equilibrium and Manning counterion condensation was employed to discuss the results.     

Tautomeric Equilibrium in Polyfluoroalkylated 5,6,7,8-Tetrahydrofurans by IR Spectroscopy

The tautomeric equilibrium in substituted 5,6,7,8-tetrahydroquinazolines was studied by IR spectroscopy. The effect of various substitutents in the pyrimidine ring and the solvent on the state of the tautomeric equilibrium was evaluated.     

复杂酸碱平衡系统的信号流图解法

用两种方法构建了二元酸平衡系统信号流图,应用信号流图操作规则对图操作,得到了关于二元酸平衡系统的正确计算结果.建立表示混合酸碱平衡系统信号流图,由图能简捷准确给出酸碱任意混合时溶液的[H ]精确式.     

Thermodynamic equilibrium of adsorbed phases

The types of phase equilibrium behavior for adsorbed binary mixtures that can be predicted by an equation of state (EOS) based on the lattice gas theory are investigated. The equilibrium conditions were obtained by solving the isofugacity equations between adsorbed phases. It is observed that the investigated EOS can predict complex behavior for adsorbed phases such as the existence of azeotropes, and retrograde and double retrograde phase transition phenomena, that are analogous to those found in bulk phase equilibrium. Furthermore, it was possible to find systems that presented phase equilibrium between two dense adsorbed phases, analogously to liquid–liquid equilibrium for bulk phases. Experimental data would be necessary to confirm the types of adsorbed phase behavior predicted by the calculations presented.     

Redox equilibria of iron oxides in aqueous-based magnetite dispersions: effect of pH and redox potential

The effect of pH and redox potential on the redox equilibria of iron oxides in aqueous-based magnetite dispersions was investigated. The ionic activities of each dissolved iron species in equilibrium with magnetite nanoparticles were determined and contoured within the Eh-pH framework of a composite stability diagram. Both standard redox potentials and equilibrium constants for all major iron oxide redox equilibria in magnetite dispersions were found to differ from values reported for noncolloidal systems. The "triple point" position of redox equilibrium among Fe(II) ions, magnetite, and hematite shifted to a higher standard redox potential and an equilibrium constant which was several orders of magnitude higher. The predominant area of magnetite stability was enlarged to cover a wider range of both pH and redox potentials as compared to that of a noncolloidal magnetite system.