反应密度泛函理论的构建与初步应用

提高化学反应的选择性和转化率是发展绿色化学的重要内容。大部分化学反应都在溶液中发生,溶剂对于反应速率、平衡过程甚至反应机理都有重要的影响。溶剂效应对化学反应影响的理论研究比较缺乏。综述了近年来发展的理论模型及最近本课题组提出的反应密度泛函理论,分别介绍了反应密度泛函理论在水相、有机相、界面体系和限域体系中的应用,分析了不同反应溶剂结构对化学反应自由能分布的影响,总结了溶剂效应的影响机制,最后展望了自洽反应密度泛函理论的构建、反应-扩散耦合研究、聚合物反应密度泛函理论及反应密度泛函理论在反应溶剂筛选、界面反应和电解液设计中的应用。     

伴有平衡反应的分离过程的数学模拟（Ⅲ）化学吸收塔的模拟计算

提出了在绝热填料塔中进行的平衡反应化学吸收的数学模型。应用数值积分法对模型方程进行了求解。模型考虑了反应过程的热效应，应用于伴有快速可逆反应的多组分吸收，非理想系统。对弱电解质体系同样适应。本算法能快速稳定收敛。提出的算法对ＮＨ＿３／Ｈ＿２Ｏ／Ｈ＿２Ｓ过程进行计算，其结果与工业操作数据吻合。     

Calculation of multicomponent multiphase equilibria

An algorithm which gives very good first trial values for the computation of chemical equilibrium composition is proposed. It is based on writing the chemical reactions in “canonical form” and changing the independent component set until it is formed by the species present in greatest quantity at equilibrium. The advancement degrees ξ_r of the reactions are calculated considering the reactions to occur independently of any other. By applying a similar procedure to the series reactor method, a new powerful solution algorithm of the Rosenbrook's type is obtained. In the first method we linearize the equilibrium equations written making null the gradient of the free energy of the system with respect to the corresponding ξ_r whilst in the second one we make successive unidimensional searches solving the equations for ξ_r     

Computing multi-species chemical equilibrium with an algorithm based on the reaction extents

A mathematical model for the solution of a set of chemical equilibrium equations in a multi-species and multiphase chemical system is described. The computer-aid solution of model is achieved by means of a Newton–Raphson method enhanced with a line-search scheme, which deals with the non-negative constrains. The residual function, representing the distance to the equilibrium, is defined from the chemical potential (or Gibbs energy) of the chemical system. Local minimums are potentially avoided by the prioritization of the aqueous reactions with respect to the heterogeneous reactions. The formation and release of gas bubbles is taken into account in the model, limiting the concentration of volatile aqueous species to a maximum value, given by the gas solubility constant.The reaction extents are used as state variables for the numerical method. As a result, the accepted solution satisfies the charge and mass balance equations and the model is fully compatible with general reactive transport models.     

Modeling of vapor-liquid equilibrium of gasoline-ethanol blended fuels for flash boiling simulations

Flash boiling is a physical phenomenon which governs the non-equilibrium phase change of a high temperature fluid as it is depressurized below its vapor pressure. The modeling of this process is of importance to a number of industrial applications and requires the vapor-liquid equilibrium properties of the fluid under consideration. The highly non-ideal nature of gasoline-ethanol fuel blends makes vapor-liquid equilibrium calculations extremely difficult for such fluids. A simple model known as GEFlash (Gasoline-Ethanol Flash), based on existing literature and fundamental chemical engineering thermodynamics is proposed to calculate the properties of gasoline-ethanol fuel blends that are required to perform flash boiling simulations. In addition, a second model based on the chemical engineering software Aspen Plus is also proposed and the predictions of the two models are validated against experimental data available in open literature. The results indicate that both models reproduce the trend in experimental data for vapor pressures and saturated liquid density for blends with different ethanol contents. The GEFlash model does not match the vapor mole fraction predictions of the Aspen Plus model for fuels with low ethanol content (E20 and E40). However, the vapor mole fractions for high ethanol content fuels (greater than E60) are accurate over the majority of the temperature range tested.     

What does the NRTL model look like? Determination of boundaries for different fluid phase equilibrium regions

The adequate correlation of experimental phase equilibrium data by using any thermodynamic model represents a key point for the rigorous design of the chemical processes. However, this data correlation process remains a challenging problem, due to the high nonlinearity of the models used and the consequent problems of convergence. The present work analyzes the nonrandom two-liquids mode (NRTL) model to check the relation between the values of the binary interaction parameters and the corresponding phase equilibria that the NRTL model can or cannot reproduce. Additionally, in the case of the LLE, empirical equations have been established as a function of the nonrandomness parameter, to model the trajectory of the different miscibility boundaries observed. These functions can be used as constraints in the experimental data correlation procedure to reduce the search space and guarantee the consistency of the obtained binary interaction parameters with the experimental behavior of the system under study.     

Analysis of P32 and Ca45 Exchange Between Hydroxyapatite and its Equilibrium Solution

The isotopic exchange of P³² and Ca⁴⁵ with hydroxyapatite was studied along its solubility isotherm. The solution was in a chemical equilibrium with the solid, thus, only isotopic exchange reactions took place in the system. Isotopic dilutions during the exchange process enabled the measurement of a compartment with a very high exchange rate. The other compartments were analyzed using exchange kinetics.     

Reactions at lead electrodes in 5 mol dm−3H2SO4 near the equilibrium potential

The nature of the anodic reactions of lead near the PbSO₄/Pb equilibrium potential depends strongly upon the state of the metal. By an electrochemical etching process a lead surface is produced which participates in a solution controlled dissolution process; a simple chemical etching process results in a solid state process. The natures of these processes are investigated and discussed. The addition of expander materials to the electrolyte solution apparently inhibits both the solution and the solid state processes.On study leave from Chemistry Department, University of Technology, Dresden.     

Mechanism of Flue Gas Desulfurization with Sodium Phosphate Solution

To provide theoretical instructions for experiments and industrial application of regenerative flue gas desulfurization by sodium phosphate solution, the properties of phosphate solution and multiple buffer solution system of phosphoric acid‐sulfurous acid‐sodium salts formed from the desulfurization process were analyzed using the theory of multiple buffer solution combined with the chemical equilibrium principle and computer numerical calculation methods. The influence of pH and phosphate concentration on the distribution coefficient and buffer capacity was calculated and validated by experiments. Results indicate that the distribution coefficient of the species in buffer solution only varied with the solution pH value. The experimental buffer performance was similar to the theoretical value.     

The general theory of polarographic kinetic currents

A unified mathematical formulation of the transport problem to the dropping electrode, accounting for diffusion, chemical reactions in solution and electrode reactions, is given. The method for the reduction of the problem to a diffusion problem where the effect of chemical reactions is restricted to boundary conditions is described. Conditions are defined for appearance of a kinetic current and, on the contrary, of a diffusion current dependent on equilibrium constants of chemical reactions. The general results are exemplified by the case of a single chemical and a single electrode reaction.     

Fuel Conditioning Facility Electrorefiner Model Predictions versus Measurements

Abstract

Electrometallurgical treatment of spent nuclear fuel is performed in the Fuel Conditioning Facility (FCF) at the Idaho National Laboratory (INL) by electrochemically separating uranium from the fission products and structural materials in a vessel called an electrorefiner (ER). To continue processing without waiting for sample analyses to assess process conditions, an ER process model predicts the composition of the ER inventory and effluent streams via multi-component, multi-phase chemical equilibrium for chemical reactions and a numerical solution to differential equations for electro-chemical transport. The results of the process model were compared to the electrorefiner measured data.     

The removal of copper,cadmium, and lead ions from dilute aqueous solutions using foam fractionation

The removal of copper, lead and cadmium ions from aqueous solution by foam fractionation using sodium dodecylbenzene sulphonate (NaDBS) has been experimentally studied and theoretically predicted for solutions with a pH less than 4. A mathematical model of the system consisting of the equilibrium relations of chemical reactions occurring in the system was solved for the equilibrium concentration of all ions in the solution. Based on this equilibrium concentration and the effective radius of the hydrated ion, a modified theory of the Gouy-Chapman diffuse double layer⁽⁹⁾ was used to predict the distribution factor of the metal ions. The work was extended to systems containing two metal ions for the determination of the separability of the ions with respect to each other. It was found that the distribution factor for solutions containing one metal ion could be predicted theoretically for a bulk solution pH less than four. Deviation of results above this pH was attributed to the limitations of the bulk solution reaction model because it did not include reactions for the formation of poly hydroxyl and poly nuclear hydroxyl complexes. Good agreement was also obtained between experiment and theory in the separability study. The results indicate that the order of removal of the ions from solution is Pb⁺⁺ > Cd⁺⁺ > Cu⁺⁺. This sequence is the reverse order of the effective radii of the hydrated ions. The results support the fact that the mechanism for removal of the ions from solution is that of electrical attraction and that selectivity depends upon the charge and size of the hydrated ion.     

Dependence of Equilibria in the Modified Chemical Vapor Deposition Process on SiCl4, GeCl4, and O2

The high-temperature equilibrium concentration of the gaseous species and of the deposited glass formed by the oxidation of the chlorides of silicon and germanium was measured and compared with thermodynamic calculations. The equilibrium incorporation of germanium in phosphate-silicate particles formed from the gas at 1650 K is shown to form a theoretical basis from which the actual composition of completed preforms and optical fibers made by the modified chemical vapor deposition process can be calculated. The efficiency of incorporation of germanium dioxide in the silica glass system is determined as a function of the oxygen concentration and the ratio of germanium to silicon. The recently redeveloped element potential method is used to minimize the Gibbs energy of the system and obtain the temperature and compositional dependences. The agreement of calculated and experimental results obtained in this work suggests a broad spectrum of uses of the method for understanding and calculating chemical reactions. The method is exceptionally well suited for applications where the determination of species concentrations for multiphase processes is desired over broad ranges of concentrations, temperatures, and pressures.     

Modelling of a post-combustion carbon dioxide capture absorber using potassium carbonate solvent in Aspen Custom Modeller

The process models for an equilibrium CO₂ absorber and a rate based CO₂ absorber using potassium carbonate (K₂CO₃) solvents were developed in Aspen Custom Modeller (ACM) to remove CO₂ from a flue gas. The process model utilised the Electrolyte Non-Random Two Liquid (ENRTL) thermodynamic model and various packing correlations. The results from the ACM equilibrium model shows good agreement with an inbuilt Aspen Plus® model when using the same input conditions. By further introducing a Murphree efficiency which is related to mass transfer and packing hydraulics, the equilibrium model can validate the experimental results from a pilot plant within a deviation of 10%. A more rigorous rate based model included mass and energy flux across the interface and the enhancement effect resulting from chemical reactions. The rate based model was validated using experimental data from pilot plants and was shown to predict the results to within 10%. A parametric sensitivity analysis showed that inlet flue gas flowrate and K₂CO₃ concentration in the lean solvent has significant impact on CO₂ recovery. Although both models can provide reasonable predictions based on pilot plant results, the rate based model is more advanced as it can explain mass and heat transfer, transport phenomena and chemical reactions occurring inside the absorber without introducing an empirical Murphree efficiency.     

Thermodynamic analysis of the thermochemical decomposition of H2S in the presence of iron sulphide

The decomposition of H₂S by a two-step closed loop thermochemical decomposition process was investigated. In the first step, H₂S decomposes by reacting with iron sulphide to produce hydrogen and a solid solution consisting of FeS and S₂. In the second step, the solid solution is decomposed at high temperature to recover sulphur and the iron sulphide which is reused in the first step. The thermodynamics of the first reaction were studied in detail by taking into account 12 gas phase chemical reactions and the phase equilibrium that is established between the sulphur in the gas and in the solid solution. The non-linear system of 13 equations, which relate the fugacities of the components at equilibrium to the equilibrium constants, were numerically solved by the Newton-Raphson iteration technique. The calculation results showed that the gas phase at equilibrium contains predominantly H₂S, H₂, and H₂S₂. The equilibrium conversion was found to decrease with increasing temperature; however, when the sulphur content of the solid solution was small, high hydrogen yields were possible even at high temperatures.     

An ion-exchange process with thermal regeneration XIII. Treatment of feedwater containing bicarbonate by adjustment of the pH of the regenerant with carbon dioxide

A theoretical model based on resin and solution equilibria is presented, which demonstrates that the effect of bicarbonate ions on the equilibrium and column behaviour of the Sirotherm** process is to load the acid resin with cations and so reduce its operating capacity. Using the model, it is predicted that the problem may be overcome by independent adjustment of the pH of the feed and regeneration waters. This is confirmed by experimental column studies in which the pH of the regenerant water is adjusted by saturating it with carbon dioxide at a suitable partial pressure. The optimum regeneration pH is found to be slightly lower than that predicted by equilibrium considerations, but the chemical requirement is still considerably less than that for full dealkalization and the need for a separate pretreatment stage is thereby eliminated. Mineral acid can also be used for pH control and the process is applicable to waters containing divalent as well as monovalent cations.     

Studies in Solvent Interesterification I: Interesterification of Mahua (Madhuca latifolia) Oil in Hexane

Random and directed interesterification characteristics of Mahua (Madhuca latifolia) oil in solution in n-hexane (60% w/w) were investigated. The results obtained were comparable with the corresponding conventional non-solvent reactions with respect to the physical and chemical properties induced by the interesterification reactions, although the time for reaching equilibrium was longer in the case of solvent interesterification. The results indicate the possibility of commercial utilization of the process for the production of plastic fats with greater ease and economy than the conventional non-solvent interesterification.     

Simulation of polymer flow using smoothed particle hydrodynamics method

Reactive rotational molding (RRM) is a process to manufacture hollow plastic articles. Comparing to rotational molding of thermoplastics, it decreases the process cycle time due to the reactivity of the system. However, the number of influent parameters is relatively high and optimization of the process is complex. During RRM, the viscosity is one of the key parameters and varies according to the polymer molecular weight due to chemical reactions. Simulation is a way to optimize this process. Prediction of the reactive flow is of great interest to optimize process conditions and wall thickness distribution of the molded part. We developed a solver based on smoothed particle hydrodynamics method. This Lagrangian meshfree method is well adapted to simulate free surface flows like those occurring in RRM. First, we validated the code comparing the simulation results to analytical Couette flow solution and experimental measurements of dam break problem. Then, we performed two‐dimensional (2D) and 3D simulations to observe the influence of the change of viscosity on the flow, due to the chemical reactions. Adhesion of the polymer on the mold surface is modeled by new boundary conditions. POLYM. ENG. SCI., 53:2509–2518, 2013. © 2013 Society of Plastics Engineers     

Membrane reactors in chemical production processes and the application to the pervaporation-assisted esterification

When appropriate membrane was used for the assistance of chemical and biochemical equilibrium reactions, it is possible to enhance the yield and the purity of the reaction product by selectively adding educts or selectively removing products and to a lower the energy input and the reaction time compared to conventional process. In this paper a review on membrane reactors with special emphasis on membrane-assistance of esterification reactions and a continuous tube membrane reactor for the pervaporation-assistance of the esterification are presented. The heterogeneously catalyzed esterification of ethanol and acetic acid to ethyl acetate and water was investigated as a typical chemical equilibrium reaction. The selective and simultaneous water separation from the reaction mixture of the esterification with polyvinyl alcohol pervaporation membranes is considered to be an interesting process alternative to the conventional distillation process. Compared to the distillation process, for the pervaporation-assisted process a decrease of the energy input of over 75% and of the investment and operating coasts of over 50% each was calculated.