Gibbs energy calculations for the distillation of a dilute solution in a multistep separation cascade

Calculations of a decrease in Gibbs energy in the distillation of an ideal dilute solution at cascade steps are presented. A thermodynamic interpretation of the total useful work of the separation of binary mixture components is suggested.     

Thermodynamic interpretation of a single event of separation of the components during the distillation of an ideal solution

The results of a thermodynamic analysis of an elementary process of distillation in which the separation of the components of the solution occurs due to the absence of thermodynamic equilibrium between the phases are summarized and compared with results of studies of a single event of separation of a mixture at the expense of the energy supplied from an external source. A thermodynamic interpretation is proposed for optimum conditions of fine separation of an equimolar binary mixture by single-stage distillation.     

Gibbs energy increment and minimum work of separation during the distillation of a dilute solution in a multistep cascade

The Gibbs energy increment during the distillation of a dilute solution in a separation cascade was calculated. An interpretation of the minimum work thermodynamically required during the symmetric separation of a binary mixture is suggested.     

Thermodynamic work of separation during the distillation of an ideal binary solution in a multistep cascade

The decrement in Gibbs energy during the distillation of an isotopic mixture in a separation cascade is calculated. A thermodynamic interpretation of the total useful work performed by the cascade during fine separation is proposed.     

Fluid phase topology of ethanol+benzene+cyclohexane at 101.3 kPa

In this article, isobaric vapor–liquid equilibria for the ternary mixture of ethanol?+?benzene?+?cyclohexane was experimentally investigated at atmospheric pressure. Vapor–liquid equilibria data for ethanol?+?benzene?+?cyclohexane at 101.3?kPa were obtained with a Othmer-type ebulliometer. Data were tested and considered thermodynamically consistent. The experimental results showed that this ternary mixture is completely miscible and exhibits three binary homogeneous azeotropes and a ternary minimum azeotrope at the studied conditions. Satisfactory results were obtained for correlation of equilibrium compositions with UNIQUAC activity coefficients model and also for prediction with UNIFAC method. In both cases, low root mean square deviations of vapor mole fraction and temperature were calculated. The capability of ethanol as modified distillation agent at atmospheric condition is discussed in terms of the thermodynamic topological analysis. However, owing to the complex topology of the ternary mixture it leads to a distillation scheme with three columns and difficult operation and thus, ethanol is not recommended as a separating agent for benzene?+?cyclohexane azeotrope.     

Azeotropic behaviour of (benzene + cyclohexane + chlorobenzene) ternary mixture using chlorobenzene as entrainer at 101.3 kPa

In this paper, the azeotropic behaviour of the (benzene + cyclohexane + chlorobenzene) ternary mixture was experimentally investigated with the aim of enhancing the knowledge for the feasible use of chlorobenzene as an entrainer for the azeotropic distillation of the binary azeotrope. Such a study has not been reported in the literature to the best of the authors’ knowledge. (Vapour + liquid) equilibria data for (benzene + cyclohexane + chlorobenzene) at 101.3 kPa were obtained with a Othmer-type ebulliometer. Data were tested and considered thermodynamically consistent. The experimental results showed that this ternary mixture is completely miscible and exhibits an unique binary homogeneous azeotrope, an unstable node at the conditions studied, and the propitious topological characteristics (residual curve map and relative volatility) to be separated. Satisfactory results were obtained for the correlation of equilibrium compositions with the UNIQUAC activity coefficients model and also for prediction with the UNIFAC method. In both cases, low root mean square deviations of the vapour mole fraction and temperature were calculated. The capability of chlorobenzene as a modified distillation agent at atmospheric condition is discussed in terms of the thermodynamic topological analysis. A conceptual distillation scheme with reversed volatility is proposed to separate the azeotropic mixture. In order to reduce the operational cost requirements of the sequence of columns proposed, the range for optimal reflux and the ratio for feed flow conditions were studied.     

精馏节能过程非平衡热力学分析——模型方程的建立

通过对精馏过程进行热力学分析,建立了通用性较强的非平衡热力学数学模型.该模型可对精馏过程中用能情况进行非平衡热力学分析和熵均分分析,也可用于评价塔板性能.模型建立的基础只适用于线性非平衡热力学区,即近平衡区,有较大的局限性.     

Measurement of viscosity and electrical conductivity and a thermodynamic model

According to the need of industrial design and application of new desulfurization technique, we determine viscosities and electrical conductivities of dilute SO₂ mixture gas in dimethyl sulfoxide mixture absorbents, and establish a thermodynamic model based on experimental data. The viscosities and electrical conductivities calculated by the model show good agreement with experimental data.     

Equation of state and phase behavior of a propane-tetrafluoroethane mixture

A general equation of state was derived for a propane-tetrafluoroethane mixture in a form representing the free Helmholtz energy of a mixture as the function of density, temperature, and composition. Coefficients of equation were determined according to data on the density of the mixture and assuming the equilibrium condition of phases. The equation describes the thermodynamic properties of vapor and liquid in the temperature range from 255 to 400 K under pressures up to 6 MPa. The thermodynamic behavior of the mixture at the saturation state was analyzed. It is established that the difference between the temperatures of saturated vapor and of liquid on isobars for four compositions did not exceed 1.8 K.     

Transformations of thermodynamic systems with the retention of projective invariants

Equations that determined the transformations of thermodynamic properties with the retention of projective invariants and had a solution for thermodynamic systems whose fundamental equation satisfied a certain phenomenological condition were obtained. (The geometric meaning of this condition is the possibility of projective bending of the surface described by the fundamental equation.) It was shown that, for a mixture of ideal gases, there were three sets of solutions, and, for a mixture of real gases in the region of convergence of the virial expansion (with an accuracy to at least the forth virial coefficient inclusive), there was one solution. A second solution appeared if the virial coefficients of intermolecular interactions were related by an additional equation.     

Modeling of supramolecular ordering and physicochemical properties in cyclohexane-ethanol mixtures

The quasichemical model of the nonideal associated solution (QCNAS) was used to analyze the excess thermodynamic functions and permittivity of cyclohexane-ethanol mixtures in the entire range of compositions and in a wide temperature range. A new model of supramolecular organization was substantiated, taking into account chain and cyclic aggregation of alcohol with the formation of chain aggregates of arbitrary size, which describes a set of physicochemical properties of this mixture with complicated behavior of both thermodynamic and dielectric properties. Equilibrium constants and thermodynamic parameters of H bonding having cooperative character and integral and differential characteristics of aggregation and the structural parameters of aggregates were determined. It was established that the role of nonpolar cyclic structures increases as alcohol concentration decreases. The model describes the permittivity of solutions in the entire range of compositions and reproduces a minimum of the dipolar correlation factor in the range of dilute alcohol solutions. The new data obtained on the supramolecular ordering characterized by the long-range molecular correlations due to H bonding are discussed in detail.     

Crossover Equation of State and Microstructural Properties of Infinitely Dilute Solutions Near the Critical Point of a Pure Solvent

Microstructural (correlation integrals, cluster size) and related thermodynamic (partial molar volume, Krichevskii parameter) properties of infinitely dilute solutions near the critical point of a pure solvent are studied in terms of nonclassical (crossover) equations of state. The Krichevskii parameter was evaluated for a number of binary solutions by analyzing the initial slopes of the critical lines and the properties of a pure solvent. Qualitative explanation is offered for the physicochemical mechanism of the anomalously high solubility of slightly volatile substances in a supercritical solvent based on microstructural and thermodynamic characteristics of a supercritical fluid mixture.     

Measurement of surface tension of desulfurization solution and thermodynamic model-(I)

According to the need of industrial design and application of new desulfurization technique, we determine surface tension of dilute SO₂ mixture gas in DMSO and DMSO?+?Mn²⁺ mixture absorbents, and establish their thermodynamic model based on experimental data, and the surface tension calculated by the model shows good agreement with experimental data.     

内部热耦合精馏系统节能研究

针对传统精馏塔系统和内部热耦合精馏塔系统两种不同的精馏系统,以苯―甲苯物系和丙烯―丙烷物系两种理想的二组分物系分别作为研究对象,以系统的热力学效率、公用工程费用和节能百分率作为研究评价基准,模拟并研究分析压缩比、进料热状态等参数对传统精馏塔和内部热耦合精馏塔节能效果的影响,两种不同的理想物系下内部热耦合精馏系统之间的差异,并分析内部热耦合精馏节能的影响因素,为内部热耦合精馏塔内部节能研究提供参考。     

Heat of Reaction of the Hydrolysis-Polymerization Process of Tetraethyl Orthosilicate in Acidic Condition

Heat of reaction of the hydrolysis-polymerization process of tetraethyl orthosilicate with water in acidic condition was investigated to clarify the thermodynamic driving force of sol-gel reactions. Heat of reaction was measured using an isoperibol calorimeter by mixing a dilute tetraethyl orthosilicate (TEOS) ethanolic solution with another solution of water, ethanol, and hydrochloric acid. The temperature change of the reaction cell had been measured more than 24 hours after mixing under the quasi-isothermal condition. Large exothermic reaction (12.9 kJ·mol^–1 for 1 mole of TEOS) due to the hydrolysis of TEOS was observed. A slow exothermic reaction followed it, and after that, the sol-gel reaction was changed to a small endothermic one.     

Effect of Temperature on Micellization and Thermodynamic Behavior of Gadolinium Alkanoates in Nonaqueous Media

The conductometric measurements were employed to determine the critical micellar concentration (CMC), degree of dissociation and dissociation constant of dilute solutions of Gadolinium decanoate and dodecanoate in benzene and methanol mixture (7:3 v/v). The results show that the Gadolinium alkanoates behave as moderate electrolyte below the CMC. The various thermodynamic parameters were also evaluated for both dissociation and association process.     

Micellization and gelation of mixed copolymers P123 and F127 in aqueous solution

The micellization in dilute aqueous solution of Pluronic copolymers P123 (E21P67E21) and F127 (E98P67E98) and mixtures of the two was investigated using static and dynamic light scattering. Gelation of concentrated solutions of the two copolymers and their mixtures was studied using tube inversion and oscillatory rheometry. The two copolymers comicellized to give micelles with narrow size distributions. Clouding temperatures and critical micelle temperatures decreased as the proportion of P123 in the mixture was increased. Micelle association numbers of the mixed micelles lay between the values found for micelles of P123 and F127 alone, whereas micelle radii passed through maximum values in the range 0-50 wt % P123. As judged by the ratio of the thermodynamic to the hydrodynamic radius, the micelle interaction potential changes gradually from soft to hard as the proportion of P123 in the mixture is increased. Regions of cubic and hexagonal (birefringent) gel were defined for concentrated solutions. The high-temperature boundary of the 30 wt % cubic gel decreased monotonically from 90 to 43 degrees C as the proportion of P123 in the mixture was increased from 0 to 100 wt %, whereas the low-temperature boundary was essentially constant at 15 +/- 3 degrees C. Increasing the proportion of P123 in the mixture at 25 degrees C increased the concentration at which the cubic gel was first formed and decreased the concentration at which the hexagonal gel was first formed.     

Thermodynamic interpretation of the elementary act of separation in the liquid extraction of an equimolar binary mixture

Results of a thermodynamic analysis of a liquid extraction process in which the separation of the components of the mixture is associated with the presence of thermodynamically nonequilibrium phases were summarized and compared to the available data on the act of separation of a mixture due to the energy supplied from an external source. A thermodynamic interpretation was proposed for optimum conditions of separation of an equimolar binary mixture by liquid extraction.     

Hydration numbers and the state of water in hydration spheres of magnesium chloride and magnesium sulfate solutions

An equation for determining hydration numbers and molar adiabatic compressibilities has been derived by correct thermodynamic processing of a data set comprising ultrasound velocity, density, and isobaric heat capacity in aqueous magnesium chloride and sulfate solutions for concentrations ranging from very dilute solutions to the complete solvation boundary and temperatures of 273.15?C323.15 K. One basic innovation of the derived equation consists in that it accounts for the dependence of solvation numbers on solution concentration and in that all changes experienced by the solution are associated with the solvation of a stoichiometric mixture of electrolyte ions or nonelectrolytes molecules.