An equipment for dynamic measurements of vapour–liquid equilibria and results in binary systems containing cyclohexylamine

doi:10.1016/j.fluid.2005.05.003

Fluid Phase Equilibria

Volume 233, Issue 2, 30 June 2005, Pages 170-175

https://doi.org/10.1016/j.fluid.2005.05.003 Get rights and content

Abstract

A computer-aided equipment for precise measurements of vapour–liquid equilibrium (VLE) data at normal and low pressures using the dynamic method will be introduced. The apparatus consists of a circulation still which allows isothermal and isobaric measurements. The digital measurement and control system is accomplished by a multimeter coupled with a PC via IEEE-card. The quality of the measurement data is demonstrated by a comparison of the measured vapour pressure data of the pure substances toluene, n-octane and cyclohexylamine with the vapour pressure equation of Daubert and Danner. Furthermore, vapour–liquid equilibrium data were measured in the binary systems cyclohexylamine + aniline or water or n-octane. The measured data were regressed according to the activity coefficient models NRTL, UNIQUAC and to the Elliott–Suresh–Donohue-equation of state (ESD-EOS).

Introduction

A knowledge of phase equilibrium is essential for the planning and realisation of separation processes in chemical engineering. Phase equilibrium data are a requirement especially for the construction of thermal separation operations. In fact, experimental data are available in data collections and electronic media; correlation methods exist as G^E-models and equations of state, but in some cases it is still indispensable to measure the phase equilibrium because the required parameters are unavailable or unsuitable for the pressure and temperature range of interest.

There are two primary methods for measuring vapour–liquid equilibria. The static method has the problem of dissolved gases but it is easier in sampling and analysis. The other option is the dynamic method, where the mentioned problem does not appear but the automation is more difficult. In continuation of the work of our research group [1] the existing dynamic apparatus was completely revised. The new equipment allows a faster and more comfortable measurement of vapour–liquid equilibria. Precise isothermal measurements are an important aim of the new equipment, since isobaric VLE data do not allow to distinguish between the concentration dependence and the temperature dependence of the data.

Section snippets

Experimental details

The central part of the equipment is made up by a Röck and Sieg [2] type circulation still purchased from QVF Process Systems Ltd. shown in Fig. 1. The circulation still consists of a boiling part (B) equipped with a tempering jacket (4) and a condensing part (C).

A heater provides the energy for the boiling process in the boiling flask (1). Ascending vapour entrains liquid through the Cottrell-pump (2) to the temperature measuring point (3). The vapour–liquid mixture separates into ascending

Control algorithm

The following section delineates the development of the algorithm, in particular for isothermal runs. The aim was to obtain software which is able to calculate the pressure changes needed to attain the desired temperature. The challenge in this is to achieve a generally applicable and not substance or mixture specific algorithm. It should be noted that, if the pressure change is too small, it will take a long time to achieve the target temperature. On the other hand, if the pressure change is

Results and discussion

The quality of measurement is demonstrated by means of experimental results for pure substance vapour pressure and binary VLE. The substances toluene, n-octane and cyclohexylamine were obtained from Acros Organics with purity greater than 99 %. For further purification, toluene and n-octane were distilled in a bubble-cap tray column. Cyclohexylamine was used without further purification. A verification of the obtained purity by gas chromatography showed a purity of at least 99.98 %. Distilled

Conclusion

An equipment for the measurement of precise isothermal vapour–liquid equilibria using the dynamic method at normal and low pressures was developed. Vapour pressure measurements of pure substances were compared to the vapour pressure equation of Daubert and Danner, all the deviations are small and within the range of the denoted quality code for this vapour pressure equation. Furthermore, vapour–liquid equilibria were determined for three binary systems. The measured VLE data are proved

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Vapor-liquid equilibrium for binary systems containing n-alkanes and cycloalkanes
2024, Fluid Phase Equilibria
In this study, VLE data for five binary systems comprising n-octane, n-nonane, methylcyclopentane, and methylcyclohexane were measured using the total pressure method at 393.15 K, 433.15 K, and 473.15 K. The NRTL-HOC and the UNIQUAC-HOC models were used to successfully correlate all VLE data and determine binary interaction parameters. No azeotropic behavior was observed in any of the binary systems under the operating conditions. The predictive UNIFAC-DMD and COSMO-SAC models were implemented to predict binary VLE phase diagram and unveiled the mechanism of the separation efficiency of alkanes–cycloalkanes. Through the examination of the COSMO-SAC based molecular surface charge profile (σ-profile), the variance in non-hydrogen bonding segments within the σ-profiles of the analyzed alkanes determines both the strength of electrostatic interactions and the temperature-dependent VLE separation behaviors. The results indicate that σ-profile could be suggested as a good indicator to assess operating conditions of the alkanes VLE separation.
Measurement and prediction of liquid-liquid equilibria in ternary systems containing water, an organic component, and cyclohexanol
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Citation Excerpt :
The phase equilibria were measured under isothermal conditions using a digital system for measurement and control that was developed in our group. A relationship based on the Clausius-Clapeyron equation is used to connect the measured value of temperature with the pressure as control parameter [9]. The binary mixtures were filled into the boiling flask of the apparatus.
The liquid-liquid equilibria of the four ternary mixtures water + heptane + cyclohexanol, water + toluene + cyclohexanol, water + cyclohexane + cyclohexanol, and water + cyclohexylamine + cyclohexanol were measured at 298.15 K and 323.15 K at atmospheric pressure. The binodal curves were determined by photometric turbidity titration.
Our experimental data are compared with the prediction results from both UNIQUAC and NRTL activity coefficient models and the equation of state proposed by Elliott, Suresh, and Donohue (ESD EOS). For this purpose, interaction parameters were determined using binary phase equilibrium data. Due to the sparse amount of binary equilibrium data in literature, the vapour-liquid equilibrium in the binary toluene + cyclohexanol system was determined at 333.15 K and 363.15 K at reduced pressure. When predicting the experimental LLE behaviour of the considered systems, ESD EOS seems to be superior to the UNIQUAC and NRTL approach.
Thermodynamic properties of cyclohexanamines: Experimental and theoretical study
2015, Thermochimica Acta
Vapor pressures of cyclohexanamine, N-methyl-cyclohexanamine, N,N-dimethyl-cyclohexanamine, and N-cyclohexyl-cyclohexanamine were measured using the transpiration method. Molar enthalpies of vaporization of cyclohexanamine derivatives were derived from vapor pressure temperature dependences. Thermodynamic data on cyclohexanamine derivatives available in the literature were collected and treated uniformly. Consistency of the experimental data was proved with a group- contribution method and quantum-chemical calculations. Evaluated vaporization and formation enthalpies of cyclohexanamine derivatives were recommended for practical thermochemical calculations.
VLE and LLE in ternary systems of two associating components (water, aniline, and cyclohexylamine) and a hydrocarbon (cyclohexane or methylcyclohexane)
2014, Fluid Phase Equilibria
Citation Excerpt :
The isothermal VLE measurements were carried out in a Röck and Sieg circulation still [16] modified in different details as described by Schmelzer et al. [17]. The control algorithm for isothermal measurements was developed in our group [18] and has been successfully applied already to a large number of systems containing associating components and hydrocarbons, for example water + phenols + toluene or water + phenols + octane [19]. The relevant ternary mixture was filled into the boiling flask of the circulation still and equilibrated at 333.15 K.
The isothermal vapour–liquid equilibria (VLE) of the five ternary mixtures water + cyclohexane + aniline (A), water + cyclohexane + cyclohexylamine (B), water + methylcyclohexane + aniline (D), water + methylcyclohexane + cyclohexylamine (E), and methylcyclohexane + aniline + CHA (F) with industrial relevance were determined at temperatures between 333.15 K and 363.15 K at reduced pressures. Additionally, the liquid–liquid equilibria (LLE) of the four ternary systems (B), (D), (E), and cyclohexane + aniline + cyclohexylamine (C) were determined at temperatures between 298.15 K and 333.15 K at atmospheric pressure. In total, 185 LLE and 121 VLE measurement points are presented and discussed.
The experimental results were compared with the predictions of the activity coefficient models UNIQUAC and NRTL, and of the equation of state proposed by Elliott, Suresh, and Donohue (ESD EOS) based on binary interaction parameters. In order to estimate the binary parameters required for calculation, the VLE of the binary cyclohexane + aniline (G) system was measured at 333.15 K and 353.15 K at reduced pressures. Furthermore, the prediction results of the group contribution method modified UNIFAC (Dortmund) are included. Interaction parameters of new amine group at cycloaliphatic hydrocarbon have been used in the calculation.
Introduction of the amine group at cycloaliphatic hydrocarbon (c-CHNH <inf>2</inf>) for the modified UNIFAC (Dortmund) model and validation in multicomponent systems containing cyclohexylamine
2012, Fluid Phase Equilibria
The group interaction parameters for modified UNIFAC (Dortmund) of the newly defined amine group at cycloaliphatic hydrocarbon occurring for example in cyclohexylamine with six established groups were determined using binary data available from literature and new experimental data presented in this paper. The calculations of binary and ternary systems are compared to the predictions using the amine group at aliphatic hydrocarbon. The liquid–liquid and vapour–liquid equilibria of the quaternary system water + toluene + aniline + cyclohexylamine were determined at two temperatures, each, and predicted with mod. UNIFAC (Do) using the new group interaction parameters. Furthermore, the predictions for the ternary and quaternary systems with mod. UNIFAC (Do) are compared to the predictions with NRTL, UNIQUAC, and Elliott–Suresh–Donohue equation of state using binary interaction parameters.
Experimental determination of the isothermal (vapour + liquid) equilibria of binary aqueous solutions of sec-butylamine and cyclohexylamine at several temperatures
2012, Journal of Chemical Thermodynamics
Citation Excerpt :
The purpose of the present work is to investigate (vapour + liquid) equilibria (VLE) of (sec-butylamine (CAS #13952-84-6) + water) or (cyclohexylamine (CAS #108-91-8) + water) binary mixtures with a view to use the results to determine the interaction parameters for predictive group contribution methods. A survey of the literature shows that there are data in the open literature for the pure cyclohexamine and (cyclohexylamine + water) binary mixture [5–8]. The components sec-butylamine and cyclohexylamine were supplied by Sigma–Aldrich Chem. (
The vapour pressures of (sec-butylamine + water), (cyclohexylamine + water) binary mixtures, and of pure sec-butylamine and cyclohexylamine components were measured by means of two static devices at temperatures between 293 (or 273) K and 363 K. The data were correlated with the Antoine equation. From these data, excess Gibbs functions (G^E) were calculated for several constant temperatures and fitted to a fourth-order Redlich–Kister equation using the Barker’s method. The (cyclohexylamine + water) system shows positive azeotropic behaviour for all investigated temperatures. The two binary mixtures exhibit positive deviations in G^E for all investigated temperatures over the whole composition range.

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An equipment for dynamic measurements of vapour–liquid equilibria and results in binary systems containing cyclohexylamine

Abstract

Introduction

Section snippets

Experimental details

Control algorithm

Results and discussion

Conclusion

Fluid Phase Equilib.

Chem. Tech.

Zeitschrift für Phys. Chem. Frankfurt/Main

Physical and Thermodynamic Properties of Pure Chemicals: Data Compilation

AIChE J.

AIChE J.

Ind. Eng. Chem. Res.

Ind. Eng. Chem. Res.

J. Stat. Phys.