Elsevier

Fluid Phase Equilibria

Volume 314, 25 January 2012, Pages 169-179
Fluid Phase Equilibria

Introduction of the amine group at cycloaliphatic hydrocarbon (c-CHNH2) for the modified UNIFAC (Dortmund) model and validation in multicomponent systems containing cyclohexylamine

https://doi.org/10.1016/j.fluid.2011.09.010Get rights and content

Abstract

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.

Highlights

► New group cycloaliphatic amine c-CHNH2 is introduced for mod. UNIFAC (Do). ► Binary and ternary predictions are compared to the results with the CNH2-group. ► Ternary and quaternary predictions are compared to the results of NRTL, UNIQUAC, ESD EOS. ► c-CHNH2-group provides very successful predictions in systems with cyclohexylamine.

Introduction

So far components containing the amine group at cycloaliphatic rings e.g. cyclohexylamine (CHA) could not be incremented correctly using the modified UNIFAC model (Dortmund) [1] since only the amine group at aliphatic or aromatic systems was available. This lack leads to limitations of the applicability of the mod. UNIFAC (Do) model or to acceptance of higher deviations if the amine group of aliphatic hydrocarbons is used instead.

For correct incrementation of components containing amine groups at cycloaliphatic rings the c-CHNH2 group was defined. The relative van der Waals volume Rk and the relative van der Waals surface area Qk of the existing amine group in secondary aliphatic hydrocarbons CHNH2 (subgroup no. 33 in [2]) can be used due to geometrical similarity.

Group interaction parameters were determined for the new c-CHNH2 group with the aliphatic group (CH2), the aromatic group (ACH), the alkyl aromate group (ACCH2), the water group (H2O), the aromatic amine group (ACNH2), and the cyclic group (c-CH2). All available binary information was included like vapour–liquid equilibrium (VLE) data, heats of mixing, and activity coefficients at infinite dilution. Due to the low number of literature data available for systems containing CHA and alkanes or cycloalkanes the VLE of the system nonane + CHA was determined at 363.15 K and 393.15 K and of the system methylcyclohexane + CHA at 333.15 K and 363.15 K at reduced pressures by the dynamic method. Furthermore, activity coefficients at infinite dilution were measured for the systems CHA + cyclohexane, +methylcyclohexane, and +ethylcyclohexane.

The predictive capabilities were evaluated in the ternary systems water + toluene + CHA, water + octane + CHA, water + aniline + CHA, toluene + aniline + CHA, and octane + aniline + CHA. Furthermore, in the quaternary system water + toluene + aniline + CHA the liquid–liquid equilibrium (LLE) was determined at 298.15 K and 333.15 K and the VLE at 333.15 K and 363.15 K. The experimental results of the measurements in the quaternary system are also compared with the prediction results of the mod. UNIFAC (Do) model using the new cycloaliphatic amine group. Further, the prediction results for the multicomponent systems were compared to the predictions obtained with the activity coefficient models NRTL [3] and UNIQUAC [4] and the equation of state proposed by Elliott, Suresh, and Donohue (ESD EOS) [5], [6].

Section snippets

Materials and purities

The components nonane (99+%), cyclohexane (>99.5%), methylcyclohexane (>99.0%), ethylcyclohexane (>98.0%), and CHA (purity p.a.) were purchased from Acros Organics, Belgium. Cyclohexane was fractionally distilled in a Vigreux column at reduced pressure under a N2 atmosphere; the other substances were used without further purification. All substances were stored over sodium sulphate. The purities were judged by and mass fraction determined by gas–liquid chromatography and by comparison of

Calculation of the group interaction parameters for the cycloaliphatic amine group (c-CHNH2)

In view of the modified UNIFAC (Dortmund) model (as in view of all group contribution methods) the phase equilibrium behaviour is assumed to depend on interaction of functional groups instead of molecules. The activity coefficient which is needed for all phase equilibrium calculations for each component is composed of the combinatorial and the residual part.lnγi=lnγiC+lnγiR

The combinatorial part considers the entropic contribution which is mainly caused by number, size, and volume of the

Water + toluene + CHA

Fig. 7 shows the LLE of the ternary system water + toluene + CHA. The experimental data evince that the heterogeneous region increases with increasing temperature. This behaviour is predicted with both parameter sets for CHNH2 from literature and c-CHNH2 presented in this work. With the parameter set for CHNH2 the two phase region is predicted far too large; furthermore, an experimentally disproved immiscibility in the binary system water + CHA is predicted. The prediction with the new parameter set

Conclusion

The gap in the parameter matrix for the modified UNIFAC Dortmund model for components containing an amine group at cycloaliphatic structures was filled by introducing the new group cycloaliphatic amine c-CHNH2. The group interaction parameters with the CH2, ACH, ACCH2, H2O, ACNH2, and c-CH2-groups were determined. Therefore, an extended search for binary data (VLE, HE, γ) was completed. Additionally, VLE data were measured for the binary systems nonane + CHA and methylcyclohexane + CHA and

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