(387k) Measurement and Modelling of Vapour-Liquid Equilibria for Reactive Systems

B. P. Francois^*1, P. Naidoo¹, D. Ramjugernath¹

¹Thermodynamics Research Unit, School of Engineering

 University of Kwa-Zulu Natal, King George V Avenue, Glenwood, Durban, 4041

* Corresponding Author:

Email: brucephilip.francois@gmail.com; Cell: +2784 811 0490

In many industrial applications, particular product conversions and system efficiencies cannot be attained with ordinary reaction vessels¹. Heat sources and sinks are also required for flash purposes with the implementation of distillation columns following reactors being common practice to separate products. Reactive distillation is a fairly new process whereby the chemical reactor also serves as the still enabling separation of the products from the reaction mixture in a single step¹. With this accomplished, equilibrium is disturbed and due to the continuous removal of products, conversions can be increased beyond what would normally be expected. Equipment costs are evidently reduced, heterogeneous catalyst may act as packing for distillation and energy costs substantially lowered by the utilisation of the heat of reaction in the separation of products¹. Implementation of this energy efficient process is however restricted to systems whereby reactions take place in the liquid phase, reactions that are equilibrium limited with fast reaction rates and cases whereby the volatilities of components result in easy removal of the products from solution². Some of the most notable applications include: esterification, etherification, hydrolysis and alkylation². Due to the availability of numerous literature sources, the system involving the esterification of 1-pentanol with acetic acid was investigated in this study as a test system. The desired product; n-Amyl acetate, is a widely used solvent, extractant and polishing agent³. This system may however, form a ternary azeotrope in the mixture of amyl alcohol/ amyl acetate/ water. Implementation of reaction distillation may serve as a viable method to overcome this problem. Ethyl acetate is also a widely used solvent in industrial processes although few recent publications for VLE data for this quaternary system are available⁴. The esterification of ethyl alcohol and acetic acid was therefore investigated as a novel system. The quaternary VLE measurements were performed on a low pressure dynamic recirculating VLE apparatus. Chemical and phase equilibria were achieved in an equilibrium chamber packed with a heterogeneous solid ion-exchange catalyst, Amberlyst 15. Experiments were carried out at isobaric and isothermal conditions. The resultant VLE data were regressed for parameters of Gibbs excess model equations. The vapour phase was corrected using the Hayden-O’ Connell equation of state. A distillation simulation model was developed in Aspen Plus for the system studied.

References:

1. Taylor. R, R. Krishna, 2000, Chemical Engineering Science, Vol. 55, pp 5183-5229

2. Luyben. W. L, C. C. Yu, 2008, John Wiley and Sons, USA

3. Lee. L. S, S. J. Lang, 1998, Fluid Phase Equilibria, Vol. 149, pp 57-74

4. Calvar. N, A. Dominguez, J. Togo, 2005, Fluid Phase Equilibria, Vol. 235, pp 215-222