Fluid Phase Equilibria 309 (2011) 121–127 Contents lists available at ScienceDirect Fluid Phase Equilibria j our na l ho me page: www.elsevier.com/locate/fluid Phase equilibria in binary mixtures with monoethyl succinate Alvaro Orjuela a,b , Abraham J. Yanez a , Jonathan Evans a , Abu M. Hassan a , Dennis J. Miller a , Carl T. Lira a,∗ a Michigan State University, Department of Chemical Engineering & Material Science, 2527 Engineering Building, East Lansing, MI 48824, United States b Universidad Nacional de Colombia, Ciudad Universitaria, Dept. de Ingeniería Química y Ambiental, Bogotá, Colombia a r t i c l e i n f o Article history: Received 29 December 2010 Received in revised form 7 June 2011 Accepted 17 June 2011 Available online 2 July 2011 Keywords: Monoethyl succinate Esterification Vapor liquid equilibria Vapor pressure VLE NRTL a b s t r a c t Monoethyl succinate was produced by partial esterification of succinic anhydride with ethanol using Amberlyst 15 ® as catalyst. After separation and purification, the purity of monoethyl succinate was con- firmed by nuclear magnetic resonance (NMR). Vapor pressure of monoethyl succinate was measured and correlated with Antoine equation. Vapor–liquid equilibria at constant temperature were mea- sured for the binary systems ethyl acetate + monoethyl succinate, acetic acid + monoethyl succinate, and water + monoethyl succinate at 323.15 K, and ethanol + monoethyl succinate at 313.15 K. Binary parame- ters for the NRTL equations were obtained by fitting experimental data using the regression tool in ASPEN Plus ® using the Hayden–O’Connell method for vapor phase fugacities. The model agrees reasonably well with the experimental data. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Esterification of succinic acid (SA) present in dilute solutions is considered a viable recovery and separation alternative for com- plex mixtures produced by fermentation [1–5]. Because the extent of esterification is limited by chemical equilibrium, separation of reaction products is necessary to obtain high conversions. As rec- ognized by some researchers [2,3] this can be accomplished using reactive distillation units in which water (H 2 O) and succinate are preferentially removed by distillation as top and bottom streams respectively while SA is completely esterified at intermediate stages. In general the fermentation broth generated during suc- cinic acid production also contains other carboxylic acids, mainly acetic acid (AcOH) [6–8]. Hence esterification of mixed acids occurs providing acetates and succinates as the major products. In the specific case of esterification with ethanol (EtOH), the reaction proceeds sequentially through a series–parallel reaction scheme (Fig. 1) with monoethyl succinate (MES) as intermediate product and diethyl succinate (DES) as the final product. Ethyl acetate (EtAc) is also produced when AcOH is present in the mix- ture. In addition to the several applications reported for the major product (DES) [1], the intermediate MES can be used in the treat- ment of diabetes and starvation [9–13]. MES can also be used as raw material for asymmetric succinic esters and other derivatives [14]. ∗ Corresponding author. Tel.: +1 517 355 9731; fax: +1 517 432 1105. E-mail address: lira@egr.msu.edu (C.T. Lira). In order to exploit a reactive distillation technology to recover SA though esterification with EtOH, computational modeling of the VLE in the reactive column is required including the behavior of the MES. Specifically, for SA or succinic derivatives there is a lack of information on phase equilibria in multicomponent systems. Gen- eralized group contribution methods have been used to predict activity coefficients in mixtures with succinic species, but predic- tions do not agree with experimental data [15,16]. In previous work from our group, phase equilibria of binary and ternary mixtures with DES were studied [17,18]. Binary interaction parameters for the NRTL equation [19] were obtained. In this study experimental vapor–liquid equilibrium (VLE) data for the systems MES + EtOH, MES + EtAc, MES + H 2 O, and MES + AcOH are presented. These data were correlated with the NRTL equation using a regression tool included in ASPEN Plus ® [20]. We also present a comparison with predictions using a group contribution method (UNIFAC) [21,22]. 2. Materials and methods 2.1. Materials Succinic anhydride (99.3%, Sigma–Aldrich), succinic acid (100%, Sigma–Aldrich), monoethyl succinate (89.1%, Sigma–Aldrich), diethyl succinate (99.8%, Sigma–Aldrich), ethanol (200 proof, Decon Labs), water (HPLC grade, J.T. Baker), ethyl acetate (99.99%, EMD), acetic acid (99.9%, Aristar), n-butanol (99.9%, Mallinckrodt), and acetonitrile (HPLC grade, EMD) were used for experiments and cal- ibration. Purity of all compounds except MES was confirmed by gas 0378-3812/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2011.06.020