This study investigates the influence of electrolytes on the performance of extracting 5-hydroxymethylfurfural (HMF) from aqueous media using methyl isobutyl ketone (MIBK). For that purpose, liquid-liquid phase equilibria (LLE) of quaternary systems containing HMF, water, MIBK and salts were measured at atmospheric pressure and 298.15 K. The salts under investigation were composed of one of the anions NO(3-), SO4(2-), Cl(-), or CH3COO(-) and of one of the alkali cations Li(+), Na(+), or K(+). On the basis of these LLE data, the partition coefficient of HMF between the aqueous and the MIBK phase KHMF was determined. It could be shown that KHMF significantly depends on the kind and concentration of the added salt. Weak electrolytes (e.g., sulfates, acetates) caused salting-out, whereas nitrates caused salting-in of HMF to the aqueous phase. Unexpectedly, LiCl caused salting-out at low LiCl concentrations and salting-in at LiCl concentrations higher than 3 mol/kgH2O. The model electrolyte perturbed-chain SAFT (ePC-SAFT) was used to predict the salt influence on the LLE in the quaternary systems water/MIBK/HMF/salt in good agreement with the experimental data. On the basis of ePC-SAFT, it could be concluded that the different salting-out/salting-in behavior of the various salts is mainly caused by their different tendency to form ion pairs in aqueous solutions.
Levulinic acid was esterified with methanol, ethanol, and 1-butanol with the final goal to predict the maximum yield of these equilibrium-limited reactions as function of medium composition. In a first step, standard reaction data (standard Gibbs energy of reaction Δ g ) were determined from experimental formation properties. Unexpectedly, these Δ g values strongly deviated from data obtained with classical group contribution methods that are typically used if experimental standard data is not available. In a second step, reaction equilibrium concentrations obtained from esterification catalyzed by Novozym 435 at 323.15 K were measured, and the corresponding activity coefficients of the reacting agents were predicted with perturbed-chain statistical associating fluid theory (PC-SAFT). The so-obtained thermodynamic activities were used to determine Δ g at 323.15 K. These results could be used to cross-validate Δ g from experimental formation data. In a third step, reaction-equilibrium experiments showed that equilibrium position of the reactions under consideration depends strongly on the concentration of water and on the ratio of levulinic acid: alcohol in the initial reaction mixtures. The maximum yield of the esters was calculated using Δ g data from this work and activity coefficients of the reacting agents predicted with PC-SAFT for varying feed composition of the reaction mixtures. The use of the new Δ g data combined with PC-SAFT allowed good agreement to the measured yields, while predictions based on Δ g values obtained with group contribution methods showed high deviations to experimental yields.
This work provides experimental data and thermodynamic modeling on phase equilibria of binary mixtures that are relevant for esterification reactions. The components under investigation include water, succinic acid (SA), ethanol (EtOH), 1-butanol (1-BuOH), and the diesters of SA, namely, diethyl succinate (DES) and dibutyl succinate (DBS), respectively, as well as the organic solvents acetonitrile (ACN) and tetrahydrofuran (THF). Liquid−liquid equilibria (LLE) of water/DBS were measured at ambient pressure for temperatures between 313 and 353 K. Isobaric vapor−liquid equilibria (VLE) were measured for the binary systems ACN/DES, ACN/DBS, 1-BuOH/DBS, and THF/DBS at pressures of 10 or 20 or 30 kPa. Temperature ranges for the isobaric VLE varied between 300 and 500 K. The measured data and phase equilibria reported in literature were accurately modeled using perturbed-chain statistical associating fluid theory (PC-SAFT). For this purpose, pure-component PC-SAFT parameters, which were not already reported in the literature, were adjusted to experimental literature purecomponent data. Applying binary interaction parameters allowed precise phase-equilibrium modeling results of the binary systems under investigation. Two different association schemes for water were used ("2B" and "4C"). Both schemes appeared to be suitable to describe phase equilibria of aqueous mixtures; however, a binary parameter for the Wolbach−Sandler mixing rule was required for aqueous mixtures modeled with the 4C scheme. For LLE modeling the 2B scheme was found to give better modeling results. In general, the 4C association scheme for water yields better results for mixtures with two self-associating components while the 2B association scheme for water should be preferred if mixtures are considered with water and a non-selfassociating component. Further, the modeling concept of "induced association" has been investigated and discussed. Especially for mixtures with esters, which are of main importance for esterification mixtures, the induced-association approach turned out to be a more accurate modeling strategy compared to the nonassociative approach.
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