Vapor-liquid Equilibrium in the Ternary Systems Acetic Acid + Water + (Xylose or Glucose)

Abstract

Hydrolysates of lignocellulosic biomass are aqueous solutions containing, among others, sugars andacetic acid. They are concentrated by evaporation. Only little is known on the influence of the sugars onthe volatility of the low-molecular-weight components in those mixtures. Therefore, in the present workthe isobaric vapor-liquid equilibrium of the systems (acetic acid (AA) þ water (W) þ xylose (X)) and(acetic acid (AA) þ water (W) þ glucose (G)) was studied at 20.0 kPa in a thin film evaporator. The resultsshow that the volatility of acetic acid is increased by the sugars and that xylose and glucose have asimilar influence. The vapor-liquid equilibrium data were correlated using the NRTL model for describingthe liquid phase non-ideality and taking the dimerization of acetic acid in the vapor phase into account.

Measurement and Modeling of Phase Equilibria in Systems Containing Water, Xylose, Furfural, and Acetic Acid

“…The chromatographic method was adopted from our previous work. 7 In the present work, however, pure water with a flow rate of 0.7 mL min −1 was used as the mobile phase. Xylose was detected with a refractive index detector (Agilent 1260 Infinity), while furfural was detected with an UV detector (Agilent 1100 Series).…”

“…The mass fraction of water was measured by Karl Fisher titration and the mass fraction of acetic acid was measured by an acid−base titration method with sodium hydroxide as titrant as both described in our previous work. 7 For the LLE, SLE, and SLLE measurements of the ternary system (W + X + F), the mass fractions of the two components present in lower quantity were analyzed and the mass fraction of the third component was calculated using the following closure condition:…”

“…In a recent work of our group, vapor− liquid equilibria (VLE) in systems containing water (W), xylose (X), glucose (G), and acetic acid (AA) were studied. 7 Xylose was selected as model substance of C5 sugars, glucose as model substance of C6 sugars. It was found that xylose and glucose have a similar impact on the VLE in the system.…”

“…The data were used, together with the data of this work, to design an evaporation + distillation downstream process that yields a concentrated sugar solution as well as pure furfural. 8 Our previous work on VLE 7 is extended in the present study to furfural (F) and to other types of phase equilibria: liquid− liquid equilibria (LLE), solid−liquid equilibria (SLE), and solid−liquid−liquid equilibria (SLLE), which were measured in the system (W + X + F) at 298.15 and 333.15 K. Furthermore, the LLE in the system (W + X + F + AA) was studied at 298.15 K. The study is motivated by the fact that the LLE can be used for designing recovery processes by extraction or heteroazeotropic distillation. 5,9−11 The LLE in the system (W + F) is well-studied, 12−21 but the influence of adding acetic acid and xylose has been studied only scarcely 22−25 or not at all, respectively.…”

“…9,38 However, to our knowledge, there is no experimental data of the LLE of the ternary mixture (W + X + F) that is studied in this work. The phase equilibria that were studied in the present work were modeled using the same approach as in our earlier work, 7 in which the nonrandom two-liquid (NRTL) model was used for describing the liquid phase nonideality. The model was parametrized using, among others, the LLE data for the system (W + X + F).…”