Abstract
Deep eutectic solvents (DESs) have properties that make them suitable candidates to be used as entrainers for extractive distillation. In the previous work, it was proven that DES(1:2) (tetrabutylammonium bromide: levulinic acid, 1:2, molar ratio) can break the cyclohexane-benzene azeotrope. In the present work, the HBA and HBD ratio and molar concentration of DES were optimized to obtain a better constitute and condition of DES to be utilized in cyclohexane and benzene extractive distillation. The physical properties and structure of the prepared DESs were characterized. Vapor–liquid equilibrium data of the ternary system (benzene + cyclohexane + DESs) were also measured at atmospheric pressure. All experimental equilibrium data were correlated with Wilson, nonrandom two-liquid (NRTL), and universal quasichemical (UNIQUAC) activity coefficient models, from which the coefficient of determination (R2) of the three pseudo-ternary systems fitting was calculated. From the obtained results, the best HBA and HBD ratio in the DESs is elucidated as 1:2, the best molar concentration of DES is 0.1, and the NRTL model predicts the experimental data more accurately than the Wilson and UNIQUAC models. From the derived mechanism, the formation of stronger hydrogen bond and π–π bond interactions between DES and benzene is obtained when HBA and HBD ratio in DES is 1:2. In other conditions, the azeotrope cannot be broken, or the efficiency is low. The present work provides an environmentally friendly method to separate aromatic/aliphatic mixtures and act as a guide for further study of DESs in extractive distillation.
Highlights
A new family of solvents originally called “deep eutectic solvents” (DESs), which are formed by a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA), is proposed by Abbott, firstly, as an appropriate substitute to ILs [1], called “low transition temperature mixtures” (LTTMs) [2–4]
To study the interactions that exist in HBA and HBD, the Fourier-transformed infrared (FT-IR) analysis is carried out for Deep eutectic solvents (DESs), HBD, and HBA
The glass transition temperatures of all DES are lower than the melting point of HBD, substantiating that the hydrogen bonding is formed in the prepared DESs, which is very essential
Summary
A new family of solvents originally called “deep eutectic solvents” (DESs), which are formed by a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA), is proposed by Abbott, firstly, as an appropriate substitute to ILs [1], called “low transition temperature mixtures” (LTTMs) [2–4]. They possess properties that gain great advantages in the field of mixtures separation, such as liquid-liquid extraction [5–26], extractive distillation [2,27–29], and gas absorption [30]. It was proven that the DES(1:2) (tetrabutylammonium bromide: levulinic acid, 1:2, molar ratio) can break the cyclohexane-benzene azeotrope. FT-IR and NMR are used in the study for determining the extractive mechanism
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