Computer-Aided Screening of Ionic Liquids As Entrainers for Separating Methyl Acetate and Methanol via Extractive Distillation

Mechanistic Analysis and Process Simulation of Ethyl Acetate-Ethanol Separation by Complex Solvent Extractive Distillation

Developing high-performance solvents for extraction and optimizing process technologies is crucial for efficient extractive distillation (ED) separation of azeotrope mixtures. In this paper, computer-aided screening was used to study the ED of azeotrope mixtures in ethyl acetate and ethanol systems using organic solvent dimethyl sulfoxide (DMSO) and ionic liquid (IL) ([EMIM][Ac]). The structural relationship between the ILs and the azeotrope mixture was analyzed by σ-profile, molecular surface electrostatic potential, interaction energy, and separation gradient. Subsequently, process simulation was carried out using Aspen Plus software and global optimization was performed with genetic algorithm, which found that both traditional organic solvents and ILs have good separation effects. But considering the high volatility of organic solvents and low saturation vapor pressure of ILs, it is considered to combine them to further explore the cost and carbon emission advantages in extractive distillation separation. Compared with pure organic solvent and pure ILs separation processes, the TAC of the process using an IL-based mixed solvent process decreased by 5.11 and 21.98%, respectively. The carbon emissions of the mixed extractant process were slightly higher than those of the pure organic solvent process, but the addition of ILs made very little volatilization of organic solvents, saving a charge for extractant use. By improving the process, waste heat is effectively recovered, which can save most of the utility engineering costs, and compared with the previous process, the total alkali consumption and carbon dioxide emissions are reduced by 9.43 and 27.17%, respectively. This exploration provides a theoretical reference for the development application and industrial research of ED processes using IL-based mixed solvents.

Computer-Aided Molecular Design of Ionic Liquids as Advanced Process Media: A Review from Fundamentals to Applications

The unique physicochemical properties, flexible structural tunability, and giant chemical space of ionic liquids (ILs) provide them a great opportunity to match different target properties to work as advanced process media. The crux of the matter is how to efficiently and reliably tailor suitable ILs toward a specific application. In this regard, the computer-aided molecular design (CAMD) approach has been widely adapted to cover this family of high-profile chemicals, that is, to perform computer-aided IL design (CAILD). This review discusses the past developments that have contributed to the state-of-the-art of CAILD and provides a perspective about how future works could pursue the acceleration of the practical application of ILs. In a broad context of CAILD, key aspects related to the forward structure-property modeling and reverse molecular design of ILs are overviewed. For the former forward task, diverse IL molecular representations, modeling algorithms, as well as representative models on physical properties, thermodynamic properties, among others of ILs are introduced. For the latter reverse task, representative works formulating different molecular design scenarios are summarized. Beyond the substantial progress made, some future perspectives to move CAILD a step forward are finally provided.

The azeotropy eliminating mechanism of ethyl acetate-acetonitrile system via ionic liquid entrainer: A combination of FTIR and DFT study

Ionic liquids (ILs) are good candidates for azeotropy separation. Knowledge of the microstructure properties of azeotrope - IL mixtures is important because they could reveal the molecular intrinsic cause of the elimination of azeotropy and represent the basis for the practical process. In this work, the microstructures of ethyl acetate-acetonitrile azeotrope mixtures and a representative IL, 1‑butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N], which could eliminate the azeotropy of the ethyl acetate-acetonitrile system, were studied by Fourier transform infrared spectroscopy with the assistance of quantum chemical calculations and excess spectra. The C≡N stretching vibrational region of acetonitrile was closely examined. The interaction complexes of ethyl acetate-acetonitrile and ion cluster/ion pair/ion - acetonitrile were identified. Weak strength hydrogen-bonds with electrostatically dominant and closed-shell interaction properties were found in these complexes. The interactions between [BMIM][Tf2N] and acetonitrile were stronger than those between ethyl acetate and acetonitrile, which caused the addition of IL to easily destroy the ethyl acetate-acetonitrile interaction complex. The interactions between [BMIM][Tf2N] and acetonitrile were stronger than those between [BMIM][Tf2N] and ethyl acetate, which would influence the relative volatility of ethyl acetate and acetonitrile in the azeotrope system. When x(IL) was larger than 0.027, all the interaction complexes between acetonitrile and ethyl acetate were completely broken apart, and the azeotrope was eliminated.

A FTIR and DFT Combination Study to Reveal the Mechanism of Eliminating the Azeotropy in Ethyl Propionate-n-Propanol System with Ionic Liquid Entrainer

Ionic liquids (ILs) have presented excellent behaviors in the separation of azeotropes in extractive distillation. However, the intrinsic molecular nature of ILs in the separation of azeotropic systems is not clear. In this paper, Fourier-transform infrared spectroscopy (FTIR) and theoretical calculations were applied to screen the microstructures of ethyl propionate-n-propanol-1-ethyl-3-methylimidzolium acetate ([EMIM][OAC]) systems before and after azeotropy breaking. A detailed vibrational analysis was carried out on the v(C=O) region of ethyl propionate and v(O-D) region of n-propanol-d₁. Different species, including multiple sizes of propanol and ethyl propionate self-aggregators, ethyl propionate-n-propanol interaction complexes, and different IL-n-propanol interaction complexes, were identified using excess spectroscopy and confirmed with theoretical calculations. Their changes in relative amounts were also observed. The hydrogen bond between n-propanol and ethyl propionate/[EMIM][OAC] was detected, and the interaction properties were also revealed. Overall, the intrinsic molecular nature of the azeotropy breaking was clear. First, the interactions between [EMIM][OAC] and n-propanol were stronger than those between [EMIM][OAC] and ethyl propionate, which influenced the relative volatilities of the two components in the system. Second, the interactions between n-propanol and [EMIM][OAC] were stronger than those between n-propanol and ethyl propionate. Hence, adding [EMIM][OAC] could break apart the ethyl propionate-n-propanol complex (causing the azeotropy in the studied system). When x([EMIM][OAC]) was lower than 0.04, the azeotropy still existed mainly because the low IL could not destroy the whole ethyl propionate-n-propanol interaction complex. At x(IL) > 0.04, the whole ethyl propionate-n-propanol complex was destroyed, and the azeotropy disappeared.

Process of separating acetonitrile and water using LTTMs as entrainer

New extractive distillation configurations, which use low transition temperature mixtures (LTTMs) as entrainers, have attracted widespread attention among scholars due to their green processes. Furthermore, the design and comparison of different processes can promote the application of new solvents in the future. In this study, two extractive distillation processes, the extractive distillation column (ED) and the extraction dividing wall column (EDW), were selected from previous work. The separation process of acetonitrile (ACN)-water ternary mixtures was studied, and GC3:1(choline chloride/glycolic acid mixture (molar mass 1:3)) and EC2:1((choline chloride/ethylene glycol 1:2 molar mass) were used as entrainers. Minimum consumption energy and the purity of ACN and water were set as the goals, and our sensitivity analysis and economic evaluation results showed that both ED and EDW were effective. As a result, LTTMs can be used in extractive distillation for azeotrope separation.

Expanding the Solubility Parameter Method MOSCED to Pyridinium-, Quinolinium-, Pyrrolidinium-, Piperidinium-, Bicyclic-, Morpholinium-, Ammonium-, Phosphonium-, and Sulfonium-Based Ionic Liquids

MOSCED (modified separation of cohesive energy density) is a solubility parameter method that offers an improved treatment of association interactions. Solubility parameter methods are well known for their ability to both make quantitative predictions and offer a qualitative description of the underlying molecular-level driving forces, lending themselves to intuitive solvent selection and design. Currently, MOSCED parameters are available for 130 organic solvents, water, and 33 imidazolium-based room temperature ionic liquids (ILs). In this work, we expand MOSCED to cover 66 additional ILs containing the pyridinium, quinolinium, pyrrolidinium, piperidinium, bicyclic, morpholinium, ammonium, phosphonium, and sulfonium cations using 10,052 experimental limiting activity coefficients. The resulting parameters may readily be used to predict the phase behavior in mixtures involving ILs.

Thermodynamic Assessment of the Suitability of the Limiting Selectivity to Screen Ionic Liquid Entrainers for Homogeneous Extractive Distillation Processes

As a result of their high tuneability and low volatility, room temperature ionic liquids have been proposed as replacement solvents in a wide range of industrial applications. They are particularly well-suited for use as an entrainer (or solvent) in extractive distillation processes to separate close boiling and azeotropic mixtures. The limiting selectivity is a common, fundamental parameter used to screen and rank entrainer candidates. In the present study, we present a detailed thermodynamic analysis to understand the basis for its use along with the necessary, underlying assumptions. We find that, while for many cases the limiting selectivity can correctly rank ionic liquid entrainer candidates for homogeneous extractive distillation processes, it is not always able to capture the correct phase behavior. We, instead, recommend the use of composition dependent activity coefficients.