Separation of ternary mixtures by extractive distillation with 1,2-ethandiol and glycerol

https://doi.org/10.1016/j.cherd.2015.04.032Get rights and content

Highlights

  • A design of distillation process has been elaborated for three ternary industrial mixtures.

  • Effective entrainers have been chosen on the basis of thermodynamic criterion.

  • Selectivity diagrams were used to determine favorable composition regions for separation.

  • Modeling of ED consequences with selected entrainers was performed, energy consumptions were evaluated.

Abstract

Continuous extractive distillation is a widely used method to separate binary and multicomponent azeotropic mixtures. Large-scale application and heavy energy usage play an important role in discovering more efficient separating agents. Separating agent (entrainer) selection for extractive distillation of binary mixtures is usually based on the analysis of relative volatility diagrams of components to be separated. Selective effect of entrainer is due to the differences in character and intensity of intermolecular interactions between entrainer and original mixture compounds. Accordingly, it is reasonable to additionally evaluate excess Gibbs energy magnitudes in binary systems formed by compounds of original mixture and entrainer (Raeva et al., 2011a).

Separating agent selection based on thermodynamic criterion is not uniquely defined for ternary mixtures yet. It establishes some steps of entrainer choice for extractive distillation of ternary mixtures containing several azeotropes. Substantiation of entrainer efficiency is proved by separation of industrial mixtures: tetrahydrofuran–methanol–water, ethyl acetate–ethanol–water and acetonitrile–methanol–water.

1,2-Ethandiol is well known to be an effective entrainer for different type of systems, including aqueous mixtures of organic substances (Gomez and Gil, 2009, Frolkova and Raeva, 2010). Glycerol is becoming more embroiled into separation processes due to environmental issues. They both fill in the common requirements for entrainer: by sufficiently changing the relative volatility of the substances to be separated and avoiding formation of new azeotropes with components of separating mixtures.

Introduction

One of the main concerns, related to major health and environmental issues in the chemical, pharmaceutical and special industry, is solvent waste (Kim and Smith, 2004, Jimenez-Gonzalez et al., 2005), which frequently contains different compounds, e.g. alcohols, ethers, esters, and water.

Separation of such mixtures is complicated by azeotrope phenomenon, which makes conventional processes based on vapor–liquid equilibria (VLE) not feasible. Although interesting membrane techniques not governed by VLE are investigated in literature (Brüschke and Tusel, 1986), they do not allow for separation of large amounts of solvents, and currently present additional technological features which cause regeneration difficulties. Also, in recent years, ionic liquids (Han and Row, 2010, Marciniak, 2010, Lei et al., 2014) have been introduced in the separation field, which, due to their remarkable properties, can be considered as very effective non-volatile entrainers, but in large scale chemistry are not yet widely applied, mostly due to financial and economic reasons. However, it is shown that in some cases high boiling entrainers are of more efficiency than ionic liquids (Navarrete-Contrerasa et al., 2014)

Another interesting solution based on VLE, is represented by extractive distillation process. The process implements adding entrainer, which, combined into the interactions with components of original mixture, selectively changes relative volatility of separated compounds. Correctly chosen entrainer helps to minimize energy consumptions and negative environmental impact on separation processes (Gomez and Gil, 2009).

In this paper we investigate and discuss the separation aspects of three ternary industrial systems, namely tetrahydrofuran–methanol–water, ethyl acetate–ethanol–water and acetonitrile–methanol–water at 101.3 kPa, which contain more than one azeotrope and correspond to diagrams 2.0-2b and 3.1-2 in Serafimov's classification (Kiva et al., 2003) (Fig. 1).

Though binary azeotropes compositions are sensitive to changes in pressure, pressure-swing distillation is not preferable for all compositions of ternary mixtures due to high-energy consumption.

The feasibility of ED process for separation is investigated in this paper. It is well known, that entrainer selection influences a lot on the energy consumptions, so our research work is directed to the establishing connections between physico-chemical characteristics of system in entrainer presence and selective properties of entrainer, which straightforwardly influence the energy consumptions of ED column. Its application is illustrated by separation of three industrial ternary mixtures mentioned above. This approach is suggested for further application for potential entrainer efficiency evaluation when separating systems containing several azeotropes.

Section snippets

Thermodynamic criterion to select entrainers

Excess Gibbs energy is a quantitative and qualitative characteristic of intermolecular interactions in binary and multicomponent solutions. To choose agents for extractive distillation of binary azeotropic mixtures, thermodynamic criterion was proposed, establishing a relationship between excess Gibbs energy (gE) of systems i – entrainer, j – entrainer (i, j – azeotrope forming components) and the relative volatility of substances to be separated. Entrainer efficiency is evident when difference

ED modeling

Conceptual ED flowsheets of tetrahydrofuran–methanol–water and ethyl acetate–ethanol–water using 1,2-ethandiol are presented in Fig. 5, Fig. 6. Conceptual flowsheet for acetonitrile–methanol–water separation with glycerol is equivalent to tetrahydrofuran–methanol–water flowsheet and therefore is not necessary to be presented here. In the case of ethyl acetate–ethanol–water system ED process is performed in two columns.

Calculations of distillation and vapor–liquid equilibria were performed via

Conclusions

The thermodynamic criterion for entrainers selection has been extended to ternary aqueous mixtures of non-electrolyte containing binary and ternary azeotropes. The criterion needs to be applied to all binary azeotropic constituents of ternary system. Separating agent should increase relative volatility of component forming two binary azeotropes in ternary system, in our case those are THF, ACN and EtAc (THF–methanol–water, ACN–methanol–water and EtAc–ethanol–water correspondingly). This

Acknowledgement

The reported study was partially supported by RFBR, research project No. 14-03-00523.

References (20)

  • V.N. Kiva et al.

    Azeotropic phase equilibrium diagrams: a survey

    Chem. Eng. Sci.

    (2003)
  • A. Marciniak

    Influence of cation and anion structure of the ionic liquid on extraction processes based on activity coefficients at infinite dilution. A review

    Fluid Phase Equilib.

    (2010)
  • H.E.A. Brüschke et al.

    Economics of Industrial Pervaporation Processes. Membranes and Membrane Processes

    (1986)
  • A.K. Frolkova et al.

    Bioethanol dehydration: state of the art

    Theor. Found. Chem. Eng.

    (2010)
  • P.A. Gomez et al.

    Simulation of the tetrahydrofuran dehydration process by extractive distillation

    Lat. Am. Appl. Res.

    (2009)
  • D. Han et al.

    Recent applications of ionic liquids in separation technology

    Molecules

    (2010)
  • C. Jimenez-Gonzalez et al.

    Expanding GSK's solvent selection guide – application of life cycle assessment to enhance solvent selections

    Clean Technol. Environ.

    (2005)
  • K.J. Kim et al.

    Parallel multiobjective evolutionary algorithms for waste solvent recycling

    Ind. Eng. Chem. Res.

    (2004)
  • Z. Lei et al.

    Extractive distillation with ionic liquids: a review

    AIChE J.

    (2014)
  • S.O. Momoh

    Assessing the accuracy of selectivity as a basis for solvent screening in extractive distillation processes

    Sep. Sci. Technol.

    (1991)
There are more references available in the full text version of this article.

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