Measurement and correlation of liquid-liquid equilibrium for the ternary system (water+1,2-dichloroethane+sulfolane) at 288.15,298.15,and 308.15 K

Zhansheng Li,Jiayu Song,Shouhai Zhang,Jinyan Wang,Xigao Jian

State Key Laboratory of Fine Chemicals,Liaoning High Performance Polymer Engineering Research Center,School of Chemical Engineering,Dalian University of Technology,Dalian,116024,China

Keywords:Phase equilibria Thermodynamics Parameter estimation Sulfolane NRTL model UNIQUAC model

ABSTRACT Sulfolane is an important aprotic polar solvent.Liquid-liquid equilibrium (LLE) data for the ternary systems of water+1,2-dichloroethane+sulfolane were measured at temperatures of 288.15,298.15 and 308.15 K under the atmospheric pressure.The distribution coefficient and selectivity were determined from the measured LLE data,which showed that 1,2-dichloroethane is a suitable extractant for the recovery of sulfolane from its aqueous solution.The nonrandom two-liquid (NRTL) model and the universal quasi-chemical (UNIQUAC) model were utilized to correlate the experimental LLE data.The low values of RMSD indicated that the ternary system could be fitted well by the NRTL and UNIQUAC models.The consistency of the binary interaction parameters for the two thermodynamic models obtained was confirmed by the topological information contained in the Gibbs energy of mixing function (GM/RT).

1.Introduction

Sulfolane is an excellent aprotic polar solvent and an important chemical raw material,which is often used as an aromatic extractant,solvent for polymer spinning and many organic reactions[1-3].In the polymerization process of the high-performance polyarylether resin,sulfolane is usually used as the solvent [4-6],which will produce a large amount of wastewater containing low-concentration sulfolane.Currently,the sulfolane wastewater from polyarylether resin polymerization process is treated by the four-effect evaporation process,which is very energy-intensive since a large amount of water with high latent heat has to be evaporated[7].Furthermore,due to the increasingly stringent environmental regulations,the effluent from the current four-effect evaporation process cannot meet the discharge standard.Fortunately,liquid-liquid extraction is often used to recover organics in wastewater,which has shown many advantages,such as high efficiency and low energy consumption [8,9].

A suitable solvent is crucial for an effective liquid-liquid extraction[10].In the previous work,with dichloromethane as an extractant,the extraction-distillation hybrid process was developed for the sulfolane wastewater treatment,and the treated water and sulfolane can be reused [11].However,the boiling point of dichloromethane is only 39.75 °C,thus the overhead vapor of the extractant recovery column cannot be condensed economically by the circulating cooling water,which will increase the cost of the hybrid process.Therefore,an extractant with higher boiling point is needed to further reduce the cost of the hybrid process.Similar to dichloromethane,1,2-dichloroethane as the solvent in the synthesis of the special monomer DHPZ of polyarylethers is partially miscible with water and completely miscible with sulfolane.Moreover,the boiling point of 1,2-dichloroethane is 83.48°C,which is higher than that of dichloromethane.So,1,2-dichloroethane might be an extractant that could further reduce energy consumption of the hybrid process.However,to the best of our knowledge,the liguid-liguid equlibrium(LLE)data for mixtures(water+1,2-dichloroethane+sulfolane)has not been issued in the literature,which is the basis for designing of an efficient extraction process.

In this work,the LLE data for the ternary systems (water+1,2-dichloroethane+sulfolane) were measured at 288.15,298.15 and 308.15 K under atmospheric pressure (101.3 kPa).The extraction ability of 1,2-dichloroethane was investigated by the selectivity(S) and distribution coefficient (D).The empirical equations,such as Othmer-Tobias [12],Hand [13] and Bachman [14] equations were utilized to verify the reliability of the experimental LLE data.Because of the flexibility and ability to fit the immiscible multicomponent liquid-liquid systems,the nonrandom two-liquid(NRTL) [15] and the universal quasi-chemical (UNIQUAC) [16]models are widely used[8-10,17].The experimental LLE data were correlated by NRTL and UNIQUAC models,and the binary interaction parameters of the two thermodynamic models were obtained.The consistency of the correlation results was checked by the method suggested by Marcillaet al.[17],which was conducted by using the MATLAB software code (GMcal_TieLinesLL) [18].

2.Materials and Methods

2.1.Materials

1,2-dichloroethane and sulfolane were all purchased from Sigma-Aldrich.All chemical reagents were analytical agents and used without further purification.The ultrapure water produced by Milli-Q reference system was used herein.The details of the chemical reagents are listed in Table 1.

2.2.Experimental apparatus and procedure

A digital analytical balance (BS224S,Sartorius AG,Germany)was used to weigh the reagents with a resolution of ± 0.0001 g.The LLE of the ternary system (water+1,2-dichloroethane+sulfo lane) were conducted in a homemade jacketed glass equilibrium cell with a volume of 100 ml.The equilibrium cell was connected to a thermostatic bath (TMS8005-8R25,Zhejiang Thomossci Co.,China) with an accuracy of ± 0.1 K.Firstly,the ternary mixtures(water+1,2-dichloroethane+sulfolane) of known compositions were prepared gravimetrically.Secondly,the mixtures thermostated at the set temperatures,i.e.,288.15,298.15,and 308.15 K were stirred vigorously for 3 h to ensure that the solution was completely mixed.Thirdly,the mixtures were allowed to stand for 6 h to separate completely into two phases,which was sufficient to achieve phase equilibrium.Finally,the samples from the two phases were collected by a syringe for analysis.

2.3.Analysis

The samples were analyzed by a gas chromatograph (GC,Agilent 8860,USA)that was equipped with a flame ionization detector(FID)and an automatic sampler.The column was a DB-FFAP capillary column(Agilent Technologies Inc.),30 m length,0.53 mm i.d.,1.0 μm film thickness.The temperature of the injector and detector was kept at 523.15 K.The initial column temperature was kept at 353.15 K for 3 min,then programmed to 473.15 K at a rate of 10 K·min-1,and maintained for 8 min.Nitrogen was used as the carrier gas with a flow rate of 4.5 ml·min-1.The injection volumewas 0.2 μl,the split ratio was 8:1.The mass fractions of sulfolane and 1,2-dichloroethane were analyzed with the external standard method.The water content was calculated by the normalization method [19,20].Each sample was analyzed at least three times,and the average values were reported in Table 2.

Table 1Details of the chemical reagents

Table 2Experimental LLE data (mass fraction),distribution coefficient (D),and selectivity (S) of water(1)+1,2-dichloroethane(2)+sulfolane(3) at 288.15,298.15,and 308.15 K under 101.3 kPa

3.Results and Discussion

3.1.Experimental LLE data

The experimental data of the ternary system of water(1)+1,2-dichloroethane(2)+sulfolane(3) measured at 288.15 K,298.15 K,and 308.15 K were presented in Table 2,and the ternary diagrams were shown in Figs.1-3.As can be seen from Figs.1-3,the ternary systems exhibit the Treybal’s type I phase behavior[21],which has two pairs of completely miscible components (water+sulfolane and solfolane+1,2-dichloroethane),and one pair of partially miscible components (water+1,2-dichloroethane).In addition,the slopes of tie-lines are positive,which indicate that sulfolane is more soluble in the organic phase than in the aqueous phase [9].The two-phase regions are not changed significantly with the increasing temperature from 288.15 K to 308.15 K,which has been reported elsewhere [22].The fitting results of the Othmer-Tobias equation,the Hand equation,and the Bachman equation were presented in Supplementary Material.As listed in Table S4,all the values of correlation coefficients (R2) are greater than 0.99,which indicts that the LLE data measured in this work are reliable.The distribution coefficient(D)and selectivity(S)were utilized to evaluate the extraction performance of 1,2-dichloroethane.DandSare defined as follows [22-25],

whereandrepresent the mass fractions of water and sulfolane in aqueous phase (α),respectively.andrepresent the mass fractions of water and sulfolane in organic phase (β),respectively.The values ofDandSwere listed in Table 2 and illustrated graphically in Figs.4 and 5.

Fig.1.LLE phase diagram for the system of water(1)+1,2-dichloroethane(2)+sulfolane(3) at 288.15 K.●-●,experimental data;▲-▲,NRTL model;-,UNIQUAC model.

Fig.2.LLE phase diagram for the system of water(1)+1,2-dichloroethane(2)+sulfolane(3) at 298.15 K.●-●,experimental data;▲-▲,NRTL model;-,UNIQUAC model.

Fig.3.LLE phase diagram for the system water(1)+1,2-dichloroethane(2)+sulfolane(3) at 308.15 K.●-●,experimental data;▲-▲,NRTL model;-,UNIQUAC model.

As shown in Table 2,the values ofSin all cases are much greater than 1.0,which confirms that 1,2-dichloroethane is a feasible extractant for the separation of sulfolane from water.As can be seen from Figs.4 and 5,the values ofDandSdecrease with the increase of sulfolane concentration and temperature,which is similar to the experimental results published elsewhere [19,22,24].

3.2.LLE data correlation

In the current work,the experimental LLE data of the ternary system water(1)+1,2-dichloroethane(2)+sulfolane(3)were correlated with the NRTL and UNIQUAC models.According to the principle of thermodynamics,the following relationship should be satisfied after reaching the phase equilibrium.w hereandare the mole fraction and activity coeff icient of componentiin the aqueous phase,respectively;andare the mole fraction and activity coeff icient of componentiin the organic phase,respectively.The activity coeff icients are given by the thermodynamic models.

Fig.4.Distribution coeff icient versus mass fraction of sulfolane in the aqueous phase at different temperatures under 101.3 k Pa.●,288.15 K;▲,298.15 K;,308.15 K.

Fig.5.Selectivity versus mass fraction of sulfolane in the aqueous phase at different temperatures under 101.3 k Pa.●,288.15 K;▲,298.15 K;,308.15 K.

The equation of the NRTL model is as follow s,

Where,Ris the gas constant,xstands for mole fraction,nfor the number components.The non-randomness factor(α) of w ater and sulfolane,1,2-dichloroethane and sulfolane are f ixed at 0.3,and the α of w ater and 1,2-dichloroethane is f ixed at 0.2.τijand τjiare the adjustable parameters,w hich are related to the interaction energiesgijandgjjbetw een ai-jandj-ipair of molecules,respectively.

For the UNIQUAC model,the activity coeff icient of component is given by,

The binary interaction parameters for NRTL model and UNIQUAC model could be acquiredviaminimizing the maximum likelihood objective function(OF) [24],w hich w as conducted w ith Aspen Plus softw are (version 8.4) [29].The experimental LLE data in mass fraction w ere automatically converted to mole fraction by Aspen Plus softw are prior to the correlation.The f itting procedure w as performed w ith data in mole fraction.

w hereNrepresents the total number of tie-lines.represent the mole fractions of the experimental results and calculated values,respectively.The subscriptsi,landmrefer to the component,phase,and the tie-line,respectively.Generally,the root-mean-square deviation (RMSD) is applied to evaluate the consistency betw een the experimental data in mass fraction and the calculated results in mass fraction by the thermodynamic models [24,30].The RMSD equation is as follow s,

w here,represent the mass fractions of the experimental results and calculated values,respectively.

For the ternary system studied herein,the optimized binary interaction parameters of the NRTL and UNIQUAC models at 288.15,298.15 and 308.15 K are listed in Table 4.As show n in Table 4,all the RMSD values are less than 0.0091,w hich indicates that the NRTL and UNIQUAC models f it successfully the experimental LLE data.Furthermore,the calculated parameters of theNRTL and UNIQUAC models were checked by the method suggested by Marcillaet al.[17],which was conducted by using a GUI-MATLAB tool [18].The results confirmed the consistency of the correlation parameters obtained.Moreover,as illustrated in Figs.1-3,the results calculated by the NRTL and UNIQUAC models are consistent with the experimental LLE data.The graphical representations for the checking of correlation results are depicted in Supplementary Material.

Table 3UNIQUAC structural parameters (r and q)

Table 4Binary interaction parameters of NRTL and UNIQUAC models for the ternary system of water(1)+1,2-dichloroethane(2)+sulfolane(3) at 288.15,298.15,and 308.15 K under 101.3 kPa

4.Conclusions

In the current work,the LLE data for the ternary system of water+1,2-dichloroethane+sulfolane were measured at 288.15,298.15,and 308.15 K under 101.3 kPa.The distribution coefficient and selectivity showed that 1,2-dichloroethane is a feasible extractant for the separation of sulfolane from water.The experimental data were correlated by the NRTL and UNIQUAC models to obtain the binary interaction parameters.The values of RMSD are less than 0.0091,which means that the NRTL and UNIQUAC models fit successfully the experimental LLE data.Moreover,the coherence of the binary interaction parameters obtained was confirmed by the topological information contained in the Gibbs energy of mixing function (GM/RT).The binary interaction parameters obtained herein are essential for the simulation and optimization of the extraction-distillation hybrid process for the treatment of sulfolane wastewater with 1,2-dichloroethane as the extractant.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by National Key Research and Development Program of China (2017YFB0307600),Liaoning Revitalization Talents Program (XLYC1802073),and Dalian Highlevel Talent Innovation Support Program (2019RD08).

Supplementary Material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2021.09.006.

Nomenclature

Ddistribution coefficient

ginteraction energy between molecules pair,J·mol-1

Ntotal number of tie-lines

nnumber of component

qsurface parameter of UNIQUAC model

rvolume parameter of UNIQUAC mode

Rgas constant,J·mol-1·K-1

Sselectivity

Ttemperature,K

uinteraction energy between molecules pair,J·mol-1

wmass fraction

xmole fraction

zcoordination number

α non-randomness factor of NRTL model

γ activity coefficient

θ area fraction

τ adjustable parameter

φ segment fraction

Superscript

Ccombinatorial activity coefficient

Rresidual activity coefficient

α aqueous phase

β organic phase

Subscripts

icomponenti

jcomponentj

kcomponentk

lphase

mtie-line

1 water

2 1,2-dichloroethane

3 sulfolane