Excess properties and spectroscopic studies for binary system polyethylene glycol 600+dimethyl sulfoxide at T=(298.15,303.15,308.15,313.15,and 318.15)K

Liang Ma,Feng Sha,Xianshu Qiao,Qiang Li,Jianbin Zhang*

College of Chemical Engineering,Inner Mongolia University of Technology,Hohhot 010051,China

1.Introduction

Sulfur dioxide(SO2),which is mainly from fossil fuel combustion,has become a serious environmental and health issue[1].Removal of SO2from flue gases,namely flue gas desulfurization(FGD),has been an increasingly concerned environmental challenge and a mandatory policy of many countries[2].

In recent years,organic liquids are often used to remove SO2,which is a better choice because of its high efficiency,low cost,and without byproducts.Meanwhile,dimethyl sulfoxide(DMSO)was seen as a widely used organic solvent.In our recent work[3],DMSO showed a strong capability to absorb SO2with about 0.73 g SO2per 1.00 g DMSO.However,pure DMSO was limited to scrub SO2due to its relatively high freezing point(18°C).To overcome disadvantages,PEG400 was added into DMSO to drop the freezing point of DMSO and improve SO2absorption performance[3].In order to systematically study regularity ofethylene glycolderivative(EGs)+DMSOmixtures with the polymerization degree of EG increasing,polyethylene glycol 600(PEG)was added into DMSO.In addition,PEG comprises a series of linear chain polymers of oxyethylene units and its low toxicity,and high solubility in water make itused widely in the pharmaceutical,chemical,cosmetic,and food industries[4].

Physicochemical properties ofabsorbents,including density(ρ),viscosity(η),and excess properties data,were necessary for industrial application and in modeling,simulation and design ofgas–liquid contactor columns in SO2absorption and regeneration processes[5,6].However,these data were very lacking as the basic data,so we had to determine these data for the binary system PEG(1)+DMSO(2)for future industrial application.

This work was mainly focused on investigating density and viscosity data of the system PEG(1)+DMSO(2)for the entire composition range atT=(298.15,303.15,308.15,313.15,and 318.15)K.On the basis ofexperimentalresults,excess molarvolume(VmE),viscosity deviation(Δη),excess free energies of activation(ΔG*E),apparent molar volume(Vφ,1andVφ,2),partial molar volumes(V1andV2),and isobaric thermal expansion coefficient(αp)were calculated.Moreover,the possible intermolecular interaction of PEG with DMSO was investigated using FTIR and UV spectroscopic techniques.

2.Experimental Section

2.1.Materials

PEG600(CAS NO:25322-68-3)was purchased from Beijing Reagent Company(Beijing,China,Content≥99.0%).DMSO(CAS NO:67-68-5)was purchased from Tianjin Reagent Company(Tianjin,China,Residue on ignition≤0.1%).The high-performance liquid chromatography tivity lower than 0.1 mS·cm?1(25 °C)and HPLC grade ethanol were used to correct the pycnometer and Ubbelohde viscometer,respectively.All information of chemicals was listed in Table 1.

FTIR spectra were recorded on a Nicolet(Nexus 670)FTIR spectrometer with a resolution of 1 cm?1in the range from 4000 to 400 cm?1.The spectrometer possesses auto-align energy optimization and a dynamically aligned interferometer and is fitted with two constringent BaF2pellets forthe measurementofaqueous solution.Abaseline correction was made for the spectra recorded in air;and then 10 μl solutions were used to perform on the FTIR spectrometer in each measurement and the thickness of sample layers was less than a typical thickness of 2 μm.All spectral experiments of PEG600(1)+DMSO(2)were performed at room temperature and atmospheric pressure.

UV spectra were recorded on a Shimadzu(UV-2450)UV–Vis spectrometer with a resolution of 0.5 nm in the range of 190 to 700 nm at room temperature.The PEG600 could be used to make a baseline correction for the spectra because then→σ*electronic transition of oxygen atom in PEG600 was often found at the vacuum ultraviolet region.(HPLC)grade ethanol(CAS No:64-17-5)with a purity of minimum mass fraction of 99.8%was purchased from Beijing Reagent Company(Beijing,China,Content≥99.8%).All chemicals were used after drying over 4×10?10m molecular sieves and ultrasonic degassing.The mass purity of final PEG600 and DMSO,as found by gas chromatography(GC),was betterthan 99.3%and 99.5%.Bidistilled waterwith itsconduc-

Table 1Specification of chemical samples

2.2.Measurements

All measurements of mass were performed on an electronic balance with an accuracy of 0.1 mg(Sartorius BS224S).Densities of pure liquids and their mixtures were determined with a bicapillary pycnometer having a bulb volume of 25 cm3.The volume of pycnometer was calibrated with bidistilled water as a function of temperature.The pycnometer filled with liquid was kept in thermostatically controlled and wellstirred water bath(precision:±0.01 K)for 25 min to obtain the thermal equilibrium.The uncertainty of mole fraction was estimated to be±0.0001.Density was measured atT=(298.15,303.15,308.15,313.15 and 318.15)K,respectively.Each final experimental density value was an average of atleastthree measurements,and the expanded uncertainty of the density measurement was estimated to be±0.020 g·cm?3.

Viscosity values of both pure components and their mixtures were determined with a commercial Ubbelohde-type capillary viscometer,which was calibrated with bidistilled water and ethanol(HPLC grade)within the experimental temperature range.The viscometer filled with liquid was keptin waterbath for 25 min to attain the thermalequilibrium.After thermal stability was reached,the flow time was determined with a digital stopwatch(±0.01 s).All the measurements were accomplished in a transparentglass-walled waterbath with the thermal stability at 0.01 K.The average of 16 flow times for each fluid was used to calculate its kinematic viscosity(v)value.The expanded uncertainty of the viscosity measurements was estimated to be ±0.028 m2·s?1.Comparison of the literature values and experimental values for pure substances were listed in Table 2[7–19],and the agreement between the experimental and literature values was found to be satisfactory.

3.Results and Discussion

3.1.Density and viscosity

The measured density and viscosity values of PEG,DMSO and their mixtures under atmospheric pressure in the temperature range from 298.15 Kto 318.15 Kwere listed in Table 3,and the density and viscosity data were respectively plotted in Figs.1 and 2 with component concentration and temperature as independent variable.

In particular,the kinematic viscosity(v)values were calculated from Eq.(1):

wheretis its flow time in the viscometer,andAandBare viscometer constants,which were determined with the calibration fluids of bidistilled water and HPLC grade ethanol.

The absolute viscosity(η)value was calculated from Eq.(2):

where ρ is density value of PEG(1)+DMSO(2)mixtures.

As shown in Fig.1,the density values of PEG(1)+DMSO(2)mixtures increased with the increasing PEG concentration at the same temperature;meanwhile,the density values gradually decreased with increasing temperature at the same concentration.The viscosity values(Fig.2)increased with increasing mole fraction of PEG and decreased with increasing temperature at the same concentration.

Table 2Comparison of experimental density and viscosity values of PEG and DMSO with literature values at various temperatures

Table 3Experimental density and viscosity values for PEG(1)+DMSO(2)in the temperature range from 298.15 K to 318.15 K which the step of 5 K①

To forecast density and viscosity data over the entire concentration range,the experimental density and viscosity values were fitted with Eqs.(3)–(6)[20,21].Specifically,Eq.(3)was used to infer the relationship between density and composition,Eq.(4)was used to infer the relationship between viscosity and composition,Eq.(5)was used to estimate the relationship between density and temperature,and Eq.(6)was used to estimate the relationship between viscosity and temperature:

Fig.1.Experimental density values with mole fraction for PEG(1)+DMSO(2):□,298.15 K;○,303.15 K;△,308.15 K;+,313.15 K;and×,318.15 K.

Fig.2.Experimentalabsolute viscosity values with mole fraction for DMSO(1)+PEG(2):□,298.15 K;○,303.15 K;△,308.15 K;+,313.15 K;and×,318.15 K.

whereai,bj,c0,c1,c2,and η0are the undetermined parameters,ω1is the mass fraction of PEG,x1is the mole fraction of PEG,Ris ideal gas constant,Tis absolute temperature of mixtures,Eais activation energy,ρcal.1and ρcal.2refer to the density calculated value by Eqs.(3)and(5),and ηcal.1and ηcal.2are the viscosity calculated value by Eqs.(4)and(6).

The absolute average deviations(AAD)were calculated by Eq.(7):

whereYexp.refers toρexp.orηexp.andYcal.isρcal.orηcal.,respectively,andndenotes the number of experimentalpoints.Allabove parameters and AAD were listed in Tables 4 and 5.

3.2.Excess properties

The excess molar volume(VmE)values were calculated from experimental densities according to Eq.(8)[22]:

Table 4The fitting parameters for density and viscosity against componentconcentration,and the values of average absolute deviation and the degree of fitting

Table 5The fitting parameters for density and viscosity against temperature,and the values of average absolute deviation and the degree of fitting

where ρmrepresents density of mixtures;andx1,ρ1,M1,x2,ρ2,andM2denote the mole fractions,densities,and relative molecular mass of pure PEG and pure DMSO.The results ofVmEwere plotted in Fig.3.

Fig.3.Excess molar volumes(V mE)with mole fraction for DMSO(1)+PEG(2):□,298.15 K;○,303.15 K;△,308.15 K;+,313.15 K;and×,318.15 K.

Fig.3 showed that theVmEvalues of binary system PEG(1)+DMSO(2)were negative for all of the mixtures over the entire mole fraction range,and the minimum was obtained at aboutx1≈0.35,which showed that the volume of the tow-component was minimum.The negative contributions were a consequence of the following effects:(1)from a macroscopic point of view,the negativeVmEvalues indicated that there was a volume contraction on mixing,and considering the physical interactions important in these mixtures,(2)structural effects which arise from suitable interstitial accommodation giving more compact structure of mixtures,and(3)strong intermolecular interactions attributed to the charge-transfer,hydrogen bonding between unlike molecules finally leading to the more efficient packing in the mixture than in the pure liquids[23,24].DMSO molecules enter into the space among PEG molecules when these two kinds of liquids are mixed,and it is worth noting that the minimum is aboutx1≈0.35,which indicated that PEG molecule could combine DMSO molecule and the intermolecular binding most closely when the molar of PEG and DMSO was at about 1:2 in mixtures.The reason can be related to the intermolecular interaction between PEG and DMSO,and the reason was proved by FTIR and UV–Vis in the next section.

The viscosity deviation(Δη)values were calculated from absolute viscosity values according to Eq.(9):

whereη1andη2represented the absolute viscosity ofpure PEGand pure DMSO,respectively.The results of Δη were plotted in Fig.4.

Fig.4 showed the dependence of Δη on composition and temperature.It could be seen from each Δη curve of the system PEG(1)+DMSO(2)that the Δη change trend was similar and there were two extreme points:the minimum was aboutx1≈0.05 and maximum was aboutx1≈ 0.5,respectively,and the absolute values of Δη decreased with the increasing temperatures.

The ΔG*Evalues were calculated using Eq.(10)[25]:

whereV,V1andV2are the molar volumes of mixtures,PEG,and DMSO.The ΔG*Evalues were plotted in Fig.5.

Fig.4.Viscosity deviations(Δη)with mole fraction for PEG(1)+DMSO(2):□,298.15 K;○,303.15 K;△,308.15 K;+,313.15 K;and×,318.15 K.

Fig.5.Excess free energies of activation(ΔG*E)for viscous flow with mole fraction for DMSO(1)+PEG(2):□,298.15 K;○,303.15 K;△,308.15 K;+,313.15 K;and×,318.15 K.

As shown in Fig.5,theΔG*Evalues were positive over the entire concentration range for the binary system PEG(1)+DMSO(2)at all temperature points,and the maximum values were presented at aboutx1≈0.3.

The values ofVmE,Δη,and ΔG*Ecould be correlated by the Redlich–Kister type polynomial,respectively[26]:

whereZdenotesVmEcal.,Δηcal.,or ΔG*Ecal.,nis the polynomial degree,and the coefficients ofBiare parameters,which were obtained by fitting Eq.(11)to the experimental values with a least-squares method.

To investigate the fitting efficiency forVmE,Δη and ΔG*E,the standard deviation(σ)values between the calculated and experimental data were obtained by Eq.(12)[27]:

whereYreferred toVmE,Δη,or ΔG*E,andNandmwere the number of experimental points and number of parameters retained in the respective equations.All the fitting parameters and the degree of fitting(R2)were given in Table 6.Apparentmolar volume and partialmolar volume were shown in Tables 1 and 2.

3.3.Coef ficient of thermal expansion

The isobaric thermal expansion(αp)was one of the most important fundamental properties,which described how fluid volume changed with temperature.It was closely related to various thermophysical properties,including heatcapacity,thermalpressure coefficient,and internal pressure[28].In general,the thermal expansively data cannot be ignored for industrial application,and the coefficient of thermal expansion was de fined by Eq.(13)[29]:

Fig.6 showed that the experimental values of lnρ against(T—298.15)were fitted by the method of the least-squares for each binary mixture.The coefficient of thermal expansion was obtained from the slope of the straight line,and the coefficientof thermal expansion values and the degree of fitting were listed in Table 7.

3.4.Spectral properties

3.4.1.UV–Vis spectra

As shown in Fig.7,absorption bands at nearly 233 nm belonged to then→ π*electronic transition of the unshaped electronic pair ofoxygen atom in DMSO.With the increase of DMSO concentration,the characteristic absorption peak red shifted and strengthened.The absorption peak red shifted from the possible reasons:hydrogen bonding interaction between the hydroxyl hydrogen atoms of PEG and oxygen atoms of DMSO,which weakened the constraints of the oxygen atoms for the lone pair electrons to make the transition easier.In this process,hydrogen bonding interaction between the hydroxyl oxygen atoms of PEG and oxygen atoms of DMSO was possibly expressed as(CH3)2S=O…H--(OCH2--CH2--OO)600--H…O=S(CH3)2.

Table 6Coefficients of Redlich–Kister equation,standard deviations and degree of fitting values(R2)for excess molar volumes,viscosity deviation,and excess Gibbs free energies of activation for PEG(1)+DMSO(2)at T=(298.15,303.15,308.15,313.15,and 318.15)K

Fig.6.Plots of lnρ against(T?298.15)/K for the PEG(1)+DMSO(2)system at various concentrations,the molar fractions corresponding to lines as follows:A 0.0000;B 0.0068;C 0.0143;D 0.0225;E 0.0315;F 0.0416;G 0.0529;H 0.0655;I 0.0799;J 0.0903;K 0.1152;L 0.1373;M 0.1634;N 0.1947;O 0.2330;P 0.2809;Q 0.3425;R 0.4246;S 0.5396;T 0.7122;and U 1.0000.

Table 7The values ofcoefficientofthermalexpansion,the degree of fitting and standard deviation

Fig.7.UV–Vis spectra ofbinary system ofDMSO+PEGand electronic transitions red-shift from 232 to 247 nm with the decreasing DMSO concentrations.

3.4.2.FTIR spectra

As shown in Fig.8,the peak at 3465 cm?1was due to the stretching vibration of hydroxylgroup in PEG.The stretching vibration of hydroxyl shifted from 3465 to 3370 cm?1with increasing mass fraction of DMSO in the binary system PEG(1)+DMSO(2),because the intermolecular hydrogen bond of alcoholic hydroxyl in PEG was gradually destroyed with the increase of DMSO concentration,and the new hydrogen bonds between PEG and DMSO were formed with the absorption peak moving towards lower wavenumber.The stretching vibration of S=O(1055 cm?1)in DMSO was split into two new absorption bands at 1103 and 1055 cm?1[30].The former could be assigned to the interaction of S=O with hydroxyl in PEG,while the latter to the free S=O groups or S=Ogroups forming cyclic dimmer with another DMSO molecule[31].Although FTIR results showed that there were hydrogen bonding between the intramolecular molecules of PEG,the interaction of hydroxyl hydrogen in PEG with oxygen in DMSO was much stronger,which was similar to that between DMSO and methanol[32].

Fig.8.FTIR spectra of PEG,DMSO,and PEG(1)+DMSO(2)mixtures with various concentrations.

According to UV–Vis and FTIR spectral results,intermolecular interactions in the binary system PEG(1)+DMSO(2)included hydrogen bonding and interactions between PEG and DMSO as the formation of(CH3)2S=O…H--(OCH2--CH2--O)PEG--H…O=S(CH3)2.

4.Conclusions

This paper reported experimental data for the densities and viscosities for the binary system PEG(1)+DMSO(2)over the entire concentration range atT=(298.15,303.15,308.15,313.15,and 318.15)K as a function of composition under atmospheric pressure.At the same time,these data were used to calculate excess molar volume,viscosity deviation,excess free energies ofactivation,and coefficientofthermalexpansion of the system.TheVmEvalues of binary system PEG(1)+DMSO(2)were negative and the minimum was obtained at aboutx1≈0.35,while the values of ΔG*E,apparent molar volume and partial molar volumes were positive for all of the mixtures over the entire mole fraction range.Moreover,the spectral results for the mixture indicated that there were the hydrogen bonding and interactions of hydroxyl hydrogen atoms in PEG with oxygen atoms in DMSO to form the structure of(CH3)2S=O…H--(OCH2--CH2--O)PEG--H…O=S(CH3)2.

Acknowledgments

This work was supported by the NaturalScience Foundation of Inner Mongolia Autonomous Region(2016JQ02),the Program for Grassland Excellent Talents of Inner Mongolia Autonomous Region,Program for New Century Excellent Talents in University(NCET-12-1017),and training plan of academic backbone in youth of Inner Mongolia University of Technology.

Appendix A.Supplementary Data

Apparent molar volume and partial molar volume.Supplementary data associated with this article can be found in the online version,at http://dx.doi.org/10.1016/j.cjche.2017.01.001.

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