Temperature dependence of the volumetric properties of some alkoxypropanols + n-alkanol mixtures

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Abstract

The excess molar volumes VmE for binary liquid mixtures containing dipropylene glycol monomethyl ether or dipropylene glycol monobutyl ether and methanol, 1-propanol, 1-pentanol and 1-heptanol have been measured as a function of composition using a continuous dilution dilatometer at T=(288.15, 298.15, and 308.15) K and atmospheric pressure over the whole concentration range. The excess volume results allowed the following mixing quantities to be reported in all range of concentrations or at equimolar concentrations: α, volume expansivity; (∂VmE/∂T)p; (∂HE/∂P)T at T=298.15 K. The obtained results have been compared at T=298.15 K with the calculated values by using the Flory theory of liquid mixtures. The theory predicts the α, and αE values rather well, while the calculated values of (∂VmE/∂T)p and (∂HE/∂P)T show general variation with the alkyl chain length of the alkoxypropanols. The results are discussed in terms of order or disorder creation.

Introduction

Liquid mixtures containing alcohols and ethers seem to be very interesting from a practical point of view due to their increasingly used as additives to gasoline owing to their octane-enhancing and pollution reducing properties [1]. Binary systems of alkoxypropanols and 1-alkanols might generate interesting properties due to their complexity, specific interaction, hydrogen bond effects [2], [3], [4], [5]. A detailed understanding about the effect of the simultaneous presence of the ether (–O–) and hydroxyl (–OH) groups in the same molecule on the excess thermodynamic properties and the corresponding behavior of liquid mixtures containing two associating components is thus an interesting topic for study from both practical and fundamental view points.

So, the mixtures containing alcohols and ethers exhibit a particular challenge in order to describe their interaction behavior occurring in the solutions. Thermodynamic properties of the alkanol + alkane [6], [7], glyme + alkane [8], [9], polyether + alkanol or alkane [10], [11], [12] mixtures have been well studied. It seems interesting, therefore, to investigate the mixing functions in order to analyze the order effects in this class of mixtures and to check the Flory theory.

In previous papers [13], [14], [15] we reported excess molar volumes VmE, speeds of sound u and viscosities η of dipropylene glycol monomethyl ether + methanol, 1-propanol, 1-pentanol and 1-heptanol at T=298.15 K, and also excess molar volumes and viscosities [15] of dipropylene glycol monobutyl ether + 1-propanol at T=298.15 K. In the present paper, we report excess molar volumes VmE for mixtures of dipropylene glycol monomethyl ether and dipropylene glycol monobutyl ether with methanol, 1-propanol, 1-pentanol or 1-heptanol at T=(288.15, 298.15, and 308.15) K and atmospheric pressure over the complete composition range. The present study was therefore undertaken to assess the effect of specific interactions on the excess properties with the increase of temperature, and the influence of both the alkyl chain length in the alkanol and the alkyl group size of alkoxypropanols. An attempt is also made to interpret the results by deriving the different mixing properties like α, αE, (∂VmE/∂T)p and (∂HE/∂P)T at T=298.15 K. By using the Flory theory, the above thermodynamic mixing functions have been calculated and compared with experimental results.

Section snippets

Materials

Spectroscopic grade alcohols were dried and fractionally distilled as described elsewhere [16]. Dipropylene glycol monomethyl ether (DGME) (Merck-Schuchardt, F.R.G., g.c. mass fraction >0.95), and dipropylene glycol monobutyl ether (DGBE) (Aldrich, mass fraction >0.99) were used without further purification. All samples were stored and protected from atmospheric moisture and CO2. Before measurements, all liquids were partially degassed under vacuum and carefully dried over 0.4 nm molecular

Experimental results

Experimental results of the excess molar volumes of all the binary mixtures as a function of mole fraction and temperature are reported in table 2. The values of VmE for all systems were fitted to the Redlich–Kister equation of the form:VmE=x(1−x)∑j=1naj(2x−1)j−1,where aj is the polynomial coefficients, n is the polynomial degree, x and (1−x) are the mole fraction of alkoxypropanol and alkanol, respectively. The values of coefficients aj were determined by a multiple regression analysis based

Theoretical model

The Flory model [31], [32] has been commonly employed to analyze the molar volume of the mixture and the excess molar volume parting from the equation of the state in function of the reduced variables:P̃ṽ/T̃=[ṽ1/3/(ṽ1/3−1)]−1/(ṽT),whereV=V/ṽ=V[(1+αT)/(1+(4/3)αT)]3,P=P/P̃=[(αTṽ2)/κT],T=T/T̃=ṽ4/3/(ṽ1/3−1).Theoretical values of dVmE/dT [33] were calculated from the Flory theory usingT(dVmE/dT)=i=12xiVi[T(dṽ/dT)]−∑i=12xiVi[T(dṽ/dT)]i,whereT(dṽ/dT)=ṽ(1−ṽ−1/3)/[(4/3)ṽ−1/3−1].In

Results and discussion

FIGURE 2, FIGURE 3 show VmE data for binary mixtures of (DGBE + 1-propanol) at T=298.15 K and of (DGME + alcohol) at 308.15 K, respectively. We have not reported the experimental data at other temperatures as the curves are similar in nature. For all the mixtures studied, the VmE values are negative over the whole mole fraction range with exception of DGME with 1-pentanol and 1-heptanol at T=(288.15 and 298.15) K and decrease with increased temperature. The magnitude of VmE increases at each

Acknowledgements

Harsh Kumar thanks the Council of Scientific and Industrial Research (CSIR), New Delhi for a Senior Research Fellowship (Fellowship No. 9/105/107/2001/EMR-I) and financial assistance.

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