Excess volumes and partial molar volumes of binary liquid mixtures of furfural or 2–methylfuran with alcohols at 298.15 K

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Highlights

  • Densities and volumetric properties were determined for furfural + alcohols.

  • Densities and volumetric properties were determined for 2-methylfuran + alcohols.

  • Excess molar volumes were correlated with Redlich-Kister equation.

  • Solute partial molar volumes increase with the alcohol carbon chain length.

  • Excess molar volumes are smaller for furfural systems than for 2–methylfuran.

Abstract

In this work, densities, excess molar volumes, partial molar volumes and excess partial molar volumes for binary liquid mixtures of furfural and 2–methylfuran with 1–propanol or 2–propanol or 2–butanol or 1–pentanol or 2–pentanol or 1–hexanol at 298.15 K and 0.1 MPa over the entire range of composition were determined. Excess molar volumes were correlated with Redlich–Kister equation with average absolute deviations smaller than 0.0164. Excess molar volumes were negative for furfural + 1–propanol or 2–propanol and positive for all other studied binary systems. Solute partial molar volumes determined increase as alcohol carbon chain length increase, except for furfural + 2–pentanol, which presented smaller values than 2–butanol for molar fractions below 0.2. A maximum/minimum was observed from the excess partial molar volume plots. FTIR spectra data indicate bands at 3135 cm−1, for furfural systems, and 3122 cm−1 for 2–methylfuran systems, are related to the behavior found for excess molar volumes and that H–bonds are smaller for furfural systems than for 2–methylfuran.

Introduction

Ethanol and biodiesel have been thought of as the market–leading gasoline alternative due to the strong environmental appeal and to its mass production methods [1]. However, some limitations of these biofuels as a direct substitute to petroleum have inspired the development of alternative chemical catalytic transformation products and furfural and 2–methylfuran (furan type biofuel) are some examples [2].

Furfural is a raw material for production of furfuryl alcohol [3], a compound which in turn can produce biofuels additive [4]. Furfural can be produced either as a principal or secondary product from lignocellulose bio–refineries through dehydration of pentoses [5]. Besides, 2–methylfuran is considered better than ethanol in terms of production efficiency, energy density, handling and storage. It is particularly very attractive due to its physical and chemical properties, such as the research octane number (RON = 103) and its motor octane number (MON = 86) that are similar to those of gasoline [6]. Additionally, it is not soluble in water and can be used directly or blended with gasoline in motor vehicles [2]. 2–methylfuran is obtained from carbohydrates or cellulosic biomass and through reaction between furfural and hydrogen [7], [8]. Its production process involves separation from the synthesis (hydrogenolysis) of HMF over a CuRu catalyst, extracting solvent and unreacted intermediates. Several solvents have been tested in the 2–methylfuran and furfural production and purification, among them 1–butanol, 2–butanol, 1–hexanol, methylisobutylketone and toluene [9], [10].

In order to explore furfural and 2–methylfuran production processes and their applications as fuels and fuel additives, it is necessary to study excess thermodynamic properties of their mixtures with solvents [8], [11], [12], [13], [14]. The knowledge of thermodynamic properties of binary liquid mixtures is very important to process design and scale up and can be used as compound content monitoring tool for chemical process streams including mixing, reaction, separation and storage equipment. Such information are required, for instance, to obtain excess Gibbs energy of activation and excess molar enthalpies [11], [15], [16], [17]. From a practical point of view, the ability of different available models to predict volumetric properties can be tested using such values [18].

A survey of the literature shows that densities and volumetric properties data available for {furfural or 2–methylfuran} + alcohols are scarce. 2–methylfuran binary mixtures with solvents were investigated previously employing 1,1,2,2–tetrachloroetane a solvent [19]; and furfural were investigated with 1–propanol, 2–propanol, 1–butanol and 2–butanol at 308.15 K [20]. The excess molar volumes of binary liquid mixtures of furfural + 1–butanol/2–butanol as function of the composition were measured by Bendiaf et al. [21] at 283.15, 293.15, 303.15 and 313.15 K, but no data were founded at 298.15 K.

Volumetric behavior of solutions is commonly obtained through density measurements and molecular interactions between solute and solvent can be qualitatively investigated using excess and partial molar volumes [12], [22], [23], [24], [25]. Nature of such intermolecular interactions can be studied through FTIR analyses, such as those determined by Hasan et al. [26] for n–butyl acetate + primary alcohols systems. Thus, the study of excess thermodynamic properties with FTIR analyses for binary liquid mixtures containing furfural/2–methylfuran and alkanols is of considerable interest to understanding the behavior of intermolecular interactions, such as H–bonding interactions, presented in such systems.

In this work, densities, excess molar volumes, partial molar volumes and excess partial molar volumes were determined for binary liquid mixtures of furfural + 1–propanol /1–pentanol/1–hexanol/2–propanol/2–butanol/2–pentanol and 2–methylfuran + 1–pentanol/1–hexanol/2–propanol/2–butanol/2–pentanol at T = 298.15 K and 0.1 MPa. Furthermore, FTIR investigations for some mixtures were carried out to get information regarding the nature of molecular interactions between component molecules. To the best of our knowledge, these data were not reported before.

Section snippets

Chemicals

All substances were degassed for 2 h by an ultrasonic method before each experiment and the glass vials were washed with detergent, water, methanol and doubly deionized water, and dried before use. The 2–methylfuran, furfural and alcohols utilized were purchased from Sigma–Aldrich (USA). The purities of all reagents are given on the certificate by the manufacturer as shown in Table 1.

As can be observed in Table 1, the combined standard uncertainties for the density of 1–propanol (0.997 of mass

Excess molar volumes and Redlich–Kister correlation

Density measurements were utilized to determine excess molar volumes, VmE, for binary liquid mixtures, through Eq. (1):VmE=i=12xiMi1ρ-1ρi=x1M11ρ-1ρ1+x2M21ρ-1ρ2where xi is molar fraction of ith component; Mi is the ith component’s molar mass (kg.kmol−1); ρ is the mixture’s density (kg.m−3); ρi is the ith component’s density (kg.m−3); x1, M1 and ρ1 are molar mass and density of solute (kg.m−3), respectively; and x2, M2 and ρ2 are molar mass and density of solvent (kg.m−3), respectively.

Excess

Furfural + alcohol systems

Densities, excess molar volumes, partial molar volumes and excess partial molar volumes determined for furfural (1) + alcohols (2) liquid mixtures at 298.15 K and 0.1 MPa are shown in Table 2.

Results presented for the furfural + alcohol liquid mixtures shown a higher combined standard uncertainty for furfural mass fraction uc(x1) equal to 0.65%. For these mixtures, the combined standard uncertainty of VmE increased from 0.9 to 2.2 × 10−7 m3.mol−1. The higher combined standard uncertainty of VmE

Conclusions

Densities were experimentally measured for {furfural or 2–methylfuran} + {1–propanol or 2–propanol or 2–butanol or 1–pentanol or 2–pentanol or 1–hexanol} at 298.15 K and 0.1 MPa. Such data were used to obtain excess molar volumes, solute and solvent partial molar volumes and excess partial molar volumes. Excess molar volumes were correlated with Redlich–Kister equation presenting average of absolute deviations smaller than 0.0164. Systems with furfural + 1–propanol or 2–propanol presented

Acknowledgment

The authors wish to acknowledge FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil. Grants: 2016/05950–5, 2012/05027–1 and 2014/21252–0) for their financial support.

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