Mutual diffusion coefficients of n-butanol + n-heptane and n-pentanol + n-heptane from 288.15 K to 318.15 K

Highlights

• New data of mutual diffusion coefficients of n-butanol/n-pentanol + n-heptane were proposed at 288.15–318.15 K.

• Correlations as functions of mass fraction and temperature were presented.

• The modified Darken model and the Vignes model were used to interpret the concentration dependence of mutual diffusion coefficients.

Abstract

The mutual diffusion coefficients of n-butanol + n-heptane and n-pentanol + n-heptane were measured over the mass fraction of n-butanol or n-pentanol from 0.05 to 0.95 at intervals of 0.10 and the temperatures 288.15 K, 298.15 K, 308.15 K and 318.15 K at 0.101 MPa. The measurements were carried out using a digital holographic interferometry system. The expanded relative uncertainty of the mutual diffusion coefficients was estimated to be less than 2.4%. The influences of temperature and composition on the mutual diffusion coefficients were investigated. Moreover, equations for the mutual diffusion coefficients of the two binary mixtures were fitted to the data as functions of mass fraction and temperature. The correlations represent the data with the absolute average of relative deviations (AARDs) of 1.1% for n-butanol + n-heptane and 0.77% for n-pentanol + n-heptane, respectively.

Introduction

Alcohols have been suggested as fuel additives, which can significantly enhance the octane rating, reduce the exhaust emissions of diesel engine and improve the combustion efficiency [1], [2]. Compared with ethanol, n-butanol and n-pentanol have higher energy density, lower hygroscopicity, and lower volatility [3]. Recently, there has been increased interest in the performance and emission characteristics of diesel engines operating with n-butanol/diesel or n-pentanol/diesel fuel [1], [4], [5], [6]. n-Butanol and n-pentanol are also used as cosolvents [7] and hydrophobic solvents [8].

As for the complex compositions of diesel oil, n-heptane, which has a cetane number and combustion characteristics similar to diesel oil, is usually considered as the standard substances substituted for diesel oil in experimental and theoretical combustion studies [9], [10]. In recent years, many studies have focused on the thermodynamic properties and transport properties of n-butanol + n-heptane or n-pentanol + n-heptane mixtures, including vapor-liquid equilibria [11], [12], excess molar volume [13], [14], density [14], [15], viscosity [15], [16], speed of sound [17] and limiting activity coefficients [18].

Mutual diffusion is one of the most essential transport properties, critical for investigating the mass transfer mechanism for catalytic reactions and separation processes [19], [20]. Moreover, accurate knowledge of the mutual diffusion coefficients of fuel or fuel additives are necessary to study and optimize spray, atomization and combustion processes [21]. Nevertheless, there are no available reports on the mutual diffusion coefficients of n-butanol + n-heptane and n-pentanol + n-heptane up to now. Therefore, this work was undertaken to investigate the mutual diffusion coefficients of n-butanol + n-heptane and n-pentanol + n-heptane.

The diffusion behaviors of some alcohol + alkane binary mixtures have been studied, such as [22], [23]. Previously, our group has investigated the mutual diffusion coefficients of isopropanol + n-heptane and isobutanol + n-heptane at temperatures from 288.15 K to 323.15 K by the digital holographic interferometry method [24]. In this work, the mutual diffusion coefficients of n-butanol + n-heptane and n-pentanol + n-heptane are measured at temperatures from 298.15 K to 318.15 K and pressure 0.101 MPa, mass fractions from 0.05 to 0.95 at intervals of 0.10. The effects of composition and temperature on the mutual diffusion coefficients are discussed.