Elsevier

Thermochimica Acta

Volume 624, 20 January 2016, Pages 1-7
Thermochimica Acta

Mutual diffusion behavior of short chain alcohols + n-octane mixtures

https://doi.org/10.1016/j.tca.2015.11.024Get rights and content

Highlights

  • Mutual diffusion coefficients of alcohols + n-octane mixtures were measured.

  • The influence factors of the mutual diffusion coefficient are investigated.

  • A new correlation is proposed to fit the experiment data.

Abstract

Mutual diffusion coefficients of several short chain alcohols (ethanol, n-propanol and n-butanol) + n-octane mixtures in the temperature range from 283.2 K to 313.2 K at different concentrations were measured using holographic interferometry. The relation between the mutual diffusion coefficient with temperature, viscosity, concentration and molecular weight is investigated, respectively. The Onsager–Fuoss model is applied to analyse the various influence factors. A new correlation taking into account the effect of the temperature and concentration on the mutual diffusion coefficient is proposed to fit well the experimental data.

Introduction

Biodiesel mainly refers to the fatty acid monoalkyl ester produced by the transesterification of the grease, vegetable oils or animal fats with short chain alcohols. It has been proven to be a promising alternative fuel for diesel engine. Compared with traditional fuels, it has lots of advantages: excellent environmental performance, low-temperature startup, stability, renewability and so on [1], [2]. But in the production of biodiesel the grease and alcohols are not miscible with each other, and the mass transfer is limited. The immiscibility will leads to the formation of two phases and so the reaction only takes place in the interphase boundary, which will result in a obvious drop in the reaction conversion and reaction rate [3]. This problem can be overcome by the addition of the cosolvent in reaction system. The cosolvent helps to create a single homogeneous phase of the grease and alcohols, and greatly accelerates the reaction conversion and reaction rate [4], [5]. The cosolvent used in the production of biodiesel mainly includes the following categories: (i) alkanes and cycloalkanes; (ii) ketone; (iii) ether; (iv) alcohols; (v) other common solvents [6].

The mutual diffusion coefficients of short chain alcohols + cosolvent mixtures strongly affect the catalytic reaction and separation processe in the production of biodiesel [7], [8]. The accurate data is used for predicting the rate-limiting factors in chemical reaction and further optimizing the design of processing equipment. Bosse et al. [9] measured the mutual diffusion coefficients of alcohols + n-hexane and alcohols + cyclohexane at 298.15 K over the whole concentration range; Ramakanth et al. [10] measured the mutual diffusion coefficients of alcohols + cyclohexane at 298.15 K and different concentrations. n-Octane, one kind of alkanes, has attracted the increasing interest as an excellent cosolvent in the production of biodiesel [8]. But there are no the mutual diffusion coefficient data of short chain alcohols + n-octane.

Therefore, in this work, the mutual diffusion coefficients of different short chain alcohols (ethanol, n-propanol and n-butanol) + n-octane mixtures were measured by holographic interferometry. The mass fraction and temperature range are from 0.1 to 0.9 and from 283.2 K to 313.2 K, respectively. The relation between the mutual diffusion coefficient with temperature, viscosity, concentration and molecular weight is investigated, respectively. A new correlation was presented for the experimental data.

Section snippets

Materials

All chemicals in this work were supplied by Aladdin Industrial Corporation and used without any further purification. Table 1 presented molecular formula, molecular weight and purities of the chemicals. For the sample preparation, the chemicals were weighted by an electronic balance (Shanghai Shunyu FA2004, uncertainty: 0.1 mg). Two chemicals are thoroughly stirred in a 100 mL reagent bottle, and then let them stand for about 24 h before using them.

Experimental system

Fig. 1 shows the schematic of the holographic

Results and discussion

To verify the accuracy and reliability of the experimental system used in this work, the mutual diffusion coefficient of 0.33 mol L−1 KCl aqueous solution was measured at 298.15 K as a reference point. The experimental value is compared with those from the literatures, as shown in Table 2. Our experimental result agrees well with others and the maximum relative deviation is 1.07%.

The mutual diffusion coefficients of short chain alcohols (ethanol, n-propanol and n-butanol) + n-octane mixtures at

Conclusions

In this study, the mutual diffusion coefficients of several short chain alcohols (ethanol, n-propanol and n-butanol) + n-octane mixtures were measured by holographic interferometry. The temperature and mass fraction ranges are from 0.1 to 0.9 and from 283.2 K to 313.2 K. It is observed that the mutual diffusion coefficients of binary mixtures decrease with the increasing molecular weight of the solute at constant concentration and temperature, and increase with the increasing T/η. With the

Acknowledgements

This work was supported by the National Science Fund for Distinguished Young Scholars of China (Grant No. 51525604). The authors gratefully acknowledge for financial support.

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