Elsevier

Fluid Phase Equilibria

Volume 354, 25 September 2013, Pages 147-155
Fluid Phase Equilibria

LLE for the systems ethyl palmitate (palmitic acid)(1) + ethanol(2) + glycerol (water)(3)

https://doi.org/10.1016/j.fluid.2013.06.027Get rights and content

Highlights

  • We measured LLE for the ethanol-based biodiesel systems. Ethyl palmitate + ethanol + glycerol (or water) were measured.

  • Palmitic acid + ethanol + water were also measured.

  • Tie lines and binodal curves were measured for all systems.

  • The experimental data were modeled using NRTL, UNIQUAC and UNIFAC models.

Abstract

This work reports a new experimental set of liquid–liquid equilibrium measurements for the systems ethyl palmitate(1) + ethanol(2) + glycerol(3) and ethyl palmitate(1) + ethanol(2) + water(3) at atmospheric pressure and at 298.15 K and 313.15, and for the system palmitic acid(1) + ethanol(2) + water(3) at 338.15 K. The liquid-phases compositions were measured by determining their refractive index and densities. Solubility curves (binodal) were also obtained by cloud-point method for ternary systems. The experimental data were satisfactorily correlated by NRTL and UNIQUAC equations. A comparative analysis was performed using the UNIFAC-LL and UNIFAC-Dortmund group contribution method. Interesting results from thermodynamics models were obtained for the systems studied in this work.

Introduction

Now a days, intensive researches have been carried out with the main objective of developing renewable and economically sustainable alternative sources focusing the biodiesel processes development and production. Biodiesel consists of a mixture of alkyl esters of fatty acids, which can be obtained from renewable biomass sources [1].

In biodiesel production two main routes can be pointed; the transesterification, in which glycerol is produced as a byproduct and it must be separated from biodiesel, and the second one is the esterification, in which water is produced as byproduct. In both cases the liquid–liquid phases occurrence is possible due to high immiscibility between esters of fatty acids–glycerol, esters of acids–water, and fatty acid–water. In the systems related these two routes (transesterifications and esterification) the alcohol (methanol or ethanol) is the solute that can solubilize the immiscible pairs. Then, the LLE phase behavior knowledge of these systems is a fundamental issue on the biodiesel plant design and optimization.

An increasing demand on the thermodynamic properties of biodiesel related systems has been viewed due to the great interest in the biodiesel production processes. In this sense, volumetric properties, as LLE, have an important rule in the reaction and separation plant designs, modeling process, simulation and optimization steps aiming an economically based biodiesel production.

Although methanol is the commonly used alcohol for biodiesel production, due to its low cost and physical and chemical advantages in the process [2], [3], ethanol presents less toxicity and higher dissolving capability when compared to methanol. Besides, ethyl ester-based biodiesel can be advantageous instead of methyl esters since fatty acid ethyl esters have higher heat content and cetane number, and improved storage properties due to the extra carbon added [3], [4]. Additionally, the ethyl ester biodiesel can be considered entirely carbon-neutral, differently from methyl esters, once methanol is obtained from natural gas or coal via synthesis gas [5], [6]. Lastly, the use of ethanol can be also preferred over methanol in regions where feedstock is largely cultivated and it is produced in large-scale.

From a practical standpoint, the separation of ethanol from water is more difficult than water and methanol separation (for recycle purposes in the esterification process), and this could have a great impact on process economics. Since ethanol increases the solubility of glycerol in the biodiesel phase, it can likely lead to separation difficulties in transesterification process. In this sense, although there is a growing industrial interest in the separation processes related to the production of components of fatty acid ethyl esters biodiesel, there are few experimental data regarding the ethyl ester, fatty acid, ethanol, water and/or glycerol available in the open literature [1], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. Most of this works presented in the literature are liquid–liquid (or vapor–liquid) studies using biodiesel mixtures (mixtures of fatty acid ethyl – or methyl esters) [1], [8], [9], [11], [12], [13], [14], [15], [16]. Experimental data of liquid–liquid equilibrium of systems involving pure esters of fatty acid (such as ethyl palmitate and palmitic acid) are scarce in the literature. Recently, Follegatti-Romero et al. presented LLE data for the systems ethyl palmitate + ethanol + water [17], [18] and ethyl palmitate + ethanol + glycerol [19]. In this context, new measurements of liquid–liquid equilibrium for the following three different ternary systems ethyl palmitate(1) + ethanol(2) + water(3), ethyl palmitate(1) + ethanol(2) + glycerol(3), and palmitic acid(1) + ethanol + water(3) were performed at different temperatures and are presented in this work.

Section snippets

Chemicals

Commercial products were used without further purification (Table 1) and deionized water was used in this work.

LLE apparatus and procedures

The binodal curves were determined using the titration method in a jacketed glass cell of 60 mL volume with a magnetic stirrer, in which the titration of the two-component mixture (known concentrations) with a third component was performed until clouding of the solution, at constant temperature. This is also known as the turbidity point technique. The two-component mixture was kept in a

LLE phase calculations and parameter estimations

For the LLE calculation and parameter estimation of thermodynamic model it was used the algorithm presented by Ferrari et al. [22]. In this algorithm, the LLE calculations are performed based on the phase stability test by analyzing the Gibbs surface tangent plane distance, and once the instability is verified the liquid–liquid equilibrium calculation is performed by applying the multiphase liquid–liquid flash algorithm. After calculating the LLE, one phase is tested again, if instability is

Results and discussion

The binodal curves (solubility) measured for the systems ethyl palmitate(1) + ethanol(2) + glycerol(3), ethyl palmitate(1) + ethanol(2) + water(3) and palmitic acid(1) + ethanol(2) + water(3) are presented for each isotherms in Table 4, Table 5, Table 6. Tie lines obtained for ethyl palmitate(1) + ethanol(2) + glycerol(3), ethyl palmitate(1) + ethanol(2) + water(3) are presented in Table 7, Table 8, respectively, for isotherms at 298.15 K and 313.15 K. Table 9 presents the tie lines for the system palmitic acid(1) + 

Conclusions

In this study, LLE equilibrium data are reported for ternary systems ethyl palmitate + ethanol + water (or glycerol) at investigated temperatures of 298.15 K, 313.15 K and 328.15 K. The system palmitic acid + ethanol + water was investigated only at 338.15 K, comprising solubility data (binodal curves) and tie lines. The NRTL and UNIQUAC activity coefficient models showed to be able to satisfactorily correlate the experimental data for such highly non-ideal mixtures. UNIFAC-LL and UNIFAC-Dortmund models

Acknowledgements

The authors are grateful to MEC/Reuni, CAPES, CNPq and Fundação Araucária-Paraná (Brazilian governmental agencies) for the financial support and scholarships.

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