NaCl and KCl effect on (vapour + liquid) equilibrium of binary, ternary and quaternary systems involving water, ethanol and glycerol at low pressures
Introduction
Biodiesel is becoming a strategic fuel in the search for renewable energy sources that reduces the pressure on global demand for fossil fuels. The transesterification of oils and fats in atmospheric pressures has been the most used technique in the biodiesel production. In such process, the reaction is catalysed by alkoxide, which is produced from strong base such as sodium hydroxide (NaOH) and potassium hydroxide (KOH). The neutralization of this system leads to formation of salts such as sodium chloride (NaCl) and potassium chloride (KCl), which affect the quality of the final product and influences the steps of separation and purification of the products (biodiesel), by-products (glycerol and water) and reagents used (alcohol) [1], [2], [3]. In countries like Brazil, due to the fact that ethanol is produced on a large scale and from renewable sources, ethanol route has received special attention [4], [5].
Due to the high solubility of these salts in water, its effect is more evident in the separation and purification of glycerol. The presence of salts change the volatility of the solvents due to molecular interaction between the electrolytes and non-electrolytes, leading to salting-out effects (increasing the volatility) and salting-in (reducing the volatility) [6]. In some cases, it is observed the simultaneous presence of both effects of salting-in and salting out [7], [8], [9], [10].
Over the past few years, some work has been done trying to understand the thermodynamic behaviour of phase equilibrium (VLE and LLE) involving components in biodiesel production close to atmospheric pressures [4], [11], [12], [13], [14]. However, the NaCl effect on (vapour + liquid) equilibrium for systems involving compounds related to biodiesel process has only recently been reported [15].
In this work measurements of (vapour + liquid) equilibrium for the binary systems (ethanol + glycerol), (water + NaCl) and (water + KCl), ternary systems (ethanol + glycerol + NaCl), (water + glycerol + NaCl) and (water + glycerol + KCl) and quaternary system (water + ethanol + glycerol + NaCl) are reported at low pressures using an Othmer-type ebulliometer.
Section snippets
Chemicals
Ethanol (>0.995), glycerol (>0.995), sodium chloride (>0.999) and potassium chloride (>0,999) were supplied by Carlo Erba. All reagents were used without further purification. Water used for the preparation of solutions was distilled and deionized. See table 1.
Apparatus and procedure
The experimental (vapour + liquid) equilibrium was determined using a Othemer-type ebulliometer (figure 1) in which only the vapour phase is recirculated. The experimental procedure is based on the same adopted by Coelho et al. [4]. Liquid
(Vapour + liquid) equilibria of binary systems
The isobaric VLE data (P–T–w1) were determined for (ethanol + glycerol) system at pressure of 91.2 kPa and are shown in table 3. From figure 3 one can see that the data obtained in this work has the same tendency that observed by Coelho et al. [4], Oliveira et al. [16] and Zaoui-Djelloul-Daouadji et al. [17]. It is observed some deviation between these authors for this system. These deviations are due to experimental difficulties involved in obtaining VLE values for the systems with high
Conclusions
Experimental values of VLE at low pressures were obtained for the binary systems (ethanol + glycerol), (water + NaCl) and (water + KCl), for the ternary systems (ethanol + NaCl + glycerol), (water + NaCl + glycerol) and (water + KCl + glycerol) and quaternary system (water + ethanol + NaCl + glycerol) employing an Othmer-type ebulliometer. System (ethanol + glycerol) at 91.2 kPa showed satisfactory agreement with data presented in the literature.
The NaCl and KCl effect on vapour pressure of water was obtained in the
Acknowledgements
The authors thank CAPES – Brazil (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for the scholarships and CNPq – Brazil (Conselho Nacional de Desenvolvimento Científico e Tecnológico – 477246/2010-9) and Fundação Araucária – Brazil (project 15588/2010) for the financial support.
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