Isobaric vapor–liquid equilibria for the binary and ternary mixtures of 2-propanol, water, and 1,3-propanediol at P = 101.3 kPa: Effect of the 1,3-propanediol addition

doi:10.1016/j.fluid.2014.02.006

Fluid Phase Equilibria

Volume 368, 25 April 2014, Pages 104-111

https://doi.org/10.1016/j.fluid.2014.02.006 Get rights and content

Abstract

Isobaric vapor–liquid equilibrium (VLE) at P = 101.3 kPa have been measured for the ternary system of 2-propanol + water + 1,3-propanediol and its constituent binary systems of 2-propanol + water and 2-propanol + 1,3-propanediol using an equilibrium still with circulation of both vapor and liquid phases. The ternary system of 2-propanol + water + 1,3-propanediol was prepared with three mass fractions (0.10, 0.30, and 0.50) of 1,3-propanediol in the overall liquid mixtures. The equilibrium compositions of mixtures were analyzed by gas–liquid chromatography. The liquid activity coefficients were obtained using the modified Raoult's law. The relative volatilities of 2-propanol to water were also determined. The results showed that the azeotropic point of 2-propanol + water can be eliminated when the mass fraction of 1,3-propanediol in the liquid phase is up to 0.50. Thermodynamic consistency tests were performed for the VLE data of these two binary systems. The new binary and ternary VLE data were successfully correlated with the Wilson, non-random two-liquid (NRTL), and universal quasi-chemical activity coefficient (UNIQUAC) models. The models with their best-fitted interaction parameters of the binary systems were used to predict the ternary VLE data. A comparison of model performances was made by using the criterion of mean deviations in boiling point and in vapor-phase composition.

Introduction

Alcohol as an organic compound is vitally interrelated to our daily life. Alcohol types such as ethanol, tert-butanol, and 2-propanol are widely used as an industrial solvent and as a fuel or as fuel supported chemicals. Among them, 2-propanol is important as a dehydration solvent to clean the parts and electric circuit in the process of the electronic industry. Accordingly, the purification of the aqueous 2-propanol mixture to recover 2-propanol is a necessary step to reduce the pollution problem and the capital cost for the electronic industries. Unfortunately, the aqueous 2-propanol solution displays markedly a non-ideal behavior, forming an azeotrope with a minimum boiling temperature on vapor–liquid equilibrium, and this likely makes the recovery process uneconomical. The main problem and hence the research interest is thus reallocated toward the study of separation techniques for the azeotropic mixture to achieve efficiently a lower economic cost process.

Several methods have been adopted, and distillation is the most widely utilized operation. However, when azeotrope is involved, the separation of mixture components by ordinary distillation is not feasible since no enrichment of the vapor phase occurs at this point. Therefore, azeotropic mixtures require special methods to help their separation such as utilize a mass separating agent that can cause or improve a selective mass transfer of the azeotrope-forming components. This separating agent is often introduced to increase the relative volatility of one component and make the separation more efficient. One of the separating agents is an entrainer (salts or solvents), which is used for extractive distillation, is the most common medium to facilitate the effective separation of azeotropic mixtures.

Recently, various salts are reported in the studies of the separation of the (2-propanol + water) system [1], [2], [3], [4], [5]. Such a technique offers many advantages such as lower energy consumption and small amount of separating agent, and the purity of the distilled product is high since the slats are non-volatile. The disadvantages are mainly related to the treatment of solid salts, the corrosion of the equipment, and the pollution due to the waste stream. On the other hand, as a class of green solvents with negligible vapor pressure and excellent solvation properties, ionic liquids will not cause corrosion in distillation column and other separation units. At present, ionic liquids are becoming a kind of promising solvent used for this special separation purpose [6], [7], [8]. However, the ionic liquids may exist with the problems such as high production cost, toxicity to aquatic organisms [9], and lacking in the thermodynamic data necessary for the design of separation process.

New alternative substitutes need to be explored to expedite the separation in minimizing the drawbacks of the salts and ionic liquids. In these substitutes, 1,3-propanediol is a compound of low toxicity, low vapor pressure, good hydrophilic capability, and lower production cost than ionic liquids, which enables its potential use as a green solvent for the separation of 2-propanol + water. Hence, the objective of the present paper is mainly concerned with an experimental determination of the amount of the solvent, 1,3-propanediol, required to shift or break the azeotrope of 2-propanol + water. This work has been carried out as part of a project to study the possibility of separating the azeotropic mixture using a kind of green agent as the extractive solvent.

For this reason, the isobaric vapor–liquid equilibrium (VLE) behavior for the ternary mixtures of 2-propanol + water + 1,3-propanediol has been investigated at P = 101.3 kPa by means of a dynamic method using a re-circulating still. As far as we know, no such information has been reported in the open literature. Of three constituent binary systems, the isobaric VLE data of 2-propanol + water at P = 101.3 kPa can be found in the literature [3], [5], [8], and those of water + 1,3-propanediol at P = 101.3 kPa have been stated in our previous work [10]. But for one of them, the 2-propanol + 1,3-propanediol binary system is still not available in the literature. Although the VLE data of 2-propanol + water have been existed, they were also investigated to validate our experimental method. Furthermore, the relative volatilities of 2-propanol to water were calculated. The results of the investigation were used to analyze the effect of 1,3-propanediol on the azeotropic behavior of aqueous 2-propanol solution.

Section snippets

Materials

The chemicals used were of analytical grade. The sources and mass fraction purities of the chemicals employed are as follows: 2-propanol (Merck, >0.998); water (Merck, conductivity ≤1.5 μS cm⁻¹ at 25 °C); 1,3-propanediol (Alfa Aesar, >0.99). All chemicals were used without further purification. No further purification was performed for these chemicals. 2-Propanol and 1,3-propanediol were stored over molecular sieves (Merck 0.4 nm beads). The purity of the chemicals was checked by gas chromatography

Results and discussion

The experimental VLE data for the binary systems of 2-propanol (1) + water (2) and 2-propanol (1) + 1,3-propanediol (2) at P = 101.3 kPa are presented in Table 2, Table 3, respectively. The VLE data contain equilibrium temperature (T), equilibrium mole fractions of liquid and vapor phases (x₁, y₁), activity coefficients (γ₁, γ₂), reduced excess molar Gibbs energy (g^E/RT), and relative volatility (β₁₂) of 2-propanol to water. The activity coefficient of component i and relative volatility of 2-propanol

Conclusions

The isobaric VLE data of the ternary system of 2-propanol + water + 1,3-propanediol and two constituent binary systems of 2-propanol + water and 2-propanol + 1,3-propanediol were determined experimentally at P = 101.3 kPa. Only the binary system of 2-propanol + water reveals a minimum boiling azeotrope. The activity coefficients of pure liquids in the mixtures were obtained from the modified Raoult's law. The VLE data of the binary systems were shown to be acceptable in thermodynamic consistency using the

Acknowledgments

The authors wish to extend their deep gratitude for the support by the National Science Council of Republic of China under grant NSC 99-2221-E-126-013-MY2.

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Isobaric vapor–liquid equilibria for the binary and ternary mixtures of 2-propanol, water, and 1,3-propanediol at P = 101.3 kPa: Effect of the 1,3-propanediol addition

Abstract

Introduction

Section snippets

Materials

Results and discussion

Conclusions

Acknowledgments

Fluid Phase Equilib.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Thermochim. Acta

J. Chem. Thermodyn.

Fluid Phase Equilib.

Fluid Phase Equilib.

Sep. Sci. Technol.

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

Water Res.

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data