Elsevier

Fluid Phase Equilibria

Volume 425, 15 October 2016, Pages 393-401
Fluid Phase Equilibria

Liquid–liquid equilibria for the extraction of furfural from aqueous solution using different solvents

https://doi.org/10.1016/j.fluid.2016.06.040Get rights and content

Abstract

Liquid-liquid equilibria data are reported for the furfural-water system with p-xylene and also toluene as solvents at 298.15 and 323.15 K. Other solvents including methyl iso-butyl carbinol (MIBC) at 298.15 K, benzyl alcohol and acetophenone at 323.15 K have been investigated as well. The distribution coefficient and selectivity were calculated according to the LLE data. Both the NRTL and the UNIQUAC models were successfully applied to fit the data for these five ternary systems. All the root mean square deviation (RMSD) values of the two models were less 0.01.

Introduction

Furfural is a highly versatile and key derivative used in the manufacture of a wide range of important chemicals where it is used as a solvent for extractive refining of lubricating oils, as a raw material for pharmaceuticals and phenolic resins, as well as an intermediate in the manufacture of lubricants, nylon, adhesives, plastics and solvents [1], [2], [3].

Furfural can be produced by digestion of cellulose wastes with steam and sulfuric acid in the range of temperatures between 413.15 and 458.15 K, pressure between 3.5 and 10 atm, forming a dilute aqueous solution [4]. Solubility of furfural in water is limited to less than 8.3 wt % at 293.15 K. Separation of furfural from this solution can be performed by azeotropic distillation, supercritical CO2 extraction, adsorption, organic solvent extraction, and membrane separation. However, separation of furfural from aqueous mixtures by azeotropic distillation is of large investment and high energy consumption [5]. The supercritical CO2 extraction technology is still in the experimental stage due to its high equipment investment and operating cost [6]. Besides, the adsorption separation and the membrane separation technology are limited to a certain concentration of the solution and difficult to realize mass production [7], [8]. In this way, liquid−liquid extraction of furfural appears as the most convenient choice for furfural upgrading at the moment. To facilitate development of furfural extraction units, many different solvents including chlorinated hydrocarbons, various aliphatic alcohols and aliphatic ketones have been studied for their ternary liquid−liquid equilibria with water and furfural [9], [10].

As a result of the limited solubility of furfural in water, phase splitting occurs easily at high content of furfural in aqueous solution. In this work, low concentration of furfural in aqueous solution is studied which is practical and meaningful. Experimental liquid–liquid equilibrium data were determined for five systems, including water + furfural + p-xylene and also toluene at 298.15 and 323.15 K, water + furfural + methyl iso-butyl carbinol (MIBC) at 298.15 K, water + furfural + benzyl alcohol and acetophenone at 323.15 K as well. Considering the similar density of benzyl alcohol and acetophenone with water, a higher temperature of 323.15 K was used to speed up the molecular motion which greatly shortened the time to reach the equilibrium. To the best of our knowledge, all the LLE data determined in this paper have not been reported up to now. Tie-lines were determined for the ternary systems according to the LLE data. The distribution coefficient and separation factor were calculated and were used as the standard to evaluate the separation efficiency. The experimental data were also correlated with Non-Random Two Liquids (NRTL) [11] and Universal Quasi-Chemical (UNIQUAC) [12] activity coefficient models.

Section snippets

Materials

Materials such as furfural, p-xylene, toluene, methyl iso-butyl carbinol, benzyl alcohol and acetophenone were purchased from Sinopharm Chemical Reagent. Double distilled water was employed throughout. All the chemicals were used without further purifications. The major information of the used chemicals were displayed in Table 1.

Apparatus and procedure

LLE data for the studied ternary system were obtained at desired temperature under atmospheric pressure. The details about experimental equipment have been presented in

Thermodynamics modeling

The NRTL and UNIQUAC models were applied to correlate the experimental mole fractions by using the Aspen Plus software (version 7.3).

The NRTL model is based on the local composition concept and there are three adjustable parameters gij, gji, and αij in it. The recommended αij values for different types of mixtures are commonly between 0.1 and 0.47.

A combinatorial term related to differences in size and shape between the components and a residual term accounting for energy differences between

Experimental data

The LLE data for the ternary systems (Water + Furfural + Solvents) at desired temperatures are shown in Table 3, Table 4 with all concentrations expressed in mole fraction. The phase diagrams for the ternary mixtures are presented in Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7. The tie-lines and feed composition are also plotted in Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7. As shown in these figures, the points of the feed compositions agree the tie line with great

Conclusions

The liquid-liquid equilibria for Water + Furfural + Solvents ternary system were investigated at desired temperatures under atmospheric pressure. It was found that furfural have a much higher solubility in selected solvents than that in water. All the separation factors were much larger than one, implying the feasibility of selected solvents to extract the furfural from aqueous solution. Generally the distribution coefficients tended to increase when the concentration of furfural increased.

Acknowledgements

This study is supported by Qingdao postdoctoral fund (NO. T1504117) and the Project of Natural Science Research of Higher Education Institutions of Jiangsu Province (NO. 15KJD530001).

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