Elsevier

Fluid Phase Equilibria

Volume 242, Issue 2, 25 April 2006, Pages 154-163
Fluid Phase Equilibria

Phase diagrams of binary systems containing n-alkanes, or cyclohexane, or 1-alkanols and 2,3-pentanedione at atmospheric and high pressure

https://doi.org/10.1016/j.fluid.2006.02.001Get rights and content

Abstract

Phase equilibria, for the binary systems {n-alkanes (tridecane, octadecane, or eicosane), or cyclohexane, or 1-alkanol (1-hexadecanol, or 1-octadecanol, or 1-eicosanol) + 2,3-pentanedione} have been determined using a cryometric dynamic method at atmospheric pressure. The influence of pressure on liquidus curve up to 800 MPa was determined for (tridecane, or cyclohexane + 2,3-pentanedione) systems. A thermostated apparatus for the measurements of transition pressures from the liquid to the solid state in two component isothermal solutions (pressometry) was used. The freezing and melting temperatures at a constant composition increase monotonously with pressure. The high-pressure experimental results obtained at isothermal conditions (px) were interpolated to well known Tx diagrams.

Immiscibility in the liquid phase was observed only for the n-alkanes mixtures. The solubility decreases with an increase of the number of carbon atoms in the n-alkane, or 1-alkanol chain. The higher intermolecular solute–solvent interaction was observed for the 1-alkanols.

Experimental solubility results are compared with values calculated by means of the NRTL equation (n-alkanes) and the NRTL and UNIQUAC ASM equations utilizing parameters derived from SLE and LLE results. The existence of a solid–solid first-order phase transition in tridecane, eicosane and 1-alkanols has been taken into consideration in the calculations. The correlation of the solubility data has been obtained with the average root-mean-square deviation of temperature σ < 1.0 K with both equations. The pressure–temperature–composition relation of the high-pressure (solid + liquid) phase equilibria, was satisfactorily presented by the polynomial.

Introduction

2,3-Pentanedione (PD) is one of two diacetales obtained in sugar production. Diacetales are of increasing importance in food technology as flavour additives for example in the beer or wine production [1], [2]. Diketones are also very well known as biodegradable solvents, as inhibitors in many polymerization reactions and as substrates in the pharmaceutical industry. (Solid + liquid) equilibrium data of PD systems are useful for design purposes in fat, cosmetic and oil technology.

The (solid + liquid) phase equilibria (SLE) of n-alkane systems have also gained increasing interest in the recent decade. For petroleum products mixtures of n-alkanes with branch chain hydrocarbons, or an aromatic hydrocarbons, or cyclic hydrocarbons are very important in a wide range of temperature and pressure [3], [4]. Phase equilibrium data of n-alkane systems with these solvents are of importance for the safe and efficient operation of chemical plants. Examples are necessary for high-pressure polymerization processes and oil-recovery processes. Further, SLE data provides a good tool for studying the thermodynamic behaviour of many systems.

The molecular structure of PD is:

PD is a polar solvent with high selectivity. It has two large carbonyl groups substituted in the short carbonyl chain, which influences the solute–solvent structure and the solubility of the solute under investigation. PD is an electron donor and can form hydrogen bonds with the proton of an alcohol. The interactions between PD and 1-alkanol are believed to occur via hydrogen bond formation between the two species. Thus, the structure of the solution and the molecular rearrangements and the variation in the solubility depend on the possibility of PD–1-alkanol cross interaction.

The present work is the continuation of our studies concerning the physicochemical properties and phase equilibria of binary mixtures involving highly polar compounds [5], [6]. The current study focuses on the solubilities of n-alkanes (tridecane, octadecane, or eicosane), or cyclohexane, or 1-alkanol (1-hexadecanol, or 1-octadecanol, or 1-eicosanol) in 2,3-pentanedione at the atmospheric pressure. Additionally we would like to show the influence of pressure up to 800 MPa on the liquidus curve of two systems: (tridecane, or cyclohexane + 2,3-pentanedione).

The purpose of these measurements was to get basic information on the interaction of PD with different solvents.

Section snippets

Experimental

The origin of the chemicals and their mass fraction purities were (in parentheses Chemical Abstracts registry numbers): tridecane (629-50-5, Koch-Light Lab., +0.99), hexadecane (544-76-3, Koch-Light Lab., 0.99), eicosane (112-95-8, Koch-Light Lab., 0.99), cyclohexane (110-82-7, Aldrich, +0.999), 1-hexadecanol (36653-82-4, Fluka AG, 0.98), 1-octadecanol (112-92-5, POCH, 0.98), 1-eicosanol (629-96-9, Merck AG, 0.98). 2,3-Pentanedione (C5H8O2, 600-14-6, Aldrich, 0.97) was purified by fractional

Experimental results

Table 3, Table 4, Table 5, Table 6 list the experimental results of the SLE, or LLE temperatures, T versus x1, the mole fraction of the n-alkane, or cyclohexane, or 1-alkanol. Table 4 list the experimental and calculated at constant temperature values for the experimental point in the n-alkane rich phase, or PD rich phase. Table 5, Table 6 present the equilibrium temperature and mole fractions for cyclohexane and 1-alkanol mixtures, respectively. Table 7 collected (solid + liquid) phase

Conclusions

Phase diagrams for three systems of n-alkanes (tridecane, hexadecane and eicosane + PD) and one of (cyclohexane + PD) at normal pressure were measured. The alkanes have shown the miscibility gap at solute mole factions between 0.1 and 0.6. For the longer chain n-alkanes the LLE region is shifted to the higher temperatures (the UCST is higher). This can be simply explained on the basis of lower combinatorial entropy (Flory–Huggins theory). The solubility of tridecane in 2,3-pentanedione at normal

Acknowledgement

The authors gratefully acknowledge the Warsaw University of Technology for the financial support.

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