Combined effects of salinity and temperature on the solubility of organic compounds

doi:10.1016/j.jct.2011.11.020

The Journal of Chemical Thermodynamics

Volume 48, May 2012, Pages 54-64

https://doi.org/10.1016/j.jct.2011.11.020 Get rights and content

Abstract

This study deals with the solubility limits of organic liquids liable to be spilled at sea during ship-wrecking or other incidents at sea. The effects under consideration are induced by both salinity and temperature. The former is described through use of the Setchenov relationship, and the latter by using the Van’t Hoff equation. A coupling of both relationships led to an equation applicable to scarcely soluble liquids and expressed in a simplified form usable in decision-support systems as a result of the choice of the reference state when writing the thermodynamic relationships. The mathematical relation we found was tested on experimental data about four compounds, i.e. dimethyldisulfide (DMDS), methyl methacrylate (MMA), 1-butanol (1-But), and methyl ethyl ketone (MEK), chosen because of their wide use in the industry and frequent transport by sea. All of them were studied at four salinity values and five temperatures, and the mathematical relation under test proved to be quite satisfactory.

Graphical abstract

LL equilibria in three component systems.

Highlights

► DMDS, MMA, 1 butanol, and MEK are chemicals able to be spilled over during ship wrecking. ► Their solubilities were studied at four salinities and temperatures among marine ones. ► Thermodynamic equations can correctly calculate solubility values. ► Data show this is possible from three experimental parameters in marine conditions.

Introduction

The solubility behaviour of a wide variety of compounds is of key-importance in many natural or accidental environmental processes: for example, literature data about the solubility of carbon dioxide or dioxygen in natural fresh or salty waters are available in [1], [2], or about the dissolution and re-precipitation of solid compounds between rocks and water in [3], [4].

Recently, attention has also been focused on the physical fate of cargos accidentally spilled during ship-wrecking or other incidents at sea [5], [6], [7]. Questions have been raised about the parts of the cargo liable to be dissolved and their dependence or not on temperature and water salinity.

The fundamental laws ruling dissolution phenomena are thermodynamic by nature [1], [8], [9], [10]. The analyses of the temperature-induced effects on these particular phase changes are based on the Van’t Hoff equation. The salt effects are described through the Setchenov [11] formula, which is a very old and empirical relationship between salinity and solubility. However, to the best of our knowledge, till now no comprehensive description of the conjugate effect of temperature and salinity on solubility has been elaborated though it would constitute a very useful tool to devise and develop decision-support systems (software), in order to determine the conduct to be adopted in the case of spills at sea. The studies used in the development of this approach are either related to other fields of science [2], [12], [13], or more theoretical [14], [15], [16], [17], or in relation to the effects of molecular and ionic structures [18], [19]. However the status of Setchenov relationship in marine environment has also been examined [20], [21] without any reference to temperature effects. The first among these papers [2] describes a very serious study of the calculation of activity coefficients from the Spitzer equation of state, but the reported work is too detailed and complicated with respect to the purpose of the present study; the chemicals under concern are gases or very light hydrocarbons. The second one is a compilation of data about hydrocarbons and some organic acids.

The study reported here is focused on dimethyldisulfide (DMDS), methyl methacrylate (MMA), methyl ethyl ketone (MEK), and 1-butanol (1-But) because of their numerous industrial uses and frequent transport by sea in large quantities. DMDS is a very volatile and nauseous liquid, known to be noxious at large amounts and frequently used, for example, as marker of fuel-gases, or nematicid, and also in petrochemistry as CO-formation inhibitor and as catalyst. MMA is the monomer for the manufacturing of polymers and copolymers leading to huge applications; MEK is a widely used solvent, a chemical agent and a catalyst; 1-butanol is currently employed in extractions and syntheses. All of them are transported by sea and in large amounts, though unknown for DMDS [22] conversely to MMA (132,766 tons/year), MEK (112,047 tons/year) and n-butanol (129,649 tons/year) according to [23] where these mean values were calculated for the 2002 to 2004 period. These characteristics led us to choose them as example of slightly- (DMDS), moderately- (MMA, 1-but) or rather well-soluble compounds (MEK) likely to be implied in shipwrecks. Though the transported cargo volume cannot be really considered as a chemical criterion in favour of this choice, we shall see that these examples interestingly supplement the kind of studies made by other authors about the role of the chemical functions contained in the studied molecules played on factors like the Setchnov constant [18], [19].

The fundamentals of dissolution thermodynamics will be recalled in Section 2 of this paper. Then they will be carefully adapted to the case of scarcely soluble solutes in order to find simple relationships between solubility and temperature and to clearly establish the useful approximations that would not be alike in studies made with other types of systems, e.g. more soluble solutes. Section 3 briefly reports on experimental studies carried out on DMDS, MMA, 1-butanol, and MEK. They were developed on salinity and temperature ranges from 0 to 34 g · L⁻¹ and 10 to 30 °C, respectively.

Section snippets

Generalities

At constant temperature (T) and pressure (P), the dissolution equilibrium is reached when the Gibbs free energy is the lowest: $G = \sum_{i, α} n_{i}^{α} μ_{i}^{α},$ where i is a component, $n_{j}^{α}$ is the number of i-moles in the α-phase, and $μ_{i}^{α}$ is its chemical potential. In a multi-phase system, the lowest value is reached when the chemical potential of each component taken in turn is alike in every phase. Let us assume that the system under study contains three shared between two phases, α and β; the equilibrium is

Overall experimental process

To take into account the temperatures and salinities usually met in the marine environment, the experimental conditions in use were: (0, 10, 20, and 34) NaCl g · kg⁻¹ for salinities and (10, 15, 20, 25, and sometimes 30) °C for temperatures.

All of the samples were prepared by weighting both the required quantity of the compound under study and the quantity of solvent (either pure or salty water) in order to obtain the solution composition in the molar fractions or molalities, since these units are

Data

TABLE 3, TABLE 4, TABLE 5, TABLE 6 give the solubility limits (with the uncertainties) respectively for DMDS, MMA, 1-butanol, and MEK, in pure water, at several salinities (typically 10 g · kg⁻¹, 20 g · kg⁻¹, and 34 g · kg⁻¹) and at several temperatures, (10, 15, 20, and 25) °C for all components and additionally at 30 °C for 1-butanol and MEK.

Salinity influence

The Setchenov formula (6′) was tested, at first, on the data from TABLE 3, TABLE 4, TABLE 5, TABLE 6, then under graphical forms in FIGURE 2, FIGURE 3, FIGURE 4,

Conclusion

On the basis of a rigorous thermodynamic analysis, we established an equation, denoted here as equation (11′), which is simple enough to be used in decision-support softwares in order to evaluate the solubility of a sparingly soluble liquid compound at any temperature and salinity in the following range of environmental mean conditions: 10 < t < 30 °C, 0 < sal < 34 g · L⁻¹. The parameters required to use equation (11′) are a single solubility value at given salinity (eventually zero) and temperature, the

Acknowledgement

This study was supported by a grant from ARKEMA society and by grant-in-aid from ANR-PRECOD (France).

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Combined effects of salinity and temperature on the solubility of organic compounds

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Generalities

Overall experimental process

Data

Salinity influence

Conclusion

Acknowledgement

Sci. Total Environ.

Chemosphere

J. Chem. Thermodyn.

Mar. Chem.

Mar. Environ. Res.

Chem. Eng. J.

Chemical, Biochemical, and Engineering Thermodynamics

Chem. Rev.

Curr. Sci.

Soil Sci. Soc. Am. J.

J. Phys. Chem. Ref. Data

Can. J. Chem.

Chemical Thermodynamics