Thermodynamic analysis of the mutual solubilities of hydrocarbons and water

• Published in: Fluid phase equilibria Vol. 186; no. 1; pp. 185 - 206
• Main Author: Tsonopoulos, Constantine
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-08-2001; Elsevier Science
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Heat of solution; Hydrocarbon Henry’s constant; Hydrocarbon solubility; Solubility; Solutions; Water solubility; Water solubility; Hydrocarbon solubility; Heat of solution; Hydrocarbon Henry’s constant; Water; Structure effect; Cyclohexane derivatives; Hydrocarbon; Chain length; Solubility; Theoretical study; Alkene; Alkane; Benzenic compound; Thermodynamic analysis; Aromatic compound; Thermodynamic properties
• ISSN: 0378-3812; 1879-0224
• DOI: 10.1016/S0378-3812(01)00520-9

The analysis of mutual solubilities and calorimetric heats of solution carried out for normal alkanes and water close to 298
K [Fluid Phase Equilib. 156 (1999) 21] is extended to normal alkylcyclohexanes, linear 1-alkenes, and normal alkylbenzenes. Extensive solubility data are available for alkylbenzenes, but relatively little is known about alkylcyclohexanes and alkenes in water. All of these hydrocarbons are more soluble than the corresponding alkanes, but are less volatile than the alkanes (their Henry’s constants descending in the order alkanes>alkenes>alkylcyclohexanes>alkylbenzenes). The solubility minimum for hydrocarbons in water is confirmed by calorimetric data for C
6–C
9 alkylbenzenes (∼291
K) and cyclohexane (298.5
K). It appears that the heat capacity of solution is independent of temperature and increases linearly with carbon number, in the descending order alkanes>alkylcyclohexanes>alkylbenzenes. In the absence of calorimetric data, the relatively limited solubility data for alkenes in water do not allow a reliable determination of the solubility minimum or of the heat capacity of solution.
As is the case for water in alkanes, the solubility of water in hydrocarbons at 298
K is relatively insensitive to carbon number (CN), but, unlike that in alkanes and alkylcyclohexanes, the solubility of water in alkenes and alkylbenzenes decreases slightly with increasing CN. Less is known about the heat of solution, but for each family it appears to be independent of temperature and CN, covering the range 24
kJ
mol
−1 (alkylbenzenes) to 35
kJ
mol
−1 (alkanes and alkylcyclohexanes). The latter is a better measure of the hydrogen bond energy in hydrocarbon/water systems, since alkanes and alkylcyclohexanes have the least affinity for water. This affinity is measured by the heat of hydrophobic interaction, which makes a negative contribution to the heat of solution, and therefore, as observed, the heat of solution of water in alkenes (33
kJ
mol
−1) and alkylbenzenes is smaller than that in alkanes and alkylcyclohexanes.