# Calculating H2O solubility, Henry's Law constant for cycloalkanes in crude

Feb. 1, 2010
Water solubility and Henry's law constant in cycloalkanes found in crude oil have been calculated and set in an easy-to-use table.

Water solubility and Henry's law constant in cycloalkanes found in crude oil have been calculated and set in an easy-to-use table.

In addition, we have developed a new correlation for solubility of water in crude oil that provides reliable solubility values down to very low concentrations (ppm). The correlation is based on boiling-point temperature of the hydrocarbon. Correlation values and experimental data are in agreement.

The results are usable in engineering applications involving processing, safety, hazard, and environmental considerations.

Water solubility

The importance of the solubility of water in crude oil will increase in view of processing, safety, hazard, and environmental considerations focusing on product quality and equipment sustainability. The following brief discussion illustrates the importance.

Any processing that lowers temperatures to near the freezing point of water may result in formation of solids (freezing of water or hydrate formation). Such formation will affect both fluid flows in piping and operational characteristics of equipment.

For catalytic reactions, any water in the hydrocarbon may poison the catalyst that promotes the hydrocarbon reaction.

For reactions in general, any water in the reaction species may result in formation of undesirable by-products issuing from the hydrocarbon reaction. The presence of water in the product may degrade quality and, if sufficient water is in the product, it may prove to be unusable by the customer.

This brief discussion indicates that solubility of water in hydrocarbons contained in crude oil is important in engineering applications involving processing, safety, hazard, and environmental considerations.

Correlation

Earlier works correlated the solubility of hydrocarbons and other chemical types in water as a function of the boiling point of the compound.11 In this work, it was determined that the boiling-point method was also applicable for correlation of solubility of water in cycloalkanes (cyclopentanes and cyclohexanes):

log10(S) = A + B*TB

where: S = solubility of water in compound at 25° C., ppm (wt)

TB = boiling point temperature of compound, K

A = 2.7470

B = –1.50 E-03

The correlation applies to a range for boiling-point temperatures of about 280 K to 590 K.

The coefficients (A and B) for the correlation were determined from regression of the available data. In preparing the correlation, we conducted a literature search to identify data source publications.1-15 The compilations by Englin et. al., International Union of Pure and Applied Chemistry, and Sorensen and Artl were consulted for solubility of water.2 5 6 7 The compilation of Yaws was used for boiling point temperature.13

We screened the publications and copied appropriate data, then keyed the data into the computer to provide a data base for which experimental data are available. The data base also served as a basis to check the accuracy of the correlation.

The accompanying diagram shows the solubility of water vs. boiling-point temperature of compound for cyclopentanes and cyclohexanes. The data of Englin and compilation of Sorensen that are applicable at ambient conditions were selected for the graph.2 7 The graph discloses favorable agreement of correlation values and experimental data.

Solubility; Henry's Law constant

The accompanying table gives the results for solubility of water and Henry's law constant. In the tabulation, the results for Henry's law constant are based on water solubility and vapor pressure at ambient conditions with appropriate thermodynamic relationships.10 The compilation of Yaws was used for vapor pressure.14 The presented values are applicable for water in a wide variety of cycloalkanes.

The tabulated values are based on both experimental data and estimates. In the absence of data, the estimates for isomers and large compounds (compounds with more than 10 carbons, i.e., compounds larger than C10) should be considered rough values useful for initial analysis. If initial analysis is favorable, follow-up experimental determination is recommended.

The results in an easy-to-use tabular format are especially applicable for rapid engineering use with a personal computer or hand calculator. The tabulation is arranged by carbon number (C5, C6, C7, …). This provides ease of use in quickly locating data with the chemical formula.

Examples

The results for solubility and Henry's law constant are useful in engineering applications involving water in cycloalkanes, per the following examples:

Example 1. In hydrocarbon processing, cyclohexane (C6H12) comes into contact with water at ambient conditions (25° C., 1 atm). The organic and aqueous phases are subsequently separated. Estimate the concentration of water in the cyclohexane after separation.

Substitution of the coefficients and boiling point temperature into the correlation equation yields:

log10(S) = 2.747 – 1.50 E-03*353.87

= 2.2162

S = 164.51 ppm (wt)

Example 2. A hydrocarbon spill of cyclohexane (C6H12) into a body of water at ambient conditions (25° C., 1 atm). After separation, the concentration of water in the hexane at the surface is 0.000737 mol fraction (xi = 0.000737). Estimate the concentration of water in the vapor at the surface.

From thermodynamics at low pressure, the vapor concentration is given by yi = Hi/Pt*xi.

Substitution of Henry's law constant from the table, total pressure (Pt = 1 atm) and liquid concentration into the above equation yields:

yi = 42.53/1*0.000737 = 0.0313

yi = 3.13 % (mol)

References

1. Black, C., et al., Journal of Chemical Physics, Vol. 16 (1948), p. 537.

2. Englin, B.A., et al., Khim. Tekhnol. Topl. Massel, Vol. 42 (1965), No. 9.

3. Marche, C., et al., Journal of Chemical Engineering Data, Vol. 51 (2006), p. 355.

4. Ng, H.J., and Chen, C.J., "Mutual Solubility in Water-Hydrocarbon Systems," Tulsa: Gas Processors Association Research Report 150, 1995.

5. Solubility Data Series, International Union of Pure and Applied Chemistry, Vol. 37, Hydrocarbons with Water and Seawater, Part 1—Hydrocarbons C5 to C7, Oxford: Pergamon Press, 1989.

6. Solubility Data Series, International Union of Pure and Applied Chemistry, Vol. 38, Hydrocarbons with Water and Seawater, Part 1—Hydrocarbons C8 to C36, Oxford: Pergamon Press, 1989.

7. Sorensen, J.M., and Artl, W., Liquid Liquid Equilibrium Data Collection, Vol. V, Part 1, Frankfurt: Dechema Chemistry Data Series, 1979.

8. Tsonopoulos, C., and Wilson, G.M., "Mutual Solubilities of Hydrocarbons—Part I," AIChE Journal, Vol. 29 (1983), p. 990.

9. Tsonopoulos, C., et al., "Mutual Solubilities of Hydrocarbons—Part II," AIChE Journal, Vol. 31 (1985), p. 376.

10. Tsonopoulos, C., et al., "Mutual Solubilities of Hydrocarbons—Part III," AIChE Journal, Vol. 43 (1997), p. 535.

11. Tsonopoulos, C., Fluid Phase Equilibrium, Vol. 186 (2001), p. 185.

12. Yaws, C.L., Chemical Properties Handbook, New York: McGraw-Hill Inc., 1999.

13. Yaws, C.L., Yaws Handbook of Physical Properties for Hydrocarbons and Chemicals, Houston: Gulf Publishing Co., 2005.

14. Yaws, C.L., Yaws Handbook of Vapor Pressure—Antoine Coefficients, Houston: Gulf Publishing Co., 2007.

15. Yaws, C.L., Yaws Handbook of Properties for Environmental and Green Engineering, Houston: Gulf Publishing Co., 2008.

The author

Carl L. Yaws ([email protected]) is professor of chemical engineering at Lamar University, Beaumont, Tex. His research interests include technology development; thermodynamic, transport, and environmental property data. He holds BS in chemical engineering from Texas A&I University and an MS and PhD in chemical engineering from University of Houston.

 CorrectionThe table headline in "Table, correlation give water solubility, Henry's Law constant for alkanes in crude," Carl L. Yaws and Manish Rahate (OGJ, Mar. 2, 2009, p. 52), should have read "Solubility and Henry's Law constant for water in alkanes."