Model accurately predicts HC solubility in methanol

Sept. 3, 2007
A newly developed model accurately predicts solubility of hydrocarbon components in methanol.

A newly developed model accurately predicts solubility of hydrocarbon components in methanol.

Quantifying the absorption of hydrocarbons, primarily methane and ethane, in methanol is critical in minimizing hydrocarbon losses or optimizing hydrocarbon recovery, depending on the objective of the process.

This article presents model results for an accurate prediction of solubility of light alkanes in methanol, in which the obtained results of the proposed method have been compared with experimental data showing good agreement between reported experimental data with the model results.

The average absolute deviation is 1.5289%.

HC solubility

In gas processing, methanol is commonly injected into gas streams to inhibit hydrate formation. After chilling and separation from the hydrocarbon phases, the aqueous methanol phase is usually stored in atmospheric pressure tanks for disposal.

Because the atmospheric storage tanks are at less than the separator pressure, hydrocarbons absorbed by the injected methanol may flash.

This article examines the influence of temperature and pressure on hydrocarbon solubility, which is a major factor in any consideration of using a physical solvent.

Also, for environmental reasons, a great amount of work has gone into determining the solubility of hydrocarbons in water and hydrate inhibitors at various temperatures. These solubility data have been compiled and correlated.

The prediction of light alkanes’ solubility in methanol is usually based on use of the pure component solubilities and the mole fraction of the components in the mixture. In most cases, however, the current models may be insufficient.

The goal of the work presented here is to contribute to the modeling and understanding of methanol solubility behavior of light alkanes. Using this simple model, we explain the observed solubility behavior and compare results with experimental data.1

Model

An easy-to-use model predicts the solubility of methane and ethane components in methanol.2 Equation 1 (see accompanying box on p. 40) presents the correlation for predicting the solubility of solutes in which four coefficients correlate the mole fraction of individual components and reduced partial pressure of the component.

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Equations 2-4 calculate the required coefficients for Equation 1; Equations 6 and 7 convert solute and solvent mole fraction to volumetric dimensions.

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This model only needs data to tune the coefficients and accurately predict a wide range of data.

Results

Table 1 presents the obtained results of the model for determining the solubility of methane and ethane components in methanol with the experimental data. As can be seen, the average absolute deviation for model is 1.5289%. The proposed method is therefore accurate in predicting the solubility of light alkanes in methanol.

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Figs. 1a and 1b illustrate the solubility trends of methane components in methanol at different temperatures and pressures, applying the model from Reference 2 and in molar and volumetric dimensions.

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Figs. 2a and 2b show the solubility of ethane in methanol at different temperatures and pressures applying the same model and in molar and volumetric dimensions.

References

  1. Wang, L.K., et al., “Experimental Study on the Solubility of Natural Gas Components in Water with or without Hydrate Inhibitor,” Fluid Phase Equilibria, No. 207 (2003), pp. 143-154.
  2. Bahadori, A., “New model predicts solubility in glycols,” OGJ, Feb. 26, 2007, p. 50.

The author

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Alireza Bahadori ([email protected]) is a senior process engineer in the petroleum engineering department of National Iranian South Oil Co., Ahwaz, Iran. Previously he worked 4 years as a CIS technologist for Aghajari Oil and Gas Co. He has a technical diploma (1991) in control instrument services from NIOC Technical School in Aghajari. He also holds a BSc in chemical engineering (1998) from Petroleum University of Technology (Abadan Institute of Technology) Abadan, Iran, and an MSc (2000) in chemical engineering from the University of Shiraz, Iran. Bahadori is a member of Iranian Association of Chemical Engineers.