Predicting water-hydrocarbon systems mutual solubility

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1 From the SelectedWorks of ali ali 2008 Predicting water-hydrocarbon systems mutual solubility ali ali Available at:

2 Chem. Eng. Technol. 2008, 31, No. 12, Alireza Bahadori 1 Hari B. Vuthaluru 1 Moses O. Tadé 1 Saeid Mokhatab 2 1 Department of Chemical Engineering, Curtin University of Technology, Perth, WA, Australia. 2 Process Technology Department, Tehran Raymand Consulting Engineers, Tehran, Iran. Research Article Predicting Water-Hydrocarbon Systems Mutual Solubility Describing the mutual solubilities of hydrocarbons and water is very important in the energy industry. The presence of water in a hydrocarbon mixture can affect the product quality and damage the operation equipment due to corrosion and formation of gas hydrates. Tracing the concentration of hydrocarbons in aqueous media is also important for technical purposes like preventing oil spills and for ecological concerns such as predicting the fate of these organic pollutants in the environment. Over the past three decades, a number of difficult thermodynamic approaches to the description of the mutual solubilities of hydrocarbons and water have been attempted. However, there was no easy-to-use model available for a qualitative description of the mutual solubility of water and hydrocarbons for a broad range of systems, over a wide range of thermodynamic conditions. This paper presents an easy-to-use correlation for an excellent prediction of the mutual solubility of water-hydrocarbon systems in a broad range of temperatures between 0 and 120 C, and heavy hydrocarbons between C 3 and C 10. The average absolute deviation from available data is 3 %. Keywords: Correlation, Hydrocarbon, Modeling, Solubility, Water Received: May 6, 2008; revised: September 10, 2008; accepted: September 11, 2008 DOI: /ceat Introduction The knowledge of the mutual solubility of liquid hydrocarbons in the aqueous phase is important in a wide variety of applications in the oil and gas industry, such as design and selection of operating conditions of oil/gas pipelines and production/ processing facilities, storage of natural gas/sequestration of acid gases in underground caverns, produced water disposal and gas hydrate calculations. The knowledge of the phase equilibria of aqueous mixtures with hydrocarbons is also important for environmental purposes since hydrocarbons, like other pollutants, must be removed from refinery wastewater streams and the sea or freshwaters when oil spills occur. For this purpose, knowing the solubility of hydrocarbons is required to describe their phase distribution through the removal process and also to assist in the design of separation equipment [1]. Various thermodynamic models are available that can calculate the phase equilibrium in water-hydrocarbon systems. However, all the thermodynamic models use difficult approaches to model the fluid phases. Considering this, there is Correspondence: A. Bahadori(Alireza.bahadori@postgrad.curtin.edu.au), Department of Chemical Engineering, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia. an essential need for developing an easy-to-use correlation for a qualitative description of the mutual solubility of water and hydrocarbons for a broad range of systems over a wide range of thermodynamic conditions. The solubility of light alkanes (methane and ethane) in pure water has been studied extensively over the past few decades. More recently, Bahadori et al. [2] have presented an easy-to-use approach for this purpose. 2 Newly Developed Correlation Based on a recently developed method [3, 4, 5], an easy-to-use correlation is proposed in this study to predict the water-hydrocarbon mutual solubility. Eq. (3) presents the new correlation for predicting the water-hydrocarbon mutual solubility in which four coefficients are used to correlate solubility as a function of s and n of the component: s ˆ T (1) T Ci n ˆ TNBPi T Ci (2) x i ˆ a a bs cs 2 d s 3 (3)

3 1744 A. Bahadori et al. Chem. Eng. Technol. 2008, 31, No. 12, a ˆ A 1 B 1 n C 1 n 2 D 1 n 3 (4) b ˆ A 2 B 2 n C 2 n 2 D 2 n 3 (5) c ˆ A 3 B 3 n C 3 n 2 D 3 n 3 (6) d ˆ A 4 B 4 n C 4 n 2 D 4 n 3 (7) In the above equations, x i is the mole fraction of solute components (i) in the water phase and kilograms of water dissolved in 100 kg of hydrocarbon. s and n are calculated using Eqs. (1) and (2). The constants evaluated are given in Tabs. 1 and 2; a is for calculating hydrocarbon solubility in water and it is equal to 1 for water solubility in hydrocarbons. T NBPi and T Ci are the normal boiling point and critical temperature, respectively, for component i. are reported by Wagner [6]. Table 1. Coefficients evaluated for predicting hydrocarbon solubility in water (see Eqs. (4 7)). Coefficient Propane-Hexane Hexane-Decane A B C D A B C D A B C D A B C D Results Figs. 1 and 2 illustrate the solubility trends of C 3 to C 10 components in water at different temperatures. As can be seen, good agreement was observed between the reported data by Wagner [6] and the results obtained from the new correlation. These graphs also show that light hydrocarbons such as propane are more soluble than heavy hydrocarbons such as decane Table 2. Coefficients evaluated for predicting water solubility in hydrocarbons (see Eqs. (4 7)). Coefficient Propane-Hexane Hexane-Decane A B C D A B C D A B C D A B C D in water, and the solubility of hydrocarbon in water increases with higher temperatures. Table 3. Accuracy of hydrocarbon solubility in water. Hydrocarbon Component (solute) Temperature [K] Reported solubility [mole fraction] [6] Calculated solubility [mole fraction] C C C C C C C C C C C C *Average absolute deviation percent (AADP) = 3 %. Absolute Deviation Percent (ADP)*

4 Chem. Eng. Technol. 2008, 31, No. 12, Water-hydrocarbon systems Hydrocarbon Solubility in Water, Mole Fraction Propane Butane Pentane Hexane Figure 1. Predicting the aqueous solubility of C 3 to C 6 based on the newly developed correlation. Hydrocarbon Solubility in Water, Mole Fraction Heptane Octane Nonane Decane Figure 2. Predicting the aqueous solubility of C 6 to C 10 based on the newly developed correlation. Figs. 3 and 4 illustrate the solubility trends of water in different hydrocarbon components over a wide range of temperatures. These graphs illustrate good agreement between the reported data by Wagner [6] and the results obtained from the new correlation. These graphs also show that water is more soluble in light hydrocarbons compared with the heavy hydrocarbon components. Tabs. 3 and 4 show the accuracy of the proposed correlation to calculate solubility of hydrocarbons in water and water in hydrocarbons, respectively. These tables show the accuracy of the correlation is good and the average absolute deviation percent (AADP) is 3 %. 4 Conclusion The predictions of the correlation developed were compared to the experimental data and good agreement was observed which demonstrates the ability of the new easy-to-use ap-

5 1746 A. Bahadori et al. Chem. Eng. Technol. 2008, 31, No. 12, Water Solubility in Hydrocarbon, (kg Water/(100 Kg of Hydrocarbon)) Propane Butane Pentane Hexane Figure 3. Predicting the solubility of water in C 3 to C 6 based on the newly developed correlation. Water Solubility in Hydrocarbon, (kg Water/(100 Kg of Hydrocarbon)) Hexane Heptane Octane Decane Figure 4. Predicting the solubility of water in C 6 to C 10 based on the newly developed correlation. proach for a qualitative description of the mutual solubility of water and hydrocarbons in a broad range of hydrocarbon components and temperatures. Acknowledgements The lead author acknowledges both the Australian Department of Education, Science and Training for Endeavour International Postgraduate Research Scholarship and the Office of Research & Development at Curtin University of Technology, Perth, Western Australia, for providing a Postgraduate Research Scholarship to pursue higher studies at Curtin University. References [1] M. B. Oliveira, J. A. P. Coutinho, A. J. Queimada, Fluid Phase Equil. 2007, 258, 58.

6 Chem. Eng. Technol. 2008, 31, No. 12, Water-hydrocarbon systems 1747 Table 4. Accuracy of water solubility in hydrocarbons. Hydrocarbon Component (solvent) Temperature [K] Reported solubility of water in hydrocarbons [kg of water per 100 kg of hydrocarbons] [6] Calculated solubility [mole fraction] C C C C C C C C Absolute Deviation Percent (ADP)* [2] A. Bahadori, H. B. Vuthaluru, S. Mokhatab, J. Energy Resour. Technol. 2008, accepted. [3] A. Bahadori, H. B. Vuthaluru, Chem. Eng. Technol. 2008, 31 (9), [4] A. Bahadori, Oil Gas J. 2007, 105 (8), 50. [5] A. Bahadori, Korean J. Chem. Eng. 2007, 24 (3), 418. [6] J. Wagner, Research Report 169, GPSA Engineering Book Revitalization and Maintenance, Gas Processors Suppliers Association, Tulsa, OK, USA, June *Average absolute deviation percent (AADP) = 3.2 %.