ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Experimental and modeling study of molecular diffusion of carbon dioxide in light oil

Mohammad Rezaei Behbahani, Shima Azizi, Zoha Azizi, S. M. Peyghambarzadeh, and Bijan Ghanavati

Department of Chemical Engineering, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran

E-mail: s.azizi.chem@gmail.com

Received: 4 December 2022  Accepted: 10 March 2023

Abstract:

In this work, the pressure decay method was implemented to measure the diffusion coefficient of carbon dioxide in light oil at different temperatures and pressures. The mechanism of molecular diffusion of gas inside the liquid was studied by evaluating the kinetics of gas absorption. Assuming one-way diffusion from the gas phase to the liquid, mathematical modeling was developed based on Fick’s second law, and a mathematical relation was obtained for predicting the gas phase pressure versus time. Finally, the molecular diffusion coefficient was calculated using two methods including graphical and trial-and-error methods. Results showed that for carbon dioxide-crude oil system, the numerical values of the molecular diffusion coefficient were in the order of 10^–8 m²/s which were greater than the values expected for the gas diffusion in liquids. It was also found that the effect of temperature on the diffusion coefficient was not in accordance with the behavior of diffusion mechanism, i.e., by increasing temperature, the effective diffusion coefficient decreased. It was concluded that in addition to the molecular diffusion, there should be a stronger mass transfer mechanism such as natural convection within the liquid phase whose origin is the concentration gradient within the liquid column. Therefore, the value of diffusion coefficient obtained in this work was assigned as effective diffusion coefficient (D_eff). The solubility decreases with increasing temperature, and it causes the concentration gradient to be smaller. Therefore, natural convection is expected to be weaker at higher temperatures which leads to lower effective diffusion coefficient.

Keywords: Pressure decay method; Effective diffusion coefficient; Natural convection; Carbon dioxide; Light oil

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-023-02784-6

Chemical Papers 77 (8) 4355–4368 (2023)