Determining the molecular diffusion coefficient of naphthenic acid in water as a heavy oil pollutant by experimental method.

Naphthenic acids are the most significant environmental pollutants created by the extraction of oil from oil sand deposits. Since the diffusion coefficient of naphthenic acid has a direct effect on the modeling of diffusion and advection and determining its behavior and movement in water, this number is needed for modeling work and future studies. In this study, the diffusion coefficient of this substance in water was determined experimentally and in a laboratory. The researchers used the device of the Armfield company, known as the device for determining the diffusion coefficient in liquids. In this research, after examining different methods of determining the concentration of naphthenic acid in the water, including UV-vis, chemical oxygen demand (COD), crystal violet, oxidation reduction potential, pH meter, and electrical conductivity meter, the COD method was the best method in determining the concentration at different times, which provided a suitable numerical range for the concentrations and a device was built for heavy oil pollutants with poor solubility in water to specify the diffusion coefficient, and for the first time, the diffusion coefficient of naphthenic acid in water was obtained with experiments and experimental equations as 0.69 × 10^-9 m²/s which indicates the weak diffusion of this substance in water.