Prediction of methane diffusion coefficient in water using molecular dynamics simulation

Hojatollah Moradi,Hedayat Azizpour,Hossein Bahmanyar,Mohammad Mohammadi,Mahdi Akbari

doi:10.1016/j.heliyon.2020.e05385

Abstract

Diffusion coefficient is one the most effective factors in mass transfer calculation, which plays an important role in study at the molecular scale. In this study, Material Studio software was used to simulate the diffusion coefficient of methane in water through molecular dynamics. COMPASS force field was also used for optimization of atomic structures of methane and water, and Group-Based method was applied to model to calculate both van der Waals and electrostatic forces. In addition, Universal force field was used to optimize of amorphous cell, while Ewald and Atom-Based methods were applied for modeling and calculation of van der Waals and electrostatic potential energy at constant temperatures. The simulation duration for equilibrium of amorphous cell in both state of NVT and NVE was assumed 5ps. The impact of temperature as well as concentration on diffusion coefficient were investigated and results showed that the diffusion coefficient had linear relationship with temperature and third-degree polynomial relationship with concentration. As a result, of the simulation, the diffusion coefficient function versus temperature and concentration was developed.

Highlights

The diffusion coefficient in liquids is an important parameter to discover the mechanism of complicated mass transfer phenomenon and to design different types of separation columns such as distillation and adsorption column [1]
The experimental molecular diffusion coefficients in studies are slightly different from the results of simulation with molecular dynamics, which can be due to distinct in the samples and the corresponding methods [8, 9]
Materials Studio software was used for molecular dynamics simulation to calculate the molecular diffusion coefficient of methane in water

Summary

Introduction

The diffusion coefficient in liquids is an important parameter to discover the mechanism of complicated mass transfer phenomenon and to design different types of separation columns such as distillation and adsorption column [1]. Due to costly prolonged procedure of experimental data acquiring and significant error of presented models, the calculation of diffusion coefficient using molecular dynamics simulation has attracted much attention. The dependence of molecular diffusion coefficient on mass transfer operations is often underestimated, while this factor plays an important role in the transfer study of gases into liquids. Khalifi et al [13] investigated the effect of different concentrations of Ethane on the molecular diffusion coefficient of this gas in liquid Toluene. The results proved that there is a significant dependence on the concentration of the gas in the liquid mixture They used the obtained data to investigate the dependence impact of molecular diffusion coefficient on concentration in mass transfer of ethane in toluene. The impact of temperature and concentration on the molecular diffusion coefficient was investigated to find an appropriate equation

Models and method

Force field and model validation

Effect of temperature on diffusion coefficient of methane in water

Effect of concentration on diffusion coefficient of methane in water

Findings

Conclusion