Molecular dynamics predictions of transport properties for carbon dioxide hydrates under pre-nucleation conditions using TIP4P/Ice water and EPM2, TraPPE, and Zhang carbon dioxide potentials

TL;DR

This study evaluates molecular dynamics models for predicting the viscosity of carbon dioxide hydrate systems at pre-nucleation conditions, finding EPM2 provides the most accurate predictions among tested force fields.

Contribution

It validates and compares the accuracy of different molecular dynamics force fields in predicting hydrate system viscosity under pre-nucleation conditions.

Findings

EPM2 force field yields lower discrepancies in viscosity predictions.

All force fields overpredict viscosity compared to experimental data.

EPM2 models molecular behavior consistent with macroscopic viscosity trends.

Abstract

(1) Introduction: New technologies that leverage gas hydrates phenomena include carbon capture and sequestrations. These processes are often semi-continuous and require regulation of the system's flow properties for proper operation. Accurate computational models for the viscosity of carbon dioxide hydrate systems at pre-nucleation conditions can be important for process design and control of such technologies. (2) Methods: This work validates the viscosity predictions of molecular dynamics simulations using previously measured experimental data. The TIP4P/Ice force field was used to model water, while the EPM2, TraPPE, and Zhang force fields were used for carbon dioxide. The Green-Kubo and Einstein formulations of viscosity and diffusivity were used in this work. (3) Results: All force fields overpredicted viscosity when compared to experimental data, but EPM2 resulted in lower discrepancies. Additionally, EPM2 was determined to model molecular behavior expected from the macroscopic trends in viscosity with respect to temperature and pressure. (4) Conclusions: The EPM2 force field more accurately predicted the viscosity of carbon dioxide hydrates systems at pre-nucleation conditions relative to TraPPE and Zhang.