Volume 33: CCUS Technologies for the Carbon Neutrality: Part I

Molecular Simulation of Adsorption and Flow of Carbon Dioxide in Kaolinite Pores Guodong Sun, Yi Zhang, Mingkun Chen, Jingru Zhang

Abstract

With the rapid development of China’s economy, a series of environmental problems have emerged, and the large-scale emission of CO2 has become the main cause of global warming. Carbon capture, utilization, and storage (CCUS) is an important technological means to address climate change. The technology mainly captures CO2 in the energy production process and converts it into useful products or safely stores it in underground reservoirs, thereby reducing the concentration of CO2 in the atmosphere. CO2 storage technology, as an important part of carbon neutrality, has become the key to solving the problem of carbon emissions. Shale clay minerals, as a key site for CO2 geological storage, provide a large surface area and a large number of pores for adsorption, but the adsorption mechanism and the transport law of CO2 in the pores during storage still require extensive research. First, the Monte Carlo method was used to simulate the adsorption characteristics of CO2 in kaolinite pores. The adsorption configuration was established using the molecular simulation software Lammps, and the changes in CO2 density, isothermal adsorption curve, and CO2 potential energy distribution in kaolinite pores were analyzed. The main factors affecting CO2 adsorption and the reasons for the differences in adsorption were comprehensively analyzed. Secondly, based on the research on adsorption characteristics, molecular dynamics method was used to carry out simulation research on supercritical CO2 flow during adsorption. During the flow process, the potential energy of CO2 adsorbed on the kaolinite wall changed, causing desorption. Moreover, the larger the pore size, the greater the degree of desorption. In addition, slip occurred at the kaolinite wall during supercritical CO2 flow, resulting in slip length. With the increase of driving force, the slip length gradually increased, which was due to the decrease of the wall resistance to flow caused by the decrease of CO2 density in the first adsorption layer with the increase of driving force. Temperature changes also affected the CO2 slip length. When the temperature rose, the movement of CO2 molecules became more intense, the curvature radius of the flow curve gradually increased, and the slip length calculated increased with the increase of temperature. At the same time, the increase in temperature caused the potential energy of CO2 to increase, and the macroscopic behavior of CO2 molecules became less likely to be adsorbed. On the other hand, when the temperature decreased, the potential energy of CO2 decreased, and the difference in potential energy between CO2 molecules and the wall increased, making CO2 molecules more easily adsorbed and increasing the adsorption amount.

Keywords CCUS, GCMC, MD, Adsorption, scCO2