Title:	Understanding of the mechanism of the impact of organic and inorganic interfaces on gas clathrate
DNr:	NAISS 2023/22-497
Project Type:	NAISS Small Compute
Principal Investigator:	Yang Zhao <zyatdlut@mail.dlut.edu.cn>
Affiliation:	Stockholms universitet
Duration:	2023-06-27 – 2024-01-01
Classification:	10403
Keywords:

Abstract

The uneven distribution of energy in time and space, and the emission of greenhouse gases have always been the concerns of humankind. Therefore, the convenient utilization and storage of clean energy are particularly vital to industrial production. Compared with traditional fossil fuels such as coal and gasoline, natural gas has greater energy density and fewer carbon atoms per unit mass hence producing less harmful emissions to the environment. Natural gas clathrate, a kind of promising clean energy stored in permafrost and seabed sediments, which was thought to be the alternative energy source in the future as its abundant reserves, inspired a new approach of gas storage, transportation and separation. Methane and other gas molecules could be captured in cages composed of hydrogen-bonded water molecules under mild pressure and temperature conditions. Ideally, up to 216 units of methane or CO2 gas can be trapped per unit volume of water. Furthermore, the self-preservation property enables cage structure stable in proper temperature even if the storage pressure is lower than the phase equilibrium condition, as the surface ice layer of gas hydrate could prevent gas molecules from escaping. Considering this, the ice-liked hydrate may be an efficient way to address both economic and safety concerns. The unfavorable factors resulting from kinetics and thermodynamics in the growth of hydrate nonetheless need to be further improved by manual intervention, considering it’s imperative to make it be worthwhile for practical application. Numerous works have focused on porous materials as medium for storing hydrates. The large specific surface area could provide abundant nucleation sites as the nucleation sites usually occur at the intersection of solid-liquid-gas interface. Moreover, sufficient gas-liquid contact area could solve the problem of mass transfer hindering during growth process. MOFs, aerogels, active carbon and carbon nanotubes has been reported as reliable gas hydrate storage medium. Additionally, the interaction of solid surface with water could also affect the hydrogen bonding environment. By regulating the hydrophilicity and hydrophobicity of surface, the layer of water molecules on the solid surface could be induced to form hydrogen bonds as nucleation sites for hydrate cage structures. However, there’s no consensus on how the hydrophilicity and hydrophobicity, the polarity of surface atoms and the surface modified functional groups affect hydrate nucleation. On the one hand, it is challenging to use intuitive means to investigate the state of interface adsorption under high pressure and low temperature. On the other hand, the influence of surface atoms mainly comes from their electronic structure. So, the molecular configuration and electronic structure of hydrate adsorption need to be studied with DFT simulation software such as VASP. A typical cubic structure I-type methane clathrate basic unit has more than 70 atoms, and the number of atoms in the whole system will exceed 200 if adding the atoms of the interface model. Such a task can’t be done properly on a small work station thus it’s necessary to be assisted by NAISS.