Advances in Nanomaterials for Sustainable Gas Separation and Storage: Focus on Clathrate Hydrates

Abstract

ConspectusClathrate hydrates, also known as gas hydrates, are a type of inclusion compound formed in highly developed nanoporous lattice spaces created by water molecules, where gas molecules such as CO₂, H₂, CH₄, and other low-molecular-weight liquid molecules are trapped. The nanoporous cage formed by water molecules serves as the "host", while the trapped gas or low-molecular-weight liquid molecules such as tetrahydrofuran act as "guests". Early on, clathrate hydrates drew attention as a potential replacement for conventional natural gas due to their natural gas hydrate form, which contains natural gases as guests and exists in permafrost or sea floors. Recently, based on the unique physicochemical properties of clathrate hydrates, efforts are being made to utilize synthetic clathrate hydrates in various separation processes such as post- and pre-combustion CO₂ capture, H₂ storage, natural gas storage and transportation, wastewater desalination, and more. While it is undeniable that clathrate hydrates are based on principles that are beneficial for the separation and storage of gas molecules, there are several challenges that must be addressed for their practical application. These challenges include (i) the limitation of gas storage capacity due to the confined size of nanoporous cages, (ii) the relatively high-pressure and low-temperature thermodynamic storage conditions typically required for clathrate hydrate formation, and (iii) slow formation kinetics and low gas hydrate conversion, which are also essential issues that need to be resolved for the meaningful implementation of clathrate hydrates. In this Account, we aim to introduce recent noteworthy research findings, including those from our research team, focusing on addressing these challenges. We explored the untapped potential of clathrate hydrates by bridging the gap between macroscopic and microscopic properties. This has led to breakthroughs in sustainable gas separation and storage applications. By revealing the hidden nature of these hydrates, we have effectively mitigated their inherent limitations, setting the stage for more feasible and efficient H₂ storage solutions through the introduction of hydrogen-natural gas blends to clathrate hydrates. Additionally, we have demonstrated the tuning effect on all naturally formed hydrate structures, offering new insights into their underlying properties and macroscopic behavior. Furthermore, our research has proposed a highly efficient hydrate-based pre-combustion CO₂ capture approach that leverages porous media with appropriate wettability and considers the implications of microstructure properties. This emphasizes the crucial connection between nano-structure and macroscopic properties, underscoring the significance of understanding their interplay for economic feasibility. We believe that our efforts to unveil the hidden nature of gas hydrates provide strategies to address challenges and lay the groundwork for practical applications.