Phase equilibrium of double-guest clathrates of methane and CO2, ethane, or propane as measured by high-pressure microcalorimetry

The world's increasing energy demand has led to considering methane hydrates as a promising alternative energy source to oil, gas, and coal. Due to the growing concerns about climate change, carbon capture via hydrate formation is considered a potential pathway for decarbonization. Understanding the phase equilibria is crucial for the development of these applications. This study presents new experimental data on the dissociation temperatures of double-guest clathrates at high pressure. Specifically, aqueous systems containing binary mixtures of methane and low-molecular-weight gases, such as ethane, propane, and carbon dioxide, were investigated. The experimental data were obtained using High-Pressure Microcalorimetry, covering pressures up to 100 MPa. The performance of a multicycle Differential Scanning Calorimetry (DSC) procedure was evaluated to determine the influence of the amount of non-clathrated water on the equilibrium properties of the binary guest systems. The experimental results were successfully modeled using the CSMGem and Multiflash software, demonstrating good agreement. The impact of the diffusivity and solubility of different guest species in water on the hydrate structure and its thermodynamic properties is discussed. The suitability of sI and sII clathrate structures to accommodate distinct molecules, the degree of cavity occupation, and the gas composition were evaluated to elucidate their effects on the dissociation temperatures.