Natural Hydrophilic Amino Acids as Environment-Friendly Gas Hydrate Inhibitors for Carbon Capture and Sequestration

Abstract

Carbon capture and sequestration using gas hydrates are receiving a great deal of attention as clean processes since hydrates produce water as a major byproduct. The formation of hydrates in pipelines for CO2 transport and oil/gas production systems is also of great importance due to safety and cost issues. The use of chemical additives is necessary to optimize operating temperature and pressure conditions for the proper control and management of hydrate formation. Accordingly, their potential environmental impacts have led to the surging demand for eco-friendly hydrate additives. Amino acids have been recognized as a promising class of hydrate inhibitors as they interact with water via hydrogen-bonding and electrostatic interactions. However, insufficient inhibitory effects of amino acids and low solubility in liquid water have been considered to limit their applications. In this work, we report the effective use of hydrophilic amino acids as promising inhibitors for CO2 hydrates. Superior inhibitory efficiency of l-serine is achieved by its hydroxy group, which lowers the water activity through hydrogen bonding, thus shifting hydrate formation conditions to lower-temperature and higher-pressure regions. When added at 0.1 mol %, l-serine retards hydrate formation kinetics primarily by disrupting the water hydrogen-bond network. The thermodynamic inhibitory effect of l-proline even exceeds that of methanol due to its abnormally high hydrophilicity originating from the unique structural characteristics, and it works at high concentrations as a dual-function inhibitor affecting both phase equilibria and formation kinetics. The use of amino acids is highly preferred as they are natural and biodegradable substances, and therefore the potential environmental risk can be minimized. The corrosion issue often caused by the use of salts can also be neglected. The high solubility of hydrophilic amino acids allows them to be applied for a wide range of temperature and pressure conditions required for carbon capture and sequestration processes using gas hydrates.