Trace amounts of renewable surfactants enable rapid and high-density methane storage in clathrate hydrates: sustainable alternatives to synthetic promoters

Abstract

The escalating global demand for natural gas necessitates the development of efficient and environmentally benign storage and transportation technologies. In this study, six anionic renewable surfactants with different counterions – lithium (LO), sodium (SO), potassium (PO), ammonium (AO), ethanolamine (EAO), and diethanolamine (DEAO) – were synthesized and tested as gas hydrate promoters. The entire preparation process of these surfactants utilized water as the sole solvent, eliminating the reliance on hazardous organic solvents. AO, EAO, and PO achieved superior water-to-hydrate conversion (≥94%). At ultralow dosages, all renewable surfactants delivered conversion rates ≥85% and storage capacities up to 159.19 v/v, with EAO achieving 92.96% conversion at just 2 ppm. This work represents highly efficient and truly green promoters for methane storage that outperform SDS at only 2 ppm. LO maintained high efficiency even in saline water, with 81.25% conversion and a 142.70 v/v storage capacity, demonstrating its potential for seawater-based gas storage applications. Pelletization experiments under static conditions produced methane hydrate pellets with good structural integrity, retaining 85.8% of stored methane after 15 days at −5 °C. Environmental assessments confirmed that all renewable surfactants are readily biodegradable (65–89% mineralization in 28 days) and exhibited low cytotoxicity at operational concentrations, which validates their safety for industrial applications. Additionally, the renewable surfactants minimized foam formation during hydrate dissociation, enabling efficient methane recovery (>90%). This study establishes renewable surfactants as sustainable alternatives to conventional synthetic promoters. The renewable surfactants adhere to green chemistry principles by lessening ecological persistence, reducing toxicological risks, and ensuring both biodegradability and biocompatibility of the surfactants. The promising results highlight the significant potential of these promoters in advancing environmentally sustainable solidified natural gas technologies for energy storage and transport applications.