Kinetic Study of Methane Hydrate Formation in Cysteine Systems: Effects of Salinity and Cysteine–Nanoparticle Synergistic Promotion

Abstract

As global natural gas demand continues to grow, traditional storage and transportation methods are facing increasing pressure, making hydrate-based technology a key research focus. To address the challenges of slow formation rate, low gas storage density, and high industrial costs, this study investigates the effects of salinity on methane hydrate formation kinetics, gas storage characteristics, and growth morphology, with the addition of cysteine as an environmental-friendly kinetic promoter. The aim is to evaluate the applicability of cysteine on hydrate formation acceleration in diluted seawater or treated industrial wastewater. Experimental results reveal a threshold effect of salinity concentration on methane hydrate storage performance, with a critical salinity of approximately 0.2 wt %. Beyond this threshold, salt ions significantly inhibit methane hydrate formation rate, gas storage capacity, and crystal growth orientation. This inhibition occurs through mechanisms such as reduced water activity, disruption of hydrogen bond networks, and impaired mass/heat transfer. To overcome the kinetic limitations in low-salinity environments, this study proposes a synergistic promotion strategy combining cysteine with nanofluids. Experimental results show that cysteine exhibits strong synergistic effects with Al₂O₃ and CuO nanoparticles, while an antagonistic effect with ZnO nanoparticles. Due to their high surface area and superior thermal conductivity, nanoparticles could significantly enhance the nucleation and formation rates of methane hydrates, though they have negligible impact on gas storage capacity. This work advances the industrial application of hydrate-based gas storage technologies by clarifying salinity impacts and demonstrating effective nanoparticle–cysteine synergies.