Kinetic Characterization of CH4 Hydrate Formation in Metal–Organic Framework Nanomaterials and l-Tryptophan Complex Systems

Abstract

Metal–organic frameworks (MOFs) and amino acids are promising hydrate promoters for improving methane hydrate formation kinetics in solid natural gas technology. This study examines the effects of four MOFs─MIL-101(Cr), MIL-101(Fe), ZIF-8_CP, and ZIF-8_MC─on methane hydrate formation in both pure water and l-tryptophan-containing systems. MIL-101(Cr) and MIL-101(Fe) significantly reduced the induction time by 38% and 44%, respectively, compared to pure water, while ZIF-8_CP and ZIF-8_MC extended it by 145% and 90%, respectively. During the growth phase, MIL-101(Cr) exhibited a notable promoting effect, while MIL-101(Fe) and ZIF-8_MC had minimal influence. In contrast, ZIF-8_CP markedly suppressed both methane uptake and absorption rate. A strong synergistic effect was observed between MIL-101(Cr) and l-tryptophan, reducing induction time to 33% of that in pure water and achieving the highest gas uptake rate. Conversely, ZIF-8_MC and ZIF-8_CP counteracted the effects of l-tryptophan, with the kinetics of the 0.5 wt % ZIF-8_CP + 0.5 wt % l-tryptophan system closely resembling those of pure water. Scanning electron microscopy and contact angle analyses suggest that MOFs’ hydrophilicity and polyhedral structure primarily influence nucleation, while particle size plays a dominant role in the growth phase. These findings provide new insights into the design of MOF-based hydrate promoters for enhanced methane storage and transport applications.