Investigation of CH4 Hydrate Formation Under the Synergistic Effects of Graphite Nanofluids and Cyclopentane and Its Storage Stability at Subzero Temperatures

The solidified natural gas (SNG) technology presents a prospective strategy for CH4 storage and transportation. Low gas storage capacity and slow formation rate remain the key challenges for its field applications. This study suggested a compound system of cyclopentane (CP) + graphite nanoparticle (GNP) nanofluid to enhance the formation kinetics of CH4 hydrate. Results indicated that both gas consumption and hydrate formation rate were higher at a higher CP concentration, peaking at 14 wt%, where t90 (the time to reach 90% of the final gas uptake) was 65.7 min, and the gas uptake reached 0.1346 mol/mol. However, an excessive CP (21 wt%) negatively affected CH4 hydrate generation kinetics due to the excessive cage occupancy of CP in 51264 cavities. A lower temperature was determined to be more favorable for CH4 hydrate formation within nanofluids, which was visually demonstrated by the denser hydrate crystals formed at 275.15 K. Moreover, storage stability analysis revealed that CH4 hydrate formed in CP + GNP nanofluids can be preserved at atmospheric pressure and 268.15 K without significant decomposition. This work provides a superior scheme for hydrate-based CH4 storage, offering great contributions to SNG technology advancement.