Influence of Powder Cryogel on the Reacted Formation of Methane Hydrates

This study examines how variations in the composition of powdered polyvinyl alcohol cryogel (PPVACG) affect its capacity to sustain repeated cycles of methane hydrate formation and dissociation without a decline in gas storage performance. The powder cryogels are dispersed systems composed of polyvinyl alcohol (PVA) cryogel microdroplets, which may contain a cross-linking agent and are stabilized by hydrophobized silica nanoparticles. The influence of the content of PVA, stabilizer, and cross-linking agent (boric acid) on the methane absorption capacity of powder cryogel during hydrate formation/dissociation cycles was investigated. It was demonstrated that increasing the PVA concentration from 5 to 7 wt % enhanced methane absorption capacity by 47 VCH4/Vhyd (methane volume at STP per methane hydrate volume) in the ninth cycle. A further increase in stabilizer concentration from 2 to 5 wt % resulted in an additional gas uptake of approximately 18 VCH4/Vhyd. However, the addition of a cross-linking agent (boric acid) significantly reduced the methane uptake capacity during cycles of hydrate formation/dissociation. It was found that, as a result of repeated methane hydrate formation/dissociation cycles, water contained within the polymer particles of polyvinyl alcohol cryogels can migrate into the stabilizer-filled interparticle space. Based on this observation, a mechanism explaining the reduction in the methane absorption capacity of cryogels during multiple hydrate formation/dissociation cycles is proposed. Furthermore, methane hydrates formed in powdered PVA cryogels exhibit the self-preservation effect, demonstrating anomalously slow dissociation at a temperature of 268.2 K and a pressure of 0.1 MPa. These results highlight the critical role of cryogel composition in enhancing hydrate stability and gas storage efficiency.