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.
Podenko et al. (Mon,) studied this question.