Methane hydrate formation promoted by eco-friendly hydrogels carrying with trace SDS

Hydrate-based natural gas storage and transportation is in urgent need of efficient and eco-friendly promotion methods. Here, we employed a kind of eco-friendly hydrogels, which were polyvinyl alcohol-co-acrylic acid (PVA-co-PAA), as carriers for trace SDS solution to construct a co-promoter for methane hydrate formation. Under static condition without stirring, trace SDS solution that was lower than or equal to 0.4 mmol L⁻¹ had no or had extremely weak promoting effects on hydrate formation kinetics, whereas hydrogel-carried trace SDS exhibited excellent synergistic promoting effects. The HS-0.4 under a SDS concentration of 0.4 mmol L⁻¹ and at a swelling ratio of 200 g g⁻¹ achieved the most remarkable promotion, and the induction time was 0 min, the hydrate growth rate at t₉₀ was 0.1552 ± 0.0068 mmol mL⁻¹ min⁻¹, the methane uptake was 121.70 ± 1.58 mmol mol⁻¹ and the water-to-hydrate conversion was 0.730 ± 0.009. During synergistic promotion process, on the one hand, hydrogels keeping with large surface area increased gas–liquid interface, and were in charge of facilitating hydrate nucleation and shortening induction time; on the other hand, trace SDS produced strong capillary effect and sharply boosted mass transfer during hydrate growth period, which drastically enhanced hydrate growth rate and methane uptake. Morphology observation on hydrate evolutions unveiled that the co-promoter significantly improved poor hydrate compactness and partly relieved foam problem caused by SDS. Hydrogel-carried trace SDS can serve as an effective, eco-friendly and economical promotion approach for methane hydrate formation, which might be of great benefit for hydrate-based natural gas storage and transportation.