Chang Li,Kang Tan,Fangzheng Hua,Changxue Wang,Mengting Sun,Fei Wang,Xiaolin Wang
Natural gas hydrate (NGH) technology has broad application prospects in natural gas storage & transportation. In this work, we used eco-friendly hydrogel-based carriers to retain water, which were biodegradable polyvinyl alcohol-co-acrylic acid (PVA-co-PAA) hydrogels, and to react with methane gas and form hydrates. Results indicated that hydrates could be formed in the presences of swollen hydrogel particles without stirring or promoter adding, which might be owed to the enlarged gas–liquid interface and bulk of hydrophilic groups. When mass ratio of PVA to AA (MR) was 1:4, hydrogels performed best in improving hydrate formation kinetics: the induction time was 20.3 ± 20 min, the hydrate growth rate was 0.0217 ± 0.0088 mmol mL −1 min −1 , and the methane uptake was 75.84 ± 4.70 mmol mol −1 water. Morphological observations revealed the water retaining behaviors of hydrogels during hydrate formation-dissociation process: a part of absorbed water transferred out of hydrogels to participate in hydrate formation, and afterwards hydrogels could re-absorbed the water released by hydrate dissociation. Moreover, hydrogels kept excellent recycling performance in seven repeated hydrate formation-dissociation cycles. Collectively, PVA-co-PAA hydrogels used as water carriers could improve mass transfer and reaction efficiency during methane hydrate formation-dissociation process, and meanwhile exhibited good recyclability due to strong water absorbing and retaining capabilities, implying that PVA-co-PAA hydrogels might potentially have broad applications in NGH technology.
Chang Li,Kang Tan,Fangzheng Hua,Changxue Wang,Xiaolin Wang,Fei Wang,Mengting Sun
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 t 90 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.
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