Eco-friendly hydrogels serving as water carriers for improving methane hydrate formation and dissociation processes

Abstract

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.