Grafting of nano-Ag particles on -SO3--coated nanopolymers for promoting methane hydrate formation

Sodium dodecyl sulfate (SDS) has been reported to be the most efficient promoter for hydrate-based natural gas storage and transportation, however, foam generation during hydrate dissociation seriously affects its application. Nano-metal particles have also been demonstrated to be efficient promoters, nevertheless their poor stability is a serious problem. In this work, we first fixed -SO3- groups (similar to the hydrophilic group of SDS) covalently on polystyrene through soap-free emulsion polymerization to synthesize -SO3--coated nanopolymers, and by tuning their morphology they existed as amorphous polystyrene macromolecules (-SO3-@PSMM) or uniform polystyrene nanospheres (-SO3-@PSNS). Afterwards, we grafted nano-Ag particles with the size of 2-5 nm on the -SO3--coated nanopolymers through electrostatic adsorption and in situ reduction to prepare Ag&-SO3--coated nanopolymers (denoted as Ag&-SO3-@PSMM and Ag&-SO3-@PSNS), which were then used for the first time to promote methane hydrate formation. When 0.5 mmol L-1 amorphous Ag&-SO3-@PSMM was used at an initial pressure of 6 MPa and temperature of 275.15 K, the induction period was 32.2 +/- 7.9-60.8 +/- 14.2 min, the growth period was 108.8 +/- 8.2-177.1 +/- 38.9 min and the methane storage capacity reached 143.9 +/- 3.7-145.2 +/- 1.2 v/v, whereas when the spherical Ag&-SO3-@PSNS was used at 0.5 mmol L +/- 1, the induction period and growth period were 17.8 +/- 2.8-38.5 +/- 8.0 and 39.6 +/- 2.8-42.1 +/- 0.9 min, respectively; and the storage capacity reached 149.3 +/- 1.2-151.3 +/- 3.0 v/v, indicating that Ag&-SO3-@PSNS were much better promoters compared with Ag&-SO3-@PSMM. Moreover, Ag&-SO3-@PSNS exhibited excellent recycling performance for 10 cycles of methane hydrate formation-dissociation. To sum up, the Ag&-SO3--coated nano-promoters developed in this work showed significant potential in achieving the industrial application of hydrate-based natural gas storage and transportation.