Preparation of -SO3--coated nanopromoters for methane hydrate formation: effects of the existence pattern of -SO3- groups on the promotion efficiency

Sodium dodecyl sulfate (SDS) has been confirmed to be the most efficient promoter of gas hydrate formation; however, the foam generation during hydrate dissociation severely limits its application. In this study, the -SO3- group, similar to the hydrophilic group of SDS, was covalently fixed on polystyrene nanoparticles to prepare -SO3- -coated nanopromoters (-SO3-@PSNS) for methane hydrate formation. The existing form of -SO3- groups was controlled by varying the ratio of the hydrophobic and hydrophilic monomers during emulsion polymerization, which produced significant influence on the promotion efficiency. At the initial pressure of 5 MPa, when -SO3- groups existed irregularly with the macromolecules of -SO3- @PSNS in solution (-SO3- @PSNS-1), the growth rate was merely 8.02 +/- 0.95 x 10(-6) mol min(-1) mL(-1); however, when -SO3- groups were uniformly arrayed on the surface of the -SO3- @PSNS nanospheres (-SO3- @PSNS-2-3-4), the growth rate reached 18.08 +/- 3.29-40.97 +/- 2.89 x 10(-6) mol min(-1) mL(-1). When nanopromoters with regularly arrayed -SO(3)(-)groups (-SO3- @PSNS-2-3) were used at the initial pressure of 6 MPa, the entire hydrate formation process was completed within 1-2 h and the methane storage capacity reached 142 and 137 v/v, indicating much better promotion compared to other common promoters, such as SDS, nanofluids, and activated carbon. Moreover, -SO3- @PSNS-3 resulted in no foam generation during hydrate dissociation and produced excellent recycling performance in 8 cycles of methane hydrate formation. Therefore, the -SO3- -coated nanopromoters developed in this study have significant potential in the industrial application of hydrate-based natural gas storage and transportation.