An investigation on repeated methane hydrates formation in porous hydrogel particles

Abstract

Porous hydrogel particles of poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(N-isopropylacrylamide) (PNIPAAm) with varying water absorbability and quantities were investigated upon their ability and stability to support the reversible methane hydrates storage in the presence of silica nanoparticles and water. Results from experimental and computational simulation indicated that the equilibrium water content and types of hydrogels, and the quantity of the hydrogel particles used in the mixture affect the hydrate formation kinetics. At the experimental condition of 4.5 MPa, all types of porous hydrogel particles were proved to be effective to store methane in the hydrates form. A storage capacity of 206 cm3 methane gas (as at standard temperature and pressure) per gram water was achieved when the hydrate forming mixture contained four parts of PHEMA20, one part of silica nanoparticles and fifteen parts of water. Quantitative analysis using the shrinking-core model indicated that the presence of the hydrogel particles could increase the overall methane diffusivity and improve the hydrate formation kinetics, therefore the overall water conversion rate also enhanced. A strong reversibility was demonstrated by the added porous hydrogel particles. Changing water uptake by the hydrogel particles during the cool-thawing procedure was evident by the simulated water distribution data. The hydrogels with higher equilibrium water content, greater pore volumes and more stable porous structures and the lower operational pressure have shown better methane storage capacity and reversibility.