2 research outputs found
SI methane hydrate confined in C8-grafted SBA-15: A highly efficient storage system enabling ultrafast methane loading and unloading
Confinement of water and methane in mesopores of hydrophobized SBA-15 is
demonstrated to promote methane hydrate formation. In comparison to
as-synthesized SBA-15, hydrophobization by C8 grafting accelerates the kinetics
of methane storage in and delivery from the hydrate. C8 grafting density was
determined at 0.5 groups nm-2 based on TGA and quantitative NMR spectroscopy.
Multinuclear 1H-1H DQSQ and 1H-1H RFDR NMR provided spectroscopic evidence for
the occurrence of C8 chains inside the mesopores of SBA-15, by showcasing close
spatial proximity between the grafted C8 chains and pore-intruded water
species. X-ray diffraction demonstrates formation of Structure I hydrate on
SBA-15 C8. At 7.0 MPa and 248 K, the water-to-hydrate conversion on
hydrophobized SBA-15 C8 reaches 96 pct. as compared to only 71 pct. on a
pristine SBA-15 sample with comparable pore size, pore volume and surface area.
The clathrate loading amounted to 14.8 g g-1. 2D correlation NMR spectroscopy
(1H-13C CP-HETCOR, 1H-1H RFDR) reveals hydrate formation occurs within pores of
SBA-15 C8 as well as in interparticle volumes. Following the initial
crystallization of SBA-15 C8-supported methane hydrate taking several hours, a
pressure swing process at 248 K allows to desorb and re-adsorb methane from the
structure within minutes and without thawing the frozen water structure. Fast
loading and unloading of methane was achieved in 19 subsequent cycles without
losses in kinetics. The ability to harvest the gas and regenerate the structure
without the need to re-freeze the water represents a 50 pct. energy gain with
respect to melting and subsequently recrystallizing the hydrate at 298 K and
248 K, respectively. After methane desorption, a small amount of residual
methane hydrate in combination with an amorphous yet locally ordered ice phase
is observed using 13C and 2H NMR spectroscopy
Enabling hydrate-based methane storage under mild operating conditions by periodic mesoporous organosilica nanotubes
Biomethane is a renewable natural gas substitute produced from biogas. Storage of this sustainable energy vector in confined clathrate hydrates, encapsulated in the pores of a host material, is a highly promising avenue to improve storage capacity and energy efficiency. Herein, a new type of periodic mesoporous organosilica (PMO) nanotubes, referred to as hollow ring PMO (HR-PMO), capable of promoting methane clathrate hydrate formation under mild working conditions (273 K, 3.5 MPa) and at high water loading (5.1 g water/g HR-PMO) is reported. Gravimetric uptake measurements reveal a steep single-stepped isotherm and a noticeably high methane storage capacity (0.55 g methane/g HR-PMO; 0.11 g methane/g water at 3.5 MPa). The large working capacity throughout consecutive pressure-induced clathrate hydrate formation-dissociation cycles demonstrates the material’s excellent recyclability (97% preservation of capacity). Supported by ex situ cryo-electron tomography and x-ray diffraction, HR-PMO nanotubes are hypothesized to promote clathrate hydrate nucleation and growth by distribution and confinement of water in the mesopores of their outer wall, along the central channels of the nanotubes and on the external nanotube surface. These findings showcase the potential for application of organosilica materials with hierarchical and interconnected pore systems for pressure-based storage of biomethane in confined clathrate hydrates