In this work a novel method for enhancing the gas storage capacity of metal-organic frameworks (MOFs), i.e. saturating the MOF with a suitable quantity of water and forming hydrates in it, was proposed. Commercialized ZIF-8 was adopted as it is very stable under an atmosphere of water. The adsorption and hydrate formation behaviors of methane in wet ZIF-8 with five different water contents (0.0%, 16.3%, 27.7%, 30.6%, and 35.1%, mass percentages) were investigated under hydrate formation conditions and the storage capacities of both ZIF-8 frameworks and ZIF-8 particle beds were determined. Our results show that hydrates can form in wet ZIF-8 pores and thus increase the overall storage capacities of both ZIF-8 frameworks and ZIF-8 particle beds remarkably. The contribution of hydrates to the total gas uptake of a ZIF-8 framework can be as high as 45%. Compared with dry ZIF-8 frameworks, the net storage capacity of the wet analogue with a water content of 35.1% increases from 5.954 to 9.304 mmol g À1 at 269.15 K and 2.85 MPa, in other words, raised by more than 56%. The ideal volume storage capacity of the wet ZIF-8 framework can achieve more than 190 V/V at 3.0 MPa or so, 7% higher than the DOE target (180 V/V) for methane storage. In addition, our SEM measurements and XRD analysis demonstrate that ZIF-8 is stable during the saturation and hydrate formation processes, illustrating that it can be used repeatedly.
The anti-agglomeration performance of single or compounded commercial chemical additives with/without the addition of alcohol as a co-surfactant was evaluated using a sapphire cell and an autoclave reactor with a focused beam reflectance measurement (FBRM) probe. Five kinds of gas hydrate morphologies, clumpy-like, slush-like, flocculent-like, slurry-like, and powder-like, were found during evaluating the effect of the commercial additives in (water + oil) systems. The experimental results showed that AEO-3 combined with some commercial chemical additives, especially Span 20, exhibits good antiagglomeration performance. The hydrate slurry thus formed has a high stability and will not result in agglomeration for a long period of time. A compounded inhibition mechanism, in which one of the components disperses water droplet in the oil phase and the other component prevents formed hydrate from agglomeration, was proposed. A new structure of hydrate antiagglomerant was designed according to the evaluating results of the single or compounded commercial additives with/without the addition of alcohol material.
We report for the first time an experimental investigation of gas storage in porous graphene with nanomeshes. High capacity methane storage (236 v(STP)/v) and a high selectivity to carbon dioxide adsorption were obtained in the nanomesh graphene with a high specific surface area (SSA) and a SSA-lossless tightly stacking manner.
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