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A standard X-observe NMR probe was equipped with a z-gradient coil to enable high-sensitivity pulsed field gradient NMR diffusion studies of Li+ and Cs+ cations of aqueous salt solutions in a high-porosity mesocellular silica foam (MCF) and of CO2 adsorbed in metal-organic frameworks (MOF). The coil design and the necessary probe modifications, which yield pulsed field gradients of up to ±16.2Tm-1, are introduced. The system was calibrated at 2H resonance frequency and successfully applied for diffusion studies at 7Li, 23Na, 13C and 133Cs frequencies. Significant reductions of the diffusivities of the cations in LiClac and CsClac solution introduced into MCFs are observed. By comparison of the diffusion behavior with the bulk solutions, a tortuosity of the silica foam of 4.5±0.6 was derived. Single component self-diffusion of CO2 and CH4 (measured by 1H NMR) as well as self-diffusion of the individual components in CO2/CH4 mixtures was studied in the MOF CuBTC. The experimental results confirm high mobilities of the adsorbed gases and trends for diffusion separation factors predicted by MD simulations.

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With the increasing demand for alternative fuels the storage of natural gas (NG) in adsorbents like metal organic frameworks (MOFs) will become more important. In order to use MOFs as storage media in fuel delivery systems, the optimization of mass and energy transfer of the system is crucial. For rapid NG filling of a tank, molecules need to reach the adsorption sites within a reasonable time while the heat of adsorption should be dissipated to the environment. In this article, mass transfer in shaped bodies of MOFs was determined by permeability measurements and pulsed field gradient (PFG) NMR spectroscopy. The heat dissipation was also experimentally measured and both data sets were used to set up a theoretical density function theory model to predict the behavior of MOFs for NG storage.

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Für NMR‐Diffusionsmessungen wurde ein z‐Gradientensystem zur Erzeugung intensiver Feldgradientenimpulse überarbeitet. Dazu wurde das Gradientenfeld einer aktiv abgeschirmten Spule mittels der Finite‐Elemente‐Methode optimiert. Das System wurde aus Glaskeramik als Spulenträger aufgebaut. Es besitzt kein 1H‐NMR‐Eigensignal und weist einen hohen Strom/Gradienten‐Wandlerfaktor von 0,37 T m–1A–1 auf. Mit dem Nachweis isotroper und anisotroper Diffusion in wässrigen Lösungen eines PEO‐PPO‐PEO Triblock‐Copolymers und adsorbierten Methans in zwei verschiedenen mikroporösen kristallinen Adsorbentien wird die Funktionstüchtigkeit des Systems demonstriert.

Unlike conventional gas reservoirs, shale gas reservoirs contain organic mesopores that have pore sizes ranging from 2 to 50 nm. These organic pores may cause capillary condensation of confined hydrocarbons due to the non-negligible capillary pressure. A novel phase equilibrium model has been developed to quantify effects of pore size distribution on the phase behavior of confined hydrocarbons, including the occurrence of capillary condensation. However, it remains a challenge to assess the phase behavior of confined hydrocarbons by laboratory experiments. This is because the conventional pressure-volume-temperature (PVT) method measures the phase behavior of a bulk fluid. Here, we employ low- and high-field nuclear magnetic resonance (NMR) techniques to experimentally probe the capillary effect on phase behavior using retrograde condensates in synthetic porous media and shale rock samples. In low-field NMR experiments, water-wet porous glass and oil-wet polymer-based spherical activated carbon (PBSAC) beads are used as porous media. NMR relaxation times are used to observe the occurrence of capillary condensation for pure and mixed hydrocarbons at room temperature under controlled pressure. High-field NMR is employed to gain further sensitivity and resolution for the phase behavior of a confined methane-butane mixture. NMR spectroscopic signatures of the dew point were identified, enabling the comparison of dew-point pressures of the bulk hydrocarbons and hydrocarbons confined in grinded shale rock. NMR-measured dew point of confined hydrocarbons is ~115 psi higher than that of bulk phase. This pressure shift agrees well with simulation results. In summary, we present NMR experimental studies and model validation on the capillary condensation effect, showing a shift of dew-point pressures of confined hydrocarbons mixtures in porous media. The agreement between NMR and simulation results validates the novel phase equilibrium model implemented in the newly developed PVT simulation software. The lab measurements and model validation results show that a) oil-wet is one key condition for the occurrence of capillary condensation of confined hydrocarbons; b) the shift of an upper dew-point pressure of hydrocarbons confined in shale rock can be tens of psi to slightly over 100 psi for the retrograde condensate system being used; c) the phase equilibrium model is valid for modeling phase behavior of multi-component hydrocarbons confined in mesopores.