Structural characterisation of porous materials in relation to entrapment of non-wetting fluids

An understanding of the physical mechanisms by which non-wetting fluids become entrapped is important to oil recovery techniques from reservoir rocks, and the structural characterization of porous media. The mechanisms of entrapment and the spatial distribution of non-wetting fluid (mercury) within model materials with similar chemical and geometrical properties to oil reservoir rocks have been investigated using mercury porosimetry and computed X-ray tomography. The combination of both techniques has allowed the direct observation of entrapped mercury within the model materials. In this thesis, a novel experimental technique involving combined mercury porosimetry and mercury thermoporosimetry techniques has been used to determine pore size distributions for disordered porous solids. Mercury porosimetry was conducted, and the mercury entrapped following porosimetry was used as the probe fluid for thermoporosimetry. The fully integrated combination of techniques described here permits the validation of assumptions used in one technique by another. Mercury porosimetry scanning curves were used to establish the correct correspondence between the appropriate Gibbs-Thomson parameter, and the nature of the meniscus geometry in melting, for thermoporosimetry measurements on entrapped mercury. Mercury thermoporosimetry has been used to validate the pore sizes, for a series of sol-gel silica materials, obtained from mercury porosimetry data using the independently-calibrated Kloubek correlations. A Liquid-liquid exchange (LLE) process within mesoporous materials has also been investigated using NMR relaxometry and NMR diffusimetry experiments. In this method, a high affinity liquid (water) displaced a low affinity liquid (cyclohexane) from the sol-gel silica samples. Entrapment of low affinity liquid was observed which was similar to the entrapment of non- wetting fluid observed in mercury porosimetry. In addition, the molecular diffusion of n-pentane has been measured in mesoporous sample using PFG NMR method in a broad temperature range

Structural characterisation of porous materials in relation to entrapment of non-wetting fluids

An understanding of the physical mechanisms by which non-wetting fluids become entrapped is important to oil recovery techniques from reservoir rocks, and the structural characterization of porous media. The mechanisms of entrapment and the spatial distribution of non-wetting fluid (mercury) within model materials with similar chemical and geometrical properties to oil reservoir rocks have been investigated using mercury porosimetry and computed X-ray tomography. The combination of both techniques has allowed the direct observation of entrapped mercury within the model materials. In this thesis, a novel experimental technique involving combined mercury porosimetry and mercury thermoporosimetry techniques has been used to determine pore size distributions for disordered porous solids. Mercury porosimetry was conducted, and the mercury entrapped following porosimetry was used as the probe fluid for thermoporosimetry. The fully integrated combination of techniques described here permits the validation of assumptions used in one technique by another. Mercury porosimetry scanning curves were used to establish the correct correspondence between the appropriate Gibbs-Thomson parameter, and the nature of the meniscus geometry in melting, for thermoporosimetry measurements on entrapped mercury. Mercury thermoporosimetry has been used to validate the pore sizes, for a series of sol-gel silica materials, obtained from mercury porosimetry data using the independently-calibrated Kloubek correlations. A Liquid-liquid exchange (LLE) process within mesoporous materials has also been investigated using NMR relaxometry and NMR diffusimetry experiments. In this method, a high affinity liquid (water) displaced a low affinity liquid (cyclohexane) from the sol-gel silica samples. Entrapment of low affinity liquid was observed which was similar to the entrapment of non- wetting fluid observed in mercury porosimetry. In addition, the molecular diffusion of n-pentane has been measured in mesoporous sample using PFG NMR method in a broad temperature range

Combining mercury thermoporometry with integrated gas sorption and mercury porosimetry to improve accuracy of pore-size distributions for disordered solids

The typical approach to analysing raw data, from common pore characterization methods such as gas sorption and mercury porosimetry, to obtain pore size distributions for disordered porous solids generally makes several critical assumptions that impact the accuracy of the void space descriptors thereby obtained. These assumptions can lead to errors in pore size of as much as 500%. In this work, we eliminated these assumptions by employing novel experiments involving fully integrated gas sorption, mercury porosimetry and mercury thermoporometry techniques. The entrapment of mercury following porosimetry allowed the isolation (for study) of a particular subset of pores within a much larger interconnected network. Hence, a degree of specificity of findings to particular pores, more commonly associated with use of templated, model porous solids, can also be achieved for disordered materials. Gas sorption experiments were conducted in series, both before and after mercury porosimetry, on the same sample, and the mercury entrapped following porosimetry was used as the probe fluid for theromporometry. Hence, even if one technique, on its own, is indirect, requiring unsubstantiated assumptions, the fully integrated combination of techniques described here permits the validation of assumptions used in one technique by another. Using controlled-pore glasses as model materials, mercury porosimetry scanning curves were used to establish the correct correspondence between the appropriate Gibbs–Thomson parameter, and the nature of the meniscus geometry in melting, for thermoporometry measurements on entrapped mercury. Mercury thermoporometry has been used to validate the pore sizes, for a series of sol–gel silica materials, obtained from mercury porosimetry data using the independently-calibrated Kloubek correlations. The pore sizes obtained for sol–gel silicas from porosimetry and thermoporometry have been shown to differ substantially from those obtained via gas sorption and NLDFT analysis. DRIFTS data for the samples studied has suggested that the cause of this discrepancy may arise from significant differences in the surface chemistries between the samples studied here and that used to calibrate the NLDFT potentials

Detection of the delayed condensation effect and determination of its impact on the accuracy of gas adsorption pore size distributions

Macroscopic, highly disordered, mesoporous materials present a continuing challenge for accurate pore structure characterization. The typical macroscopic variation in local average pore space descriptors means that methods capable of delivering statistically representative characterizations are required. Gas adsorption is a representative but indirect method, normally requiring assumptions about the correct model for data analysis. In this work we present a novel method to both expand the range, and obtain greater accuracy, for the information obtained from the main boundary adsorption isotherms by using a combination of data obtained for two adsorptives, namely nitrogen and argon, both before and after mercury porosimetry. The method makes use of the fact that nitrogen and argon apparently ‘see’ a different pore geometry following mercury entrapment, with argon, relatively, ‘ignoring’ new metal surfaces produced by mercury porosimetry. The new method permits the study of network and pore–pore co-operative effects during adsorption that substantially affect the accuracy of the characteristic parameters, such as modal pore size, obtained for disordered materials. These effects have been explicitly quantified, for a typical sol-gel silica catalyst support material as a case study. The technique allowed the large discrepancies between modal pore sizes obtained from standard gas adsorption and mercury thermoporometry methods to be attributed to the network-based delayed condensation effect, rather than spinodal adsorption. Once the network-based delayed condensation effect had been accounted for, the simple cylindrical pore model and macroscopic thermodynamic Kelvin-Cohan equation were then found sufficient to accurately describe adsorption in the material studied, rather than needing a more complex microscopic theory. Hence, for disordered mesoporous solids, a proper account of inter-pore interactions is more important than that of intra-pore adsorbate density distribution, to obtain accurate pore size distributions