Neutron Scattering Measurements of Carbon Dioxide Adsorption in Pores within the Marcellus Shale: Implications for Sequestration.

Shale is an increasingly viable source of natural gas and a potential candidate for geologic CO2 sequestration. Understanding the gas adsorption behavior on shale is necessary for the design of optimal gas recovery and sequestration projects. In the present study neutron diffraction and small-angle neutron scattering measurements of adsorbed CO2 in Marcellus Shale samples were conducted on the Near and InterMediate Range Order Diffractometer (NIMROD) at the ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory along an adsorption isotherm of 22 °C and pressures of 25 and 40 bar. Additional measurements were conducted at approximately 22 and 60 °C at the same pressures on the General-Purpose Small-Angle Neutron Scattering (GP-SANS) instrument at Oak Ridge National Laboratory. The structures investigated (pores) for CO2 adsorption range in size from Å level to ∼50 nm. The results indicate that, using the conditions investigated densification or condensation effects occurred in all accessible pores. The data suggest that at 22 °C the CO2 has liquid-like properties when confined in pores of around 1 nm radius at pressures as low as 25 bar. Many of the 2.5 nm pores, 70% of 2 nm pores, most of the <1 nm pores, and all pores <0.25 nm, are inaccessible or closed to CO2, suggesting that despite the vast numbers of micropores in shale, the micropores will be unavailable for storage for geologic CO2 sequestration.

Scanning of Adsorption Hysteresis In Situ with Small Angle X-Ray Scattering.

Everett's theorem-6 of the domain theory was examined by conducting adsorption in situ with small angle x-ray scattering (SAXS) supplemented by the contrast matching technique. The study focuses on the spectrum differences of a point to which the system arrives from different scanning paths. It is noted that according to this theorem at a common point the system has similar macroscopic properties. Furthermore it was examined the memory string of the system. We concluded that opposite to theorem-6: a) at a common point the system can reach in a finite (not an infinite) number of ways, b) a correction for the thickness of the adsorbed film prior to capillary condensation is necessary, and c) the scattering curves although at high-Q values coincide, at low-Q values are different indicating different microscopic states. That is, at a common point the system holds different metastable states sustained by hysteresis effects. These metastable states are the ones which highlight the way of a system back to a return point memory (RPM). Entering the hysteresis loop from different RPMs different histories are implanted to the paths toward the common point. Although in general the memory points refer to relaxation phenomena, they also constitute a characteristic feature of capillary condensation. Analogies of the no-passing rule and the adiabaticity assumption in the frame of adsorption hysteresis are discussed.

Investigation of confined ionic liquid in nanostructured materials by a combination of SANS, contrast-matching SANS, and nitrogen adsorption.

Small-angle neutron scattering (SANS), contrast-matching SANS, and nitrogen adsorption have been utilized to investigate the confined ionic liquid (IL) [bmim][PF(6)] phase in ordered mesoporous silica MCM-41 and SBA-15. The results suggest that the pores of SBA-15 are completely filled with IL whereas a small fraction of the pore volume, the pore "core", of MCM-41 is empty. The contrast-matching SANS measurements confirm the enhanced solubility of water in IL. In addition, they provide strong evidence that water does not enter the empty pore core of MCM-41, possibly because of the preferred orientation of the IL molecules in the adsorbed layer.

Grafting of imidazolium based ionic liquid on the pore surface of nanoporous materials--study of physicochemical and thermodynamic properties.

Supported ionic liquid phase (SILP) systems were prepared by immobilizing a methylimidazolium cation based ionic liquid onto the pore surface of two types of support, MCM-41 and Vycor. The "grafting to" method was applied, involving (3-chloropropyl)-trialkoxysilane anchoring on the supports' silanol groups, followed by treatment with 1-methylimidazole and ion exchange with PF(6)(-). Optimum surface pretreatment procedures and reaction conditions for enhanced ionic liquid (IL) loading were properly defined and applied for all modifications. A study on the effect of different pore sizes on the physical state of the grafted 1-(silylpropyl)-3-methylimidazolium-hexafluorophosphate ([spmim][PF(6)(-)]) was also conducted. The [spmim][PF(6)(-)] crystallinity under extreme confinement in the pores was investigated by modulated differential scanning calorimetry (DSC) and X-ray diffraction (XRD) and was further related to the capacity of the developed SILP to preferentially adsorb CO(2) over CO. For this purpose, CO(2) and CO absorption measurements of the bulk ionic liquid [bmim][PF(6)(-)] and the synthesized alkoxysilyl-IL were initially performed at several temperatures. The results showed an enhancement of the bulk IL performance to preferentially adsorb CO(2) at 273 K. The DSC analysis of the SILPs revealed transition of the melting point of the grafted alkoxysilyl-IL to higher temperatures when the support pore size was below 4 nm. The 2.3 nm MCM-41 SILP system exhibited infinite CO(2)/CO separation capacity at temperatures below and above the melting point of the bulk IL phase, adsorbing in parallel significant amounts of CO(2) in a reversible manner. These properties make the developed material an excellent candidate for CO(2)/CO separation with pressure swing adsorption (PSA) techniques.