Determination of the average micropore diameter of an Illinois No. 6 coal by xenon-129 NMR

Wernett, P.C.; Larsen, John W.; Yamada, Osamu; Yue, Hong

doi:10.1021/ef00022a014

Cited by 33 publications

(18 citation statements)

References 1 publication

(2 reference statements)

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“…The technique has been applied to a carbonaceous material of reasonably well defined pore structure by Wernett et al (1990), and the calculated pore diameter was within the expected range. Thus, the technique may be applicable to coal, though it must be borne in mind that coal is much more heterogeneous than either zeolites or microporous carbons, and that paramagnetic species and/or impurities in coal can affect the NMR data.…”

Section: Technical Progress Task 1 129xe N M R Spectra Of Coalsmentioning

confidence: 88%

Effects of surface chemistry on the porous structure of coal. Technical progress report, September 1994--October 1995

Anderson¹,

Radović²,

Hatcher³

1995

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Section: Technical Progress Task 1 129xe N M R Spectra Of Coalsmentioning

confidence: 88%

Effects of surface chemistry on the porous structure of coal. Technical progress report, September 1994--October 1995

Anderson¹,

Radović²,

Hatcher³

1995

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“…51 After performing Xe-129 NMR experiments on spherocarb, which gave results very close to the manufacturer's specifications of microporosity, they found that the average micropore diameter of Illinois #6 coal was 5.2 A. 51 More recently, in 1991, Tsiao and Botto use this technique to determine the average micropore size of APCS coals and to investigate the effect of weathering on the average micropore size of coals. 52 This information was then used to develop a model to approximate pore sizes and pore size swelling chacteristics.…”

Section: Xe-129 Nmrmentioning

confidence: 95%

Section: Xe-129 Nmrmentioning

confidence: 99%

“…51,52 Xe-129 NMR was used in 1990 by Wernet et al to determine average micropore diameters in Illinois #6 bituminous coal. 51 After performing Xe-129 NMR experiments on spherocarb, which gave results very close to the manufacturer's specifications of microporosity, they found that the average micropore diameter of Illinois #6 coal was 5.2 A. 51 More recently, in 1991, Tsiao and Botto use this technique to determine the average micropore size of APCS coals and to investigate the effect of weathering on the average micropore size of coals.…”

Section: Xe-129 Nmrmentioning

confidence: 99%

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Molecular Accessibility in Oxidized and Dried Coals

Kispert¹

1999

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Changes in physical and chemical structure of the micropore system in eight solvent swelled Argonne Premium Coal Sample (APCS) coals upon weathering were studied using the EPR spin probe method. Spin probes, which are allowed to diffuse into the coal structure during swelling, are trapped when the swelling solvent is removed. Excess spin probes are removed from the coal surface and larger pores so that only the presence of spin probes trapped in pores which closely approximate the size of the spin probe are detected. Detailed explanations and illustrations of the experimental procedure used are given.Careful examination of the weathering process on coal as a function of rank was accomplished using the EPR spin probe method. The retention of spin probes in eight APCS coals provided valuable insight into both the loss of water and the oxidation which occur during the weathering process. The results could be explained in terms of the autoxidation process observed in other polymeric systems. It was shown that initial oxidation of coal can result in increased cross-linking in the coal structure. As the oxidation process continued, both the covalent and hydrogen bonded character of the coal were significantly altered. The retention character of some coals during oxidation was shown to change by as much as three orders of magnitude. Experiments were performed to study the effects of short term oxidation and dehydration on coal structure by exposing the coal samples to argon or oxygen for time periods up to five minutes. The results indicate that the structure of coal is extremely sensitive to environmental changes and exhibits significant changes in as little as 30 seconds. Exposure of Illinois #6 coal to argon or oxygen for 30 seconds caused a decrease in the retention of polar spin probes by as much as an order of magnitude.The studies presented here suggest that the structure of coal is dynamic in nature, and has an intimate relationship with the nature of its environment. This method has been shown to be very sensitive to structural changes brought about in coal by oxidation and dehydration, and can be used to follow changes in coal during the swelling process. Additional ideas for future studies using the EPR spin probe method are also discussed.iv

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“…Following along similar methods ,applied to zeolites, Ryoo and coworkers [127] studied several types of amorphous carbon and concluded that xenon was useful in studying such materials and might provide a simple means to spaces were observed in Illinois # 6 coals [128,129] where two peaks in the 129Xe NMR spectrum had different pressure dependences. Tsaio el al.…”

Section: Coalsmentioning

confidence: 99%

Optical pumping and xenon NMR

Raftery¹

1991

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Nuclear Magnetic Resonance (NMR) spectroscopy of xenon has become an important tool for jnvestigating a wide variety of materials, especially those with high surface area. The sensitivity of its chemical shift to environment, and its chemical inertness . and adsorption properties make xenon a particularly useful NMR probe. This work discusses the application of optical pumping to enhance the sensitivity of xenon NMR " experiments, thereby allowing them to be Used in the study of systems with lower surface area.A novel method of optically-pumping 129Xe in low magnetic field below an NMR spectrometer and subsequent transfer of the gas to high magnetic field is described.NMR studies of the highly polarized gas adsorbed onto powdered samples with low to moderate surface areas are now possible. For instance, NMR studies of optically~ pumped xenon adsorbed onto polyacrylic acid show that xenon has alarge interaction with the surface. By modeling the low temperature data in terms of a sticking probability and the gas phase xenon-xenon interaction, the diffusion coefficient for xenon at the surface of the polymer is determined. The sensitivity enhancement afforded by optical pumping also allows the NMR observation of xenon thin films frozen onto the inner surfaces of different sample cells. The geometry of the thin films results in interesting line shapes that are due to the bulk magnetic susceptibility of xenon.Experiments are also descriped that combine optical pumping with optical detection for high sensitivity in low magnetic field to observe the quadrupolar evolution of 131 Xe spins at the surface of the pumping cell~. In cells with macroscopic asymmetry, a residual quadrupolar interaction causes a splitting in the 131XeNMR frequencies in bare Pyrex glass cells and cells with added hydrogen.Conventional xenon NMR experiments conducted on coadsorbed organic molecules _ in Na-Y zeolites show that the xenon chemical shift is sensitive to the identity and concentration of these guests. Clusters of xenon trapped in Na-A zeolite have interesting statistical distributions due to the finite atomic size of the xenon. The statistics can be described in the low to moderate loading regime by binary and hypergeometric distribution functions.Finally, a comprehensive review of the xenon NMR literature, including previous optical pumping studies, is provided.; ; "

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Determination of the average micropore diameter of an Illinois No. 6 coal by xenon-129 NMR

Cited by 33 publications

References 1 publication

Effects of surface chemistry on the porous structure of coal. Technical progress report, September 1994--October 1995

Effects of surface chemistry on the porous structure of coal. Technical progress report, September 1994--October 1995

Molecular Accessibility in Oxidized and Dried Coals

Optical pumping and xenon NMR

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