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Download or read book Characterization of Porosity Via Secondary Reactions written by and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 January 1995-31 March 1995 written by and published by . This book was released on 1995 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 July 1994-30 September 1994 written by and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Characterization of Porosity Via Secondary Reactions: Quarterly Technical Progress Report, 1 October 1994-31 December 1994 written by and published by . This book was released on 1995 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
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ISBN 13 :
Total Pages : 20 pages
Book Rating : 4.:/5 (727 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 15 June 1992--30 September 1992 written by and published by . This book was released on 1992 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Specific surface area, as well as its accessibility to gaseous reactants, are of paramount importance for all heterogeneous interactions occurring at coal char surfaces. Accessibility of this surface area is governed by the pore structure morphology of the char; i.e., pore size distribution, tortuosity, intersections, shape, etc. The porosity morphology of coal chars varies over a considerable range and is determined by a large number of factors including the nature of the porosity of the precursor material prior to carbonization, the carbonization process, and extent and method of any subsequent activation or gasification. A persistent problem in this area has been the reliable, quantitative measurement and characterization of the resultant porosity, especially the micropores. For example, electron microscopy tends to be qualitative; small angle X-ray or small angle neutron scattering (SAXS/SANS) can suffer from sensitivity to interpretive models, and the inability to distinguish porosity that communicates with the surface from that which does not; and gas adsorption techniques also have several well known drawbacks. The latter, however, are perhaps the most reliable in general, but yield pore size distributions indirectly via surface area and pore volume measurements, and can also be laborious and time-consuming. Therefore, there is still a critical need for practical and fade techniques to characterize the porosity of coal chars.
Download or read book Characterization of Porosity Via Secondary Reactions: Quarterly Technical Progress Report, October 1 - December 31, 1993 written by and published by . This book was released on 1993 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
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ISBN 13 :
Total Pages : 19 pages
Book Rating : 4.:/5 (871 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 July 1995--1 October 1995 written by and published by . This book was released on 1995 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: The following was accomplished during the reporting period: The random pore model was extended to correlate the development of microporosity in resin and Wyodak coal char. Conclusions derived from this analysis include: the random pore model can be extended to microporosity development for chars which are initially (i.e., at zero burn-off) microporous, assuming a normal micropore volume distribution. The resultant mean pore radius and variance prior to oxidation were, respectively, 1.04 nm and 0.24 nm for Wyodak coal char, and 0.64 nm and 0.18 nm for resin char. Consequently, the pore size is larger, and the pore distribution is broader for Wyodak coal char than for resin char prior to activation. The rate of mean micropore radius decrease with burn-off at high conversion is slower for resin char than for Wyodak coal char. This result suggests that the percentage of micropores converted to larger pores is smaller for resin char than for Wyodak coal char; i.e., resin char remains more microporous with burn-off. The nonmicroporous surface area was estimated by difference from the total surface area as determined from nitrogen adsorption data. These values correlate reasonably well with nonmicroporous surface areas determined from the [alpha]{sub s}-plot method.
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ISBN 13 :
Total Pages : 17 pages
Book Rating : 4.:/5 (727 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 15 December 1991--15 March 1992 written by and published by . This book was released on 1992 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: The new TPD-MS/TGA system has been constructed and successfully tested. This system is constructed around a new Cahn D-200 digital recording microbalance, which was purchased for this purpose. The TPD reactor is the ''hangdown'' tube for the microbalance. The system can operate at pressures from vacuum to atmospheric. Control and data logging of this new experimental system are performed using a Macintosh II microcomputer with a GW Instruments 625 Jr. interface. All the control software has been written and tested. A new furnace with low ''thermal capacitance'' was constructed for this system which allows linear heating rates to 1100°C at rates as high as 20OK/min. This system will become a principal apparatus for obtaining some of the data required for the development of porosity characterization techniques via TPD. Software has been written for the analysis of small angle scattering (SAS) data, obtained with either X-rays (SAXS) or neutrons (SANS), which will be used in addition to gas adsorption techniques to characterize porosity for comparison with secondary reaction data.
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ISBN 13 :
Total Pages : 23 pages
Book Rating : 4.:/5 (685 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 January 1994--31 March 1994 written by and published by . This book was released on 1994 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: The following was accomplished during the reporting period: (1) CO TPD spectra were obtained as a function of heating rate from Wyodak coal char samples gasified in 0.1 MPa oxygen at 390°C to 10% burn-off. (2) The spectra were corrected for high temperature CO evolution from the sample bucket. (3) The spectra were fit to two desorption features using both Gaussian and first order desorption peak shapes. The conclusions derived from these data and their analysis include: (4) The CO TPD spectra can be adequately represented by the sum of two Gaussian or first order desorption peaks. (5) The first order peak fits indicated that the second peak decreases at the expense of the first with decreasing heating rate. This is consistent with the theory that the second peak arises from CO rechemisorption. (6) Small angle neutron scattering data were obtained on char samples using the SAD diffractometer at the IPNS at Argonne National Laboratory. Data were obtained for both ''dry'' samples and the same samples saturated with deuterated toluene for ''contrast-matching.'' (7) The data demonstrate that contrast-matching techniques can be quite useful for decoupling gasification porosity from non-accessible porosity.
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ISBN 13 :
Total Pages : 18 pages
Book Rating : 4.:/5 (683 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 April 1995--30 June 1995 written by and published by . This book was released on 1995 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the previous quarterly report (DE-FG22-91PC91305-14), we presented an analysis of small angle neutron scattering (SANS) data obtained for Pittsburgh {number_sign}8 coal char. These samples exhibited considerable scattering. However, when the voids between the particles were filled with a liquid that had the same neutron scattering density as the carbon, the amount of scattering was reduced by more than two orders of magnitude. Analysis of the scattering invariant in terms of surface area showed that the char had very little porosity. To date this has been the only contrast matching SANS study of carbon and the first recognition that interparticle scattering effects are important. In this report, we focus on SANS data obtained for a very different char--a phenolic resin char (PRC). The following was accomplished during the reporting period: contrast matching, SANS data obtained for resin char has been analyzed in detail. Conclusions derived from this analysis include: contrast matching SANS has been demonstrated to be a useful technique for monitoring the activation/gasification process. It is demonstrated how this technique can be used to address such important issues as the role of ''closed'' vs ''open'' porosity, and interparticle scattering. It has been used here to establish that the development of porosity in phenolic resin char upon gasification in air proceeds primarily by ''opening '' or originally ''closed'' porosity. This is quite different than the behavior of Pittsburgh {number_sign}8 coal char. for example, as presented in the previous quarterly report.
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ISBN 13 :
Total Pages : 17 pages
Book Rating : 4.:/5 (258 download)
Download or read book Allerunterthänigstes Pro memoria ad causam des Sachssen-Weissen-Felssischen Debit-Weesens, in specie die Erfurthische Praetension betreffend ... written by and published by . This book was released on 1738 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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ISBN 13 :
Total Pages : 28 pages
Book Rating : 4.:/5 (727 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 15 September 1991--15 December 1991 written by and published by . This book was released on 1991 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the course of recent work applying temperature programmed desorption (TPD) to the determination of energetic distributions of oxygen complexes on the surfaces of oxidized coal chars, we discovered that secondary interactions occurring within the char structure during TPD produce characteristic features in the resultant spectra that appear to be quite sensitive to char porosity. The relative and absolute extents of these secondary interactions from the basis of a potential characterization technique. The use of such a method to characterize coal char porosity is potentially attractive because the requisite spectra can be obtained in a single TPD experiment -- a very facile experimental procedure. However, the unambiguous and quantitative interpretation of such data in terms of parameters that can be used to characterize coal char porosity still requires development and an improved understanding of the controlling phenomena. These issues define the primary focus of the current proposal.
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ISBN 13 :
Total Pages : 16 pages
Book Rating : 4.:/5 (685 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 October 1993--31 December 1993 written by and published by . This book was released on 1993 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: The following was accomplished during the reporting period: TPD spectra were obtained from Wyodak coal char samples CO and CO2 prepared at varying burn-offs in 0.1 MPa oxygen at 410°C. Both the CO and CO2 spectra were fit to two Gaussian peaks. Nitrogen isotherms (77K) were obtained for all the samples in order to characterize their porosity. The conclusions were derived from these data include: (1) The TPD desorption data indicated the same general porosity development with burn-off as the nitrogen adsorption isotherms. (2) The two high temperature CO2 peaks are attributable to secondary interactions of desorbed CO with surface oxygen complexes as it percolates out through the pore structure. This reaction may be catalyzed by the mineral matter in the Wyodak char.
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ISBN 13 :
Total Pages : 17 pages
Book Rating : 4.:/5 (727 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 January 1993--31 March 1993 written by and published by . This book was released on 1993 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Temperature-programmed desorption spectra from steam-gasified chars were examined. At least two major CO-liberating features were identified for the resin char samples, one centered 1000 C and the other 1050 C. Presence of catalytic mineral matter appears to be related to the appearance of an additional low temperature feature for the Wyodak char. Although total amount of surface oxygen seems to be a gross indicator of reactivity, analysis of the desorption data assuming two different types of oxygen surface complexes, each exhibiting a single desorption activation energy, shows that the reactivity cannot be explained by the desorption rates of the complexes alone. 6 figs, 4 tabs, 9 refs.
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ISBN 13 :
Total Pages : 25 pages
Book Rating : 4.:/5 (685 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 July 1993--30 September 1993 written by and published by . This book was released on 1993 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: Specific surface area is of paramount importance for all heterogeneous interactions occurring at coal char surfaces. Accessibility of this surface area is governed by the pore structure morphology of the char, which varies over a considerable range and which is determined by a large number of factors including the nature of the porosity prior to carbonization, the carbonization process, and extent and method of any subsequent activation or gasification. A persistent problem in this area has been the reliable, quantitative measurement of the resultant porosity, especially the micropores. The current project is directed at the development of a new approach to this very old problem. During the course of recent work applying temperature programmed desorption (TPD) to the determination of energetic distributions of oxygen complexes on the surfaces of oxidized coal chars, the authors discovered that secondary interactions occurring within the char structure during TPD produce characteristic features that appear to be quite sensitive to char porosity. The relative and absolute extents of these secondary interactions form the basis of a potential characterization technique. Here the authors report on the progress that has been made in the construction, development and testing of a new TPD-MS/TGA system being developed in their laboratory. The project plan also includes the use of other techniques to characterize porosity for the purposes of comparison, quantification, and validation. It is noted that at least two other more well established methods will be used in such a manner: specifically, gas adsorption techniques and small angle scattering.
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ISBN 13 :
Total Pages : 25 pages
Book Rating : 4.:/5 (727 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 15 March 1992--15 June 1992 written by and published by . This book was released on 1992 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: All our past work on thermal desorption of oxygen surface complexes from coal chars was conducted in a temperature programmed desorption (TPD) reactor apparatus separate from the TGA system (Cahn Model 113) in which the chars were prepared. This procedure was found to work quite well for most of the types of studies that were previously conducted. However, in the current project it is essential to obtain quantitative data of a higher precision than previously in order to develop and validate the secondary interaction approach. This requirement necessitates a system wherein the coal char sample is never exposed to the atmosphere between preparation and thermal desorption. In addition, in order to improve the sensitivity of the technique, the bulk of the desorbed gases must be sampled directly into the mass spectrometer, rather than simply sampling a small fraction from the one atmosphere mixture of carrier gas and desorbed gases, as was done in the predecessor system. This necessitates thermal desorption at subatmospheric pressures. In order to meet these more stringent requirements, a new TPD-MS/TGA system was designed. A schematic of this system, which has now been constructed. This system is built around a new Cahn D-200 digital recording microbalance, which was purchased for this purpose. The TPD reactor is the ''hangdown'' tube for the microbalance. The system can operate under vacuum conditions to atmospheric pressure, and, most importantly, the coal char sample need never be handled and exposed to undesirable conditions, such as the ambient atmosphere.
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ISBN 13 :
Total Pages : 21 pages
Book Rating : 4.:/5 (682 download)
Download or read book Characterization of Porosity Via Secondary Reactions. Quarterly Technical Progress Report, 1 April 1993--30 June 1993 written by and published by . This book was released on 1993 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: TPD spectra from oxygen-gasified chars were examined as a function of burn-off: 10 - 30% burn-off. The total amount of CO desorbed increased steadily with burn-off. Two major CO-liberating features were identified for the Wyodak coal char samples - one centered ca. 700°C and the other ca. 900°C. The total amount of CO2 desorbed also increased steadily with burn-off. Two features were clearly evident in the CO2 spectra: one preceded the 700°C CO peak, and the other was sharper, and coincided with the 700°C CO peak. These sharp features are attributed to mineral matter in the Wyodak coal char. TPD spectral features of steam-gasified char were investigated. Demineralization of the Wyodak coal char demonstrated that the first, low temperature peak, prominent in normal Wyodak coal char spectra, is attributable to the mineral matter in the char. Demineralization also caused a significant decrease in reactivity. It was concluded that the oxygen surface complexes associated with the first, low temperature peak control the bulk of the steam reactivity for this coal char.
