ACERC
Abstracts - 1992 |
ACERC
Abstracts - 1992 |
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Thrust Area 1: Fuel Structure and Reaction Mechanisms |
Yun, Y.; Meuzelaar, H.L.C.;
Chakravarty, T.; and Metcalf, G.S.
Chapter 12, Advances in Coal Sprectroscopy, (H.L.C. Meuzelaar, ed.),
Plenum Publishing Corp., New York, 1992. [Previously published in Computer
Enhanced Analytical Spectroscopy, Volume II, (Meuzelaar, H.L.C., ed.), Plenum
Publishing Corp., New York, 1990]. Funded by Pittsburgh Energy Technology Center/CFFLS
and ACERC.
Coals may be regarded as highly complex, fossilized assemblages of more or less strongly decomposed plant matter, microorganisms and humic substances in addition to a range of possible mineral constituents. Specific coal seams may represent peat-forming palaeoenvironments as diverse as river delta swamps, salt-water marshes or rain forest bogs, thus explaining the intrinsic heterogeneity of coal at the macroscopic as well as microscopic levels. Macroscopically, coal heterogeneity is often readily visible in the form of discrete bands representing successions of different depositional environments or, perhaps, catastrophic events such as floods and forest fires. At the microscopic level most coals display an even broader scale of diversity and heterogeneity in the form of microscopically distinct coal components generally referred to as "macerals."
Meuzelaar, H.L.C.; Schrenk,
W.G.; Grove, E.L.; Frei, R.W.; Lawrence, J.F.; Isenhour, T.L.; Small, H.; Freiser,
H.; Yergey, A.L.; Edmonds, C.G.; Lewis, I.A.S.; Vestal, M.L.; Wehry, E.L.; Carlson,
T.A.; Janata, J. and Griffiths, P.R.
(H.L.C. Meuzelaar, ed.) Plenum Publishing Corp., New York, 1992. Funded by Pittsburgh
Energy Technology Center/Consortium for Fossil Fuel Liquefaction and ACERC.
In order to promote and increased level of interaction and collaboration between coal spectroscopists, as well as to create an updated record of the current state of the art in this very active field, a three-day Symposium on Advances in Coal Spectroscopy was organized from June 14-16, 1989 at the Snowbird Mountain Resort in Utah. This book contains the keynote lectures presented by a group of preeminent coal spectroscopists involved in a broad range of different techniques and applications thought to represent current trends and developments in the field. Of necessity, the coverage of the field is far from comprehensive and in many ways the topics selected do reflect the personal preference and biases of the editor.
The fifteen chapters of this book focus on novel characterization methods (with special emphasis on sulfur forms), in situ microspectroscopic procedures, on-line process analysis methods, and computerized data analysis techniques.
Orendt, A.M.; Solum, M.S.;
Sethi, N.K.; Pugmire, R.J. and Grant, D.M.
Chapter 10, Advances in Coal Spectroscopy, (H.L.C. Meuzelaar, ed.), Plenum
Publishing Corp., New York, 1992. Funded by Pittsburgh Energy Technology Center/Consortium
for Fossil Fuel Liquefaction, US Department of Energy and ACERC.
Techniques in C-13 nuclear magnetic resonance spectroscopy applied in the study of coal and coal chars are discussed along with details of the analysis of the spectral results. The results are compared for various methods of analysis: cross polarization with magic angle spinning (CP/MAS), dipolar dephasing (DD), MAS with block decays (BD), and chemical shielding anisotropy (CSA) measurements. Results of the CP/MAS and DD experiments on the Argonne premium coals as well as other coals and coal chars are reported in terms of twelve structural parameters, including aromaticity. Methods used to determine average cluster size and molecular weight are discussed. Models of coal structure and devolatilization processes are presented along with an analysis of the information obtained from the C-13 NMR experiments.
Simmleit, N.; Yun, Y.; Meuzelaar,
H.L.C. and Schulten, H.R.
Chapter 13, Advances in Coal Spectroscopy, (H.L.C. Meuzelaar, ed.), Plenum
Publishing Corp., New York, 1992. Funded by Pittsburgh Energy Technology Center/Consortium
for Fossil Fuel Liquefaction, US Department of Energy and ACERC.
Analytical pyrolysis techniques are widely used for the thermochemical analysis of coals and coal-derived products. During heating, complex mixtures of chemical substances are released from coal by distillation, desorption and thermal degradation processes. The amount and chemical nature of the volatilized coal products are dependent mainly on the composition and structure of the coal and on heating conditions. Therefore, the results of chemical analyses of the volatilized coal products should provide information on the original structure of coal. For detailed on-line analysis of volatilized coal products usually chromatographic and/or spectroscopic methods have been used. For positive identification of compounds gas chromatography/mass spectrometry (GC/MS) is a common approach, e.g. in direct combination with pyrolysis techniques. However, due to the relatively long analysis times, in particular for high molecular weight products, GC/MS is not suited for a universal on-line monitoring of evolving coal products during heating. For rapid fingerprinting of volatilized coal products on a molecular basis direct MS analysis is often the preferred method. Small amounts of coal or coal-derived products are heated in front of th ionization region under high vacuum conditions. Depending on the type of mass spectrometer used and the experimental conditions, on-line monitoring of evolving coal products is possible for a wide range of heating rate. Heating rates as low as 10-2 C/s may be used in the combined thermogravimetry (TG)/MS whereas heating rates in the 104 - 106 C/s range can be obtained by CO2 laser heating.
Butler, B.W.
An Experimental Evaluation of Radiant Energy Transport in Particle-Laden Flames,
Ph.D./BYU, August 1992. Advisor: Webb
Monson, C.R.
Char Oxidation at Elevated Pressure, Ph.D./BYU, December 1992. Advisor:
Germane
Solomon, P.R.; Fletcher,
T.H. and Pugmire, R.J.
Fuel, 1992 (in press). Funded by US Department of Energy and ACERC.
The heterogeneous nature of coal and the complexity of the pyrolysis process has made it very difficult to perform unambiguous experiments to determine the rates and mechanism in coal pyrolysis. The last several years have, however, provided a number of new experimental and theoretical approaches that shed new light on the subject. This paper will consider the recent progress on the topics of: kinetics, the formation of volatile products, network models, crosslinking, rank effects, and the "two-component model of coal structure." In kinetics, recent experiments that measure coal particle temperatures at high heating rates provide reasonable agreement on kinetic rate constants. The rates also agree with those derived from low heating rate experiments. In tar formation and transport, a consensus is being reached on the central role of the tar molecule's volatility in explaining the variation with operating parameters (pressure, heating rate, particle size, etc.) in the tar's amount and molecular weight distribution. Progress in the quantitative prediction of tar and char is being made by recently developed models for the fragmentation of the macromolecular network. These models, which provide quantitative description of the relationship between the chemical structure of the coal and the physical and chemical properties of the resultant pyrolysis products (gas, tar, soot, and char), are an exciting advancement in the understanding of the pyrolysis process. Such models are linking the occurrence of the coal's plastic phase with the "liquid" fragments formed during pyrolysis. On the subject of retrogressive crosslinking reactions, both solvent swelling and NMR measurements confirm important rank dependent differences in reaction rates. These appear related to the oxygen functionalities. Reasonable agreement is also seen for rank variations of kinetics rates derived from low heating rate experiments. Experiments suggest that the recently revived "two-component hypothesis" of coal structure has application to low rank coals that are a mix of polymethylenes and a more aromatic network. Bituminous coals, however, appear far more homogeneous. These coals appear to behave in a manner that is described by the network decomposition models. The presentation will provide a brief report on these topics.
Fletcher, T.H.; Solum, M.S.;
Grant, D.M. and Pugmire, R.J.
Energy & Fuels, 6(5):643-650, 1992. [Also included in the ACS Division
of Fuel Chemistry Preprints, 37(2):677-684, 1992 (203rd ACS National
Meeting, San Francisco, CA, April 1992)]. Funded by Sandia National Laboratories,
Brigham Young University and ACERC.
Coal devolatilization experiments are generally conducted separately from char oxidation experiments, and the relationship between the chars generated in the two types of research is often ignored. However, char is one of the most important products of coal devolatilization and must be characterized as a function of temperature and heating rate in a manner similar to that for gaseous behavior. In this work, the chemical structures of chars from five coals of different rank are examined, and implications on char reactivity are discussed. Chars were obtained as a function of residence time in a devolatilization experiment (1250 K, 2 x 104 J/s in nitrogen) and just subsequent to devolatilization in a laminar flame-fired experiment (1500 K, 5 x 104 K/s). Quantitative measurements of chemical structure were performed on the coals and chars using C-13 nuclear magnetic resonance (NMR). Results show that the chemical structures of fully devolatilized chars are very similar, even though a wide diversity is seen in the parent coal structures. For example, the average cluster molecular weights of the chars span a range of only 50 amu, and the side-chain molecular weights of the chars span a range of only 6 amu. The similarity in chemical structure of fully devolatilized coal chars suggests that differences in measured heterogeneous char reactivities are caused by differences in the physical structure of the char.
Rasband, P.B. and Hecker,
W.C.
Journal of Catalysis, 1992 (in press). Funded by Brigham Young University.
Qualitative FTIR has been and continues to be one of the most utilized tools in the characterization of supported metal catalysts. Quantitative FTIR has the potential to allow catalysis researchers to determine the surface concentrations of active intermediates. However, its successful application depends upon an understanding of the factors affecting integrated absorption intensities (coefficients relating IR absorbance to surface concentration). This work addresses the effect of metal particle size and temperature on the absorption intensities for CO chemisorbed on Rh/SiO2. Absorption intensities for both linear and bridged CO surface species (a1 and Ab) were determined by combining peak area data fro, IR spectra with uptake measurements obtained in gravimetric experiments. This resulted in an A1 value of 13 (± 2) and an Ab value of 42 (± 6) cm/µmol. No statistically significant particle size effect has been observed for average spherical particle diameters ranging from 13 to 58 angstroms (100 to 22% dispersion). Also, integrated absorption intensities for linear and bridged CO were shown to vary little over the temperature range of 323 to 473 K. The discovery that absorption intensities determined for one temperature and metal dispersion may be used for other temperatures and dispersions is a welcome result that may broaden the application of quantitative FTIR.
Rh dispersions were determined for Rh/SiO2 sample of 5 different weight loadings using the absorption intensities determined in this study. The variation of Rh dispersion with Rh loading was practically identical to that observed in hydrogen chemisorption experiments conducted on another series of Rh/SiO2 catalysts. Also, it was observed that the ratio of linear to bridges CO surface concentrations increased from 2 to 5 as Rh dispersion increased from 22 to 100%. These observations demonstrate the usefulness of a more fully developed quantitative FTIR technique.
Wang, H.P.; Lo, R.; Sommerfeld,
D.A.; Huai, H.; Pugmire, R.J.; Shabtai, J.S. and Eyring, E.M.
Fuel, 71(7):723-729, 1992. Funded by US Department of Energy.
Demineralized Hiawatha (Utah) coal was divided into narrow density fractions of resinite and vitrinite macerals using a density gradient centrifugation technique. The distribution of an iron-based catalyst in the coal maceral matrix was studied using an electron probe microanalyser. The data indicate that the iron catalyst is evenly dispersed inside the vitrinite. This uniform dispersion is preserved upon mild (275ºC) hydrotreatment and attendant partial depolymerization of the vitrinite maceral. However, the iron catalyst does not completely penetrate into the resinite maceral matrix due to a lack of microporosity. The small amount of dispersed iron catalyst in the resinite causes some depolymerization of maceral components, e.g. dimers, trimers, or higher polymers, into monomers. Due to the insufficient dispersion of the iron catalyst in the resinite a competing thermal breakdown of the maceral occurs. This apparently involved a partial dehydrogenation reaction that may be favored during the hydrotreatment of resinite.
Hu, J.Z.; Pugmire, R.J.;
Orendt, A.M.; Grant, D.M. and Ye, C.
Solid State Nuclear Magnetic Resonance, 1:185-195, 1992. [Also included
in ACS Division of Fuel Chemistry Preprints, 37(2):646-659, 1992 (203rd
ACS National Meeting, San Francisco, CA, April 1992)]. Funded by US Department
of Energy and Pittsburgh Energy Technology Center/Consortium for Fossil Fuel
Liquefaction.
Taking advantage of the long C-13 T1 values generally encountered in solids, selective saturation and inversion of more than one resonance in C-13 CP/MAS experiments can be achieved by sequentially applying several DANTE pulse sequences centered at different transmitter frequency offsets. A new selective saturation pulse sequence is introduced composed of a series of 90% DANTE sequences separated by interrupted decoupling periods during which the selected resonance is destroyed. Applications of his method, including the simplification of the measurement of the principal values of the C-13 chemical shift tensor under slow MAD conditions are described. The determination of the aromaticity of coal using a relatively slow MAS spinning rate is also described.
Soderquist, A.; Hughes,
C.D.; Horton, W.J.; Facelli, J.C. and Grant, D.M.
Journal of American Chemistry Society, 114(8):2826-2832, 1992. Funded
by National Institutes of Health and US Department of Energy.
Measurements of the principal values of the C-13 chemical shift tensor are presented for the three carbons in triphenylene and for three different alpha-carbons in phenanthrene. The measurements in triphenylene were made in natural abundance samples at room temperature, while the phenanthrene tensors were obtained from selectively labeled compounds (99% C-13) at low temperatures (~25 K). The principal values of the shift tensors were oriented in the molecular fram using ab initio LORG calculations. The steric compression at C4 in phenanthrene and in corresponding positions in triphenylene is manifested in a sizable upfield shift in the alpha33 component relative to the corresponding alpha33 values at C1 and C9 in phenanthrene. The upfield shift in alpha33 is mainly responsible for the well-known upfield shift of the isotropic chemical shifts of such sterically perturbed carbons. In phenanthrene C9 exhibits a unique a22 value reflecting the greater localization of pi-electrons in the C9-C10 bond. This localization of the pi-electrons at the C9-C10 bond in the central ring of phenanthrene also corresponds with the most likely ordering of electrons described by the various Kekulé structures in phenanthrene. The analysis of the C-13 chemical shieldings of the bridgehead carbons in triphenylene provides significant experimental information on bonding between rings in polycyclic aromatic compounds. The results confirm that the electronic structure of triphenylene is best described by three fairly isolated benzene rings linked by C-C bonds of essentially single bond character. Similarly in phenanthrene, the bonding structure that correlates the shielding information may be characterized by the dominance of two benzene rings comprising the biphenyl moiety. A strong C9-C10 pi-bond with only limited pi-electron character n the C8a-C9 and C10-C10a bonds is indicated by both the experimental and theoretical results.
Carlson, R.E.; Critchfield,
S.; Vorkink, W.P.; Dong, J.-Z.; Pugmire, R.J.; Bartle, K.D.; Lee, M.L.; Zhang,
Y. and Shabtai, J.S.
Fuel, 71(1):1-29, 1992. Funded by US Department of Energy, Gas Research
Institute and ACERC.
A selective, low temperature depolymerization procedure has been applied to four Argonne coals of different rank to produce products that are representative of the original coal macromolecular structure, and that are amenable to chromatographic analysis. The products of this depolymerization procedure retained most of the original aromatic and functional group structures of the original coals. A comparison of liquid C-13 NMR spectra of the products and solid-state C-13 NMR spectra of the original coals showed only minor changes in the aromaticities of two of the coals, and some loss of the carbonyl carbons in all of the coals.
Tetrahydrofuran pre-extracts of the four coals and their depolymerized products were separated into chemical classes by adsorption chromatography. Two of these fractions, which contained aliphatic hydrocarbons and polycyclic aromatic hydrocarbons were analyzed using gas chromatography/mass spectrometry. Structural identifications were based on a combination of chromatographic retention and mass spectral fragmentation data. For the lower rank coals, the compositions of the pre-extracts were quite different from the corresponding depolymerized products, and they contained an abundance of molecular biological markers. The compositions of the pre-extracts became more similar to the depolymerized products as rank increased.
McDonald, K.M.; Hyde, W.D.
and Hecker, W.C.
Fuel, 71(3):319-323, 1992. Funded by ACERC.
Chars derived from Beulah-Zap (lignite A) and Dietz (sub-bituminous B) coals were prepared by three different methods utilizing three different reactor systems. These included a high heating rate method achieved in a methane flat flame burner, a moderate heating rate method achieved in a drop tube reactor, and a slow heating rate method achieved in a muffle furnace. The flat flame char was produced in a flame environment with excess oxygen, while the drop tube and muffle furnace chars were produced in inert environments. Low temperature oxidation rates and kinetic parameters were determined using isothermal thermogravimetric analysis (TGA) at temperatures between 550 and 950 K. Reactivities at different oxidation burnout levels (10%-75%) were compared on both an initial mass and an available mass basis. Using the available mass basis, rates in the intrinsic regime were found to be nearly identical for the different burnout levels. It was also found that the lower burnout levels are more highly influenced by diffusion effects. This was manifest by a decrease in the slope of the Arrhenius plot that began at a temperature of about 750 K for the char at 10% burnout compared to a temperature of nearly 900 K for the char at 75% burnout. In comparing the chars produced by the three different methods, reactivities in the reaction control regime showed that, for both coals, the drop tube char was more reactive than either the flat flame or muffle furnace char. Further tests indicated that the drop tube chars had a hydrogen to carbon ratio that was 2.5 to 5 times greater than the char from either of the other reactors and the devolatilization conversion was significantly less. The activation energies for all three Beulah-Zap chars and for the Dietz muffle furnace and flat flame chars were found to be 28.1±0.6 kcal/mol. A comparison of the reactivities for the flat flame burner chars of the lignite and the sub-bituminous showed that the lignite chars were more reactive by a factor of two. This was consistent over all burnout levels. Further work with the Dietz flat flame char showed the dependency on oxygen concentration, yielding an apparent reaction order of 0.67±0.03. This is in excellent agreement with data found in the literature.
Foster, M.P.; Mayne, C.L.;
Dunkel, R.; Pugmire, R.J.; Grant, D.M.; Kornprobst, J.-M.; Verbist, J.-F.; Biard,
J.-F. and Ireland, C.M.
Journal of the American Chemistry Society, 114(3):1110-1111, 1992. Funded
by National Institutes of Health and US Department of Energy.
The two-dimensional structure of bistramide A (a.k.a. bistratene A) has been revised. The bis-amide polyether was isolated from a Lissoclinum sp. ascidian collected in the Fiji islands. The structure was established by a combination of modern NMR methods including 2D INADEQUATE, PS-DQF-COSY, HMQC and HMBC experiments. Critical to establishing the carbon-carbon backbone was CCBond, a new program for automated analysis of 2D INADEQUATE spectra. Bistramide A demonstrated in vitro cytotoxicity towards human colon tumor HCT-116 and murine leukemia L1210 cell lines with an IC50 of 0.1 µg/mL.
Orendt, A.M.; Sethi, N.K.;
Facelli, J.C.; Horton, W.J.; Pugmire, R.J. and Grant, D.M.
Journal of the American Chemistry Society, 114(8):2832-2836, 1992. Funded
by US Department of Energy and ACERC.
The principal values of the C-13 chemical shift tensor were measured for the aromatic carbons of 1,4,5,8-tetramethylnaphthalene, 1,2,3,6,7,8-hexadropyrene, and pyracene using the variable angle spinning technique. Ab initio calculations of the complete shielding tensors are also reported and provided the orientation of the principal values in the molecular frame. Good agreement between theory and experiment is obtained. The chemical shift principal values and orientations of these substituted naphthalenes correspond to those found in naphthalene; the observed differences can be rationalized in terms of the strain introduced by the alkyl substituent. In the naphthalenic derivatives studied, the bridgehead carbons exhibit relatively extensive pi-electron delocalization not found in some bridgeheads in more highly condensed aromatic systems.
Pugmire, R.J.; Jiang, Y.J.;
Solum, M.S. and Grant, D.M.
Bulletin of Magnetic Resonance, 14:144, 1992. (Presented at ISMAR
92, Vancouver, B.C., July 1992.) Funded by ACERC.
An efficient large sample volume system has been developed to carry out MAS solid-state NMR experiments. The system components are primarily zirconia and macor and no background C-13 is observed. The stator design employs separate air bearing and drive systems and is run using dry air at a bearing pressure of about 32 psi. the rotor can be spun in a stable manner from less than one hundred Hz (with a driving pressure of 5 psi) to 4.3 KHz (24 psi driving pressure). This low gas pressure feature makes the system easy to operate. The volume of the rotor is 1.8 cm³ and it can hold 1.1 g of HMB. The S/N ratio obtained is a factor of 4.6 better than the rotor previously designed and used in our laboratory (volume 0.6 cm³ : 0.28g HMB). This increased sample size allows us to obtain the same S/N ratio in a MAS spectrum with a factor of 21 saving in spectrometer time. The time saving achieved with this rotor system is extremely useful in obtaining data on biological samples and polymers, and is especially useful when experiments on fossil fuels require the use of the Bloch delay technique. Examples of relevant applications will be discussed.
Dunkel, R.; Mayne, C.L.;
Pugmire, R.J. and Grant, D.M.
Analytical Chemistry, 64 (24):3133-3149, 1992. Funded by US Department
of Energy, Pittsburgh Energy Technology Center and ACERC.
The carbon skeleton of a molecule can be determined by using the powerful 2D INADEQUATE experiment, but the method suffers from very poor sensitivity at natural carbon-13 abundance. A computer program, described previously, has been significantly improved in its ability to recognize AB spectral patterns corresponding to carbon-carbon bonds which makes it possible to evaluate reliably spectra with rms S/N ratio as low as 2.5, i.e., nearly 1 order of magnitude below the level required for routine manual interpretation. Application of the INADEQUATE experiment to samples containing as little as 20 µmol of a compound of interest is now possible. The method is described in detail and critically evaluated by means of examples and simulations.
Dunkel, R.; Mayne, C.L.;
Foster, M.P.; Ireland, C.M.; Li, D.; Owen, N.L.; Pugmire, R.J. and Grant, D.M.
Analytical Chemistry, 64:3150-3160, 1992. Funded by US Department of
Energy, Pittsburgh Energy Technology Center and ACERC.
This paper illustrates the use of the program CCBond to determine the carbon skeletons of bioorganic molecules in low concentration samples. Discussed is the structure elucidation of bistramide A, a compound extracted from a Fijian Lissocllnum sp. and cholesterol in 71- and 20-µmol samples, respectively. The detection limit of the automated bond extraction is shown to be improved compared to the manual interpretation of 2D INADEQUATE spectra.
Huai, H. and Meuzelaar,
H.L.C.
ACS Division of Fuel Chemistry Preprints, 37(1):424-431, 1992 (203rd
ACS National Meeting, San Francisco, CA, April 1992). Funded by Pittsburgh
Energy Technology Center/Consortium for Fossil Fuel Liquefaction and ACERC.
A novel, low temperature (<300 C) coal liquefaction method described by Shabtai et al., consisting of a mild hydrotreatment (HT) step followed by base-catalyzed depolymerization (BCD) is thought to proceed by selective scission of C-C and C-O type bonds in the bridges connecting the aromatic and hydroaromatic clusters making up the bulk of the coal matrix, while minimizing secondary condensation reactions. Consequently, the resulting liquid products are expected to consist primarily of "monomeric" building blocks of the type and size inferred from solid state NMR measurements, i.e., corresponding to (hydro)aromatic structures with 10-15 aromatic carbons, 2-3 aliphatic carbons and 1-2 substituted oxygens (in addition to more sporadic sulfur, nitrogen or metal substituents) depending on coal rank, maceral composition, depositional environment and weathering status. In agreement with these expectations, the cyclohexane soluble "oil" fractions of the HT-BCD product, comprising up to 70% of the daf coal, were found to be completely vacuum distillable and to contain significant quantities of volatile, low MW components when analyzed by combined gas chromatography/mass spectrometry (GC/MS).
In order to further verify the mechanistic assumptions underlying the HT-BCD method as well as to obtain valuable information regarding type and size of the monomeric building blocks in coals, we decided to determine the precise molecular weight distribution (MWD) of HT-BCD oil fractions. The term MWD will be used interchangeably here with MMD (molecular or molar mass distribution). In view of the relatively low molecular weight and high polarity of the HT-BCD oil fractions, the use of gel permeation chromatography (GPC), also referred to as size exclusion chromatography, techniques was rejected in favor of mass spectrometry (MS) using "soft ionization" methods, such as field ionization (FI) and chemical ionization (CI), which tend to produce little or no fragmentation of molecular ions. Direct probe FIMS measurements were performed by Dr. H.R. Schulten (Fresenius Institute, Wiesbaden, GFR) whereas CIMS analyses were carried out in our laboratory using on-line preseparation by short column capillary gas chromatography (GC) and sample injection by means of Curie point flash evaporation. Well-known shortcomings of MS techniques include: possible loss of volatile components during sample introduction (in particular during direct probe MS); incomplete transport of low volatile components into the ion source (especially when using GC/MA); compound dependent response differences; and inability to analyze nonvolatile residues. Therefore, vacuum thermogravimetry (VTG) was selected as a tool for quantitative calibration, similar to its well-established use for calibrating simulated distillation (SIMDIS) methods. The results of these DP-FIS, GC/CIMS and VTG experiments with a mixture of coal liquid like model compounds as well as with HT-BCD oil fractions from three ANL-PCSP (Argonne National Laboratory - Premium Coal Sample Program) coals, viz. Beulah Zap lignite, Illinois #6 hvCb and Blind Canyon hvBb coals, will be reported here.
Pugmire, R.J.; Solum, M.S.;
Fletcher, T.H. and Grant, D.M.
Fifth Australian Coal Science Conference, Melbourne, Australia, November
1992. Funded by ACERC.
In contrast to previous efforts where coal-general devolatilization model input parameters describing chemical structure are adjusted to force agreement between predicted and measured tar and total volatiles yields, coal-dependent chemical structure coefficients for the Chemical Percolation Devolatilization (CPD) model developed by the authors and others are taken directly from C-13 NMR analyses of parent coals. This procedure, outlined in the paper eliminates most adjustable parameters from the model, and predictions of tar and total volatiles yields become true tests of the model and the NMR data, rather than mere results of curve fitting. Resulting model predictions of tar and total volatiles yields as a function of coal type, temperature, heating rate, and pressure comparable with available experimental data, showing the value of both the model and the NMR chemical structure data.
Pugmire, R.J.; Solum, M.S.;
Grant, D.M. and Fletcher, T.H.
Second International Conference on Coal Structure, Krakow, Poland, September
1992. Funded by ACERC.
Recent coal devolatilization models have attempted to incorporate coal structural information to predict product yields and composition. The chemical structure of the parent coal directly affects devolatilization behavior. The parent coal structure also has implications for pyrolysis char structure and reactivity. C-13 NMR data have been used to obtain coal-dependent chemical structural data that is used as input parameters to the chemical percolation devolatilization (CPD) model. The CPD model describes the devolatilization behavior of rapidly heated coal based on the chemical structure of the parent coal. Data will be presented on 20 different coals and the value of NMR data in predicting gas and tar yields will be discussed. The use of C-13 NMR data will also be used to describe the relationship between chemical structure features of the parent coals and the resultant pyrolysis chars.
Maswadeh, W.; Fu, Y.; Dubow,
J. and Meuzelaar, H.L.C.
ACS Division of Fuel Chemistry Preprints, 37(1):699-706, 1992 (203rd
ACS National Meeting, San Francisco, CA, April 1992). Funded by ACERC.
Recently, Maswadeh et al. reported on the design, construction and testing of a single particle levitation/laser devolatilization apparatus featuring an on-line gas chromatograph/mass spectrometer (GC/MS) system, enabling coal devolatilization experiments of heating rates in the 10-5-106 K/s range. Analysis of bituminous coal particles revealed a high degree of qualitative correspondence with pyrolysis patterns obtained at much slower (10-2-100 K/s range) TG/MS heating rates, thus providing mechanistic justification for extrapolating kinetic parameters obtained by slow pyrolysis techniques (e.g., TG/MS and TG/IR) to the high heating rates characteristic of full scale, suspension fired coal combustors.
A second observation made with the aid of laser pyrolysis GC/MS was that the distribution of devolatilization products observed at very high heating rates was not measurably influenced by the presence or absence of air. A subsequent redesign of the system permitted the use of electron microscopy (EM) grids to support individual coal particles, thereby simplifying the experimental set up, improving collection efficiency of volatile products and facilitating optical alignment of the particles (microscopy, optical micropyrometry) as well as retrieval of residual char particles.
Arnold, N.S.; Hars, G.;
Cole, P.A. and Meuzelaar, H.L.C.
US Army Chemical Research Development and Engineering Center Scientific Conference
on Chemical Defense Research, Aberdeen Proving Ground, MD, November 1992.
Funded by Army Research Office.
A novel technique for laser mass spectrometry of individual particles, e.g. microorganisms, is being developed. Present paper gives a detailed discussion on the theoretical and experimental aspects of trapping a submicron size charged particles pressures from atmospheric down to <10-7 torr. The ability to trap particles under UHV conditions has provided a new opportunity to study "ion trajectories" as they perform the solution of Mathieu equation.
Individual microparticles, mainly microorganisms, have been aerosolized and charged by a quasi-electrospray technique. A Paul type three-dimensional quadruple "trap" was constructed to combine the properties of an EDB (Electro-Dynamic Balance), capable of capturing the stabilizing micro-sized particles, with those of an ITMS (Ion Trap Mass Spectrometer), capable of trapping and mass selectivity detecting ionic species up to several thousand amu. A TEA CO2 laser (300 mJ per 200 µsec pulse) with focusing optics designed to produce a 50-80 µm beam waist through the center of the trap is used. A typical analysis cycle starts with the trap in EDB mode, thereby enabling capture and stabilization of one or more particles, followed by evacuation of the trap to high vacuum (<10-3 torr).
Hughes, C.D.; Sherwood,
M.H.; Alderman, D.W. and Grant, D.M.
Fifth Coal Chemistry Conference and Workshop, Rockford, IL, June 1992.
Funded by US Department of Energy.
Sample reorientation during the mixing time of a two-dimensional NMR exchange experiment allows the measurements of chemical shift tensors in powdered samples whose one-dimensional powder patterns are too complex to reliably analyze. This technique has the advantages that the chemical shift anisotropy has an unscaled representation, the artifacts caused by cross polarization, spin relaxation and partial sample orientation can be accounted for, the experiment is relatively easy to perform, and no spinning sidebands interfere. The method is useful for sorting out the principal values of overlapping chemical shift tensors.
Hecker, W.C.; Wardinsky,
M.D.; Clemmer, P.G. and Rasband, P.B.
Proceedings of the Twelfth Canadian Symposium on Catalysis, 211-218,
Alberta, Canada, May 1992. Funded by Brigham Young Unversity.
The kinetics of the reduction of NO by CO over Rh/molybdena/silica, Rh/ceria/silica, Rh/niobia/silica, and Rh/ceria/alumina catalysts have been studied. Catalysts have been characterized using H2 chemisorption and quantitative FTIR techniques for dispersion determination, and using in-situ and post reaction FTIR spectroscopy for site distribution study. The chief effect of molybdena, ceria, and niobia addition under the conditions of this study appears to be in the alteration of effective Rh particle size (dispersion) although Mo addition does seem to more directly affect catalyst activity. A plot of turnover does seem to more directly affect catalyst activity. A plot of turnover frequency versus Rh particle ize shows that all of the catalysts with the exception of the Rh/molybdena/silica exhibit a common structure sensitivity. This sensitivity has been explained qualitatively through mechanistic arguments.
Hecker, W.C.; McDonald,
K.M.; Reade, W.; Jackson, C.D. and Cope R.F.
Twenty-Fourth Symposium (International) on Combustion, Sydney, Australia,
July 1992. (Previously presented at the 1991 Annual Meeting of the American
Institute of Chemical Engineers, Los Angeles, CA, November 1991). Funded
by ACERC.
The development and validation of accurate coal combustion modeling requires separate characterization of the coal devolatilization and char oxidation processes. The characteristic time for heterogeneous oxidation of a char particle in a commercial combustor is 1-2 orders of magnitude greater than the time required for devolatilization and homogeneous oxidation of the volatiles. Thus the rate of combustion and hence the efficiency of the coal combustion process will be governed by the rate of oxidation of the nonvolatile coal char.
The effects of both extent of burnout and type of burnout on char oxidation rates and rate parameters have been investigated for chars prepared from Dietz (subbituminous B) coal. Intrinsic rates and rate parameters (reaction order, activation energy, and pre-exponential factor) were determined using isothermal thermogravimetric analysis (TGA). N2BET and CO2DP surface areas were measured, as was hydrogen to carbon ratio. Three types of burnout were studied and compared. Devolatilization mass loss (DML) was studied by devolatilizing the Dietz coal to various extents in a flat-flame methane burner (FFB) and then comparing the oxidation rates and other properties of the resulting chars. High-temperature oxidation burnout was studied by taking a given FFB Dietz char and oxidizing it to various conversion levels in a drop tube reactor at high temperatures characteristic of industrial combustors. The oxidation rates and kinetics of these partially burned out char samples were then determined using TGA. Low-temperature oxidation burnout was studied by oxidizing the given FFB Dietz char to a continuum of burnout levels in the TGA at low temperature (550 to 750 K) and obtaining the instantaneous oxidation rates, which are inherent in the TGA experiment.
The rate of oxidation was found to decrease with increasing devolatilization residence time, even after devolatilization mass loss has become constant. Increasing N2 and CO2 surface areas with devolatilization residence time are inverse to the decreasing rates, and a constant difference between N2 and CO2 surface areas indicates dramatic changes in the mesopore surface area during devolatilization, but not in the micropore surface area. Intrinsic rates of chars oxidized at high temperatures were found to decrease with burnout level, while those of chars oxidized at low temperatures were essentially constant with burnout level.
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