ACERC
Abstracts - 1997 |
ACERC
Abstracts - 1997 |
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Thrust Area 1: Fuel Structure and Reaction Mechanisms |
Black, D.L.
Exp. Invest. of Particle Dispersion with Spherical and Nonspherical Particles,
Ph.D./BYU, December 1997. Advisor: McQuay
Hu, J.Z.; Zhou, J.; Yang,
B.; Li, L.; Qiu, J.; Ye, C.; Solum, M.S.; Wind, R.A.; Pugmire, R.J. and Grant,
D.M.
SOLID STATE: Nuclear Magnetic Resonance, 8:129-37(1997). Funded by US
Department of Energy/Basic Energy Services and ACERC.
A N-15 dynamic nuclear polarization (DNP) experiment is reported in which a N-15 DNP enhancement factor of approximately 2.6 x 10² is obtained on free radical doped samples of 99% N-15 labeled benazmide. The free radicals BDPA (1:1 complex of alpha, gamma-bisdiphenylene-beta-phenylallyl with benzene) and DDPH (2,2 -Di (4 - tert - octylphenyl) -1-picrylhydrazyl) are used as dopants and the spin relaxation effects of adding these dopants are studied by means of changes in proton and nitrogen T1 values of the samples. The combination is solids of a very low natural abundance, 0.37%, a small gyromagnetic ration, and a log spin - lattice relaxation time for N-15 nuclei create severe sensitivity problems that, in large part, are ameliorated by the signal enhancement observed in the N-15 DNP experiment on samples containing free electrons.
Strohmeir, M.; Orendt, A.M.;
Facelli, J.C.; Solum, M.S.; Pugmire, R.J.; Pery, R.W. and Grant, D.M.
Journal of the American Chemical Society, 119:7114-120(1997). Funded
by National Institutes of Health, US Department of Energy.
The principal values both the C-13 and N-15 chemical shift tensors are reported in the Zn, Ni, and Mg 5, 10, 15, 20- tetraphenylporphyrin (TTP) complexes. The principal values of the 15N chemical shift tensors were obtained from static powder patterns of N-15 enriched samples. Due to overlap between the powder patterns of the different carbons, the C-13 values were obtained using the recently developed magic angle turning (MAT) 2D experiment on unenriched materials. The measured principals values are presented along with theoretical calculations of the chemical shift tensors and a discussion of the effects that the metal bonding has on the chemical shift tensors in these compounds. Both the isotropic chemical shift and the principal values of the N-15 chemical shift tensor are nearly identical for the Mg and Zn complexes. The N-15 isotropic chemical shift for the NiTPP, however, changes by nearly 80 ppm relative to the Mg and Zn values, with large changes observed in each of the tree principal values. Calculations show that the differences between the N-15 chemical shifts are almost entirely determined by the metal-nitrogen separation. In addition, both the experimental data and the calculations show only very minor differences in the 13C chemical shift tensor components as the metal is changed.
Genetti, D. and Fletcher,
T.H.
ACS Division of Fuel Chemistry Pre Prints, 42(1) 194-98, April 1997.
Funded by US Department of Energy/University Coal Research and ACERC.
Devolatilization models based on quantitative measurements of chemical structure, such as available through C-13 NMR analysis, have been successful in predicting tar volatiles yields as a function of heating rate, temperature, pressure, and coal type. An example of such a devolatilization model is the CPD model, developed in ACERC. However, due to limited resources, C-13 NMR structural parameters have only been obtained for about 35 coals at the present time. Industrial interest in coal devolatilization has led to several attempts to correlate structural parameters affecting devolatilization as a function of the ultimate analysis of coals. A triangular (i.e., linear) interpolation technique is used to estimate the input parameters for one current devolatilization model, while another popular model uses a procedure that estimates the coal structural parameters based on simple linear correlations of ultimate analysis.
An extensive statistical analysis to determine the validity of linear correlations of C-13 NMR structural parameters based on ultimate analysis was performed. A database including elemental composition, the ASTM volatile matter content, and C-13 NMR structural parameters for 30 coals of widely varying rank and composition was used in the analysis. The database was closely examined using the SPSS® statistical computer package. Using SPSS®, a correlation matrix was calculated between all of the chemical structural parameters obtained from the NMR analysis. From the correlation matrix, the strength of relationships between the individual elements and the derived parameters were easily determined. The parameters were also examined for relationships among themselves. Multi-variate linear regression was then performed to derive equations that predict each of the parameters as a function of the elemental composition and volatile matter content. The r² value was the determined for each correlation. The r² value is the coefficient of determination which determines the relative strength of correlation (r²=1 is a perfect correlation). In this analysis the r² values ranged from 0.17 for sigma+1 to 0.59 for Md (r²=0.49 Po and r²=0.38 for MWcl). The low r² values indicate only a weak linear correlation between the C-13 NMR structural parameters and the ultimate analysis. However, even when r² is zero, a strong non-linear correlation is possible. As a result of this study, it was determined that correlations base on linear regressions of ultimate analysis are unsuitable for predicting C-13 NMR structural parameters with reasonable accuracy.
A non-linear correlation has now been developed that predicts the chemical structure parameters generally measured by C-13 NMR and required for the CPD devolatilization model: (1) the average molecular weight per side chain (Mdelta); (2) the average molecular weight per aromatic cluster (MWcl); (3) the ratio of bridges to total attachments (Po); and (4) the total attachments per cluster (sigma+1). The correlation is based on ultimate and proximate analyses, which are generally known for most coals.
The correlation has been used to estimate the chemical structure parameters generally obtained from C-13 NMR measurements, and then coal devolatilization predictions were performed using the CPD model and compared with measured total volatiles yields. The combination of the empirical model and the CPD model accurately predicts tar and total volatiles yields for coals with carbon content (daf) ranging from 65 percent to 94 percent.
Guo, F. and Hecker, W.C.
Carbon 97:392(1997). Presented at the 23rd Biennial Conference on
Carbon, Penn State University, July 16, 1997. Funded in part by ACERC.
The heterogeneous reaction of NO with coal char has potential as the basis for both reburning and post-combustion clean-up processes to control NOx Emission from coal Combustion. The reaction is also very important in understanding the formation and reduction of NO during coal combustion. However, the heterogeneous kinetics and mechanism of the NO-char reaction are still poorly understood. Many questions regarding the mechanism and kinetics of the reaction, regarding the effects of char surface area, mineral matter, coal rank, burnout, and flue gases on the reaction remain. In this work, we explore the effects of coal rank, burnout level, and burnout conditions on the kinetics of the NO-char reaction.
Hickenlooper, J.L. and Hecker,
W.C.
Environmental Catalysis II, (in press), 1997. Also presented at the AIChE
Annual Meeting, Los Angeles, California, November 17, 1997. Funded in part
by ACERC.
The application of quantitative FTIR to heterogeneous catalysis allows the determination of surface concentrations of active intermediates. Successful application of quantitative FTIR depends upon understanding the factors affecting integrated extinction coefficients. Extinction coefficients relate integrated IR absorbance to surface concentration. Research on catalyst systems with 1% Rh has determined the Rh-CO extinction coefficients are not dependent upon oxide support, using the following supports: SiO2, Al2O3, Ce/SiO2, Ce/Al2O3, TiO2, and MgO. In addition, varying temperatures between 50° and 200°C and varying weight loadings from 0.2% to 9% appeared to have no effect on the extinction coefficients for Rh/SiO2 catalysts. Similar studies are being carried out on Rh/ASM-5. The following band frequencies have been observed on 0.8% Rh/AMS-5 catalyst: 2181 and 2150 cm^-1, 2100 (sh) and 2020 (sh) cm^-1, 2114, and 2048 cm^-1, 2117 and 2083 cm^-1 and 2069 cm^-1. The two weak bands at 2181 and 2150 cm^-1 are assigned to Rh (III)-CO where CO is bonded reversibly to the Rh(III) ion (Shannon et al. 1984). The bands at 2100 (sh) and 2020 (sh) cm^-1, 2114, and 2048 cm^-1, 2117 and 2083 cm^-1 are assigned to three types of RH(I) carbonyls (Shannon et al. 1984). The band at 2069 cm^-1 is proposed to be a linear Rh-CO species. Extinction coefficients for these Rh-Co species are being determined by combining peak areas from IR placed in a high temperature transmission reactor cell. The effects of temperature on the extinction coefficients for CO chemisorbed on Rh/ZMS-5 are also being determined. The results of this study will allow catalysis researched to apply quantitative FTIR to better understand catalytic surface reaction or Rh/ZMS-5 as well as demonstrate the use of an analytical system for determining extinction coefficients.
Hu, J.Z.; Alderman, D.W.;
Pugmire, R.J. and Grant, D.M.
Journal of Magnetic Resonance, 126:120-26(1997). Funded by US Department
of Energy.
A 3D separated-local-field (SLF) experiment based on the 2D PHORMAT technique is described. In the 3D experiment, the conventional 2D SLF powder pattern for each chemically inequivalent carbon is separated according to their different isotropic chemical shifts. The dipolar coupling constant of a C-H pair, hence the bond distance, and the relative orientation of the chemical-shift tensor tot eh C-H vector can all be determined for the protonated carbons with a single measurement. As the sample turns at only about 30 Hz in a MAT experiment, the SLF patterns obtained approach those of a stationary sample, and an accuracy in the measurement similar to that obtained on a stationary sample is expected. The technique is demonstrated on 2,6-dimethoxynaphthalene, where the C-13-H-1 separated-local-field powder patterns for the six chemically inequivalent carbons are clearly identified and measured. The observed dipolar coupling for the mothoxy carbons is effectively reduced by the fast rotation of the group about its C3 symmetry axis. The average angle between the C-H bond direction and the C3 rotation axis in the OCH3 group is found to be about 66°.
Kelemen, S.R.; Gorbaty,
M.L.; Kwiatek, P.J.; Fletcher, T.H.; Watt, M.; Solum, M.S. and Pugmire, R.J.
Energy & Fuels, 12:159-72(1997). Funded by ACERC, Exxon and Federal Energy
Technology Center.
X-ray photoelectron spectroscopy (XPS) was used to identify and quantify the changes in organically bound nitrogen forms present in the tars and chars of coal after pyrolysis. For fresh coal, pyrrolic nitrogen is the most abundant form of organically bound nitrogen, followed by pyridinic, quaternary, and amino types. Some of the quaternary nitrogen species initially present in coal are lost upon mild pyrolysis, prior to hydrocarbon devolatilization. These quaternary species are attributed to pyridinic or basic nitrogen species associated with hydroxyl groups from carboxylic acids or phenols. A portion of the quaternary nitrogen species is lost at the very earliest stage of pyrolysis. Upon devolatilization, the resultant tar and char contain mostly pyrrolic and pyridinic forms; however, a portion of the quaternary nitrogen initially present in the coal appears in the coal char and tar. The relatively strong bonding interactions associated with theses quaternary species suggests that there may be other quaternary nitrogen, in addition to protonated pyridines, in low-rank coal. For low-rank coal, amino groups are preferentially released and concentrate in the tar. XPS analysis of chars and tars produced during rapid heat-up (104 deg/s) pyrolysis show similar trends. However, sever pyrolysis of the devolatilized char results in the appearance of asymmetric carbon (1s) line shape indicative of very large polynuclear "graphitic-like" units. This transformation is accompanied by a rise in the relative number of quaternary nitrogen forms and occurs over a relatively narrow temperature range. Quaternary and pyridinic nitrogen forms become the dominant forms in severely pyrolyzed chars. The relatively low level of quaternary nitrogen in the rapid heat up chars indicates that very large polynuclear aromatic structures are not fully developed under these pyrolysis conditions.
Solum, M.S.; Pugmire, R.J;
Grant, D.M.; Kelemen, S.R.; Gorbaty, M.L. and Wind, R.A.
Energy & Fuels, 11:491-94(1997). Funded by ACERC and US Department of
Energy.
N-15 NMR data are reported for the Argonne Premium Coals. Arguments are presented to explain discrepancies between observations and conclusions obtained from NMR experiments and those obtained by XPS and XANES techniques. Delectability of different types of nitrogens is discussed in terms of cross-polarization dynamics together with effects of the large chemical shift anisotropy that is found in different types of nitrogen functional groups. Data on acid-treated coals confirm the presence of pyridinic type nitrogens that were not observed in a previous N-15 NMR study of coals.
Pugmire, R.J.; Solum, M.S.;
Grant, D.M.; Fletcher, T.H. and Wind, R.A.
Proceedings of the 9th International Conference on Coal Science, Essen,
Germany, September 7-12, 1997. Funded by ACERC, US Department of Energy/University
Coal Research and New Energy and Industrial Technology Development Organization.
N-15 NMR spectra are reported for a number of coals from Pacific Rim countries. Arguments are presented to explain discrepancies between observations and conclusions obtained from NMR experiments and those obtained by XPS and XANES techniques. Detection of different types of nitrogen species is discussed in terms of cross polarization dynamics together with the effects of the large chemical shift anisotropy that are found in different types of nitrogen functional groups. Significant differences are observed in the types of nitrogen present in these coals and these variations are associated with coal rank as has been in a previous study of the Argonne Premium coals. We have also begun to examine pyrolysis char and tar samples. The NMR data indicate that significant differences exist between the types of nitrogen structures observed in coal, char and tar samples. These differences suggest that different mechanisms may exist for nitrogen release from tar and char samples.
Guo, F. and Hecker, W.C.
Western States Section/ The Combustion Institute, Livermore, California,
Paper #97S-068 (1997). (Also presented at the Western State Section/The Combustion
Institute, Livermore, California, April 15, 1997.)
The heterogeneous reaction of NO with coal char has potential as the basis for both reburning and post-combustion clean-up processes to control NOx emissions from combustion. The reaction is also very important in understanding the formation and reduction of NO during coal combustion. In this study the kinetics of NO reduction by chars made from coals ranging in rank from lignite to low-volatile bituminous (Beulah-Zap, Dietz, Utah Blind Canyon, Pittsburgh #8, and Pocahontas #3) were investigated in a packed bed reactor at temperatures between 723 and 1173 K. Graphite and coconut char were also studied.
The reaction is first order with respect to NO partial pressure and exhibits an activation energy shift from 20-40 kcal/mol at low temperature to 45-60 kcal/mol at high temperatures for all chars studied. The low-temperature activation energy increases as coal rank increases. The shift to a distinctly different and higher activation energy at higher temperature is opposite to what would be expected if a reaction is shifting from chemical rate control to mass transfer control, and suggests different mechanisms or rate determining steps at high and low temperatures. The low rank chars are generally more reactive than the high rank chars. Also, the reactivity of char seemingly depends not only on organic char surface area, but also on mineral content and specifically CaO surface area. The experimental data also indicate that for NO formation in coal combustion the heterogeneous reduction of NO by char is significant, compared with homogenous reburning of NO by Chi.
The trend of variation of rate constant with char burnout significantly depends on char burnout conditions. The rate constant consistently decreases burnout when the chars are burnt out to different levels in a drop tube reactor at 1800 K and 3-5% O2. However, the rate constant increases as char burnout increases (up to 90%) when the char burnout levels result from reacting the char with 3000 ppm NO in a packed bed at 723-1173K. For the latter case, the relationship of rate constant (based on maf char mass) and char burnout is approximately linear with roughly the same slope between 20 and 80% burnout for all coal chars. The activation energy to the reaction is apparently independent of both char burnout level and burnout conditions.
Fletcher, T.H.
University Coal Research Contractors Review, Pittsburgh, Pennsylvania,
April 1997. Funded by ACERC and US Department of Energy/University Coal Research.
OBJECTIVE: The primary objective of this project is to determine the forms of nitrogen in coal that lead to nitrogen release during devolatilization. Specific questions to be addressed are:
Why do low rank coals (i.e., lignites) release as much nitrogen during devolatilization as hva bituminous coals when the tar yields are markedly different?
Why do coals of similar rank and elemental composition release different amounts of nitrogen during devolatilization?
It is thought that these questions can be answered in terms of the chemical structural features of the coal. This work focuses on determining the chemical structural features of coal tar and char at varying degrees of devolatilization. These features are determined through the use of C-13 and N-15 NMR and XPS. Two reactor systems are utilized in this project. A drop tube reactor (HPCP) is used to produce partially devolatilized samples and a flat flame burner (FFB) is used to provide high temperature, high heating rate pyrolysis products.
ACCOMPLISHMENTS AND CONCLUSIONS:
Mild pyrolysis experiments (900 K, 160 ms) were performed on three bituminous coals. The coal and char were analyzed with solid-state C-13 NMR. The tar was partially dissolved in deuterated methylene chloride (CD2Cl2). The nonsoluble tar portion was analyzed in the same manner as the coal and char, while the soluble portion was analyzed using a recently developed high-resolution C-13 NMR technique developed for liquid phases. This is the first time these kind of data have been available.
In these analyses, the tar structure was found to be significantly different from the structure of the char and coal. The number of bridges and loop per cluster in the tar was up to 655 lower than in the char. In addition, the number of aromatic carbons per cluster in the tar was significantly lower than that found in either the coal or the char. Since the molecular weight per cluster in the tar is lower than reported average tar molecular weights, these data imply that tar is made up of a number of multiple clusters (dimers, trimers, etc.) as well as single clusters (i.e., monomers).
Additionally, the mass of nitrogen per cluster in the tar was found to be significantly lower in the tar than in either the coal or the char. These experimental findings suggest that changes may be necessary in current network devolatilization models to accurately describe the changes in chemical structure.
The Argonne Premium Coal (APC) samples were analyzed using N-15 NMR; these are the first published n-15 NMR data on the APC samples.
The Argonne Premium Coal (APC) samples were treated with strong acid and analyzed using N-15 NMR. This resulted in an increase in the signal from the pyridinium (quaternary) type nitrogens, thus implying that pyridine type nitrogens are present in the coal but are undetectable by standard solid state NMR techniques. These experimental results indicate that N-15 NMR analyses are now in general agreement with XPS data which indicate that approximately 25% of the nitrogens are present as pyridine types.
A preliminary nitrogen-specific chromatograph analysis of coal tars was completed. This analysis showed that there are extremely complex mixtures of nitrogen-containing compounds in coal tar. Due to this extreme complexity, the quantitative resolution of the resulting in coal tar. Due to this extreme complexity, the quantitative resolution of the resulting chromatograms was poor. However, despite the lack of good resolution, thirty nitrogen-containing polycyclic aromatic compounds were tentatively identified in these tars. These compounds were mainly pyridinic and pyrrolic, with numbers of fused aromatic rings ranging from 2 to 5.
Terry, R.E. and Hecker,
W.C.
Presented at the AIChE Annual Meeting, Los Angeles, California. November
17, 1997. Funded in part by ACERC.
We have conducted several surveys to identify needs and successes in the area of outcomes assessment. A survey of engineering recruiters was conducted to determine the characteristics of graduates being sought for by these recruiters and to determine the characteristics that make employees successful in their companies. A second survey involving alumni and current students was conducted to determine forms of outcomes assessment that had the most meaning to them as students and to them as working engineers.
The survey conducted with engineering recruiters has supported the hypothesis that differing factors are important in the initial recruiting of college students and in the success of the company employees after joining the work force. These results will be presented in detail.
The survey conducted with alumni and current students has been used to guide the direction of assessment techniques in the chemical engineering curriculum at Brigham Young University. The paper will present the results of the survey and attempts to incorporate meaningful assessment techniques into the curriculum.
Guo, F. and Hecker, W.C.
Presented at the Combustion Reaction Engineering Symposium at the AIChE
Annual Meeting, Los Angeles, California, November 17, 1997. Funded in part
by ACERC.
The heterogeneous reaction of NO with coal char has potential as the basis for both reburning and pos-combustion lean-up processes to control NOx emissions from coal combustion. The reaction is also very important in understanding the formation and reduction of NO during coal combustion. However, the heterogeneous kinetics and mechanism of the NO-char reaction are still poorly understood. Many questions regarding the mechanism and kinetics of the reaction, and the effects of char surface area, mineral matter, coal rank, burnout, and flue gases on the reaction remain. In this work, we explore the effects of coal rank, burnout level, and burnout conditions on the kinetics of the NO-char reaction. We also present and discuss a model that predicts the rate of the NO-char reaction over a wide range of temperatures, coal types, and burnout levels.
Haneberg, A.L.
Soot Volume Fraction Determined by Two-Color Extinction in a Practical Scale
Pulverized Coal Flame, M.S./BYU, April 1997. Advisor: Tree
Nazeer, W.
Species and Temperature Measurements in a Pulverized Coal Controlled Profile
Reactor with Natural Gas Reburning, M.S./BYU, August 1997. Advisor: Tree
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