Bartholomew, CH

1998

Mineral-Catalyzed Formation of Natural Gas During Coal Maturation

Bartholomew, C.H.; Butala, T.Q.; Medina, J.C.; Lee, M.L.; Taylor, S.J. and Andrus, D.B.
Proceedings of the International Conference on Coal Seam Gas and Oil, Brisbane, Australia, March 23-25, 1998.

Coal seam reservoirs are important worldwide commercial sources of natural gas. It is commonly assumed that hydrocarbon gases are formed in coal seams by thermolysis (cracking) of coal organic matter. Recently, however, the reliability of this geologic process model has been questioned. In fact, results of artificial maturation experiments indicate that raw (mineral-containing) coal generates hydrocarbon gas at substantially higher rates than demineralized coal. This difference suggests that mineral catalysis could be a critical variable affecting hydrocarbon gas formation during coal maturation.

The objective of our combined literature and experimental study is to evaluate potential roles of minerals in catalyzing coal-bed methane formation. In the first phase of this study, rate and product selectivity data for hydrocarbon thermolysis and mineral-catalyzed cracking or synthesis reactions were compiled in a comprehensive review of technical literature sources. Kinetic models were used to predict conversion rates and product yields at typical low-temperature conditions of coal maturation. It was found that under these conditions hydrocarbon thermolysis reactions would be too slow to generate, even over geologic times, large, self-sourced coal seam natural gas deposits. By contrast, acid-mineral- and transition-metal-catalyzed reactions would occur at sufficiently high rates in geologic time and at geologic conditions to generate large quantities of natural gas, although the product distribution over acid-mineral catalysis is very different than for natural gas. Two potentially viable catalytic routes involving naturally occurring transition metal species and capable of forming large natural gas deposits within hours to several years are: (1) hydrogenolysis of alkanes and/or alkenes over iron and nickel and (2) CO2 methanation on iron and nickel. Selectivities of these catalysts in both reactions for methane are high, and the product distributions are similar to those of natural gases. We were also able to identify several geologically viable catalytic and noncatalytic routes for production of H2, a reactant typically found in coal gas and important in the catalytic production of methane from hydrocarbons or CO2.

In the second phase of this work, potential methane-forming reactions were conducted for 100-hour periods at 180°C in 1 atm of H2 in the presence or absence of reduced or unreduced iron-silica catalysts. Carbon dioxide and 1-dodecene, both found in coal beds, were utilized as model substrates. A computer-automated batch reactor system with Pyrex reactor, glass stirrer, and on-line GC analysis was used to measure reactant and product concentrations as a function of time.

Significant rates of methane formation are observed in both reactions in the presence of the prereduced catalyst after just a few hours. However, induction time and methane yield vary with substrate. In carbon dioxide methanation, the induction time is 1 h compared to 17 h for olefin hydrogenolysis, and the rate of methane production is an order of magnitude higher in CO2 methanation relative to olefin hydrogenolysis (262 and 32 mmol gFe^-1 d^-1 respectively). The latter rate compares favorably with data reported for C8 olefin hydrogenolysis. Production rates of light alkanes other than methane (i.e., ethane, propane, and butane) are also significant, although an order-of magnitude lower than for methane; thus the product distributions are characteristics of natural gas. On the other hand, no products are observed over 100 h for either reaction if no catalyst or the unreduced catalysts (Fe2O3/silica) is present.

These data suggest that natural gas may be formed in coal seams by either CO2 methanation or liquid hydrocarbon hydrogenolysis on reduced iron minerals present in the coal. An important implication of our analysis is that iron-mineral catalysis rather than homogeneous thermolysis leads to natural gas formation during coal maturation. This, in turn, suggests using coal minerals rather than currently used coal thermal maturity parameters for gas resource assessment and exploration.

 

 

1997

Catalytic Effects of Mineral Matter on Natural Gas Formation During Coal Maturation

Butala, S.; Medina, J.C.; Bowerbank, C.R.; Lee, M.L.; Felt, S.A.; Taylor, T.Q.; Andrus, D.B.; Bartholomew, C.H.; Yin, P. and Surdam, R.C.
Gas Research Institute, GRI-97/0213, July 1997. Funded in part by ACERC.

Coal seam reservoirs are important commercial sources of natural gas in the U.S. It is commonly assumed that coals function as self-sourced reservoirs for hydrocarbon gases formed by temperature-controlled thermolysis (cracking) of the bulk coal organic matter. However, this geologic process model may be an unreliable exploration guide. Artificial maturation results indicate that raw coal generates more hydrocarbon gas than demineralized coal. This difference suggests that mineral catalysis merits evaluation as a critical variable affecting hydrocarbon gas formation during coal maturation.

Kinetic modeling of temperature-controlled hydrocarbon thermolysis reactions using coal maturation geologic times and temperatures indicate that thermolysis reaction rates would be too slow to generate large, self-sourced coal seam natural gas deposits. By contrast, acid mineral, transition metal, and metal oxide mineral catalyzed reactions would occur at rates sufficiently fast under geologic time and temperature conditions to generate large quantities of natural gas. The unavailability of suitable benchmark coal reactivity data preclude assessment of whether catalytic reactions actually control hydrocarbon gas formation during coal maturation.

 

1996

 

Effects of Pyrolysis Heating Rate on Intrinsic Reactivities of Coal Chars

Gale, T.K.; Bartholomew, C.H. and Fletcher, T.H.
Energy & Fuels, 10(3):766-755, 1996. Funded by ACERC.

The main objective of this work was to determine the effects of pyrolysis heating rate on intrinsic O2 reactivity of coal chars. Relationships of intrinsic reactivity to other pyrolysis conditions and char physical and chemical structure were also investigated, and empirical correlations were obtained. Two different entrained flow reactors (a flat flame methane-air burner and a drop tube reactor) were used to prepare chars under a variety of different pyrolysis conditions at maximum particle temperatures and heating rates of 840-1627 K and 104 to 2 s 105 K/s, respectively. Intrinsic reactivities of a lignite and two bituminous coal chars decrease with increasing preparation heating rate. Maximum particle temperature and heating rate are difficult preparation parameters to separate and were closely coupled in this work, as in most entrained flow coal research. Indeed, much of the work described in the literature defining the effects of pyrolysis heating rate on coal char reactivity; has utilized vast residence time differences, comparing data from fixed bed (residence time of ~ 1 h) and entrained flow reactors (residence time of ~100 ms). It is concluded from this work that observations made on the basis of such experimentation are a function more of residence time and reactor variations (packed or fixed bed, as opposed to entrained flow) than particle heating rate. This work also provides evidence that intrinsic reactions of O2 with coal char (for the three coals observed in this study) are not significantly influenced by large differences in char meso- or micropore surface area obtained by varying pyrolysis conditions.

 

Effects of CaO, High-Temperature Treatment, Carbon Structure, and Coal Rank on Intrinsic Char Oxidation Rates

Gopalakrishnan, R. and Bartholomew, C.H.
Energy & Fuels, 10:689-695, 1996. Funded by ACERC.

The low temperature kinetics of oxidation of Dietz sub-bituminous coal char prepared in methane flat-flame burner (4% post-flame oxygen) was studied by TGA both in the presence and in the absence of calcium minerals. The reactivities of untreated and calcium-reloaded chars at 600 K are 5 and 2 times higher than acid-washed char, indicating a significant catalytic effect for CaO. The intrinsic reactivities of these chars after oxidation in a drop-tube reactor at a particle temperature of about 1900 K and 5% O2 also show a similar trend, although the reactivity of each char is lowered by about a factor of 10 due to this high-temperature oxidation. The physical properties of these chars are also significantly altered due to high-temperature oxidation treatment. Comparison of intrinsic oxidation rates of unloaded Spherocarb and demineralized (acid-washed) chars of Zap and Dietz coals based on available carbon mass shows a trend of increasing intrinsic rate with decreasing skeletal density suggesting that the intrinsic rate is a function of carbon structure. However, in the presence of CaO, the intrinsic oxidation rate based on CaO surface area is found to increase with decreasing coal rank. Dispersion of CaO is significantly higher for the original Dietz char prepared in a flat-flame burner (34%) than for the Ca-loaded char (12%), indicating that the Ca-reloading procedure could be improved.

1994

Catalytics Reactor Design: Keeping the Catalyst in Mind From the Beginning

Bartholomew, C.H. and Hecker, W.C.
Chemical Engineering, 70-75, June 1994. Funded by Brigham Young University.

Most major processes in the chemical process industries are built around heterogeneous chemical reactions. A solid catalyst is an integral part of almost all these operations. In new-construction or retrofit project for such plants, process engineers must design and specify not only the reactors but also the catalysts. Independent design of the two, without concern for how they will mesh, can mean a more costly design, a low production rate and more-frequent shutdowns. It may even cause the catalyst to fail. Consider, for instance, this debacle at a methanol plant. A carbon-steel pipe had been installed at the entrance to the methanol reactor. High-pressure carbon monoxide in the feed stream reacted with the steel to produce iron carbonyls, which poisoned the catalyst. Remedying the situation cost several million dollars.

With the hope of avoiding such situations, we first summarize the principles of catalyst and reactor design, with emphasis on maintaining interdependence between the two activities. Then we apply the principles to industrial reactors. The focus is solely on heterogeneous catalysis, in which the catalyst (virtually always in solid form) is not the same phase as the process stream. Even with this limitation, the technology is far too detailed for full presentation here. Instead, out aim is to enable readers to keep the big picture in mind whenever getting immersed in the specifics of the project.

Decreases in the Swelling and Porosity of Bituminous Coals During Devolatilization

Gale, T.K.; Bartholomew, C.H. and Fletcher, T.H.
Combustion and Flame, 1994 (in press). (Also presented at the 25th International Symposium on Combustion, Irvine, CA, August 1994). Funded by ACERC.

Concern about comparability and validity of different methods for producing coal chars for reactivity experiments has led to research on the effect of devolatilization conditions on the char physical and chemical structure. Particle diameter and porosity changes during devolatilization significantly affect char oxidation rates. In particular, physical properties of chars prepared in drop tube reactors differ greatly from chars prepared in flat flame burner experiments. Recent data indicate that the presence of oxygen in the gas atmosphere has no effect on swelling until char oxidation has begun. The present research concentrates on the effects of heating rate, particle temperature and residence time on the swelling and porosity of a plastic coal, and compares these results with a non-plastic coal. The heating rate at which the transition from increasing swelling to decreasing swelling occurs in approximately 5 x 10³ K/s for swelling coals. Swelling coals also reach a maximum porosity near this heating rate. At low particle heating rates swelling gradually increases versus heating rate in contrast to a decline in the swelling at high heating rates in a narrow heating rate region of 2 x 10^4 to 7 x 10^4 K/s. Non swelling bituminous and lignite coals continue to increase in porosity beyond the heating rate of 2 x 10^4 K/s.

Effects of Pyrolysis Conditions on Internal Surface Areas and Densities of Coal Chars Prepared at High Heating Rates in Reactive and Non-Reactive Atmospheres

Gale, T.K.; Fletcher, T.H. and Bartholomew, C.H.
Energy & Fuels, 1994 (in press). Funded by ACERC.

Concern about comparability and validity of different methods for producing coal chars for research has motivated this investigation of the effects of devolatilization conditions on the physical properties of coal chars. It is evident from the findings of this study that care must be taken to prepare chars under conditions similar to those of full-scale coal combustion boilers prior to performing char oxidation studies. Two different entrained flow reactors were used to prepare chars under a variety of different pyrolysis conditions at maximum particle temperatures and heating rates between 840 to 1627 K and 10^4 to 2 x 10^5 K/s respectively. Under these conditions micro-pore (CO2) surface area generally increases with residence time and mass release for lignite and bituminous coals, as does true density. Micro-pore surface area also increases somewhat with increasing maximum particle temperature and heating rate. Meso-pore (N2) surface area is most affected by reactive gas atmospheres (carbon activation). The presence of steam in the post flame gases of methane/air flat flame burners is a significant factor in increasing meso-pore surface are of chars prepared in such burners, even though the mass conversion by steam gasification is small. Partial char oxidation with O2 significantly affects char N2 and CO2 surface area at these heating rates and residence times (50 to 100 ms), sometimes increasing and sometimes decreasing internal surface area. Low rank lignite and sub-bituminous coals have higher potentials for forming chars with increased N2 surface are than bituminous coals. The moisture content of low rank coals may be more important than rank. Lignite with high moisture content yields char with a significantly higher N2 surface area than char prepared from lower moisture content lignite. However, initial coal moisture has less effect on CO2 surface area.

Catalyst Deactivation in Hydrotreating of Residua: A Review

Bartholomew, C.H.
Catalytic Hydroprocessing of Petroleum and Distillates, Marcel Dekker, Inc., New York, NY, 1994. Funded by Brigham Young University.

Hydrotreating, the catalytic conversion and removal of organic sulfur, nitrogen, oxygen and metals from petroleum crudes at high hydrogen pressures and accompanied by hydrogenation of unsaturates and cracking of petroleum feedstocks to lower molecular hydrocarbons plays an ever increasing key role in the refinery. Indeed, hydrotreating capacity has been growing steadily (at about 6% per year since 1976) and represents today nearly 50% of the total refining capacity. The increased application of hydrotreating can be ascribed to (i) the ever decreasing availability of light, sweet crudes and thus the increasing fraction of heavy, sour crudes that must be processed and (ii) the trend to increase upgrading of feedstocks for improvement of downstream processing such as catalytic reforming and catalytic cracking.

Hydrotreating of petroleum residua feedstocks involves three important reactions: hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodemetallization (HDN) for removal of organically-bound sulfur, nitrogen, and metals respectively. Sulfided Mo, CoMo, and NiMo catalysts used in these reactions are prepared by impregnating catlyst extrudates with solutions of Co, Mo and Ni followed by drying, calcinations at 400-500°C, and sulfiding with H2S/H2 at 350-400°C. The active sites for HDS and HDN are thought to be sulfur vacancies at the surface of a sulfide phase, e.g. CoxMoyS.

Hydrotreating involves a number of catalytic steps. For example, reaction steps in HDS include: (i) adsorptions of H2 and the organic sulfide, (ii) hydrogenolysis of the carbon-sulfu bond, (iii) hydrogenation of unsaturates, (iv) hydrocracking, and (v) desorptions of hydrocarbons and H2S. An important objective in hydrotreating is to maximize the rates of S, N, and metal removal, while minimizing the rates of hydrogenation and hydrocracking and therewith hydrogen consumption.

Sulfided resid hydrotreating catalysts are deactivated over a period of months by coke, metals and nitrogen compounds. The deactivation process involves a combination of uniform poisoning, pore mouth poisoning and pore blockage by (i) decomposition of organometallic compounds and (ii) buildup of soft coke and its transformation over a period of time to hard, crystalline coke. These problems are minimized by careful selection of uard beds, reactor design, and catalyst design; moreover, it is possible to regenerate coked catalysts with an oxygen burn.

Deactivation of hydrotreating catalysts has been fairly extensively studied. Several previous reviews of the literature and an international symposium have covered in some depth most aspects of this subject. Nevertheless, an updated overview of the key aspects of residua hydrotreating deactivation, including coke formation chemistry, metals deposition chemistry, catalyst and reactor design, and the use of mathematical models to simulate the deactivation process may be timely.

This review focuses on the deactivation of sulfide Mo, CoMo, and NiMo catalysts in hydrotreating of heavy residuum feedstocks. Coke formation, metals deposition, the roles of catalyst and reactor design in minimizing catalyst decline, and the application of modeling to design and prediction of deactivation rates are discussed in this review in the sections which follow.

Catalysis of Char Oxidation by Calcium Minerals: Effects of Calcium Compound Chemistry on Intrinsic Reactivity of Doped Spherocarb and Zap Chars

Gopalakrishnan, R.; Fullwood, M. and Bartholomew, C.H.
Energy & Fuels, 8:984-989, 1994. Funded by ACERC.

Catalysis by CaO, CaCo3, and CaSO4 of the oxidation of a well-defined, high purity synthetic char, Spherocarb, was investigated at low reaction temperatures using thermogravimetric analysis. The results indicate significant catalytic effects-up to 160-fold increase for CaCO3 catalysis, 290-fold increase for CaSO4, and up to 2700 times for CaO. Oxidation rates were likewise measured for fresh, demineralized, and Ca-loaded chars prepared from Beulah-Zap lignite coal in a flat flame burner at 1473 K. The oxidation rates of CaO-catalyzed Spherocarb and Zap are the same within experimental error, suggesting that the high reactivity of the Zap char is due in large part to catalysis by CaO. It was also found that chlorine added to Ca-loaded char had a negligible effect on its low-temperature reactivity.

Sintering Kinetics of Supported Metals: Perspectives from a Generalized Power Law Approach

Bartholomew, C.H.
Catalyst Deactivation 1994, 88, 1994. Funded by ACERC.

Studies of sintering kinetics of conventional supported metal catalysts are reviewed. Available kinetic data for sintering have been reanalyzed using the new General Power Law Expression (GPLE), which provides the capability of treating these data in a consistent, unifying fashion such that quantitative comparisons regarding effects of reaction conditions and catalyst properties are possible for the first time. It is shown that all available dispersion versus time data can be fitted to second order GPL kinetics. From the analysis of these data new conclusions arise regarding the effects of atmosphere, time, temperature, support, promoters, and metal on the thermal stability of supported metals.

Hydrotreating involves a number of catalytic steps. For example, reaction steps in HDS include: (i) adsorptions of H2 and the organic sulfide, (ii) hydrogenolysis of the carbon-sulfur bond, (iii) hydrogenation of unsaturates, (iv) hydrocracking, and (v) desorptions of hydrocarbons and H2S. An important objective in hydrotreating is to maximize the rates of S, N, and metal removal, while minimizing the rates of hydrogenation and hydrocracking and therewith hydrogen consumption.

Sulfided resid hydrotreating catalysts are deactivated over a period of months by coke, metals and nitrogen compounds. The deactivation process involves a combination of uniform poisoning, pore mouth poisoning and pore blockage by (i) decomposition of organometallic compounds and (ii) buildup of soft coke and its transformation over a period of time to hard, crystalline coke. These problems are minimized by careful selection of guard beds, reactor design, and catalyst design; moreover, it is possible to regenerate coked catalysts with an oxygen burn.

Deactivation of hydrotreating catalysts has been fairly extensively studied. Several previous reviews of the literature and an international symposium have covered in some depth most aspects of this subject. Nevertheless, an updated overview of the key aspects of residua hydrotreating deactivation, including coke formation chemistry, metals deposition chemistry, catalyst and reactor design, and the use of mathematical models to simulate the deactivation process may be timely.

This review focuses on the deactivation of sulfided Mo, CoMo, and NiMo catalysts in hydrotreating of heavy residuum feedstocks. Coke formation, metals deposition, the roles of catalyst and reactor design in minimizing catalyst decline, and the application of modeling to design and prediction of deactivation rates are discussed in this review in the sections which follow.

Catalysts for Cleanup of NH3, NOx and CO from a Nuclear Waste Processing Facility

Gopalakrishnan, R.; Davidson, J.E.; Stafford, P.R.; Hecker, W.C. and Bartholomew, C.H.
ACS Symposium Series, 552:74-88, 1994. Funded by Westinghouse Idaho Nuclear Company, Brigham Young University and ACERC.

Performance of Cu-ZSM-5, Pt/Al2O3 and Cu-ZSM-5 + Pt/Al2)3 for NH3 (425-750 ppm) and CO (~1%) oxidation in the presence of NO (250 ppm), O2 (14-15%) and H2O (~20%) was studied as a function of temperature. Pt/Al2O3 is more active for NH3 and CO oxidation, while Cu-ZSM-5 is more selective for conversion of NO and NH3 to N2. NH3 and CO are completely oxidized above 300°C on Pt/Al2O3, while on Cu-ZSM-5 about 99% of NH3 and NO are converted to N2 at 450-500°C, although only about 50% of CO is converted to CO2. The selectivity of Cu-ZSM-5 for conversion of NH3 and NO to N2 is about 100%, while selectivities of Pt/Al2O3 for N2 and N2O are 35-40% and 20-40% respectively. However, the activity and selectivity of a Cu-ZSM-5 + Pt/Al2O3 dual catalytic systems are very high, converting 99% of NH3, 94% of NO, and 100% of CO simultaneously at 485°C with a 100% selectivity to N2.

1993

Comparison of Reactivity and Physical Structure of Chars Prepared Under Different Pyrolysis Conditions, i.e. Temperature, Gas Atmosphere, and Heating Rate

Gale, T.K.; Bartholomew, C.H. and Fletcher, T.H.
Proceedings of the International Conference on Coal Science, Banff, Canada, September 1993. Funded by ACERC.

Coal combustion consists of basically two main steps: 1) pyrolysis and oxidation of the liquid and volatile matter, and 2) subsequent oxidation of the residual porous char matrix. Char oxidation is the slower of these two steps and is difficult to bring to completion. Pyrolysis significantly affects the resulting char structure, porosity, internal surface area and chemical composition (e.g. H/C ratios) and hence the char oxidation rate. A highly porous char particle is more accessible to reactant molecules and will, therefore, have a higher reactivity in the reaction zone influenced by pore diffusion. Under surface reaction controlled conditions, reactivity increases with increasing internal surface area and H/C ratio.

A number of different experimental methods and reactor types are currently used to produce chars for laboratory study. These different reactors typically operate under conditions that are quite reproducible from one run to another. However, variations in pyrolysis conditions from one method to another and from one reactor type to another may be large. Comparisons of data obtained in different laboratories are often rationalized by matching experimental conditions thought to be most critical such as temperature and residence time, or temperature and total volatiles yield. However, comparing chars at the same residence time or the same mass loss may not be valid, because at different heating rates and/or gas-phase oxygen concentrations, the chemical and physical nature of the pyrolysis will vary.

The objective of this research was to determine effects of variations in pyrolysis conditions on char structure and reactivity for a group of chars prepared from coals of low to high rank. Heating rate, temperature, residence time, and gas atmosphere during pyrolysis were the main variables in the study.

Effects of CaO, CaSO4 and Coal Rank on Low- and High-Temperature Char Oxidation Rates

Gopalakrishnan, R.; Fullwood, M.; Moody, S.; Cope, R.F. and Bartholomew, C.H.
Proceedings of the 7th International Conference on Coal Science, Banff, Canada, September 1993. Funded by ACERC.

This study is part of an ongoing program to investigate (a) rates and mechanisms of Ca-catalyzed oxidation of synthetic char and chars prepared from representative U.S. coals and (b) the chemical nature of active catalytic sites for oxidation on those inorganic mineral phases present in coal chars.

Selective Catalytic Reduction of Nitric Oxide by Propane in Oxidizing Atmosphere over Copper-Exchanged Zeolites

Gopalakrishnan, R.; Stafford, P.R.; Davidson, J.E.; Hecker, W.C. and Bartholomew, C.H.
Applied Catalysis B: Environmental, 2: 165, 1993. (Presented at the Seventh Annual Symposium of the Western States Catalysis Club, Albuquerque, NM, March 1992; at the American Institute of Chemical Engineers Annual Meeting, Miami Beach, FL, November 1992 and at the 13th North American Meeting of the Catalysis Society, Pittsburgh, PA, May 1993). Funded by Shell, Brigham Young University and Winco.

Selective catalytic reduction of NO with propane and oxygen was investigated on Cu-exchanged ZSM-5, mordenite, X-type and Y-type zeolites at temperatures in the range of 200 to 600º C. Catalytic activities of Cu-X and Cu-Y are negligible, activity of Cu-mordenite moderate, and that of Cu-ZSM-5 very high, converting >90% of NO to N2 at 400ºC and a space velocity of 102,300/hr. Effects of space velocity, NO concentration, C3H8/NO ratio, oxygen concentration, and water vapor on the activities of Cu-ZSM-5 and Cu-mordenite were investigated. NO conversion decreases with increasing space velocity, decreasing propane and NO concentrations, and decreasing propane/NO ratio. Water vapor decreases the activity significantly at all temperatures. At temperatures above 400ºC, propane oxidation by oxygen is a significant competing reaction in decreasing the selectivity for NO reduction. The results indicate that Cu-ZSM-5 is a promising catalyst for SCR of NO by hydrocarbons

 

1992

Stability of Supported Catalysts: Sintering and Redispersion

Bartholomew, C.H.; Baker, T.K.; Dayburjor, D.B. and Horsley, J.S.
Catalytica Studies Division, January 1992, Funded by Catalytica.

Catalysts comprising a metallic component on a refractory support are widely used in petroleum processing, chemical synthesis, and pollution control. Supported metal catalysts are subjected to high temperatures during use or regeneration. At these high temperatures, the activity of these catalysts declines because the surface areas of the metallic component and/or the support decrease. In general, the effects of surface area loss are more difficult to overcome than the effects of carbon deposition or poisoning. The sintering processes that lead to loss of surface area involve complex physicochemical phenomena. An understanding of the mechanism of sintering is important in developing new catalysts and in regenerating deactivated catalysts, and considerable research is being devoted to understanding the mechanisms of sintering and to reversing the effects of sintering. This study analyzes the causes and mechanisms of sintering, critically reviews the relevant scientific and patent literature, and recommends ways in which sintering can be minimized and deactivated catalysts can be regenerated.

Direct MAS/MES Evidence for Electronic Metal-Support Interaction in Dilute Co-57 and Fe-57 Carbon and Alumina-Supported Catalysts

Bartholomew, C.H.; Neubauer, L.R. and Smith, P.A.
Tenth International Catalysis Congress, Budapest, Hungary, January 1992. Funded by US Department of Energy/Basic Energy Services and Brigham Young University.

Mössbauer absorption spectroscopy (MAS) and Mössbauer emissions spectroscopy (MES) studies of 1-3% 57Fe and 1% Co-57 on carbon and alumina supports were conducted as a function of a reduction temperature. Catalysts were prepared by nonaqueous evaporative deposition to maximize the reduction of cobalt and iron to the metal. Metal surface areas of the catalysts were determined by H2 adsorption, while extents of reduction to the metal were determined by both Mössbauer spectroscopy and by titration of reduced catalysts with oxygen at 673 K. MAS/MES data for 1 and 3% Fe-57/C and 1% Co-57/C catalysts reduced at 773 K indicate the presence of only one phase-superparamgnetic (SP) clusters of metal having diameters of about 1-2 nm. Room temperature isomer shifts for these carbon supported metal clusters of 0.10-0.14 mm/s indicate a decrease in electron density of the metal nuclei relative to the bulk metals. MES data for Co-57/Al2O3 suggest the existence of three phases: Cosp metal, Co(II) oxide, and Co(III) oxide, while MAS generally shows only the Fesp metal clusters and Fe(III) oxides to be present in 1-2% Fe-57/Al2O3, except for some ferromagnetic Fe metal in 2% 57Fe/Al2O3 reduced at 873 K. Isomer shifts for the metal clusters in the Al2O3-supported Co-57 and Fe-57 catalysts are -0.05 to -0.15 mm/s indicating an increase in the electron density at metal nuclei. The presence of small metals cluster of 1-5 nm in these catalysts is confirmed by H2 absorption. Moreover, Debye temperatures measured by Mössbauer are significantly lower than for bulk iron consistent with the lattice dynamics expected for small metal clusters having a large fraction of surface atoms. The very significant isomer shifts observed for SP metal phases by Mössbauer are consistent with electronic modification of small metal clusters in supported Co or Fe. That the isomer shift is positive for metal/C catalysts and negative for metal/Al2O3 catalysts indicates this effect must be due to metal-support interactions.

Selective Catalytic Reduction of Nitric Oxide by Propane in Oxidizing Atmosphere Over Copper-Exchanged Zeolites

Gopalakrishnan, R.; Stafford, P.R.; Davidson, J.E.; Hecker, W.C. and Bartholomew, C.H.
Applied Catalysis, 1992 (in press). (Also presented at the Seventh Annual Symposium of the Western States Catalysis Club, Albuquerque, NM, March 1992 and at the American Institute of Chemical Engineers Annual Meeting, Miami Beach, FL, November 1992). Funded by Shell and Brigham Young University.

Selective catalytic reduction of NO with propane and oxygen was investigated on Cu-exchanged ZSM-5, mordenite, X-type and Y-type zeolites at temperatures in the range of 200 to 600ºC. Catalytic activities of Cu-X and Cu-Y are negligible, activity of Cu-mordenite moderate, and that of Cu-ZSM-5 very high, converting >90% of NO to N2 at 400ºC and at a space velocity of 102,300/hr. Effects of space velocity, NO concentration, C3H8/NO ratio, oxygen concentration, and water vapor on the activities of Cu-ZSM-5 and Cu-mordenite were investigated. NO conversion decreases with increasing space velocity, decreasing propane and NO concentrations, and decreasing propane/NO ratio. Water vapor decreases the activity significantly at all temperatures. At temperatures above 400ºC, propane oxidation by oxygen is a significant competing reaction in decreasing the selectivity for NO reduction. The results indicate that Cu-ZSM-5 is a promising catalyst for SCR of NO by hydrocarbons.

 

1991

Changes in Surface Area, Pore Structure and Density During Formation of High-Temperature Chars from Representative U.S. Coals

White, W.E.; Bartholomew, C.H.; Hecker, W.C. and Smith, D.M.
Adsorption Science & Technology, 4:180-209, 1991. Funded by ACERC.

Multiple techniques (CO2 and N2 adsorptions, NMR spin relaxation of adsorbed water, He pycnometry, and Hg porosimetry) were combined in a comprehensive study to determine changes in surface area (CO2 and nitrogen), density (solid, particle, and bulk), and pore structure (pore size and volume distributions of micro-, meso-, and macropores) in high temperature char formation from rank-representative U.S. coals of the ANL and PETC Banks (i.e. Beulah Zap, Dietz, Utah Blind Canyon, Pittsburgh No. 8, and Pocahontas No. 3). Chars were formed at high heating rates in a flat flame burner (maximum temperature of 1473 K), a process representative of char formation in pulverized coal combustion. It was determined that most of the surface area of coals was found in micropores with radii less than 1.5 nm, while 95% or more of the pore volume in the coals (85% of that in chars) is contained in mesopores (radii > 20 nm). During high temperature formation of char in a flame: (1) CO2 surface areas (involving mainly micropores, rpore < 1.5 nm) increase 2-3 fold, while N2 surface areas, (involving mesopores, 1.5 nm < rpore < 20 nm) increase 20-200 fold, (2) solid densities increase about 25% due to graphitization, while particle densities decrease by about a factor of two due to large increases in particle porosity, (3) pore volumes are increased 5-10 fold, and (4) total porosities are increased 3-4 fold, most of this increase occurring in the macropore range. The larger surface areas and porosities of chars relative to coals may be explained by (i) the removal by pyrolysis of strongly adsorbed molecules or volatile hydrocarbons from micropores and small mesopores that would otherwise hinder access of CO2 and N2, (ii) creation of new pores during the restructuring process involved in charification, and (iii) opening up by gasification with oxygen of new pores previously blocked to gas adsorption. Preparation conditions (e.g. atmosphere, heating rate, and temperature) greatly affect the physical properties including surface area, porosity and density of the resulting chars. The degree of carbon burnout is an important correlating factor affecting these properties.

Catalysis of Char Gasification in O2 by CaO and CaCO3

Bartholomew, C.H.; Gopalakrishnan, R. and Fullwood, M.
ACS Fuel Division, 36(3):982-989, 1991 (4th Chemical Congress of North America, New York, NY, August 1991). Funded by ACERC.

Catalysis by CaO and CaCO3 of the oxidation of a well-defined, high purity synthetic char, Spherocarb, was investigated at low reaction temperatures using thermal gravimetric analysis (TGA). Oxidation rates were likewise measured for fresh, demineralized, and Ca-impregnated samples of a high temperature char prepared in a flat-flame burner at about 1300 K from Beulah Zap coal. Spherocarb and demineralized Zap char were impregnated with Ca using aqueous impregnation and ion-exchange techniques. The resulting kinetic parameters for Spherocarb indicate significant catalytic effects--up to a 100 fold increase in reaction rate for CaCO3 and 3,000 in the case of CaO. The oxidation rates of CaO-catalyzed Spherocarb and Beulah Zap char are the same within experimental error, suggesting that the high reactivity of the Zap char is due in large part to catalysis by CaO.

 

Calcium Oxide Catalysis of Char Oxidation

Bartholomew, C.H.; Gopalakrishnan, R. and Fullwood, M.
8th Annual International Pittsburgh Coal Conference, 1140, Pittsburgh, PA, October 1991. Funded by ACERC.

Catalysis by CaO and CaCO3 of the oxidation of a well-defined, high purity synthetic char, Spherocarb, was investigated at low reaction temperatures using thermal gravimetric analysis (TGA). Oxidation rates were likewise measured for fresh, demineralized, and Ca-impregnated samples of a high temperature char prepared in a flat-flame burner at about 1300 K from Beulah Zap coal. Spherocarb and demineralized Zap char were impregnated with Ca using aqueous impregnation and ion-exchange techniques. The resulting kinetic parameters for Spherocarb indicate significant catalytic effects--up to a 100 fold increase in reaction rate for CaCO3 and 3,000 in the case of CaO. The oxidation rates of CaO-catalyzed Spherocarb and Beulah Zap char are the same within experimental error, suggesting that the high reactivity of the Zap char is due in large part to catalysis by CaO.

1990

Changes in Surface Area, Pore Structure and Density During Formation of High-Temperature Chars from Representative U.S. Coals

White, W.E.; Bartholomew, C.H.; Hecker, W.C. and Smith, D.M.
Adsorption Science & Technology, 1990 (In press). Funded by ACERC.

Multiple techniques (CO2 and N2 adsorptions, NMR spin relaxation of adsorbed water, He pycnometry, and Hg porosimetry) were combined in a comprehensive study to determine changes in surface area (CO2 and nitrogen), density (solid, particle, and bulk), and pore structure (pore size and volume distributions of micro-, meso-, and macropores) in high temperature char formation from rank-representative U.S. coals of the ANL and PETC Banks (i.e. Beulah Zap, Dietz, Utah Blind Canyon, Pittsburgh No. 8, and Pocahontas No. 3). Chars were formed at high heating rates in a flat flame burner (maximum temperature of 1473 K), a process representative of char formation in pulverized coal combustion. It was determined that most of the surface area of coals was found in micropores with radii less than 1.5 nm, while 95% or more of the pore volume in the coals (85% of that in chars) is contained in mesopores (radii > 20 nm). During high temperature formation of char in a flame: (1) CO2 surface areas (involving mainly micropores, rpore < 1.5 nm) increase 2-3 fold, while N2 surface areas, (involving mesopores, 1.5 nm < rpore < 20 nm) increase 20-200 fold, (2) solid densities increase about 25% due to graphitization, while particle densities decrease by about a factor of two due to large increases in particle porosity, (3) pore volumes are increased 5-10 fold, and (4) total porosities are increased 3-4 fold, most of this increase occurring in the macropore range. The larger surface areas and porosities of chars relative to coals may be explained by (i) the removal by pyrolysis of strongly adsorbed molecules or volatile hydrocarbons from micropores and small mesopores that would otherwise hinder access of CO2 and N2, (ii) creation of new pores during the restructuring process involved in charification, and (iii) opening up by gasification with oxygen of new pores previously blocked to gas adsorption. Preparation conditions (e.g. atmosphere, heating rate, and temperature) greatly affect the physical properties including surface area, porosity and density of the resulting chars. The degree of carbon burnout is an important correlating factor affecting these properties.

 

Calcium Oxide Catalysis of Char Oxidation

Bartholomew, C.H.; Gopalakrishnan, R. and Fullwood, M.
Proc. ASME Seminar on Fouling of Western Coals, Brigham Young University, Provo, UT, 1990. (Also presented at the National AlChE Meeting, Chicago, 1990). Funded by ACERC.

Catalysis by CaO of the oxidation of a well-defined, high purity synthetic char, Spherocarb, was investigated at low reaction temperatures using thermal gravimetric analysis (TGA). Spherocarb was impregnated with Ca using aqueous impregnation and ion-exchange techniques. The resulting kinetic parameters indicate a significant catalytic effect--10 to 100-fold increases in reaction rate. CO adsorption on CaO prepared by Ca(OH)2 decomposition was investigated using temperature-programmed desorption (TPD) of CO adsorbed at 298 K. Several high temperature peaks were observed consistent with heats of adsorption of 40-115 kJ/mal. These relatively large heats of adsorption are indicative of the presence of different, strongly adsorbed CO species on CaO and have significant implications for the catalysis of carbon oxidation and of CO oxidation to CO2 during char combustion. Experiments involving temperature-programmed reaction of hydrogen with adsorbed CO also indicate by the formation of methane that CO may adsorb dissociatively or at least dissociates in the presence of hydrogen to form methane.

1989

The Effects of Rank and Preparation Method on Coal Char Oxidation Rates

Hyde, W.D.; Hecker, W.C.; Cope, R.F.; Painter, M.M.; McDonald, K.M. and Bartholomew, C.H.
Western States Section/The Combustion Institute, Livermore, California, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).

Coal char reactivity has been found to vary greatly depending on the rank and type of the parent coal. Also, the conditions under which a given coal is devolatilized to produce char can significantly effect the reactivity of the resulting char. Preparation conditions such as gas environment, heating rate, peak temperature, residence time, and particle size are very important in determining the resulting char reactivity in that they effect its chemical and physical structure.

The general objectives of this work are to (1) understand the effect of the rank of the parent coal on the oxidation rate (reactivity) of its derived char, (2) understand the effect of devolatilization conditions on the char oxidation rate, and (3) determine any correlations which may exist between char oxidation rates and the chemical and physical properties of the chars. Specifically, oxidation rates for char from 5 coals of various ranks were measured and compared. The differences in char reactivity of chars produced in three different char preparation apparatus: a muffle furnace, a flat-flame methane burner, and a high temperature inert-atmosphere reactor, were studied. The effects of peak temperature, residence time, and particle size were also studied. Finally, correlations of oxidation rate with hydrogen content, cluster size, and surface area were attempted.

Samples of chars from Beulah Zap (Lignite), Dietz (Subbituminous A), Utah Blind Canyon (hvC Bituminous), Pittsburgh #8 (hvA Bituminous), and Pocahontas #3 (lv Bituminous) were prepared at different residence times in the Flat-Flame Char Preparation Apparatus; samples of Pittsburgh #8, Beulah Zap, and Dietz were also prepared in the muffle furnace and the high temperature inert-atmosphere reactor. The low temperature reactivity of all the coal char samples was determined in a TGA using Tcrit as the reactivity indicator. Tcrit is defined at the temperature at which the mass loss of the sample reaches 11 percent per minute.

Effects of Preparation Variables on Reactivity and Surface Properties of ACERC Coal Chars

Hyde, W.D.; McDonald, K.M.; Cope, R.F.; Bartholomew, C.H. and Hecker, W.C.
Twelfth Symposium of the Rocky Mountain Fuels Society, Denver, 1989. (Also presented at the Rocky Mountain Regional AIChE Meeting, Salt Lake City, 1989). Funded by ACERC (National Science Foundation and Associates and Affiliates).

The combustion of coal consists of devolatilization and heterogenous char oxidation. The objective of this study is to understand the effect of devolatilization conditions on the oxidation rate (reactivity) and surface properties of the resultant char. Chars were produced by devolatilizing Pittsburgh No. 8 bituminous coal and North Dakota lignite at varying residence times and peak temperatures in a flat flame methane burner. Thermogravimetric analysis was used to determine the low-temperature reactivity of these chars. Trends of increased reactivity with decreased preparation temperature and residence time are observed. N2 and CO2 surface areas and pore size distributions were determined. Preliminary results indicate that surface areas increase with increased devolatilization. Char reactivity is also correlated with hydrogen content and aromatic cluster size.

 

Oxidation Rate Measurements of Coals and Derived Chars

Wells, W.F.; Hyde, W.D.; Cope, R.F.; Smoot, L.D.; Hecker, W.C. and Bartholomew, C.H.
Twelfth Symposium of the Rocky Mountain Fuels Society, Denver, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).

To aid in the development and provide validation data to the char oxidation submodel, measurements of oxidation rates at high and low temperatures are being collected for chars prepared from five select ACERC coals. Chars are prepared using a flat flame burner and a recently constructed inert atmosphere drop-tube reactor heated using an inductively coupled plasma. The drop-tube reactor is also used to obtain reaction rates at high temperatures; low temperature rates were measured in a TGA. Chemical and physical properties of the fuel were measured. Multivariate statistics are used to correlate fuel properties to reaction rates.

 

Surface Properties and Pore Structure of ACERC Coals and Chars

White, W.E.; Bartholomew, C.H.; Thornock, D.; Wells, W.F.; Hecker, W.C. and Smoot, L.D.
Twelfth Symposium of the Rocky Mountain Fuels Society, Denver, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).

Results of an ongoing collaborative study of the surface properties and pore structure of a suite of 11 coals selected for comprehensive study by ACERC are reported. The principal objective is to correlate the surface, pore, and chemical properties of coals and chars with their rates of combustion. Surface areas, pore volumes, pore size distributions, and solid densities were measured for Pittsburgh No. 8, Wyodak, Beulah Zap Lignite, Lower Wilcox, Dietz and a Utah Scofield coal and for chars derived from these coals. Surface areas, pore volumes and pore size distributions were measured using nitrogen and carbon dioxide adsorptions, mercury porosimetry and NMR spin-lattice relaxation measurements for samples saturated with water vapor. Solid densities were obtained using helium displacement. The results indicate that chars have larger surface areas and pores volumes relative to coals. New mesopores are created and micropore volume increases during devolatilization. Large fractions of the internal pore volume of coals are not penetrated by nitrogen molecules during adsorption, but are penetrated by carbon dioxide, suggesting that a fraction of the pore volume is microporous, or involves blocked pores. By using several techniques for measuring surface properties (e.g. N2 and CO2 adsorption isotherms, NMR,etc.), the pore structure of coals and chars can be defined more accurately, and char oxidation models can be evaluated with more understanding.

 

Pore Structure Characterization of Coals & Chars Via NMR

Davis, P.J.; Smith, D.M.; Bartholomew, C.H.; White, W.E. and Hecker, W.C.
Twelfth Symposium of the Rocky Mountain Fuels Society, Denver, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).

Due to the wide pore size range and complexity of coals and chars, it is difficult to study the pore structure. Multiple techniques such as gas adsorption, mercury porosimetry, and density measurements are often used. These techniques suffer from limited pore size range, pore shape assumption, network/percolation effects, and sample changes during analysis. To obtain a more complete description of coals and chars, NMR spin-lattice relaxation measurements of water saturated coals and chars have been performed. The NMR technique does not suffer from network/percolation effects, sample changes, pore shape assumption (rp>5nm). Three coals and their chars were compared.

Surface Areas and Pore Structures of ANL and PETC Coals and Derived Chars

Bartholomew, C.H.; White, W.E. ; Hecker, W.C.; Smith, D.M.
4th Annual Meeting of the Western States Catalysis Club, Denver, Colorado , 1989. (Also presented at the Western States Section,The Combustion Institute, Livermore, California, 1989). Funded by ACERC (National Science Foundation and Associates and Affiliates).

Surface areas, pore volumes, and pore size distributions of five Argonne National Lab (ANL) coals (Pittsburgh No. 8, Illinois No. 6, Pocahontas No. 3, Beulah Zap lignite, and Utah Blind Canyon) and of two PETC coals (Lower Wilcox and Dietz) and chars derived from these coals area being measured in an ongoing study. Data obtained for several of these coals and chars will be reported. Surface areas, pore volumes and pore size distributions were measured by nitrogen and carbon dioxide adsorptions at 77 K and 195-300 K respectively; pore volumes and pore size distributions were also determined by NMR spin-relaxation measurements of samples saturated with water. Comparisons of accuracy and precision for static vacuum and flow desorption methods were made. Surface areas and pore volumes measured by adsorption in a static vacuum system and by desorption in a flow/TC detector system agree to better than 1-5% where adsorption equilibrium has obtained.

The results provide new insights into the surface and pore structure of coals and chars as functions of rank and charification. Surface areas of coals generally increase with decreasing rank. Chars have larger surface areas and pore volumes than the parent coals; indeed surface areas measured by nitrogen adsorption are up to two orders of magnitude larger, while those measured by carbon dioxide adsorption are 2-3 times larger. Pore volumes of chars measured by nitrogen adsorption are 10-20 time those of the parent coals. Large fractions of the internal surfaces of coals and pore diameters are microporous (pore diameters of 1 nm or smaller) and are not easily penetrated by nitrogen molecules at 77 K. In the case of some coals, while the pore volume increases during devolatilization, the shape of the pore size distribution stays the same. For other coals, the pore size distribution changes radically during devolatilization. This systematic study of surface areas and pore structures of coals and chars provides insights into physical changes that occur during coal devolatilization and char burnout. This information can be useful in characterizing the evolution of pore structure and its effect on diffusion of reactant in and products out during combustion of coal chars.

 

1988

 

Fuel Characteristics and Reaction Mechanisms

Lee, M.L.; Bartholomew, C.H. and Hecker, W.C.
ERC Symposium, Annual ASEE Meeting, 1987, Reno, Nevada. Funded by ACERC (National Science Foundation and Associates and Affiliates).

The main goal of the Advanced Combustion Engineering Research Center is the development and implementation of advanced combustion models. The Center research is organized around six major thrust areas focused on the clean and efficient use of low-grade fuels such as coal. These thrust areas will provide data on kinetics, fuel properties, and process-performance design characteristics that will be integrated into a comprehensive computer model used in the design and optimization of advanced combustion systems. This paper deals with the work in the fuel characterization and reaction mechanisms thrust area.

The research project in the fuel characteristics and reaction mechanisms thrust area are focused on relating the kinetic rates and mechanisms of rapid coal devolatilization and char reactivity with the physical and chemical structure of coal and pyrolysis tars and chars. This paper summarizes the results from four integrated research programs in this thrust area.

Supercritical solvent extraction is employed to determine the amount and nature of hydrocarbons that are physically absorbed or only weakly bound within the coal structure and are expected to be liberated early in the devolatilization process. Both paraffin (n-alkanes, isoprenoids, and pentacyclic triterpanes) and polycyclic aromatic (two to five fused aromatic rings) hydrocarbons have been identified. Pyrolysis mass spectroscopy provides both rate data and pyrolysis tar data on coals during slow devolatilization. The physical properties (surface area and pore size distribution) of the parent coals and pyrolysis chars are studied in order to relate these properties to coal and char reaction rates. Advanced solid-state NMR techniques are used to obtain the carbon skeletal structure of the parent coals and pyrolysis chars. High field, high-resolution NMR spectroscopy experiments provide data on the structural features of the pyrolysis tars.

The experiments in this thrust area are carried out on a common set of standard coals. The devolatilization studies to be initially carried out in collaboration with other laboratories will be summarized. A description will be provided for the analysis and integration of the various experimental data. These data are used in the development of coal devolatilization and char reaction sub-models in comprehensive combustion models. The means for integrating the chemical data into the combustion code will be described.

Surface and Pore Properties of ANL and PETC Coals

Bartholomew, C.H.; White, W.E.; Thornock, D.; Wells, W.F.; Hecker, W.C.; Smoot, L.D.; Smith, D.M. and Williams, F.L.
Preprint ACS Fuels Chem. Divl., 1988, Los Angeles. 9 pgs. Funded by ACERC (National Science Foundation and Associates and Affiliates).

Surface areas, pore volumes, pore size distributions, and solid densities were measured for three ANL coals (Pittsburgh No. 8, Wyodak, and Beulah Zap Lignite), two PETC coals (Lower Wilcox, and Dietz) and a Utah Scofield coal and for chars derived from these coals. Surface areas were measured using nitrogen and carbon dioxide adsorptions; pore volumes were determined using nitrogen adsorption, mercury porosimetry, and NMR spin-lattice relaxation measurements of samples saturated with water. Solid densities were obtained using helium displacement. The results indicated that chars have larger surface areas and pores relative to coals; large fractions of the internal surfaces of coals are not penetrated by nitrogen molecules but are penetrated by carbon dioxide suggesting that the pores are mostly smaller than 1 NM

 

Char Preparation Facility

Merrill, R.; Bartholomew, C.H. and Hecker, W.C.
ACERC Report, 1987. Funded by ACERC (National Science Foundation and Associates and Affiliates).

During summer 1987 a facility for preparation of coal chars was designed and constructed in a cooperative effort of the catalysis and combustion laboratories. The system devolatilizes coal particles fed up through a flat-flame burner after which they are collected on a water-cooled, gas-quenched probe. The system has been successfully tested in the preparation of a char from a Texas lignite coal. The system is capable of producing about 5-10 g/hr of high-temperature char.

Advanced Combustion Modeling at ACERC

Bartholomew, C.H.
National AICHE Meeting, 1987, New York City. Funded by ACERC (National Science Foundation and Associates and Affiliates), and US Department of Energy.

Basic and high technology industries are highly reliant upon an adequate supply of high-quality energy, the production of which depends upon combustion technology. The Advanced Combustion Engineering Research Center (ACERC) at Brigham Young University and the University of Utah conducts fundamental and experimental research leading to the development of advanced combustion technology. The new Center involves the cooperative efforts of two national laboratories, 24 industrial/research organizations located through the nation and two universities. Funding is provided by NSF, DOE, the State of Utah, 24 companies/laboratories, and the two universities. The principal objective of ACERC is to develop and implement advanced computer-aided design methods in combustion-related industry, with the emphasis on clean and efficient use of low-grade fuels. The approach is to integrate kinetic and mechanistic data, physical/chemical-fuels property data, and process-performance characteristics into comprehensive state-of-the-art computer models for use in the simulation, design and optimization of advanced combustion systems. The underlying philosophy is that a fundamental system approach applied to a few carefully selected systems can have wide application to many important combustion problems. Products of the Center include (1) new computer-aided-design combustion technology, (2) new understanding of combustion mechanisms and their relation to fuel properties, and (3) students educated in a fundamental of combustion engineering who can solve a wide range of problems. The heart of the Center's research program consists of 21 research projects at Brigham Young University and the University of Utah which are focused into six thrust areas: (1) comprehensive model development, (2) fuel characterization and reaction mechanisms, (3) fuel minerals, fouling, and slagging, (4) mechanisms of pollutant formation and hazardous-waste incineration, (5) process characterization/model evaluation, and (6) advanced combustion concepts. Examples of ongoing projects include NMR, mass spectrometry, and chromatographic studies of the products of coal devolatilization; reactor and surface studies of chars; development of pollutant submodels for sulfur dioxide removal by dry sorbent injection; development of a comprehensive 3D model for pulverized coal combustion; and CARS laser studies of pulverized coal combustion. Basic features of the presently used 2D model and plans for development of a new 3D model are discussed.

 

Fuel Characteristics and Reaction Mechanisms

Lee, M.L.; Bartholomew, C.H. and Hecker, W.C.
ERC Symposium, Annual ASEE Meeting, 1987, Reno, Nevada. Funded by ACERC (National Science Foundation and Associates and Affiliates).

The main goal of the Advanced Combustion Engineering Research Center is the development and implementation of advanced combustion models. The Center research is organized around six major thrust areas focused on the clean and efficient use of low-grade fuels such as coal. These thrust areas will provide data on kinetics, fuel properties, and process-performance design characteristics that will be integrated into a comprehensive computer model used in the design and optimization of advanced combustion systems. This paper deals with the work in the fuel characterization and reaction mechanisms thrust area.

The research project in the fuel characteristics and reaction mechanisms thrust area are focused on relating the kinetic rates and mechanisms of rapid coal devolatilization and char reactivity with the physical and chemical structure of coal and pyrolysis tars and chars. This paper summarizes the results from four integrated research programs in this thrust area.

Supercritical solvent extraction is employed to determine the amount and nature of hydrocarbons that are physically absorbed or only weakly bound within the coal structure and are expected to be liberated early in the devolatilization process. Both paraffin (n-alkanes, isoprenoids, and pentacyclic triterpanes) and polycyclic aromatic (two to five fused aromatic rings) hydrocarbons have been identified. Pyrolysis mass spectroscopy provides both rate data and pyrolysis tar data on coals during slow devolatilization. The physical properties (surface area and pore size distribution) of the parent coals and pyrolysis chars are studied in order to relate these properties to coal and char reaction rates. Advanced solid-state NMR techniques are used to obtain the carbon skeletal structure of the parent coals and pyrolysis chars. High field, high-resolution NMR spectroscopy experiments provide data on the structural features of the pyrolysis tars.

The experiments in this thrust area are carried out on a common set of standard coals. The devolatilization studies to be initially carried out in collaboration with other laboratories will be summarized. A description will be provided for the analysis and integration of the various experimental data. These data are used in the development of coal devolatilization and char reaction sub-models in comprehensive combustion models. The means for integrating the chemical data into the combustion code will be described.