Maswadeh, W
1994
Devolatilization Studies of Single Coal Properties at High Heating Rates
Maswadeh, W.
Devolatilization Studies of Single Coal Properties at High Heating Rates, Ph.D./U of U, January 1994. Advisor: Meuzelaar
1993
Development of a Laser Devolatilization Gas Chromatography/Mass Spectrometry Technique for Single Coal Particles
Maswadeh, W.; Arnold, N.S.; McClennen, W.H.; Tripathi, A.; DuBow, J. and Meuzelaar, H.L.C.
Energy & Fuels, 7 (6):1006-1012, 1993. Funded by ACERC.
A CO2 laser Py-GC/MS system capable of identifying substantial numbers of pyrolysis products from single coal particles in the 50-15-µm range is reported. Also, a specially designed two-wavelength radiation thermometer module with integral video microscope produces reliable temperature/time profiles of single coal particles during rapid laser heating. A novel microbeam footprint technique using thin quartz wafers in combination with videomicroscopy greatly facilitates laser beam focusing and alignment operations. Comparison of an EDB type particle levitator with an EM grid type particle support system reveals considerable advantages of the EM grid approach with regard to tar collection efficiency, particle position stability, particle visualization, and recoverability of residual char particles. However, possible cooling effects of the grid on highly thermoplastic particles require further study. The feasibility of simulating PCC conditions with regard to heating rates and final particle temperatures is demonstrated with complete devolatilization of 100 µm diameter particle being observed within 10 ms. The nature and relative abundance of major pyrolysis products observed at typical laser heating rates (>=105 K/s) are found to be closely similar to those observed with Curie-point pyrolysis techniques at heating rates in the 10²-10³ K/s range. Spherocarb particles of approximately 102-µm diameter, e.g., impregnated with suitable coal tar compounds are shown to provide useful model samples for system optimization and calibration purposes.
High Speed, Two-Wavelength Radiation Thermometry of Single Micro Particles During CO2 Laser Heating
Maswadeh, W.; Tripathi, A.; Arnold, N.S.; DuBow, J. and Meuzelaar, H.L.C.
Journal of Analytical and Appl. Pyrolysis, 1993 (in press). Funded by ACERC.
A high speed, two-wavelength radiation thermometer that is capable of monitoring the surface temperature of 50-150 µm diameter particles in the 600-2000 K range at heating rates of up to 106 K/s, characteristic of pulverized coal combustion, was designed and constructed. To meet the above characteristics, special attention was paid to detector wavelength range and speed, detection electronics and optical system alignment. The thermometer was calibrated using an in-house constructed, black cavity radiation source. Spherocarb model particles, which have a more uniform size; physical properties and emissivity than coal particles, were used to demonstrate the level of short-term reproducibility attainable. Consistent, reproducible temperature-time profiles obtained for particles from different coals indicate that non-grey effects do not dominate these measurements.
Investigation of Physical Control Mechanisms in the Thermal Decomposition of Coal by Means of On-Line Mass Spectrometric Techniques
Nie, X.; Lui, K.; Maswadeh, W.; Tripathi, A. and Meuzelaar, H.L.C.
Proceedings ACS Conference Fuel Chem. Division, ACS Preprints, Fuel Chem. Div., 1993 (in press). Funded by ACERC.
During the past decade marked progress has been made with regard to our understanding of the chemical processes occurring during the thermal degradation ("devolatilization," "desorption + pyrolysis") of coal and several advanced mechanistic models offering a qualitative and quantitative description of these processes, e.g., FG-DVC and CPD models, are now available. By contrast, there appears to be a comparative lack of progress in the description and understanding of the physical processes involved. It is becoming increasingly clear that the frequent lack of interlaboratory reproducibility almost invariably originates within the physical parameters of the experiment. Although heating rate, particle size and reactor pressure have long been recognized as the dominant physical parameters influencing the rates and product yields of coal devolatilization processes, current models pay little or no attention to heat and mass transport limitations. In fact, particle size is not an input parameter in these models. Furthermore, although most industrial scale coal devolatilization processes occur at near ambient pressures, current renewed interest in high pressure coal conversion processes would seem to dictate a more detailed look at the effects of pressure. The objective of the research reported here is to exploit the capabilities of two novel experimental techniques, based on the on-line coupling of microscale, TG-type reactors to mass spectrometry and combined gas chromatography/mass spectrometry systems. The TG/GC/MS technique has high-pressure TG capabilities and will be described separately at this meeting. The direct TG/MS instrument is characterized by a heated, all quartz interface and will be discussed here. The complementary nature of both systems enables us to investigate the nature and extent of physical control mechanisms over a broad range of experimental conditions.
Man-Portable GC/MS; Opportunities, Challenges, and Future Directions
Meuzelaar, H.L.C.
International Symposium Field Screening Methods for Hazardous Wastes and Toxic Chemicals, 1:35-54, Pittsburgh, PA, 1993. (also presented at the International Symposium on Field Screening Methods for Hazardous Wastes and Toxic Chemicals, Las Vegas, NV, June 1993. Funded by Hewlett Packard, US Department of Defense and ACERC.
Simultaneous advances in miniaturized mass spectrometry (MS) equipment and in field-portable gas chromatography (GC) devices have brought development of man portable GC/MS instruments within reach. Among the various levels of man portability, viz. "luggable," "wearable" or "hand-portable," the latter category is likely to remain an elusive target for GC/MS for the remainder of this millennium. Since hand-portables are unlikely to become feasible soon and "luggables" obviously leave much to be desired, "wearable" GC/MS systems would appear to constitute a logical development benchmark for the immediate future.
Our laboratory has described a wearable, GC/MS system for air monitoring applications based on the integration of a fully automated, repetitive air sampling inlet, a short isothermal capillary GC column, a low power quadruple mass filter (modified HP MSD), a hybrid (bulk getter/ion getter) vacuum system and a PC notebook computer. The system weights 60 lbs, consumes 90 W of battery power and should run 2-3 hrs on high-density disposable batteries. Other man portable GC/MS prototype systems scheduled for completion in the near future are under development at Jet Propulsion Laboratory and at Lawrence Livermore National Laboratory. Major remaining challenges include the need for: further weight reduction; 102-103 times higher sensitivity; and improved man/machine interfaces. Possible future directions are likely to include: drone-portables; use of neural network processors; and, eventually hand-portable GC/MS systems.
1992
Structure/Reactivity Studies of Single Coal Particles at Very High Heating Rates by Laser Pyrolysis GC/MS
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.
1991
Laser Pyrolysis Gas Chromatography/Mass Spectrometry of Single Spherocarb Particles Impregnated with Bituminous and Polymeric Substances
Maswadeh, W.; Huai, H. and Meuzelaar, H.L.C.
ASC Preprints, Division of Fuel Chemistry, 36(2):733-740, 1991 (201st ACS National Meeting, Atlanta, GA, April 1991). Funded by ACERC.
A major bottleneck in the development of novel coal characterization methods, such as laser pyrolysis GC/MS, capable of analyzing individual coal particles, is the unavailability of suitable standard samples. Although carefully homogenized and characterized standard coals are now available through the Argonne National Laboratory Premium Coal Sample Program (ANL-PCSP) such "statistically homogenous" coal powders are of limited value as reference materials for single particle analysis methods. Even if it would be feasible to prepare particles of closely similar chemical composition and size, e.g., by using highly concentrated coal maceral fractions and careful sieving, remaining variations in shape, density, porosity or thermal conductivity could still introduce an unacceptably high level of uncertainty for most optimization and calibration purposes.
In an attempt to find model coal char particles with well-defined chemical and physical properties, e.g., for the purpose of modeling char oxidation reactions, several authors have used Spherocarb® particles. Flagan et al have even prepared spherical char particles spiked with mineral matter components in order to more closely mimic actual coal char particles. Although Spherocarb particles still show considerable variability with regard to size (rel. s.d. ~20% on a volume basis), other characteristics such as shape, density, porosity, thermal conductivity and chemical composition are assumed to be quite constant.
Unfortunately, Spherocarb particles are of little value for modeling coal devolatilization reactions due to their very low volatile matter yields. This prompted us to think of ways to increase volatile matter yields by introducing a variety of model compounds, ranging from low molecular weight, bitumen-like components to polymeric materials such as soluble lignins or resins. To the best of our knowledge this article represents the first reported use of bitumen and polymer impregnated Spherocarb particles for modeling devolatilization processes in individual coal particles.
Laser Pyrolysis GC/MS of Single Coal and Coal Model Particles
Maswadeh, W. and Meuzelaar, H.L.C.
Proceedings of the 39th ASMS Conference on Mass Spectrometry and Allied Topics, 192-193, Nashville, TN, May 1991. Funded by ACERC.
Laser pyrolysis GC/MS using an electronically pulsed cw CO2 laser focused at the center of a Paul trap type particle levitation device connected to a Paul trap type spectrometer (Finnigan MAT ITMS) by means of a short, ballistically heated capillary GC column has proved to be a valuable technique for studying the devolatilization (pyrolysis + desorption) behavior of single, 100-150 µm sized coal particles at very high heating rates (105-106 K/s).
A modified experimental set-up, has been designed in which an electrodynamic balance cell is replaced with a simple electron microscopy (EM) grid (400 mesh, 78% open) to support and stabilize particles while providing markedly improved collection efficiency for laser pyrolysis and desorption products. Comparison of the two GC/MS profiles shows a high degree of qualitative similarity while illustrating the higher yield and improved signal to noise ratio of the EM grid technique. The improved signal quality is especially important for detecting and identifying minor components, reflecting subtle changes in pyrolysis mechanisms as a result of the high laser heating rate.
1990
Laser Pyrolysis-Transfer Line Chromatography/Mass Spectrometry of Single, Levitated Coal Particles
Maswadeh, W.; Arnold, N.S. and Meuzelaar, H.L.C.
Proc. of the 38th ASMS Conference on Mass Spectrometry and Allied Topics, Tucson, AZ, 599-600, 1990. (Also presented at Pyrolysis 90, Amsterdam, The Netherlands, 1990; ACS Joint 45th Northwest/Rocky Mountain Regional Meeting, Salt Lake City, UT, 1990; ACS Division of Fuel Chemistry and Preprints for Papers Presented at the 200th ACS National Meeting, 35 (3), 755-762, Washington, D.C., 1990). Funded by ACERC.
A laser pyrolysis transfer line gas chromatography/mass spectrometry (laser Py-TLGC/MS) system based on the combination of an electronically pulsed CW C02 laser with an electrodynamic balance (EDB), a heated capillary ("transfer line") GC column and an ion trap mass spectrometer (ITMS) was constructed.
The main purpose of the system is to study the devolatilization behavior of single, levitated coal particles at very high heating rates, e.g., 105 - 106 K/sec, while comparing the composition of the devolatilization products to those observed at much lower heating rates, e.g., 10-2 - 10-2 K/sec.
Effect of Mineral Matter on Coal Devolatilization Kinetics
Bae, I.; Maswadeh, W.; Yun, Y.; Meuzelaar, H.L.C. and DuBow, J.
Accepted for publication in the ACS National Meeting Preprints, Boston, Massechusetts,Spring, 1990. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Coal pyrolysis is a fundamental first step in combustion processes. Yet coals exhibit a wide variation in pyrolysis behaviors. The origins of these wide variations are, for a given set of experimental conditions, both structural and compositional in nature. Because of its thermochemical and catalytic properties, mineral matter plays an important role in both the thermodynamics (product mixes, activation energies) and kinetics of coal pyrolysis. The issue is further complicated by the manner in which mineral matter is distributed in various coals. While many classifications are possible, grouping into three classics is most common. These classes are: (1) discrete minerals such as clays, oxides (basic and acidic) and sulfides; (2) organometallic matter such as ion-exchangeable cations; and (3) dispersed trace elements and compounds. A considerable body of research exists for studying equilibrium and non-equilibrium effects of the various forms of coal minerals on coal combustion.
In the present paper the mineral matter effects on coal pyrolysis are being analyzed using an approach whereby observable spectroscopic (TG/MS) differences in the pyrolytic decomposition between fresh coal and demineralized coal are reconstructed from the sum of mineral matter effects on pyrolysis arising from adding back, singly and in pairs, individual minerals in various forms.
Mineral Matter Effects in Coal Pyrolysis
Bae, I.; Anani, M.; Maswadeh, W.; Yun, Y.; Meuzelaar, H.L.C. and DuBow, J.
199th ACS National Meeting, 35 (2), 489-493, Boston, Massachusetts, 1990. Funded by ACERC.
Coal pyrolysis is a fundamental first step in combustion processes. Yet coals exhibit a wide variation in pyrolysis behaviors. The origins of these wide variations are for a given set of experimental conditions, both structural and compositional in nature. Because of its thermochemical and catalytic properties, mineral matter plays an important role in both the thermodynamics (product mixes, activation energies) and kinetics of coal pyrolysis. The issue is further complicated by the manner in which mineral matter is distributed in various coals. While many classifications are possible, grouping into three classes is most common. These classes are: (1) discrete minerals such as clays, oxides (basic and acidic) and sulfides; (2) organometallic matter such as ion-exchangeable cations; and (3) dispersed trace elements and compounds. A considerable body of research exists for studying equilibrium and non-equilibrium effects of the various forms of coal minerals on coal combustion.
In the present paper the mineral matter effects on coal pyrolysis are being analyzed using an approach whereby observable spectroscopic (TG/MS) differences in the pyrolytic decomposition between fresh coal and demineralized coal are reconstructed from the sum of mineral matter effects on pyrolysis arising from adding back, singly, and in pairs, individual minerals in various forms.
1989
Mineral Matter Effects in Coal Pyrolysis
Bae, I.; Anani, M.; Maswadeh, W.; Yun, Y.; Meuzelaar, H.L.C. and DuBow, J.
199th ACS National Meeting, 35 (2), 489-493, Boston, Massachusetts, 1990. Funded by ACERC.
Coal pyrolysis is a fundamental first step in combustion processes. Yet coals exhibit a wide variation in pyrolysis behaviors. The origins of these wide variations are for a given set of experimental conditions, both structural and compositional in nature. Because of its thermochemical and catalytic properties, mineral matter plays an important role in both the thermodynamics (product mixes, activation energies) and kinetics of coal pyrolysis. The issue is further complicated by the manner in which mineral matter is distributed in various coals. While many classifications are possible, grouping into three classes is most common. These classes are: (1) discrete minerals such as clays, oxides (basic and acidic) and sulfides; (2) organometallic matter such as ion-exchangeable cations; and (3) dispersed trace elements and compounds. A considerable body of research exists for studying equilibrium and non-equilibrium effects of the various forms of coal minerals on coal combustion.
In the present paper the mineral matter effects on coal pyrolysis are being analyzed using an approach whereby observable spectroscopic (TG/MS) differences in the pyrolytic decomposition between fresh coal and demineralized coal are reconstructed from the sum of mineral matter effects on pyrolysis arising from adding back, singly, and in pairs, individual minerals in various forms.
Laser Pyrolysis Mass Spectrometry of Single Levitated Coal Particles
Maswadeh, W.; Roberts, K.A.; McClennen, W.H.; Meuzelaar, H.L.C. and Arnold, N.S.
37th ASMS Conference on Mass Spectrometry and Allied Topics, Miami Beach, Florida, 304-305, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates), US Department of Energy, and the State of Utah.
A laser pyrolysis mass spectrometry experiment was designed to study the devolatilization behavior of individual coal particles at high heating rates (104-106 K/s), characteristic of pulverized coal combustion reactors. The experimental set-up consists of an electrostatic particle levitation cell, also known as an "electrodynamic balance", a 50 W cw CO2 laser and a Finnigan-MAT ITMS system. The particle levitation cell was constructed by modifying a regular ion trap electrode assembly in such a way as to provide line-of-sight access to the center of the cell for the CO2 laser beam as well as for visual observation by means of a stereo microscope. Typical cell operating parameters for levitating a 120 mm dia. Spherocarb particle are: ring electrode 3000 V (60 Hz ac), upper end-cap +100 V dc, lower end-cap -100 V dc. The CO2 laser (Apollo 3050 OEM) is capable of electronic pulsed beam operation. The 8 mm dia. beam is split equally into 2 opposing beams focused at the center of the levitation cell (beam waist ca. 400 um, power density ca. 4-10 MW/m2), as a co-linear parfocal HeNe laser beam permits positioning the levitated particle in the optical and electrical center of the cell. Two IR detectors measure the integrated pulse and time-resolved pulse energy.
A heated transfer line column (2m x .18 mm DB5) equipped with a special air sampling inlet enables intermittent sampling of volatiles from the center of the levitation cell into the ITMS vacuum system. Feasibility studies were performed on 120-150 mm Spherocarb particles impregnated with an alkylnaphthalenes mixture and heated with a single 10 ms CO2 laser pulse. Ample signal intensities were obtained with the first laser pulse to permit the recording of "transfer line" GC/MS profiles. By contrast, the second laser pulse produced <10% of the volatiles observed from the first pulse, thereby demonstrating nearly complete devolatilization of the impregnated particle by a single laser pulse.
Finally, a series of experiments was performed with actual coal particles in the 100-130 mm size range, prepared by careful sieving of two coals from the Argonne National Laboratory Premium Coal Sample bank, namely a Pittsburgh #8 seam (Illinois) coal and a Blind Canyon seam (Utah) coal of comparable rank. From previous studies of Pitt. #8 coal using time-resolved Curie-point pyrolysis, pyrolysis temperatures necessary to produce these phenolic building blocks at heating rates of 105 K/sec are estimated to be ca. 900 K. Of course, kinetic parameters obtained at the much lower heating rates of the Curie-point pyrolysis MS experiment (approx. 102 K/s) may only be extrapolated to the laser pyrolysis experiment if the underlying reaction mechanisms are comparable. Evidence supporting this assumption is presented showing similar C1 and C2-alkyl phenol profiles for the Pitt. #8 coal obtained by Curie-point pyrolysis GC/MS using a 15 m fused silica capillary with temperature programming.
Development of a Mobile Ion Trap Mass Spectrometer for Environmental Monitoring
Meuzelaar, H.L.C.; McClennen, W.H.; Arnold, N.S.; Maswadeh, W.; Reynolds, T.K.; Urban, D.T. and Jones, P.R.
Proc. 37th ASMS Conference on Mass Spectrometry and Allied Topics, Miami Beach, Florida, 1424-1426, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, US Department of Energy, the Department of Defense Chemical Research Development and Engineering Center and Finnigan-MAT Corp.
The objective of the work reported here is to develop a compact, mobile mass spectrometer with EI, CI and MSn capabilities. Moreover, the mobile MS system should be capable of analyzing gases, vapors and aerosols in air at low ppb levels while allowing positive identification of individual components in complex mixtures. In view of the size and weight restrictions inherent in the mobility requirement, a special miniaturized version of the Finnigan MAT Ion Trap Mass Spectrometer (ITMS?) was constructed in close collaboration with the manufacturer. This MINITMASS Miniaturized Ion Trap Mass Spectrometer) system is equipped with automatic gain control, automatic reaction control, selective mass storage and axial modulation options, in addition to the required EI/CI and MSn operating modes. The 2x2x2 ft MINITMASS module is mounted within a 6 ft high mobile rack together with all gas supplies, pumps, inlet controls and a PC 80386 workstation. The entire system requires approx. 1000 W of ac power. A 6x7x8 ft, self-contained mobile laboratory module, which fits on a standard 3/4 ton pick-up truck, enables operation of the MINITMASS in remote locations and rugged terrain. Also, the MINITMASS system can be remotely controlled from a distance up to several miles using a second PC workstation, and Carbon Copy© software. A direct air-sampling inlet enables repetitive collection of 10-50 microliter air samples at 15-60 sec intervals. Use of "transfer line chromatography" provides additional resolution and specificity for complex mixtures. Minimum detectable levels of gases and vapors in air are in the low to medium ppb range without the use of concentration devices. Alternatively, a special automated inlet enables electrostatic precipitation of air particulate matter on a ferromagnetic filament with subsequent analysis by Curie-point pyrolysis (GC)/MSn. The system has been successfully operated in the desert (at temperatures up to 100 F), as well as under a variety of indoor conditions, e.g., for monitoring laboratory-scale combustion reactors.
A Mobile, Tandem Ion Trap Mass Spectrometer System for Environmental Monitoring of Vapors
Arnold, N.S.; McClennen, W.H.; Maswadeh, W.; Urban, D.T.; Reynolds, T.K.; Jones, P.R. and Meuzelaar, H.L.C.
Proceedings of the 1989 U.S. Army Chemical Research Development and Engineering Center Scientific Conference on Chemical Defense Research, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, US Department of Energy, the Department of Defense Chemical Research Development and Engineering Center, Geocenter, Inc. and Finnigan-MAT Corp.
A fieldable, Miniaturized Ion Trap Mass Spectrometer (MINITMASS) was constructed for tandem mass spectrometry of environmental vapors. Furthermore, a vapor sampling inlet for transfer line gas chromatography/mass spectrometry was developed which permits direct on-column introduction of atmospheric vapor samples. The transfer line gas chromatography/tandem mass spectrometry combination provided for direct introduction of complex vapor samples with short overall analysis times for on-line monitoring of changing environmental conditions. Work to date has shown the capability for low ppb analysis of substituted aromatic hydrocarbons, corresponding to subpicogram quantities per compound, in MS as well as MS/MS mode.
Development and Testing of a Mobile Tandem Mass Spectrometer for Monitoring Gases, Vapors, and Aerosols
Meuzelaar, H.L.C.; Arnold, N.S.; McClennen, W.H. and Maswadeh, W.
Conference on Environmental Chemistry, Jeckyll Island, Georgia, 1989. Funded by ACERC (National Science Foundation Associates and Affiliates), the State of Utah, US Department of Energy, the Department of Defense Chemical Research Development and Engineering Center, Geocenter, Inc. and Finnigan-MAT Corp.
Recent advances in Ion Trap/Mass Spectrometry (ITMS) technology now enable the assembly of compact ITMS systems with Chemical Ionization (CI) as well as tandem MS (MSn) capabilities. In combination with the proven high sensitivity (full spectra have been recorded on less than 1 pg of sample) and the favorable vacuum characteristics, ITMS devices appear especially well suited for a variety of environmental monitoring tasks.
Based on these assessments, we undertook the development of a mobile Miniaturized Ion Trap Mass Spectrometer (MINITMASS) equipped with specialized air sampling inlets for gases/vapors as well as for aerosols. Both inlet systems employ the so-called transfer line chromatography (TLGC) approach in order to increase specificity and minimize exposure of transfer line, ion source and electron multiplier to oxygen.
Gases and vapors are sampled as 1-2 sec wide air "pulses" at 15-60 second intervals depending on the degree of chromatographic separation required. Minimum detectable concentration levels were found in the low to medium ppb range. The aerosol inlet uses electrostatic precipitation of aerosol particles (0.5-5 um range) on a ferromagnetic filament. After a preselected collection period (e.g., 1-10 minutes) the filament is automatically inserted into a Curie-point pyrolysis reactor with subsequent production of the pyrolysis GC/MS patterns of the collected aerosol particles.
Thus far, the system has been tested with synthetic polymers, biopolymers and bacterial spores.
Maswadeh, W
1994
Devolatilization Studies of Single Coal Properties at High Heating Rates
Maswadeh, W.
Devolatilization Studies of Single Coal Properties at High Heating Rates, Ph.D./U of U, January 1994. Advisor: Meuzelaar
1993
Development of a Laser Devolatilization Gas Chromatography/Mass Spectrometry Technique for Single Coal Particles
Maswadeh, W.; Arnold, N.S.; McClennen, W.H.; Tripathi, A.; DuBow, J. and Meuzelaar, H.L.C.
Energy & Fuels, 7 (6):1006-1012, 1993. Funded by ACERC.
A CO2 laser Py-GC/MS system capable of identifying substantial numbers of pyrolysis products from single coal particles in the 50-15-µm range is reported. Also, a specially designed two-wavelength radiation thermometer module with integral video microscope produces reliable temperature/time profiles of single coal particles during rapid laser heating. A novel microbeam footprint technique using thin quartz wafers in combination with videomicroscopy greatly facilitates laser beam focusing and alignment operations. Comparison of an EDB type particle levitator with an EM grid type particle support system reveals considerable advantages of the EM grid approach with regard to tar collection efficiency, particle position stability, particle visualization, and recoverability of residual char particles. However, possible cooling effects of the grid on highly thermoplastic particles require further study. The feasibility of simulating PCC conditions with regard to heating rates and final particle temperatures is demonstrated with complete devolatilization of 100 µm diameter particle being observed within 10 ms. The nature and relative abundance of major pyrolysis products observed at typical laser heating rates (>=105 K/s) are found to be closely similar to those observed with Curie-point pyrolysis techniques at heating rates in the 10²-10³ K/s range. Spherocarb particles of approximately 102-µm diameter, e.g., impregnated with suitable coal tar compounds are shown to provide useful model samples for system optimization and calibration purposes.
High Speed, Two-Wavelength Radiation Thermometry of Single Micro Particles During CO2 Laser Heating
Maswadeh, W.; Tripathi, A.; Arnold, N.S.; DuBow, J. and Meuzelaar, H.L.C.
Journal of Analytical and Appl. Pyrolysis, 1993 (in press). Funded by ACERC.
A high speed, two-wavelength radiation thermometer that is capable of monitoring the surface temperature of 50-150 µm diameter particles in the 600-2000 K range at heating rates of up to 106 K/s, characteristic of pulverized coal combustion, was designed and constructed. To meet the above characteristics, special attention was paid to detector wavelength range and speed, detection electronics and optical system alignment. The thermometer was calibrated using an in-house constructed, black cavity radiation source. Spherocarb model particles, which have a more uniform size; physical properties and emissivity than coal particles, were used to demonstrate the level of short-term reproducibility attainable. Consistent, reproducible temperature-time profiles obtained for particles from different coals indicate that non-grey effects do not dominate these measurements.
Investigation of Physical Control Mechanisms in the Thermal Decomposition of Coal by Means of On-Line Mass Spectrometric Techniques
Nie, X.; Lui, K.; Maswadeh, W.; Tripathi, A. and Meuzelaar, H.L.C.
Proceedings ACS Conference Fuel Chem. Division, ACS Preprints, Fuel Chem. Div., 1993 (in press). Funded by ACERC.
During the past decade marked progress has been made with regard to our understanding of the chemical processes occurring during the thermal degradation ("devolatilization," "desorption + pyrolysis") of coal and several advanced mechanistic models offering a qualitative and quantitative description of these processes, e.g., FG-DVC and CPD models, are now available. By contrast, there appears to be a comparative lack of progress in the description and understanding of the physical processes involved. It is becoming increasingly clear that the frequent lack of interlaboratory reproducibility almost invariably originates within the physical parameters of the experiment. Although heating rate, particle size and reactor pressure have long been recognized as the dominant physical parameters influencing the rates and product yields of coal devolatilization processes, current models pay little or no attention to heat and mass transport limitations. In fact, particle size is not an input parameter in these models. Furthermore, although most industrial scale coal devolatilization processes occur at near ambient pressures, current renewed interest in high pressure coal conversion processes would seem to dictate a more detailed look at the effects of pressure. The objective of the research reported here is to exploit the capabilities of two novel experimental techniques, based on the on-line coupling of microscale, TG-type reactors to mass spectrometry and combined gas chromatography/mass spectrometry systems. The TG/GC/MS technique has high-pressure TG capabilities and will be described separately at this meeting. The direct TG/MS instrument is characterized by a heated, all quartz interface and will be discussed here. The complementary nature of both systems enables us to investigate the nature and extent of physical control mechanisms over a broad range of experimental conditions.
Man-Portable GC/MS; Opportunities, Challenges, and Future Directions
Meuzelaar, H.L.C.
International Symposium Field Screening Methods for Hazardous Wastes and Toxic Chemicals, 1:35-54, Pittsburgh, PA, 1993. (also presented at the International Symposium on Field Screening Methods for Hazardous Wastes and Toxic Chemicals, Las Vegas, NV, June 1993. Funded by Hewlett Packard, US Department of Defense and ACERC.
Simultaneous advances in miniaturized mass spectrometry (MS) equipment and in field-portable gas chromatography (GC) devices have brought development of man portable GC/MS instruments within reach. Among the various levels of man portability, viz. "luggable," "wearable" or "hand-portable," the latter category is likely to remain an elusive target for GC/MS for the remainder of this millennium. Since hand-portables are unlikely to become feasible soon and "luggables" obviously leave much to be desired, "wearable" GC/MS systems would appear to constitute a logical development benchmark for the immediate future.
Our laboratory has described a wearable, GC/MS system for air monitoring applications based on the integration of a fully automated, repetitive air sampling inlet, a short isothermal capillary GC column, a low power quadruple mass filter (modified HP MSD), a hybrid (bulk getter/ion getter) vacuum system and a PC notebook computer. The system weights 60 lbs, consumes 90 W of battery power and should run 2-3 hrs on high-density disposable batteries. Other man portable GC/MS prototype systems scheduled for completion in the near future are under development at Jet Propulsion Laboratory and at Lawrence Livermore National Laboratory. Major remaining challenges include the need for: further weight reduction; 102-103 times higher sensitivity; and improved man/machine interfaces. Possible future directions are likely to include: drone-portables; use of neural network processors; and, eventually hand-portable GC/MS systems.
1992
Structure/Reactivity Studies of Single Coal Particles at Very High Heating Rates by Laser Pyrolysis GC/MS
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.
1991
Laser Pyrolysis Gas Chromatography/Mass Spectrometry of Single Spherocarb Particles Impregnated with Bituminous and Polymeric Substances
Maswadeh, W.; Huai, H. and Meuzelaar, H.L.C.
ASC Preprints, Division of Fuel Chemistry, 36(2):733-740, 1991 (201st ACS National Meeting, Atlanta, GA, April 1991). Funded by ACERC.
A major bottleneck in the development of novel coal characterization methods, such as laser pyrolysis GC/MS, capable of analyzing individual coal particles, is the unavailability of suitable standard samples. Although carefully homogenized and characterized standard coals are now available through the Argonne National Laboratory Premium Coal Sample Program (ANL-PCSP) such "statistically homogenous" coal powders are of limited value as reference materials for single particle analysis methods. Even if it would be feasible to prepare particles of closely similar chemical composition and size, e.g., by using highly concentrated coal maceral fractions and careful sieving, remaining variations in shape, density, porosity or thermal conductivity could still introduce an unacceptably high level of uncertainty for most optimization and calibration purposes.
In an attempt to find model coal char particles with well-defined chemical and physical properties, e.g., for the purpose of modeling char oxidation reactions, several authors have used Spherocarb® particles. Flagan et al have even prepared spherical char particles spiked with mineral matter components in order to more closely mimic actual coal char particles. Although Spherocarb particles still show considerable variability with regard to size (rel. s.d. ~20% on a volume basis), other characteristics such as shape, density, porosity, thermal conductivity and chemical composition are assumed to be quite constant.
Unfortunately, Spherocarb particles are of little value for modeling coal devolatilization reactions due to their very low volatile matter yields. This prompted us to think of ways to increase volatile matter yields by introducing a variety of model compounds, ranging from low molecular weight, bitumen-like components to polymeric materials such as soluble lignins or resins. To the best of our knowledge this article represents the first reported use of bitumen and polymer impregnated Spherocarb particles for modeling devolatilization processes in individual coal particles.
Laser Pyrolysis GC/MS of Single Coal and Coal Model Particles
Maswadeh, W. and Meuzelaar, H.L.C.
Proceedings of the 39th ASMS Conference on Mass Spectrometry and Allied Topics, 192-193, Nashville, TN, May 1991. Funded by ACERC.
Laser pyrolysis GC/MS using an electronically pulsed cw CO2 laser focused at the center of a Paul trap type particle levitation device connected to a Paul trap type spectrometer (Finnigan MAT ITMS) by means of a short, ballistically heated capillary GC column has proved to be a valuable technique for studying the devolatilization (pyrolysis + desorption) behavior of single, 100-150 µm sized coal particles at very high heating rates (105-106 K/s).
A modified experimental set-up, has been designed in which an electrodynamic balance cell is replaced with a simple electron microscopy (EM) grid (400 mesh, 78% open) to support and stabilize particles while providing markedly improved collection efficiency for laser pyrolysis and desorption products. Comparison of the two GC/MS profiles shows a high degree of qualitative similarity while illustrating the higher yield and improved signal to noise ratio of the EM grid technique. The improved signal quality is especially important for detecting and identifying minor components, reflecting subtle changes in pyrolysis mechanisms as a result of the high laser heating rate.
1990
Laser Pyrolysis-Transfer Line Chromatography/Mass Spectrometry of Single, Levitated Coal Particles
Maswadeh, W.; Arnold, N.S. and Meuzelaar, H.L.C.
Proc. of the 38th ASMS Conference on Mass Spectrometry and Allied Topics, Tucson, AZ, 599-600, 1990. (Also presented at Pyrolysis 90, Amsterdam, The Netherlands, 1990; ACS Joint 45th Northwest/Rocky Mountain Regional Meeting, Salt Lake City, UT, 1990; ACS Division of Fuel Chemistry and Preprints for Papers Presented at the 200th ACS National Meeting, 35 (3), 755-762, Washington, D.C., 1990). Funded by ACERC.
A laser pyrolysis transfer line gas chromatography/mass spectrometry (laser Py-TLGC/MS) system based on the combination of an electronically pulsed CW C02 laser with an electrodynamic balance (EDB), a heated capillary ("transfer line") GC column and an ion trap mass spectrometer (ITMS) was constructed.
The main purpose of the system is to study the devolatilization behavior of single, levitated coal particles at very high heating rates, e.g., 105 - 106 K/sec, while comparing the composition of the devolatilization products to those observed at much lower heating rates, e.g., 10-2 - 10-2 K/sec.
Effect of Mineral Matter on Coal Devolatilization Kinetics
Bae, I.; Maswadeh, W.; Yun, Y.; Meuzelaar, H.L.C. and DuBow, J.
Accepted for publication in the ACS National Meeting Preprints, Boston, Massechusetts,Spring, 1990. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Coal pyrolysis is a fundamental first step in combustion processes. Yet coals exhibit a wide variation in pyrolysis behaviors. The origins of these wide variations are, for a given set of experimental conditions, both structural and compositional in nature. Because of its thermochemical and catalytic properties, mineral matter plays an important role in both the thermodynamics (product mixes, activation energies) and kinetics of coal pyrolysis. The issue is further complicated by the manner in which mineral matter is distributed in various coals. While many classifications are possible, grouping into three classics is most common. These classes are: (1) discrete minerals such as clays, oxides (basic and acidic) and sulfides; (2) organometallic matter such as ion-exchangeable cations; and (3) dispersed trace elements and compounds. A considerable body of research exists for studying equilibrium and non-equilibrium effects of the various forms of coal minerals on coal combustion.
In the present paper the mineral matter effects on coal pyrolysis are being analyzed using an approach whereby observable spectroscopic (TG/MS) differences in the pyrolytic decomposition between fresh coal and demineralized coal are reconstructed from the sum of mineral matter effects on pyrolysis arising from adding back, singly and in pairs, individual minerals in various forms.
Mineral Matter Effects in Coal Pyrolysis
Bae, I.; Anani, M.; Maswadeh, W.; Yun, Y.; Meuzelaar, H.L.C. and DuBow, J.
199th ACS National Meeting, 35 (2), 489-493, Boston, Massachusetts, 1990. Funded by ACERC.
Coal pyrolysis is a fundamental first step in combustion processes. Yet coals exhibit a wide variation in pyrolysis behaviors. The origins of these wide variations are for a given set of experimental conditions, both structural and compositional in nature. Because of its thermochemical and catalytic properties, mineral matter plays an important role in both the thermodynamics (product mixes, activation energies) and kinetics of coal pyrolysis. The issue is further complicated by the manner in which mineral matter is distributed in various coals. While many classifications are possible, grouping into three classes is most common. These classes are: (1) discrete minerals such as clays, oxides (basic and acidic) and sulfides; (2) organometallic matter such as ion-exchangeable cations; and (3) dispersed trace elements and compounds. A considerable body of research exists for studying equilibrium and non-equilibrium effects of the various forms of coal minerals on coal combustion.
In the present paper the mineral matter effects on coal pyrolysis are being analyzed using an approach whereby observable spectroscopic (TG/MS) differences in the pyrolytic decomposition between fresh coal and demineralized coal are reconstructed from the sum of mineral matter effects on pyrolysis arising from adding back, singly, and in pairs, individual minerals in various forms.
1989
Mineral Matter Effects in Coal Pyrolysis
Bae, I.; Anani, M.; Maswadeh, W.; Yun, Y.; Meuzelaar, H.L.C. and DuBow, J.
199th ACS National Meeting, 35 (2), 489-493, Boston, Massachusetts, 1990. Funded by ACERC.
Coal pyrolysis is a fundamental first step in combustion processes. Yet coals exhibit a wide variation in pyrolysis behaviors. The origins of these wide variations are for a given set of experimental conditions, both structural and compositional in nature. Because of its thermochemical and catalytic properties, mineral matter plays an important role in both the thermodynamics (product mixes, activation energies) and kinetics of coal pyrolysis. The issue is further complicated by the manner in which mineral matter is distributed in various coals. While many classifications are possible, grouping into three classes is most common. These classes are: (1) discrete minerals such as clays, oxides (basic and acidic) and sulfides; (2) organometallic matter such as ion-exchangeable cations; and (3) dispersed trace elements and compounds. A considerable body of research exists for studying equilibrium and non-equilibrium effects of the various forms of coal minerals on coal combustion.
In the present paper the mineral matter effects on coal pyrolysis are being analyzed using an approach whereby observable spectroscopic (TG/MS) differences in the pyrolytic decomposition between fresh coal and demineralized coal are reconstructed from the sum of mineral matter effects on pyrolysis arising from adding back, singly, and in pairs, individual minerals in various forms.
Laser Pyrolysis Mass Spectrometry of Single Levitated Coal Particles
Maswadeh, W.; Roberts, K.A.; McClennen, W.H.; Meuzelaar, H.L.C. and Arnold, N.S.
37th ASMS Conference on Mass Spectrometry and Allied Topics, Miami Beach, Florida, 304-305, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates), US Department of Energy, and the State of Utah.
A laser pyrolysis mass spectrometry experiment was designed to study the devolatilization behavior of individual coal particles at high heating rates (104-106 K/s), characteristic of pulverized coal combustion reactors. The experimental set-up consists of an electrostatic particle levitation cell, also known as an "electrodynamic balance", a 50 W cw CO2 laser and a Finnigan-MAT ITMS system. The particle levitation cell was constructed by modifying a regular ion trap electrode assembly in such a way as to provide line-of-sight access to the center of the cell for the CO2 laser beam as well as for visual observation by means of a stereo microscope. Typical cell operating parameters for levitating a 120 mm dia. Spherocarb particle are: ring electrode 3000 V (60 Hz ac), upper end-cap +100 V dc, lower end-cap -100 V dc. The CO2 laser (Apollo 3050 OEM) is capable of electronic pulsed beam operation. The 8 mm dia. beam is split equally into 2 opposing beams focused at the center of the levitation cell (beam waist ca. 400 um, power density ca. 4-10 MW/m2), as a co-linear parfocal HeNe laser beam permits positioning the levitated particle in the optical and electrical center of the cell. Two IR detectors measure the integrated pulse and time-resolved pulse energy.
A heated transfer line column (2m x .18 mm DB5) equipped with a special air sampling inlet enables intermittent sampling of volatiles from the center of the levitation cell into the ITMS vacuum system. Feasibility studies were performed on 120-150 mm Spherocarb particles impregnated with an alkylnaphthalenes mixture and heated with a single 10 ms CO2 laser pulse. Ample signal intensities were obtained with the first laser pulse to permit the recording of "transfer line" GC/MS profiles. By contrast, the second laser pulse produced <10% of the volatiles observed from the first pulse, thereby demonstrating nearly complete devolatilization of the impregnated particle by a single laser pulse.
Finally, a series of experiments was performed with actual coal particles in the 100-130 mm size range, prepared by careful sieving of two coals from the Argonne National Laboratory Premium Coal Sample bank, namely a Pittsburgh #8 seam (Illinois) coal and a Blind Canyon seam (Utah) coal of comparable rank. From previous studies of Pitt. #8 coal using time-resolved Curie-point pyrolysis, pyrolysis temperatures necessary to produce these phenolic building blocks at heating rates of 105 K/sec are estimated to be ca. 900 K. Of course, kinetic parameters obtained at the much lower heating rates of the Curie-point pyrolysis MS experiment (approx. 102 K/s) may only be extrapolated to the laser pyrolysis experiment if the underlying reaction mechanisms are comparable. Evidence supporting this assumption is presented showing similar C1 and C2-alkyl phenol profiles for the Pitt. #8 coal obtained by Curie-point pyrolysis GC/MS using a 15 m fused silica capillary with temperature programming.
Development of a Mobile Ion Trap Mass Spectrometer for Environmental Monitoring
Meuzelaar, H.L.C.; McClennen, W.H.; Arnold, N.S.; Maswadeh, W.; Reynolds, T.K.; Urban, D.T. and Jones, P.R.
Proc. 37th ASMS Conference on Mass Spectrometry and Allied Topics, Miami Beach, Florida, 1424-1426, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, US Department of Energy, the Department of Defense Chemical Research Development and Engineering Center and Finnigan-MAT Corp.
The objective of the work reported here is to develop a compact, mobile mass spectrometer with EI, CI and MSn capabilities. Moreover, the mobile MS system should be capable of analyzing gases, vapors and aerosols in air at low ppb levels while allowing positive identification of individual components in complex mixtures. In view of the size and weight restrictions inherent in the mobility requirement, a special miniaturized version of the Finnigan MAT Ion Trap Mass Spectrometer (ITMS?) was constructed in close collaboration with the manufacturer. This MINITMASS Miniaturized Ion Trap Mass Spectrometer) system is equipped with automatic gain control, automatic reaction control, selective mass storage and axial modulation options, in addition to the required EI/CI and MSn operating modes. The 2x2x2 ft MINITMASS module is mounted within a 6 ft high mobile rack together with all gas supplies, pumps, inlet controls and a PC 80386 workstation. The entire system requires approx. 1000 W of ac power. A 6x7x8 ft, self-contained mobile laboratory module, which fits on a standard 3/4 ton pick-up truck, enables operation of the MINITMASS in remote locations and rugged terrain. Also, the MINITMASS system can be remotely controlled from a distance up to several miles using a second PC workstation, and Carbon Copy© software. A direct air-sampling inlet enables repetitive collection of 10-50 microliter air samples at 15-60 sec intervals. Use of "transfer line chromatography" provides additional resolution and specificity for complex mixtures. Minimum detectable levels of gases and vapors in air are in the low to medium ppb range without the use of concentration devices. Alternatively, a special automated inlet enables electrostatic precipitation of air particulate matter on a ferromagnetic filament with subsequent analysis by Curie-point pyrolysis (GC)/MSn. The system has been successfully operated in the desert (at temperatures up to 100 F), as well as under a variety of indoor conditions, e.g., for monitoring laboratory-scale combustion reactors.
A Mobile, Tandem Ion Trap Mass Spectrometer System for Environmental Monitoring of Vapors
Arnold, N.S.; McClennen, W.H.; Maswadeh, W.; Urban, D.T.; Reynolds, T.K.; Jones, P.R. and Meuzelaar, H.L.C.
Proceedings of the 1989 U.S. Army Chemical Research Development and Engineering Center Scientific Conference on Chemical Defense Research, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, US Department of Energy, the Department of Defense Chemical Research Development and Engineering Center, Geocenter, Inc. and Finnigan-MAT Corp.
A fieldable, Miniaturized Ion Trap Mass Spectrometer (MINITMASS) was constructed for tandem mass spectrometry of environmental vapors. Furthermore, a vapor sampling inlet for transfer line gas chromatography/mass spectrometry was developed which permits direct on-column introduction of atmospheric vapor samples. The transfer line gas chromatography/tandem mass spectrometry combination provided for direct introduction of complex vapor samples with short overall analysis times for on-line monitoring of changing environmental conditions. Work to date has shown the capability for low ppb analysis of substituted aromatic hydrocarbons, corresponding to subpicogram quantities per compound, in MS as well as MS/MS mode.
Development and Testing of a Mobile Tandem Mass Spectrometer for Monitoring Gases, Vapors, and Aerosols
Meuzelaar, H.L.C.; Arnold, N.S.; McClennen, W.H. and Maswadeh, W.
Conference on Environmental Chemistry, Jeckyll Island, Georgia, 1989. Funded by ACERC (National Science Foundation Associates and Affiliates), the State of Utah, US Department of Energy, the Department of Defense Chemical Research Development and Engineering Center, Geocenter, Inc. and Finnigan-MAT Corp.
Recent advances in Ion Trap/Mass Spectrometry (ITMS) technology now enable the assembly of compact ITMS systems with Chemical Ionization (CI) as well as tandem MS (MSn) capabilities. In combination with the proven high sensitivity (full spectra have been recorded on less than 1 pg of sample) and the favorable vacuum characteristics, ITMS devices appear especially well suited for a variety of environmental monitoring tasks.
Based on these assessments, we undertook the development of a mobile Miniaturized Ion Trap Mass Spectrometer (MINITMASS) equipped with specialized air sampling inlets for gases/vapors as well as for aerosols. Both inlet systems employ the so-called transfer line chromatography (TLGC) approach in order to increase specificity and minimize exposure of transfer line, ion source and electron multiplier to oxygen.
Gases and vapors are sampled as 1-2 sec wide air "pulses" at 15-60 second intervals depending on the degree of chromatographic separation required. Minimum detectable concentration levels were found in the low to medium ppb range. The aerosol inlet uses electrostatic precipitation of aerosol particles (0.5-5 um range) on a ferromagnetic filament. After a preselected collection period (e.g., 1-10 minutes) the filament is automatically inserted into a Curie-point pyrolysis reactor with subsequent production of the pyrolysis GC/MS patterns of the collected aerosol particles.
Thus far, the system has been tested with synthetic polymers, biopolymers and bacterial spores.