Schulten, HR
1992
Thermochemical Analysis of US Argonne Premium Coal Samples by Time-Resolved Pyrolysis Field Ionization Mass Spectrometry
Simmleit, N.; Yun, Y.; Meuzelaar, H.L.C. and Schulten, H.R.
Chapter 13, Advances in Coal Spectroscopy, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1992. Funded by Pittsburgh Energy Technology Center/Consortium for Fossil Fuel Liquefaction, US Department of Energy and ACERC.
Analytical pyrolysis techniques are widely used for the thermochemical analysis of coals and coal-derived products. During heating, complex mixtures of chemical substances are released from coal by distillation, desorption and thermal degradation processes. The amount and chemical nature of the volatilized coal products are dependent mainly on the composition and structure of the coal and on heating conditions. Therefore, the results of chemical analyses of the volatilized coal products should provide information on the original structure of coal. For detailed on-line analysis of volatilized coal products usually chromatographic and/or spectroscopic methods have been used. For positive identification of compounds gas chromatography/mass spectrometry (GC/MS) is a common approach, e.g. in direct combination with pyrolysis techniques. However, due to the relatively long analysis times, in particular for high molecular weight products, GC/MS is not suited for a universal on-line monitoring of evolving coal products during heating. For rapid fingerprinting of volatilized coal products on a molecular basis direct MS analysis is often the preferred method. Small amounts of coal or coal-derived products are heated in front of th ionization region under high vacuum conditions. Depending on the type of mass spectrometer used and the experimental conditions, on-line monitoring of evolving coal products is possible for a wide range of heating rate. Heating rates as low as 10-2 C/s may be used in the combined thermogravimetry (TG)/MS whereas heating rates in the 104 - 106 C/s range can be obtained by CO2 laser heating.
1991
Vacuum Pyrolysis Mass Spectrometry of Pittsburgh #8 Coal; Comparison of Three Different, Time-Resolved Techniques
Yun, Y.; Meuzelaar, H.L.C.; Simmleit, N. and Schulten, H.R.
Energy & Fuels, 5:22-29, 1991. Funded by ACERC.
Three different vacuum pyrolysis mass spectrometry techniques, viz. Pyrolysis-Field Ionization Mass Spectrometry, Thermogravimetry/Low Voltage Electron Ionization Mass Spectrometry and Curie-point Pyrolysis-Low Voltage Electron Ionization Mass Spectrometry were used to analyze samples of Pittsburgh #8 coal obtained from the Argonne National Laboratory Premium Coal Sample Program. The primary objective was to assess the effects of differences in experimental techniques and conditions, e.g., with regard to heating rates, pyrolysis methods and soft ionization procedures (FI vs. Low Voltage EI) on the mass spectral patterns. A second objective was to further characterize and study the pyrolysis behavior of Pittsburgh #8 coal. The results indicate that the distribution and the type of the primary pyrolysis products are largely independent of marked differences in heating rate (10-2 K/s - 104 K/s range) and sample size (2.5 x 10-5g - 5.0 x 10-2g range) as well as overall vacuum pyrolysis MS configurations and conditions used. All three vacuum pyrolysis MS techniques produce remarkably similar mass spectral patterns when analyzing Pittsburgh #8 coal. The results show that Pittsburgh #8 coal contains a significant amount of low temperature (<380ºC) evolving "bitumen" consisting primarily of alkyl-substituted aromatic components. The bitumen evolution step is followed by a partially overlapping "bulk pyrolysis" step characterized by the evolution of abundant hydroxy- and dihydroxy substituted aromatic compounds, thought to be primarily derived from vitrinitic components. During the bitumen evolution step the average MW of the compounds increases with temperature while maintaining a relatively narrow distribution. By contrast, during the bulk pyrolysis step, the average MW tends to decrease while exhibiting a much broader distribution.
1990
Thermochemical Analysis of U.S. Argonne Premium Coal Samples by Time-Resolved Pyrolysis Field Ionization Mass Spectrometry
Simmleit, N.; Yun, Y.; Meuzelaar, H.L.C. and Schulten, H.R.
Advances in Coal Spectroscopy, Meuzelaar, H.L.C., Editor, Plenum Publishing Corp., New York, 1990 (In press). Funded by ACERC (National Science Foundation and Associates and Affiliates).
Analytical pyrolysis techniques are widely used for the thermochemical analysis of coals and coal-derived products. During heating, complex mixtures of chemical substances are released from coal by distillation, desorption and thermal degradation processes. The amount and chemical nature of the volatilized coal products are dependent mainly on the composition and structure of the coal and on heating conditions. Therefore, the results of chemical analyses of the volatilized coal products should provide information on the original structure of coal. For detailed on-line analysis of volatilized coal products usually chromatographic and/or spectroscopic methods have been used. For positive identification of compounds gas chromatography/mass spectrometry (GC/MS) is a common approach, e.g. in direct combination with pyrolysis techniques. However, due to the relatively long analysis times, in particular for high molecular weight products, GC/MS is not suited for a universal on-line monitoring of evolving coal products during heating. For rapid fingerprinting of volatilized coal products on a molecular basis direct MS analysis is often the preferred method. Small amounts of coal or coal-derived products are heated in front of the ionization region under high vacuum conditions. Depending on the type of mass spectrometer used and the experimental conditions, on-line monitoring of evolving coal products is possible for a wide range of heating rate. Heating rates as low as 10-2 C/s may be used in the combined thermogravimetry (TG)/MS whereas heating rates in the 104 - 106 C/s range can be obtained by CO2 laser heating.
Vacuum Pyrolysis Mass Spectrometry of Pittsburgh #8 Coal; Comparison of Three Different, Time-Resolved Techniques
Yun, Y.; Meuzelaar, H.L.C.; Simmleit, N. and Schulten, H.R.
Energy & Fuels, 1990 (In press). Funded by ACERC.
Three different vacuum pyrolysis mass spectrometry techniques, viz. Pyrolysis-Field Ionization Mass Spectrometry, Thermogravimetry/Low Voltage Electron Ionization Mass Spectrometry and Curie-point Pyrolysis-Low Voltage Electron Ionization Mass Spectrometry were used to analyze samples of Pittsburgh #8 coal obtained from the Argonne National Laboratory Premium Coal Sample Program. The primary objective was to assess the effects of differences in experimental techniques and conditions, e.g., with regard to heating rates, pyrolysis methods and soft ionization procedures (FI vs. Low Voltage EI) on the mass spectral patterns. A second objective was to further characterize and study the pyrolysis behavior of Pittsburgh #8 coal. The results indicate that the distribution and the type of the primary pyrolysis products are largely independent of marked differences in heating rate (10-2 K/s - 104 K/s range) and sample size (2.5 x 10-5g - 5.0 x 10-2g range) as well as overall vacuum pyrolysis MS configurations and conditions used. All three vacuum pyrolysis MS techniques produce remarkably similar mass spectral patterns when analyzing Pittsburgh #8 coal. The results show that Pittsburgh #8 coal contains a significant amount of low temperature (<380ºC) evolving "bitumen" consisting primarily of alkyl-substituted aromatic components. The bitumen evolution step is followed by a partially overlapping "bulk pyrolysis" step characterized by the evolution of abundant hydroxy- and dihydroxy substituted aromatic compounds, thought to be primarily derived from vitrinitic components. During the bitumen evolution step the average MW of the compounds increases with temperature while maintaining a relatively narrow distribution. By contrast, during the bulk pyrolysis step, the average MW tends to decrease while exhibiting a much broader distribution.
The Mobile Phase in Coal Viewed from a Mass Spectrometric Perspective
Yun, Y.; Meuzelaar, H.L.C.; Simmleit, N. and Schulten, H.R.
Recent Advances in Coal Science: A Symposium in Remembrance of Peter H. Given, Schobert, H.; Bartle, K. and Lynch, L., Editors, ACS Symposium Series, American Chemical Society, Washington, D.C., 1990 (In press). Funded by ACERC.
Seven Argonne Premium coal samples ranging from lignite to low volatile bituminous in rank were analyzed by Pyrolysis-Field Ionization Mass Spectrometry (Py-FIMS) in order to determine the existence and structural nature of a thermally extractable "mobile phase." In addition, Curie-point Pyrolysis-Low Voltage Mass Spectrometry (Py-LVMS) was employed to demonstrate the importance of mild oxidation on the thermally extractable mobile phase components. Py-FIMS results clearly reveal the existence of a thermally extractable, bitumen-like fraction which is chemically distinct from the remaining coal components.
Py-FIMS results clearly reveal the existence of a thermally extractable, bitumen-like fraction that is chemically distinct from the remaining coal components. In lignite, several biomarker compounds were noticeable in the mobile phase components while bituminous coals contain various alkylsubstituted aromatic compounds in the mobile phase. Blind Canyon coal, which contains 11% resinite, exhibits mobile phase components believed to originate from terpenoid aromatization. Curie-point Py-LVMS results illustrate the importance of the oxidation status of coal for studying the mobile phase since mild air oxidation severely changes the structural characteristics of the thermally extractable mobile phase.
1989
Estimation of Coal Devolatilization Modeling Parameters from Thermogravimetric and Time-Resolved Soft Ionization Mass Spectrometric Data
Yun, Y.; Maswadeh, W.; Meuzelaar, H.L.C.; Simmleit, N. and Schulten, H.R.
ACS Preprint, Div. of Fuel Chemistry, Miami Beach, Florida, 34 (4), 1308-1316, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Nowadays it is widely recognized that the initial pyrolysis step in coal conversion processes has a profound effect on the yield and distribution of end products such as coal-derived liquids, gases, coke, or pollutant emissions. Two general approaches for modeling coal pyrolysis reactions can be distinguished, namely: (a) phenomenological modeling and (b) chemical modeling. The phenomenological modeling approach is useful in conversion processes such as high temperature gasification where detailed chemical information may be advantageous but is probably not indispensable. Other conversion processes, however, e.g., liquefaction and hydropyrolysis, may require more detailed chemical information to predict the distribution of final products. Whether pyrolysis ("devolatilization") models for pulverized coal combustion processes require detailed information on coal structure and reactivity or can be based primarily on a phenomenological approach is still a matter of considerable debate.
Heated screen pyrolysis techniques have been widely used to provide modeling parameters for phenomenological models based on the thermal behavior of light gas components detected by gas chromatography, mass spectrometry (MS) and other spectroscopic techniques. Due to limitations of the analytical techniques used, tar components are generally lumped into a single component.
Since time-resolved mass spectrometry (TR-MS) data can be used to analyze single mass profiles or mass spectra as a function of temperature, TR-MS data. Our estimations will be based on the chemical assignment of tar components observed in soft ionization mass spectra in combination with kinetic evaluation or temperature-resolved intensity profiles of single mass peaks and measured or simulated thermogravimetric weight loss curves.
The Mobile Phase in Coal Viewed From a Mass Spectrometric Perspective
Meuzelaar, H.L.C.; Yun, Y.; Simmleit, N. and Schulten, H.R.
ACS Preprint, Div. of Fuel Chemistry, Miami Beach, Florida, 34 (3), 693-701, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
In recent years few topics have generated a more spirited discussion among coal scientists than the issue of the putative binary (mobile + network) phase nature of coals. Initially based on NMR observations, the concept of a "mobile phase" in coal soon came to encompass a broad range of more or less readily extractable and/or distillable lower molecular weight (MW) components, variously referred to as "guest molecules", "clathrates" or simply, and perhaps most succinctly, "bitumen". None of these terms appears to be completely satisfactory. The concept of "mobility" in NMR spectroscopy is quite different from that in the field of separation science, where mobility generally requires a measurable degree of solubility and/or distillability in liquid or gaseous media, respectively. For example, polymethylene-like moieties, such as found in some coal components, are highly "mobile" in NMR terms, without necessarily being extractable by solvents or distillable by nondestructive heating. The term "guest molecules", originally introduced to indicate specifically labeled marker molecules used in NMR studies of coal, is equally unsatisfactory for mobile phase components indigenous to the coal itself. Also, there appears to be insufficient evidence for the presence of sizeable quantities of true "clathrates" to rule out other possibilities, e.g., strong noncovalent bonding rather than physical entrapment. Finally, completely equating the "mobile phase" with solvent (e.g. pyridine) extractable "bitumen" in coal ignores the potential presence of colloidal particulate matter in the pyridine extracts as well as possible solvent-induced scission of weak chemical bonds. Furthermore, the solvent-extractable fraction may well include macromolecular components, such as resinites.
Mass spectrometric observations have thus far played a rather limited role in the "mobile phase" discussions but are starting to shed some light on the key question: is there conclusive evidence for the presence of a chemically and/or physically distinct "mobile phase", as opposed to a continuum of possible molecular sizes and structures? In the context of the present discussion, the term "mobile phase" will be used to describe those components which can be thermally extracted ("distilled" "desorbed") under vacuum at temperatures below the thermal degradation range of the coal. The residue, designated as the nonmobile ("network") phase, is thermally degraded in the pyrolysis temperature range. Of course, the onset of pyrolysis may vary considerably, depending on heating rate, rank and coal type.
Schulten, HR
1992
Thermochemical Analysis of US Argonne Premium Coal Samples by Time-Resolved Pyrolysis Field Ionization Mass Spectrometry
Simmleit, N.; Yun, Y.; Meuzelaar, H.L.C. and Schulten, H.R.
Chapter 13, Advances in Coal Spectroscopy, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1992. Funded by Pittsburgh Energy Technology Center/Consortium for Fossil Fuel Liquefaction, US Department of Energy and ACERC.
Analytical pyrolysis techniques are widely used for the thermochemical analysis of coals and coal-derived products. During heating, complex mixtures of chemical substances are released from coal by distillation, desorption and thermal degradation processes. The amount and chemical nature of the volatilized coal products are dependent mainly on the composition and structure of the coal and on heating conditions. Therefore, the results of chemical analyses of the volatilized coal products should provide information on the original structure of coal. For detailed on-line analysis of volatilized coal products usually chromatographic and/or spectroscopic methods have been used. For positive identification of compounds gas chromatography/mass spectrometry (GC/MS) is a common approach, e.g. in direct combination with pyrolysis techniques. However, due to the relatively long analysis times, in particular for high molecular weight products, GC/MS is not suited for a universal on-line monitoring of evolving coal products during heating. For rapid fingerprinting of volatilized coal products on a molecular basis direct MS analysis is often the preferred method. Small amounts of coal or coal-derived products are heated in front of th ionization region under high vacuum conditions. Depending on the type of mass spectrometer used and the experimental conditions, on-line monitoring of evolving coal products is possible for a wide range of heating rate. Heating rates as low as 10-2 C/s may be used in the combined thermogravimetry (TG)/MS whereas heating rates in the 104 - 106 C/s range can be obtained by CO2 laser heating.
1991
Vacuum Pyrolysis Mass Spectrometry of Pittsburgh #8 Coal; Comparison of Three Different, Time-Resolved Techniques
Yun, Y.; Meuzelaar, H.L.C.; Simmleit, N. and Schulten, H.R.
Energy & Fuels, 5:22-29, 1991. Funded by ACERC.
Three different vacuum pyrolysis mass spectrometry techniques, viz. Pyrolysis-Field Ionization Mass Spectrometry, Thermogravimetry/Low Voltage Electron Ionization Mass Spectrometry and Curie-point Pyrolysis-Low Voltage Electron Ionization Mass Spectrometry were used to analyze samples of Pittsburgh #8 coal obtained from the Argonne National Laboratory Premium Coal Sample Program. The primary objective was to assess the effects of differences in experimental techniques and conditions, e.g., with regard to heating rates, pyrolysis methods and soft ionization procedures (FI vs. Low Voltage EI) on the mass spectral patterns. A second objective was to further characterize and study the pyrolysis behavior of Pittsburgh #8 coal. The results indicate that the distribution and the type of the primary pyrolysis products are largely independent of marked differences in heating rate (10-2 K/s - 104 K/s range) and sample size (2.5 x 10-5g - 5.0 x 10-2g range) as well as overall vacuum pyrolysis MS configurations and conditions used. All three vacuum pyrolysis MS techniques produce remarkably similar mass spectral patterns when analyzing Pittsburgh #8 coal. The results show that Pittsburgh #8 coal contains a significant amount of low temperature (<380ºC) evolving "bitumen" consisting primarily of alkyl-substituted aromatic components. The bitumen evolution step is followed by a partially overlapping "bulk pyrolysis" step characterized by the evolution of abundant hydroxy- and dihydroxy substituted aromatic compounds, thought to be primarily derived from vitrinitic components. During the bitumen evolution step the average MW of the compounds increases with temperature while maintaining a relatively narrow distribution. By contrast, during the bulk pyrolysis step, the average MW tends to decrease while exhibiting a much broader distribution.
1990
Thermochemical Analysis of U.S. Argonne Premium Coal Samples by Time-Resolved Pyrolysis Field Ionization Mass Spectrometry
Simmleit, N.; Yun, Y.; Meuzelaar, H.L.C. and Schulten, H.R.
Advances in Coal Spectroscopy, Meuzelaar, H.L.C., Editor, Plenum Publishing Corp., New York, 1990 (In press). Funded by ACERC (National Science Foundation and Associates and Affiliates).
Analytical pyrolysis techniques are widely used for the thermochemical analysis of coals and coal-derived products. During heating, complex mixtures of chemical substances are released from coal by distillation, desorption and thermal degradation processes. The amount and chemical nature of the volatilized coal products are dependent mainly on the composition and structure of the coal and on heating conditions. Therefore, the results of chemical analyses of the volatilized coal products should provide information on the original structure of coal. For detailed on-line analysis of volatilized coal products usually chromatographic and/or spectroscopic methods have been used. For positive identification of compounds gas chromatography/mass spectrometry (GC/MS) is a common approach, e.g. in direct combination with pyrolysis techniques. However, due to the relatively long analysis times, in particular for high molecular weight products, GC/MS is not suited for a universal on-line monitoring of evolving coal products during heating. For rapid fingerprinting of volatilized coal products on a molecular basis direct MS analysis is often the preferred method. Small amounts of coal or coal-derived products are heated in front of the ionization region under high vacuum conditions. Depending on the type of mass spectrometer used and the experimental conditions, on-line monitoring of evolving coal products is possible for a wide range of heating rate. Heating rates as low as 10-2 C/s may be used in the combined thermogravimetry (TG)/MS whereas heating rates in the 104 - 106 C/s range can be obtained by CO2 laser heating.
Vacuum Pyrolysis Mass Spectrometry of Pittsburgh #8 Coal; Comparison of Three Different, Time-Resolved Techniques
Yun, Y.; Meuzelaar, H.L.C.; Simmleit, N. and Schulten, H.R.
Energy & Fuels, 1990 (In press). Funded by ACERC.
Three different vacuum pyrolysis mass spectrometry techniques, viz. Pyrolysis-Field Ionization Mass Spectrometry, Thermogravimetry/Low Voltage Electron Ionization Mass Spectrometry and Curie-point Pyrolysis-Low Voltage Electron Ionization Mass Spectrometry were used to analyze samples of Pittsburgh #8 coal obtained from the Argonne National Laboratory Premium Coal Sample Program. The primary objective was to assess the effects of differences in experimental techniques and conditions, e.g., with regard to heating rates, pyrolysis methods and soft ionization procedures (FI vs. Low Voltage EI) on the mass spectral patterns. A second objective was to further characterize and study the pyrolysis behavior of Pittsburgh #8 coal. The results indicate that the distribution and the type of the primary pyrolysis products are largely independent of marked differences in heating rate (10-2 K/s - 104 K/s range) and sample size (2.5 x 10-5g - 5.0 x 10-2g range) as well as overall vacuum pyrolysis MS configurations and conditions used. All three vacuum pyrolysis MS techniques produce remarkably similar mass spectral patterns when analyzing Pittsburgh #8 coal. The results show that Pittsburgh #8 coal contains a significant amount of low temperature (<380ºC) evolving "bitumen" consisting primarily of alkyl-substituted aromatic components. The bitumen evolution step is followed by a partially overlapping "bulk pyrolysis" step characterized by the evolution of abundant hydroxy- and dihydroxy substituted aromatic compounds, thought to be primarily derived from vitrinitic components. During the bitumen evolution step the average MW of the compounds increases with temperature while maintaining a relatively narrow distribution. By contrast, during the bulk pyrolysis step, the average MW tends to decrease while exhibiting a much broader distribution.
The Mobile Phase in Coal Viewed from a Mass Spectrometric Perspective
Yun, Y.; Meuzelaar, H.L.C.; Simmleit, N. and Schulten, H.R.
Recent Advances in Coal Science: A Symposium in Remembrance of Peter H. Given, Schobert, H.; Bartle, K. and Lynch, L., Editors, ACS Symposium Series, American Chemical Society, Washington, D.C., 1990 (In press). Funded by ACERC.
Seven Argonne Premium coal samples ranging from lignite to low volatile bituminous in rank were analyzed by Pyrolysis-Field Ionization Mass Spectrometry (Py-FIMS) in order to determine the existence and structural nature of a thermally extractable "mobile phase." In addition, Curie-point Pyrolysis-Low Voltage Mass Spectrometry (Py-LVMS) was employed to demonstrate the importance of mild oxidation on the thermally extractable mobile phase components. Py-FIMS results clearly reveal the existence of a thermally extractable, bitumen-like fraction which is chemically distinct from the remaining coal components.
Py-FIMS results clearly reveal the existence of a thermally extractable, bitumen-like fraction that is chemically distinct from the remaining coal components. In lignite, several biomarker compounds were noticeable in the mobile phase components while bituminous coals contain various alkylsubstituted aromatic compounds in the mobile phase. Blind Canyon coal, which contains 11% resinite, exhibits mobile phase components believed to originate from terpenoid aromatization. Curie-point Py-LVMS results illustrate the importance of the oxidation status of coal for studying the mobile phase since mild air oxidation severely changes the structural characteristics of the thermally extractable mobile phase.
1989
Estimation of Coal Devolatilization Modeling Parameters from Thermogravimetric and Time-Resolved Soft Ionization Mass Spectrometric Data
Yun, Y.; Maswadeh, W.; Meuzelaar, H.L.C.; Simmleit, N. and Schulten, H.R.
ACS Preprint, Div. of Fuel Chemistry, Miami Beach, Florida, 34 (4), 1308-1316, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Nowadays it is widely recognized that the initial pyrolysis step in coal conversion processes has a profound effect on the yield and distribution of end products such as coal-derived liquids, gases, coke, or pollutant emissions. Two general approaches for modeling coal pyrolysis reactions can be distinguished, namely: (a) phenomenological modeling and (b) chemical modeling. The phenomenological modeling approach is useful in conversion processes such as high temperature gasification where detailed chemical information may be advantageous but is probably not indispensable. Other conversion processes, however, e.g., liquefaction and hydropyrolysis, may require more detailed chemical information to predict the distribution of final products. Whether pyrolysis ("devolatilization") models for pulverized coal combustion processes require detailed information on coal structure and reactivity or can be based primarily on a phenomenological approach is still a matter of considerable debate.
Heated screen pyrolysis techniques have been widely used to provide modeling parameters for phenomenological models based on the thermal behavior of light gas components detected by gas chromatography, mass spectrometry (MS) and other spectroscopic techniques. Due to limitations of the analytical techniques used, tar components are generally lumped into a single component.
Since time-resolved mass spectrometry (TR-MS) data can be used to analyze single mass profiles or mass spectra as a function of temperature, TR-MS data. Our estimations will be based on the chemical assignment of tar components observed in soft ionization mass spectra in combination with kinetic evaluation or temperature-resolved intensity profiles of single mass peaks and measured or simulated thermogravimetric weight loss curves.
The Mobile Phase in Coal Viewed From a Mass Spectrometric Perspective
Meuzelaar, H.L.C.; Yun, Y.; Simmleit, N. and Schulten, H.R.
ACS Preprint, Div. of Fuel Chemistry, Miami Beach, Florida, 34 (3), 693-701, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
In recent years few topics have generated a more spirited discussion among coal scientists than the issue of the putative binary (mobile + network) phase nature of coals. Initially based on NMR observations, the concept of a "mobile phase" in coal soon came to encompass a broad range of more or less readily extractable and/or distillable lower molecular weight (MW) components, variously referred to as "guest molecules", "clathrates" or simply, and perhaps most succinctly, "bitumen". None of these terms appears to be completely satisfactory. The concept of "mobility" in NMR spectroscopy is quite different from that in the field of separation science, where mobility generally requires a measurable degree of solubility and/or distillability in liquid or gaseous media, respectively. For example, polymethylene-like moieties, such as found in some coal components, are highly "mobile" in NMR terms, without necessarily being extractable by solvents or distillable by nondestructive heating. The term "guest molecules", originally introduced to indicate specifically labeled marker molecules used in NMR studies of coal, is equally unsatisfactory for mobile phase components indigenous to the coal itself. Also, there appears to be insufficient evidence for the presence of sizeable quantities of true "clathrates" to rule out other possibilities, e.g., strong noncovalent bonding rather than physical entrapment. Finally, completely equating the "mobile phase" with solvent (e.g. pyridine) extractable "bitumen" in coal ignores the potential presence of colloidal particulate matter in the pyridine extracts as well as possible solvent-induced scission of weak chemical bonds. Furthermore, the solvent-extractable fraction may well include macromolecular components, such as resinites.
Mass spectrometric observations have thus far played a rather limited role in the "mobile phase" discussions but are starting to shed some light on the key question: is there conclusive evidence for the presence of a chemically and/or physically distinct "mobile phase", as opposed to a continuum of possible molecular sizes and structures? In the context of the present discussion, the term "mobile phase" will be used to describe those components which can be thermally extracted ("distilled" "desorbed") under vacuum at temperatures below the thermal degradation range of the coal. The residue, designated as the nonmobile ("network") phase, is thermally degraded in the pyrolysis temperature range. Of course, the onset of pyrolysis may vary considerably, depending on heating rate, rank and coal type.