Lee, ML
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
Determination of Volatile Hydrocarbons in Coals and Shales Using Supercritical Fluid Extraction and Chromatography
Li, W.; Lazar, I.M.; Wan, Y.J.; Butala, S.; Shen, Y.; Malik, A. and Lee, M.L
Energy & Fuels, 1996 (in press). Funded by ACERC and Gas Research Institute.
Conventional analytical techniques, such as headspace gas chromatography and Soxhlet extraction, can provide compositional information for the gaseous (C1-5) and heavy (C15+) hydrocarbon constituents, respectively. The volatile (C6-14) hydrocarbons, if present, usually go undetected because of volatility fractionation and loss. In this study supercritical CO2 was used to extract the C6-C14 volatile hydrocarbons from pulverized coal samples. Capillary column gas chromatography/mass spectrometry was used to identify the mixture components, and packed capillary column supercritical fluid chromatography was used to separate and quantify the aliphatic and aromatic hydrocarbon class fractions. It was found that the compositions of the light hydrocarbon fractions included several homologous series of normal and branched aliphatic hydrocarbons, cyclic and aromatic hydrocarbons, and alkyl-substituted benzenes and naphthalenes; the concentrations of these volatile hydrocarbons ranged between 0.01 to 0.2% (by weight) of the bulk material for the different coal and shale samples.
Analysis of Coal Structure Via Successive Catalytic Depolymerization and Supercritical Fluid/Enhanced Liquid Extraction
Wan, Y.J.; Butala, S.; Li, W. and Lee, M.L.
Proceedings of the Pittcon '96 (Pittsburgh Conference), Chicago, Illinois, March 6, 1996. Funded by ACERC.
To understand the original chemical features of the intact coal structure, a new method has been developed for depolymerization and extraction of coal. It involves successive catalyzed depolymerization reactions under mild and organic solvent free conditions, each immediately followed in in-situ supercritical fluid (carbon dioxide) extraction and enhanced solvent (methylene chloride) extraction of the reaction matrix. The procedure is simple and the system is easy to operate. The timely removal of coal products avoids any retrograde reactions that complicate the products. Compared with coal head distillation, supercritical fluid extraction and enhanced liquid extraction is fast and can be used to analyze a very small amount of coal for analytical purposes. Experimental detail, extraction yields, and GC and GC/MS characterization of the products associated with coal structure will be presented. From the comparison of the composition of products from different depolymerization steps, it appears that coal has a common macromolecular skeletal structure, despite the well-established heterogeneity of coal.
1993
Origin of Long-Chain Alkylcyclohexanes and Alkylbenzenes in a Coal-Bed Wax
Dong, J.-Z.; Vorkink, W.P. and Lee, M.L.
Geochimica et Cosmochimica Acta, 57:837-849, 1993. Funded by Gas Research Institute.
A coal-bed wax was fractionated and analyzed using capillary column GC and combined GC/MS. It was found that the major components in the wax were n-alkanes (55.6%), cyclic/branched alkanes (26.0%), and several homologous series of alkylbenzenes (5.7%). All alkylbenzene isomers (except 6-n-alky-m-xylene) were positively identified by comparison with the retention times and mass spectra of newly synthesized authenic standards. 5-n-Alkyl-m-xylene, 2-n-alkyl-p-xylene, 4-n-alkyl-m-xylene, 4-n-alkyl-o-xylene, 2-n-alkyl-m-xylene, and 3-n-alkyl-o-xylene were identified for the first time from geological sources. All of these long-chain alkyl compounds (e.g., n-alkylcyclohexanes, n-alkylbenzenes, n-alkyl-o-toluenes, n-alkyl-p-toluenes, and 5-n-alkyl-m-xylenes) have similar total carbon number distributions and maxima with a slight even over odd carbon number preference between C28-C30. Moreover, the carbon number distributions of these compounds resembled those of the n-alkanes found in the same wax with slight odd over even carbon preference between C-C27class="sub">31. This indicates that the alkylcyclohexanes and alkylbenzenes may have the same fatty acid precursors as the n-alkanes. The alkylcyclohexanes and alkylbenzenes could have been formed by direct cyclization and aromatization, while the n-alkanes could have been formed by decarboxylation of the straight chain fatty acids. This explanation is further supported by the identification of homologous series of tetramethyl-n-alkylbenzenes and pentamethyl-n-alkylbenzenes with relatively high abundances at C15, C16, and C18, and a fatty acid distribution with maxima at C16 and C18. Based on these findings, mechanisms for the conversion of fatty acids or alcohols to alkylcyclohexanes and alkylbenzenes are proposed.
1992
High-Resolution Chromatographic Characterization of Depolymerized Coals of Different Rank: Aliphatic and Aromatic Hydrocarbons
Carlson, R.E.; Critchfield, S.; Vorkink, W.P.; Dong, J.-Z.; Pugmire, R.J.; Bartle, K.D.; Lee, M.L.; Zhang, Y. and Shabtai, J.S.
Fuel, 71(1):1-29, 1992. Funded by US Department of Energy, Gas Research Institute and ACERC.
A selective, low temperature depolymerization procedure has been applied to four Argonne coals of different rank to produce products that are representative of the original coal macromolecular structure, and that are amenable to chromatographic analysis. The products of this depolymerization procedure retained most of the original aromatic and functional group structures of the original coals. A comparison of liquid C-13 NMR spectra of the products and solid-state C-13 NMR spectra of the original coals showed only minor changes in the aromaticities of two of the coals, and some loss of the carbonyl carbons in all of the coals.
Tetrahydrofuran pre-extracts of the four coals and their depolymerized products were separated into chemical classes by adsorption chromatography. Two of these fractions, which contained aliphatic hydrocarbons and polycyclic aromatic hydrocarbons were analyzed using gas chromatography/mass spectrometry. Structural identifications were based on a combination of chromatographic retention and mass spectral fragmentation data. For the lower rank coals, the compositions of the pre-extracts were quite different from the corresponding depolymerized products, and they contained an abundance of molecular biological markers. The compositions of the pre-extracts became more similar to the depolymerized products as rank increased.
1991
Structural Comparison of Low-Molecular-Weight Extractable Compounds in Different Rank Coals Using Capillary Column Gas Chromatography
Chang, H.-C.K.; Bartle, K.D.; Markides, K.E. and Lee, M.L.
Advances in Coal Spectroscopy, 141-164, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1991. Funded by Gas Research Institute and ACERC.
In this chapter, results from the analysis of the low-molecular-weight organic constituents in six vitrinite-rich coals of ranks ranging from lignite to low volatile bituminous are reported. Aliphatics, neutral aromatics, nitrogen-containing aromatics, and sulfur-containing aromatics were first isolated from the coal extracts using column absorption and complexation chromatography, and then they were resolved and identified using capillary column gas chromatography coupled with sulfur- and nitrogen-selective detectors, and mass spectrometry.
Methanol/CO2 Phase Behavior in Supercritical Fluid Chromatography and Extraction
Page, S.H.; Goates, S.R. and Lee, M.L.
The Journal of Supercritical Fluids, 4:109-117, 1991. Funded by Gas Research Institute.
Mixed mobile phases have often been used improperly in supercritical fluid chromatography (SFC) and supercritical fluid extraction (SFE). Phase separation is unavoidable at certain conditions where conventional SFC and SFE are performed, resulting in inhomogeneous mobile phases. We describe here a relatively rapid and accurate approach to determining transition pressures at different temperatures and modifier concentrations. There is close agreement between the experimental values determined in this work and those published by others for methanol and carbon dioxide. The results have been used to test the predictions of several common methods for estimating the critical pressures of mixtures. The methods failed to predict the critical pressure to within 20 atm between approximately 4-20 mol % of modifier. Chromatographic performance was shown to be severely degraded when the pressure in the column is below the gas-liquid transition pressure. The effect of pressure drop in the column on phase behavior is discussed.
Analysis of Depolymerization Products of Various Rank Coals Using High Resolution Chromatographic Techniques
Carlson, R.E.; Vorkink, W.P.; Lee, M.L.; Zhang, Y. and Shabtai, J.S.
1991 Pittsburgh Coal Conference and Exposition on Analytical Chemistry and Applied Spectroscopy, Chicago, IL, March 1991. Funded by ACERC.
Elucidation of the organic structure of coal is vital to designing and optimizing processes for direct coal usage (e.g., combustion or coal conversion), and the efficient utilization of this abundant natural resource. Due to the extremely complex macromolecular structure of coal, present structural information is sparse. The analysis of coal and coal derived materials has been approached by numerous analytical and chemical techniques. However, many of those methods fail to yield specific information concerning the macromolecular network, or they significantly alter the network. Solvent extracts have provided valuable information concerning the "easily" extractable portion of the coal matrix, again leaving the macromolecular skeleton virtually unexplored. Structural investigations of coal carried out at high temperatures (>300ºC) lead to free radical rearrangement, crosslinking and thermal cracking of the sample.
A mild depolymerization method has been developed which yields a tetrahydrofuran (THF) soluble product that represents 50 to >70% of the original material, depending on coal rank. Detailed analysis of these products was performed using high-resolution gas chromatography and gas chromatography/mass spectrometry. The qualitative and quantitative results of four depolymerized Argonne coals (Beulah Zap, Illinois No. 6, Utah Blind Canyon, Pocahontas No.3) will be discussed and compared to room temperature solvent extracts (THF) of the same coals.
1990
Multidimensional Packed Capillary Coupled to Open Tubular Column Supercritical Fluid Chromatography Using a Valve-Switching Interface
Juvancz, Z.; Payne, K.M.; Markides, K.E. and Lee, M.L.
Analytical Chemistry, 62, 1990. Funded by Brigham Young University.
An on-line two-dimensional supercritical fluid chromatographic system (SFC/SFC) was constructed by utilizing a rotary valve interface to provide independent flow control of the two dimensions. A cold trap was employed to refocus solutes from single or multiple fractional cuts, after being transferred to the second dimension. Improved performance, including time savings, was achieved with a packed capillary to open tubular column arrangement and two independently controlled pumps, compared to earlier reported single-pump open tubular column SFC/SFC and packed capillary column SFC/SFC systems. The packed capillary in the first dimension provided a rapid chemical class separation, while the open tubular column in the second dimension provided high resolution of closely related isomers.
High Resolution Chromatographic Characterization of Depolymerized Coals of Different Rank: Aliphatic and Aromatic Hydrocarbons
Carlson, R.E.; Critchfield, S.; Vorkink, W.P.; Dong, J.-Z.; Pugmire, R.J.; Bartle, K.D. and Lee, M.L.
Fuel, 1990 (In Press). Funded by US Department of Energy, Gas Research Institute and ACERC.
A selective, low temperature depolymerization procedure has been applied to four Argonne coals of different rank to produce products that are representative of the original coal macromolecular structure, and that are amenable to chromatographic analysis. The products of this depolymerization procedure retained most of the original aromatic and functional group structures of the original coals. A comparison of liquid C-13 NMR spectra of the products and solid-state C-13 NMR spectra of the original coals showed only minor changes in the aromaticities of two of the coals, and some loss of the carbonyl carbons in all of the coals.
Tetrahydrofuran pre-extracts of the four coals and their depolymerized products were separated into chemical classes by adsorption chromatography. Two of these fractions, which contained aliphatic hydrocarbons and polycyclic aromatic hydrocarbons were analyzed using gas chromatography/mass spectrometry. Structural identifications were based on a combination of chromatographic retention and mass spectral fragmentation data. For the lower rank coals, the compositions of the pre-extracts were quite different from the corresponding depolymerized products, and they contained an abundance of molecular biological markers. The compositions of the pre-extracts became more similar to the depolymerized products as rank increased.
Determination of Sulfur-Containing Polycyclic Aromatic Compounds in Coal Extracts Using Capillary Column Gas Chromatography with Radio Frequency Plasma Detection
Chang, H.-C.K.; Skelton, R.J. Jr.; Markides, K.E. and Lee, M.L.
Polycyclic Aromatic Compounds, 1:251-264, 1990. Funded by Gas Research Institute and ACERC.
Detailed identification of sulfur-containing polycyclic aromatic compounds (S-PAC) was accomplished for solvent extracts of five different coals. The S-PAC were isolated by ligand-exchange chromatography. Due to the great complexities of these samples, capillary gas chromatography (GC) was employed for their analysis. An element selective radio frequency plasma detector was used to provide sulfur selective detections. Gas chromatography-mass spectrometry was used to identify individual compounds in isolated sulfur fractions. Condensed thiophenic compounds were found to be the major constituents in all five S-PAC fractions. Diaryl sulfides were also detected in the high volatile bituminous Illinois #6 coal. The prevalence of various S-PAC in different coal extracts was observed as a function of their rank.
Conditions and Effects of Mixed Mobile Phases on Capillary Column Chromatographic Performance in the Near Critical Region
Page, S.H.; Goates, S.R. and Lee, M.L.
Twelfth International Symposium on Capillary Chromatography, Kobe, Japan, 1990. Funded by Gas Research Institute.
The phase behaviors of binary compositions of carbon dioxide with organic modifiers (acetonitrile, methanol and propylene carbonate) were studied using laser light scattering in the near critical region (0-20 mol%, 80-400 atm, and 60-120ºC). In order to maintain supercritical fluid conditions, the pressure, temperature, and mole percent must be properly adjusted for each composition. The three regions of two-phase phenomena are described.
1989
A Method for the Preparation of Binary Mobile Phase Mixtures for Capillary Supercritical Fluid Chromatography
Raynie, D.E.; Fields, S.M.; Djordevic, N.M.; Markides, K.E. and Lee, M.L.
J. High Resoln. Chromatogr., 12, 51, 1989. Funded by Gas Research Institute.
Here, we describe a simple, inexpensive method for the preparation of mixed mobile phase (especially gas + liquid mixtures) for SFC. This method does not require cryogenic freezing of the organic modifier, and vacuum is needed only for initial evacuation of the closed system. Simple calculations allow determination of the exact concentrations of mixtures transferred to the SFC pumping system, accounting for loss of CO2 (or other gaseous primary fluid) during the transfer process.
Multidimensional Open-Tubular Column Supercritical Fluid Chromatography Using a Flow-Switching Interface
Davies, I.L.; Xu, B.; Markides, K.E.; Bartle, K.D. and Lee, M.L.
J. Microcol. Sep., 2, 71, 1989. Funded by Gas Research Institute and the Utah Centers of Excellence.
A multidimensional system based on capillary supercritical fluid chromatography (SFC) was constructed that utilizes a simple flow-switching interface between two open-tubular 50-mm i.d. columns. A novel solvent-venting injection technique was incorporated in the system that enables single or multiple 0.5-mL volumes to be injected into an uncoated, yet deactivated, length of capillary precolumn without flooding of the analytical column. The effectiveness of multidimensional capillary SFC (SFC-SFC) for complex mixtures is demonstrated by the analysis of polycyclic aromatic hydrocarbons (PAH) in a coal tar extract, the trace determination of a methylcarbonate pesticide and its metabolites in a bird extract, and a group-type separation of hydrocarbons in a high-boiling petroleum distillate. These examples show for the first time that capillary SFC-SFC is a complementary alternative to other multidimensional chromatographic methods involving liquid or gaseous mobile phases.
Radio Frequency Plasma Detector for Sulfur Selective Capillary Gas Chromatographic Analysis of Fossil Fuels
Skelton, R.J. Jr.; Chang, H.-C.K.; Farnsworth, P.B.; Markides, K.E. and Lee, M.L.
Anal. Chem., 61, 2292, 1989. Funded by Gas Research Institute and the Utah Centers of Excellence.
Polycyclic aromatic compounds (PAC) are known to be major constituents in coal and petroleum products. Polycyclic aromatic hydrocarbons (PAH) are by far the most common PAC in these materials. However, nitrogen-, oxygen- and sulfur-containing PAC are also often found in significant quantities. Because of the widespread interest in and use of fossil fuels, detailed study of their compositions has become an important task.
1988-1986
Ultraviolet-Absorption Detector for Capillary Supercritical Fluid Chromatography with Compressible Mobile Phases
Fields, S.M.; Markides, K.E. and Lee, M.L.
Analytical Chemistry, 60, 802-806, 1988. 5 pgs. Funded by Dow Chemical Company and Gas Research Institute.
A major emphasis on current research in capillary supercritical fluid chromatography (SFC) is concerned with the use of mixed mobile phases to expand the analytical capabilities of SFC to more polar and higher molecular weight solutes than possible with single fluid mobile phases such as CO2. The mixed mobile phases that have been studied are primarily polar organic liquids in CO2. Low percentages (less than 1 mol %) of modifiers do not appear to cause any significant change in solute retention. Higher percentages (up to 20 mol %) have been shown to produce significant retention charges.
Since mobile phase flow rates and solute quantities are low in capillary SFC, it is desirable to analyze the entire effluent. However, the high percentages of organic modifiers anticipated in mixed mobile phase studies preclude the use of a flame ionization detector due to high background levels and to baseline changes during pressure or density programming. Ultraviolet-adsorption provides a simple and inexpensive detection system for use with mixed mobile phases.
Capillary SFC analysis creates stringent demands on allowable UV-absorption cell volumes, so an optical cell was developed based on fused silica capillary tubing available for gas chromatography. Highly compressible mobile phases such as CO2 create a problem in capillary UV-absorption detection that is not present for high critical temperature, low compressibility mobile phases such as n-pentane. The compressibility of CO2 produces significant density changes in the cell during pressure or density programming which leads to refractive index changes and significant base-line drift.
These effects were reduced to acceptable levels by cooling a newly designed and constructed detector cell. The system is sensitive and useful in studies of mixed mobil phases in capillary SFC. An 8.9 mol % mixture of 2-propanol or nitromethane in CO2 produced significant decreases in retention of polar and nonpolar polycyclic aromatic compounds. The 2-propanol/CO2 mobile phase effects the elution of ovalene at moderate temperature and pressure.
Identification and Comparison of Low-Molecular-Weight Neutral Constituents in Two Different Coal Extracts
Chang, H.-C.K.; Nishioka, M.; Bartle, K.D.; Wise, S.A.; Bayona, J.M.; Markides, K.E. and Lee, M.L.
Fuel, 67, 45-48, 1988. 4 pgs. Funded by Gas Research Institute.
Determination of the chemical structural features of coals is a continuing major goal of fuel science because of the vital energy source represented by this material. Coals are now perceived to be cross-linked macromolecular networks in which are trapped lower molecular weight materials either in sites readily accessible to solvent or in 'cages' analogous to clathrates. How representative this extractable material is of the multipolymeric macromolecular structure in which it is embedded in clearly open to question. However, the generally lower molecular weights of components in solvent extracts lead to much greater ease of analysis, and such extracts may provide insights into metamorphic changes undergone by the macromolecular structure during coal formation.
A two-step pyridine and then tetrahydrofuran solvent extraction procedure at room temperature under nitrogen gas flow was used to extract two different US coals, PSOC-592 (Illinois No. 5) and PSOC-521 (Rock Springs No. 7, Wyoming). Aliphatic and aromatic hydrocarbons were separated using neutral alumina column chromatography. The aromatics were then fractionated according to the number of aromatic carbons by high performance liquid chromatography. These neutral compounds were identified by gas chromatography (g.c.) and gas chromatography/mass spectrometry. n-Alkanes (C17-C31), pristane, phythane, hopanes (17aH, 21bH), and moretanes (17bH, 21aH) were found in aliphatic fractions of both coal extracts. Low-molecular-weight (2-4 rings) polycyclic aromatic hydrocarbons (PAH) were the major compounds in the aromatic fraction of the PSOC-592 coal extract. However, pentacyclic triterpenoid-like hydroaromatic hydrocarbons were the major components in the extract of the PSOC-521 coal. A number of new compounds were identified for the first time.
Direct Coupling of Capillary Supercritical Fluid Chromatography to High Resolution Mass Spectrometry with Minimum Modification
Huang, E.C.; Jackson, B.J.; Markides, K.E. and Lee, M.L.
Chromatographia, 25, 51-54, 1988. 4 pgs. Funded by US Department of Energy and Gas Research Institute.
It is estimated that the majority of analyses by supercritical fluid chromatography (SFC) involves the use of the flame ionization detector (FID) or the UV-absorbance detector. Unfortunately, each of these detectors can only be used when the SFC mobile phase and the sample being chromatographed fill certain requirements; the FID is limited to the use of only a few supercritical mobile phases, and the UV-absorbance detector can be used only when the sample molecules contain chromophores. The demand for a universal detector for SFC has intensified as the range of applicability of the technique has expanded. Coupled chromatography/mass spectrometry systems are among the most powerful analytical instruments available today for the analysis of organic mixtures. The successful marriage of gas chromatography/mass spectrometry (GC/MS) and the considerable progress in coupling liquid chromatography with the mass spectrometer (LC/MS) have naturally led to studies of SFC/MS.
The coupling of a capillary supercritical fluid chromatograph with a high resolution double focusing mass spectrometer has been accomplished without any modifications to the pumping or ion source systems. The interface utilizes a direct insertion probe (DIP), which was originally designed for the direct analysis of solid samples, together with a frit restrictor as a decompression device. The DIP is placed opposite to the SFC restrictor, and it provides sufficient heat to prevent cluster formation and cooling resulting from the expansion of the supercritical fluid into the vacuum environment. Excellent mass spectra of standard polycyclic aromatic hydrocarbons under chemical-ionization (CI) conditions using methane as the reagent gas, and under charge-exchange (CE) conditions using CO2 as the charge exchange medium were obtained.
Preferred Annellated Structures of Polycyclic Aromatic Compounds in Coal-Derived Materials
Nishioka, M. and Lee, M.L.
ACS Symp. Ser., 14, 235-253, 1988. 19 pgs. Funded by US Department of Energy.
Coal-derived material such as coal liquids and coal tars are highly aromatic, and these materials contain polycyclic aromatic compounds (PACs) as major components. Although average descriptive parameters such as molecular weight range, aromaticity, and abundances of functional groups are usually obtained to characterize such materials, detailed chemical analysis is also important for properly assessing health risks due to exposure to such materials and for understanding fundamental chemical reactions involved in upgrading technologies such as coal gasification and liquefaction. In addition, detailed identification of constituents in coal-derived products could provide important information relevant to coal structure.
The structures and relative abundances of polycyclic aromatic compounds (both hydrocarbons and heterocycles) in a solvent-refined coal liquid and in a coal tar were compiled and compared. These structures and relative abundances were determined by detailed analyses performed in our laboratory during the past 7 years. The purpose of this comparison was to determine (1) if preferred aromatic structural features exist in the complex mixture of compounds present in a single coal-derived material and (2) to what extent these preferred structures are evident in different coal-derived materials produced from different feedstocks and under different conditions. Although different feedstocks and process conditions were associated with each of the two coal-derived products studied, remarkably similar structural trends could be seen. If one disregards the structures of the compounds produced by mild autocatalytic hydrogenation in the solvent-refined coal-liquefaction process, the structures of the remaining polycyclic aromatic compounds in both samples are similar. These results suggest that the major compounds identified are either representative of similar aromatic moieties in the original coal feedstock or are a result of processing conditions involving complex reactions that lead to similar stable final products. Because many similar aromatic moieties are found in coal in comparison with coal-derived materials many of the same complex reactions may occur during diagenesis. Such reactions may include cyclo-coupling dehydrogenation.
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.
Structural Characteristics of Polycyclic Aromatic Hydrocarbon Isomers in Coal Tars and Combustion Products
Nishioka, M.; Chang, H.-C. K. and Lee, M.L.
Environ. Sci. Technol. 20, 1023-1027, 1986. 4 pgs. Funded by US Department of Energy.
Coal-derived products and thermally cracked petroleum oils are highly aromatic in nature and contain polycyclic aromatic hydrocarbons (PAH) as major components. Although average descriptive parameters are usually obtained for such materials (i.e., distillation curve, molecular weight range, aromaticity, etc.), it is oftentimes very important to obtain detailed compositional and structural information.
Isomeric polycyclic aromatic hydrocarbons (PAH) with two to six rings in coal-derived products and in a carbon black were separated, identified, and quantified by using capillary column gas chromatography and gas chromatography-mass spectrometry. A newly synthesized smectic liquid-crystalline polysiloxane and a conventional polymethylsiloxane were utilized as stationary phases. Many previously difficult-to-separate isomeric PAH (i.e., methylphenanthrenes/methylanthracenes, triphenylene/chrysene, methylchrysenes, benzofluoranthenes, and pentaphene/benzo [b] chrysene) were identified. The relative abundances of the PAH in these samples were compared and correlated to the reaction conditions during their production. The relationship between abundance and structure for the identified PAH was also discussed.
Sulphur Heterocycles in Coal-Derived Products: Reduction Between Structure and Abundance
Nishioka, M.; Lee, M.L. and Castle, R.N.
Fuel, 65, 390-97, 1986. 7 pgs. Funded by US Department of Energy.
Sulphur is present in various forms in all crude fossil fuels. The organic sulphur compounds found in these materials have been categorized according to functionality; thio (-SH) disulphide (-S-S-) sulphide (-S-), and thiophene. The thiophenes are the major organosulphur compounds in shale oils, coal-derived liquids and heavy petroleum distillates. In thermally cracked oils and coal liquids, multi-ring polycyclic aromatic sulphur heterocycles (PASH) are especially abundant.
The sulphur content in coal and crude oil varies in the range 0.2-12-wt %. Sulphur-containing gases produced at fossil fuel combustion facilities are major contributors to air pollution. The detailed identification of heteroatom-containing polycyclic aromatic compounds, such as the PASH, in coal-derived products could provide important information relevant to coal structure.
Sulphur heterocyles in a coal tar and in a coal liquid vacuum residue were isolated by ligand exchange chromatography using PdCl2 on silica gel. Subsequent fractions were analyzed by capillary column gas chromatography and gas chromatography-mass spectrometry. Two new selective stationary phases (a smectic liquid-crystalline polysiloxane and a biphenyl polysiloxane), as well as a methylpolysiloxane, were used to resolve the numerous isomers. All major sulphur heterocyles with 3 - 6 rings were identified by comparison of retention times of mixture components with those of standard reference compounds. The structures and relative abundances of the major sulphur heterocyles were analogous to those of the major polycyclic aromatic hydrocarbons in the same or similar samples.
Supercritical Fluid Injection of High-Molecular-Weight Polycyclic Aromatic Compounds in Capillary Supercritical Fluid Chromatography
Jackson, W.P.; Markides, K.E. and Lee, M.L.
J. High Resoln. Chromatogr./Chromatogr. Commun. 9, 213-217, 1986. 5 pgs. Funded by Dow Chemical Company and Gas Research Institute.
One class of compounds which is particularly well-suited for analysis by capillary supercritical fluid chromatography (SFC) is the large, non-volatile polycyclic aromatic hydrocarbons (PAH). These aromatic compounds typically occur in very complex samples, particularly those samples derived from coal.
As is the case with any form of chromatography, sample introduction and detection must be optimized in capillary SFC to prevent a loss of resolution due to extra-column effects. Several modes of sample introduction into the SFC system have been reported. The most widely used and apparently most successful method appears to be valved, sample-loop liquid injection as is used in HPLC.
In this study, a sample introduction system for capillary supercritical fluid chromatography, which allows the dissolution of the sample in the supercritical mobile phase before being introduced into the column, was constructed and evaluated. Supercritical n-pentane was shown to solvate high-molecular-weight polycyclic aromatic compounds that could not be solvated using cyclic aromatic compounds that could not be solvated using typical liquid solvents. In addition, split injection of a supercritical fluid solution was bound to be more reproducible than split injections of a liquid solution. The potential of such an injection system was demonstrated, although further developments are needed in order to make the technique of practical utility.
Evaluation of a Thermionic Detector for Capillary Supercritical Fluid Chromatography of Nitrated Polycyclic Aromatic Compounds
West, W.R. and Lee, M.L.
Journal of High Resolution Chromatography and Chromatography Communications, 9, 161-167, 1986. 7 pgs. Funded by Coordinating Research Council.
A thermionic detector was evaluated for capillary supercritical fluid chromatography of polar nitro-containing polycyclic aromatic compounds (nitro-PAC). Three modes of detector operation were studied. The best performance was obtained using a nitro-selective mode of detection. Although linearity was confined to a narrow range for a given source current, the sensitivity was excellent; 20 pg injected for p-nitrophenol gave a signal-to-noise ratio of 3. Conventional thermionic detection also produced good sensitivity; however, serious baseline drift was observed at high operating temperatures using density programming. A third mode, flame thermionic detection, was not acceptable because of low sensitivity. A number of nitro-PAC were successfully chromatographed using density programming at 101ºC. Hydropxynitropyrenes, nitropyrene quinones, and 9-hydroxy-2-nitrofluorene, which could not be eluted in capillary gas chromatography, were successfully chromatographed here. Retention of these compounds increased sequentially on 50% n-octyl-, 5% phenyl-, and 25% biphenyl polysilozane stationary phases, respectively. Stationary phase interactions appeared to be more a function of the polar functional groups on the aromatic rings than of the hydrocarbon character of the compounds. Solute solubility in the mobile phase and volatility were additional factors contributing to the elution of these molecules. Finally, these results were used to identify a number of nitro-PAC in a polar subfraction of a diesel particulate extract.
Lee, ML
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
Determination of Volatile Hydrocarbons in Coals and Shales Using Supercritical Fluid Extraction and Chromatography
Li, W.; Lazar, I.M.; Wan, Y.J.; Butala, S.; Shen, Y.; Malik, A. and Lee, M.L
Energy & Fuels, 1996 (in press). Funded by ACERC and Gas Research Institute.
Conventional analytical techniques, such as headspace gas chromatography and Soxhlet extraction, can provide compositional information for the gaseous (C1-5) and heavy (C15+) hydrocarbon constituents, respectively. The volatile (C6-14) hydrocarbons, if present, usually go undetected because of volatility fractionation and loss. In this study supercritical CO2 was used to extract the C6-C14 volatile hydrocarbons from pulverized coal samples. Capillary column gas chromatography/mass spectrometry was used to identify the mixture components, and packed capillary column supercritical fluid chromatography was used to separate and quantify the aliphatic and aromatic hydrocarbon class fractions. It was found that the compositions of the light hydrocarbon fractions included several homologous series of normal and branched aliphatic hydrocarbons, cyclic and aromatic hydrocarbons, and alkyl-substituted benzenes and naphthalenes; the concentrations of these volatile hydrocarbons ranged between 0.01 to 0.2% (by weight) of the bulk material for the different coal and shale samples.
Analysis of Coal Structure Via Successive Catalytic Depolymerization and Supercritical Fluid/Enhanced Liquid Extraction
Wan, Y.J.; Butala, S.; Li, W. and Lee, M.L.
Proceedings of the Pittcon '96 (Pittsburgh Conference), Chicago, Illinois, March 6, 1996. Funded by ACERC.
To understand the original chemical features of the intact coal structure, a new method has been developed for depolymerization and extraction of coal. It involves successive catalyzed depolymerization reactions under mild and organic solvent free conditions, each immediately followed in in-situ supercritical fluid (carbon dioxide) extraction and enhanced solvent (methylene chloride) extraction of the reaction matrix. The procedure is simple and the system is easy to operate. The timely removal of coal products avoids any retrograde reactions that complicate the products. Compared with coal head distillation, supercritical fluid extraction and enhanced liquid extraction is fast and can be used to analyze a very small amount of coal for analytical purposes. Experimental detail, extraction yields, and GC and GC/MS characterization of the products associated with coal structure will be presented. From the comparison of the composition of products from different depolymerization steps, it appears that coal has a common macromolecular skeletal structure, despite the well-established heterogeneity of coal.
1993
Origin of Long-Chain Alkylcyclohexanes and Alkylbenzenes in a Coal-Bed Wax
Dong, J.-Z.; Vorkink, W.P. and Lee, M.L.
Geochimica et Cosmochimica Acta, 57:837-849, 1993. Funded by Gas Research Institute.
A coal-bed wax was fractionated and analyzed using capillary column GC and combined GC/MS. It was found that the major components in the wax were n-alkanes (55.6%), cyclic/branched alkanes (26.0%), and several homologous series of alkylbenzenes (5.7%). All alkylbenzene isomers (except 6-n-alky-m-xylene) were positively identified by comparison with the retention times and mass spectra of newly synthesized authenic standards. 5-n-Alkyl-m-xylene, 2-n-alkyl-p-xylene, 4-n-alkyl-m-xylene, 4-n-alkyl-o-xylene, 2-n-alkyl-m-xylene, and 3-n-alkyl-o-xylene were identified for the first time from geological sources. All of these long-chain alkyl compounds (e.g., n-alkylcyclohexanes, n-alkylbenzenes, n-alkyl-o-toluenes, n-alkyl-p-toluenes, and 5-n-alkyl-m-xylenes) have similar total carbon number distributions and maxima with a slight even over odd carbon number preference between C28-C30. Moreover, the carbon number distributions of these compounds resembled those of the n-alkanes found in the same wax with slight odd over even carbon preference between C-C27class="sub">31. This indicates that the alkylcyclohexanes and alkylbenzenes may have the same fatty acid precursors as the n-alkanes. The alkylcyclohexanes and alkylbenzenes could have been formed by direct cyclization and aromatization, while the n-alkanes could have been formed by decarboxylation of the straight chain fatty acids. This explanation is further supported by the identification of homologous series of tetramethyl-n-alkylbenzenes and pentamethyl-n-alkylbenzenes with relatively high abundances at C15, C16, and C18, and a fatty acid distribution with maxima at C16 and C18. Based on these findings, mechanisms for the conversion of fatty acids or alcohols to alkylcyclohexanes and alkylbenzenes are proposed.
1992
High-Resolution Chromatographic Characterization of Depolymerized Coals of Different Rank: Aliphatic and Aromatic Hydrocarbons
Carlson, R.E.; Critchfield, S.; Vorkink, W.P.; Dong, J.-Z.; Pugmire, R.J.; Bartle, K.D.; Lee, M.L.; Zhang, Y. and Shabtai, J.S.
Fuel, 71(1):1-29, 1992. Funded by US Department of Energy, Gas Research Institute and ACERC.
A selective, low temperature depolymerization procedure has been applied to four Argonne coals of different rank to produce products that are representative of the original coal macromolecular structure, and that are amenable to chromatographic analysis. The products of this depolymerization procedure retained most of the original aromatic and functional group structures of the original coals. A comparison of liquid C-13 NMR spectra of the products and solid-state C-13 NMR spectra of the original coals showed only minor changes in the aromaticities of two of the coals, and some loss of the carbonyl carbons in all of the coals.
Tetrahydrofuran pre-extracts of the four coals and their depolymerized products were separated into chemical classes by adsorption chromatography. Two of these fractions, which contained aliphatic hydrocarbons and polycyclic aromatic hydrocarbons were analyzed using gas chromatography/mass spectrometry. Structural identifications were based on a combination of chromatographic retention and mass spectral fragmentation data. For the lower rank coals, the compositions of the pre-extracts were quite different from the corresponding depolymerized products, and they contained an abundance of molecular biological markers. The compositions of the pre-extracts became more similar to the depolymerized products as rank increased.
1991
Structural Comparison of Low-Molecular-Weight Extractable Compounds in Different Rank Coals Using Capillary Column Gas Chromatography
Chang, H.-C.K.; Bartle, K.D.; Markides, K.E. and Lee, M.L.
Advances in Coal Spectroscopy, 141-164, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1991. Funded by Gas Research Institute and ACERC.
In this chapter, results from the analysis of the low-molecular-weight organic constituents in six vitrinite-rich coals of ranks ranging from lignite to low volatile bituminous are reported. Aliphatics, neutral aromatics, nitrogen-containing aromatics, and sulfur-containing aromatics were first isolated from the coal extracts using column absorption and complexation chromatography, and then they were resolved and identified using capillary column gas chromatography coupled with sulfur- and nitrogen-selective detectors, and mass spectrometry.
Methanol/CO2 Phase Behavior in Supercritical Fluid Chromatography and Extraction
Page, S.H.; Goates, S.R. and Lee, M.L.
The Journal of Supercritical Fluids, 4:109-117, 1991. Funded by Gas Research Institute.
Mixed mobile phases have often been used improperly in supercritical fluid chromatography (SFC) and supercritical fluid extraction (SFE). Phase separation is unavoidable at certain conditions where conventional SFC and SFE are performed, resulting in inhomogeneous mobile phases. We describe here a relatively rapid and accurate approach to determining transition pressures at different temperatures and modifier concentrations. There is close agreement between the experimental values determined in this work and those published by others for methanol and carbon dioxide. The results have been used to test the predictions of several common methods for estimating the critical pressures of mixtures. The methods failed to predict the critical pressure to within 20 atm between approximately 4-20 mol % of modifier. Chromatographic performance was shown to be severely degraded when the pressure in the column is below the gas-liquid transition pressure. The effect of pressure drop in the column on phase behavior is discussed.
Analysis of Depolymerization Products of Various Rank Coals Using High Resolution Chromatographic Techniques
Carlson, R.E.; Vorkink, W.P.; Lee, M.L.; Zhang, Y. and Shabtai, J.S.
1991 Pittsburgh Coal Conference and Exposition on Analytical Chemistry and Applied Spectroscopy, Chicago, IL, March 1991. Funded by ACERC.
Elucidation of the organic structure of coal is vital to designing and optimizing processes for direct coal usage (e.g., combustion or coal conversion), and the efficient utilization of this abundant natural resource. Due to the extremely complex macromolecular structure of coal, present structural information is sparse. The analysis of coal and coal derived materials has been approached by numerous analytical and chemical techniques. However, many of those methods fail to yield specific information concerning the macromolecular network, or they significantly alter the network. Solvent extracts have provided valuable information concerning the "easily" extractable portion of the coal matrix, again leaving the macromolecular skeleton virtually unexplored. Structural investigations of coal carried out at high temperatures (>300ºC) lead to free radical rearrangement, crosslinking and thermal cracking of the sample.
A mild depolymerization method has been developed which yields a tetrahydrofuran (THF) soluble product that represents 50 to >70% of the original material, depending on coal rank. Detailed analysis of these products was performed using high-resolution gas chromatography and gas chromatography/mass spectrometry. The qualitative and quantitative results of four depolymerized Argonne coals (Beulah Zap, Illinois No. 6, Utah Blind Canyon, Pocahontas No.3) will be discussed and compared to room temperature solvent extracts (THF) of the same coals.
1990
Multidimensional Packed Capillary Coupled to Open Tubular Column Supercritical Fluid Chromatography Using a Valve-Switching Interface
Juvancz, Z.; Payne, K.M.; Markides, K.E. and Lee, M.L.
Analytical Chemistry, 62, 1990. Funded by Brigham Young University.
An on-line two-dimensional supercritical fluid chromatographic system (SFC/SFC) was constructed by utilizing a rotary valve interface to provide independent flow control of the two dimensions. A cold trap was employed to refocus solutes from single or multiple fractional cuts, after being transferred to the second dimension. Improved performance, including time savings, was achieved with a packed capillary to open tubular column arrangement and two independently controlled pumps, compared to earlier reported single-pump open tubular column SFC/SFC and packed capillary column SFC/SFC systems. The packed capillary in the first dimension provided a rapid chemical class separation, while the open tubular column in the second dimension provided high resolution of closely related isomers.
High Resolution Chromatographic Characterization of Depolymerized Coals of Different Rank: Aliphatic and Aromatic Hydrocarbons
Carlson, R.E.; Critchfield, S.; Vorkink, W.P.; Dong, J.-Z.; Pugmire, R.J.; Bartle, K.D. and Lee, M.L.
Fuel, 1990 (In Press). Funded by US Department of Energy, Gas Research Institute and ACERC.
A selective, low temperature depolymerization procedure has been applied to four Argonne coals of different rank to produce products that are representative of the original coal macromolecular structure, and that are amenable to chromatographic analysis. The products of this depolymerization procedure retained most of the original aromatic and functional group structures of the original coals. A comparison of liquid C-13 NMR spectra of the products and solid-state C-13 NMR spectra of the original coals showed only minor changes in the aromaticities of two of the coals, and some loss of the carbonyl carbons in all of the coals.
Tetrahydrofuran pre-extracts of the four coals and their depolymerized products were separated into chemical classes by adsorption chromatography. Two of these fractions, which contained aliphatic hydrocarbons and polycyclic aromatic hydrocarbons were analyzed using gas chromatography/mass spectrometry. Structural identifications were based on a combination of chromatographic retention and mass spectral fragmentation data. For the lower rank coals, the compositions of the pre-extracts were quite different from the corresponding depolymerized products, and they contained an abundance of molecular biological markers. The compositions of the pre-extracts became more similar to the depolymerized products as rank increased.
Determination of Sulfur-Containing Polycyclic Aromatic Compounds in Coal Extracts Using Capillary Column Gas Chromatography with Radio Frequency Plasma Detection
Chang, H.-C.K.; Skelton, R.J. Jr.; Markides, K.E. and Lee, M.L.
Polycyclic Aromatic Compounds, 1:251-264, 1990. Funded by Gas Research Institute and ACERC.
Detailed identification of sulfur-containing polycyclic aromatic compounds (S-PAC) was accomplished for solvent extracts of five different coals. The S-PAC were isolated by ligand-exchange chromatography. Due to the great complexities of these samples, capillary gas chromatography (GC) was employed for their analysis. An element selective radio frequency plasma detector was used to provide sulfur selective detections. Gas chromatography-mass spectrometry was used to identify individual compounds in isolated sulfur fractions. Condensed thiophenic compounds were found to be the major constituents in all five S-PAC fractions. Diaryl sulfides were also detected in the high volatile bituminous Illinois #6 coal. The prevalence of various S-PAC in different coal extracts was observed as a function of their rank.
Conditions and Effects of Mixed Mobile Phases on Capillary Column Chromatographic Performance in the Near Critical Region
Page, S.H.; Goates, S.R. and Lee, M.L.
Twelfth International Symposium on Capillary Chromatography, Kobe, Japan, 1990. Funded by Gas Research Institute.
The phase behaviors of binary compositions of carbon dioxide with organic modifiers (acetonitrile, methanol and propylene carbonate) were studied using laser light scattering in the near critical region (0-20 mol%, 80-400 atm, and 60-120ºC). In order to maintain supercritical fluid conditions, the pressure, temperature, and mole percent must be properly adjusted for each composition. The three regions of two-phase phenomena are described.
1989
A Method for the Preparation of Binary Mobile Phase Mixtures for Capillary Supercritical Fluid Chromatography
Raynie, D.E.; Fields, S.M.; Djordevic, N.M.; Markides, K.E. and Lee, M.L.
J. High Resoln. Chromatogr., 12, 51, 1989. Funded by Gas Research Institute.
Here, we describe a simple, inexpensive method for the preparation of mixed mobile phase (especially gas + liquid mixtures) for SFC. This method does not require cryogenic freezing of the organic modifier, and vacuum is needed only for initial evacuation of the closed system. Simple calculations allow determination of the exact concentrations of mixtures transferred to the SFC pumping system, accounting for loss of CO2 (or other gaseous primary fluid) during the transfer process.
Multidimensional Open-Tubular Column Supercritical Fluid Chromatography Using a Flow-Switching Interface
Davies, I.L.; Xu, B.; Markides, K.E.; Bartle, K.D. and Lee, M.L.
J. Microcol. Sep., 2, 71, 1989. Funded by Gas Research Institute and the Utah Centers of Excellence.
A multidimensional system based on capillary supercritical fluid chromatography (SFC) was constructed that utilizes a simple flow-switching interface between two open-tubular 50-mm i.d. columns. A novel solvent-venting injection technique was incorporated in the system that enables single or multiple 0.5-mL volumes to be injected into an uncoated, yet deactivated, length of capillary precolumn without flooding of the analytical column. The effectiveness of multidimensional capillary SFC (SFC-SFC) for complex mixtures is demonstrated by the analysis of polycyclic aromatic hydrocarbons (PAH) in a coal tar extract, the trace determination of a methylcarbonate pesticide and its metabolites in a bird extract, and a group-type separation of hydrocarbons in a high-boiling petroleum distillate. These examples show for the first time that capillary SFC-SFC is a complementary alternative to other multidimensional chromatographic methods involving liquid or gaseous mobile phases.
Radio Frequency Plasma Detector for Sulfur Selective Capillary Gas Chromatographic Analysis of Fossil Fuels
Skelton, R.J. Jr.; Chang, H.-C.K.; Farnsworth, P.B.; Markides, K.E. and Lee, M.L.
Anal. Chem., 61, 2292, 1989. Funded by Gas Research Institute and the Utah Centers of Excellence.
Polycyclic aromatic compounds (PAC) are known to be major constituents in coal and petroleum products. Polycyclic aromatic hydrocarbons (PAH) are by far the most common PAC in these materials. However, nitrogen-, oxygen- and sulfur-containing PAC are also often found in significant quantities. Because of the widespread interest in and use of fossil fuels, detailed study of their compositions has become an important task.
1988-1986
Ultraviolet-Absorption Detector for Capillary Supercritical Fluid Chromatography with Compressible Mobile Phases
Fields, S.M.; Markides, K.E. and Lee, M.L.
Analytical Chemistry, 60, 802-806, 1988. 5 pgs. Funded by Dow Chemical Company and Gas Research Institute.
A major emphasis on current research in capillary supercritical fluid chromatography (SFC) is concerned with the use of mixed mobile phases to expand the analytical capabilities of SFC to more polar and higher molecular weight solutes than possible with single fluid mobile phases such as CO2. The mixed mobile phases that have been studied are primarily polar organic liquids in CO2. Low percentages (less than 1 mol %) of modifiers do not appear to cause any significant change in solute retention. Higher percentages (up to 20 mol %) have been shown to produce significant retention charges.
Since mobile phase flow rates and solute quantities are low in capillary SFC, it is desirable to analyze the entire effluent. However, the high percentages of organic modifiers anticipated in mixed mobile phase studies preclude the use of a flame ionization detector due to high background levels and to baseline changes during pressure or density programming. Ultraviolet-adsorption provides a simple and inexpensive detection system for use with mixed mobile phases.
Capillary SFC analysis creates stringent demands on allowable UV-absorption cell volumes, so an optical cell was developed based on fused silica capillary tubing available for gas chromatography. Highly compressible mobile phases such as CO2 create a problem in capillary UV-absorption detection that is not present for high critical temperature, low compressibility mobile phases such as n-pentane. The compressibility of CO2 produces significant density changes in the cell during pressure or density programming which leads to refractive index changes and significant base-line drift.
These effects were reduced to acceptable levels by cooling a newly designed and constructed detector cell. The system is sensitive and useful in studies of mixed mobil phases in capillary SFC. An 8.9 mol % mixture of 2-propanol or nitromethane in CO2 produced significant decreases in retention of polar and nonpolar polycyclic aromatic compounds. The 2-propanol/CO2 mobile phase effects the elution of ovalene at moderate temperature and pressure.
Identification and Comparison of Low-Molecular-Weight Neutral Constituents in Two Different Coal Extracts
Chang, H.-C.K.; Nishioka, M.; Bartle, K.D.; Wise, S.A.; Bayona, J.M.; Markides, K.E. and Lee, M.L.
Fuel, 67, 45-48, 1988. 4 pgs. Funded by Gas Research Institute.
Determination of the chemical structural features of coals is a continuing major goal of fuel science because of the vital energy source represented by this material. Coals are now perceived to be cross-linked macromolecular networks in which are trapped lower molecular weight materials either in sites readily accessible to solvent or in 'cages' analogous to clathrates. How representative this extractable material is of the multipolymeric macromolecular structure in which it is embedded in clearly open to question. However, the generally lower molecular weights of components in solvent extracts lead to much greater ease of analysis, and such extracts may provide insights into metamorphic changes undergone by the macromolecular structure during coal formation.
A two-step pyridine and then tetrahydrofuran solvent extraction procedure at room temperature under nitrogen gas flow was used to extract two different US coals, PSOC-592 (Illinois No. 5) and PSOC-521 (Rock Springs No. 7, Wyoming). Aliphatic and aromatic hydrocarbons were separated using neutral alumina column chromatography. The aromatics were then fractionated according to the number of aromatic carbons by high performance liquid chromatography. These neutral compounds were identified by gas chromatography (g.c.) and gas chromatography/mass spectrometry. n-Alkanes (C17-C31), pristane, phythane, hopanes (17aH, 21bH), and moretanes (17bH, 21aH) were found in aliphatic fractions of both coal extracts. Low-molecular-weight (2-4 rings) polycyclic aromatic hydrocarbons (PAH) were the major compounds in the aromatic fraction of the PSOC-592 coal extract. However, pentacyclic triterpenoid-like hydroaromatic hydrocarbons were the major components in the extract of the PSOC-521 coal. A number of new compounds were identified for the first time.
Direct Coupling of Capillary Supercritical Fluid Chromatography to High Resolution Mass Spectrometry with Minimum Modification
Huang, E.C.; Jackson, B.J.; Markides, K.E. and Lee, M.L.
Chromatographia, 25, 51-54, 1988. 4 pgs. Funded by US Department of Energy and Gas Research Institute.
It is estimated that the majority of analyses by supercritical fluid chromatography (SFC) involves the use of the flame ionization detector (FID) or the UV-absorbance detector. Unfortunately, each of these detectors can only be used when the SFC mobile phase and the sample being chromatographed fill certain requirements; the FID is limited to the use of only a few supercritical mobile phases, and the UV-absorbance detector can be used only when the sample molecules contain chromophores. The demand for a universal detector for SFC has intensified as the range of applicability of the technique has expanded. Coupled chromatography/mass spectrometry systems are among the most powerful analytical instruments available today for the analysis of organic mixtures. The successful marriage of gas chromatography/mass spectrometry (GC/MS) and the considerable progress in coupling liquid chromatography with the mass spectrometer (LC/MS) have naturally led to studies of SFC/MS.
The coupling of a capillary supercritical fluid chromatograph with a high resolution double focusing mass spectrometer has been accomplished without any modifications to the pumping or ion source systems. The interface utilizes a direct insertion probe (DIP), which was originally designed for the direct analysis of solid samples, together with a frit restrictor as a decompression device. The DIP is placed opposite to the SFC restrictor, and it provides sufficient heat to prevent cluster formation and cooling resulting from the expansion of the supercritical fluid into the vacuum environment. Excellent mass spectra of standard polycyclic aromatic hydrocarbons under chemical-ionization (CI) conditions using methane as the reagent gas, and under charge-exchange (CE) conditions using CO2 as the charge exchange medium were obtained.
Preferred Annellated Structures of Polycyclic Aromatic Compounds in Coal-Derived Materials
Nishioka, M. and Lee, M.L.
ACS Symp. Ser., 14, 235-253, 1988. 19 pgs. Funded by US Department of Energy.
Coal-derived material such as coal liquids and coal tars are highly aromatic, and these materials contain polycyclic aromatic compounds (PACs) as major components. Although average descriptive parameters such as molecular weight range, aromaticity, and abundances of functional groups are usually obtained to characterize such materials, detailed chemical analysis is also important for properly assessing health risks due to exposure to such materials and for understanding fundamental chemical reactions involved in upgrading technologies such as coal gasification and liquefaction. In addition, detailed identification of constituents in coal-derived products could provide important information relevant to coal structure.
The structures and relative abundances of polycyclic aromatic compounds (both hydrocarbons and heterocycles) in a solvent-refined coal liquid and in a coal tar were compiled and compared. These structures and relative abundances were determined by detailed analyses performed in our laboratory during the past 7 years. The purpose of this comparison was to determine (1) if preferred aromatic structural features exist in the complex mixture of compounds present in a single coal-derived material and (2) to what extent these preferred structures are evident in different coal-derived materials produced from different feedstocks and under different conditions. Although different feedstocks and process conditions were associated with each of the two coal-derived products studied, remarkably similar structural trends could be seen. If one disregards the structures of the compounds produced by mild autocatalytic hydrogenation in the solvent-refined coal-liquefaction process, the structures of the remaining polycyclic aromatic compounds in both samples are similar. These results suggest that the major compounds identified are either representative of similar aromatic moieties in the original coal feedstock or are a result of processing conditions involving complex reactions that lead to similar stable final products. Because many similar aromatic moieties are found in coal in comparison with coal-derived materials many of the same complex reactions may occur during diagenesis. Such reactions may include cyclo-coupling dehydrogenation.
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.
Structural Characteristics of Polycyclic Aromatic Hydrocarbon Isomers in Coal Tars and Combustion Products
Nishioka, M.; Chang, H.-C. K. and Lee, M.L.
Environ. Sci. Technol. 20, 1023-1027, 1986. 4 pgs. Funded by US Department of Energy.
Coal-derived products and thermally cracked petroleum oils are highly aromatic in nature and contain polycyclic aromatic hydrocarbons (PAH) as major components. Although average descriptive parameters are usually obtained for such materials (i.e., distillation curve, molecular weight range, aromaticity, etc.), it is oftentimes very important to obtain detailed compositional and structural information.
Isomeric polycyclic aromatic hydrocarbons (PAH) with two to six rings in coal-derived products and in a carbon black were separated, identified, and quantified by using capillary column gas chromatography and gas chromatography-mass spectrometry. A newly synthesized smectic liquid-crystalline polysiloxane and a conventional polymethylsiloxane were utilized as stationary phases. Many previously difficult-to-separate isomeric PAH (i.e., methylphenanthrenes/methylanthracenes, triphenylene/chrysene, methylchrysenes, benzofluoranthenes, and pentaphene/benzo [b] chrysene) were identified. The relative abundances of the PAH in these samples were compared and correlated to the reaction conditions during their production. The relationship between abundance and structure for the identified PAH was also discussed.
Sulphur Heterocycles in Coal-Derived Products: Reduction Between Structure and Abundance
Nishioka, M.; Lee, M.L. and Castle, R.N.
Fuel, 65, 390-97, 1986. 7 pgs. Funded by US Department of Energy.
Sulphur is present in various forms in all crude fossil fuels. The organic sulphur compounds found in these materials have been categorized according to functionality; thio (-SH) disulphide (-S-S-) sulphide (-S-), and thiophene. The thiophenes are the major organosulphur compounds in shale oils, coal-derived liquids and heavy petroleum distillates. In thermally cracked oils and coal liquids, multi-ring polycyclic aromatic sulphur heterocycles (PASH) are especially abundant.
The sulphur content in coal and crude oil varies in the range 0.2-12-wt %. Sulphur-containing gases produced at fossil fuel combustion facilities are major contributors to air pollution. The detailed identification of heteroatom-containing polycyclic aromatic compounds, such as the PASH, in coal-derived products could provide important information relevant to coal structure.
Sulphur heterocyles in a coal tar and in a coal liquid vacuum residue were isolated by ligand exchange chromatography using PdCl2 on silica gel. Subsequent fractions were analyzed by capillary column gas chromatography and gas chromatography-mass spectrometry. Two new selective stationary phases (a smectic liquid-crystalline polysiloxane and a biphenyl polysiloxane), as well as a methylpolysiloxane, were used to resolve the numerous isomers. All major sulphur heterocyles with 3 - 6 rings were identified by comparison of retention times of mixture components with those of standard reference compounds. The structures and relative abundances of the major sulphur heterocyles were analogous to those of the major polycyclic aromatic hydrocarbons in the same or similar samples.
Supercritical Fluid Injection of High-Molecular-Weight Polycyclic Aromatic Compounds in Capillary Supercritical Fluid Chromatography
Jackson, W.P.; Markides, K.E. and Lee, M.L.
J. High Resoln. Chromatogr./Chromatogr. Commun. 9, 213-217, 1986. 5 pgs. Funded by Dow Chemical Company and Gas Research Institute.
One class of compounds which is particularly well-suited for analysis by capillary supercritical fluid chromatography (SFC) is the large, non-volatile polycyclic aromatic hydrocarbons (PAH). These aromatic compounds typically occur in very complex samples, particularly those samples derived from coal.
As is the case with any form of chromatography, sample introduction and detection must be optimized in capillary SFC to prevent a loss of resolution due to extra-column effects. Several modes of sample introduction into the SFC system have been reported. The most widely used and apparently most successful method appears to be valved, sample-loop liquid injection as is used in HPLC.
In this study, a sample introduction system for capillary supercritical fluid chromatography, which allows the dissolution of the sample in the supercritical mobile phase before being introduced into the column, was constructed and evaluated. Supercritical n-pentane was shown to solvate high-molecular-weight polycyclic aromatic compounds that could not be solvated using cyclic aromatic compounds that could not be solvated using typical liquid solvents. In addition, split injection of a supercritical fluid solution was bound to be more reproducible than split injections of a liquid solution. The potential of such an injection system was demonstrated, although further developments are needed in order to make the technique of practical utility.
Evaluation of a Thermionic Detector for Capillary Supercritical Fluid Chromatography of Nitrated Polycyclic Aromatic Compounds
West, W.R. and Lee, M.L.
Journal of High Resolution Chromatography and Chromatography Communications, 9, 161-167, 1986. 7 pgs. Funded by Coordinating Research Council.
A thermionic detector was evaluated for capillary supercritical fluid chromatography of polar nitro-containing polycyclic aromatic compounds (nitro-PAC). Three modes of detector operation were studied. The best performance was obtained using a nitro-selective mode of detection. Although linearity was confined to a narrow range for a given source current, the sensitivity was excellent; 20 pg injected for p-nitrophenol gave a signal-to-noise ratio of 3. Conventional thermionic detection also produced good sensitivity; however, serious baseline drift was observed at high operating temperatures using density programming. A third mode, flame thermionic detection, was not acceptable because of low sensitivity. A number of nitro-PAC were successfully chromatographed using density programming at 101ºC. Hydropxynitropyrenes, nitropyrene quinones, and 9-hydroxy-2-nitrofluorene, which could not be eluted in capillary gas chromatography, were successfully chromatographed here. Retention of these compounds increased sequentially on 50% n-octyl-, 5% phenyl-, and 25% biphenyl polysilozane stationary phases, respectively. Stationary phase interactions appeared to be more a function of the polar functional groups on the aromatic rings than of the hydrocarbon character of the compounds. Solute solubility in the mobile phase and volatility were additional factors contributing to the elution of these molecules. Finally, these results were used to identify a number of nitro-PAC in a polar subfraction of a diesel particulate extract.