Anal. Chem. 2001, 73, 2791-2804
Petroleum and Coal Bhajendra N. Barman*
Equilon Enterprises LLC, Westhollow Technology Center, P.O. Box 1380, Houston, Texas 77251-1380 Vicente L. Cebolla
Instituto de Carboquı´mica CSIC, C/ Miguel Luesma 4, 50015 Zaragoza, Spain Anil K. Mehrotra
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Alberta, Canada T2N 1N4 Cliff T. Mansfield
8805 Belhaven Court, Clemmons, North Carolina 27012 Review Contents General Reviews and ASTM Methods General Reviews ASTM Methods Coal Coal Structure, Composition, and Reactivity Coal Structure Interactions between Coal and Organic Compounds Coal Reactivity and Properties Coal Bed Gas Formation Characterization of Inorganic Elements in Coal Impact of Inorganic Elements on Coal Combustion Operation and Environment Other Coal Combustion Byproducts Coal-Derived Products from Pyrolysis and Liquefaction Reviews Crude Oil and Heavy Oils Hydrocarbon Identification and Characterization Reviews Hydrocarbon Type and Composition Analyses Characterization of Asphaltenes/Heavy Ends Asphaltenes Waxes/Paraffins Trace Elements Metals Sulfur and Nitrogen Physical Properties Thermal Techniques Natural Gas and Refined Products Natural Gas Gasoline Chromatographic Techniques Spectroscopic Techniques Kerosene, Diesel, Aviation Fuel, and Gas Oil Chromatographic Techniques Spectroscopic Techniques Gasoline and Diesel Additives Lubricants Base Oils Additives Condition-Based Monitoring Oxidation Stability Viscosity Miscellaneous Literature Cited 10.1021/ac010415i CCC: $20.00 Published on Web 05/03/2001
© 2001 American Chemical Society
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This review covers a two-year period dating from around October 1998. As compared to the last biennial review on this subject (A1), this is much more condensed in order to limit the total number of references to less than 200. Therefore, our focus has been to highlight only breakthroughs, advances in analytical technology, and other important issues. This review period saw some advances that fall beyond the normal improvements in the identification and determination of petroleum components. This paper highlights a number of useful reviews published between 1998 to date. Also included is a list of new analytical methods that were approved and published by the American Society for Testing and Materials (ASTM). There were efforts to develop better analytical approaches that dramatically improve the precision and detection limits to assay samples related to environmental issues. Examples include the determination of mercury in natural gas liquid and condensates and the assay of inorganic elements in coal. There were some new developments in analytical methodologies. For example, there were new methods such as hydrocarbontype determination using thin-layer chromatography (TLC) on silica gel plate impregnated with berberine sulfate and ultraviolet (UV)-fluorescence detection. Additionally, growth occurred in the fast analysis of gasoline and diesel range samples using fast gas chromatography (GC). Similar fast techniques using spectroscopic methods include the use of infrared (IR) spectroscopy for chemical and physical properties of gasoline and diesel and nuclear magnetic resonance (NMR) techniques for base oil properties. Multidimensional techniques were applied to gasoline, gasoline additives, and diesel range samples. Specifically, GC × GC using multiple columns and multiple detectors were applied to the detailed characterization of some complex samples. GENERAL REVIEWS AND ASTM METHODS Bhajendra N. Barman General Reviews. Barman et al. highlighted recent developments in major chromatographic techniques for the separation and characterization of petroleum and coal-derived liquids (A2). This review with 416 references covered various methods for * Corresponding author: (phone) 281-544-6205; (fax) 281-544-6218; (e-mail)
[email protected].
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separation, identification, and determination of individual components, measurement of boiling range distribution, and determination of hydrocarbon group types. Hyphenated and multitechnique chromatographies were also described. Chester and Pinkston (A3) reviewed theory, instrumentation, and techniques of supercritical fluid chromatography (SFC) and discussed recent developments in SFC and its applications to various sample types including fossil fuels, lubricants, and waxes. Major separation techniques were the subjects of the Encyclopedia of Separation Science published by Academic Press (A4). There are reviews as well as application articles on coal, crude oil, petroleum products, fuels, and lubricants in this multivolume encyclopedia. Nadkarni provided a critical review on common techniques for the determination of sulfur in petroleum products and lubricants (A5). Determination of total mercury and speciation of mercury compounds were reviewed by Wilhelm and Bloom (A6). They discussed analytical techniques that determine mercury in hydrocarbon matrixes in the sub-ppb levels. These authors also discussed sampling techniques and types of mercury compounds present in samples such as crude oils, gas condensates, and different processed fuels. The effectiveness of sorbents to remove mercury varied with the forms of mercury. For examples, colloidal mercury (mercuric sulfide) evades capture by sorbent beds while the degree of adsorption of organic mercury compounds depends on the sorbent. Cave et al. presented a review with 859 references on the application of atomic spectroscopy to the chemical analysis of environmental samples (A7). Some of these studies dealt with petroleum and coal samples. ASTM Methods. Between 1998 and 2000, a number of new methods for the characterization of petroleum products were approved and published by the ASTM. These are listed below under the respective analytical techniques. Chromatography: D 6293soxygenates and paraffins, olefins, naphthenes, and aromatics (O-PONA) in gasoline by GC; D 6299s total olefins in gasoline by GC; D 6352sboiling range distribution of petroleum distillates boiling from 174 to 700 °C by GC; D 6379s aromatic hydrocarbon types in aviation fuels and distillates by high-performance liquid chromatography (HPLC); D-6417sengine oil volatility by GC. Spectroscopy and spectrometry: D 6277sbenzene in gasoline using mid infrared spectroscopy; D 6334ssulfur in gasoline by wavelength-dispersive X-ray fluorescence; D 6445ssulfur in gasoline by energy-dispersive X-ray fluorescence. Thermal techniques: D 6186soxidation induction time of lubricating oils by pressure differential scanning calorimetry (PDSC); D 6375sevaporation loss of lubricating oils by thermogravimetric analysis (TGA). Electrochemical method: D 6447shydroperoxide number of aviation turbine fuels by voltametric analysis. COAL Vicente L. Cebolla COAL STRUCTURE, COMPOSITION, AND REACTIVITY Coal Structure. Sharma et al. (B1) obtained direct evidence of layered structures in various types of coals using high-resolution 2792
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transmission electron microscopy (HRTEM) lattice fringe. According to this work, coal structure can be altered during observation in high-resolution lattice fringe mode, and the authors proposed a low-intensity-based procedure to avoid irradiation damage. Electron paramagnetic resonance (EPR) spectroscopy has become a powerful tool for studying paramagnetic species in coal. From a study carried out on eight well-characterized Argonne premium coals and their model compounds, Ikoma et al. (B2) proposed a new index for coal ranking based on 13C/1H ratio of the hyperfine sublevel correlation spectra at room temperature. From the comparison with model radicals and semiempirical molecular orbital calculations, they considered the main coal radicals as two-dimensionally condensed π-radicals with more than seven aromatic rings. Thomasson and co-workers (B3) described the measurement of IR microspectra of coals using an attenuated total reflection (ATR) objective. This objective contains a 100-µm silicon crystal that allows spectra to be measured rapidly from standard polished petrography blocks. Unlike a specular or diffuse reflection technique, ATR spectra were similar to normal absorption spectra although they show lower spatial resolution. Murata and others (B4) evaluated the distribution of oxygen functional groups in four brown coals by the combined use of chemical analyses and solid-state single-pulse excitation/magic angle spinning (MAS) 13C NMR. Carbonyl and ether groups accounted for ∼20% of the total amount of oxygen in the coal, while the distribution of alcohol, phenol, and carboxyl groups depended on the type of coal. Interactions between Coal and Organic Compounds. Interactions between five Argonne premium coals and various organic compounds were investigated by Takanohashi et al. (B5) using inverse liquid chromatographic techniques. Chromatographic capacity factors were determined for the studied compounds using coal as stationary phase and acetonitrile, toluene, and methanol as alternative mobile phases. Interactions were discussed in the light of contributions from H-bonding and electrostatic and steric effects. Norinaga and others (B6) characterized the microdomain structure of a swollen coal in deuterated solvents by 1H NMR spin diffusion experiments and small-angle neutron scattering (SANS) measurements. The former technique allows qualitative monitoring of nanoscale structural changes. Solvent-impenetrable regions were found to exist in swollen coals even at high solvent-to-coal ratios. SANS qualitatively verified these results, revealing the development of phase-separated domains. Time-resolved smallangle X-ray scattering (SAXS) was applied by Winans et al. (B7) to observe in situ changes in the structure of the eight Argonne premium coals during solvent swelling. For certain coals, structural changes occurred in just a few minutes. The changes in fractal dimensionality, size, and type of porosity were found to be rank-dependent. Coal Reactivity and Properties. Several techniques were developed to study the changes in coal structure during thermal treatment. Saito and co-workers (B8) carried out a systematic in situ variable-temperature NMR microimaging study of several coals between 25 and 500 °C. This technique is based on 3-D single-point imaging and allows observing the behavior of mobile
components at high temperature in heterogeneous coal specimens. Miura and others (B9) employed an in situ diffuse reflectance IR technique (DRIFT) to estimate the change in hydrogen bonding in eight Argonne premium coals through heat treatment from room temperature up to 300 °C. Neat, undiluted coal samples were used and spectra collected at every 20 °C. The strength distribution of hydrogen bonding was estimated through the analysis of six O-H peaks in the 2200-3650-cm-1 region, taking into account the changes in absorption coefficients. A measure of degree of coalification (coal rank) using TGA was proposed by Huang et al. (B10). It is based on the strong correlation found between the derivative peak maximum for volatile matter evolution and vitrinite reflectance. The authors claim that the method is convenient to avoid expensive and timeconsuming petrographic analysis. Bustin and Guo (B11) showed that sudden decreases or increases in functional groups in inertinites, as determined by Fourier transform IR (FT-IR), are coincident with jumps in reflectance. The distribution of reflectance values and FT-IR characteristics of inertinite in some western Canadian coals are consistent with a model of charring that incorporates discrete compositional jumps. Sinninghe Damste´ and others (B12) studied organosulfur compounds in the extract and pyrolysates of Rasa coal using Curie point pyrolysis GC with flame ionization detection (FID), flame photometric detection (FPD), and mass spectrometric (MS) detection and pyrolysis GC/MS. Alkylated benzo[b]- and dibenzothiophenes were the majority components in the extracts and alkylated thiophenes and benzo[b]thiophenes in the pyrolysates. Sulfur polycyclic aromatics with more than one sulfur atom per molecule were also identified. The low pristane/phytane ratio, the distribution of alkylated alkylthiophenes and alkylbenzenes, and the anomalous high level of organic sulfur corroborate that Rasa coal is different from other coals. Coal Bed Gas Formation. A batch reactor system with online analysis and data processing for the measurement of gas formation rate under well-defined conditions was described by Medina et al. (B13). This system provided qualitative and quantitative analysis of gases desorbed from coal samples in realtime measurements. Characterization of Inorganic Elements in Coal. Davidson (B14) reported the results of a collaborative research project to determine the modes of occurrence of trace elements in coals. The nature of trace elements in coal-fired power stations is partially dependent on their mode of occurrence in the original coal. For this, different research teams fractionated coals by using variants of either physical separation or sequential leaching. Querol and nine other collaborators (B15) proposed a new methodology for determining element affinities, which combines density fractionation with a mathematical treatment of analytical results from coal samples. The results showed good agreement for most elements when compared to a previously reported sequential leaching. Ferna´ndez-Pe´rez et al. (B16) reported the use of a focused microwave Soxhlet device for a rapid (45-50 min) extraction of mercury, arsenic, and selenium from coal prior to atomic fluorescence detection. As in conventional Soxhlet extraction, the contact between sample and fresh nitric acid in each cycle allows the equilibrium to be displaced to total extraction of target
elements. Each cycle of this modified Soxhlet is equivalent to a conventional microwave wet digestion. The modes of occurrence of arsenic and chromium in four U.S. coals were investigated by Kolker et al. (B17) and Huggins et al. (B18). They used an integrated analytical approach which includes selective leaching, X-ray absorption fine structure (XAFS) spectroscopy, electron microprobe, scanning electron microscopy equipped with an energy-dispersive X-ray analyzer (SEM-EDX), X-ray diffraction (XRD), and Mossbauer spectroscopy. In three bituminous coals, pyrite is the main source of arsenic. The major occurrence of chromium is associated with the macerals and is believed to be an oxyhydroxide phase. A significant amount of arsenate was derived from pyrite oxidation. In the subbituminous coal, arsenic appears to be mostly associated with organics, as As3+ or as arsenate. The authors did not find evidence for the Cr6+ oxidation state in any coal. Senior and 12 other collaborators (B19) studied the distribution of trace elements in the previously mentioned coals (B17, B18) as a function of particle size and density. Thus, neutron activation analysis was used to measure the absolute concentration of elements in parent coals and in the size- and density-fractionated samples, while chemical leaching and XAFS were used to provide information on the modes of occurrence of elements in parent coals. Kolker et al. (B20) employed the Stanford high-resolution ion microprobe with reversed geometry (SHRIMP-RG), using the oxygen ion source, to investigate the distribution of chromium and other trace metals in illite/smectite, a group of clay minerals in which chromium is present. Concentrations of chromium (11176 ppm), vanadium (23-248 ppm), and manganese (2-30 ppm) were determined. According to the authors, the reversed geometry, in which the electrostatic sector is downstream of the magnetic sector of the mass spectrometer, provides superior mass resolution compared to one that had forward geometry. Research on inductively coupled plasma-mass spectrometry (ICPMS) was also active in this period. Booth and Spears (B21) determined elements by laser ablation-ICPMS in the ppb range while spatial resolution was as low as low as 10 µm. Two different calibration techniques were developed for determining trace elements (As, Cd, Pb, and Hg in the low-ppb range) in coals, macerals, and minerals. Rodushkin et al. (B22) studied four sample preparation techniques for determining 70 elements in coal and certified reference materials, using a combination of ICPatomic emission spectroscopy (AES) and high-resolution ICPMS. Among the dissolution mixtures studied, the combination of nitric and hydrofluoric acids with hydrogen peroxide provided the best agreement with the reference values, although fusion was necessary to quantitatively recover Si, Cr, Hf, W, Zr, and Y. IMPACT OF INORGANIC ELEMENTS ON COAL COMBUSTION OPERATION AND ENVIRONMENT Inorganic elements impact on coal combustion systems in their operational (corrosion, slagging, fouling) and environmental (emission of toxic metals) performance. A FT-IR technique was developed by Seshadri and Smith (B23) to analyze Mg2Ca(SO4)3 in the presence of CaSO4 and other compounds in a pressurized fluidized bed combustion (PFBC) power plant. This compound is the main cause of excessive cake strength that occurs during filtration of fine particles from PFBC hot gases when dolomitic limestone is used as the SOx sorbent. The FT-IR technique allows Analytical Chemistry, Vol. 73, No. 12, June 15, 2001
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one to relate the filter cake physical properties and operating problems of PFBC systems to Mg2Ca(SO4)3 concentrations. Davidson and others (B24) developed and tested an on-line detection system for measurements of alkali metal species in flue gas from combustion of either coal (in a PFBC unit) or both biomass and coal (in an AFBC unit). This on-line system is based on surface ionization at a hot platinum filament and was dimensioned for in situ measurements at pressures up to 30 bar. The alkali concentration data were continuously recorded at a frequency of 1-100 Hz and useful detection interval ranged from 1 ppb to 150 ppm. Diaz-Somoano and Martı´nez-Tarazona (B25) applied a microwave oven digestion procedure and ICPMS (using standard additions) to determine the retention of arsenic from combustion and gasification flue gases in sorbents with high levels of silica (such as coal fly ash mixed with sand). This method was compared with the hydride generation atomic absorption spectrometry (AAS) method. Olson and others (B26) have developed a GC/MS-based method to separate and identify a mixture of two volatile oxidized mercury species, HgCl2 and Hg(NO3)2‚H2O. The second compound was identified as a volatile form of mercury when a simulated flue gas stream containing NO2 and SO2 was used. These compounds were trapped from the gas phase into acetonitrile or collected by desorption from a solid phase in a small trapping vial before injecting into a GC/MS injection port. A new and highly sensitive (sub-ppb) method of phosphorus (P) determination, based on a successful coupling of sorption preconcentration of P as vanadomolybdophosphoric heteropoly acid with luminol chemiluminescence detection was developed by Zui and Birks (B27). This method was applied to the analysis of P in a turbine condensate of a coal-fired power plant. To improve the prediction of problems related to ash deposition in boilers, Hansen et al. (B28) developed a quantitative method, based on simultaneous thermal analysis (STA), in which ash melting is detected as an endothermic reaction involving no change in mass. Signals are transferred into a fusion curve showing the melt fraction in the ash as a function of temperature. This technique enables identification of the chemical species melting in different temperature ranges when used in combination with computer-controlled SEM. Analysis of trace elements in coal fly ash was investigated by different techniques. Several ICPMS techniques were developed. The isotope dilution method was used by Liao and Jiang (B29) for the detection of cadmium, mercury, and lead in the reference NIST SRM 1633a coal fly ash. The isotope ratios of each element were calculated from the respective peak areas. In this case, samples were introduced by an ultrasonic slurry sampling and electrothermal vaporization technique. Precision and accuracy for the whole analysis were better than 6 and 4%, respectively. Likewise, Wang and others (B30) proposed a sample digestion method prior to ICPMS analysis for determining arsenic in coal fly ash using NIST SRM 1633b as reference material. They proposed the dissolution of coal fly ash by acid mixture (HNO3 + H2O2 + HF) high-pressure bomb digestion with a low evaporation procedure. Jackson and Miller (B31) used ion chromatography coupled with ICPMS to determine soluble arsenic and selenium species in coal fly ash and organic waste-contaminated soils. Detection limits were 0.03, 0.03, 0.05, 0.16, 0.5, and 0.7 µgL-1 2794
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for dimethylarsinate, As(III), monomethylarsonate, As(V), Se(IV), and Se(VI), respectively. Veranth et al. (B32) carried out iron speciation in coal fly ash using Mossbauer spectroscopy. They found that ferric iron in an aluminosilicate glass phase is the source of bioavailable iron in coal fly ash and that this iron species is associated with particles formed at high temperatures during combustion. A method for determining uranium in coal fly ash was developed by Pancras and Puri (B33). It is based on uranium detection by fourth-derivative spectrophotometry after complexation of uranium with 2-5-bromo-2-pyridylazo-5-diethylaminophenol and preconcentration on an ammonium tetraphenylborate naphthalene adsorbent. Speciation of Cr(VI) in solid environmental samples is complicated because of the transformation between Cr (VI) and Cr(III) (EPA 3060A method). Huo and Kingston (B34) used speciated isotope dilution mass spectrometry (SIDMS) to mathematically and quantitatively correct for bidirectional interconversions between such species. They validated their approach using spiked mixtures of chromium species and fly ash and other chromium-containing samples. OTHER COAL COMBUSTION BYPRODUCTS Nicholls and Nelson (B35) detected isocyanic acid (HNCO) from coal char combustion by gas-phase FT-IR. Detection was performed on gas exiting the reaction system after cooling to room temperature. Ledesma et al. (B36) used HPLC with UV diode array detection to analyze condensed products from the combustion of a bituminous coal primary tar. They identified four cyclopentafused polycyclic aromatic hydrocarbons (PAHs) and two ethynylsubstituted PAHs. Roberts and others (B37) used solid-phase extraction, reversedphase HPLC, and capillary electrophoresis with fluorescence linenarrowing spectroscopy (CE-FLNS) at 4.2 K to separate and identify 7-(benzo[a]pyren-6-yl)guanine adduct in urine extracts of coal smoke-exposed humans. The authors proposed that this adduct could serve as effective biomarker for risk assessment of benzo[a]pyrene exposure. COAL-DERIVED PRODUCTS FROM PYROLYSIS AND LIQUEFACTION A comparison of molecular mass distribution in a coal tar pitch obtained by laser desorption mass spectrometry (LD-MS) and 252Cf plasma desorption mass spectrometry (252Cf PD-MS) was carried out by Johnson and co-workers (B38) using narrow fractions previously separated by size exclusion chromatography with N-methyl-2-pyrrolidinone as the mobile phase. Although a true comparison is not possible because of differences in the ion extraction voltages, both techniques showed molecular masses far higher than other MS techniques. Ito et al. (B39) applied in situ 1H NMR thermal analysis to monitor the mesophase formation of a coal tar pitch, which exhibit spherical mesophase and flow optical texture. This pitch became mobile in the temperature region between 400 and 700 K. Becker and co-workers (B40) reported a contribution of thiaarenes to overall toxicity of coal tar pitch volatiles in workplace air of an aluminum reduction plant. They quantified a variety of tetra-, penta-, and hexacyclic aromatic sulfur heterocycles (thiaarenes) by GC with sulfur-selective atomic
emission detection (AED) without previous separation of thiaarenes from PAHs. Kershaw et al. (B41) used constant-energy synchronous fluorescence spectroscopy to monitor the concentration of large (three or more) aromatic ring systems in pyrolysis tars. Synchronous fluorescence intensity per unit absorbance was shown to be a useful parameter to examine structural features of tars as well as to obtain information about the operational pyrolysis parameters and mechanisms. Moessner and Wise (B42) described a detailed analytical procedure for separation, identification, and quantification of a large number of polycyclic aromatic sulfur heterocycles (PASHs) using a reference coal tar (SRM 1597). This procedure involved solid-phase extraction (SPE) using aminopropylsilane cartridges, normal-phase HPLC for sample cleanup, capillary GC using either 5 or 50% phenyl methylpolysiloxane column, and selective MS and AED detection. Yu et al. (B43) followed the evolution of nitrogen-containing compounds within the coal tars under severe thermal conditions using GC coupled with a nitrogen-specific chemiluminescence detector. The results were useful to propose mechanisms for secondary pyrolysis of tars. Coal tar-contaminated soils were also studied. Meyer and coworkers (B44) reported a simple, reproducible, precise, and sensitive method, which provides the simultaneous determination of PAHs and hetero-PAHs (N, S, O) and their metabolites in soils contaminated by coal tar creosote. Contaminants were extracted and separated by polarity and acid-base characteristics using SPE with silica gel and strong basic anion- and strong acid cationexchange materials. Identification of compounds was accomplished using GC and HPLC methods. Apart from typical structures, metabolites predominantly with ketonic or quinonic structures were also identified at the ppm level. Heteroatom-containing species in oils from coal hydroliquefaction plants in Japan were identified and quantified by Sumbogo Murti et al. (B45) using GC with AED. Carbon, sulfur, nitrogen, and oxygen atomic emissions at 179, 181, 174, and 171 nm, respectively, were used for detection. Thiophenes, pyridines, and phenols were the major heteroatomic compounds in the lighter oils (with bp
