Aromatic Cluster Size Research Articles

Characterization of biochar from fast pyrolysis and gasification systems

AbstractThermochemical processing of biomass produces a solid product containing char (mostly carbon) and ash. This char can be combusted for heat and power, gasified, activated for adsorption applications, or applied to soils as a soil amendment and carbon sequestration agent. The most advantageous use of a given char depends on its physical and chemical characteristics, although the relationship of char properties to these applications is not well understood. Chars from fast pyrolysis and gasification of switchgrass and corn stover were characterized by proximate analysis, CHNS elemental analysis, Brunauer‐Emmet‐Teller (BET) surface area, particle density, higher heating value (HHV), scanning electron microscopy, X‐ray fluorescence ash content analysis, Fourier transform infrared spectroscopy using a photo‐acoustic detector (FTIR‐PAS), and quantitative 13C nuclear magnetic resonance spectroscopy (NMR) using direct polarization and magic angle spinning. Chars from the same feedstocks produced under slow pyrolysis conditions, and a commercial hardwood charcoal, were also characterized. Switchgrass and corn stover chars were found to have high ash content (32–55 wt %), much of which was silica. BET surface areas were low (7–50 m2/g) and HHVs ranged from 13 to 21 kJ/kg. The aromaticities from NMR, ranging between 81 and 94%, appeared to increase with reaction time. A pronounced decrease in aromatic CH functionality between slow pyrolysis and gasification chars was observed in NMR and FTIR‐PAS spectra. NMR estimates of fused aromatic ring cluster size showed fast and slow pyrolysis chars to be similar (∼7–8 rings per cluster), while higher‐temperature gasification char was much more condensed (∼17 rings per cluster). © 2009 American Institute of Chemical Engineers Environ Prog, 2009

Influence of doping (Ti, V, Zr, W) and annealing on the sp2 carbon structure of amorphous carbon films

The influence of the transition metal (Ti, V, Zr, W) doping on the carbon matrix nanostructuring during the thin film growth and subsequent annealing is investigated. Pure and metal-doped amorphous carbon films (a-C, a-C:Me) were deposited at room temperature by nonreactive magnetron sputtering. The carbon structure of as-deposited and postannealed (up to 1300 K) samples was analyzed by x-ray diffraction (XRD) and Raman spectroscopy. The existence of graphenelike regions in a-C is concluded from a (10) diffraction peak. A comparison of the XRD and Raman results suggests that XRD probes only the small amount of 2–3 nm large graphenelike regions, whereas the majority of the sp2 phase is present in smaller distorted aromatic clusters which are probed only by Raman spectroscopy. Annealing leads to an increase in the graphene size and the aromatic cluster size. During the carbon film growth the addition of metals enhances ordering of sp2 carbon in sixfold aromatic clusters compared to a-C; Ti, and Zr showing the strongest effect, W the lowest. This order qualitatively corresponds with the catalytic activity of the respective carbides found during graphitization of carbide-doped graphites published in the literature. With annealing, carbide crystallite formation and growth occurs in a-C:Me films, which destroys the initial carbon structure, reduces the size of the initially formed aromatic clusters and the differences in carbon structure introduced by different dopants. For high annealing temperatures the carbon structure of a-C:Me films is similar to that of a-C, and is determined only by the annealing temperature.

Structural characterization of vitrinite-rich and inertinite-rich Permian-aged South African bituminous coals

Two South African coals of the same rank and age, but different in maceral composition were subjected to extensive structural analyses. Inertinite-rich Highveld coal (dominated by semifusinite) and vitrinite-rich Waterberg coal were studied to determine structural differences and similarities. The two coals had similar carbon content (∼ 84%, dmmf) and vitrinite reflectance (mean-maximum 0.71% for vitrinite-rich vs. 0.75% for inertinite-rich), but differed in hydrogen content (6.23% for vitrinite-rich and 4.53% for inertinite-rich). The inertinite-rich coal was more aromatic (86% for inertinite-rich and 76% for vitrinite-rich) and more polycondensed (indicated by a higher bridgehead carbon content). The inertinite-rich coal was structurally more ordered, with a higher degree of crystalline stacking. Both coals had similar average aromatic cluster sizes (16 carbons for vitrinite-rich and 18 carbons for inertinite-rich) and number of cluster attachments (6 attachments for vitrinite-rich and 5 attachments for inertinite-rich). Mass spectrometry showed that both coals consist of similar molecular weight distributions; ranging to approximately 1700 m/z with a maximum abundance of ∼ 450 m/z for the vitrinite-rich coal and ∼ 550 m/z for the inertinite-rich coal. Compared to the Argonne Premium coals the South African vitrinite-rich Waterberg coal was comparable to the coals in the high-volatile bituminous range and inertinite-rich Highveld was closer to the medium- to low-volatile bituminous range. Both coals were surprisingly similar in bulk characterization, although inertinite-rich Highveld coal was structurally more ordered, hydrogen deficient, and more aromatic.

Calibration of Size-Exclusion Chromatography Columns with 1-Methyl-2-pyrrolidinone (NMP)/Chloroform Mixtures as Eluent: Applications to Petroleum-Derived Samples

This paper presents work on the size-exclusion chromatography (SEC) of petroleum-derived fractions, using a Mixed D column (Polymer Laboratories, U.K.), where pure 1-methyl-2-pyrrolidinone (NMP), as well as several NMP/CHCl3 mixtures were used as eluents. The column calibration was performed using a variety of polymeric molecular mass standards and model polycyclic aromatic hydrocarbon (PAH) and heterocyclic compounds. Mixing CHCl3 into the eluent was observed to reduce the structure dependence of elution times of sample polymers compared to NMP alone. Elution times of a set of PAHs and heterocyclic compounds gave a line with a different slope for these smaller mass model compounds (<500 units). The mixing of CHCl3 with NMP as the eluent appears to extend the elution times of these aromatic and polar compounds, possibly because of the marginal promotion of surface effects. However, the mixed solvents allowed elution of the fractions of petroleum asphaltenes that were insoluble in NMP alone, indicating that these materials were both aromatic and of a larger size than the NMP-soluble fractions. The excluded peak observed in chromatograms of asphaltene samples became more intense when using the mixed solvent compared to SEC using pure NMP as eluent. Synchronous UV-fluorescence spectra confirmed that petroleum-derived components with the largest chromophores are insoluble in NMP but soluble in chloroform and observable by UV-fluorescence spectroscopy. The fraction insoluble in NMP was of larger aromatic cluster size and presumably attached to very large aliphatic groups that rendered the material insoluble in NMP but soluble in both chloroform and the mixed solvent. The work has shown that careful consideration of solvent properties may be instrumental in bringing together data from structurally very different polymeric standards. However, we have seen that the combination of NMP with chloroform has generated a SEC system, with its corresponding calibration, able to dissolve and elute petroleum asphaltene samples that were only partly characterized when using pure NMP as eluent.

Black (pyrogenic) carbon: a synthesis of current knowledge and uncertainties with special consideration of boreal regions

Abstract. The carbon (C) cycle in boreal regions is strongly influenced by fire, which converts biomass and detrital C mainly to gaseous forms (CO2 and smaller proportions of CO and CH4), and some 1–3% of mass to pyrogenic C (PyC). PyC is mainly produced as solid charred residues, including visually-defined charcoal, and a black carbon (BC) fraction chemically defined by its resistance to laboratory oxidation, plus much lower proportions of volatile soot and polycyclic aromatic hydrocarbons (PAHs). All PyC is characterized by fused aromatic rings, but varying in cluster sizes, and presence of other elements (N, O) and functional groups. The range of PyC structures is often described as a continuum from partially charred plant materials, to charcoal, soot and ultimately graphite which is formed by the combination of heat and pressure. There are several reasons for current interest in defining more precisely the role of PyC in the C cycle of boreal regions. First, PyC is largely resistant to decomposition, and therefore contributes to very stable C pools in soils and sediments. Second, it influences soil processes, mainly through its sorption properties and cation exchange capacity, and third, soot aerosols absorb solar radiation and may contribute to global warming. However, there are large gaps in the basic information needed to address these topics. While charcoal is commonly defined by visual criteria, analytical methods for BC are mainly based on various measures of oxidation resistance, or on yield of benzenepolycarboxylic acids. These methods are still being developed, and capture different fractions of the PyC structural continuum. There are few quantitative reports of PyC production and stocks in boreal forests (essentially none for boreal peatlands), and results are difficult to compare due to varying experimental goals and methods, as well as inconsistent terminology. There are almost no direct field measurements of BC aerosol production from boreal wildfires, and little direct information on rates and mechanisms for PyC loss. Structural characterization of charred biomass and forest floor from wildfires generally indicates a low level of thermal alteration, with the bulk of the material having H/C ratios still &gt;0.2, and small aromatic cluster sizes. Especially for the more oxidation-resistant BC fraction, a variety of mainly circumstantial evidence suggests very slow decomposition, with turnover on a millennial timescale (in the order of 5–7 ky), also dependent on environmental conditions. However, there is also evidence that some PyC may be lost in only tens to hundreds of years due to a combination of lower thermal alteration and environmental protection. The potential for long-term PyC storage in soil may also be limited by its consumption by subsequent fires. Degraded, functionalized PyC is also incorporated into humified soil organic matter, and is transported eventually to marine sediments in dissolved and particulate form. Boreal production is estimated as 7–17 Tg BC y−1 of solid residues and 2–2.5 Tg BC y−1 as aerosols, compared to global estimates of 40–240 and 10–30 Tg BC y−1, respectively. Primary research needs include basic field data on PyC production and stocks in boreal forests and peatlands, suitable to support C budget modeling, and development of standardized analytical methods and of improved approaches to assess the chemical recalcitrance of typical chars from boreal wildfires. To accomplish these goals effectively will require much greater emphasis on interdisciplinary cooperation.

Nuclear Magnetic Resonance and Ruthenium Ion Catalyzed Oxidation Reaction Analysis for Further Development of Aromatic Ring Size through the Heat Treatment of Coking Coals at &gt;500 °C

The development of aromatic cluster size in heat-treated coals by heating above 500 °C is discussed. Heat treatment of coal was performed at 500, 600, and 700 °C to obtain semicoke samples. The temperature range was above the resolidification temperature of the coal samples. For comparison, a strongly coking coal, Australian Goonyella coal, and a slightly coking coal, Chinese Enshu coal, were used as the sample coals. Analysis of the virgin coals and the semicoke samples with solid-state 13C NMR indicated that the strongly coking coal tended to develop the aromatic ring size to a greater degree than the slightly coking coal as the heat-treatment temperature increased. To examine this tendency, a ruthenium ion catalyzed oxidation reaction was applied to the semicoke samples to obtain information concerning the distribution of the aromatic ring size. The products from this reaction also implied that the semicoke samples obtained from the strongly coking coal had an aromatic ring of larger size on average. A schematic representation of the behavior of molecules in the two coal samples during heating was established.

Catalytic hydrocracking of petroleum-derived asphaltenes by transition metal-loaded zeolite catalysts

In this study, correlation between structural parameters and reactivity for hydrocracking of asphaltene samples was investigated. Two different crude oils- (Arabian light/medium mixture and Brazilian Marlim) and Indonesian natural asphalt-derived asphaltenes were employed as samples. These asphaltene samples were submitted to elemental and spectroscopic analyses to obtain structural information such as H/C atomic ratio, heteroatom contents, carbon aromaticity, average size of aromatic clusters, and number-average molecular weight. These asphaltenes were also submitted to hydrocracking reaction at 400–450 °C for 3 h under H 2 pressure in the presence of palladium and nickel co-loaded Y-type zeolite catalyst. Reactivities of these samples were different to each other depending on their properties, the order of the reactivity obeying the following sequence: Indonesian natural asphalt-derived one>Arabian mixture-derived one>Brazilian Marlim-derived one. By increasing reaction temperature for hydrocracking or a pre-treatment with tetralin or with H 2-catalyst prior to hydrocracking, more than 60% of asphaltene feeds could be converted to C 1–C 4 hydrocarbon gases, H 2S, naphtha, and gas oil. Based on these experimental results, the correlation between structural features and reactivity of the samples was discussed. Among the parameters examined, both average molecular weight and nitrogen contents of the samples were found to be correlated with the reactivity.

03/02485 Modeling for pyrolysis of solid particle: kinetics and heat transfer effects: Babu, B. V. and Chaurasia, A. S. Energy Conversion and Management, 2003, 44, (14), 2251–2275

A wide selection of thermal, chemical and optical methods have been proposed for the quantification of black carbon (BC) in environmental matrices, and the results to date differ markedly depending upon the method used. A new approach is hydropyrolysis (hypy), where pyrolysis assisted by high hydrogen pressures (150 bar) facilitates the complete reductive removal of labile organic matter, so isolating a highly stable portion of the BC continuum (defined as BChypy). Here, the potential of hypy for the isolation and quantification of BC is evaluated using the 12 reference materials from the International BC Ring Trial, comprising BC-rich samples, BC-containing environmental matrices and BC-free potentially interfering materials. By varying the hypy operating conditions, it is demonstrated that lignocellulosic, humic and other labile organic carbon material (defined as non-BChypy) is fully removed by 550 °C, with hydrogasification of the remaining BChypy not commencing until over 575 °C. The resulting plateau in sample mass and carbon loss is apparent in all of the environmental samples, facilitating BC quantification in a wide range of materials. The BChypy contents for all 12 ring trial samples fall within the range reported in the BC inter-comparison study, and systematic differences with other methods are rationalised.All methods for BC isolation, including hypy are limited by the fact that BC cannot be distinguished from extremely thermally mature organic matter; for example in high rank coals. However, the data reported here indicates that BChypy has an atomic H/C ratio of less than 0.5 and therefore comprises a chemically well-defined polyaromatic structure in terms of the average size of peri-condensed aromatic clusters of >7 rings (24 carbon atoms), that is consistent across different sample matrices. This, together with the sound underlying rationale for the reductive removal of labile organic matter, makes hypy an ideal approach for matrix independent BC quantification. The hypy results are extremely reproducible, with BChypy determinations from triplicate analyses typically within ±2% across all samples, limited mainly by the precision of the elemental analyser.

Solid-state 13C NMR characterization of matched tars and chars from rapid coal devolatilization

Matehed tar/char sets were prepared by pyrolysis of a lignite and a bituminous coal in two entrained flow reactors at temperatures between 900 K and 1650K and heating rates of 104–105 K/s. Detailed chemical structural characterization of these tars and chars was performed using elemental analysis and solid-state 13C NMR. This is the first set of detailed solid-state 13C nuclear magnetic resonance (NMR) data on coal tar samples. The average aromatic cluster sizes of the primary tars from these experiments are quite similar to those of their parent coals, confirming an assumption often made in network devolatilization models. Carbon aromaticities increase in char and tar samples until about 1250 K, after which line broadening in the NMR signal is observed. This line broadening is interpreted as formation of large aromatic radicals. Increases in bridges and loops per cluster are evidence for increased crosslinking above 1250 K. The measured molecular weights per cluster of the primary tars are lower than expected, indicating that some multiple cluster molecules (i.e., dimers) may exist in the tar. Tar and char nitrogen chemical structure is shown to correlate with changes in the carbon aromaticity, which may have implications for nitrogne release models that treat secondary reactions in the tar.

Planar chromatographic separation of petroleum residues and coal-derived liquids

Vacuum distillation residues from two petroleum crudes, a coal liquefaction extract and a coal tar pitch have been fractionated by planar chromatography (PC) using two solvent sequences: pyridine–acetonitrile and tetrahydrofuran (THF)–toluene. Fractions recovered from PC were examined by UV-fluorescence spectroscopy (UV-F), size-exclusion chromatography (SEC). UV-F and SEC of the whole samples showed differences in aromatic cluster size and molecular mass (MM) ranges which could be related to the different origins of the samples. The MM ranges indicated by SEC were greater for the vacuum residues than for coal-derived materials. However, the UV-F spectra of the fractions indicated that the petroleum residue fractions contained similar aromatic types, whereas the fractions from coal liquids contained significantly different aromatic types. SEC profiles of the fractions indicated a separation of coal-derived samples by increasing molecular size with increasing immobility in PC, whereas for petroleum fractions, the same trend was not apparent. MALDI-mass spectra of the set of original samples showed broadly similar ranges of MM distributions but additional work is necessary to identify appropriate matrices and procedures in order to improve the MALDI spectra.

99/00655 Furnace water-wall slag deposition testing in a 0.5 MWT combustion pilot plant

Elemental analysis, CP/MAS 13C NMR, FTIR, XRD, XPS and ion-exchange experiment were used to study the structural characteristics of Longkou, Huadian and Yilan kerogens in an increasing order of humic degree. The relationship between their humic degree and structural characteristics was studied from three aspects: aliphatic structure, aromatic structure and heteroatom species (O, N and S). The results show that the kerogens are mainly composed of aliphatic structure, dominantly as CH2 chain. Moreover, the ratio of aliphatic carbon (fal, aliphaticity) and average methylene chain length (Cn) decrease with the increase of humic degree. In these kerogens, most of their aromatic clusters are separated by various bridge bonds or many CH2 long chains. Furthermore, the ratio of aromatic carbon (fa, aromaticity) and average aromatic cluster size increase while the substitutive degree of aromatic ring decreases with increasing humic degree. With an increase in humic degree, the content of OCO (carboxyl and ester) decreases and the contents of CO (alcohol, phenol, and ether) increase. Moreover, the content of phenolic hydroxyl groups increases and the content of carboxyl groups decreases with increasing humic degree. The organic nitrogen in the kerogens is distributed as pyridinic nitrogen, amine nitrogen, pyrrolic nitrogen and chemisorbed nitrogen oxides. The contents of pyridinic nitrogen and chemisorbed nitrogen oxides increase while the contents of amino nitrogen and pyrrolic nitrogen decrease with increasing humic degree. In addition, organic sulfur in these kerogens exists as aromatic and aliphatic sulfur, sulfone and sulfoxide. The contents of aromatic sulfur and sulfoxide increase while the contents of aliphatic sulfur and sulfone decrease with increasing humic degree.

石炭の固体ＮＭＲ測定による芳香族クラスター平均サイズの推定

Measurements of solid-state NMR of eight Argonne Premium Coal Samples were conducted to estimate the average aromatic cluster size in these coals. Firstly, the carbon distribution was obtained from SPE/MAS 13C-NMR. Secondary, 1HCRAMPS NMR spectra gave the hydrogen aromaticity of coal. Combination use of the hydrogen aromaticity and elemental analysis data could afford the amount of tertiary aromatic carbon. The parameter of χb, the mole fraction of aromatic bridgehead carbons in all aromatic carbons, could be derived from above NMR data and elemental analysis of coal. χb is directly correlated to the number of aromatic carbon atoms per aromatic cluster, C. In this study, the value of C varied from 10 (corresponding to the size of naphthalene) for Beulah-Zap and Wyodak coals to 23 (corresponding to the size of coronene) for Pocahontas No.3 coal.

98/01807 Linkages between aromatic structures in the Argonne Premium Coal Samples : Winans, R. E. and Tomczyk, N. A. Prepr. Pap. Am. Chemical Soc., Div. Fuel Chem., 1997, 42, (1), 181–184

The objective of this study is to elucidate the nature of the important linkages between aromatic clusters and variations of these links with coal rank. From studies using methods such as NMR and mass spectrometry, the authors have considerable information on the size and types of aromatic clusters in the Argonne coals. In this study, extracts, model polymers, extracted coals, and modified coals are examined by temperature resolved high resolution mass spectrometry. There is evidence that strong bond cleavage may be very important for volatile release in pyrolysis of higher rank coals.

97/00834 Coal liquefaction method

Catalysts of the CoMo type were prepared on four different surface-modified alumina supports: (1) TiO2-coated by impregnation, (2) ZrO2-coated by impregnation, (3) TiO2-coated by deposition, and (4) carbon-coated by pyrolysis. These catalysts were used in a catalytic coal liquefaction microreactor. The coke deposits on the spent catalysts were investigated using 13C solid-state nuclear magnetic resonance techniques of cross polarization with magic angle spinning (CP-MAS) and dipolar dephasing (DD). CP-MAS 13C spectral data of the coke deposits were used to quantify the aromatic and aliphatic carbon types, and 13C DD spectral data of the same samples to quantify the aromatic quaternary carbon types, from which the aromatic cluster size of the coke deposits was determined. Catalysts which promote the most coke deposition were found to perform poorly in terms of coal liquefaction conversion. The aromatic cluster size of the coke deposited on the spent catalysts appears to depend on the initial pore volume of the fresh catalyst and on the percentage of surface coating of the alumina support.

97/00828 Characterization and activity of ferric-sulfide-based catalyst in model reactions of direct coal liquefaction: effect of preparation conditions

Catalysts of the CoMo type were prepared on four different surface-modified alumina supports: (1) TiO2-coated by impregnation, (2) ZrO2-coated by impregnation, (3) TiO2-coated by deposition, and (4) carbon-coated by pyrolysis. These catalysts were used in a catalytic coal liquefaction microreactor. The coke deposits on the spent catalysts were investigated using 13C solid-state nuclear magnetic resonance techniques of cross polarization with magic angle spinning (CP-MAS) and dipolar dephasing (DD). CP-MAS 13C spectral data of the coke deposits were used to quantify the aromatic and aliphatic carbon types, and 13C DD spectral data of the same samples to quantify the aromatic quaternary carbon types, from which the aromatic cluster size of the coke deposits was determined. Catalysts which promote the most coke deposition were found to perform poorly in terms of coal liquefaction conversion. The aromatic cluster size of the coke deposited on the spent catalysts appears to depend on the initial pore volume of the fresh catalyst and on the percentage of surface coating of the alumina support.

Carbon-13 solid-state n.m.r. investigation of coke deposits on spent catalysts used in coal liquefaction

Catalysts of the CoMo type were prepared on four different surface-modified alumina supports: (1) TiO 2-coated by impregnation, (2) ZrO 2-coated by impregnation, (3) TiO 2-coated by deposition, and (4) carbon-coated by pyrolysis. These catalysts were used in a catalytic coal liquefaction microreactor. The coke deposits on the spent catalysts were investigated using 13C solid-state nuclear magnetic resonance techniques of cross polarization with magic angle spinning (CP-MAS) and dipolar dephasing (DD). CP-MAS 13C spectral data of the coke deposits were used to quantify the aromatic and aliphatic carbon types, and 13C DD spectral data of the same samples to quantify the aromatic quaternary carbon types, from which the aromatic cluster size of the coke deposits was determined. Catalysts which promote the most coke deposition were found to perform poorly in terms of coal liquefaction conversion. The aromatic cluster size of the coke deposited on the spent catalysts appears to depend on the initial pore volume of the fresh catalyst and on the percentage of surface coating of the alumina support.

The thermal evolution indicator of carbonate rocks

It has been studied by the solid state 13C NMR analysis that the chemical composition and the structure feature of kerogen of carbonate rocks are characteristic of different types and evolution degree. The purpose is to show the evolution degree using the structure parameters of kerogen of carbonate rocks. The detailed analysis of the carbon aromaticity (fa), the hydrogen aromaticity (Ha) and the average aromatic cluster size (Xb) indicates that Xb is the most effective indicator of evolution degree, and it is not influenced by the type and evolution degree of kerogen. The correlation between the average aromatic cluster size and vitrinite reflectance value of kerogen has also been established.

SOLID STATE13C NMR STUDY OF CHINESE COALS

ABSTRACT Ten coals of different metamorphic degree have been investigated by the use of 13 C CP/MAS NMR technique, of which the spin-lattice relaxation, variable contact time and dipolar dephasing experiments were performed on each coal. The data from above experiments, together with normal CP/MAS integration over selected chemical shift ranges, were used to derive 12 parameters of carbon skeletal structure including the aromaticity. These parameters are correlated with carbon content (weight per cent) in coal and we find that there are close relations between the NMR parameters and metamorphic degree of coals- From the ratio of aromatic bridgehead to aromatic peripheral carbons as measured by NMR, the aromatic cluster size may be estimated for each coal.

Evolution of carbon structure in chemically activated wood

13C NMR and FTIR analyses have been employed to follow the evolution of chemical structure in relation to porosity development, as a function of heat treatment temperature (HTT), for activated carbons produced from white oak by phosphoric acid activation. The chemical changes effected by acid treatment at low HTT are: by 50 °C there is significant alteration of the lignin structure; by 100 °C a significant portion of the cellulose has reacted, with the formation of ketones and esters; the formation of phosphate esters becomes apparent around 150 °C; crosslinking reactions are initiated below 150 °C, consistent with the higher carbon yield obtained in chemical activation; and generally there is an increase in aromaticity and loss of aliphatic, carboxyl, and carbonyl groups. The low temperature phenomena precede, and relate to, the development of porosity and structural dilation that commences around 250 °C, and attains a maximum between 350 and 450 °C. Up to 450 °C, pore volume is found to correlate with crosslink density. Above 450 °C, there is a dimensional contraction and a reduction in porosity. Among the accompanying phenomena are: the elimination of cellulose phosphates and oxygen functionalities; and a dramatic increase in the estimated aromatic cluster size. The latter would require a reduction in crosslink density to facilitate cluster growth, and the resulting structural rearrangement and increased alignment of clusters would produce a more densely packed structure with reduced porosity.

STUDY OF STRUCTURAL FEATURE OF PEAT, LIGNITE AND HUMIC ACID BY SOLID STATEl3C NMR SPECTROSCOPY

Abstract Four low rank coals (peat and lignite) and their derived humic acids have been investigated by thel3C CP/MAS/TOSS NMR technique. The NMR analysis indicates that the peat contains a significant amount of unaltered plant components including cellulose, hemicellulose, lignin, waxes, and resins. Variable contact time and dipolar dephasing experiments were performed on each sample. The data from above experiments, together with normal CP/MAS integration over selected chemical shift range, were used to derive 12 parameters of carbon skeletal structure including the aromaticity.From the ratio of aromatic bridgehead carbons, fa cp, to the aromatic peripheral carbons, fcpxBp as measured by NMR, the aromatic cluster size may be estimated for each coal.