Aromatic Cluster Size Research Articles

Structural parameters and molecular model of Shendong subbituminous coal

Coal has a highly complex chemical structure, similar to polymers, coal is a macromolecular structure composed of a large number of “similar compounds”, which is called the basic structural unit. Understanding coal structure is the basis of its transformation and utilization. Shendong (SD) coal was analyzed by FTIR, XRD, XPS, and NMR. The results show that SD coal normalized structure formula is C100H68.5O35.7N1.2S0.2 and the average number of aromatic rings is 1.98. –CH2— content accounts for about 82% in aliphatic C–H region, and the ratio of ether bond C–O, aromatic ether C–O and CO is about 2:1:11 in oxygen-containing functional group region. The d002, LC, La and NC of SD coal microcrystalline structure parameters are 0.1832 nm, 1.4688 nm, 2.0852 nm and 9.017, respectively. Aromatic carbon and aliphatic carbon ratios of SD coal are 55.67% and 29.97%, aromatic cluster size and average methylene chain length are 0.224 and 1.817. Based on these structural parameters, molecular model of SD coal was constructed with 13C SSNMR experimental spectra as a reference. The model was constructed with an atom composition of C214H214O49N2S.

Biochar data into structure: A methodology for generating large-scale atomistic representations

A well-defined methodology for constructing appropriate atomistic representations of biochar will aid in visualizing the structural features and elucidating biochar behavior with molecular dynamics (MD) simulations. Such knowledge will facilitate engineering biochars tailored to specific applications. To achieve this goal, we adapted modeling strategies applied in coal science by employing multi-cross-polarization 13C nuclear magnetic resonance, ultimate analysis, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy to identify functional groups. Helium density, surface area, and porosity were used to assess structural features. Biochar's aromatic cluster size distribution was proposed based on data from the benzene polycarboxylic acid method. The computational framework reduces bias by incorporating chemical information derived from density functional theory, reactive MD simulations, and advanced characterization data. The construction approach was successfully applied to cellulose biochars produced at four temperatures, obtaining independent representations with a relative error on the atomic contents of <10 % for oxygen and nitrogen and <5 % for carbon and hydrogen. The atomistic representations were validated using X-ray diffraction, electron spin resonance data, and laser desorption/ionization Fourier-transform ion cyclotron resonance-mass spectrometry. The code will assist others in overcoming structural creation barriers and enable the utilization of the generated structures for further simulations.

A study on the structures and primary reaction products of kerogens in Longkou oil shale with different densities through supercritical ethanolysis

The difference in the density of oil shale significantly affects the structural characteristics of the kerogen, which brings the change in the pyrolysis behavior, thus leading to different retorting oil yields. The primary reaction (the cleavage of weak covalent bonds into free radicals) in the pyrolysis of oil shale greatly affects the retorting oil yield and quality. In this work, the structural characteristics and primary reaction products of the kerogens in Longkou oil shale (LKOS) with three different densities (<1.3, 1.4 − 1.5, 1.8 − 1.9 g/cm3) were investigated by supercritical ethanolysis, 13C nuclear magnetic resonance (13C NMR) and Fourier transform infrared spectroscopy (FTIR). The weak covalent bonds in the kerogens were broken by ethanolysis at 350 °C to obtain small molecular substances (SMSs) with the carbon conversions of 28 %, 47 % and 54 %, respectively. The SMSs can be divided into aliphatic acid esters, aromatics, alkanes and N-containing organic compounds (NCCs). Among the SMSs, the relative contents of the aliphatic acid esters, whose aliphatic chain lengths distribute in C3-C23, C1-C24 and C1-C28, are the highest. The aromatics are mainly monocyclic, and the NCCs mainly exist as amines. The possible pathways for these ethanolysis products were proposed. The 13C NMR and FTIR analyses of the kerogens and their ethanolysis residues show that the aliphaticity (fal) and average methylene chain length (Cn) increase, while the aromaticity (fa) and average aromatic cluster size (Xb) decrease with the increasing oil shale density. After ethanolysis, the value of fa gradually increases, while that of fal and Cn decrease. Furthermore, the contents of C=O and O-C=O decrease, while that of O-C-O and C-OH increase. The results suggest that the SMSs are connected to the kerogen matrix by weak covalent bonds. The cleavage of C=O, O-C=O and C-O bonds dominates the early stage of the oil shale pyrolysis. During the pyrolysis of oil shale, these weak covalent bonds are first broken and the above SMSs are the most primary reaction products and then undergo the second reactions to yield oil and gas.

Large-scale atomistic model construction of subbituminous and bituminous coals for solvent extraction simulations with reactive molecular dynamics

Large-scale atomistic models for complex polycyclic aromatic hydrocarbon systems help understand the chemical properties and behaviors of complex feedstocks such as coal or petroleum. However, the development and utilization of large-scale models remain limited due to the difficulty in achieving the varied structural characteristics necessary to capture stochastic nature of these feedstocks. We demonstrate a systematic workflow to construct stochastic molecular systems from a broad analytical suite: high-resolution transmission electron microscopy (HRTEM), carbon-13 nuclear magnetic resonance spectroscopy (13C NMR), laser desorption ionization mass spectroscopy (LDI-MS), and elemental analysis. We present a model construction and analysis utility of a new Python-based module. We selected one subbituminous and three high-volatile bituminous coals to construct large-scale models (∼40,000 atoms). The constructed models were utilized to examine the affinity for solvent extraction (naphthalene or tetralin) and the effect of structural properties (e.g., aromatic cluster size, functional groups, and cross-linking) in reactive molecular dynamics simulations. Complex chemical reactions were monitored with bond order transitions, intermediates formation, and mass distributions. Reactive molecular dynamics simulations suggest a plausible chemical extraction process and products for the complex fossil feedstocks. The results indicated that radical formations with bond breaking of bridging oxygens and carbons were required at high temperatures to facilitate hydrogeneration and extraction of gas molecules from radical-free molecules. We observed that aliphatic chains of tetralin were easily decomposed and combined with radicals to form small size of molecules with aryl bonding, mainly increasing molecules in the 500–1000 Da, while naphthalene had little impact on chemical extraction process.

Molecular Modelling and Characterization of Metal Incorporated Biochar from Industrial Wastes

Globally, manufacturing industries are generating a large volume of solid waste during their processes. These wastes, when spread through soil/water affect public health. This work focuses on the use of solid industrial waste from herbal medicine and TiO2 manufacturing industries to produce iron oxide incorporated biochar, which can be served as adsorbent and low cost catalyst for many reactions. Biochar was produced by the slow pyrolysis of waste collected from herbal manufacturing units using tubular furnace at 550°C at a heating rate of 5°C/min. The iron oxide waste collected from Kerala Minerals and Metals Limited, Kerala, India (KMML), was incorporated into the produced biochar by using planetary ball mill apparatus. Structural and elemental analysis of produced biochar and Fe2O3 incorporated biochar was conducted using XRD, SEM and SEM-EDS, BET surface area analysis, ICP-OES, and CHNS analysis. The H/C ratio of prepared biochar shows it has a rectangular layered structure of 50*50 aromatic cluster size. The changes in bonds and groups before and after metal incorporation were studied using FTIR spectroscopic analysis and temperature stability of prepared samples were analyzed using TGA. The molecular structure of produced biochar and changes in their bond length was studied and optimized employing Avogadro and Chemcraft software. The BET analysis shows the surface area of biochar become increased after the metallic incorporation. The same results were concluded from the molecular modelling data obtained from Chemcraft software. These results proved that the biochar surface area and pore volume can be increased by incorporation of iron oxide from industrial waste.

Structural evolution characteristics of lignite during pyrolysis based on alkaline-oxygen oxidation, NMR and FTIR

Pyrolysis is a crucial conversion process for lignite to improve its quality and produce chemicals. Here, the evolution characteristics and pathways of lignite during pyrolysis were investigated by the combination of oxidation product distribution and physical structural parameters, which reflected the correlations between the size of aromatic clusters and pyrolysis temperature. The results showed that with increasing the pyrolysis temperature up to 500 ℃, the aromatic structures were enriched, and the average size of aromatic clusters increased with pyrolysis temperature. A little variation of interlayer spacing (d002) was observed, while the stacking height (Lc) and the average lateral size (La) increased gradually. Before 400 ℃, double-aromatic clusters were dominant in chars, and the corresponding chars were abundant with precursor structures of the alkaline-oxygen oxidation products benzene tricarboxylic acid (BCA3), benzene tetracarboxylic acid (BCA4) and benzene pentacarboxylic acid (BCA5). Above 400 ℃, more triple- or quadruple-ring aromatic clusters were present, and the precursor structures of benzene dicarboxylic acid (BCA2), benzene tricarboxylic acid (BCA3), and benzene tetracarboxylic acid (BCA4) increased considerably. The results indicate that the benzene carboxylic acids (BCAs) from oxidation are an effective evaluation method to reflect the abundance of aromatic rings in the parent structure of coals.

CO2 Gasification Reactivity of Char from High-Ash Biomass

Biomass char produced from pyrolysis processes is of great interest to be utilized as renewable solid fuels or materials. Forest byproducts and agricultural wastes are low-cost and sustainable biomass feedstocks. These biomasses generally contain high amounts of ash-forming elements, generally leading to high char reactivity. This study elaborates in detail how chemical and physical properties affect CO2 gasification rates of high-ash biomass char, and it also targets the interactions between these properties. Char produced from pine bark, forest residue, and corncobs (particle size 4–30 mm) were included, and all contained different relative compositions of ash-forming elements. Acid leaching was applied to further investigate the influence of inorganic elements in these biomasses. The char properties relevant to the gasification rate were analyzed, that is, elemental composition, specific surface area, and carbon structure. Gasification rates were measured at an isothermal condition of 800 °C with 20% (vol.) of CO2 in N2. The results showed that the inorganic content, particularly K, had a stronger effect on gasification reactivity than specific surface area and aromatic cluster size of the char. At the gasification condition utilized in this study, K could volatilize and mobilize through the char surface, resulting in high gasification reactivity. Meanwhile, the mobilization of Ca did not occur at the low temperature applied, thus resulting in its low catalytic effect. This implies that the dispersion of these inorganic elements through char particles is an important reason behind their catalytic activity. Upon leaching by diluted acetic acid, the K content of these biomasses substantially decreased, while most of the Ca remained in the biomasses. With a low K content in leached biomass char, char reactivity was determined by the active carbon surface area.

An evaluation of kerogen molecular structures during artificial maturation

13C solid-state NMR and XPS techniques were used to investigate structural changes in kerogen during oil generation process across a range of maturity. Kerogen was isolated from an shale rock collected from Well W161 in the Dongying Depression, Bohai, China. An artificial pyrolysis experiment was carried out in a closed gold tube system using a heating rate of 2 ℃/h during which 11 temperature-point samples were collected between 350 ℃ and 450 ℃ (Easy%Ro = 0.80 to 1.98). The initial kerogen was analysed using Rock-Eval and the samples were analysed using X-ray photoelectron spectroscopy (XPS) and solid-state 13C nuclear magnetic resonance (13C NMR) to study their functional groups and chemical structures. Six averaged molecular structure models of the initial kerogen and its residues (can not be dissolved by organic reagent) were established to study the changes occurring during oil and gas generation. The results showed that with an increase in temperature, the proportion of aliphatic carbon declined while aromatic carbon increased. After reaching peak oil maturity, a condensation reaction occurred in the residue; some aromatic carbons cracked from the kerogen and combined with the residue structure. Average aromatic cluster increment was calculated to quantify the increase in the size of aromatic clusters within the structures. It was established to evaluate the changes occurring in the molecular structure of type Ⅰ kerogen during heating. Based on these results, ConU (maximum condensation degree) and ConL (lowest condensation degree) are proposed to estimate the degree of condensation of samples with different maturities.

Spectroscopic analyses combined with Gaussian and Coats-Redfern models to investigate the characteristics and pyrolysis kinetics of sugarcane residue-derived biochars

Abstract Biomass and biochars are considered good potential materials for environmental applications and their positive or negative effects on an ecosystem are mainly derived from the diverse physicochemical and pyrolytic kinetic properties. However, the characteristics of biomass resulted biochars have not been fully recognized. In this study, three biochars derived from dried sugarcane residue were prepared under 300, 500 and 700 °C. Spectroscopic techniques coupled with a Gaussian model were applied to innovatively de-convolute the existences and contributions of distinct overlapping peaks in the spectra, and then quantitatively evaluated the functional groups, sizes of aromatic clusters, and the degree of aromatic condensation of the sugarcane residue and biochars. Aromatic carbon/carbon-carbon double bond, single bonded oxygen, and pyrrolic nitrogen were dominant surface elements of the sugarcane residue and biochars. Decomposition and formation of different functional groups were quantitatively distinguished for pyrolysis temperature dependent biochars by Gaussian model. The changes of different carbon types and structures were attributed to the progressive dehydration, decarboxylation, aromatization reactions and structural formations of condensed carbon during the conversion of sugarcane residue into biochars. The biochars produced at higher pyrolysis temperatures exhibited higher fractions of bridgehead carbons, aromatic ring cluster sizes, and macromolecular aromatics. The sugarcane residue and biochars had fewer substituent groups at each aromatic ring and the biochars produced under 500 °C and 700 °C had an average of 14 more carbons in average aromatic cluster. The pyrolysis reactions of sugarcane residue and biochars were mainly associated with the degradation of hemicellulose, cellulose, and lignin components. The novel application of using spectroscopy coupled with a Gaussian model presented in this study has shown great potential as a valuable and effective characterization technique for studying the characteristics and pyrolysis kinetics of biochars. Results from this study benefit the greater understanding of the properties and reactivity of biomass and biochars, and their effects on pyrolysis optimization, carbon/pollutant sequestration, potential energy generation, and many other applications in the future.

Effects of thermal dissolution in different solvents on structural characteristics and pyrolysis behaviors of lignite

Thermal dissolution (TD) of Xilinhaote lignite (XL) in n-hexane, toluene and methanol were carried out, and then the residues of thermal dissolution (RTDs) and XL were pyrolyzed at a low temperature of 550 °C to explore the effect of TD on structural characteristics and pyrolysis behaviors of XL. Results show that RTDs present higher aromatic carbon content (fa), lower aliphatic carbon (fal) and oxygen-linked carbon content (fO), indicating that the molecular structure of XL becomes more ordered after TD, especially that in n-hexane. Among three RTDs, the RTD in methanol obtained at 290 °C (RTDM,290) exhibits the largest aromatic cluster size. The influences of TD at 290 °C on the pyrolysis behaviors of XL are remarkable. Compared with XL , the pyrolysis of RTDs obtained at 290 °C (RTD290s) present higher char yields, lower tar, gas and water yields. The pyrolysis of RTD in n-hexane obtained at 290 °C (RTDH,290) exhibits extremely low tar yield, suggesting that the low molecular weight compounds (LMWCs) isolated from XL during TD can transport into tar and/or act as hydrogen donors to stabilize the radical fragments during pyrolysis processes. Although the methanol soluble portion (SP) yield is up to 9.45% at 290 °C, the tar yield of RTDM,290 is almost equal to that of XL, indicating that the swelling effect of XL in methanol is significant and it is conducive to the production of tar.

Production and Composition of Pyrogenic Dissolved Organic Matter From a Logical Series of Laboratory-Generated Chars

Though pyrogenic carbon (pyC) has been assumed to be predominantly stable, degradation and transfers of pyC between various pools have been found to influence its cycling and longevity in the environment. Dissolution via leaching may be the main control on loss processes such as microbial or abiotic oxidation, mineral sorption, or export to aquatic systems. Yet, little is known of the controls on pyrogenic dissolved organic matter (pyDOM) generation or composition. Here, the yield and composition of pyDOM generated through batch leaching of a thermal series of oak and grass biochars, as well as several non-pyrogenic reference materials, was compared to that of their parent solids. Over 17 daily leaching cycles, biochars made from oak at 250 to 650° C released decreasing amounts of C on both a weight (16.9 to 0.3%, respectively) and C yield basis (7.4 to 0.2% C, respectively). Aryl-C represented an estimated 32 to 82% of C in the parent solids (identified by 13C-NMR), but only 7 to 38% in the leachates (identified by 1H-NMR), though both increased with pyrolysis temperature. PyC, often operationally defined as condensed aromatic carbon (ConAC), was quantified using the benzenepolycarboxylic acid (BPCA) method. Tri- and tetra-carboxylated BPCAs were formed from non-pyrogenic reference materials, thus, only penta- and hexa-carboxylated BPCAs were used to derive a BPCA-C to ConAC conversion factor of 7.04. ConAC made up 24 to 57% of the pyrogenic solid C (excluding the 250 °C biochar), but only about 9 to 23% of their respective leachates’ DOC, though both proportions generally increased with pyrolysis temperature. Weighted BPCA compound distributions, or the BPCA Aromatic Condensation (BACon) Index, indicate that ConAC cluster size increased in pyrogenic solids but not in leachates. Additional evidence presented suggests that both aromatic cluster size and O-containing functional group contents in the pyrogenic solid control pyC solubility. Overall, pyDOM was found to be compositionally dissimilar from its parent chars and contained a complex mixture of organic compound groups. Thus, it is expected that estimates of dissolved pyC production and export, made only by detection of ConAC, are too low by factors of 4 to 11.

A study on average molecular structure of eight oil shale organic matters and radical information during pyrolysis

Eight oil shale samples from different mines are demineralized and characterized to understand the average molecular structure of the organic matters (OMs). The active radicals generated during pyrolysis of the OMs are quantified to evaluate the relation between average molecular structure and bond cleavage. Results indicate that all the OMs are similar to lignite in metamorphic grade and their carbon contents range from 64 wt% to 70 wt%, H/C molar ratios range from 1.0 to 1.5, and the volatile contents range from 52.7 wt% to 82.2 wt%. The aliphaticity and aromaticity of the OMs are 0.45–0.77 and 0.18–0.49, respectively. The H/C molar ratio is in direct proportion to the aliphaticity and the volatile content of the OMs while in inverse proportion to the aromaticity. Pyrolysis experiments at 420 °C in the presence of 9,10-dihydrophenanthrene (DHP) show that the active radicals generated by bond cleavage are in a range of 15.1–24.3 mmol/g in 12 min, with half of them generated in 2 min. The bonds cleaved in the pyrolysis are mainly those between α–Cal and β–Cal in Car–Cal–Cal chains and Cal–O. The quantity of radicals survived in the pyrolysis product (i.e. stable radicals) determined by electron spin resonance (ESR) correlates linearly with the quantity of active radicals. The probability of stable radicals’ formation in the pyrolysis correlates poorly with the aromaticity of the OMs and the concentration and size of the average aromatic clusters, although the stable radicals are considered to be un-paired electrons confined in aromatic structure.

The structural characteristics of kerogens in oil shale with different density grades

The oil yields of oil shale with different density grades are different, which depend on not only the content of kerogen but also the structural characteristic of kerogen in the oil shales. However, no studies focus on the structural characteristics of kerogens in oil shale with different density grades. Therefore, the structural characteristics of kerogens isolated from Longkou oil shale with different densities (1.3–1.4, 1.4–1.5, 1.7–1.8, 1.9–2.0 g/cm3) were studied by 13C NMR, FTIR, XRD and XPS. The structural characteristics of the kerogens were studied from three aspects: aliphatic structure, aromatic structure and heteroatom species (O, N and S). The results show that with increasing the density of corresponding oil shales, the ratio of aliphatic carbon and average methylene chain length of the kerogens increase, and the substitutive degree of aromatic ring increases, while the ratios of aromatic carbon and average aromatic cluster size decrease. The aromatic structures in the studied kerogens are mainly 1 and 2 rings. A small amount of aromatic clusters with more than 2 rings are found in the kerogen isolated from the oil shale with the density grade of 1.3–1.4 g/cm3. The oil yield from Fischer Assay is the highest when the density of oil shale is 1.4–1.5 g/cm3. In addition, the organic oxygen exists as CalO (alcohol and ether), CarO (phenol and ether), OCO and CO and the orderings for the amount of these oxygen functional groups are different in different kerogens. The content of amino nitrogen decreases while the content of chemisorbed nitrogen oxides increases with increasing the density of oil shales. The organic sulfur exists as aliphatic sulfur, aromatic sulfur, sulfoxide and sulfone in the studied kerogens. As the density of oil shales increases, the contents of aliphatic sulfur and sulfone increase while the contents of aromatic sulfur and sulfoxide decrease in their kerogens.

A Nuclear Magnetic Resonance study: Implications for coal formation in the Witbank Coalfield, South Africa

In this study, carbon-13 cross-polarization magic-angle-spinning solid-state nuclear magnetic resonance (13C CP-MAS SS NMR) was undertaken on a parent coal sample and its density-fractionated derivatives, an inertinite-rich and a vitrinite-rich sample, obtained from the Witbank Coalfield of South Africa (medium rank C bituminous coal). The formation of inertinite macerals has been extensively researched and the conclusions remain largely controversial. However, most research has been confined to northern hemisphere coals, which are typically dominated by vitrinite. South African coals are widely known for their high inertinite content. Earlier workers have ascribed the inertinite macerals, in their diversity, to aerial oxidation. However, this oxidation-only pathway fails to recognize that inertinite macerals can form through other processes such as charring of plant matter. Microscopically, charred matter possesses anatomical structures that closely resembles those observed in inertinite macerals, with lignin and/or cell walls largely preserved, perhaps mechanically fragmented or compressed in some instances. Based on the NMR structural parameters, the average aromatic cluster size in the inertinite-rich sample (petrographically dominated by fusinite, semifusinite of varying reflectance, and inertodetrinite) corresponds to monocyclic, 6-aromatic carbon rings. In the vitrinite-rich sample of the same coal, the cluster sizes are larger, corresponding to multi-ring aromatic hydrocarbons. The 6-carbon rings in the inertinite-rich sample are interpreted to correspond to guaiacol and syringol, the principal products of low-temperature (below 400 °C) lignin pyrolysis. Since charring depletes cellulose and moisture, fire-affected plant matter is interpreted to have a lower compaction potential than vitrinite-forming material, sustaining 6-aromatic carbon ring isolation in the former. Lignin-derived aromatic rings in compactable plant matter merge to form the multi-ring clusters present in the collotelinite- and collodetrinite-rich sample of the same coal.

Temperature-Induced Changes in the Optical and Material Characteristics of HAMR Media COC and Its Effect on Recording Performance

The carbon overcoat (COC) on heat-assisted magnetic recording (HAMR) media was deposited at increasing temperature. The optical extinction ( ${k}$ ) of this media was measured with ellipsometry and found to increase with temperature from 0.2 to 0.9 over the temperature range from 220 °C to 360 °C. Raman spectroscopy of these COC surfaces had an increasing G-peak position and decreasing G-peak width along with an increasing I(D)/I(G). An increasing sp2 ring/chain and aromatic cluster size and decreasing optical gap were inferred from these changing parameters. HAMR writing on this media was found to require incrementally less laser power (from 100% to 92%) with increasing optical extinction to attain a fixed track width. This was determined to be due to the increased imaginary component of the dielectric function in this film ( 2nk ). The SNR of these written tracks was observed to improve by approximately 0.65 dB with deposition temperature. A finite-element method model of the head and media showed that the thermal gradient of the hot spot in the media increases with optical extinction and increases the SNR. A small decrease in the COC density with temperature was observed and was calculated to further decrease the COC thermal conductivity and thus enhance the increased thermal gradient.

13C-NMR Study on Structure Evolution Characteristics of High-Organic-Sulfur Coals from Typical Chinese Areas

The structure evolution characteristics of high-organic-sulfur (HOS) coals with a wide range of ranks from typical Chinese areas were investigated using 13C-CP/MAS NMR. The results indicate that the structure parameters that are relevant to coal rank include CH3 carbon (fal*), quaternary carbon, CH/CH2 carbon + quaternary carbon (falH), aliphatic carbon (falC), protonated aromatic carbon (faH), protonated aromatic carbon + aromatic bridgehead carbon (faH+B), aromaticity (faCP), and aromatic carbon (farC). The coal structure changed dramatically in the first two coalification jumps, especially the first one. A large number of aromatic structures condensed, and aliphatic structures rapidly developed at the initial stage of bituminous coal accompanied by remarkable decarboxylation. Compared to ordinary coals, the structure evolution characteristics of HOS coals manifest in three ways: First, the aromatic CH3 carbon, alkylated aromatic carbon (faS), aromatic bridgehead carbon (faB), and phenolic ether (faP) are barely relevant to rank, and abundant organic sulfur has an impact on the normal evolution process of coal. Second, the average aromatic cluster sizes of some super-high-organic-sulfur (SHOS) coals are not large, and the extensive development of cross bonds and/or bridged bonds form closer connections among the aromatic fringes. Moreover, sulfur-containing functional groups are probably significant components in these linkages. Third, a considerable portion of “oxygen-containing functional groups” in SHOS coals determined by 13C-NMR are actually sulfur-containing groups, which results in the anomaly that the oxygen-containing structures increase with coal rank.

Observation of structure transition as a function of temperature in depositing hydrogenated sp2-rich carbon films

In this study, we carried out the transition experiments of graphite-like (GL) to fullerene-like (FL) structures by placing high temperature steel substrates in the depositing environment which can form FL hydrogenated carbon films. We investigated the changes of bond mixtures, H content, aromatic clusters and internal stress at the transition process, and proposed the transformation mechanism inferred from Raman, TEM cross-section, FTIR and XPS results. It was found that the size of aromatic clusters and accordingly graphene planes and the formation of edge dangling bonds were the key steps. H+ bombardment leaded to the splitting of large graphene planes (at GL stage) into more and smaller planes (at FL stage) and the formation of edge dangling bonds; Some of these dangling bonds were reduced by the formation of pentagons and subsequent curving of the smaller planes, which were an indicator of FL structures.

Structures of Aromatic Clusters of Different Coals Based on Benzene Carboxylic Acids from Coal via Oxidation

Benzene carboxylic acids (BCAs) are considered to be an important group of chemicals and widely used in the chemical industry. The generation of BCAs from coal via oxidation is widely studied, indicating that the distributions of BCAs are various with different coals and the yields of BCAs with lower numbers of carboxyl groups increase in the process of coalification. However, the relationship between distributions of BCAs and the aromatic clusters of coal is unclear. In this work, combined with the results of distributions of BCAs and 13C NMR, the most probable aromatic clusters in different coals were proposed. The result indicates that, in the process of coalification (from lignite to anthracite), the aromatic cluster size and the degree of condensed aromatic rings both increase with an increase in carbon content or coal rank, but the substituted degree of aromatic rings decreases. When the carbon content of coal is lower than 87%, the aromatic rings in coal are arranged in a linear catenation manner. ...

The relationship between the humic degree of oil shale kerogens and their structural characteristics

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.

FTIR and Raman spectroscopy characterization of functional groups in various rank coals

Coals varying in rank from lignite to anthracite were comprehensively characterized with regard to chemical structure using FTIR and Raman spectroscopy. Structural parameters were determined from spectrum deconvolution, and correlations were established for these parameters. The evolution of coal structure is complex with three stage characteristics at Ro=0.4–1.3%, 1.3–2.0% and 2.0–4.0%, respectively. At Ro=0.4–1.3%, the rapid decline in oxygen-containing functional groups accompanied with the enrichment of aliphatic compounds is the main characteristic. When Ro=1.3–2.0%, the sharp changes of the band position difference (G-D1), AD1/AG and apparent aromaticity (fa) are caused by the strongest aromatization at this period. The aromatic rings and degree of graphitization are significantly enhanced, with the length of aliphatic chains (A(CH2)/A(CH3)) decreasing to the lowest level. When Ro=2.0–4.0%, the slow variation of parameters (fa, ‘C’, G-D1 and AD1/AG) confirms that most of heterocycle compounds and amorphous carbon structures have been lost. The size of aromatic clusters and graphite crystallite continuously increase, and the microcrystalline structure in coal is gradually perfected, closer to graphite structure. These findings can provide a comprehensive understanding of chemical and physical properties of coals.