Aromatic Structural Units Research Articles

Evolution mechanism of organic macromolecular structure during lignite pyrolysis

Understanding the mechanisms governing coal pyrolysis reactions, particularly in relation to the coal macromolecular structure, is crucial for improving energy efficiency and facilitating the transition of coal into a clean energy source. This study employs cutting-edge techniques, such as High-Resolution Transmission Electron Microscopy (HRTEM) and Thermogravimetric Analysis coupled with Fourier Transform Infrared Spectroscopy and Mass Spectrometry (TG–FTIR–MS), to analyze lignite and its residual solid samples subjected to pyrolysis across a range of temperatures from 300 °C to 1100 °C. The variational characteristics of the macromolecular structure during coal pyrolysis are examined. Utilizing molecular dynamics simulations, we analyze the evolution mechanism of the macromolecular carbon structure of organic matter during the coal pyrolysis process. The results show that the pyrolysis can be divided into three distinct phases: activation (30–300 °C), pyrolysis (300–650 °C), and condensation (650–1200 °C). During these phases, the coal structure undergoes complex transformations, including folding, twisting, shedding of small molecular side chains, and breaking of macromolecular side chains, ultimately leading to the directional arrangement of structural fragments. The structural units initially undergo decomposition, followed by growth and alignment in a certain direction. The spatial distribution of aromatic structural units evolves from local ordering to complete disordering, culminating in larger-scale, three-dimensional ordering. The order of bond breaking within the macromolecular structure of lignite pyrolysis is: oxygen-containing functional groups (such as C–O and COOH) > aliphatic structure (N–C and C–C) > aromatic structure (CC). By uncovering the reaction intermediates and pathways involved in lignite pyrolysis, this research provides a comprehensive quantitative description of the coal pyrolysis process. These insights offer invaluable theoretical support for the industrial-scale pyrolysis of coal, paving the way for more efficient and sustainable utilization of this crucial energy resource.

Mechanistic analysis of chemical structure evolution for coals under igneous intrusion

Thermally altered coals (TACs) have different chemical properties compared to normally buried coals owing to the influence of igneous intrusion. This discrepancy in chemical components of TACs has not been fully revealed, which leads to their underutilization and potential risks in exploitation. Igneous intrusion causes the rearrangement of aromatic rings and the formation of graphite-like features in TACs. Several studies have examined the changes in coal rank and aromaticity during this process but have not explored the overall evolution. In particular, the lateral extension and vertical stacking of aromatic layers in TACs during graphitization are still unknown. To this aim, a range of TACs was collected, from bituminous to semi-graphite. Four experimental analyses were conducted to characterize the chemical structure evolution of TACs, including Raman spectroscopy, Fourier-transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The analysis of the measured parameters indicates that the chemical structure of TACs undergoes evolution as it approaches igneous intrusion. These changes involve an increase in the size of the aromatic structural units, a reduction in structural defects, and an increase in the degree of order. In addition, there is a gradual transition of sp2-sp3 hybridized aromatic rings to sp2 hybridized aromatic rings, resembling the process of graphite formation. The HRTEM micrographs also reveal an enlargement in the size and angular orientation of aromatic fringes. In summary, the evolution of TACs can be categorized into three stages: a) rapid growth of basic structural units (BSU) from bituminous coal to anthracite; b) lateral connections of BSUs from anthracite to meta-anthracite; and c) lateral straightening of BSUs from meta-anthracite to semi-graphite. Understanding this evolutionary mechanism is highly significant in analyzing the formation of pores and in enhancing the utilization and safety of TACs.

Electrostatic force promoted intermolecular stacking of polymer donors toward 19.4% efficiency binary organic solar cells

Conjugated polymers are generally featured with low structural order due to their aromatic and irregular structural units, which limits their light absorption and charge mobility in organic solar cells. In this work, we report a conjugated molecule INMB-F that can act as a molecular bridge via electrostatic force to enhance the intermolecular stacking of BDT-based polymer donors toward efficient and stable organic solar cells. Molecular dynamics simulations and synchrotron X-ray measurements reveal that the electronegative INMB-F adsorb on the electropositive main chain of polymer donors to increase the donor-donor interactions, leading to enhanced structural order with shortened π-π stacking distance and consequently enhanced charge transport ability. Casting the non-fullerene acceptor layer on top of the INMB-F modified donor layer to fabricate solar cells via layer-by-layer deposition evidences significant power conversion efficiency boosts in a range of photovoltaic systems. A power conversion efficiency of 19.4% (certified 18.96%) is realized in PM6/L8-BO binary devices, which is one of the highest reported efficiencies of this material system. The enhanced structural order of polymer donors by INMB-F also leads to a six-fold enhancement of the operational stability of PM6/L8-BO organic solar cells.

Synthesis and Properties of Polyamide 6 Random Copolymers Containing an Aromatic Imide Structure.

In order to adjust the properties of polyamide 6 (PA6) and expand its application, a new strategy of introducing an aromatic imide structure into the PA6 chain through the random copolymerization method is reported. The diimide diacid monomer was first synthesized by the dehydration and cyclization of pyromellitic dianhydride and 6-aminocaproic acid before it reacted with 1,6-hexamethylene diamine to form poly(amide imide) (PAI) salt, and finally synthesized PA6/PAI random copolymers containing an aromatic imide structure by the random copolymerization of ε-caprolactam and PAI salt. The introduction of an aromatic imide structural unit into the PA6 chain could have a great influence on its properties. As the content of PAI increases, the crystallinity (Xc) and melting temperature (Tm) of the PA6/PAI random copolymer gradually decrease, but its glass transition temperature (Tg) increases obviously. When the PAI content is 20 wt%, the copolymer PA6/PAI-20 has the best comprehensive performance and not only has high thermal stabilities but also excellent mechanical properties (high strength, high modulus, and good toughness) and dielectric properties (low dielectric constant and dielectric loss). Moreover, these properties are significantly superior to those of PA6. Such high-performance PA6 random copolymers can provide great promise for the wider applications of PA6 materials.

Processing of methane and acetylene ices by galactic cosmic rays and implications to the color diversity of Kuiper Belt objects.

Kuiper Belt objects exhibit a wider color range than any other solar system population. The origin of this color diversity is unknown, but likely the result of the prolonged irradiation of organic materials by galactic cosmic rays (GCRs). Here, we combine ultrahigh-vacuum irradiation experiments with comprehensive spectroscopic analyses to examine the color evolution during GCR processing methane and acetylene under Kuiper Belt conditions. This study replicates the colors of a population of Kuiper Belt objects such as Makemake, Orcus, and Salacia. Aromatic structural units carrying up to three rings as in phenanthrene (C14H10), phenalene (C9H10), and acenaphthylene (C12H8), of which some carry structural motives of DNA and RNA connected via unsaturated linkers, were found to play a key role in producing the reddish colors. These studies demonstrate the level of molecular complexity synthesized of GCR processing hydrocarbon and hint at the role played by irradiated ice in the early production of biological precursor molecules.

Influence of Air Leakage on the Risk of Spontaneous Combustion in Close Coal Seam Groups

ABSTRACT To study the effect of air leakage on the risk of spontaneous combustion of close coal seam clusters, the heat release characteristics and microstructural evolution of coal samples during primary and secondary oxidation at different air volumes were compared with the help of a high precision calorimeter and an X-ray diffractometer. The Arrhenius formula was applied to calculate the effect of different air volumes on the activation energy. The results show that: The effect of air volume on coal spontaneous combustion is found to have stage adaptation, low airflow is more conducive to coal self-ignition in the pre-heat storage, and the effect of high air volume on coal spontaneous combustion becomes increasingly significant after the temperature rises to a certain degree. The effect of air volume on secondary oxidation and primary oxidation has high affinity. The risk of spontaneous combustion of secondary versus primary oxidation is not absolute, but there is a critical temperature, and secondary oxidation has a higher risk of spontaneous combustion only when the temperature is higher than the critical temperature. The effect of wind volume on the morphological characteristics of the aromatic layer structural unit is achieved mainly by changing the side chain structure.

Molecular structure model construction and pyrolysis characterization of four typical coals: a case study

ABSTRACT This paper constructed the molecular structures of four types of coal with different ranks and investigated the correlation between coal molecular structure and pyrolysis characteristics by using 13C NMR, XPS, TG-FTIR, and GC-MS. The results demonstrate that the structural model formulas of lignite (HM), weakly caking coal (RN), long-flame coal (CY), and gas coal (QM) are C104H111NO20S, C93H109NO13, C167H191NO15S, and C142H129N3O9S, respectively. The aromatic structural units of HM and RN consist of benzene and naphthalene, which are connected by ether bonds or aliphatic chains. The molecular structures of HM and RN contain a large amount -OH and -COOH, which are easily broken to generate gases, such as H2O, CO, and CO2 during pyrolysis. The gas yield of RN is 28.90%, which is higher than the others. The ether bonds in HM breakage to form groups are easily combined with each other to form tar, while the aliphatic chains in RN fracture to form fragments to generate gas. The light component (C≦10) is the dominant form of tar in HM and RN, with a content of 95.62% and 87.78%, respectively. Phenols are the dominant components in HM tar; alcohols are the primary components in RN tar. In CY, the aromatic structures consisted of benzene, naphthalene, anthracene, and phenanthrene; the aliphatic structures mainly included cycloalkanes and long-chain alkanes. The QM structural units are dominated by phenanthrene and naphthalene, with the highest aromaticity. The pyrolysis gas in CY and QM is composed of CH4; the tar component consists of alcohols, phenols, and alkanes. The coke yield in RN is the lowest at 52.84%, and QM is the highest at 80.20%.

Investigation on the mechanism of carbon structural evolution of Huolinhe lignite during different pretreatment processes

The depth understanding of the organic structure characteristics of coal and its evolution is beneficial to the clean and efficient coal directional conversion. This research probes the evolution path and mechanism of carbon structure of lignite during the hydrothermal transitions dewatering (HTD) and tetralin solvent thermal transitions dewatering (TTD). The structural evolution with these two transitions was explored using 13C NMR and XRD in an autoclave at different temperatures. The moisture content in lignite is effectively decreased during HTD and TTD processes, and this is mainly due to the removal of O-containing functional groups and the decrease of water holding capacity. The TTD process is achieved a higher dehydration and deoxidation for lignite compared with HTD process. This is possibly due to that the dehydrating energy of TTD process not only comes from the thermal energy, but also the tetralin is more likely to form hydrogen bonds with water. The aromaticity is increased during HTD and TTD processes, and this increase is possibly contributed by aromatization while the contribution of aromatic rings condensation was limited because the molar ratio of aromatic bridgehead carbon has changed little. Also, from the XRD data, the stacking of aromatic structural units are significantly promoted and are not obvious for the lateral extended size for crystal structural evolution during HTD and TTD processes. when the pretreatment temperature was at 310 °C, the aromaticity increase from 60.94% to 69.50% and 69.68% during HTD and TTD processes, respectively. The stacking height increase from 8.94 Å to 12.06 Å and 13.27 Å, and the stacking number increase from 2.49 to 3.51 and 3.86, the lateral sizes have changed little. The increase of aromaticity is finally manifested in aromatic units vertical stacking height and stacking layer number. These results indicate that the graphitization and ordering are promoted to some degree during HTD and TTD processes. Compared with the HTD, the TTD had the greater impact on the conversion of lignite carbon structure to high-rank coal. Those results are potentially useful to the clean and efficient utilization of lignite.

New insights into the coalification of lignite from lignin: A comparison of their chemical structures

The structure of coal is considered to be a highly cross-linked network of macromolecules, which is formed by the polymerization of many structurally similar but not totally identical aromatic structural units. It is generally believed that coal is converted from biomass, which is composed of cellulose, hemicellulose, and lignin. Considering lignin as the only aromatic structure in biomass and lignite as a low-rank coal, we believe that there is an inextricable link between the structures of lignin and lignite. In this work, both Huolinhe lignite and enzymatic lignin can be oxidized to benzene carboxylic acids (BCAs), and the yield distribution of BCAs is very similar. By 13C NMR characterization, we have found that both lignin and lignite contain polycyclic aromatic clusters and their mole fractions of aromatic bridgehead carbon (Xb) are very close, which indicates that polycyclic aromatic clusters in lignite may be preserved from lignin. Combining the analysis of the supercritical ethanolysis products of Huolinhe lignite and enzymatic lignin, we found the structural units of enzymatic lignin contained more methoxy, phenolic hydroxyl groups, and C-O ether bonds, but fewer methylene chains than those of Huolinhe lignite.

Structural Model Construction and Optimal Characterization of High-Volatile Bituminous Coal Molecules

The structural characteristics of coal at the molecular level are important for its efficient use. Bituminous coal from the Baozigou Coal Mine is investigated, using elemental analysis, 13C nuclear magnetic resonance, X-ray photoelectron spectroscopy, and Fourier transform infrared. The molecular structure was determined. The aromatic compounds of bituminous coal molecules are primarily two- and three-ring structures, and the aliphatic structures are primarily in the form of methyl, ethyl side chains, and naphthenic hydrocarbons. The ratio of aromatic bridge carbon to peripheral carbon in the molecular structure is 0.279. Oxygen atoms in the form of carbonyl, phenolic hydroxyl and C–O, and nitrogen atoms in pyrroles. Thus, the average structure model of bituminous coal macromolecules was constructed; the molecular formula was C169H128O10N2S, and the molecular weight was 2378. The aromatic structural units in the macromolecular structure of coal include four naphthalenes, three anthracenes, two tetracenes, and heteroatoms in the form of three carbonyl groups, one phenolic hydroxyl group, one pyrrole, and one pyridine. The structure optimization and annealing kinetic simulation of a single macromolecular structure model were performed. Chemical bonds such as bridge bonds and aliphatic bonds were found to be twisted, and π–π interactions between the aromatic sheets in the molecule produced adjacent aromatic sheets. This arrangement tends to be approximately parallel, and the total energy decreases from 6713.401 to 2667.595 kJ/mol, among which the bond stretching energy and van der Waals energy dominate. We used 20 bituminous coal macromolecular models to construct aggregated structural models. After optimization by molecular dynamics simulation, the macromolecules were constrained by the surrounding molecules, and the sheet-like aromatic carbon structures that were originally approximately parallel were distorted. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant.

Recent Development and Perspectives of Solvents and Electrode Materials for Electrochemical Oxidative Degradation of Lignin

AbstractLignin is the most abundant potential renewable resource of aromatic structural units. Turning lignin into high‐value compounds, such as fuels, adhesives or refined chemicals, is the cornerstone and focus of biorefinery in the future. Depolymerization of lignin can convert its macromolecules towards smaller molecules (monomers or oligomers) allowing it to be used for further applications. Electrochemical depolymerization is an excellent method of green and sustainable transformation, which can effectively avoid reagent waste and mild reaction. This review pretents the research progress of lignin electrochemical oxidation in recent years, summarizes the effects of solvent system (alkaline solvent, ionic liquid and deep eutectic solvents, as well as different lignin concentration and medium), electrode materials (platinum, gold, copper, nickel, cobalt, lead dioxide, tin dioxide and titanium‐based metal electrodes) and electrolytic parameters (current density, temperature, reaction time and photocatalysis) on the oxidative degradation efficiency and product distribution of lignin, and prospects its development. The development of low‐cost electrode materials and efficient solvent systems will still be an important direction for the high‐value and high‐quality application of lignin.

Preparation of size-controlled all-lignin based carbon nanospheres and their electrochemical performance in supercapacitor

Lignin, as the second most abundant biomass material in nature, is regarded as an ideal carbon precursor due to the presence of a larger amount of aromatic ring structural unit. Carbon nanospheres, as one of the vital members of carbon materials, are promising advanced materials for various areas. However, lignin-based carbon spheres suffered a complex fabrication process, high crosslinking between spheres, and non-adjustable micron size. Here, all-lignin based carbon nanospheres (LCNS) with tunable size and microstructure were prepared via self-assembly, stabilization treatment, and carbonization. Subsequently, their applications in supercapacitor electrode material were investigated. The results showed that the monodispersed, ordered, and regular carbon nanospheres could be constructed. The size of LCNS could be tuned ranging from 256 to 416 nm via changing the initial concentration of lignin between 0.5 and 2 mg mL−1. The as-prepared LCNS provided a specific surface area between 652 and 736 m2 g−1 through adjusting the size and microstructure. When the LCNS was assembled into the electrochemical capacitor, the LCNS electrode materials exhibited a high specific capacitance of 147 F g−1. Additionally, the LCNS-based symmetrical capacitor showed an ultralow characteristic relaxation time (0.86 s) and long cycle stability for 10,000 cycles. The capacitance properties could be regulated via reconciling the size of nanospheres and microstructure induced by carbonization temperature. The governable capacitance performance indicates that the as-prepared LCNS should be a promising candidate material for energy storage.

Study on the evolution pattern of the chemical structure of Fenton pretreated lignin during hydrothermal carbonization

Two new lignin feedstocks (HLF and DALF) were obtained by Fenton pretreatment of herbal lignin (HL) and de-alkalized lignin (DAL), and hydrothermal carbonization of each lignin sample was carried out at 290 °C with different holding times to investigate the impact of Fenton pretreatment on the physicochemical properties of the hydrothermal materials. The analyses based on 13C solid-state NMR, XPS, FTIR, SEM and fully automated calorimetry showed that the optimal holding time for hydrothermal carbonization of lignin at 290 °C was 30 min. The two types of lignin were treated with Fenton pretreatment to remove some methoxy groups and make the aromatic structural units more compact. Hydrothermal carbonization removed a small amount of αO4 and βO4 bonds from the structure, increased the guaiacyl units [G], decreased the syringyl units [S], and formed more stable 4-O-5 and CC bonds, which in turn polymerized into 10–300 µm irregular spherical carbon particles or porous honeycomb carbon blocks. The calorific values of HLF290-30 and DALF290-30 were increased to 31.04 MJ/kg and 32.17 MJ/kg, respectively, by the combination of Fenton pretreatment and hydrothermal carbonization. Overall, the Fenton pretreatment of lignin enhanced the degree of aromatization and removal of methoxylation during hydrothermal carbonization of lignin. This study provides a sustainable and green strategy for the preparation of high calorific value hydrochar as well as all-round utilization of lignin.

Versatile Porous Poly(arylene ether)s via Pd-Catalyzed C-O Polycondensation.

Porous organic polymers (POPs) with strong covalent linkages between various rigid aromatic structural units having different geometries and topologies are reported. With inherent porosity, predictable structure, and tunable functionality, POPs have found utility in gas separation, heterogeneous catalysis, sensing, and water treatment. Poly(arylene ether)s (PAEs) are a family of high-performance thermoplastic materials with high glass-transition temperatures, exceptional thermal stability, robust mechanical properties, and excellent chemical resistance. These properties are desirable for development of durable POPs. However, the synthetic methodology for the preparation of these polymers has been mainly limited in scope to monomers capable of undergoing nucleophilic aromatic substitution (SNAr) reactions. Herein, we describe a new general method using Pd-catalyzed C-O polycondensation reactions for the synthesis of PAEs. A wide range of new compositions and PAE architectures are now readily available using monomers with unactivated aryl chlorides and bromides. Specifically, monomers with conformational rigidity and intrinsic internal free volume are now used to create porous organic polymers with high molecular weight, good thermal stability, and porosity. The reported porous PAEs are solution processable and can be used in environmentally relevant applications including heavy-metal-ion sensing and capture.

Alternate routes to sustainable energy recovery from fossil fuels reservoirs. Part 1. Investigation of high-temperature reactions between sulfur oxy anions and crude oil

The world is undergoing a substantial transition in its energy supply. Examining the possibilities to recover and use fossil fuel energy without emitting carbon dioxide to the surface, H2S was considered as an alternative energy vector to deliver a carbon free fuel from petroleum reservoirs to the surface. In this study, we investigated the high P-T chemical oxidation of crude oil with a suite of inorganic sulfur compounds. Tested inorganic sulfur compounds can be ordered by their ability to promote chemical changes to the oil matrix with the concomitant production of hydrogen sulfide, with a reactivity series, listed in order of decreasing reactivity as: S0 > S2O32− ~ S4O62− > SO32− > SO42−. The reaction mechanisms proposed in the study also light on likely key intermediate reactants and the geological timescale process of thermochemical sulfate reduction. Polysulfide species (containing S-S bond structures), such as thiosulfate and tetrathionate, may be reactive intermediates during the redox reaction. However, the early stage of thermochemical sulfate reduction may also involve labile organic sulfur functional groups converting to more stable molecules with aromatic structural units, such as dibenzothiophenes (DBT) and benzonaphthothiophenes (BNT). The apparent formation of saturated fatty acids and O2, NO and NO2 aromatic heteroatom species indicates the oxidation of saturated and aromatic hydrocarbons or heteroatom compounds. The oxidation of aromatic species may lead to aromatic ring-opening, followed by decarboxylation forming CO2 as final products.

Construction of Buertai Coal Macromolecular Model and GCMC Simulation of Methane Adsorption in Micropores.

With the increase in high gas mines in the low coal rank mining area in the northwestern part of China, high gas mines in the low-rank coal mining area have caused many gas emission accidents. Coal is a porous material, containing a large number of micropores (<2 nm), which can absorb large amounts of methane, so it is necessary to explore methane adsorption in micropores of low-rank coal. In this work, FTIR, HRTEM, and 13C-NMR were used to test the macromolecular structural parameters of Buertai coal, which was a kind of low-rank Jurassic coal in northwestern China. The results showed that the aromatic structural units in the Buertai coal structure mainly consist of naphthalene, anthracene, and phenanthrene. The fat structure mainly occurs in the form of aliphatic side chains, cycloalkanes, and other compounds. The oxygen atoms are present in the form of carbonyl groups, ether bonds, and phenol groups with a ratio of about 6:4:9. The nitrogen atoms are present in the form of pyrrole and pyridine compounds. Finally, the macromolecular structure model of Buertai coal was built, and the calculated NMR spectrum from the model was very consistent with the experimental NMR spectrum of Buertai coal. The relationship between the macromolecular density and energy of Buertai coal was explored using the Amorphous Cell module in the simulation software, Materials Studios 8.0 (MS 8.0), and the density value at the lowest energy was determined to be about 1.23 g/cm3. The pore structure parameters of Buertai coal were also calculated. It was found that both pore volume and void fraction decreased evenly as the diameter of the probe molecule increased, but the surface area decreased rapidly when the diameter of the probe molecule was 3.46 Å. All pore sizes were found to be smaller than 10 Å from the pore size distribution (PSD) curve of Buertai coal, which provided a lot of adsorption sites for methane (CH4). The results of the CH4 adsorption simulation from Grand Canonical Monte Carlo (GCMC) showed that CH4 is adsorbed inside the micropores of coal, and the adsorption capacity of CH4 depends on the diameters of micropores when the micropores are less than 8.5 Å. There are many micropores where CH4 did not appear because these micropores are closed and did not provide a channel for CH4 to enter. The results of experimental methane adsorption indicate that the excess adsorption capacity from the GCMC simulation was very close to the experimental results of Buertai coal. This work provides a new perspective to study the methane adsorption behavior in micropores of coal.

The Chemical and Alignment Structural Properties of Coal: Insights from Raman, Solid-State 13C NMR, XRD, and HRTEM Techniques.

The chemical and alignment structures of coal impacts coalbed methane behavior: adsorption, desorption, and diffusion. Recently, the research on accurate characterization techniques for coal structure has received widespread attention. In particular, spatial alignment is critical for the molecular modeling of coal. However, due to the great challenges of quantification, spatial alignment has often been ignored in previous studies. In this study, high-resolution transmission electron microscopy (HRTEM) was employed to quantitatively characterize the fringe length, orientation, and stacking distributions of these five coal samples with different ranks. Raman spectroscopy was utilized to investigate the overall structural disorder of the coal molecules. 13C nuclear magnetic resonance (13C NMR) was conducted to characterize the chemical structures of coals, and XRD experiments recorded the transition of the microcrystallite structure. The results show that in the range of %Ro = 0.39–2.07%, the distributions of the aromatic structural units were similar: mainly composed of fringes of size equivalent to naphthalene and 2 × 2 and 3 × 3 rings. When %Ro > 2.07%, the distribution shifted to longer fringes. Moreover, all the samples showed a regional orientation, and when %Ro > 2.07%, there was significantly higher alignment. The degree of stacking of fringes were limited, most of which appeared in the form of a single layer. When %Ro < 2.07%, the stacking appeared in the form of two or three layers. However, five-layer stacking merely appeared in the sample with %Ro = 2.47%. In addition, based on the Raman data, the evolution of carbon disorder was divided into three stages: %Ro = 0.39–1.23%, 1.23–2.07%, and 2.07–2.47%, and aromatization caused the overall disorder to decrease. The 13C NMR data indicated that the chemical structure also transitioned in stages, with aliphatic carbon and oxygen-containing groups gradually decreasing and aromatic carbon increasing. Meanwhile, the XRD data supported increased organization (lower d002 values) with maturities. Thus, this study provides quantitative information about the spatial alignment and the size of aromatic rings, which helps to improve a comprehensive understanding of the chemical structure of coal and coalbed methane behaviors.

Characterization of Nanostructure Evolution in Coal Molecules of Different Ranks.

Four coals samples at different ranks were analyzed by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and solid-state 13C nuclear magnetic resonance (NMR). The calculated coal molecular model was constructed according to the experimental data. The mode of evolution of four coal molecules with different metamorphic degrees was explored. The results indicate that the nanostructures of these four coal molecules mainly consist of aromatic structures, aliphatic structures and oxygen-containing functional groups. The coal metamorphic degree is the most important factor affecting the evolution of the coal molecular nanostructure. By increasing the coal rank, the aromatic carbon content and aromatic system increase, while the aliphatic carbon content and aliphatic system decrease, and the species and content of oxygen containing functional groups are also reduced. During the evolution of the molecular microcrystalline structure, the degree of vertical order of the aromatic structural unit, the flatness of the aromatic structural unit (La), the average crystallite stacking height (Lc), and the average number of crystallites in a stack (n) increase, while the interlayer distance between aromatic sheets (d002) decreases; the short-range ordering of the coal structure is mainly caused by changes in the orientational arrangement from intramolecular aromatic layers to intermolecular aromatic layers when low-rank coal molecules evolve to high rank coal molecules. The structural evolution mechanism of coal molecules of different ranks has been revealed through the analysis of the mode of evolution of the molecular structure the coal. This study enables us to better understand the nanostructure evolution mechanism of coal molecules at different ranks.

Structure and partial ordering of terrestrial kerogen: Insight from high-resolution transmission electron microscopy

Kerogen structure impacts shale gas behavior: adsorption, desorption, and diffusion. The structural partial order (the orientation and stacking extent) varies with source and maturation. The partial order of eight terrestrial kerogen samples were evaluated using high-resolution transmission electron microscopy. The fringe length, angle, and stacking distributions were quantified. For the majority of the vitrinite equivalent reflectance (VReq) range (1.1–1.9%), the aromatic structural units were similar in distribution: mainly composed of fringes of size equivalent to naphthalene, 2 × 2, and 3 × 3 rings. When the VReq was > 1.7%, there was a shift in the distribution towards the larger molecules and some fringes equivalent to 4 × 4 ring structures were present. A slight orientation was found in the sample having the lowest VReq value, with greater alignment in the VReq range 1.5–1.9% There was significantly higher alignment for the overmature samples. Stacking was limited with 92 to 99% of fringes being an individual “layer”. There was an increase in the stacking frequency with an increase of VReq > 1.8% with some stacks exceeding four layers. Thus, the increase in the structural order for the basic structural units was not uniform with maturation. There was a continuous but slight change in partial order when the reflectance was between 1.1 and 1.7% but a transition when the reflectance was ~1.8–2.0%. The transition in partial ordering from slight to more ordered was consistent with coalification jump transitions for coal maturation at Ro,m = 1.8–2.0%. These transformations are likely to impact the shale gas adsorption and its behaviors.

Selective hydrogenolysis of lignin-derived aryl ethers over Co/C@N catalysts

Low aromaticity and a large number of oxygen-bridged bonds among the aromatic structural units of lignin make it possible to obtain chemicals directly. A novel Co/C@N catalyst with high activity towards hydrogenolysis of lignin-derived aryl ethers was synthesized according to the pyrolysis process of a predesigned ZIF-67. According to the results of characterization by powder X-ray diffraction (XRD), N2 adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), Co was reduced by the carbonized organic linker of ZIF-67, and N was doped into the carbon skeleton of the catalyst. The effects of holding time, temperature, and initial H2 pressure on the catalytic performance of Co/C@N were evaluated in the selective hydrogenolysis of benzyl phenyl ether (BPE). BPE was completely converted and the selectivity of monomer reached to 98.2% under optimized reaction conditions. The Calk-O bond in BPE was first dissociated to form toluene and phenol, and then phenol was rapidly hydrogenated to form cyclohexanol. Furthermore, the Co/C@N catalyst shows high activity for hydroprocessing and selective cleavage of other lignin-derived aryl ethers, including phenylethyl phenyl, diphenyl ether, dibenzyl ether, dinaphthalene ether, guaiacol, anisole and veratrole.