A mechanistic link between coal pore development and molecular structure evolution

Molecular structural disparities between maceral components are intrinsic factors governing their reactivity and physicochemical behaviors during storage and transportation. To investigate the molecular structural differentiation between vitrain and durain in low- to medium-rank coals (Ro,max = 0.65–1.71%), this study selected samples of long-flame coal and gas coal from the Huanglong Coalfield, coking coal from the Hedong Coalfield, and fat coal from the Weibei Coalfield. The microstructural variations in macroscopic coal components during coalification were analyzed using Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance (13C-NMR), and X-ray photoelectron spectroscopy (XPS). The results indicated that the aromatic structures of vitrain are predominantly trisubstituted, with their proportion consistently exceeding that in durain. In contrast, durain exhibits a progressive transition from trisubstituted to pentasubstituted aromatics with increasing coal rank, accompanied by higher aromaticity, condensation degree, and aromatic carbon content. The d002 size of the vitrain decreased from 3.82 to 3.47, while that of the durain decreased from 3.52 to 3.40. Both values showed a gradual decline, with the vitrain exhibiting a larger reduction than the durain. This indicates that the lateral extension of the microcrystalline structure in the durain is more developed, resulting in tighter molecular connections. 13C-NMR analysis further reveals that durain possesses higher falH/fal* and bridge carbon ratios (XBP), along with a lower faS/fa’ ratio, reflecting a greater degree of aromatic ring condensation. XPS analysis revealed that durain generally contains a higher oxygen-functional group content but lower C-C/C-H content compared to vitrain. Collectively, these findings confirm significant structural divergence between vitrain and durain during coalification, with durain exhibiting more developed aromaticity, structural condensation, and organizational order.

A study of chemical structural evolution of thermally altered coal and its effect on graphitization

The different origin of alginite and soil organic matter may be the reason of differences in their humic acids (HA) chemical structure. One of the aims of this article is to compare the chemical composition of alginite HA and HA isolated from different soil types. Another aim of this article is to compare the chemical structure of humic acids of alginite isolated with two different procedures: modified IHSS (International Humic Substances Society) method and simplified extraction method. The modified IHSS method was applied for the isolation of alginite and soil HA. To obtain sufficient amount of alginate HA for biological experiments, simplified extraction method suited for large volumes of HA was applied. The differences in elemental analysis and ash proportion in HA extracted by modified IHSS method (C = 35.4, H = 43 atomic%, ash content = 0.08%) and simplified extraction method (C = 31, H = 31 atomic%, ash content = 7.42%) can be caused by different concentration of extraction solution and also differences in purification of HA. The differences in chemical structure between alginate HA and HA isolated from different soil types according to the data of elemental analysis (C content of alginite HA = 35.4 atomic%, C content in soils HA = 38.2‒49.1 atomic%) and 13C nuclear magnetic resonance (NMR) spectra (degree of aromaticity of alginite HA = 24.4% and soil HA= 35.9‒53%) were found. Results of 13C NMR show that the content of aromatic carbon was decreasing in the following order: Haplic Chernozem HA > Andic Cambisol HA > Haplic Cambisol HA > alginite HA. Based on the obtained results, it can be concluded that the differences in the chemical structure of alginite and soil HA can be explained by the difference in the origin of organic matter in alginite and soil samples. The source of organic matter in alginite is mainly type II kerogen from algae and that of soil is lignin and cellulose (type III kerogen) of higher plants.

In freshwater ecosystems, dissolved humic substances (HS) can sorb hydrophobic organic chemicals and thereby reduce their bioconcentration and toxicity. The extent of the sorption depends both on the concentration and on the origin of HS. This paper summarizes work that characterized HS from different origins by various spectroscopic and chemical properties, and related these properties to (1) the sorption of polycyclic aromatic hydrocarbons (PAHs) by HS (measured by a fluorescence quenching method), (2) effects of HS on the bioconcentration of PAHs and (3) effects of HS on the toxicity of PAHs. The most powerful predictor of the association between 26 different HS and the PAHs pyrene, fluoranthene, and anthracene was the content of aromatic carbons of the HS. The influence of HS on the bioconcentration of PAHs was investigated by measuring the effect of seven different humic and fulvic acids on the uptake of pyrene and benzo[a]pyrene into the nematode Caenorhabditis elegans. Again, parameters describing aromatic properties of the HS, such as the content of aromatic carbons, or the specific absorptivity at 254 nm gave the best prediction of HS effects on bioconcentration. Studies on the effect of HS on the toxicity of PAHs (impact on grazing activity of Daphnia magna) gave similar results: The detoxifying ability (= reduction of toxicity) of HS could be correlated to the quotient between aromatic carbons and aliphatic carbons in the HS. Taking these results together, we can describe the relationship between structure and effects of HS on bioavailability and toxicity of PAHs as follows: HS associate with PAHs, making the PAHs unavailable for uptake into organisms, and consequently reducing toxic effects of the PAHs. Aromatic properties of the HS can be used to predict the effect of HS in each of these steps.

An appropriate pattern recognition method has been designed to visually discriminate between crude oils belonging to different geographic origins. Each oil is represented by a circular profile that consists of parameter axes that radiate from the centre like spokes on a wheel. One objective of this approach is to provide an optimum set of axes that will best differentiate one circular profile from another. Several parameters were considered for evaluating the oils: photo-acoustic spectroscopy (PAS), carbon-13 nuclear magnetic resonance (13C NMR, for %CA = aromatic carbon content), high-performance liquid chromatography (HPLC, for unsaturated, aromatic, and polar compounds), initial boiling point (IBP), American Petroleum Institute (API) gravity, and ultraviolet–visible spectrophotometry (for λmax = maximum absorption wavelength and εmax = maximum molar absorptivity). By computerized statistical evaluation, the selected parameters are PAS and HPLC for unsaturated, aromatic, and polar compounds.

Study on the interaction and coking characteristics of low-sulfur meager coal and medium-high sulfur fat coal during co-carbonization process

The accurate characterization of coal pore structure is significant for coalbed methane (CBM) development. The splicing of practical pore ranges of multiple test methods can reflect pore structure characteristics. The pore\fracture compressibility is the main parameter affecting the porosity and permeability of coal reservoirs. The difference in compressibility of different coal rank reservoirs and pore\fracture structures with changing stress have not been systematically found. The pore structure characteristics of different rank coal samples were characterized using the optimal pore ranges of high-pressure mercury intrusion (HPMI), low-temperature liquid nitrogen adsorption (LT-N2A), low-pressure carbon dioxide adsorption (LP-CDA), and nuclear magnetic resonance (NMR) based on six groups of different rank coal samples. The compressibility of coal matrix and pore\fracture were studied using HPMI data and NMR T2 spectrum under effective stress. The results show that the more accurate full pore characterization results can be obtained by selecting the optimal pore range measured by HPMI, LT-N2A, and LP-CDA and comparing it with the NMR pore results. The matrix compressibility of different rank coal samples shows that low-rank coal > high-rank coal > medium-rank coal. When the effective stress is less than 6 MPa, the microfractures are compressed rapidly, and the compressibility decreases slowly when the effective stress is more than 6 MPa. Thus, the compressibility of the adsorption pore is weak. Nevertheless, the adsorption pore has the most significant compression space because of the largest proportion in different pore structures. The variation trend of matrix compressibility and pore\fracture compressibility is consistent with the increase of coal rank. The compressibility decreases with the rise of reservoir heterogeneity and mechanical strength. The development of pore volume promotes compressibility. The research results have guiding significance for the exploration and development of CBM in different coal rank reservoirs.

Lignocellulase production from straw fermentation has been widely investigated but the research has neglected to quantify fermentation-derived residue transformation to the humus-like substance (HULIS). To investigate the conversion efficacy of corn stalk residue to HULIS, the amount of HULIS associated with chemical composition and structural changes of humic acid-like substances (HAL) was investigated in a 30 L solid-state fermentation tank during a short period of eight days. The results show that the highest decomposition rate of corn stalk and the highest activity of cellulase, xylanase, and β-glucosidase appeared at the fourth day. At the end of fermenting process, the amount of humic acid-like substances (HAL) and the percentage of HAL in humus acid (PQ value) increased 17.5% and 8.9%, respectively, indicating Trichoderma reesei facilitates the transformation of corn stalk residue to HAL. Fatty acids decreased while aromatic carbon and carboxyl content significantly increased during the ongoing fermentation, which had a positive impact on the HAL thermal stability. The FTIR spectral and thermal analysis revealed an improvement in HAL degrees of condensation, oxidation, and aromatization. The present study suggests that the residue of corn stalks fermented with T. reesei might be a good fertilizer to improve soil characteristics.

During the chlorination of drinking water, chlorine reacts with natural organic material to produce disinfection by-products, such as trihalomethanes and haloacetic acids, which are believed to be harmful to human health. The formation of these by-products is related to the aromatic carbon content of the water, for which specific ultraviolet absorbance serves as a useful surrogate. Because humic substances in water tend to have a higher aromatic carbon content and a higher specific ultraviolet absorbance than non-humic substances, they produce greater levels of disinfection by-products.

Influence of Co-based catalyst on subfractional composition of heavy oil asphaltenes during aquathermolysis

Abstract. The East Siberian Arctic Shelf (ESAS) is the broadest and shallowest continental shelf in the world. It is characterized by both the highest rate of coastal erosion in the world and a large riverine input of terrigenous dissolved organic matter (DOM). DOM plays a significant role in marine aquatic ecosystems. The chromophoric fraction of DOM (CDOM) directly affects the quantity and spectral quality of available light, thereby impacting both primary production and ultraviolet (UV) exposure in aquatic ecosystems. A multiyear study of CDOM absorption, fluorescence, and spectral characteristics was carried out over the vast ESAS in the summer–fall seasons. The paper describes observations accomplished at 286 stations and 1766 in situ high-resolution optical measurements distributed along the nearshore zone. Spatial and interannual CDOM dynamics over the ESAS were investigated, and driving factors were identified. It was shown that the atmospheric circulation regime is the dominant factor controlling CDOM distribution on the ESAS. This paper explores the possibility of using CDOM and its spectral parameters to identify the different biogeochemical regimes in the surveyed area. The analysis of CDOM spectral characteristics showed that the major part of the Laptev and East Siberian seas shelf is influenced by terrigenous DOM carried in riverine discharge. Western and eastern provinces of the ESAS with distinctly different DOM optical properties were also identified; a transition between the two provinces at around 165–170° E, also consistent with hydrological and hydrochemical data, is shown. In the western ESAS, a region of substantial river impact, the content of aromatic carbon within DOM remains almost constant. In the eastern ESAS, a gradual decrease in aromaticity percentage was observed, indicating contribution of Pacific-origin waters, where allochthonous DOM with predominantly aliphatic character and much smaller absorption capacity predominates. In addition, we found a stable tendency towards reduced concentrations of CDOM and dissolved lignin and an increase in spectral slope and slope ratio values eastward from the Lena River delta; the Lena is the main supplier of DOM to the eastern Arctic shelf. The strong positive correlation (r = 0.97) between dissolved organic carbon (DOC) and CDOM values in the surface shelf waters influenced by terrigenous discharge indicates that it is feasible to estimate DOC content from CDOM fluorescence assessed in situ using a WETStar fluorometer. This approach is reliable over the salinity range of 3 to 24.5. The fact that there is little difference between predicted and observed parameters indicates that the approach is justified. The direct estimation of DOM optical characteristics in the surface ESAS waters provided by this multiyear study will also be useful for validating and calibrating remote sensing data.

Recently collected data have shown that natural organic matter (NOM) source is an important parameter influencing the toxicity of silver to the freshwater crustacean Daphnia magna. The present study attempted to correlate the physicochemical properties of 11 naturally isolated and commercially available NOM sources with their ameliorative effects. The protection offered by these samples was standardized to the protective effect of Aldrich humic acid using geochemical modeling approaches that accounted for associated changes in water chemistry and, consequently, silver speciation. The protective ability of NOM was not correlated with reactive sulfide or nitrogen content, which are considered to be strong silver-binding ligands. Color (specific absorbance coefficient) was positively correlated with protection but narrowly eluded statistical significance. The peak wavelength of emission fluorescence following excitation at 370 nm and the fluorescence index values of NOM samples were significantly correlated with protective effects, suggesting that aromatic carbon content may govern the ameliorative actions of NOM. Simple optical properties may therefore act as a suitable indicator for the ability of a given NOM to protect against waterborne silver toxicity to D. magna as long as changes in water chemistry and, thus, silver speciation, are considered.

13C-NMR characterization of organic residues on spent hydroprocessing, hydrocracking and demetallization catalysts

Dermal carcinogenic activity of petroleum-derived middle distillate fuels

Injecting carbon dioxide into deep unminable coal seams can enhance the amount of methane recovered from the seam. This process is known as CO<sub>2<sub/>-Enhanced Coal Bed Methane production (CO<sub>2<sub/>-ECBM). The seam is a porous medium whose porous system is made of cleats (small natural fractures) and of coal pores (whose radius can be as small as a few angström). During the injection process, the molecules of CO<sub>2<sub/> get adsorbed in the coal pores. Such an adsorption makes the coal swell, which, in the confined conditions that prevail underground, induces a closure of the cleat system of the coal bed reservoir and a loss of injectivity. In this work, we develop a poromechanical model which, starting from the knowledge of an adsorption isotherm and combined with reservoir simulations, enables to estimate the variations of injectivity of the coal bed reservoir over time during the process of injection.The model for the coal bed reservoir is based on poromechanical equations that explicitly take into account the effect of adsorption on the mechanical behavior of a microporous medium. We consider the coal bed reservoir as a dual porosity (cleats and coal porosity) medium, for which we derive a set of linear constitutive equations. The model requires as an input the adsorption isotherm on coal of the fluid considered. Reversely, the model provides a way to upscale an adsorption isotherm into a meaningful swelling of the coal bed reservoir at the macroscopic scale.The parameters of the model are calibrated on data on coal samples available in the literature. Reservoir simulations of an injection of carbon dioxide in a coal seam are performed with an in-house finite volume and element code. The variations of injection rate over time during the process of injection are obtained from the simulations. The effect of the compressibility of the coal matrix on those variations is discussed.