Chemical Structure Of Organic Matter Research Articles

Assessment of thermal maturity in Lower Cambrian organic-rich shale in south China using integrated optical reflectance and Raman spectroscopy of pyrobitumen

It is challenging to accurately determine the thermal maturity of Lower Cambrian overmature shale, which is widely distributed in South China. In this study, we report an integrated method of measuring optical reflectance and Raman spectroscopy of pyrobitumen to determine the thermal maturity of Lower Cambrian organic-rich shales that contained a highly aromatized organic matter chemical structure. The optical reflectance measurement was conducted on large-particle-size angular pyrobitumen to eliminate the interference of clay mineral matrix, and the Raman spectrum analysis is a statistical response of a highly thermally evolved pyrobitumen chemical structure. Raman analysis compensates for the limitation of optical anisotropy interference in optical reflectance measurements. There is a good agreement between optically measured pyrobitumen reflectance (PBRo) and pyrobitumen reflectance calculated by Raman parameters (RmcPBRo), reflecting only minimal effects of optical anisotropy on the average optical reflectance (PBRo) values of pyrobitumen with fine or irregular mosaic texture, further indicating reliability of this integrated method for analyzing overmature shale. Thermal maturity varies significantly in the Lower Cambrian organic-rich shales, ranging from 2.60 to 2.92% EqVRo in the western Hubei province (WHBP), 2.98–3.49% EqVRo in the southern Shaanxi province (SSXP), 3.20–3.38% EqVRo in the southern Sichuan province (SSCP) and 4.06–4.31% EqVRo in the southeastern Chongqing (SECQ). The degree of aromatization and the structural order of organic matter (OM) are abruptly intensified when thermal maturity reaches about 3.5–3.7% EqVRo, as indicated by the deconvolution of the D and G bands in the Raman spectrum of pyrobitumen. The abrupt change in chemical structure of OM provides evidence for further dividing the early and late stages of overmaturation at a boundary of 3.5–3.7% EqVRo. The Lower Cambrian organic-rich shales distributed in the Cambrian shale gas breakthrough areas are normally at the early stage of overmaturation (2.0% < EqVRo < 3.5–3.7%). Development of paleo-uplifts in the Cambrian shale gas breakthrough areas led to relatively shallow burial depth of Lower Cambrian shale distributed on the peripheral areas of paleo-uplifts and created favorable shale gas preservation condition with only rare and small-scale faults.

Combined impacts of intrinsic alkali and alkaline earth metals and chemical structure on reactivity of low-rank coal char: New explanation for the role of water-soluble AAEMs during pyrolysis and gasification

The char reactivity generally determines the overall efficiency of the whole gasification process of coal, so it is of great significance to deeply understand the factors influencing the char reactivity and the coupling mechanism between them. This study aims to investigate the combined impacts of intrinsic alkali and alkaline earth metals (AAEMs) and chemical structure of organic matter on char reactivity, and provide new evidence for confirming the controversial role of water-soluble AAEMs during char gasification. Four series of char samples prepared from Zhundong coal containing different forms of intrinsic AAEMs were isothermally gasified by air in TGA, obtaining the specific reaction-rate curves, and a reasonable evaluation index of char reactivity was established. The carbon skeleton structure of char surfaces was analyzed by Raman spectroscopy. The comprehensive discussion of chemical structure, AAEMs state and char reactivity indicates that the water-soluble AAEMs reduce the char reactivity in the early part of gasification process, which is due to the catalytic cracking of aromatic CH caused by these substances on char surfaces during pyrolysis, while improving the char reactivity in the later part because of the original catalysis of these substances on gasification; the ion-exchangeable AAEMs significantly catalyze the opening of aromatic rings in char during gasification, especially the small rings, which weakens the reaction priority of aliphatic structures; the increasing pyrolysis temperature results in the ordering of chemical structure and the enrichment of ion-exchangeable AAEMs, and the former reduces the char reactivity, while the latter has the opposite effect; at the pyrolysis temperature of 400–600°C, the enrichment of ion-exchangeable AAEMs is the main factor controlling the char reactivity, while at 700–1000°C, the ordering of chemical structure plays a dominant role.

Mechanistic study on laccase-mediated formation of Fe-OM associations in peatlands

Peatlands represent one of the largest terrestrial carbon pools. Phenol oxidase is widely considered to play a critical role in the decomposition of organic matter in peatlands, which is known as the “enzymatic latch”. However, our recent studies have indicated that the formation of iron-organic matter (Fe-OM) associations is more likely to occur in the presence of laccase, the largest class of phenol oxidases in soils. As the formation of Fe-OM associations is recognized as an important stabilization mechanism for soil organic matter, further clarification of the potential mechanisms contributes to a better understanding of the role of laccase in peatland carbon sequestration. In this study, a series of experiments using different phenolic compounds and peat-derived dissolved organic matter (DOM) were performed. The results from liquid chromatography–high-resolution mass spectrometry (LC-HRMS) and gel permeation chromatography (GPC) analyses indicated that laccase catalyzed the polymerization of phenolics and peat-derived DOM by coupling of the C-O bond, the C–C bond and the C–C/C-O bonds. The polymerized products can combine more effectively with Fe to form Fe-OM associations. FTIR spectral analysis indicated that organic matter associated with Fe under laccase catalysis contained more oxygen-containing functional groups but fewer aromatic CC bonds. Although laccase catalysis can change the chemical structure of organic matter, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed minimal influence of laccase on the Fe chemical species in the Fe-OM associations. Thus, we propose that laccase mediated the formation of Fe-OM associations by polymerizing organic matter and by increasing the O/C ratio of organic matter. In addition, laccase can improve the sequestration of organic carbon by increasing the C/Fe molar ratio of the formed Fe-OM associations. This mechanism may provide further insight into the role of laccase in the carbon cycling in peatlands.

ГАЗОГЕНЕРАЦІЙНИЙ ПОТЕНЦІАЛ БІТУМІНОЗНИХ АРГІЛІТІВ УКРАЇНСЬКИХ КАРПАТ ЗА ФОРМАЛІЗМОМ ДЖЕЙНСА

The analysis of literature was carried out and the main criteria for determining the gas generating potential of rocks were determined. These criteria are divided into two groups: the first one is geochemical, which includes the content of organic carbon and the thermal maturity of the rocks. The second group combines the geological and economic criteria that determine the suitability of rocks for the removal of hydrocarbon gases from them. In our opinion, the most important group of criteria should be considered a geochemical group. Traditionally, to determine the ability of organic matter to form hydrocarbons, the Rock-Eval analysis was used. As a result, determined are the total organic carbon (TOC) and other parameters, such as hydrogen index (HI) or production index (PI). In this paper, we are trying to expand the range of parameters that can be used to determine the gas generation potential of the rocks. The elemental composition of the organic matter dissipated in the rocks, in general terms, should affect on the composition and amount of hydrocarbons that they synthesize. To determine the influence of elemental composition on the gas-generating potential, equilibrium thermodynamics is used in conjunction with the Jaynes’ formalism. Samples for investigation – bituminous argillites from Menilite suite of Oligocene, were taken from two fields of the Ukrainian Carpathians. For samples, the elemental composition of the organic matter and the mineral composition of the inorganic part (by X-ray crystallography) are determined. The data on the elemental composition came into the calculation, the result of which is the distribution of the additive components in the organic matter and the composition of gases. The results of the calculations were compared with the results obtained by the Rock-Eval method. It was found that the calculation by the thermodynamic method gives understated results. On the other hand, it allows the establishment of a change in the chemical structure of organic matter of rocks. We are outlined ways to further improvement of the method.

Structural and Chemical Features of Organic Matter in Carbonized Wood of the Devonian and Jurassic Periods

The results of studies of the chemical structure of organic matter in Devonian and Jurassic carbonized wood using IR, ESR, and GC–MS techniques along with elemental analysis are presented. It is shown that the examined samples consist of metamorphism products of natural lignin, which confirms the hypothesis of the key role of lignin in coal formation.

Mitigation of Extreme Ocean Anoxic Event Conditions by Organic Matter Sulfurization

AbstractPast occurrences of widespread and severe anoxia in the ocean have frequently been associated with abundant geological evidence for free hydrogen sulfide (H2S) in the water column, so‐called euxinic conditions. Free H2S may react with, and modify, the chemical structure of organic matter settling through the water column and in marine sediments, with hypothesized implications for carbon sequestration. Here, taking the example of Ocean Anoxic Event 2, we explore the potential impact of organic matter sulfurization on marine carbon and oxygen cycling by means of Earth system modeling. Our model experiments demonstrate that rapid sulfurization (ksulf≥ = 105 M−1 year−1) of organic matter in the water column can drive a more than 30% enhancement of organic carbon preservation and burial in marine sediments and hence help accelerate climate cooling and Ocean Anoxic Event 2 recovery. As a consequence of organic matter sulfurization, we also find that H2S can be rapidly scavenged and the euxinic ocean volume reduced by up to 80%—helping reoxygenate the ocean as well as reducing toxic H2S emissions to the atmosphere, with potential implications for the kill mechanism at the end‐Permian. Finally, we find that the addition of organic matter sulfurization induces a series of additional feedbacks, including further atmospheric CO2 drawdown and ocean reoxygenation by the creation of a previously unrecognized net source of alkalinity to the ocean as H2S is scavenged and buried.

Impacts of chemical fractionation on Zhundong coal's chemical structure and pyrolysis reactivity

The investigation to the structure change of coal during demineralization is the prerequisite in evaluating the minerals' catalytic action in pyrolysis. In the study, Zhundong raw coal samples were first treated using the chemical fractionation method, and then the pyrolysis reactivities of the samples were measured on a thermogravimetric analyser (TGA). In order to understand the chemical structures of the samples, the Fourier transform infrared spectroscopy (FT-IR) and a series of original infrared structure parameters were employed. Finally, a correlation was established between the infrared structural parameters and the pyrolysis reactivity. It is indicated that the characteristic of Zhundong coal is different from other low-rank coals in inorganic mineral composition and chemical structure of organic matter. Dilute sulfuric acid washing can increase the carboxyl group and phenolic hydroxyl group contents, but has insignificant impacts on aliphatic hydrogen content, aromatic hydrogen content, and hydrogen atom distributions in aliphatic and aromatic structures. Washing process using concentrated HCl/HF can further increase the carboxyl group content but has little impact on the phenolic hydroxyl group content. In addition, the washing can also shorten the aliphatic side chains and bridge bonds, causing the aromatic ring fusing lower and substitution higher. Dilute sulfuric acid and concentrated HCl/HF washings increase the pyrolysis reactivity of Zhundong coal. Finally, a correlation was regressed between the infrared structural parameter S and the pyrolysis reactivity, which was proved to be effective to predict the pyrolysis reactivity of coal.

Social dynamics within decomposer communities lead to nitrogen retention and organic matter build-up in soils.

The chemical structure of organic matter has been shown to be only marginally important for its decomposability by microorganisms. The question of why organic matter does accumulate in the face of powerful microbial degraders is thus key for understanding terrestrial carbon and nitrogen cycling. Here we demonstrate, based on an individual-based microbial community model, that social dynamics among microbes producing extracellular enzymes (‘decomposers') and microbes exploiting the catalytic activities of others (‘cheaters') regulate organic matter turnover. We show that the presence of cheaters increases nitrogen retention and organic matter build-up by downregulating the ratio of extracellular enzymes to total microbial biomass, allowing nitrogen-rich microbial necromass to accumulate. Moreover, increasing catalytic efficiencies of enzymes are outbalanced by a strong negative feedback on enzyme producers, leading to less enzymes being produced at the community level. Our results thus reveal a possible control mechanism that may buffer soil CO2 emissions in a future climate.

Steam distillation of mallee leaf: Extraction of 1,8-cineole and changes in the fuel properties of spent biomass

Mallee biomass is an important renewable energy source for the future sustainable energy supply in Western Australia. Embedded in mallee leaf, 1,8-cineole is a value-added product that can be extracted for further improving the economic performance of an envisaged mallee-based biomass supply chain. This study reports the steam extraction of 1,8-cineole from mallee leaf for 1–180min and its effect on the fuel properties of the spent biomass. The experimental results show that in the first 15min, steam distillation extracts ∼90% of 1,8-cineole rapidly and the extraction follows zero-order kinetics, regulated by the rate of latent heat (provided by steam) for 1,8-cineole evaporation. After 15min, extraction is slow and follows first-order kinetics, controlled by the slow internal diffusion of the residual 1,8-cineole. Overall, 1,8-cineole extraction virtually completed after steam distillation for 60min. Steam distillation leads to little changes in the proximate and ultimate analyses and hence mass energy density of the spent leaf. However, it removes some total organic carbon and significant amount of Mg, Ca, and Cl in the spent leaf via interactions between the leaf and the steam (and/or reflux). It has also changed the chemical association of Mg and Ca with the chemical structure of organic matter in the spent leaf.

Characterization of oil shale, isolated kerogen, and postpyrolysis residues using advanced 13C solid-state nuclear magnetic resonance spectroscopy

Characterization of oil shale kerogen and organic residues remaining in postpyrolysis spent shale is critical to the understanding of the oil generation process and approaches to dealing with issues related to spent shale. The chemical structure of organic matter in raw oil shale and spent shale samples was examined in this study using advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Oil shale was collected from Mahogany zone outcrops in the Piceance Basin. Five samples were analyzed: (1) raw oil shale, (2) isolated kerogen, (3) oil shale extracted with chloroform, (4) oil shale retorted in an open system at 500C to mimic surface retorting, and (5) oil shale retorted in a closed system at 360C to simulate in-situ retorting. The NMR methods applied included quantitative direct polarization with magic-angle spinning at 13 kHz, cross polarization with total sideband suppression, dipolar dephasing, CHn selection, 13C chemical shift anisotropy filtering, and 1H-13C long-range recoupled dipolar dephasing. The NMR results showed that, relative to the raw oil shale, (1) bitumen extraction and kerogen isolation by demineralization removed some oxygen-containing and alkyl moieties; (2) unpyrolyzed samples had low aromatic condensation; (3) oil shale pyrolysis removed aliphatic moieties, leaving behind residues enriched in aromatic carbon; and (4) oil shale retorted in an open system at 500C contained larger aromatic clusters and more protonated aromatic moieties than oil shale retorted in a closed system at 360C, which contained more total aromatic carbon with a wide range of cluster sizes.

Relationship between di-(2-ethylhexyl) phthalate concentration and chemical structure of organic matter on solids in drinking water treatment processes

Di-(2-ethylhexyl) phthalate (DEHP), regarded as a toxic substance, is widely used and abundantly contaminated in environments. Via contamination of freshwater, DEHP can enter into drinking water treatment and be adsorbed on solid particles. This study was aimed at understanding the concentration phenomenon of DEHP in drinking water treatment process, focusing on the relationship between DEHP concentration and characteristics of organic matter on the solids formed in the processes as scum, suspended solid and sludge. Solid samples were collected from five drinking water treatment processes in Japan and analyzed by pyrolysis GC/MS. The solids were categorized by the sampling locations, solid types and fragment composition. The specificity of the pyrolysis fragments in each group was summarized into a matrix. When compared with concentration of DEHP and characteristics of organic matter, a solid specifically containing many specific aliphatic fragments contained significantly high concentration of DEHP.

Carbon NMR of coals: the effects of coal type and rank

Carbon-13 nuclear magnetic resonance (NMR) spectra, which provide direct measurements of the chemical structure of organic matter, have been obtained for a large number of New Zealand coals ranging from peat to semi-anthracite. Converted into numerical parameters, the spectra show differences related to coal type and rank. Four NMR parameters— f a, S ox, f CO2H and f COH—are examined, whereas only f a is commonly treated in previous publications. Previously, the effects of coal type have not been considered in interpreting whole-coal samples, although f a had been shown to vary inversely with hydrogen content in the lower rank coals. A wide variety of analytical determinations were used as rank indicators. In the present study, Rank( S r), which is type-compensated, is used as the principal rank index; T max and reflectance are also considered. Coals within the middle one-third of the New Zealand Coal Band, representing a restricted type range of moderately high hydrogen coals, exemplify the changes in NMR parameters as rank increases. These are all particularly sensitive to the earliest changes in kerogen, when the distinguishing oxygenated functional groups are abundant, both within the peat and as peat changes to the lowest-rank lignite. As rank increases, both f CO2H and f COH progressively decline, but neither f a nor S ox shows such uniform change. In particular, inflections in the f a/Rank( S r) and S ox/Rank( S r) curves closely correspond, for New Zealand coals, to the onset of oil expulsion and the culmination (before rapid decline) of coal coking properties.

A direct link between forest vegetation type and soil organic matter composition

Total carbon storage and turnover in soils can be simulated as a series of pools with different turnover rates, ranging from seasonal to millennial. This approach has emphasized the importance of climatic controls on soil organic matter (SOM) dynamics, but implicitly assumes that SOM is minimally influenced by the nature of the plant material from which it is derived. Here we test this assumption by contrasting the influence of climate and vegetation (oak, manzanita, and conifers) on SOM composition in granitic-derived soils from California. Soils developed under the same climate in the San Gabriel Mountains were compared to soils with varying climate along an elevational transect in the Sierra Nevada range. Solid state TOSS CPMAS 13C NMR was used to semiquantitatively characterize the chemical structure of organic matter in litter layers, and low-density and fine silt fractions isolated from sampled A horizons. For all soils, there was a progressive decrease in O-alkyl C, and an increase in alkyl and carbonyl C from the litter to the low-density and fine silt fractions. The NMR spectra of the low-density fractions, and even more so of the fine silt fractions exhibited clear differences in SOM composition associated with different plant genera, regardless of climate. The carbonyl C dominated under oak, O-alkyl C prevailed under manzanita, and alkyl C was prominent under coniferous vegetation. These results indicate that vegetation, not climate, was the factor controlling SOM composition in these soils, and should be taken as a caution against a simplistic climatic interpretation of storage and turnover rate of carbon in soils.

Soil organic matter processes: characterization by 13C NMR and 14C measurements

Soil organic matter (SOM) is a central contributor to soil quality as it mediates many of the chemical, physical, and biological processes controlling the capacity of a soil to perform successfully. SOM properties (e.g. C/N ratio, macro-organic matter) have been proposed as diagnostic criteria of overall soil fitness, but their use is hampered by a poor understanding of the basic biochemical principles underlying SOM processes. The objective of this project was to determine the influence of scrub oak ( Quercus dumosa Nutt.) and Coulter pine ( Pinus coulteri B. Don) vegetation on decomposition and SOM formation processes in a lysimeter installation constructed in 1936 in the San Gabriel mountains of southern California. Soil samples archived during construction of the installation, and A horizons sampled in 1987, were fractionated according to density and mineral particle size to isolate the water floatable (macro-organic matter), fine silt and clay fractions. Carbon turnover rates were determined on all fractions from AMS 14C measurements. Solid state CPMAS TOSS 13C NMR was used to semiquantitatively characterize the chemical structure of organic matter on fresh litter and soil fractions. For the two soils, there was a progressive decrease in O-alkyl C, and an increase in alkyl and carbonyl C from the litter to the floatable, fine silt and clay fractions. These compositional differences were due to the oxidative degradation of the litter material, with preferential decomposition of the cellulose and hemicellulose entities and selective preservation of recalcitrant waxes and resins. In all soil fractions, turnover rates of carbon were longer for the pine than for the oak lysimeter (up to 10 times longer). Also under pine, there was a gradual increase in turnover rate progressing from the floatable to the clay fraction, and differences in turnover rates among fractions may be explained based on differences in carbon chemistry. In contrast, under oak, rapid carbon turnover for all fractions suggested intense biological activity in this soil.

Does ultrasonic dispersion and homogenization by ball milling change the chemical structure of organic matter in geochemical samples?—a CPMAS 13C NMR study with lignin

Ultrasonic dispersion of geochemical samples suspended in water and subsequent homogenization by ball milling is widely used for fractionation of organic matter. The effect of these treatments on organic matter is investigated with lignin as a model compound. Structural alterations detectable by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy were examined. Comparison of the solid-state 13C NMR spectra of untreated lignin and lignin mixed with quartz or soil did not reveal evidence for structural changes in the organic matter composition after ultrasonic dispersion and subsequent ball-milling. The chemical structure of organic matter in geochemical samples is not affected by these treatments as far as such structural alterations can be detected by solid-state 13C NMR spectroscopy.

Characterization of chemical structure, degree of maturation and oil potential of Torbanites (type I kerogens) by quantitative FT-i.r. spectroscopy

The kerogen of Torbanites of various origins (natural and laboratory-heated samples) was examined by quantitative Fourier transform infrared spectroscopy (FT-i.r.). This study was carried out from difference spectra, obtained by low temperature ash (LTA) subtraction, or from deconvoluted regions of such spectra. The various indexes thus obtained allowed for determining the degree of natural and artificial evolution of Torbanites and the associated changes in chemical structure; comparing artificial versus natural evolution; and assessing the oil potential retained by matured Torbanite samples. The scopes and limitations of these FT-i.r. indexes were considered and compared with those of previously used methods. Quantitative FT-i.r. thus appears more efficient than elemental analysis or microspectrofluorimetry (in assessing the degree of natural evolution, in the first and last steps of maturation, respectively) and than solid-state 13C nuclear magnetic resonance (n.m.r.) (in showing the relative enrichment in ether groups during evolution). When kerogen isolation via demineralization is performed, prior to i.r. examination, the drastic acid treatments then required may alter the chemical structure of organic matter; such a drawback is not encountered in studies based on LTA preparation and difference spectra.