Percentage Of Aromatic Carbon Research Articles

Asphaltene Behavior during Thermal Recovery: A Molecular Study Based on Realistic Structures

Asphaltene precipitation and deposition can occur at both the surface and subsurface levels, leading to the formation of organic-based scales. Asphaltene precipitation can also lead to changes in petrophysical properties such as wettability, which affects the ultimate recovery. Asphaltene precipitation is linked to changes in fluid composition driven by pressure drawdown and temperature variation across the reservoir. Thus, asphaltene deposition can adversely influence the ultimate recovery. Thermal recovery methods are invoked to mitigate the adverse effects of asphaltene precipitation. The behavior of asphaltene under thermal recovery along with the link between the asphaltene molecular structure and its response to the increase in temperature during thermal recovery are not fully understood. In this paper, realistic asphaltene structures based on actual crude samples were recreated on a computational platform, and several characteristics of the asphaltene structures (density, viscosity, and interfacial tension) were evaluated during the heating process. The density of asphaltene was correlated with the percentage of aromatic carbon in its structure. The viscosity and interfacial tension decreased substantially as the temperature increased. The IFT reduced by approximately 30 mN/m as the temperature was increased from 300 K to 450 K. Moreover, the mechanical stability of asphaltene was found to be highly influenced by heating. The findings provide nanoscale insights into the behavior of asphaltene during thermal recovery, which can be used to improve the design of thermal recovery processes.

Root Uptake Pathways and Cell Wall Accumulation Mechanisms of Organophosphate Esters in Wheat (Triticum aestivum L.)

The behavior of organophosphate esters (OPEs) in plants has drawn considerable attention because of their adverse effects to biota. However, the root uptake pathways and cell wall accumulation mechanisms of OPEs in plants are still unclear. In this study, the uptake pathways, subcellular distribution, and accumulation mechanisms of OPEs in wheat roots were elucidated. The results demonstrated that the symplast is the major pathway for uptake of both tris(2-chloroethyl) phosphate (TCEP) and triphenyl phosphate (TPHP) in wheat roots. Inhibitor experiments showed that the transmembrane transport of OPEs is a passive uptake process, and aquaporins and carrier proteins contribute to the uptake of OPEs. More than 69% of TCEP was accumulated in cell sap due to its high hydrophilicity, while the hydrophobic TPHP was mainly stored in the root cell wall. The sorption affinity of TPHP decreased gradually following the sequential fractionation of wheat roots, which confirmed the significant contribution to TPHP sorption on wheat roots. A significant positive correlation between the sorption affinity values and the percentage of aromatic carbon was observed (r2 = 0.856, p < 0.01), indicating that the accumulation of hydrophobic OPEs in roots does not just depend on lipids alone, but the aromatic moieties of lignin in the cell wall also contribute to OPE accumulation.

Tuning the microwave electromagnetic properties of biochar-based composites by annealing

We report on the effects of thermal treatment of biochar embedded in epoxy-based composites on their microwave electrical properties, linking such properties to the material structure investigated by Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. Annealing temperatures in the range 900–1500 °C and biochar concentrations in the epoxy matrix in the range from 5 to 25 wt.% were investigated. The microwave analysis, in the range from 250 MHz to 6 GHz, allowed us to determine the complex permittivity of composites and, through a proper deconvolution technique, to determine the contribution of biochar inclusions alone. High values of real permittivity (up to 220) and conductivity (up to 17 S/m) were evaluated for the biochar particles at 5 GHz, after the 1500 °C thermal treatment. A clear correlation between electrical properties and the biochar microstructure emerged from the dataset, with real permittivity and conductivity increasing as carbon inclusions transform from amorphous to nanocrystalline graphite. Conversely, the percentage of aromatic carbon has a weaker influence on the microwave properties. This study opens to the possibility of tailoring the high-frequency properties of biochar and biochar composites through proper thermal treatments.

A Novel Strategy to Evaluate the Aromaticity Degree of Natural Organic Matter Based on Oxidization-Induced Chemiluminescence.

Due to its complex composition and structure, many of the properties of natural organic matter (NOM) are poorly understood. In this study, the oxidization-induced chemiluminescence (OCL) of NOM was investigated, and a flow-injection OCL method was developed using alkaline persulfate-H2O2 as the oxidizing agent. The method is suitable for the direct analysis of NOM in both homogeneous and heterogeneous samples without isolation or concentration. A strong linear relationship (p < 0.001) was found between the normalized organic carbon OCL (OCLOC) and the percentage of aromatic carbon in standard NOM and soil samples, suggesting that OCLOC can be used as an empirical indicator to assess the aromaticity degree of NOM in both homogeneous and heterogeneous samples. By using this method, the percentages of aromatic carbon in a forest soil profile with low organic carbon content were estimated, and a decrease in the degree of aromaticity in deeper soil was observed. Considering the high sensitivity (lower than 0.1 mg C L-1) and throughput (13 s per detection) and low sample consumption (less than 1 mg) of the method, the proposed OCLOC indicator shows great promise for the high-throughput evaluation of the aromaticity degree of NOM for a wide variety of environmental and geochemical samples.

Modeling Shear Viscosity of Asphalt through Nonequilibrium Molecular Dynamics Simulation

This paper investigates a quantifiable relationship between the chemical composition and the shear viscosity of the asphalt binder through the nonequilibrium molecular dynamics (NEMD) simulation. The fix Deform and fix NVT/SLLOD ensembles were used to perform a shear effect on the model. The relationship between the shear viscosity and the microstructure characteristics of the asphalt model was studied. The results indicated that the asphalt model exhibited shear thinning as the strain rate increases. The effects of energy and chemical structure (molecular weight, aromatic carbon and heteroatom percentage) on shear viscosity were studied from the perspective of microstructure. The results showed that the larger fused aromatic ring core caused a nonlinear relationship between viscosity and strain rate. The viscosity of the asphalt model increased with the molecular weight, the percentage of aromatic carbon and heteroatoms. The molecular weight had a greater effect on viscosity than aromatic carbon and heteroatom percentage. Considering energy variations with strain rate and chemical structure, the NEMD method can be used to predict the behavior of the asphalt molecules under shear strain at a certain level.

Redox interface-associated organo-mineral interactions: A mechanism for C sequestration under a rice-wheat cropping system

Paddy soils constitute the largest anthropogenic wetlands on earth. However, the biogeochemical cycles of iron (Fe) oxides and organic compounds at the redox interfaces in paddy soils are poorly understood. Here, we propose a conceptual mechanism based on our data set, which links seasonal turnover of soil aggregates and the organo-mineral associations at the aggregate interfaces in the rice-wheat cropping system. Our results showed that the application of organic amendments significantly (P < 0.05) increased the aggregate mean weight diameter (MWD) compared to chemical fertilization alone. The aggregate MWD was always higher after the wheat harvest than after the rice harvest from 2013 to 2015, indicating a seasonal dynamic management-induced process of aggregation, disaggregation and re-aggregation. The oxalate-extractable Fe oxides (Feo) may preferentially retain aromatic organic compounds as indicated by the significant positive correlation between Feo and the percentage of aromatic carbon (C). Furthermore, the specific surface area of the ferrihydrite significantly increased after the microbial reduction, showing the potential of adsorbing more aromatic organic compounds. Moreover, there were more aromatic organic compounds at the aggregate surfaces than in the entire entities, suggesting that aromatic organic compounds were selectively preserved at the aggregate interfaces possibly by forming aromatic-Fe complexes. Therefore, soil disaggregation coupled with the anaerobic conditions exposed more fresh surfaces for C accumulation by forming aromatic-Fe complexes, which were subsequently protected by soil re-aggregation in the aerobic conditions. Organic fertilization improved soil aggregation and promoted the organo-mineral interactions, thus contributing to C sequestration in the rice-wheat cropping system.

Sorption−Desorption Behavior of Atrazine on Soils Subjected to Different Organic Long-Term Amendments

Sorption of atrazine on soils subjected to three different organic amendments was measured using a batch equilibrium technique. A higher K(F) value (2.20 kg(-1)(mg L(-1))(-N)) was obtained for soil fertilized with compost, which had a higher organic matter (OM) content. A correlation between the K(FOC) values and the percentage of aromatic carbon in OM was observed. The highest K(FOC) value was obtained for the soil with the highest aromatic content. Higher aromatic content results in higher hydrophobicity of OM, and hydrophobic interactions play a key role in binding of atrazine. On the other hand, the soil amended with farmyard manure had a higher content of carboxylic units, which could be responsible for hydrogen bonding between atrazine and OM. Dominance of hydrogen bonds compared to hydrophobic interactions can be responsible for the lower desorption capacity observed with the farmyard manure soil. The stronger hydrogen bonding can reduce the leaching of atrazine into drinking water resources and runoff to rivers and other surface waters.

Organic Carbon Composition and Oxygen Metabolism across a Gradient of Seasonally Inundated Limesink and Riparian Wetlands in the Southeast Coastal Plain, USA

A set of three relatively pristine seasonally inundated limesink wetlands and one riparian wetland was studied over a 4–6 month long inundation period in 2001. Patterns in organic matter properties and oxygen consumption in the water column followed a previously documented ecological gradient based on soil composition, vegetation type, and canopy cover. The full canopy, cypress-gum swamp had the highest mean concentrations of dissolved organic carbon (DOC; 26.2 mg/l) and dissolved lignin (sum 6; 299 μg/l) with lower concentrations observed in the partial canopy, cypress savanna (22.0 mg/l DOC; 252 μg/l sum 6) and the open marsh savanna (20.6 mg/l DOC; 135 μg/l sum 6), respectively. During the inundation period, DOC increased in concentration, dissolved lignin decreased, and δ13C shifted to more positive values which collectively indicate a large reduction in the percentage of aromatic carbon during the inundation period. All wetlands had very high concentrations of organic matter, yet microbial oxygen consumption was almost always stimulated by the addition of glucose rather than inorganic nutrients. Stimulation by glucose suggests that there were very small pools of highly bioavailable forms of DOC in the wetlands. A larger pool of moderately bioavailable organic matter had the capacity to sustain microbial oxygen consumption rates under dark conditions for at least 15 d. During the inundation period, the cypress-gum swamp had the lowest average rates of whole water oxygen consumption (1.0 μM/h) with increasing rates observed in the cypress savanna (1.3 μM/h), marsh savanna (1.6 μM/h), and riparian wetland (1.9 μM/h), respectively. The lignin compositional fingerprint varied across the gradient of limesink wetlands, and was useful for identifying different sources of vascular plant-derived DOM. Vascular plant production, algal production, microbial respiration, and UV degradation are all important drivers of DOM cycling, and the consistencies observed in this initial assessment of seasonally inundated limesink wetlands suggest they vary in predictable ways across the ecological gradient.

Binding of atrazine to humic substances from soil, peat and coal related to their structure.

Partition coefficients for the binding affinities of atrazine to 16 different humic materials were determined by the ultrafiltration HPLC technique. Sources included humic acids (HA), fulvic acids (FA), and combined humic and fulvic fractions (HF) from soil, peat, and coal humic acid. Each of the humic materials was characterized by elemental composition, molecular weight, and composition of main structural fragments determined by 13C solution-state NMR. The magnitude of K(OC) values varied from 87 to 575 L/kg of C, demonstrating relatively low binding affinity of humic substances (HS) for atrazine. On the basis of the measured K(OC) values, the humic materials can be arranged in the following order: coal HA approximately = gray wooded soil HA > chernozemic soil HA and HF > sod-podzolic soil HA approximately = peat HF > sod-podzolic soil FA >> peat dissolved organic matter. The magnitude of the K(OC) values correlated strongly with the percentage of aromatic carbon in HS samples (r = 0.91). The hydrophobic binding was hypothesized as the key interaction underlying the binding of atrazine to HS.

Structural characterization of Saudi Arabian extra light and light crudes by 1H and 13C n.m.r. spectroscopy

A study of distillate fractions of Saudi Arabian light and extra light crudes by 1H and 13C n.m.r. spectroscopy describes average composition of these crudes. The 1H n.m.r. spectra of six distillate fractions indicates an increase in chain length of paraffins and of alkyl groups attached to aromatic rings. Similarly more of the aromatic carbons are substituted with alkyl and methyl groups in the high boiling fractions. 13C n.m.r. spectra show that the percentage of paraffins decreases sharply with fractionation resulting in an increase in percentage of aromatic carbons in both crudes. Moreover as also indicated by 1H n.m.r. spectra, the paraffinic chains are of shorter length in the earlier fractions and of longer length in the later fractions. The distribution of aromatic carbons, bearing alkyl groups and of bridgehead carbons also increases with fractionation. The average structure of compounds present in both the Saudi Arabian light and extra light crudes are surprisingly similar.

The carcinogenic effect of a series of petroleum-derived oils on the skin of mice

Six groups of 30 Swiss mice were treated by application to the skin in the dorsolumbar region two times a week for 12 months of a “white oil” and five samples of petroleum oils derived from the same “crude” (Middle East), which were collected in the same refinery at different stages of “solvent treatment” and which form a homogeneous series with increasing concentrations of polyaromatic hydrocarbons (PAH). The macroscopic and histopathologic examination of the animals (skin and organs) up to 18 months shows the following effects with respect to the 60-mouse control group: • —a marked irritating effect for the “aromatic extract,” the “distillate,” and a “mixture” of intermediary concentration between “distillate” and “raffinate,” • —a definite tumorigenic effect on the skin (papillomas, kerato-acanthomas, squamous cell carcinomas, and fibrosarcomas) of the “aromatic extract” and the “distillate.” The biological answer is in significant association with the PAH concentration of the samples, which is estimated by different analytical methods: viscosity index, percentage of aromatic carbon, “total PAH” according to a gravimetric method, and benzo[ a]pyrene concentration.

Studies of litter and acid insoluble soil organic matter fractions using 13C‐cross polarization nuclear magnetic resonance spectroscopy with magic angle spinning

SummaryCross polarization carbon‐13 nuclear magnetic resonance spectroscopy with magic angle spinning (CP‐MASS) was used to analyse for various forms of carbon in soils, a moss peat, hydrochloric acid insoluble residues from soils and peat, and litter from beech and pine trees. The chemical composition of the litters was also investigated by conventional techniques.The results show that hydrolysis with hydrochloric acid extraction removes nearly all oxygenated alkyl carbon from the soils used. It is shown that humification pathways in which carbohydrates are incorporated into humic substances via nonhydrolysable linkages are not important for the soils investigated in this work.CP‐MASS data suggest that the percentage of aromatic carbon in pine leaves increases with increase in ageing time. The results for the beech leaves are not sharply defined.

Evaluation of the quantitative reliability of the 13C CP/MAS technique for the analysis of coals and related materials

The percentages of aromatic carbon in three representative solid coal samples and one pitch sample have been determined by three different n.m.r. techniques. The first two involve the use of cross-polarization/magic-angle spinning (CP/MAS) and in one case, the magnetization curves were fitted to a theoretical expression and the fit parameters used to calculate the percentage of aromatic carbon. In the second case, the percentage of aromatic carbons was obtained from a choice of contact time in the cross-polarization pulse sequence which gave maximum signal intensity. The third technique used MAS together with a simple 90° carbon pulse sequence with a 5 × T 1, (for the carbon-13 nuclei) recycle time and was assumed to give the absolute quantitative values. It was found that the results obtained using cross-polarization techniques could be substantially different from those obtained using 90° pulses and that caution must be exercised in the application of these techniques to the quantitative analysis of solid carbonaceous fuels.

Compositional study of crude oils using fourier transform n.m.r. Characterisation

AbstractThe Fourier transform (FT) 1H‐ and 13C‐nuclear magnetic resonance (n.m.r.) spectra of three crude oils have been recorded at room temperature on a Jeol pulsed FT‐n.m.r. spectrometer. The branchiness index has been calculated from 1H‐n.m.r. spectra and the percentage of aromatic carbons (% CA) from the 13C‐spectra. The results are discussed and the usefulness of n.m.r. techniques in such studies considered.