Amount Of Aromatic Carbon Research Articles

The importance of aromaticity to describe the interactions of organic matter with carbonaceous materials depends on molecular weight and sorbent geometry.

Dissolved organic matter (DOM) is ubiquitous in aquatic environments where it interacts with a variety of particles including carbonaceous materials (CMs). The complexity of both DOM and the CMs makes DOM-CM interactions difficult to predict. In this study we have identified the preferential sorption of specific DOM fractions as being dependent on their aromaticity and molecular weight, as well as on the surface properties of the CMs. This was achieved by conducting sorption batch experiments with three types of DOM (humic acid, Suwannee River natural organic matter, and a compost extract) and three types of CMs (graphite, carbon nanotubes, and biochar) with different geometries and surface complexities. The non-adsorbed DOM fraction was analyzed by size exclusion chromatography and preferentially sorbed molecular weight fractions were analyzed by UV/vis and fluorescence spectroscopy. All three sorbent types were found to preferentially sorb aromatic DOM fractions, but DOM fractionation depended on the particular combination of sorbent and sorbate characteristics. Single-walled carbon nanotubes only sorbed the smaller molecular weight fractions (<1 kDa). The sorption of smaller DOM fractions was not accompanied by a preference for less aromatic compounds, contrary to what was suggested in previous studies. While graphite preferentially sorbed the most aromatic DOM fraction (1-3 kDa), the structural heterogeneity of biochar resulted in reduced selectivity, sorbing all DOM > 1 kDa. The results explain the lack of correlation found in previous studies between the amount of aromatic carbon in a bulk DOM and its sorption coefficient. DOM sorption by CMs was generally controlled by DOM aromaticity but complex sorbent surfaces with high porosity, curvatures and functional groups strongly reduced the importance of aromaticity.

Co-pyrolysis of rice straw and water hyacinth: Characterization of products, yields and biomass interaction effect

Co-pyrolysis of biomass with abundantly available materials could be an economical method for production of bio-fuels. Pyrolysis behavior of rice straw (RS) and water hyacinth (WH) were carried out in fixed bed reactor at temperature ranging from 300 to 450 °C at a heating rate of 20 °C/min. Co-pyrolysis of biomass with different reaction mixture were carried out at optimum condition 400 °C. The maximum liquid product yields for the pyrolysis of RS and WH obtained were 28.2 wt% and 24.7 wt%, respectively, whereas the maximum liquid product yield for RS+WH co-pyrolysis was 44.4 wt% at 400 °C with 5: 5 biomass mixture ratio. The bio-oils obtained from pyrolysis and co-pyrolysis was analyzed by using GC-MS, FT-IR, 1H NMR. The results of GC-MS and FT-IR analysis confirmed the interaction between RS and water hyacinth during co-pyrolysis, which resulted into increases the number of compounds and compound selectivity. The intensity of the peak enhanced at 1633 cm−1 in the case of bio-char due to an increase in the amount of aromatic carbon and decreased cellulose and hemicellulose contents in the biomass. This work aimed to summarize research progress on co-pyrolysis as well as their benefits on enhancement of bio-oils derived from biomass.

Thermal evolution of aliphatic and aromatic moieties of asphaltenes from coals of different rank: possible implication to the molecular architecture of asphaltenes

The compositional and structural changes that coal asphaltenes undergo with increasing thermal maturation were investigated using solid-state 13C NMR and Fourier transform infrared spectroscopy. The results show a gradual increase in the relative proportion of carbon content with a concomitant decrease in the hydrogen, sulphur and oxygen content. The amount of aromatic carbon also increases while the aliphatic carbon decreases with increasing maturity. Ester and carboxylic groups are particularly sensitive to maturation and decrease in relative abundance with increasing maturity while the amount of aromatic carbonyl groups increases. In general, the asphaltenes were observed to evolve towards a more thermally stable structure with increasing amounts of aromatic moieties and relatively lower amounts of aliphatic moieties. The results are in agreement with the ultimate dominance of the island molecular architecture (the Yen–Mullins model) in asphaltenes.

Charakteristika huminových kyselin pomocí EDXS a 13C NMR spektroskopie

Determination of humic acids spectral characteristics performed fast and convenient method for their quality evaluation. Humic acids (HA) were isolated from five different soil types (Luvi-haplic Chernozem, Haplic Luvisol, Haplic Cambisol, Leptic Cambisol and Eutric Cambisol) and from compost. Basic soil characteristics were determined by commonly used methods. Fractional compositon of humus showed that humic acids content was decreasing in order: compost &gt; Luvi-haplic Chernozem &gt; Haplic Luvisol &gt; Eutric Cambisol &gt; Haplic Cambisol &gt; Leptic Cambisol. Isolated humic acids preparations were characterized comparatively by chemical and spectroscopic methods. Elemental analysis showed the highest carbon content in Luvi-haplic Chernozem HA. The lowest carbon amount was in Eutric Cambisol. Energy–dispersive X-ray spectroscopy detected elementsin situin HA molecule. All samples contained Fe, Cu, Zn, Ti, Ca, K, S, P, Si and Br. Practically no differences in elements content between soil humic substances and compost were detected. The amount of aromatic carbon was higher in Luvi-haplic Chernozem to compare with other samples. Humic acids isolated from Cambisols, on the basis13C NMR spectroscopic data, showed that all samples contained less aromatic carbon and significantly more aliphatic carbon.

Non-thermal plasma enhanced heavy oil upgrading

A process was proposed for upgrading heavy oil using non-thermal plasma technology in a conventional thermal cracking system under atmospheric pressure. Results from a comparison of the reactivity of a N2, H2 and CH4 plasma showed that the plasma can increase the trap oil yield significantly. The trap oil yield increased by ∼9% when the N2 plasma was applied and showed a further increase of ∼19% when the H2 or CH4 plasma was applied. A detailed study on the H2 plasma-enhanced upgrading process was carried out and the results showed that the trap oil yields of the plasma-on runs can be 8–33% higher than those of the plasma-off runs, depending on experimental conditions. Compared with the plasma-off runs, trap oil from the plasma-on runs had a higher (H/C)atomic but less heteroatoms (S and N). Over-balanced hydrogen in the products from plasma-on runs revealed the H2 plasma reactivity, which was further demonstrated by an increase in the substitution and condensation indices of trap oil from the plasma-on runs. Although thermal cracking was mainly involved whether the plasma was applied or not, the electrical field for generating the plasma and the generated plasma may assist with hydrocarbon bond cleavage. This was shown by the increased trap oil yield with the N2 plasma and the hydrogen and carbon residue distribution. Compared with the feedstock, more aromatic and γ-hydrogen (HA and Hγ, respectively) and less α- and β-hydrogen (Hα and Hβ, respectively) were present in the residues, which agrees with the bond dissociation energy data. Similarly, the amounts of saturated (Cs) and alkyl (Cp) carbons in the residues were significantly lower than those in the feedstock while the amount of aromatic carbons (Ca) in the residues was higher than the feedstock. The changes in hydrogen and carbon distribution were more significant for the plasma-on runs. This implies that mainly side chain losses and bridged bond breakage are involved in the processes. This was demonstrated further by the molecular weight distribution. In general, the molecular weight of the residues was lower than that of the feedstock, especially for residues from the plasma-on runs. However, compared with the feedstock, the residues contained less saturated, aromatic and resin fractions but more asphaltene and toluene insoluble fractions. This implies that intra-molecular condensation was more significant than inter-molecular condensation, especially in the plasma-on runs. This should be attributed to the higher stabilization ability of the H2 plasma for fragments or radicals and gas (plasma) flow by which the fragments or radicals are separated rapidly.

Investigation on Asphaltene Structures during Venezuela Heavy Oil Hydrocracking under Various Hydrogen Pressures

Venezuela heavy oil under various hydrogen pressures has been hydrocracked to investigate the variation of asphaltene components during reaction. Asphaltenes have been isolated from the product and analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR). The experimental data revealed that the interlamellar spacing and interchain spacing of the asphaltenes increased while the layer diameter decreased with the hydrogen pressure increasing. At the same time, the amount of aromatic carbon and alkyl carbon of the asphaltenes decreased gradually and the amount of naphthenic carbon increased. As the hydrogen pressure increased, the substitution ratio and the condensation degree parameter (HAU/CA) of the aromatic system in the periphery increased gradually and the replacement index and peri-position condensation index of asphaltenes decreased obviously.

Calculation of the main carbon bonds in coals of different ranks

An equation is proposed for calculating the amount of aromatic carbon in coals. With the use of this equation, the main types of chemical bonds were calculated and the dynamics of their changes in the metamorphic series was demonstrated.

Hydrothermal Syntheses of Colloidal Carbon Spheres from Cyclodextrins

Colloidal carbon spheres have been prepared from aqueous α-, β-, and γ-cyclodextrin (CD) solutions in closed systems under hydrothermal conditions at 160 °C. Both liquid and solid-state 13C NMR spectra taken for samples at different reaction times have been used to monitor the dehydration and carbonization pathways. CD slowly hydrolyzes to glucose and forms 5-hydroxymethyl furfural (HMF) followed by carbonization into colloidal carbon spheres. The isolated carbon spheres are 70−150 nm in diameter, exhibit a core−shell structure, and are comprised of a condensed core (C═C) peppered with resident chemical functionalities including carboxylate and hydroxyl groups. Evidence from 13C solid-state NMR and FT-IR spectra reveal that the evolving carbon spheres show a gradual increase in the amount of aromatic carbon as a function of reaction time and that the carbon spheres generated from γ-CD contain significantly higher aromatic carbon than those derived from α- and β-CD.

Direct Characterization of Kerogen by X-ray and Solid-State 13C Nuclear Magnetic Resonance Methods

A combination of solid-state 13C NMR, X-ray photoelectron spectroscopy (XPS) and sulfur X-ray absorption near edge structure (S-XANES) techniques are used to characterize organic oxygen, nitrogen, and sulfur species and carbon chemical/structural features in kerogens. The kerogens studied represent a wide range of organic matter types and maturities. A van Krevelen plot based on elemental H/C data and XPS derived O/C data shows the well established pattern for type I, type II, and type III kerogens. The anticipated relationship between the Rock−Eval hydrogen index and H/C is independent of organic matter type. Carbon structural and lattice parameters are derived from solid-state 13C NMR analysis. As expected, the amount of aromatic carbon, measured by both 13C NMR and XPS, increases with decreasing H/C. The correlation between aromatic carbon and Rock−Eval Tmax, an indicator of maturity, is linear for types II and IIIC kerogens, but each organic matter type follows a different relationship. The average al...

CHARACTERIZATION OF COAL CHARS FROM A FLASH PYROLYSIS PROCESS BY CROSS POLARIZATION/MAGIC ANGLE SPINNING13C NMR

ABSTRACT Chars from the Illinois Springfield (No. 5) Coal are prepared by flash pyrolysis at progressively higher charring temperatures. The results of a study of these chars by 13C NMR with CP/MAS indicate that the initial stage of heating (300°C) produces a char with aromatic carbon fraction (far) of 68%, and successive heating gives chars with far of 70% (400°C), 73% (500°C), 89% (600°C), 95% (700°C), and 96% (800°C). However, the actual amount of aromatic and aliphatic carbon in the char can be calculated by using the NMR measurements, the organic carbon content of the char, and the weight of the char. The calculated values show that the amount of aromatic carbon in char remains relatively constant at each temperature, but the amount of aliphatic carbon in char is reduced during higher temperature charring. At 600°C, both a large reduction of the aliphatic carbon content and a maximum weight loss occur. Evidently, the aliphatic-bond carbon in coal is the principal source of volatiles derived from coal...