O-bearing Compounds Research Articles

Volatile organic compounds (VOCs) from diffuse degassing areas: Interstitial soil gases as message bearers from deep hydrothermal reservoirs

The chemical composition of volatile organic compounds (VOCs) in interstitial soil gases from hydrothermal areas is commonly shaped by both deep hydrothermal conditions (e.g., temperature, redox, sulfur fugacity) and shallow secondary processes occurring near the soil-atmosphere interface. Caldara di Manziana and Solfatara di Nepi, i.e., two hydrothermal systems characterized by diverse physicochemical conditions located in the Sabatini Volcanic District and Vicano-Cimino Volcanic District, respectively (Central Italy), were investigated to evaluate the capability of VOCs in soil gases to preserve information from the respective feeding deep fluid reservoirs. Hierarchical cluster analyses and robust principal component analyses allowed recognition of distinct groups of chemical parameters of soil gases collected from the two study areas. The compositional dissimilarities from the free-gas discharges were indeed reflected by the chemical features of soil gases collected from each site, despite the occurrence of shallow processes, e.g., air mixing and microbial degradation processes, affecting VOCs. Four distinct groups of VOCs were recognized suggesting similar sources and/or geochemical behaviors, as follows: (i) S-bearing compounds, whose abundance (in particular that of thiophenes) was strictly dependent on the sulfur fugacity in the feeding system; (ii) C4,5,7+ alkanes, n-hexane, cyclics and alkylated aromatics, related to relatively low-temperature conditions at the gas source; (iii) C2,3 alkanes, benzene, benzaldehyde and phenol, i.e., stable compounds and thermal degradation products; and (iv) aliphatic O-bearing compounds, largely influenced by shallow processes within the soil. However, they maintain a chemical speciation that preserves a signature derived from the supplying deep-fluids, with aldehydes and ketones becoming more enriched after intense interaction of the hypogenic fluids with shallow aquifers. Accordingly, the empirical results of this study suggest that the chemical composition of VOCs in soil gases from hydrothermal areas provides insights into both deep source conditions and fluid circulation dynamics, identifying VOCs as promising geochemical tracers for geothermal exploration.

Low-mass nitrogen-, oxygen-bearing, and aromatic compounds in Enceladean ice grains

ABSTRACT Saturn’s moon Enceladus is erupting a plume of gas and ice grains from its south pole. Linked directly to the moon’s subsurface global ocean, plume material travels through cracks in the icy crust and is ejected into space. The subsurface ocean is believed to be in contact with the rocky core, with ongoing hydrothermal activity present. The Cassini spacecraft’s Ion and Neutral Mass Spectrometer (INMS) detected volatile, gas phase, organic species in the plume and the Cosmic Dust Analyser (CDA) discovered high-mass, complex organic material in a small fraction of ice grains. Here, we present a broader compositional analysis of CDA mass spectra from organic-bearing ice grains. Through analogue experiments, we find spectral characteristics attributable to low-mass organic compounds in the Enceladean ice grains: nitrogen-bearing, oxygen-bearing, and aromatic. By comparison with INMS results, we identify low-mass amines [particularly (di)methylamine and/or ethylamine] and carbonyls (with acetic acid and/or acetaldehyde most suitable) as the best candidates for the N- and O-bearing compounds, respectively. Inferred organic concentrations in individual ice particles vary but may reach tens of mmol levels. The low-mass nitrogen- and oxygen-bearing compounds are dissolved in the ocean, evaporating efficiently at its surface and entering the ice grains via vapour adsorption. The potentially partially water soluble, low-mass aromatic compounds may alternatively enter ice grains via aerosolization. These amines, carbonyls, and aromatic compounds could be ideal precursors for mineral-catalysed Friedel–Crafts hydrothermal synthesis of biologically relevant organic compounds in the warm depths of Enceladus’ ocean.

Effects of Salinity and N-, S-, and O-Bearing Polar Components on Light Oil–Brine Interfacial Properties from Molecular Perspectives

Oil–brine interfaces play an important role in oil recovery and oil–brine separation, in which the effects of salinity on interfacial tension (IFT) have been much of debate in the past in experiments and modeling studies owing to complex oil compositions. In this work, we use molecular dynamics (MD) simulations to study the oil–brine interfacial properties by designing seven systems containing different oil compositions (decane with/without polar compounds) and the salinity in brine of up to ∼14 wt %. We carefully investigate the salinity and polar component effects by analyzing IFTs, density profiles, orientation parameters, hydrogen bond densities, and charge density profiles. The results indicate that O-bearing compounds (phenol and decanoic acid) can significantly reduce the oil–brine IFT and exhibit the highest Gibbs surface excess relative to water, while the others, including N-bearing compounds (pyridine and quinoline) and S-bearing compounds (thiophene and benzothiophene), only slightly decrease ...

Thermal-Decomposition Products of Hexane-Insoluble Asphaltenes from Coal Pitch

The thermal-destruction products of hexane-insoluble asphaltenes from coal pitch and petroleum asphaltenes are compared. The volatile thermal-decomposition products of the asphaltenes are studied by thermal analysis and gas–liquid chromatography and mass spectroscopy. The morphology and structure of the solid residue is investigated by scanning electron microscopy and X-ray phase analysis. By that means, the analysis of the thermal-decomposition products permits assignment of the asphaltenes to known structural types and prediction of the coke residue’s morphology. The volatile thermal-decomposition products from coal pitch are aromatic polycondensed compounds with 3–7 aromatic nuclei, including N- and S-bearing compounds. The thermal decomposition of petroleum asphaltenes is accompanied by the liberation of alkanes, alkenes, and O-bearing compounds, with chain length from C11 to C30. The content of arenes and polyaromatic hydrocarbons in the volatile thermal-decomposition products from petroleum asphaltenes is considerably less than the content of aliphatic hydrocarbons. Morphological data indicate that the solid thermolytic residues of the asphaltenes differ in structure. For petroleum asphaltenes, the structure is porous and, according to X-ray phase analysis, shows no signs of graphite-like structure. For the asphaltenes from coal pitch, the residue contains graphite-like structure and has a distinctive luster.

Reduction of C[double bond, length as m-dash]O functional groups through H addition reactions: a comparative study between H2CO + H, CH3CH2CHO + H and CH3OCHO + H under interstellar conditions.

H-addition reactions on the icy interstellar grains may play an important role in the formation of complex organic molecules. In the present work we propose a comparative study of H2CO + H, CH3CH2CHO + H and CH3OCHO + H solid state reactions at 10 K under interstellar conditions in order to characterize the main reaction pathways involved in the hydrogenation of a CHO functional group. We show that the most probable mechanism for the formation of alcohols under non-energetic conditions through the saturation of the CHO group corresponds to the attachment of the H atom to the CH group with noticeable variations of the energy barriers for each studied reaction. These energy barriers have been calculated to be 8.3, 14.6 and 32.7 kJ mol-1 for H2CO + H, CH3CH2CHO + H and CH3OCHO + H, respectively. The coupling of the experimental and theoretical analysis proves that while the simplest aldehyde, formaldehyde, is easily reduced to methanol, methylformate and propanal behave differently under H-bombardments but they cannot be a source of alcohol formation through H-addition reactions. Consequently, for the formation of alcohols larger than CH3OH, other chemical pathways should be taken into account, probably energetic processing such as the photolysis of interstellar ice analogues containing C-, H- and O-bearing compounds or the coupling of the H-addition reaction and photon-irradiation on species with a CHO functional group.

Volatile organic compounds (VOCs) in air from Nisyros Island (Dodecanese Archipelago, Greece): Natural versus anthropogenic sources

This study presents the chemical composition of VOCs in air and gas discharges collected at Nisyros Island (Dodecanese Archipelago, Greece). The main goals are i) to discriminate between natural and anthropogenic VOC sources and ii) to evaluate their impact on local air quality. Up to 63 different VOCs were recognized and quantitatively determined in 6 fumaroles and 19 air samples collected in the Lakki caldera, where fumarolic emissions are located, and the outer ring of the island, including the Mandraki village and the main harbor. Air samples from the crater area show significant concentrations of alkanes, alkenes, cyclic, aromatics, and S- and O-bearing heterocycles directly deriving from the hydrothermal system, as well as secondary O-bearing compounds from oxidation of primary VOCs. At Mandraki village, C6H6/Σ(methylated aromatics) and Σ(linear)/Σ(branched) alkanes ratios <1 allow to distinguish an anthropogenic source related to emissions from outlet pipes of touristic and private boats and buses.

In situ and laboratory investigation of the alteration of Boom Clay (Oligocene) at the air–geological barrier interface within the Mol underground facility (Belgium): Consequences on kerogen and bitumen compositions

Abstract The Boom Clay formation (Oligocene) is studied as a reference host rock for methodological studies on deep geological disposal of radioactive waste. During excavation of galleries within the Clay formation (HADES underground research facility, Mol, Belgium), the physico-chemical conditions are significantly modified as an air–clay interface is created. In order to study the long-term impact of the air–clay contact on the organic matter contained in the Boom Clay, two types of samples were studied: (1) a reference series of clay samples having been in contact with the atmosphere of the HADES gallery for increasing times up to several years and (2) unaltered clay samples submitted to artificial oxidation in a ventilated oven at 80 °C. The evolution of geochemical data of the two series was compared using Rock-Eval pyrolysis, GC–MS and size exclusion chromatography. The organic matter of the unaltered clays sampled in the HADES galleries is dominated by type III kerogen (terrestrial) with some contribution of type II (marine) and is thermally immature. The evolution of geochemical parameters during air alteration for the two series are very similar. They show progressive oxidation of kerogen accompanied by the release of bitumen enriched in low molecular weight constituents. Molecular analysis evidences the presence of a complex mixture of aliphatic and aromatic O-bearing compounds, inherited from the degradation of kerogen as well as from the clay catalyzed oxidation of the bitumen. These results show that (1) air oxidation is a major process in the in situ alteration of the organic matter of Boom Clay within the HADES galleries, (2) laboratory oxidation experiments at 80 °C yield similar results as in situ air alteration of Boom Clay and (3) artificial air oxidation may be used to assess the long term exposure of the organic matter to air.

Equilibrium mass-dependent fractionation relationships for triple oxygen isotopes

With a growing interest in small 17O-anomaly, there is a pressing need for the precise ratio, ln 17 α/ln 18 α, for a particular mass-dependent fractionation process (MDFP) (e.g., for an equilibrium isotope exchange reaction). This ratio (also denoted as “ θ”) can be determined experimentally, however, such efforts suffer from the demand of well-defined process or a set of processes in addition to high precision analytical capabilities. Here, we present a theoretical approach from which high-precision ratios for MDFPs can be obtained. This approach will complement and serve as a benchmark for experimental studies. We use oxygen isotope exchanges in equilibrium processes as an example. We propose that the ratio at equilibrium, θ E ≡ ln 17 α/ln 18 α, can be calculated through the equation below: θ a - b E = κ a + ( κ a - κ b ) ln 18 β b ln 18 α a - b where 18 β b is the fractionation factor between a compound “b” and the mono-atomic ideal reference material “O”, 18 α a−b is the fractionation factor between a and b and it equals to 18 β a/ 18 β b and κ is a new concept defined in this study as κ ≡ ln 17 β/ln 18 β. The relationship between θ and κ is similar to that between α and β. The advantages of using κ include the convenience in documenting a large number of θ values for MDFPs and in estimating any θ values using a small data set due to the fact that κ values are similar among O-bearing compounds with similar chemical groups. Frequency scaling factor, anharmonic corrections and clumped isotope effects are found insignificant to the κ value calculation. However, the employment of the rule of geometric mean (RGM) can significantly affect the κ value. There are only small differences in κ values among carbonates and the structural effect is smaller than that of chemical compositions. We provide κ values for most O-bearing compounds, and we argue that κ values for Mg-bearing and S-bearing compounds should be close to their high temperature limitation (i.e., 0.5210 for Mg and 0.5159 for S). We also provide θ values for CO 2(g)–water, quartz–water and calcite–water oxygen isotope exchange reactions at temperature from 0 to 100 °C.

Degradation of C 2–C 15 volatile organic compounds in a landfill cover soil

The composition of non-methane volatile organic compounds (hereafter VOCs) in i) the cover soil, at depths of 30, 50 and 70 cm, and ii) gas recovery wells from Case Passerini landfill site, (Florence, Italy) was determined by GC-MS. The study, based on the analysis of interstitial gases sampled along vertical profiles within the cover soil, was aimed to investigate the VOC behaviour as biogas transits from a reducing to a relatively more oxidizing environment. A total of 48 and 63 different VOCs were identified in the soil and well gases, respectively. Aromatics represent the dominant group (71.5% of total VOC) in soil gases, followed by alkanes (6.8%), ketones (5.7%), organic acids (5.2%), aldehydes (3.0%), esters (2.6%), halogenated compounds (2.1%) and terpenes (1.3%). Cyclics, heterocyclics, S-bearing compounds and phenols are ≤ 1%. In the wells the VOC composition is characterized by higher concentrations of cyclic (7.6%) and S-bearing compounds (2%) and lower concentrations of O-bearing compounds. The vertical distribution of VOCs in the cover soil shows significant variations: alkanes, aromatics and cyclics decrease at decreasing depth, whereas an inverse trend is displayed by the O-bearing species. Total VOC and CH 4 concentrations at a depth of 30 cm in the soil are comparable, inferring that microbial activity is likely affecting VOCs at a very minor extent with respect to CH 4. According to these considerations, to assess the biogas emission impact, usually carried out on the sole basis of CO 2 and CH 4 emission rates, the physical–chemical behaviour of VOCs in the cover soil, regulating the discharge of these highly contaminant compounds in ambient air, has to be taken into account. The soil vertical distribution of these species can be used to better evaluate the efficiency of oxidative capability of intermediate and final covers.

Effect of the molecular environment on the C, N, and O Auger-electron yields induced by MeV H+ and He+ ions.

The KLL Auger-electron yields from a number of C-, N-, and O-bearing compounds have been measured for either ${H}^{+}$ or ${\mathrm{He}}^{+}$ bombardment in the incident energy range of 0.6--2.0 MeV. The yields are seen to vary significantly with the chemical environment with variations of greater than 30% observed between ${\mathrm{CH}}_{4}$ and ${\mathrm{CF}}_{4}$ yields. These variations seem to be reproducible by two simple scaling laws, one based on the inelastic scattering cross sections of the various molecular components, while the second uses the effective number of valence-shell electrons about the site of the K-shell vacancy. The cross sections are reported for the ${\mathrm{He}}^{+}$-induced carbon and nitrogen Auger-electron yields from ${\mathrm{CH}}_{4}$, ${\mathrm{C}}_{2}$${\mathrm{H}}_{6}$, ${\mathrm{C}}_{2}$${\mathrm{H}}_{4}$, ${\mathrm{C}}_{2}$${\mathrm{H}}_{2}$, CO, ${\mathrm{CO}}_{2}$, ${\mathrm{C}}_{2}$${\mathrm{F}}_{6}$, ${\mathrm{CF}}_{4}$, (${\mathrm{CH}}_{3}$${)}_{2}$NH, ${\mathrm{NH}}_{3}$, ${\mathrm{N}}_{2}$, and ${\mathrm{N}}_{2}$O, as well as for the ${\mathrm{H}}^{+}$-induced carbon and oxygen Auger-electron yields from ${\mathrm{C}}_{2}$${\mathrm{H}}_{6}$, CO, ${\mathrm{CO}}_{2}$, ${\mathrm{N}}_{2}$O, and ${\mathrm{O}}_{2}$.