NITROGEN ISOTOPE FRACTIONATION ASSOCIATED WITH THE NO2− → N2O STEP OF DENITRIFICATION IN SOILS

1982 ◽  
Vol 62 (2) ◽  
pp. 227-241 ◽  
Author(s):  
A. MARIOTTI ◽  
A. LECLERC ◽  
J. C. GERMON
Keyword(s):  
Reaction Rate ◽  
Nitrogen Isotopes ◽  
Reduction Rate ◽  
Isotopic Fractionation ◽  
Nitrogen Isotope ◽  
Isotopic Enrichment ◽  
Experimental Conditions ◽  
Helium Atmosphere ◽  
Higher Temperature ◽  
Incubation Temperatures

The fractionation of the nitrogen isotopes 14N and 15N in the denitrification process has been studied in laboratory experiments for the step NO2− → N2O. This study has been carried out on natural soils under anaerobic conditions (helium atmosphere). Reduction of N2O is blocked by introduction of a small amount of acetylene in the incubator atmosphere. Variation of experimental conditions of incubation (temperatures, direct or after air-drying incubation of the soil, addition of glucose), greatly modify the reaction rate. 15N is enriched in the substrate during denitrification. The isotopic enrichment factor changes with experimental conditions from about −33 to −11‰. Greatest enrichment is obtained for the lowest reduction rate (low temperature, undried soil). For high rates of denitrification (higher temperature, addition of glucose), the isotopic fractionation decreases. An exponential relation is found between isotopic enrichment, εp/s, and the reaction rate.

scholarly journals Interpretation of Nitrogen Isotope Profiles in Petroleum Systems: A Review

2021 ◽  
Vol 9 ◽  
Author(s):  
Tracy M. Quan ◽  
Oyeleye O. Adeboye
Keyword(s):  
Nitrogen Isotopes ◽  
Isotopic Fractionation ◽  
Petroleum Reservoirs ◽  
Nitrogen Isotope ◽  
Marine Systems ◽  
Petroleum Systems ◽  
Depositional Processes ◽  
Lab Experiments ◽  
Potential Applications ◽  
General Preference

Bulk sedimentary nitrogen isotope profiles are often used as proxies for depositional redox conditions, nitrogen cycling, and nutrient uptake in modern and ancient marine systems. The general preference in terms of analysis is that the sediments measured have undergone minimal thermal alteration, as post-depositional processes might have altered the initial δ15N signal, thus complicating the interpretation of these records. Although not a traditional proxy for petroleum evaluation purposes, recently the use of nitrogen isotopes in petroleum systems has been investigated as potential proxies to reconstruct paleoenvironmental conditions such as redox, and for organic matter evaluation. In this paper we review the use of nitrogen isotope data in petroleum systems, their interpretations, and factors that may complicate their use as proxies. We review the evidence for nitrogen isotopic fractionation during diagenesis, catagenesis, and fluid migration as determined by lab experiments, and how these might impact interpretation of δ15N data in petroleum systems. We also analyze the use and interpretation of δ15N data from petroleum-producing reservoir units, including unconventional reservoirs and lacustrine basins. Lastly, we discuss potential applications for nitrogen isotopes in petroleum systems with regards to their use as both geochemical proxies and as tools to evaluate petroleum reservoirs.

Thermodynamics of Spherical Sponge Iron Reduced by Hydrogen

2012 ◽  
Vol 487 ◽  
pp. 677-681
Author(s):  
Jun Guo Li ◽  
Shou Zhang Li ◽  
Wei Tian
Keyword(s):  
Reaction Rate ◽  
Direct Reduction ◽  
Reduction Rate ◽  
Reaction Rate Constant ◽  
Sponge Iron ◽  
First Order ◽  
Higher Temperature ◽  
Lower Temperature ◽  
Apparent Reaction Rate Constant ◽  
Apparent Reaction Rate

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. To optimize the reduction technology, thermodynamics of SSI reduction was investigated. Oxygen residue ratio in SSI declined with the reaction time despite of reaction temperature. It was concluded that SSI reduced by hydrogen appeared to be the first-order reaction, and the apparent reaction rate constant k was 0.289 h-1 to 3.819 h-1. Activity energy of SSI reduction was 22.19 kJ•mol-1 and 81.58 kJ•mol-1 corresponding to the lower temperature and higher temperature. When the temperature was lower than T4, the reaction rate was lower. Consequently, the optimized temperature should be controlled more than T5 to elevate the reduction rate.

Kinetics of carbon monoxide methanation on a Ni/SiO2 catalyst

1990 ◽  
Vol 55 (7) ◽  
pp. 1678-1685
Author(s):  
Vladimír Stuchlý ◽  
Karel Klusáček
Keyword(s):  
Carbon Monoxide ◽  
Reaction Rate ◽  
Catalyst Activity ◽  
Adsorbed Hydrogen ◽  
Reaction Products ◽  
Co Methanation ◽  
Molar Ratios ◽  
Rate Determining Step ◽  
Higher Temperature ◽  
Kinetics Of

Kinetics of CO methanation on a commercial Ni/SiO2 catalyst was evaluated at atmospheric pressure, between 528 and 550 K and for hydrogen to carbon monoxide molar ratios ranging from 3 : 1 to 200 : 1. The effect of reaction products on the reaction rate was also examined. Below 550 K, only methane was selectively formed. Above this temperature, the formation of carbon dioxide was also observed. The experimental data could be described by two modified Langmuir-Hinshelwood kinetic models, based on hydrogenation of surface CO by molecularly or by dissociatively adsorbed hydrogen in the rate-determining step. Water reversibly lowered catalyst activity and its effect was more pronounced at higher temperature.

scholarly journals Nitrogen isotope effects can be used to diagnose N transformations in wastewater anammox systems

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Paul M. Magyar ◽  
Damian Hausherr ◽  
Robert Niederdorfer ◽  
Nicolas Stöcklin ◽  
Jing Wei ◽  
...  
Keyword(s):  
Isotope Effect ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Nitrogen Isotope ◽  
Anammox Bacteria ◽  
Ammonium Oxidation ◽  
Experimental Conditions ◽  
N Transformations ◽  
Natural Systems ◽  
Inverse Isotope Effect

AbstractAnaerobic ammonium oxidation (anammox) plays an important role in aquatic systems as a sink of bioavailable nitrogen (N), and in engineered processes by removing ammonium from wastewater. The isotope effects anammox imparts in the N isotope signatures (15N/14N) of ammonium, nitrite, and nitrate can be used to estimate its role in environmental settings, to describe physiological and ecological variations in the anammox process, and possibly to optimize anammox-based wastewater treatment. We measured the stable N-isotope composition of ammonium, nitrite, and nitrate in wastewater cultivations of anammox bacteria. We find that the N isotope enrichment factor 15ε for the reduction of nitrite to N2 is consistent across all experimental conditions (13.5‰ ± 3.7‰), suggesting it reflects the composition of the anammox bacteria community. Values of 15ε for the oxidation of nitrite to nitrate (inverse isotope effect, − 16 to − 43‰) and for the reduction of ammonium to N2 (normal isotope effect, 19–32‰) are more variable, and likely controlled by experimental conditions. We argue that the variations in the isotope effects can be tied to the metabolism and physiology of anammox bacteria, and that the broad range of isotope effects observed for anammox introduces complications for analyzing N-isotope mass balances in natural systems.

scholarly journals A kinetic method for the determination of phenol

2002 ◽  
Vol 67 (10) ◽  
pp. 661-667 ◽  
Author(s):  
Snezana Mitic ◽  
Valentina Zivanovic
Keyword(s):  
Standard Deviation ◽  
River Water ◽  
Reaction Rate ◽  
Kinetic Method ◽  
Potassium Periodate ◽  
Experimental Conditions ◽  
Inhibiting Effect ◽  
Relative Standard ◽  
Kinetic Expression

Akinetic method for the determination of phenol is proposed. The method is based on the inhibiting effect of phenol on the Mn(II) catalysis of the oxidation of malachite green with potassium periodate. The reaction rate was followed spectrophotometrically at 615 nm. Kinetic expression for the reaction in the presence and absence of phenol are postulated. The optimal experimental conditions for the determination of phenol were established and phenol was determined in concentrations from 30.0 to 188.0 ng/cm3 with a relative standard deviation of 5.5%. The lower detecton limit is 7.8 ng/cm3. The effects of certain foreign ions upon the reaction rate were determined for the assessment of the selectivity of the method. The method was applied for the determination of phenol in tap and river water.

scholarly journals Formation of Hydrocarbons in the Presence of Native Iron under Upper Mantle Conditions: Experimental Constraints

Minerals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 88
Author(s):  
Sokol ◽  
Tomilenko ◽  
Sokol ◽  
Zaikin ◽  
Bul’bak
Keyword(s):  
Upper Mantle ◽  
Hydrogen Permeability ◽  
Experimental Conditions ◽  
Light Alkanes ◽  
Fully Depleted ◽  
Native Iron ◽  
Consumption Rates ◽  
Higher Temperature ◽  
Direct Hydrogenation ◽  
Metal Phases

The formation of hydrocarbons (HCs) upon interaction of metal and metal–carbon phases (solid Fe, Fe3C, Fe7C3, Ni, and liquid Fe–Ni alloys) with or without additional sources of carbon (graphite, diamond, carbonate, and H2O–CO2 fluids) was investigated in quenching experiments at 6.3 GPa and 1000–1400 °C, wherein hydrogen fugacity (fH2) was controlled by the Fe–FeO + H2O or Mo–MoO2 + H2O equilibria. The aim of the study was to investigate abiotic generation of hydrocarbons and to characterize the diversity of HC species that form in the presence of Fe/Ni metal phases at P–T–fH2 conditions typical of the upper mantle. The carbon donors were not fully depleted at experimental conditions. The ratio of H2 ingress and consumption rates depended on hydrogen permeability of the capsule material: runs with low-permeable Au capsules and/or high hydrogenation rates (H2O–CO2 fluid) yielded fluids equilibrated with the final assemblage of solid phases at fH2sample ≤ fH2buffer. The synthesized quenched fluids contained diverse HC species, predominantly light alkanes. The relative percentages of light alkane species were greater in higher temperature runs. At 1200 °C, light alkanes (C1 ≈ C2 > C3 > C4) formed either by direct hydrogenation of Fe3C or Fe7C3, or by hydrogenation of graphite/diamond in the presence of Fe3C, Fe7C3, and a liquid Fe–Ni alloy. The CH4/C2H6 ratio in the fluids decreased from 5 to 0.5 with decreasing iron activity and the C fraction increased in the series: Fe–Fe3C → Fe3C–Fe7C3 → Fe7C3–graphite → graphite. Fe3C–magnesite and Fe3C–H2O–CO2 systems at 1200 °C yielded magnesiowüstite and wüstite, respectively, and both produced C-enriched carbide Fe7C3 and mainly light alkanes (C1 ≈ C2 > C3 > C4). Thus, reactions of metal phases that simulate the composition of native iron with various carbon donors (graphite, diamond, carbonate, or H2O–CO2 fluid) at the upper mantle P–T conditions and enhanced fH2 can provide abiotic generation of complex hydrocarbon systems that predominantly contain light alkanes. The conditions favorable for HC formation exist in mantle zones, where slab-derived H2O-, CO2- and carbonate-bearing fluids interact with metal-saturated mantle.

scholarly journals The influence of pressure on the spontaneous ignition of inflammable gas-air mixtures - IV—methane-, ethane-, and propane-air mixtures

1936 ◽  
Vol 154 (881) ◽  
pp. 95-112 ◽  
Keyword(s):  
Critical Pressure ◽  
Spontaneous Ignition ◽  
Lower Range ◽  
Experimental Conditions ◽  
Temperature Range ◽  
Limited Temperature ◽  
Tentative Hypothesis ◽  
Temperature Ranges ◽  
Higher Temperature ◽  
Temperature And Pressure

In previous papers the results of investigations into the influence of varying initial pressures up to 15-20 atmospheres on the spontaneous ignition of mixtures with air of butane, iso -butane, pentane, and hexane were described. On the attainment of a critical pressure, which varied both with the hydrocarbon concerned and the composition of its mixture with air, the ignition points were always found to fall sharply from a higher temperature range above 500°C to a lower range at about 300°C. At pressures just exceeding the critical transition pressures ignition occurred at first only within limited temperature ranges which widened and ultimately merged with increasing pressure. The striking relationship between the behaviours of the hydrocarbons referred to under the experimental conditions and their “knocking” propensities in an engine was also indicated. While the data available were inadequate for drawing any final con­clusion as to the character of the phenomena referred to, a tentative hypothesis was advanced that while ignition in the higher temperature range pertains mainly to the thermal decomponents of intermedially formed compounds, ignition in the lower system occurs when temperature and pressure conditions favour the survival and further oxidation of such bodies, particularly aldehydes.

Nitrogen Isotope Exchange between Liquid N2O3 and NO at Low Temperature and Elevated Pressure

1963 ◽  
Vol 18 (2) ◽  
pp. 235-241 ◽  
Author(s):  
E. U. Monse ◽  
Lois Nash Kauder ◽  
W. Spindel
Keyword(s):  
Low Temperature ◽  
Separation Factor ◽  
Isotope Exchange ◽  
Spectroscopic Data ◽  
Room Temperature ◽  
Nitrogen Isotopes ◽  
Nitrogen Isotope ◽  
Elevated Pressure ◽  
Single Stage ◽  
Stage Separation

The single stage separation factor, a, for nitrogen isotope exchange between liquid N2O3—N2O4-mixtures and their vapor has been measured at temperatures ranging from — 76°C to room temperature and pressures between 1 atm. and 7.4 atm.At —76°C and 1 atm., α = 1.061 ± 0.003;at —23°C and 1 atm., α=1.034 ± 0.002;at +23°C and 2.1 atm., α=1.017 ± 0.002;at +23°C and 7.4 atm., α=1.030 ± 0.002.The results are compared with values, calculated from spectroscopic data for N2O3, N2O4, NO and NO2. The value of α = 1.030 found at room temperature and 7.4 atm. pressure enhances the usefulness of the N2O3—NO-system for separating the nitrogen isotopes, since it eliminates the need of refrigeration.

scholarly journals Effect of precursor type on the reduction of concentrated nitrate using zero-valent copper and sodium borohydride

2017 ◽  
Vol 77 (1) ◽  
pp. 114-122 ◽  
Author(s):  
Tihitinna Asmellash Belay ◽  
C. Y. Lin ◽  
H. M. Hsiao ◽  
M. F. Chang ◽  
J. C. Liu
Keyword(s):  
Particle Size ◽  
Surface Area ◽  
Sodium Borohydride ◽  
Reaction Rate ◽  
Reduction Rate ◽  
First Order ◽  
Reducing Conditions ◽  
Pseudo First Order

Abstract In this study, we demonstrated that the choice of precursor has a strong effect on the reduction of nitrate (NO3−) using zero-valent copper (Cu0) synthesized by sodium borohydride (NaBH4). Different precursors: CuSO4, CuO, Cu2O, Cu powder, and Cu mesh were used to reduce NO3− at 677 mg-N/L under the reducing conditions of NaBH4. Compared with the prehydrolyzed samples, those prepared without prehydrolysis exhibited lower reduction rates, longer times and higher concentrations of nitrite (NO2−) intermediate. It was found that one-time addition of NaBH4 resulted in higher reduction rate and less NO2− intermediate than two-step addition. Results showed that Cu0 from CuSO4 possessed the smallest particle size (890.9 nm), highest surface area (26.0 m2/g), and highest reaction rate (0.166 min−1). Values of pseudo-first-order constant (kobs) were in the order: CuSO4 > CuO > Cu2O > Cu powder >Cu mesh. However, values of surface area-normalized reaction rate (kSA) were approximately equal. It was proposed that NO3− was reduced to NO2− on Cu0, and then converted to NH4+ and N2, respectively; H2 generated from both NaBH4 hydration and Cu (II) reduction contributed to NO3− reduction as well.

scholarly journals Quantifying N<sub>2</sub>O reduction to N<sub>2</sub> based on N<sub>2</sub>O isotopocules – validation with independent methods (helium incubation and <sup>15</sup>N gas flux method)

2017 ◽  
Vol 14 (3) ◽  
pp. 711-732 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Jürgen Augustin ◽  
Anette Giesemann ◽  
Reinhard Well
Keyword(s):  
Isotopic Fractionation ◽  
Isotopic Signature ◽  
Residual Fraction ◽  
Simultaneous Estimation ◽  
Site Preference ◽  
Isotopic Enrichment ◽  
Flux Method ◽  
Gas Flux ◽  
Isotopic Analyses

Abstract. Stable isotopic analyses of soil-emitted N2O (δ15Nbulk, δ18O and δ15Nsp = 15N site preference within the linear N2O molecule) may help to quantify N2O reduction to N2, an important but rarely quantified process in the soil nitrogen cycle. The N2O residual fraction (remaining unreduced N2O, rN2O) can be theoretically calculated from the measured isotopic enrichment of the residual N2O. However, various N2O-producing pathways may also influence the N2O isotopic signatures, and hence complicate the application of this isotopic fractionation approach. Here this approach was tested based on laboratory soil incubations with two different soil types, applying two reference methods for quantification of rN2O: helium incubation with direct measurement of N2 flux and the 15N gas flux method. This allowed a comparison of the measured rN2O values with the ones calculated based on isotopic enrichment of residual N2O. The results indicate that the performance of the N2O isotopic fractionation approach is related to the accompanying N2O and N2 source processes and the most critical is the determination of the initial isotopic signature of N2O before reduction (δ0). We show that δ0 can be well determined experimentally if stable in time and then successfully applied for determination of rN2O based on δ15Nsp values. Much more problematic to deal with are temporal changes of δ0 values leading to failure of the approach based on δ15Nsp values only. For this case, we propose here a dual N2O isotopocule mapping approach, where calculations are based on the relation between δ18O and δ15Nsp values. This allows for the simultaneous estimation of the N2O-producing pathways' contribution and the rN2O value.

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