Carbon Isotope Separation Research Articles

Carbon and hydrogen isotope systematics of bacterial formation and oxidation of methane

The diagenetic cycling of carbon within recent unconsolidated sediments and soils generally can be followed more effectively by discerning changes in the dissolved constituents of the interstitial fluids, rather than by monitoring changes in the bulk or solid organic components. The major dissolved carbon species in diagenetic settings are represented by the two carbon redox end-members CH4 and CO2. Bacterial uptake by methanogens of either CO2 or “preformed” reduced carbon substrates such as acetate, methanol or methylated amines can be tracked with the aid of carbon (13C/12C) and hydrogen (D/H≡2H/1H) isotopes. The bacterial reduction of CO2 to CH4 is associated with a kinetic isotope effect (KIE) for carbon which discriminates against 13C. This leads to carbon isotope separation between CO2 and CH4 (εC) exceeding 95 and gives rise to δ13CCH4 values as negative as −110‰ vs. PDB. The carbon KIE associated with fermentation of methylated substrates is lower (εC is ca. 40 to 60, with δ13CCH4 values of −50‰ to −60‰). Hydrogen isotope effects during methanogenesis of methylated substrates can lead to deuterium depletions as large as δDCH4=−531‰ vs. SMOW, whereas, bacterial D/H discrimination for the CO2-reduction pathway is significantly less (δDCH4 ca. −170‰ to −250‰). These field observations have been confirmed by culture experiments with labeled isotopes, although hydrogen isotope exchange and other factors may influence the hydrogen distributions. Bacterial consumption of CH4, both aerobic and anaerobic, is also associated with KIEs for C and H isotopes that enrich the residual CH4 in the heavier isotopes. Carbon fractionation factors related to CH4 oxidation are generally less than εC=10, although values >20 are known. The KIE for hydrogen (εH) during aerobic and anaerobic CH4 oxidation is between 95 and 285. The differences in C and H isotope ratios of CH4, in combination with the isotope ratios of the coexisting H2O and CO2 pairs, differentiate the various bacterial CH4 generation and consumption pathways, and elucidate the cycling of labile sedimentary carbon.

Carbon Isotope Separation by Infrared Multiple Photon Decomposition with a Free Electron Laser.

To verify infrared multiple photon decomposition (IRMPD) by our free electron laser (FEL), 0.8 Ton of CF3I was irradiated with 9.5μm FEL pulses. The fluence of the macropulse used was estimated to be 8J/cm2 at the beam waist. About 3% of the CF3I sample was found to decompose without selectivity by irradiating it with 3. 6 × 104 macropulses. In order to examine decomposition yields and isotope selectivities, 5 Torr of CHBrF2 was irradiated at a fluence of 16J/cm2 with FEL pulses in the wavelength region from 9.3 to 9.7μm. The IRMPD of CHBrF2 was found to produce C2F4. The significant enrichment of 13C in the product was obtained with the irradiation at 9.7μm. The atomic fraction of 13C obtained was as high as 6%. The decomposition yield is related to the diffusion of reactant molecules in a vicinity of a small photolysis volume.

Carbon isotope separation by infrared multiphoton dissociation of CF2HCl molecules with a separation reactor in a laser cavity

An investigation was made of isotopically selective multiphoton dissociation of CF2HCl molecules by high-intensity infrared radiation in a separation reactor placed inside the cavity of a TEA CO2 laser. Special attention was paid to the influence of the laser system parameters (linear and nonlinear cavity losses, input energy) on the time and spatial characteristics of the laser radiation, and to the dependences of the characteristics of an elementary isotope separation event (selectivity and dissociation yield) on these laser parameters. The intracavity position of the separation reactor made it possible to reach high energy densities in large volumes, to utilise efficiently the laser radiation, and to achieve high values of the selectivity (in excess of 100) and yield (over 5%) of the multiphoton dissociation process. The conditions of operation of this laser system were optimised in respect of the input energy and the CF2HCl pressure in the separation reactor.

Laser separation of carbon isotopes by two-frequency dissociation of Freons

An experimental investigation was made of the separation of carbon isotopes by selective multiphoton dissociation of CF2HCl, CF2Cl2, and CCl2HF molecules by two-frequency infrared laser radiation. It was found that two-frequency dissociation can substantially improve the parameters of the elementary separation event compared with single-frequency dissociation. In this case, a product highly enriched in 13C was obtained in a single step using laser fields of moderate energy density (less than 1–2 J/cm2). The best parameters of the separation process were achieved using CF2HCl. A final 13C concentration of up to 98% in the products could be achieved for this compound in a single step. When the enrichment was 80%, the energy consumption and the productivity of the separation process utilizing multiphoton dissociation of CF2HCl were ~ 1.9 keV/atom of 13C and ~ 7 g/h of 13C per one 1 kW of average radiation power.

Optimization of conditions for selective dissociation of trifluorobromomethane molecules in carbon isotope separation

An experimental study was made of the characteristics of multiphoton dissociation of CF3Br molecules when 13CF3Br is excited under collisional conditions. For the first time, measurements were made of the selectivity of multiphoton excitation of a natural mixture of 12C and 13C isotopes, and its dependences on the excitation frequency and buffer pressure were determined. It was observed that the selectivity of excitation of 13CF3Br molecules in the low-frequency wing of the ν1 band is governed by the absorption at the 3ν3 overtone and its thermal bands, and the dissociation selectivity is governed exclusively by the conditions of excitation of the molecules in the ν1 band. The optimum regime for selective dissociation of CF3Br in terms of energy consumption matched to the parameters of existing CO2 lasers was determined. At a radiation energy density of 2.6 J/cm2 the energy consumption is ~ 260 eV per 13C atom. This regime may be used as the first stage in laser enrichment of carbon isotopes.

Carbon-13 Separation by IRMPD of mixtures of C 2F 6 and Br 2

The infrared multiple-photon decomposition of mixtures of C 2F 6 and Br 2 has been examined as functions of various experimental parameters. Carbon-13 was found to be enriched in the main product CF 3Br; the maximum enrichment factor was 35. The combination of this process with the IRMPD of CF 3Br provides a closed chemical cycle for efficient carbon isotope separation

Second-stage enrichment in the laser separation of carbon isotopes

There is a general agreement that efficient infrafed laser induced separation of carbon isotopes requires a two-stage process. An efficient first stage 1%→50%13C enrichment was shown by Gauthier et al. [1] to be feasible and competitive with conventional technology. In this work, second-stage CO2 laser enrichment of equimolar mixtures of12CHClF2 and13CHClF2 has been demonstrated yielding tetrafluoroethylene containing 95% or 99%13C. Forward enrichment by selective decomposition of the13CHClF2 fraction was very efficient, absorbing only 6 and 16 eV, respectively, per carbon atom produced at 95% and 99%13C content.

Effect of viscosity on separation of carbon isotopes during photolysis of dibenzyl ketone

1. The change in the isotopic composition of the dibenzyl ketone and dibenzyl molecules during the photolysis of dibenzyl ketone in solutions of variable viscosity reveals that the enrichment depends on the viscosity in the glycerol-t-BuOH mixtures. 2. The main contribution to the isotopic enrichment is made by the primary radical pairs.

Carbon Isotope Separation by Absorptive Distillation

Abstract The feasibility of separating carbon isotopes by absorptive distillation has been studied for CO absorption by cryogenic solvents. Phase equilibrium, isotopic separation, and mass transfer data were taken between 77.4 and 114.3 K for the following solvents: propane, propylene, 1:1 propane-propylene, 1-butene, isobutane and nitrogen. Carbon monoxide solubility followed Henry's Law, with a maximum experimental solubility of 6.5 mole per cent. Isotopic separation between CO in the gas and liquid phases using hydrocarbon solvents was several times that for pure CO vapor-liquid equilibrium. The maximum observed isotopic separation factor was 1.029 at 77.4 K with the propane-propylene solvent mixture. Mass transfer measurements yielded calculated HTU's of 2 to 5 cm for a possible separation system. An attempt has been made to correlate isotopic separation data using Hildebrand's theory of solutions. The differential absorption of isotopic CO species is expressed as a difference in solubility of the iso...

Photolytic separation of carbon isotopes in cryogenic solutions of carbon disulfide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotolytic separation of carbon isotopes in cryogenic solutions of carbon disulfideSamuel M. Freund, William B. Maier II, Redus F. Holland, and Willard H. BeattieCite this: J. Am. Chem. Soc. 1979, 101, 16, 4522–4524Publication Date (Print):August 1, 1979Publication History Published online1 May 2002Published inissue 1 August 1979https://doi.org/10.1021/ja00510a016RIGHTS & PERMISSIONSArticle Views34Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (368 KB) Get e-Alerts Get e-Alerts

Fractionation of carbon isotopes during migration of hydrocarbons in the gas phase through rocks

This experimental investigation of the migration of a gas solution through slightly permeable rocks at high pressures revealed that it is accompanied by a chromatographic separation of the components and fractionation of the carbon isotopes of hydrocarbons. Carbon isotope separation is characteristic of methane (up to 1%) and liquid hydrocarbons (up to 0.3%). Fractionation of carbon isotopes of hydrocarbons is directly related to the degree of chromatographic separation of the gas solution. The direction of carbon isotope separation differed according to the stage of transfer of the gas solution through the rock. Both effects are determined by the mineral composition, the moisture content and permeability of the rock, and the composition of the migrating solution. The use of data on the change in the hydrocarbon and isotopic composition is useful in assessing the direction and range of the migration paths during the formation of deposits. 3 figures, 2 tables.

Multiphoton absorption and dissociation of hexafluoroacetone in a strong infrared CO2laser field

An investigation was made of the multiphoton absorption and dissociation of the hexafluoroacetone (COC2F6) molecule excited by a TEA CO2 laser. The dissociation threshold was determined as 0.7 J/cm2 and the dissociation products were identified. The dependence of the dissociation probability and the average number of absorbed photons per single molecule on the laser radiation energy density were determined. It was found that the multiphoton absorption and dissociation maximum was shifted toward the red by approximately 15 cm–1 from the linear absorption maximum. The prospects for using hexafluoroacetone for separation of carbon isotopes is discussed.

Cargon and sulfur isotope separation by ArF laser irradiation of CS 2

Single-photon isotope separation of carbon and sulfur isotopes has been carried out by irradiating a predissociative band of CS 2 with an ArF laser. Good selectivity for carbon isotopes was obtained with both broad-band and narrowed tuned laser outputs. Sulfur isotopic selectivity was found only upon irradiation with a tuned laser. The inherent simplicity of the technique suggests it should be useful for laboratory preparation of carbon-13 samples.

Carbon isotope separation by multiphoton dissociation of CF3I

A selective multiphoton dissociation process has been used to enrich carbon-13 in CF3I. A separation factor of nearly 600 has been achieved for irradiation of 0.1 torr of CF3I at -80 °C with the R (14) line of the 9.6 μ CO2 laser transition. An investigation of the dependence of the enrichment factor on pressure indicates that collisions during the dissociation are effective in destroying the selectivity. The multiphoton dissociation is quite efficient. At laser energy fluences of 1.2 J/cm2, one in every 11 absorbed photons contributes its energy to the breaking of the C–I bond.

Dye-laser-induced separation of nitrogen and carbon isotopes

A unimolecular, laser-induced dissociation reaction of s-tetrazine (C 2H 2N 4), with a quantum yield of close to unity, was used to separate nitrogen 14 15 and carbon 12 13 isotopes. The sharp Q-branch of the 0-0 band of the 5515 Å absorption system of tetrazine was irradiated for 1 minute periods with a 10 mW cw tunable dye laser output that was monochromatic to about 0.05 Å. Each of the decomposition products, found here to be HCN and N 2, as well as the starting material, could be altered in isotopic composition, in either direction, by selection of an appropriate laser wavelength. The largest one-step enrichment ratio measured was 72. It makes possible mass separation at an efficiency of 17 moles per kWh of laser energy.

Carbon isotope separation by tunable-laser predissociation of formaldehyde

Separation of carbon 12 13 isotopes has been achieved by selective predissociation of formaldehyde using a frequency-double dye laser. The enrichment factor for pure formaldehyde samples is less than expected from spectroscopic data but is greatly improved by the addition of NO. Starting from a 1:10 mixture of 12CH 2O: 13CH 2O an eighty-fold enrichment in 12CO has been obtained.

Separation of Carbon Isotopes by Thermal Diffusion of Methane. III. The Characteristics of the Thermal Diffusion Column of Concentric Cylinder Type and the Separation of Carbon Isotopes

トレーサーとして用いるための重炭素を分離する目的で,熱管型熱拡散筒を製作し,その特性を研究した。この熱拡散筒は熱管の長さ375cm,外径22.24mm,熱冷両壁間隔は6.29mmであって,その分離因子は0.76atmのとき最大で,2.67であった。分離因子の実測値と,Jones,Furryの理論から算出される理論値とを比較した結果,つぎのことが見いだされた。すなわち,Jones,Furryの理論における装置の非対称性に起因する補正項Kpは,この熱拡散筒の分離因子を算出するためには不必要であって,むしろ,実際の筒の長さのかわりに有効筒長を仮定する方が実測の分離因子を無理なく説明しうるのである。有効筒長の仮定は,さきに報告した重酸素用熱管型熱拡散筒の実験結果をもよく説明しうるものである。前に記した熱拡散筒14本を並列および直列に連結し6段階のカスケード型濃縮装置を製作し,メタンを用いて重炭素の濃縮を行なった。この装置の重炭素輸送量は13CH4 17.6cc/dayであって,21.5%13Cを含むメタンを1日に83ccずつ連続的に採取できる。また,筒下部から重炭素を採取しなければ,運転開始後36日目には,筒下部の重炭素濃度は28.2%に達した。

The Use of the Exchange Between Carbon Dioxide, Carbonic Acid, Bicarbonate Ion, and Water for Isotopic Concentration

A study was made of the exchange of oxygen and carbon in the reactions: CO2 (dissolved)+H2O⇄H2CO3,CO2 (dissolved)+OH−⇄HCO3−.It was found that the rate of the first could be increased four or five times and the rate of the second up to 2000 times by heterogeneous catalysis. Investigation of the use of these catalyzed reactions for separation of the oxygen and carbon isotopes was carried out both by the use of a static bomb technique and by the operation of fractionating columns. The effects of different operating conditions were indicated, and the necessity for turbulent flow in the gas phase was established. Pressures from one through fifty atmospheres were tried, as the increase of CO2 pressure increases the concentration of CO2 (dissolved) and thus speeds up the exchange. A comparison of the above method with the HCN – CN− method of separation of carbon isotopes shows the cyanide exchange to be somewhat faster and to require less time to come to production, somewhat doubtful advantages when they must be coupled with the polymerization and poisonous properties of the hydrogen cyanide, as well as with its greater cost.