Chromatographic Separation of Isotopic Methanes

Gant, Preston L.; Yang, Kang

doi:10.1021/ja01077a002

Cited by 44 publications

(11 citation statements)

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“…For the investigation of diffusion‐related isotope fractionation effects (see Appendix B for details), the sampling procedure was modified. Among others, Gant & Yang (1964), May et al. (1968), Gunter & Gleason (1971), Fuex (1980) and Schütze et al .…”

Section: Experimental and Analytical Methodsmentioning

confidence: 99%

“…For the investigation of diffusion-related isotope fractionation effects (see Appendix B for details), the sampling proce-dure was modi®ed. Among others, Gant & Yang (1964), May et al (1968), Gunter & Gleason (1971), Fuex (1980) andSchu Ètze et al (1989) have reported isotope fractionation effects of gases during separation on packed columns (Porapak N, molecular sieve 5 A Ê ). In order to avoid secondary fractionation effects on the cold-trap, the water removed from the¯ow cell was directly transferred via a manifold valve to stainless steel sample containers (not shown).…”

Section: Modi®cation For Isotope Fractionation Experimentsmentioning

confidence: 99%

See 1 more Smart Citation

Molecular transport of methane, ethane and nitrogen and the influence of diffusion on the chemical and isotopic composition of natural gas accumulations

Schloemer¹,

Krooss²

2004

Geofluids

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Laboratory experiments have been performed to determine diffusion coef®cients of natural gas components (methane, ethane and nitrogen) and isotope fractionation effects under simulated in situ pressure (up to 45 MPa effective stress) and temperature conditions (50±2008C) in water-saturated pelitic and coarse-grained rocks. Effective diffusion coef®-cients of molecular nitrogen (0.39 Â 10 À11 to 21.6 Â 10 À11 m 2 sec À1 at 908C) are higher than those for methane (0.18 Â 10 À11 to 18.2 Â 10 À11 m 2 sec À1 at 908C). Diffusive¯ux rates expressed in mass units are generally higher for N 2 than for CH 4 . Both methane and (to a lesser extent) nitrogen diffusion coef®cients decrease with increasing total organic carbon (TOC) content of the rock samples because of sorption processes on the organic matter. This effect decreases with increasing temperature. Effective diffusion coef®cients increase upon a temperature increase from 50 to 2008C by a factor of four. Effective diffusion coef®cients and steady-state diffusive¯ux decrease with effective stress. Stationary diffusive¯uxes drop by 50±70% for methane and 45±62% for nitrogen while effective diffusion coef®cients are reduced by 38% (CH 4 ) and 32±48% (N 2 ), respectively. Isotope fractionation coef®cients of diffusive transport are higher for methane (À1.56 and À2.77%) than for ethane (À0.84 and À1.62%). Application of the experimental results to geological systems show that diffusive transport has only a low transport ef®ciency. Signi®cant depletion of natural gas reservoirs by molecular diffusion is only expected in cases of very poor caprock qualities (in terms of thickness and/ or porosity) and over extended periods of geological time. Under these circumstances, the chemical and isotopic composition of a gas reservoir will change and maturity estimates based on these parameters may be deceptive. To account for these potential effects, nomograms have been developed to estimate diffusive losses and apply maturity corrections.

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Section: Experimental and Analytical Methodsmentioning

confidence: 99%

Section: Modi®cation For Isotope Fractionation Experimentsmentioning

confidence: 99%

Molecular transport of methane, ethane and nitrogen and the influence of diffusion on the chemical and isotopic composition of natural gas accumulations

Schloemer¹,

Krooss²

2004

Geofluids

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“…R~D , and Rc,I), based on the assumption that calibration of the chromatograph is the same for CD, and C,D, as for CH, and C2H,, respectively. CD, and C2D, may be slightly overestimated on this basis [5]. also included in Table I, was selected, at each temperature, so as to give the best fit with the calculated curves.…”

Section: Resultsmentioning

confidence: 99%

“…The columns were calibrated for nitrogen, methane, and ethane. Since we were most interested in the inhibited reaction, it was assumed that the sensitivity was the same [5] for methane-d, as for methane, and for ethane-d, as for ethane. At first the noncondensible gases Helium was the carrier gas.…”

Section: Methodsmentioning

confidence: 99%

The thermal decomposition of azomethane‐d₆

Chang

Rice

1969

Int J of Chemical Kinetics

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Abstract'Ihe thermal decomposition of azomethane-d6 has been studied. There is a short chain reaction, and measurements have been made of the rate of production of N, , CD, , and C,D, . .\ mechanism is suggested which accounts for these results fairly well. A comparison is made with some similar results of Forst for azomethane. Measurements have also been made of the reaction inhibited by NO. It is believed that the N, production, extrapolated to zero N O pressure, measures the rate of the initial step CD,N,CD, + 2 CDzi + N, . This has an activation energy at high pressures of 50.7 kcal per mole and an Arrhenius A.factor of 101s,49 sec-l. This is to be compared to values of 55.5 and found by Forst and Rice for CH,N,CH, + 2 CH, + N, . The pressure fall-off behavior for CD,N,CD, + 2 CD, + hT2 has also been investigated and compared to the theoretical curses, which seem to fit satisfactorily except a t the lowest pressure, where experimental errots may be large. Unexpectedly, the fall-off curve crosses that for CH,N,CH, + 2 CH, + N,. I t is suggested that the extrapolation to zero N O pressure may not be entirely correct in the CH,K,CH, case where the chain is longer than with CD,N,CD, .It is believed that the decomposition of azomethane-d, is a better example for unimolecular-rate theory than is that of azomethane.

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“…A simple two-column recycle system which effectively extends column length almost indefinitely was developed (526) and used to separate CHI from CD4, n-C4Hlo from n-C4D10, and cyclo-C4H7T from C4Hs. Tritium-and deuterium-substituted methanes may also be separated using a 1520 cm., highly active charcoal column (194) , while monotritiated positional isomers of olefinic hydrocarbons were separated by Lee and Rowland (399) on a 160-ft. column containing an ethylene glycol-AgX03 mixture as liquid phase. Further studies on the separation of the six hydrogen isotopic species were reported (199,656) using columns of ferric oxidecoated alumina.…”

Section: Specialized Operationsmentioning

confidence: 99%