Carbon and Oxygen Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

Abstract

The separation of carbon and oxygen isotopes in CO glow discharge has been studied. The isotope enrichment in the products was measured by quadru-pole mass spectrometer. The reaction yield and empirical formula of solid phase products were determined by the gas-volumetric analysis. The stable products obtained in our experiment are CO 2 and solid polymers formed on the discharge wall. The polymer consists of both carbon and oxygen and the oxygen/carbon mole ratio in the polymer is 0.35±0.05. The isotope enrichment coefficients show a strong negative dependence on discharge current though the relative reaction yields have an opposite tendency. Consequently, the maximum isotope enrichment coefficients for 13 C in wall deposit of 2.31 and for 18 O in CO 2 of 1.37 are obtained when the discharge current and the reaction yields are minimum in our experimental range. The experimental results of isotope enrichment have been compared with theoretical values estimated by an analytical model of literature. The dilution mechanism of the isotope enrichment of stable products is inferred from the isotopic distributions of 13 C and 18 O in products and theoretical predictions for isotope enrichment.

Numerical Analysis of Carbon Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

“…10). Although high 13 C enrichment coefficients have been obtained for stable products in our experiment with respect to the present commercial carbon isotope separation method, 3,[5][6][7] our experimental enrichment coefficients are smaller than those of theoretical predictions 11,12) and experimental results for intermedi-ates: vibrationally excited CO molecules 13) and fragmentation specie C + in the mass spectrometer, which would be the cracking pattern of gaseous C 3 O 2 .…”

“…7) To analyze isotope enrichment process and enrichment dilution mechanism, we perform numerical simulation of kinetic processes in the present study. The kinetic model is developed to reproduce experimental results and to estimate optimum discharge condition and isotope separation potential of this method.…”

“…7) That isotope separation method is due to vibration-to-vibration (V-V) energy exchange among the vibrational states of molecular gases. 8,9) The detailed explanation for the principle of this isotope separation method is presented by Ploenjes et al in Ref.…”

Non-Catalytic, Low-Temperature Synthesis of Carbon Nanofibers by Plasma-Enhanced Chemical Vapor Deposition

“…In both systems, a lowtemperature CO/Ar/O 2 plasma was used. In general, the advantages of low-temperature plasma CVD using CO instead of hydrocarbons as the carbon source gas are as follows: (1) the deposition of amorphous carbon is suppressed even at low temperatures (Muranaka et al, 1991;Stiegler et al, 1996); (2) the CO disproportionation reaction, CO+CO → CO 2 +C, is thermodynamically favorable at low temperatures; (3) vibrationally excited molecules are formed which enhance reactions at low temperature, such as CO(v)+CO(w) → CO 2 +C (Plonjes et al, 2002;Capitelli 1986;Mori et al, 2001); (4) C 2 molecules are known to be formed effectively through the reactions C + CO + M → C 2 O + M and C + C 2 O → C 2 + CO and can be precursors for the deposition of functional carbon materials (Caubet & Dorthe, 1994;Ionikh et al, 1994;McCauley et al, 1998). Figure 2(a) shows a schematic diagram of the experimental apparatus for the DC-PECVD system.…”

The Role of C2 in Low Temperature Growth of Carbon Nanofibers

“…To our knowledge, few attempts at low-temperature plasma-enhanced chemical vapor deposition (PECVD) of CNFs/CNTs using CO as the carbon source have been made (Han et al, 2002;Plönjes et al, 2002). In general, the advantages of low-temperature plasma CVD using CO instead of hydrocarbons as the carbon source gas are as follows: (1) the deposition of amorphous carbon is suppressed even at low temperatures (Muranaka et al, 1991;Stiegler et al, 1996); (2) the CO disproportionation reaction CO + CO → CO 2 + C is thermodynamically favorable at low temperature; (3) vibrationally excited molecules are formed and enhance reactions at low temperature, such as CO(v) + CO(v) → CO 2 + C (Capitelli et al, 1986;Mori et al, 2001;Plönjes et al, 2002). In the previous study, we have reported that the vertically aligned CNFs were able to be synthesized at temperature as low as 90 • C using low temperature CO/Ar/O 2 plasma system (Mori et al, 2007;Mori and Suzuki, 2008).…”