A Method of Decomposing Carbon Dioxide for Fixation of Carbon-14
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To consecutively decompose <SUP>14</SUP>CO<SUB>2</SUB> into carbon (<SUP>14</SUP>C) through its reaction with H<SUB>2</SUB>, an apparatus using microwave discharge and its conditioning were investigated. The reaction produces CO as an intermediate, and proceeds in the two steps of (1) "CO<SUB>2</SUB>+H<SUB>2</SUB>→CO+H<SUB>2</SUB>O" and (2) "CO+H<SUB>2</SUB>+C<SUB>n</SUB>→C<SUB>n+1</SUB>+H<SUB>2</SUB>O", where Cn denotes the carbon already deposited on the wall of the discharge tube. Preliminary dispersion of carbon to the wall of the discharge tube by sputtering of a graphite particle was effective to promote the reaction. Two silica discharge tubes (6mm O.D., 4mm I.D., and 150mm length each) were connected in series to proceed the former reaction in the first discharge tube and the latter one in the second one. When a 1:3 mixture of CO<SUB>2</SUB> and H<SUB>2</SUB> (total pressure 0.67kPa) was passed through the discharge tubes at a linear gas velocity of approximately 30mm/s and discharged for 60h under microwave of 30-40W supplied from two 2, 450 MHz power generators (200W each), more than 90% of CO<SUB>2</SUB> was converted into CO in the 1st tube and about 23% of the CO was then decomposed into carbon in the 2nd tube. However, about 50% of the CO escaped from the tube without being decomposed, and about 0.5% and 1% of the carbon fed were hydrogenated into CH<SUB>4</SUB> and C<SUB>2</SUB>H<SUB>2</SUB>, respectively. The rest about 25% which was not confirmed was probably evacuated from the 2nd tube as microparticles of carbon. To completely decompose CO<SUB>2</SUB> into carbon, additional discharge tubes are necessary downstream of the 2nd tube.
- Journal of Nuclear Science and Technology
Journal of Nuclear Science and Technology 35(1), 76-81, 1998-01-25
Atomic Energy Society of Japan