A Method of Decomposing Carbon Dioxide for Fixation of Carbon-14

• Published in: Journal of nuclear science and technology 1998-01, Vol.35 (1), p.76-81
• Main Authors: SAKURAI, Tsutomu, YAGI, Tomonori, TAKAHASHI, Akira
• Format: Article
• Language: English
• Subjects: acetylene; Applied sciences; carbon 14 fixation; carbon dioxide; carbon monoxide; decomposition; Energy; Exact sciences and technology; Fuels; graphite; hydrogen; material balance; methane; microwave discharge; Nuclear fuels; Preparation and processing of nuclear fuels
• ISSN: 0022-3131; 1881-1248
• DOI: 10.1080/18811248.1998.9733822

To consecutively decompose 14 CO 2 into carbon ( 14 C) through its reaction with Hz, 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 2 +H 2 → CO+H 2 O" and (2) "CO+H 2 +C n → C n+1 +H 2 O", where C n 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 (6 mm O.D., 4 mm I.D., and 150 mm 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 2 and H 2 (total pressure 0.67kPa) was passed through the discharge tubes at a linear gas velocity of approximately 30mm/s and discharged for 60 h under microwave of 30-40 W supplied from two 2,450MHz power generators (200 W each), more than 90% of CO 2 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 4 and C 2 H 2 , respectively. The rest about 25% which was not confirmed was probably evacuated from the 2nd tube as microparticles of carbon. To completely decompose CO 2 into carbon, additional discharge tubes are necessary downstream of the 2nd tube.