| 研究実績の概要 |
Leveraging the experience in lab syntheses, this study aimed to evaluate the prospective environmental impact of CNT synthesized via three selected catalytic CVD methods. First, the CO2-assisted growth on flat substrates [Carbon, 136 (2018): p.143-149], represented the established millimeter long CNT growth. Second, the fluidized-bed growth on spherical beads with sputtered catalysts [Carbon, 50(4) (2012): p. 1538-1545], contrasted the effect of 3D CNT growth to previous 2D growth. Third, the fluidized-bed CVD with chemical vapor deposited catalysts [Carbon, 49(6) (2011): p. 1972-1979], showed a repeatable single-reactor production. We quantified the global warming potential impact of 1 g CNT production with life cycle assessment (LCA). The results for the three syntheses were 28.55, 9.94, and 2.10 kg-CO2equiv/g-CNT, accordingly. By comparing the three syntheses, we showed that the strikingly high impacts could be mitigated through increasing CNT yield with fluidized bed and replacing the energy-intensive sputtering process. A scenario to substitute the remaining hotspot, argon (purging gas), with nitrogen could reduce the impact to 0.48 kg-CO2equiv/g-CNT. When considering scale-up from lab-scale (reactor diameter of 22 mm, productivity of 5 g per day) to industrial scale (diameter >30 times, productivity >3 to 104 times), the CNT production would be comparable to industrialized carbon fiber production (about 0.02 kg-CO2equiv/g-CF).
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| 今後の研究の推進方策 |
In the second year, the LCA of CNT synthesized via on-substrate and fluidized-bed CVD will be wrapped up; presentation and publication will be made as research output.
Further life cycle assessment on floating catalyst CVD will be conducted. Floating catalyst has the advantage of producing high-yield single-wall CNT in a single reactor. The experiments on floating catalyst are partially completed and on-going.
In addition, current assessment focuses only on a cradle-to-gate scope that ends at the CNT synthesis. An expansion of scope to include CNT purification, processing, and application will be considered using assumptions based on secondary data.
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