| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 97 === In the past ten years, numerous studies concerning CO2-reduction have been studied to mitigate greenhouse effect, which was mainly due to the release of CO2 from industries. Among them, mineral carbonation was a potential and promising method, though which CO2 is fixed in a “container” such as natural rocks or industrial wastes.
Based on the previous experience in our laboratory, we postulated a mechanism of the mineral carbonation of wollastonite and tried to prove it in this study. First, a high pressure pH electrode was installed to measure the pH value of solution and to discuss the pH effect on the conversion of wollastonite carbonation. Most of pH-t diagram showed that dissolution of CO2 reached equilibrium so fast that it could not be the rate-determining step. Moreover, temperature and the pH value were found to be the most important variables in wollastonite carbonation; the conversion being 78% at the highest temperature of 150℃ under 220psig, and being 40% at 80℃and an optimal pH range of 5.5~6.5.
Secondly, high pressure nitrogen and sodium bicarbonate were used respectively as destructive energy and source of carbonate ion to replace supercritical CO2. At 150℃, 15bar, 500rpm, and concentration of sodium bicarbonate 3.2M, a conversion of 48% was reached in 2h, thus proving that supercritical CO2 is not a necessary condition for mineral carbonation. Besides, a mechanism proposed in the previous research was checked using the SEM photos, and it was concluded that stirred speed was more important than pressure. A significant conversion was obtained when the wollastonite carbonation proceeded at a pressure and stirred speed higher than 6.5bar and 100rpm respectively. Finally, a more complete mechanism of wollastonite carbonation was proposed.
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