Improved Process of the Conversion of Wollastonite to Carbonate
Date Issued
2007
Date
2007
Author(s)
Su, Chien-Yuan
DOI
zh-TW
Abstract
The release of carbon-dioxide into the atmosphere has a serious consequence on the aggravation of greenhouse effect, thus the topic of carbon-dioxide reducing has been studied extensively in recent years. Using wollastonite to fix the carbon-dioxide via carbonation reaction seems to be one of the effective methods. The other objective of this research is to seek the probability of using slag to replace wollastonite.
Based on the previous experience gathered in our laboratory, this research attempted to increase the reaction conversion by performing pre-treatment to the reactant, including preheating and washing. Pre-heating of wollastonite did not increase the conversion effectively because of sintering, which leads to reduction of pore diameter within the reactant. On the other hand, acid-washing of wollastonite removed the surface calcite, and hence rendered the contact between wollastonite and carbon dioxide directly. This effectively improved the conversion of carbonation by 7%.It might still improve to 77.08% by adding sodium bicarbonate after acid-washing.
In order to increase the conversion of wollastonite carbonation, the experiment apparatus have been modified in three aspects; i,e stirring, heating and cooling to reach higher temperature and to achieve shorter cooling time. Modification made to the stirring system have enhanced the wollastonite conversion by approximately 13.35%, and slag conversion by 4%. The new cooling system reduced the cooling time from 2-3 hours to 30-45 minutes. Together with the new blade-stirring equipment, conversion reached 90.41% at 150℃, 19.74 atm and 500 rpm after 1 hours of reaction time. The result showed an effective improvement in the conversion, and a significant reduction of the reaction time.
The optimum operating temperature of wollastonite carbonation was 150℃. Once 150℃ was reached, the conversion started to drop. This was due to the fact that carbon dioxide became less soluble in water at high temperature, and hence the leaching of calcium ions was not effective due to low of hydrogen ions. Pressure did not affect the wollastonite carbonation reaction significantly. A suitable operating pressure was around 19.74 atm. Higher pressure might block the pore of the reactant, which made it difficult for further reaction. Supercritical state improved the conversion slightly due to increasing of the diffusion coefficient, but it still could not overcome the blockage of the pore by calcite.
The conversion of slag carbonation was not high, the highest conversion was 52.76% in the blade-stirred system. To replace the wollastonite for the reduction of carbon-dioxide, the conversion of slag should be improved.
Subjects
碳酸化；超臨界二氧化碳；鈣矽石；爐石
carbonation
carbon-dioxide sequestration
supercritical carbon-dioxide
wollastonite
slag
Type
thesis
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