- 學位論文
鈣矽石轉換成碳酸鹽的改良程序
Improved Process of the Conversion of Wollastonite to Carbonate
摘要
期望解決因二氧化碳過度排放而造成的溫室效應(Greenhouse Effect)，並減緩其惡化的現象，針對二氧化碳減量的研究近年內大量的增加。利用鈣矽石與二氧化碳做反應，經由碳酸化反應將其固定成為碳酸鈣，是為有效的方法之一。同時並探討以爐石取代鈣矽石之可能性。 本研究依據實驗室之前的研究為基礎，嘗試針對反應物做前處理以增加反應轉化率：將反應物預先做熱處理，部分的反應物可能因為高溫而燒結，降低了反應物內部的孔徑以及表面積，無法有效提升反應轉化率；另外將反應物預先做酸洗，除去表面的碳酸鈣顆粒，使得鈣矽石與二氧化碳接觸機會增加，有效的增加了鈣矽石碳酸化反應轉化率7%，若酸洗後再添加碳酸氫鈉做反應，轉化率可再增加至77.08%。 為增加鈣矽石碳酸化反應的反應轉化率，亦改善過去設備無法達到高反應溫度以及降溫時間過長的缺點：在舊設備方面改良攪拌設備而提升鈣矽石的反應轉化率大約13.35%；提升爐石的反應轉化率大約4%，以及架設新的冷卻系統，將原本需要2~3小時的降溫時間縮短至30~45分鐘；並且新增添了葉片攪拌高壓反應器投入研究，並在溫度為150℃、壓力為19.74 atm及攪拌速率為500rpm條件下反應1 hr，反應轉化率即可達90.41%。有效的增加反應轉化率並且縮短反應時間。 鈣矽石碳酸化反應的最佳操作溫度為150℃，超過150℃時反應會因為二氧化碳在高溫下于水中的溶解度降低，而降低轉化率；壓力對於鈣矽石碳酸化反應的影響並不大。較佳的操作壓力為19.74 atm，過大的壓力反而會造成反應物的孔徑被堵塞，影響質傳速率，造成後續反應的困難。而超臨界的狀態可因擴散係數的提升而使得轉化率有些微的上昇，但是仍然無法克服生成物堵塞孔徑的問題。 爐石的碳酸化反應的轉化率並不高，在葉片攪拌系統中最高達到52.76%，為取代鈣矽石來減量二氧化碳，轉化率有待提升。
並列摘要
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.