鈣矽石碳酸化機制之探討

Mechanism of Wollastonite Carbonation

郭耿佑(Keng-You Kuo)

指導教授 ： 戴怡德

國立臺灣大學/工學院/化學工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.00434

摘要

為解決二氧化碳過度排放而造成的溫室效應，並減緩其惡化的現象，近十年來許多研究文獻利用天然礦石或工業廢棄物，經由碳酸化將二氧化碳固定為碳酸鈣；該方法稱為礦石封存法並且為目前最有效的方法之一。
　　本研究以實驗室以往的研究為基礎，以驗證鈣矽石碳酸化機制為目的，首先以高壓電極量測溶液pH值，探討其對鈣矽石碳酸化轉化率的影響。從所有組別的pH值隨時間變化圖可發現，二氧化碳的溶解平衡相當迅速，故在碳酸化機制三步驟中二氧化碳的吸收與解離並非速率決定步驟。另外在鈣矽石碳酸化中，溫度及溶液pH值均為重要的變數：在220psig下，當反應溫度為150℃時有最高的轉化率為78%；而80℃下，當溶液pH值在最佳範圍為5.5~6.5時，最高之轉化率為40%。
　　另一方面，用氮氣提供壓力與碳酸氫鈉供應碳酸根以確認其取代超臨界二氧化碳的可行性，並比較壓力與攪拌葉片轉速等外力的效應。在溫度150℃、壓力15bar、轉速500rpm及碳酸氫鈉3.2M條件下反應2h，轉化率即可達48%，此顯示碳酸化確實可以進行，故超臨界二氧化碳並非必要條件。同時，從反應後樣品之SEM圖可驗證以往所提之反應機制無誤，且攪拌葉片轉速應為較具影響的外力來源。實驗結果顯示，當壓力與轉速分別高於6.5bar與為100rpm時，即可得到較高的轉化率。最後，由本研究之結果對此鈣矽石碳酸化機制提出一更詳細的說明。

關鍵字

鈣矽石 ； 碳酸化機制 ； 轉化率 ； 操作變數效應

並列摘要

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.

並列關鍵字

wollastonite ； carbonation mechanism ； conversion ； effects of operating variables

參考文獻

蘇乾元，“鈣矽石轉換成碳酸鹽的改良程序”，碩士論文，國立台灣大學，台北，台灣，38~52頁 (2007)。

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