主導動力學曲線模型於赤鐵礦還原反應之適用性研究

Abstract

主導動力學曲線模型(Master Kinetics Curve model, MKC)是一個以一般化學反應速率方程式為基礎推導而出的動力學模型，具有使用方便、預測準確、應用範圍廣泛三個主要優點，若可以拓展其使用範圍，可以使許多領域的資料，如：社會學的諸多統計，在模擬跟分析上更為便捷、節省許多時間成本。由於其基礎為一般化學反應速率方程式，且前人研究中也已成功將此動力學模型應用於熱分解、黏土礦物脫水、相變、燒結與油母質生油等反應，因此理論上來說，主導動力學曲線模型可能為具有普適性的動力學模型，但在以碳還原赤鐵礦的反應中，卻遇到了無法良好擬合的情況。因此本研究使用主導動力學曲線模型、Avrami方程式、Ozawa熱重分析法三種不同動力學模型對赤鐵礦還原反應進行一系列的分析，並將不同動力學模型的分析結果互相比較驗證，探討其差異處。在本研究中除了透過碳熱還原法進行實驗來蒐集以碳還原赤鐵礦的溫度、時間、反應百分比等參數，同時也從文獻中蒐集赤鐵礦以不同方式還原的相關數據，包括以氫氣還原赤鐵礦、以非晶質碳還原赤鐵礦的文獻數據，並將蒐集來的相關數據套入前述不同動力學模型做分析比較。根據分析結果，以氫氣還原赤鐵礦反應方面，主導動力學曲線模型可以得到良好的預測曲線，且與其他模型得到的結果相近。以碳還原赤鐵礦反應方面發現若單看赤鐵礦還原為磁鐵礦反應的話，主導動力學曲線模型可以得到良好的預測曲線；但若是當有赤鐵礦被還原為鐵，鐵會催化碳素溶損反應(Boudouard reaction)導致還原反應速率提升而使反應無法擬合，必須依照催化反應的活性溫度區分反應數據，才能得到良好擬合結果。本研究結果顯示主導動力學曲線模型的確可以應用於赤鐵礦以碳、氫氣還原的反應上，且具有良好的分析能力，但若是反應過程中若有催化反應參與導致反應速率或機制改變，主導動力學曲線便會出現數據點偏移。

The Master Kinetics Curve model (MKC) is a kinetics model derived from the general reaction rate equation. The reaction prediction curve can be obtained by fitting several sets of experiment data. Because the prediction curve of the reaction is based on experimental data, it is easy to use and its prediction of reaction ratios is adequately accurate. What we seek to accomplish herein is to expand the applicability of MKC, so that it can make the simulation and analysis of data more convenient. In previous studies, researchers had already successfully applied the MKC model to different reactions, such as sintering, phase transformation, oxidation, clay mineral dehydration, and thermal decomposition reactions. Besides, since the MKC model is derived from the general reaction rate equation, the MKC model may serve as a universal kinetics model. Although we consider MKC as a practical universal kinetics model, in the reaction of reducing hematite with amorphous carbon, it was found that the data didn’t fit well. Therefore, whether the MKC model can be applied to the reduction reaction of hematite was researched in this study. Besides, to get a better understanding of the applicability of MKC, the Avrami equation and the Ozawa method were also used in this study. A series of kinetics analyses of the reduction reaction of hematite was carried out with three different models. In this study, the hematite reduction experiments were carried out via the carbothermal reduction method. The reduction reaction of hematite data from the relevant literature were also collected. The isothermal experiments data were analyzed by using the MKC model and the Avrami equation, while the constant heating rate experiments were analyzed by using the MKC model and Ozawa method. According to the kinetics analysis results, we could obtain good prediction curves of the hematite reduced by hydrogen reaction via the MKC model. The results agree with the results obtained by other models, indicating that the MKC model is applicable for the reduction of hematite with hydrogen. As for the reduction of hematite with carbon, it was found that if the reaction of hematite is reduced to magnetite, the MKC model can obtain a good prediction curve, which shows that the MKC model is applicable for the reduction of hematite to magnetite. However, if some of the hematite is reduced to iron, the carbon solution loss reaction, also known as the Boudouard reaction, will be catalyzed by the iron, resulting in an increased reduction reaction rate, thereby causing the shifting of the data point. The results of this study show that the MKC model can indeed be applied to the reduction reaction of hematite with carbon and hydrogen, and is in good agreement with those of other models. However, if catalytic reactions occur, it will cause the shifting of the data point on the MKC curve.