甲醇蒸氣重組反應之複雜反應網路分析

ANALYSIS OF COMPLEX REACTION NETWORKS FOR METHANOL STEAM REFORMING

林佳燕(Chia-Yen Lin)

指導教授 ： 陳泰祥

大同大學/工程學院/化學工程學系所/碩士(2010年)

摘要

甲醇蒸氣重組反應已經成為近年來研究燃料電池的重要課題之一，因為其可以提供有效率的氫氣來源。對重組反應適當的動力學反應速率式，是提供整體燃料電池設計的重要資訊。由於甲醇蒸氣重組反應為高溫的非均相觸媒反應，其反應機構顯得相當複雜，而引起廣泛的研究與探討。本研究利用通用速率式法，來分析甲醇蒸氣重組反應的複雜網路反應。由文獻中之資訊提出五種可能的反應機構，經由網路簡化技術來推導分別之反應速率式。再由不同文獻中所發表的實驗數據與結果比較，決定合理的反應機構。並且利用非線性迴歸工具推估最好的動力學參數，包括各反應路徑之速率常數因子和活化能。
結果顯示本研究提出的第五種反應機構與文獻發表的實驗數據有較佳的吻合性，推導出的結果與原始參考文獻中各成分濃度有相似的動力學行為。不同文獻使用不同的反應觸媒，所以回歸的速率參數有所不同，但預測值與實驗值皆有相似的動力學趨勢。雖然部份物質預測的濃度曲線與實驗數據有明顯的偏差，可能導因於過於複雜的非均相反應機構與系統中一氧化碳與二氧化碳濃度相對較低，造成非線性回歸分析更加困難。本研究最後並針對最佳反應機構，進行動力學參數之敏感性分析。藉由所有反應路徑之速率常數對反應速率之敏感度，可以比較出每一反應路徑之相對重要性。此一分析之結果，可以提供後續對過於複雜之反應速率式簡化研究之重要參考。

關鍵字

甲醇蒸氣重組反應 ； 複雜網路反應 ； 燃料電池 ； 通用速率式法 ； 敏感度

並列摘要

The study on methanol steam reforming reaction has become an important issue in research for development of fuel cells. However, a suitable kinetic rate expression for the methanol steam reforming reaction is key information for global design of fuel cells. Due to the heterogeneous and high temperature reaction for methanol steam reforming, the mechanisms for the system are very complicated and hard to analyze. In this study, the general rate equation method for complex reaction network was applied to investigate the complicated reaction mechanisms. Five possible mechanisms for methanol steam reforming were proposed and the related reaction rates were derived by network reduction techniques. The feasibilities of the mechanisms were identified by comparison of experimental data published in different literatures. The kinetic parameters, including the pre-exponential factors and activity energies were fitted by nonlinear regression tools.
The advantages of using general rate equations method is that no need to assume any rate determined steps and the explicit rate of reaction can be derived systemically. The results showed that the mechanism model 5 proposed in this study presented the best consistency with the experimental data in different literatures. The kinetic behaviors of the best mechanism showed the same tendency with the experimental data. Due to the different experimental data used the different catalysts; the fitted kinetic parameters were also different for various systems. However, the predicted curve of model has same outcome. Though some concentration profiles showed apparent deviations with the experimental data, it maybe caused by the too complicated mechanisms and the concentrations of carbon oxide and carbon dioxide were too low compared with other species. It would make the nonlinear regression more difficult. Finally, the sensitivity analysis for individual rate constants to reaction rate was performed for the best kinetic model. From the analyses, we can identify the reaction pathway which would affect the formation of carbon oxide and carbon dioxide. The results of sensitivity analysis can be used to supply important information for the simplification of too complicated rate expressions for methanol steam reforming in further investigations.

並列關鍵字

methanol steam reforming reaction ； complex reaction network ； fuel cell ； general rate equations method ； sensitivity

參考文獻

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