- 學位論文
甲烷雜質對於Cu/ZnO觸媒在乙醇協助二氧化碳氫化生成甲醇反應的影響
Effect of CH4 impurity on ethanol-assisted methanol synthesis from CO2 and H2 over Cu/ZnO catalyst
摘要
二氧化碳的過度排放導致其在大氣中的濃度過高，是全球急需解決的議題。解決這個問題的其中一種方法是回收並重複使用二氧化碳，將其轉換為甲醇等高附加值的產品。作為二氧化碳排放來源之一的工業廢煙氣中，除了二氧化碳，還含有各種雜質，如甲烷是廢煙氣中常見的雜質。本研究使用了含甲烷的模擬煙氣作為甲醇生產原料，探討銅鋅氧化物（Cu/ZnO）觸媒對反應的影響，並使用乙醇作為催化溶劑，使觸媒在相對低的反應溫度下，達到較高的二氧化碳轉化率及較高的甲醇產率。本研究探討了甲醇合成的最佳操作溫度，以及進料端添加甲烷對產物的影響。研究結果顯示，在150°C時，可以在甲醇和副產物的生成取得最佳平衡。相比於其餘較高的反應溫度，在該溫度下能產生較少的副產物乙酸乙酯，從而降低後續分離程序的困難度。此外，研究結果亦顯示添加少量的甲烷可以提高甲醇產率；在氣體混合物中添加相當於總壓力1%的甲烷，可以在150°C下達到79%的二氧化碳轉化率和33% 的甲醇產率。藉由XRD、XPS和原位紅外線光譜（in-situ IR）等鑑定，推測在乙醇輔助二氧化碳和氫氣合成甲醇的反應中，甲烷可能作為還原劑，避免了Cu+ 和Cu2+ 的生成，有助於銅鋅氧化物觸媒維持在最有效的Cu0價態，減少了觸媒表面上銅氧化物。
並列摘要
The problem of CO2 emissions into the atmosphere is an issue that needs to be addressed worldwide. One of the ways to tackle this problem is to bring back CO2 and reuse it to produce higher-valued products like methanol. Nevertheless, exhausted gases emitted from many industries contain not only CO2 but also various impurities, of which CH4 is a common one. In this work, the simulated flue gas containing CH4 impurity was studied to examine its effect as the feed on the methanol production over Cu/ZnO catalyst, in the presence of ethanol as the catalytic solvent to enhance the conversion of CO2 and the yield of methanol while reducing the temperature required for synthesis. This study investigated the optimal operating temperatures for methanol production and the impact of CH4 variation in the feed. It was found that operating at 150°C achieved the best compromise between methanol production and addressing the practical challenge of unwanted by-product formation, specifically ethyl acetate, since this temperature was determined to produce less formation of ethyl acetate compared to higher temperatures, thereby reducing the complexity of separation processes. Additionally, the addition of a small amount of CH4 led to an increased methanol yield; the presence of 1% CH4 of total pressure of the gas mixture resulted in 79% CO2 conversion and 33% methanol yield at 150°C. This is attributed to CH4 potentially acting as a reducing agent, supported by characterization results, particularly from XRD, XPS, and in-situ infrared (IR) studies. This aids in maintaining the catalyst in its most efficient form, Cu0, during ethanol-assisted methanol synthesis from CO2 and H2, by mitigating the formation of copper oxides, including Cu1+ and Cu2+, on the catalyst surface.