探討以銅鋅觸媒進行二氧化碳氫化產甲醇於一階段反應器及兩階段反應器中之優劣

本研究旨在探討以銅鋅觸媒進行二氧化碳氫化反應產甲醇，並比較一階段反應器與兩階段反應器之優劣。為了改善全球暖化與氣候變遷之問題，氫能被視為綠色能源以防止額外之二氧化碳排放，然而氫能之低體積能源密度使其不易輸送與儲存之問題，近年來許多專家建議將過多之氫能轉換為能源載體，以解決氫能輸送及儲存之不便性，其中甲醇被視為最佳之能源載體之一，原因為甲醇具備高能源密度且為眾多化學品之反應物。本研究針對二氧化碳氫化產甲醇反應之現行工業兩大問題進行改善，一為低觸媒效率，二為工業過高之操作壓力。在觸媒方面，吾人以不同促進劑、銅鋅莫耳數比、混摻金屬合成銅鋅觸媒，並發現以3 mol %Mg 混摻於元素莫耳比率Cu : Zn : Ga = 6 : 3 : 1之Cu/ZnO/Ga2O3在230 ̊C及4 bar能達到2.10 %之甲醇產率及 164 mg MeOH/gcat h之時空產率，其觸媒效率為傳統商用觸媒之六倍之多。此外，吾人設計新型疏水性觸媒以銅鋅鋁鑭含浸於h-BN上以合成 20 wt%CZALa/hBN，其高度疏水性觸媒表面使甲醇選擇率相較於商用觸媒有大量之提升。最後使用 XRD、SEM、XPS、EDS、H2-TPR、CO2-TPD、接觸角分析以解釋觸媒活性。最後本研究比較一階段反應器及兩階段反應器系統應用於二氧化碳氫化產甲醇反應，由實驗結果發現本研究中之所有觸媒皆在一階段反應器中有較高之甲醇產率，其原因透過二氧化碳氫化反應與一氧化碳氫化反應比較後，得出在低壓下甲醇之生成主要藉由二氧化碳氫化反應而非一氧化碳氫化反應，因此對於以一氧化碳氫化反應為主之兩階段反應器來說，並不有利於甲醇之生成。此外，吾人以不同氣體流速、氫氣濃度、壓力比較二氧化碳氫化及一氧化碳氫化反應之效應，最終判斷在0 - 4 bar之低壓環境下二氧化碳氫化活性約為一氧化碳氫化活性之10倍，證實在低壓下進行二氧化碳氫化產甲醇須以一階段反應器為最佳選擇。

關鍵字

二氧化碳氫化；甲醇；氫；銅鋅觸媒；六方氮化硼

並列摘要

This research focus on the carbon dioxide hydrogenation to methanol using Cu/ZnO based catalysts in one-stage and two-stage packed bed reactors systems. Respecting to deal with global warming and climate change, hydrogen is regarded as green energy to avoid carbon dioxide emission, however hydrogen is difficult to transport and store due to low density by volume. Nowadays some of researchers suggest transfer hydrogen energy to energy vectors to easily store excessive energy. Methanol is one of the best energy vectors based on high energy density and raw material. In this study, we investigated carbon dioxide hydrogenation to methanol reaction, and tried to solve two kinds of problems we faced in the industry, one is low catalytic efficiency of commercial catalysts, the other is high operated pressure. For the catalyst side, we compared with different promoters, Cu : Zn molar ratio, different dopants, and found that using 3 mol % Mg as dopant synthesized Cu/ZnO/Ga2O3 with molar ratio Cu : Zn : Ga = 6 : 3 : 1 could get 2.10 % methanol yield and reach 164 mg MeOH/gcat h of STY at 230 ˚C and 4 bar , which was six times higher than commercial Cu/ZnO catalysts. Furthermore, we designed the new hydrophobic catalysts using Cu, Zn, Al, La loading on h-BN, 20 wt%CZALa/hBN showed higher methanol selectivity due to hydrophobic surface. The instruments XRD, SEM, XPS, EDS, H2-TPR, CO2-TPD, contact angle were applied to measure the characteristics of catalysts, and to explain the results of activity tests. Last but not least, we compared with one-stage reactor and two-stage reactors system, the results showed that all of the catalysts in this study got higher methanol yield in one-stage reactor, indicating that methanol would be synthesized by CO2 hydrogenation not CO hydrogenation. In addition, we investigated CO hydrogenation and CO2 hydrogenation with different overall flow rate, H2 concentration and pressure. The result showed that the methanol yield for CO2 hydrogenation was ten times larger than CO hydrogenation under 0 – 4 bar, which proved that one-stage reactor is the better choice to operate CO2 hydrogenation to methanol reaction under low pressure condition.

並列關鍵字

CO2 hydrogenation ； methanol ； H2 ； Cu/ZnO catalyst ； h-BN

參考文獻

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