- 學位論文
應用兩階段反應器在低壓下將二氧化碳氫化生產甲醇
Hydrogenation of carbon dioxide to methanol by two-stage reactors at low pressure
摘要
全球暖化是全球最受矚目的問題之一，過多的二氧化碳排放讓地球的環境愈來愈差，平均溫度愈來愈高，生態環境也愈來愈不適合生物居住。另一方面，全球的化石燃料也面臨到短缺問題。其含量只能再讓人類使用50年左右，因此必須趕緊開發可用的替代能源。因此，現在許多研究開始著重於將空氣中的二氧化碳捕捉起來，並透過觸媒催化反應將其轉化成燃料或其他高價值的化學品，甲醇就是其中的化學品之一。 一般來說，二氧化碳氫化產甲醇是直接氫化，意即只利用一個反應器，在此反應器裡直接將二氧化碳氫化成甲醇，但二氧化碳產甲醇的反應是放熱反應，在低溫甲醇選擇率較高但二氧化碳轉化率不高，高溫時則相反，另一個會伴隨的反應是逆水氣轉化反應，即二氧化碳產生一氧化碳的過程，此吸熱反應是隨著溫度升高而產率跟著升高。相比二氧化碳直接生產甲醇，以一氧化碳生產甲醇更適合在低溫反應，因此為了解決反應條件有高低溫問題，本研究提出決定使用兩個反應器，第一個反應器在高溫進行生成一氧化碳，接下來另一個反應器則在低溫將一氧化碳轉化成甲醇，兩個反應器中間以乾燥劑來吸走多餘的水氣，以利反應平衡有利甲醇的生成。 研究的結果發現兩個反應器分別定在350℃與210℃是最適合的，觸媒則是商用Cu/Zn/Al2O3，滯留時間則對反應沒有太多影響。而雙反應器系統和單一反應器比較，可以確實地將甲醇產量提高3倍左右，但是在甲醇選擇率方面沒有什麼變化。
並列摘要
Nowadays, global warming is one of the environmental problems which attracts much attention. Too much carbon dioxide emission drives the earth into a worse condition with continuously increasing temperature. Moreover, the environmental surroundings gradually become unsuitable for human and animals to live. On the other hands, people are facing the problem of shortage of fossil fuels, which makes developing an alternative energy source an urgent issue. Recently, many research focus on capturing carbon dioxide in the atmosphere, converting carbon dioxide into other fuels or more valuable products. Among all of the chemicals, methanol is one of the most popular chemicals which can be derived from carbon dioxide because it can be served as both fuels and feedstocks of chemicals. Generally, hydrogenation of carbon dioxide to methanol is direct hydrogenation, which means that there is only one reactor in whole apparatus. In this reactor, carbon dioxide is directly hydrogenated to methanol. However, hydrogenation of carbon dioxide to methanol is exothermic, which is high selective to methanol but with low conversion at low temperature. At higher temperature, the situation is reverse. Another reaction occurring simultaneously is reverse water gas shift reaction, which is the process of carbon dioxide hydrogenation to carbon monoxide. This reaction is endothermic so the yield of carbon monoxide increases with increasing temperature. In comparison to hydrogenation of carbon dioxide to methanol, water gas shift reaction is more preferable under lower temperature. To solve the problem of temperature control in the reaction, two-staged reactors are used in this research. In the first reactor, carbon dioxide is hydrogenated to carbon monoxide at high temperature, while in second reactor, carbon monoxide is converted into methanol at lower temperature. A desiccator is used between two reactors to remove water in the stream in order to produce more methanol. The results showed that the optimal reaction temperatures in two-stage reactors is 350℃ and 210℃ respectively, and the best catalyst is commercial Cu/Zn/Al2O3. The performances do not alter significantly with different space velocity. In comparison between two-staged reactor system and one-reactor system, the methanol yield increases 3.4 folds, without significant increase in methanol selectivity.
參考文獻
延伸閱讀
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