不同金屬修飾鋅金屬有機骨架材料於甘油羧化反應之應用

Metals Modified Zinc-based Metal Organic Framework Materials for Catalytic Glycerol Carboxylation Conversion

張愛倫(Ai-Lun Chang)

指導教授 ： 胡哲嘉

中原大學/工學院/化學工程研究所/碩士(2020年)

https://doi.org/10.6840/cycu202000333

摘要

近年來因為環保意識的抬頭，人們逐漸意識到能源的使用問題，因此開發再利用的能源變成一個各界所重視的議題，生產生物柴油會導致過多的甘油產生，導致價格下跌的問題，本研究製備出高比表面積及高鹼性位點之不同金屬摻雜鋅金屬有機骨架材料(ZIF-8)，並應用於甘油與二氧化碳羧化反應之應用。
首先找出甘油與二氧化碳反應之溫度、壓力、時間的最佳反應條件為175 oC、3 bar、6 h，接著再以最常見之脫水劑乙腈，使反應向產物碳酸鹽甘油移動，使之增加其轉化率，推論出5Mg-ZIF-8材料具有最佳的轉化率，高達75.7 %，接著再以XRD、SEM分析出所合成出之材料為鋅金屬有機骨架材料(ZIF-8)，且經過不同金屬的摻雜，其形貌及結晶結構不會因此改變，但在5Mg-ZIF-8材料中看到了金屬氧化物的產生，形成金屬氧化物與ZIF-8共存的結構；FT-IR與XPS圖譜分析出經過金屬摻雜後之材料的化學結構與金屬鍵結狀況；氮氣吸脫附曲線與Brunauer-Emmett-Teller計算則呈現了ZIF-8的高比表面積特性，且經過金屬摻雜後之材料的比表面積都有下降的趨勢，是由於金屬遮蔽了材料的表面所導致而成；程序升溫脫附分析中，證實出5Mg-ZIF-8材料具有高鹼性位點，可有效的提升甘油的轉化率。
接著再以對人體較為無害的不同無機脫水劑進行反應，碳酸氫鈉當作脫水劑成功的將轉化率提升至38.7 %，雖加入乙腈後轉化效率效果最為提升，但亦容易造成更多的副產物產生，而在加入碳酸氫鈉後，副產物僅有水之形成，屬物理反應，使得反應物的選擇性提升，且較易重複取得進行使用，且對人體與環境造成的傷害較小；在以相同摻雜重量百分比不同金屬的材料進行實驗，證實出5Mg-ZIF-8具有最高的轉化效率。透過不同反應時間與溫度可推論出此反應為二階反應，並利用阿瑞尼斯方程計算出活化能為38.6 kJ/mol，再以摻雜鎂不同重量百分比的材料進行比較，且經過重複性實驗，可觀察到每次重複實驗中甘油的轉化率保持了大約75 %至80 %。
在反應後之材料可以透過XRD、SEM、XPS分析其特性與結構，也證實出在反應的過程中，運用了本研究合成出之ZIF-8材料結構的鋅離子與氮原子，經過金屬的摻雜，增加材料本身的鹼性位點與缺陷，證實出本研究成功的在最佳的反應條件下，有效的將甘油的轉化率大幅提升，以解決生質柴油所造成甘油過剩的環境問題。

關鍵字

金屬有機骨架 ； 甘油 ； 碳酸鹽甘油 ； 二氧化碳 ； 乙? ； 脫水劑 ； 鹼性位點 ； 羧化反應

並列摘要

In recent years, to enhance people’s awareness of environmental protection, people have focused on the utilization of renewable energy. Therefore, the development and reuse of energy have become an important issue that affects our daily life. The production of biodiesel causes excessive generated by-product, glycerol. In this work, different metal-modified zinc metal-organic framework materials (ZIF-8) with high specific surface area and high Lewis acidity were prepared and applied to the carboxylation of glycerol with carbon dioxide.
In this work, a dehydrating agent was also used to assist the reaction, showing that the optimized reaction conditions are reacted at 175 oC, 3 bar of CO2 for 6 h. The XRD patterns and SEM images of the samples loaded with different metals did not change significantly, but trace of metal oxides was found in the 5Mg-ZIF-8; FT-IR and XPS spectra suggested that the chemical structure and bonding states of metal-loaded samples; Nitrogen adsorption and desorption curves and the specific surface area calculations based on Brunauer-Emmett-Teller equation show the high specific surface area and porous nature of ZIF-8. The specific surface area of these materials modified with metal loading decreased gradually, which is mainly because that the metal-loading covered on the surface and pores of ZIF-8; Thermo gravimetric analysis confirmed that the materials decomposed at approximately 500 oC, and the weight loss sharply to 30% owing to the destroy of the organic framework. However, it still demonstrate itsthe high stability below 500 oC; The temperature-programmed desorption analysis indicated that the 5Mg-ZIF-8 material has the highest basic site among all the samples, which can effectively improve the conversion rate of glycerol.
Then, sodium bicarbonate is used as a dehydrating agent, which is easy to reuse. The conversion of glycerol in the cycle test is maintained about 80% to 85% that retains stability and safety. Through different reaction time and temperature, it can be inferred that this reaction is a second-order reaction, and the activation energy is calculated to be 38.6 kJ/mol. For compared with materials with different weight percentages of doped magnesium and repeated experiments.
Finally, After the reaction, the characteristics and structure of the material can be analyzed by XRD pattern, SEM image, XPS pattern, and it is also confirmed that in the process of the reaction, the zinc ion and nitrogen atom of the ZIF-8 material structure synthesized by this work, Metals Modified Zinc-based Metal-Organic Framework Materials for Catalytic is the basic sites and defects of the material itself are increased, so have to solve the environmental problem of glycerol excess caused by biodiesel.

並列關鍵字

metal organic framework ； glycerol ； glycerol carbonate ； carbon dioxide ； acetonitrile ； dehydrating agent ； Lewis acid ； Bronsted base ； carboxylation

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