從生質酒精發酵液以ZSM-5觸媒一步轉化生成芳香族

Abstract

近代科技及文明急速發展，化石燃料的蘊藏量只能夠讓我們再使用約半個世紀。因此，科學家們開始致力於發展替代性能源。在各種替代能源中，生質能源是目前最具發展性的，與其直接以能源形式使用外，進一步轉化為高經濟價值化合物已成為新的趨勢。生質能源中之發酵酒精在近年蓬勃發展，且眾多文獻證實可以透過ZSM-5沸石，將其轉化成高碳數的化合物，普渡大學的張馬丁教授在近年來提出含水的進料能夠促進該反應發生，因此直接使用生質酒精(酒精含量約為12wt.%)成為本研究之主要方向，以達成節省純化所需能源與零碳足跡的目標。 在酒精轉化之眾多產物中以芳香族產物具有最高的應用價值，因此本研究欲透過自行合成之ZSM-5找到最佳反應參數並且負載不同金屬以提升芳香族之產率，此反應我們稱之為Ethanol Broth to Aromatics (簡寫為EBTA)。 經過基本參數測試後，發現當矽鋁比為20，反應溫度為 400°C。時空流速為1.1 hr-1且進料濃度為72 wt.%可以得到最高之芳香族產率。接著，利用水熱合成法以及初濕含浸法負載不同比例之Ga以及Zn金屬，經過實驗結果與儀器分析鑑定，可以證實以水熱合成法負載Ga，與Al之莫耳比為3:1之沸石有最佳效果，該觸媒之Ga金屬分散性佳且強酸比例高，能將芳香族產率(莫耳比例)從0.23提升至0.42；因為電荷平衡因素，Zn金屬較適合使用初濕含浸法負載，且與Al之莫耳比為1:1時有較佳之效果，但因為強酸比例不如負載Ga之觸媒，產率(莫耳比例)僅從0.23稍微提升至0.26。 最後本研究使用核能研究所陳文華教授研究團隊商業化之生質酒精作為進料，並成功利用蒸發器與氣相層析儀控制氣相濃度維持在72 wt.%左右，總產物的芳香族產量略高於模擬生質酒精，其來源主要來自於萘的衍生物增加，至於苯、甲苯、二甲苯(BTX)產率則是相當近似。

The technology is developing amazingly. Fossil fuel will be depleted in 50 years. Therefore, scientists are working on the development of renewable energy. Biomass is the most promising renewable energy source. In addition to using it to generate energy directly, many experts tried to convert it to more valuable compounds. In all kinds of biomass, bio-ethanol was widely used in recent years and lots of research indicated that it can be converted to long-chain hydrocarbons by ZSM-5 zeolite. Furthermore, Professor Martin Chang in Purdue University proposed that water content in reactant can enhance the ethanol conversion. Based on this concept, directly using bio-ethanol as reactant was the major objective of this research. The advantages are to save energy of purification and to achieve the goal of zero-carbon footprints. Among the hydrocarbons from ethanol conversion, aromatics are most valuable compounds because of their diverse application. Hence, this research aims to enhance the aromatics yield by performing different reaction parameters and loading metal on ZSM-5 in two loading methods. We called this study as Ethanol Broth to Aromatics which can be abbreviated as EBTA. After experiment studied by various parameters, the optimum reaction conditions that could get the highest aromatics yield were as following: Si/Al : 20, temperature: 400 °C, weight hourly space velocity: 1.1 hr-1, and the reactant concentration: 72 wt.%. The hydrothermal method and wet incipient impregnation method were used to load different amount of gallium and zinc on ZSM-5. From experiment results and catalysts characterization, gallium loaded ZSM-5 with gallium to alumina ratio = 3 by hydrothermal method gave the best performance on EBTA. Good gallium dispersion and high strong acid ratio could enhance the aromatics yield from 0.23 to 0.42. On the other hand, wet incipient impregnation method could properly load zinc on the ZSM-5 due to the charge balance. It was found that zinc loading ZSM-5 with zinc to alumina ratio = 1 showed the good performance on EBTA. However, its acid strength became low which led to just little enhancement of aromatics yield from 0.23 to 0.26. Finally, we used real bio-ethanol, which was produced fermentation from the group of Dr. Wen-Hua Chen in Institute of Nuclear Energy Research, as the feed. We successfully used evaporator and gas chromatography to control the gas concentration to near 72 wt.%. After the EBTA reaction, its aromatics yield was a little higher than that of reactant from simulated ethanol vapor due to some naphthalene derivatives while BTX (benzene, toluene and xylene) yield was comparable the same.