天然石油逐漸減少是人類近年來所共同關注的焦點，而利用烹飪所產生的廢油來生產生質柴油是一個不錯的方法來減緩天然石油的使用量。轉酯化反應為生成生質柴油的方法之一，其透過三酸甘油酯(食物油的主要成分)與醇(通常是甲醇)反應並在催化劑(目前氧化鍶是較佳的催化劑)的作用下生成生質柴油。氧化鍶催化轉酯化反應有三種可能的機制，而每個機制的初期步驟甲醇都必須先與氧化鍶表面進行鍵結。從文獻中可得知，一般廢食用油內含有很少量的水，此水也會吸附在氧化鍶奈米顆粒表面上形成氫氧化鍶而侵蝕氧化鍶表面，此氫氧化鍶不但較容易與油中的游離脂肪酸反應降低轉酯率，在回收重複使用氧化鍶催化劑的同時，此氫氧化鍶也會被除去導致氧化鍶的流失，因此氧化鍶表面上有一個吸附的競爭反應-吸附水或是吸附甲醇，透過文獻推論(110)及(310)晶面在轉酯化反應中佔有一定的反應比例且可以幫助反應進行。本研究希望透過第一原理的計算來了解在轉酯化反應中氧化鍶的表面與水及甲醇的吸附情形。吸附結構包括純水、純甲醇的吸附以及水、甲醇共同吸附在氧化鍶表面上，並透過波茲曼分布將各個吸附的結構所得到的吸附能轉變為發生機率比。最後結果顯示，當水與甲醇分子在反應中的數量足夠，氧化鍶(110)及(310)晶面上的活性位置會全被分子佔據，且水在此兩晶面上皆比甲醇還具有解離能力。根據文獻中，轉酯化反應中油與甲醇的莫耳數比在1:6的情況下可以得到最佳的轉酯效率，並考慮油的分子量，我們計算出油在有不同含量的水的情況下(110)晶面吸附結構的發生比例，假設(110)為主要轉酯化反應晶面，可得到水在油中的含量在重量百分比1.35%以下甲醇在氧化鍶表面上的吸附解離面積達80%使轉酯化能有效率的往後期反應進行。透過三酸甘油酯在此兩晶面上的吸附計算，得到氧化鍶表面上主要的轉酯化機制為ER機制。

Producing biodiesel from waste food oil is an excellent idea to preserve nature petroleum. The procedure to fulfill the idea is through transesterfication reaction, which converts triglyceride (main ingredient in food oil) to long-chain alkyl esters (biodiesel) by reaction with alcohol, usually methanol. The reaction usually needs catalyst (for example, strontium oxide) to have high conversion efficiency in low temperature (less than 100oC). From the literatures we can know that there are three possible mechanisms for SrO catalyzed transesterification reaction. The first step for these three mechanisms is the dissociation of methanol on SrO surface. But not only methanol, we know that the waste food oil contain very few amount of water inside and the water tend to adsorb on SrO nanoparticle surface thus erode the surface by forming Sr(OH)2. The erosion causes losing of SrO catalyst resulting in degrade the conversion rate. Thus there’s a competitive adsorption for water, methanol on SrO surface. The investigation of this competing reaction on several kinds of SrO surfaces was made to know more about the initial step of transesterification reaction. In this work, various adsorption structures of water and methanol molecules onto SrO surfaces were tested by ab-initio calculations to understand the mechanisms of dissociation of methanol and water molecules. The adsorption structures include pure water adsorption, pure methanol adsorption as well as water-methanol co-adsorption. The result shows that water have much higher potential to dissolve on (110) and (310) surfaces. Consider the ratio of oil and methanol used in others work, the probability of every adsorption conditions at different weight percent of water in oil was calculated. The results show that suppose (110) facet is the dominant surface in transesterification, the amount of water in waste oil should be kept lower than 1.35 % to make the initial stage of transesterification efficient. The mechanism for SrO catalyzed transesterification was also find out by calculating the adsorption of triglyceride on SrO surface.

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