水熱液化是一種不需乾燥前處理即可將生質物轉換為高熱值生質油的熱化學技術，本研究主要為分析廚餘水熱液化油的基本性質以評估其在工業應用上的潛力，並進一步對鹼前處理-水熱液化二階段製程進行最佳化，本文主要分為兩大部分，如下所述。
在本研究的第一部分為初步分析廚餘水熱液化油之特性，將廚餘置於半工業式反應器並添加碳酸鉀(K2CO3)作為催化劑在100 °C下進行前處理一小時，接著升溫至320 °C持溫30分鐘做為廚餘水熱液化之操作條件。該條件下得到之水熱液化油的熱值為34.79 MJ kg-1，其能量密度相較於原本之廚餘料源(22.74 MJ kg-1)有53%的成長。根據熱重分析結果可以發現廚餘水熱液化油相較於其他水熱液化油有較低的點火溫度及燃燼溫度，且相較於一般熱裂解油有較高的氧化起始溫度，表示水熱液化油有較好的熱穩定性。獨立平行反應模型搭配粒子群最佳化顯示水熱液化油之裂解動力式可以劃分為四個族群，且對照成分分析可知廚餘水熱液化油主要由脂肪酸類及醯胺類所組成，分別是從廚餘中的糖類及蛋白質轉換而來，綜合分析結果顯示廚餘水熱液化油有較好的能量密度及燃燒特性，是一種有潛力替代化石燃料的再生能源。
第二部分研究中，利用鳳梨皮、香蕉皮和西瓜皮作為廚餘料源進行鹼前處理-水熱液化二階段製程，鹼前處理為使用10wt%的碳酸鉀(K2CO3)作為催化劑，並藉由田口方法以最佳化前處理溫度、前處理時間、液化溫度及液化持溫時間等四個操作參數，以得到最佳的廚餘水熱液化油能源產率。研究結果顯示最佳化組合之能量產率可達到56.55%，並得到25.12 MJ kg-1的高熱值，與原料（17.22 MJ kg-1）相比，水熱液化油之能量密度提高45.88%。進一步利用田口方法和變異數分析結果皆顯示液化溫度對於水熱液化油之能量產率起著最重要的作用，且田口方法中的影響值（effect）與變異數分析中的F檢測之間存在強烈的線性關係（R2≈0.99）。而經由熱重分析（TGA）與傅立葉轉換紅外光譜儀（FTIR）之結合分析結果可發現，最佳化組合之的水熱液化油的組成相較於其他組合更為均勻。

Hydrothermal liquefaction is a promising technology to convert wet biomass into bio-oil with high calorific value and without drying process. In this study, a comprehensive analysis on the properties of liquefaction bio-oil derived from food waste was analyzed to evaluate the potential application of liquefaction bio-oil in industry, and the process optimization of hydrothermal liquefaction with alkaline pretreatment was demonstrated. Therefore, the study was divided into two parts.
In the first part of this research, the food waste is pretreated with K2CO3 at 100 °C for 1 h, followed by liquefaction in a semi-pilot reactor at 320 °C for 30 min. The higher heating value of produced bio-oil is 34.79 MJ kg-1, accounting for 53% increase when compared to the feedstock (22.74 MJ kg-1). The TGA results showed that ignition and burnout temperatures of the bio-oil are lower than other liquefaction bio-oils, reflecting its higher reactivity and combustibility. Meanwhile, the bio-oil has a higher oxidation onset temperature than pyrolysis bio-oils, showing its higher thermal stability. The independent parallel reaction model in association with the particle swarm optimization indicates that the pyrolysis kinetics of the bio-oil can be approximated by four groups. The component analysis further reveals two important groups of fatty acids and amides in the bio-oil, stemming from the conversion of carbohydrate and protein in the food waste. The comprehensive analysis shows that the liquefaction bio-oil from food waste, characterized by higher energy density and better combustibility, is a potential substitute to the fossil fuels.
In the second part of this research, bio-oil production from food waste, consisting of pineapple peel, banana peel, and watermelon peel, is investigated by a two-step process, namely, an alkaline pretreatment process with K2CO3 (10 wt% of the dry feedstock) followed by a hydrothermal liquefaction (HTL) process. Meanwhile, the Taguchi method is introduced to maximize the energy yield of the two-step process. Four parameters in the Taguchi approach are taken into account; they are the pretreatment temperature and time as well as the liquefaction temperature and holding time. The optimal combination of the four parameters gives the highest energy yield of 56.55%. The higher heating value of the bio-oil is 25.12 MJ kg-1, yielding 45.88% improvement when compared to that (=17.22 MJ kg-1) of the feedstock. A double-analysis, namely, the Taguchi approach and analysis of variance (ANOVA), suggests that the liquefaction temperature plays the most influential role in the energy yield. It is also noted that there exists a strongly linear relationship (R2 ≈ 0.99) between the effect in the Taguchi approach and the F value in ANOVA. The experiments of thermogravimetric analysis (TGA) coupled with Fourier-transform infrared spectroscopy (FTIR) indicate that the composition of the bio-oil from the optimal operation is more uniform.

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