生質能源因物料較易取得、技術發展成熟及應用範圍廣等優點，被視為一極具發展潛力之可再生能源。政府間氣候變遷小組(Intergovernmental Panel on Climate Change, IPCC)指出，生質能源已於2008年占全球再生能源供給之10%，並預測於2050年將增加至80% (IPCC, 2011)。生質燃料可透過生質作物轉換製備生成生質酒精與生質柴油，目前生質作物已從第一代糧食作物如玉米、大豆及甘蔗等發展至第二代與第三代之非糧食作物，如痲瘋樹與微藻等；未來也期許發展至第四代，藉由基因重組之細菌直接捕獲空氣中CO2，進而轉換成生質燃料。因超臨界流體可藉由壓力和溫度改變其物化性質，如黏度、密度、擴散係數等，近年來於生質酒精與生質柴油製程上相當受到矚目，成為眾多生質能源發展的前瞻技術之一。在生質酒精的製備過程中，包括前處理、酵素水解與糖類發酵三步驟，超臨界流體能有效於前處理步驟破壞植物細胞壁結構，提高後段酵素水解效率。另一方面，生質柴油則透過物料油脂進行轉酯化反應生成柴油，超臨界流體亦可扮演萃取油脂與轉酯化的角色。將超臨界流體技術運用於生質能源製程上不僅符合綠色化學之潮流，亦能達到現有製程強化、永續經營及環境保護的目的。

Bio-energy is considered as one of potential renewable energies due to abundant feedstock, well-developed technology and wide-ranged applications. Intergovernmental Panel on Climate Change (IPCC) had reported that 10% of global renewable energies came from bio-energy in 2008, and the percentage will be increased to 80% in 2050. Among all the bio-energies, biofuels such as bioethanol and biodiesel are most widely used and can be effectively derived from biomass. Up to now, the evolution of biomass is changed from food crops (e.g., corn, soybean and sugarcane) for 1st generation biofuels to non-food crops (e.g., jatropha or microalgaes) for 2nd or 3rd generation biofuels. Since the physical properties (e.g., viscosity, density and diffusivity) of supercritical fluids (SCF) can be altered by changing pressure and temperature, the application of SCF technologies in bioethanol and biodiesel production has drawn much attention recently. In the preparation of bioethanol, three stages including pretreatment, enzyme hydrolysis and fermentation are required. In the pretreatment stage, SCF can penetrate into biomass structure and destroy the cell wall, increasing the efficiency of enzyme hydrolysis in the subsequent stage. For biodiesel production, the lipids extracted from biomass by compressed fluid containing CO2 can be further reacted with supercritical methanol or ethanol to generate biodiesel via transesterification. SCF can act not only as a solvent in lipid extraction but also as reactant and/or cosolvent in transesterification. Last but not least, applying these SCF technologies into biofuel production meets the requirements of green chemistry, which also provides an alternative route for process intensification, sustainable production and environmental protection.