由於生質柴油化學結構的關係,大部分的生質柴油氧化穩定性難以符合歐洲生質柴油規範標準(EN 14214)。因此大多數的生質柴油均需藉由抗氧化劑的添加來提升其氧化穩定性。本研究主要針對(1)油酸甲基酯、(2)油酸-棕櫚油摻合甲基酯(70 wt. %油酸+30 wt. %棕櫚油)、(3)油酸-棕櫚-桐油摻合甲基酯(60 wt. %油酸+20 wt. %棕櫚油+20 wt. %桐油)、及(4)痲瘋油甲基酯四種生質柴油的氧化穩定性進行改善,所添加的抗氧化劑種類有酚類、胺類與商業化抗氧化劑等,探討抗氧化劑對於這四種生質柴油氧化穩定性之提升效果。結果顯示,以pyrogallol (PY)、ETHANOX 4760E、propyl gallate (PG)、N,N’-di-sec-butyl-p-phenylenediamine (PDA)、butylated hydroxyanisole (BHA)對於穩定這四種生質柴油皆表現出不錯的效果。並且以零階及一階反應動力學來描述生質柴油添加抗氧化劑的氧化情形,結果發現大部分的抗氧化劑在生質柴油裡的氧化情形皆可以零階或一階反應動力學描述,並且求得在110oC下各個抗氧化劑在生質柴油裡消耗的反應常數。在90-120oC下所得ETHANOX 4760E、PDA、與PY分別在油酸甲基酯、油酸-棕櫚油摻合甲基酯、與痲瘋油甲基酯裡消耗之反應常數皆符合Arrhenius方程式,並以一階動力學描述求得此三種抗氧化劑消耗之活化能的數值範圍在85.68-103.96 kJ/mol,而以零階動力學描述求得此三種抗氧化劑消耗之活化能的數值範圍在82.94-111.54 kJ/mol。此外亦探討油酸甲基酯長時間儲存的穩定性,分別添加BHA、Butylated hydroxytoluene (BHT)、ETHANOX 4760E及PY於油酸甲基酯中,儲存120天後發現此四種抗氧化劑不只對油酸甲基酯的氧化穩定性有穩定的效果外,同時亦可達到對其酸價與動黏度有控制的作用。
Due to the chemical structure of biodiesel, the oxidation stability of most biodiesels has difficulties to meet the requirements of European Biodiesel Specification Standards (EN 14214). Therefore, the addition of antioxidants into biodiesel to increase oxidation stability is needed in most cases. This study is to discuss the oxidation stability improvement of four biodiesels, including oleic acid methyl ester, Jatropha oil methyl ester, oleic acid-palm oil methyl ester blend (70 wt. % oleic acid + 30 wt. % palm oil), and oleic acid-palm-tung oil methyl ester blend (60 wt.% oleic acid + 20 wt. % palm oil + 20 wt. % tung oil) by adding various antioxidants including phenolic-types, aminic-types, and commercial antioxidants. Zero-order and first-order reaction kinetics are adopted to describe the oxidation stability of biodiesels with the addition of the antioxidant. The reaction constant and critical concentration in the reaction kinetics to characterize the enhancement of each antioxidant on the oxidation stability of biodiesels at 110℃. In addition, the variation of oxidation stability, acid value, and kinematic viscosity during the long-term storage of oleic acid methyl ester with the addition of four different antioxidants under four different storage conditions are investigate.