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  • 學位論文

不同植物種子脂肪酸組成份及其酵素轉酯化效率

The fatty acids composition and the efficiency of enzymatic transesterification of different plant oils

指導教授 : 柯淳涵
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摘要


生質柴油為一綠色替代能源,隨著傳統石化燃料的消耗,利用植物油脂、動物脂肪或廢棄油脂經由轉酯化反應的生質柴油因而受到重視。 為了生產出高品質的生質柴油,油脂中所含的脂肪酸組成非常重要。因其可直接影響反應所得生質柴油的物理及化學性質。由於過去發展生質柴油大多以大豆油等食用油脂做為原料,因此產生了糧食上的爭議。為了解決這方面的問題, 有許多的木本植物果實種子具有高含油率達50%以上,這些原料具有很高的發展潛力。在台灣,有很多的油桐(三年桐及千年桐)和烏桕,其為木本油料樹種,成熟果實種仁含油率可達50%。在脂肪酸組成分析中,桐酸為桐油的主成分;次亞麻油酸為烏桕籽油的主要成分。 利用Novozyme 435做為催化劑之酵素轉酯反應中,溫度為一重要因素。反應溫度為55oC,反應24小時後,脂肪酸甲酯轉化率棕櫚油達89.99%;大豆油達87.04%;烏桕籽油達70.82%;桐油則為57.79%為最好轉化率。在脂肪酸乙酯轉化率方面,反應溫度為50oC,反應24小時後棕櫚油達75.75%;大豆油達25.22%;桐油則為20.36%,烏桕籽油則於55oC有最好的轉化率 51.06%。而利用兩種常做為生質柴油原料的棕櫚油與大豆油去和烏桕籽油及桐油做比較,則可發現在同溫度下棕櫚油有最佳的轉酯效率,而桐油的效率最低。 比較脂肪酸甲酯和脂肪酸乙酯的轉化率,脂肪酸乙酯的轉化率明顯小了許多。由各階段的反應常數k值來做比較,可發現進行脂肪酸甲酯轉化,各階段反應皆以順反應為主;反觀脂肪酸乙酯轉化反應則以逆反應為主。此外也可發現含愈多飽和脂肪酸組成,可有效提升順反應的產生。因此棕櫚油中含80%以上的飽和脂肪酸;反觀桐油則含有75%~85%的不飽和脂肪酸。由這結果可知,油脂中脂肪酸組成可直接影響油脂的轉酯化效率。 除了溫度的變化對轉化效率有直接的影響外,油脂的脂肪酸組成也是一項重要的影響因素。此外各階段反應的反應傾向可由其中的反應常數得知,k值的變化則會進而影響整體的反應效率結果。因此不同的溫度條件,脂肪酸組成及各階段反應常數的表現皆為影響轉化結果的重要因素,然而這些因素也隨著不同的反應條件而彼此相互影響。

並列摘要


Biodiesel, a green alternative energy, is produced from vegetable oil, animal fats and waste oil through transesterification. Because of the diminishing of conventional petroleum fuel, biodiesel is concerned gradually. For producing high quality biodiesel, the fatty acid composition of oil is very important. It can straightly influence physical and chemical properties of biodiesel. In the past, edible oil is the main resource for producing biodiesel, hence the issue of grain is provoked. For solving this problem, utilization of woody oil plant is the proper material for biodiesel, because of its high oil content over 50% from mature seeds. These materials are potential for producing biodiesel. In Taiwan, there are lots of tung tree (Euphorbiaceae family, Vernicia genus) and Chinese tallow tree (Sapium sebiferum). The oil content of their mature dried kernels seeds can reach over 50%. The analysis of their fatty acid composition, ELA (eleostearic acid) is the main composition of fatty acid of tung oil, and linolenic acid is the main composition of fatty acid of Chinese tallow tree kernel oil (C.T. oil). In the transesterification with Novozyme 435 as catalyst, temperature is a critical factor for the efficiency of conversion. Under 55oC after 24 hour, the conversion of fatty acid methyl esters (FAMEs) palm oil, soybean oil, C.T. oil and tung oil is 89.99%, 87.04%, 70.82% and 57.79% individually. In the part of fatty acid ethyl esters (FAEEs) conversion, palm oil, soybean oil and tung oil reach the best efficiency of conversion 75.75%, 25.22% and 20.36 respectively at 50oC. But, C.T. oil has the best conversion rate 51.06% under 55 oC. Compare the conversion of palm oil and soybean oil, which are common materials for biodiesel, to C.T. oil and tung oil. At the same temperature condition, palm oil has the highest efficiency of conversion, and the tung oil is the lowest. Compare the efficiency of FAMEs conversion to FAEEs conversion, the rate of FAEEs conversion is far lower than FAMEs conversion. From the aspect of the reaction rate constant, k values, indicates that normal reaction is the main mechanism in every step reaction of FAMEs conversion. For FAEEs that is opposite. Otherwise, the more saturated fatty acids content can make the normal reaction happen more easily. Hence, palm oil consists of over 80% saturated fatty acids, by contrast tung oil consists of 75%~85% unsaturated fatty acids. From this result, the fatty acid composition of oil can influence the efficiency of transesterification conversion directly. Besides the various temperature conditions, different fatty acids composition can affect the efficiency of conversion directly. The k values are another key factor for evaluating the efficiency of transesterification. Because that can explain the stepwise mechanism of reaction. Concluded these factors, temperature, fatty acids composition and k values are critical factors for the efficiency of transesterification. Otherwise, these factors are also affected mutually.

參考文獻


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