反應曲面法應用於廢棄炸油產製生質柴油之 最適預酯化製程探討

Abstract

酸價代表油脂內游離脂肪酸含量，使用廢棄炸油做為產製生質柴油的料源時，若油脂內含有高量游離脂肪酸 (酸價在 1 mg KOH/g 以上)，在生質柴油鹼性轉酯化製程中將容易發生皂化現象，導致生質柴油的產量降低。 為了提升酯產量並降低皂化現象的發生，事先將廢棄炸油的酸價予以降低 (預酯化過程)是有必要的。本研究以三種酸價的廢棄炸油作為研究材料，應用反應曲面法之五階層四因子中心混層設計，針對醇/油莫耳比、酸性觸媒劑量、反應溫度與反應時間四項因子進行探討，找尋降低油脂酸價的操作條件以求得最佳的預酯化效率。 實驗結果顯示，當初始酸價分別為 2.21、4.42 與5.45 mg KOH/g 時，透過預酯化反應後可分別得到最低酸價 0.52 ± 0.02、0.73 ± 0.02 與0.83 ± 0.02 mg KOH/g，相當於 76、84 與85 % 的預酯化效率。針對上述三種操作條件建立迴歸式的 R2 分別為 0.7、0.63 及 0.61。

Acid value indicates amounts of free fatty acid in wasted fried oil. When the acid value above 1 mg KOH/g, high level of free fatty acid causes soap formation, thus reducing ester yield of biodiesel in the transesterification process for biodiesel production. In order to reduce the soap formation and increase the ester yield in biodiesel production process, to reduce the acid value of wasted fried oil is preferred. This procedure is termed pre-esterification process. The purpose of this study is to identify the optimal operating condition furing the pre-esterification process using wasted fried oil with three levels of acid value. The four factors and five levels central composite design (CCD) of the response surface methodology (RSM) was employed to evaluate the effects of methanol/oil molar ratio, catalyst amount, reaction temperature and reaction time on the efficiency of pre-esterification and the amount of reduction of the acid value of wasted fried oil. The results show that the lowest acid value obtained were 0.52 ± 0.02, 0.73 ± 0.02 and 0.83 ± 0.02 mg KOH/g equivalent to 76%, 84% and 85% pre-esterification efficiency when original acid value of wasted fried oil were 2.21, 4.42 and 5.45 mg KOH/g respectively. The R-square of regression models were 0.70、0.63 and 0.61 respectively.