應用超音波輔助程序由桐油混合油產製生質柴油之研究

Abstract

本研究針對以油桐樹(Vernicia fordii)籽油及將其與其他生質油品混合後，添加甲醇與氫氧化鉀進行超音波輔助轉酯化反應轉製生質柴油進行研究，並探討不同摻配及轉酯化程序對其酸價(acid value, AV)、碘價(iodine value, IV)、動黏度(kinematic viscosity, KV)、密度及其冷濾點(cold filter plugging point, CFPP)之影響。背景實驗條件為：超音波頻率(fUS) 20 kHz、輸出功率(PWUS) 270 W、桐油、芥菜油與棕櫚油之摻配比為20、50及30 wt.%、甲醇與油之莫耳數比(M/O) = 6:1、KOH觸媒劑量 (MC) 為1 wt.%、反應溫度 (TR) 20-30 °C、反應體積(VL) 390 mL、時間(tUS) 1-30 min。研究結果顯示，tUS ≥ 5 min時桐油生質柴油之轉酯率 (YF)可達87-91%；而混合油之tUS ≥ 1 min 時YF 更可達92-94%。當tUS = 10 min時桐油生質柴油之AV 為0.11 mg KOH/g、IV為159.36 g I2/100 g、KV 為9.17 mm2/s、密度為905 kg/m3、CFPP為-16 oC。而相同條件下獲得之混合油生質柴油之AV 為0.11 mg KOH/g、IV為120.35 g I2/100 g、KV為5.54 mm2/s、密度為887 kg/m3、CFPP 則為-5 oC。與ASTM-D6751標準值AV 需小於0.5 mg KOH/g、KV與密度需介於1.9-6 mm2/s及860-900 kg/m3對照，可知桐油須與其他生質油品混合後轉製生質柴油其性質方可符合生質柴油標準。若使用超音波輔助轉酯化程序其反應時間至少須達5 min以上可發揮其微混合與孔蝕加熱效益以使生質柴油轉酯化程序獲致高效能。相較於使用超音波輔助轉酯化程序反應1 min後，其KV值可自6.26 mm2/s降至5.54 mm2/s已可符合ASTM-D6751 規範之KV值 1.9-6.0 mm2/s之要求。 本研究其次以20、50及30 wt.% 比例混合之桐油、芥菜油與棕櫚油之混合油以超音波輔助轉酯化轉製生質柴油並量測成品之KV及YF，以評量生質油品轉酯化之成效。以PWUS = 270 W、TR = 25 oC、M/O = 6、MC = 1 wt.%、tUS = 5 min及tS = 10 min反應條件為對照組，探討其反應之操作參數TR、MC、tUS 及沈降時間 (settling time, tS) 對轉酯化之影響。當使用桐油為原料時，增加反應時溫度TR至60 oC時YF增加且KV下降，而增加MC至2 wt.%，YF可達最佳值98%，且KV可更進一步降低，且反應時間可低於5 min。而以混合油做為原料用油時，控制反應條件為MC = 2 wt.%、tUS = 5 min、tS = 30 min及M/O = 6時，其YF與KV於TR = 25與60 oC分別可達98.33%、4.26 mm2/s及99.68% 、4.08 mm2/s 。 因此，應用超音波輔助轉酯化製造桐油生質柴油之較適條件為TR = 60 oC、MC = 2 wt.%、M/O = 6、tUS = 5 min與tS = 30 min。然若考量節能，反應溫度可控制為25 oC，相較於TR = 60 oC，YF 略為減少約1.35％，而KV僅增加約0.18％。25 ℃轉製之混合油生質柴油之AV，IV和密度分別為0.06 mg KOH/g, 103.52 g I2/100 g 和 885 kg/m3，符合ASTM-D6751和EN14214標準。而其冷濾點-5℃，亦符合CNS15072標準之低於0 ℃需求。 本研究亦進一步比較不同預混合桐油、油菜籽油和棕櫚油濃度（CBT、CBC和CBP）之生質混合油及此三油品之原物料及分別轉酯化後之成品性質差異。藉由分析其成品之YF、AV、IV、KV、密度及CFPP以評量反應參數MC、CBT、PWUS之影響。使用桐油與棕櫚油的預混合油可大幅降低了棕櫚油的生質柴油之冷濾點，而油菜籽和棕櫚油與桐油混合所產製之生質柴油之IV和KV 較桐油生質柴油低。而MC = 2 wt.% 為最適之觸媒添加比例。控制PWUS/VL = 0.92-2.08 W/mL，CBT最佳可達60 wt.％，而CBC 僅為30 wt.％、CBC 僅10 wt.％，上述條件所生產之生質柴油其品質皆可符合標準之要求。 本研究成果獲得之資訊可提供桐油及混合油利用超音波輔助程序進行催化轉酯化轉製生質柴油之程序設計與建立相關操作參數之參考。

In this study, the effects of system parameters on the transesterification yield (YF) of biodiesel from tung (Vernicia fordii) and blended oils with CH3OH and KOH, and on key properties of biodiesel such as acid value (AV), iodine value (IV), kinematic viscosity (KV), density and cold filter plugging point (CFPP) were investigated. The background experimental conditions were as follws. The blended oil is consisted of 20, 50 and 30 wt.% of tung, canola and palm oils, respectively. The molar ratio of methanol to oil (M/O) and KOH catalyst concentration (MC) are 6:1 and 1 wt.%, respectively. Temperature (TR), ultrasonic frequency (fUS) and ultrasonic power (PWUS) were kept at 20 to 30 oC, 20 kHz and 270 W, respectively. The sample volume (VL) was 390 mL. The ultrasonic irradiation time (tUS) was set in the range of 1-30 min. The results showed that YF reaches high value of 87-91% for tung-oil biodiesel as tUS ≥ 5 min, while of about 92-94% for blended-oil biodiesel as tUS ≥ 1 min. At tUS = 10 min, the properties of biodiesel produced from tung oil are with AV of 0.11 mg KOH/g, IV of 159.36 g I2/100 g, KV of 9.17 mm2/s, density of 905 kg/m3 and CFPP of -16 oC, while those from blended oil are with AV of 0.11 mg KOH/g, IV of 120.35 g I2/100 g, KV of 5.54 mm2/s, density of 887 kg/m3 and CFPP of -5 oC. Comparing these values with the ASTM-D6751 standards with AV < 0.5 mg KOH/g, KV = 1.9-6 mm2/s and density = 860-900 kg/m3 points out that the tung oil should be blended with other oils in order to produce biodiesel satisfying the biodiesel standards. Moreover, the results indicated that a certain enough time, say 5 min, is needed to provide sufficient cavity heating and mixing via ultrasonic wave ensuring good properties of biodiesel produced. The KV of biodiesel using blended oil decreases from 6.26 mm2/s at tUS = 1 min to 5.54 mm2/s at tUS = 5 min, thus meeting the ASTM-D6751 value of 1.9-6.0 mm2/s. Effective performances of biodiesels produced from tung oil and blended oil consisting 20, 50 and 30 wt.% of tung, canola and palm oils employing ultrasonic irradiation also were elucidated. The YF and KV, which are essential key indices to tung-oil derived biodiesel, were measured. Appropriate conditions of TR, MC, tUS, settling time (tS) and M/O were identified. The background conditions were PWUS = 270 W, TR = 25 oC, M/O = 6, MC = 1 wt.%, tUS = 5 min and tS = 10 min. The YF increases while the KV beneficially decreases with increasing TR to 60 oC. As MC increases to 2 wt.%, the YF reaches plateau value of 98% for both tung-oil derived biodiesels without and with blending with further reduction of KV. High YF is achieved at short tUS of 5 min using MC of 2 wt.%. Steady sate is approached at tS = 30 min. At MC = 2 wt.%, tUS = 5 min, tS = 30 min and M/O = 6, the YF and KV respectively are 98.33% and 4.26 mm2/s at TR = 25 oC, while are 99.68% and 4.08 mm2/s at TR = 60 oC for the blended-oil biodiesel. Thus, the suitable conditions for the effective production of tung-oil derived biodiesels applying ultrasound irradiation are at: TR = 60 oC, MC = 2 wt.%, M/O = 6, tUS = 5 min and tS = 30 min. However, for the sake of energy-saving, the transesterification condition using TR of 25 oC may be employed, causing only slight reduction of YF of about 1.35% while increase of KV of about 0.18%. The properties of AV, IV and density of the blended-oil biodiesel produced at 25 oC are 0.06 mg KOH/g, 103.52 g I2/100 g and 885 kg/m3, respectively, satisfied with the standards of ASTM-D6751 and EN 14214. The corresponding CFPP of -5 oC, which is lower than 0 oC, also meets the standard of CNS 15072. The beneficial use of tung oil in pre-blended oil for the production of biodiesel was further studied at various blending compositions of tung, canola and palm oils (CBT, CBC and CBP). The effects of MC, CBT, PWUS and VL on the YF and the properties of AV, IV, KV, density and CFPP were investigated. The pre-blending of tung oil with palm oil greatly decreases the CFPP of palm-oil biodiesel, whereas the presence of canola and palm oils with tung oil reduces the IV and KV of tung-oil biodiesel. An MC of 2 wt.% was found to be appropriate. For PWUS/VL = 0.92-2.08 W/mL, CBT can be as high as 60 wt.% with 30 wt.% CBC and 10 wt.% CBP to produce biodiesel with high YF and satisfactory qualities of the said properties. The information obtained in this study is useful for the proper use of tung oil in conjunction with other edible oils for the production of biodiesel with satisfactory qualities and the rational design and operation of ultrasonically catalytic transesterification process.