- 學位論文
磁性固體酸觸媒之合成及其應用於高酸價油品之生質柴油製造
Synthesis of Magnetic Solid Acid Catalyst and Its Application in Biodiesel Production from High Acid Value Oil
摘要
為避免生質原油中過高的酸價(acid value, AV)，造成鹼催化轉酯化反應因皂化而降低產率，通常須要透過酯化反應或其他前處理，使油品的酸價小於2 mg KOH/g。本研究製備兩種不同的固體酸觸媒(SiO2-ZrO2和SO42--SM, SM: SiO2 on Fe3O4)，先對油酸和大豆油混合之高酸價油品(AV= 41.60 mg KOH/g，自由脂肪酸(FFA)含量為20.8%) 進行酯化反應。透過改變不同酯化條件找出最適反應條件後，對非食用性植物油脂－痲瘋油(AV= 39.41 mg KOH/g)進行酯化反應。研究中並分析酯化反應後產物之酸價、碘價(IV)、動黏度(KV)、密度(ρLO)、含水率(MW)、自由脂肪酸轉化率(ηFFA)及脂肪酸甲基酯(FAME)之產率(YF)等性質。油酸和大豆油混合油之IV、KV、ρLO、MW分別為124.98 g I2/100 g、30.01 mm2/s、918.40 kg/m3、0.082 wt%，而痲瘋油之值則為96.24 g I2/100 g、32.76 mm2/s、915.90 kg/m3、0.082 wt%。 由溶膠凝膠法所合成之SiO2-ZrO2觸媒基本特性(SEM、XRD及FTIR)雖與參考文獻相近，但由於本研究使用的反應器容積較大，參與反應的生質原油量遠多於文獻中的10 g，故於相同反應條件下，提供的能量不足，以致效果不佳。而以含浸法合成之SO42--SM觸媒(SM以溶膠凝膠法合成)之酯化能力，則隨著含浸硫酸溶液濃度(CISA)增加而提升，其中以CISA = 2.0 M時的效果最好。 使用CISA= 2.0 M製成之SO42--SM作為觸媒，對油酸和大豆油混合油進行酯化反應，所得之最適反應條件為：甲醇對油莫耳比(M/O)為12:1、觸媒添加量(MC)為5 wt%、酯化溫度(TE)為393 K、酯化時間(tE)為2 h。此時產物之酸價為1.28 mg KOH/g，相當於96.92 wt%的自由脂肪酸轉化率，YF則為40.28 wt%，碘價為116.57 g I2/100 g，動黏度為13.58 mm2/s，密度為908.8 kg/m3，含水率則為0.117 wt%。而觸媒重複使用至第四次時，仍可使酸價降低至1.89 mg KOH/g，但YF則下降至25.15 wt%。當AV由41.60 mg KOH/g降至1.28 mg KOH/g時，FFA由20.8 wt%降至0.64 wt%。FFA減量20.16 wt%酯化生成FAME，故YF之40.28 wt%中有20.12 wt% (= 40.28 – 20.16)係由三酸甘油酯轉酯化成FAME。顯示SO42--SM酸觸媒兼具酯化和轉酯化兩種功能。 根據油酸和大豆油混合油的酯化結果，以相同反應條件對痲瘋油進行酯化，酸價可降為2.05 mg KOH/g，略高出目標值2 mg KOH/g。而進一步將M/O提升至15:1時，酸價則可降為1.86 mg KOH/g，可有效使酸價降至小於2 mg KOH/g。此時YF為52.10 wt%，碘價為90.40 g I2/100 g，動黏度為12.21 mm2/s，密度為901.7 kg/m3，含水率則為0.124 wt%。AV由39.41 mg KOH/g降至1.86 mg KOH/g時，FFA由19.71 wt%減至0.93 wt%。FFA減量18.78 wt%酯化生成FAME，故YF之52.10 wt%中有33.32 wt% (= 52.10 – 18.78)係由三酸甘油酯轉酯化生成FAME。此結果亦證實SO42--SM酸觸媒兼具酯化和轉酯化兩種效果。 以SO42--SM觸媒對油酸和大豆油混合油和痲瘋油進行酯化反應，可有效將酸價降低，避免鹼催化轉酯化反應時產生皂化。而油品之碘價、動黏度亦有顯著下降(混合油分別相對降低6.73%、54.75%；痲瘋油分別相對降低6.07%、62.73%)，密度則僅略降(混合油和痲瘋油分別相對降低1.05%和1.55%)，含水率則是大幅上升(混合油和痲瘋油分別相對升高42.68%和51.22%)。雖未達生質柴油標準，但仍可透過第二階段之轉酯化反應或是摻配使用改善碘價、動黏度及密度的問題，並利用無水硫酸鎂將油品中的水分加以去除。
並列摘要
High acid value (AV) will saponify the oil in alkaline transesterification process and consequently decrease the yield of fatty acid methyl ester (FAME). In order to avoid the saponification, the AV must be decreased to less than 2 mg KOH/g by esterification or other pre-treatments. In this study, two solid acid catalysts (SiO2-ZrO2 and SO42--SM, SM: SiO2 on Fe3O4) were synthesized and applied for esterification. The mixed oil (oleic acid : soybean oil = 1 : 4) with the AV of 41.60 mg KOH/g and the free fatty acid (FFA) content of 20.8% was esterified. After a series of experiments were conducted to find the optimal esterification conditions, the non-edible jatropha oil with the AV of 39.41 mg KOH/g and FFA of 19.71% was esterified at the same conditions. The properties of the esterified oil, such as AV, iodine value (IV), kinematic viscosity (KV), density (ρLO), water content (MW), FFA conversion (ηFFA), and yield of FAME (YF) were measured. The initial IV, KV, ρLO, and MW of the mixed oil are 124.98 g I2/100 g, 30.01 mm2/s, 918.40 kg/m3, and 0.082 wt%, respectively. The initial IV, KV, ρLO, and MW of the jatropha oil are 96.24 g I2/100 g, 32.76 mm2/s, 915.90 kg/m3, and 0.082 wt%, respectively. Although the characteristics (SEM, XRD and FTIR) of the SiO2-ZrO2 catalyst made by sol-gel method are similar to those of the reference, however, the efficiency of the esterification is not good. It is because that the volume of reactor of this study is higher than that of the reference, and the amount of the oil reactant in this study is also greater than 10 g in the reference. As a result, esterifying the mixed oil in the same conditions as the reference would obtain a lower efficiency due to the short of the energy supply. The esterification ability of the SO42--SM (SM was made by sol-gel method) catalyst made by impregnation method is promoted with an increase of the concentration of the impregnation solution of sulfuric acid (CISA) and the optimal condition is CISA = 2.0 M. The optimal esterification conditions of the mixed oil are 12:1 molar ratio of methanol to oil (M/O) and 5 wt% of catalyst loading relative to oil (MC) at the esterification temperature (TE) of 393 K for esterification time (tE) of 2 h. The AV of the esterified mixed oil is 1.28 mg KOH/g. That is to say, the ηFFA is 96.92 wt%. In addition, the YF, IV, KV, ρLO, and MW are 40.28 wt%, 116.57 g I2/100 g, 13.58 mm2/s, 908.8 kg/m3, and 0.117 wt%, respectively. About the reuse of the catalyst, the AV of the oil can be effectively reduced to 1.89 mg KOH/g as the catalyst were used for four times. Nevertheless, the YF was reduced to 25.15 wt%. While the AV was reduced from 41.60 mg KOH/g to 1.28 mg KOH/g, the FFA content was reduced from 20.8 wt% to 0.64 wt%. The decrement of FFA was 20.16 wt% and it was esterified into FAME. The result shows that the 20.12 wt% (= 40.28 – 20.16) coming from 40.28 wt% of YF was transesterified into FAME from triglyceride (TG). It was confirmed that the SO42--SM catalyst had both functions of esterification and transesterification with major and supplemental roles, respectively. Jatropha oil was esterified by the same conditions as the mixed oil. The AV of the esterified jatropha oil can be reduced to 2.05 mg KOH/g, but it was slightly higher than the target value of 2 mg KOH/g. While the M/O was increased to 15:1, the AV can be reduced to 1.86 mg KOH/g, which was below 2 mg KOH/g. The YF, IV, KV, ρLO, and MW of the esterified jatropha oil were 52.10 wt%, 90.40 g I2/100 g, 12.21 mm2/s, 901.7 kg/m3, and 0.124 wt%, respectively. While the AV was reduced from 39.41 mg KOH/g to 1.86 mg KOH/g, the FFA content was reduced from 19.71 wt% to 0.93 wt%. The FFA was decreased 18.78 wt% and esterified into FAME. The result indicates that the 33.32 wt% (= 52.10 – 18.78) coming from 52.10 wt% of YF was transesterified into FAME from TG. The result also confirmed that the SO42--SM catalyst can both esterify and transesterify the oil. The esterification of mixed oil and jatropha oil by SO42--SM both can effectively decrease the AV and prevent the saponification in alkaline transesterification process. The IV and KV had remarkable decrement (mixed oil had relative decrement of 6.73% and 54.75%, while jatropha oil had relative reduction of 6.07% and 62.73%, respectively). The ρLO reduced slightly (the relative decrement were 1.05% and 1.55% respectively). The MW increased with the relative increment of 42.68% and 51.22%, respectively. Though the IV, KV, and ρLO cannot meet the standards, they can be improved by transesterification or blending with other oils. The excessive water content can be removed by adsorption using magnesium sulphate.