Properties of palm oil biodiesels derived from different alcohols
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摘要: 以棕榈油为研究对象，分别与甲醇、乙醇、异丙醇和异丁醇进行酯交换反应制备了不同酯基结构的生物柴油。利用差示扫描量热仪和应力控制流变仪分析了不同酯基结构棕榈油生物柴油的结晶行为和低温流变性能，同时分析了酯基结构对生物柴油的氧化稳定性，40℃时的动力黏度、20℃时的密度等重要性质的影响。结果表明，随着醇的碳链长度的增加，棕榈油生物柴油的析蜡点和胶凝点均降低，特别是棕榈油异丁酯的析蜡点和胶凝点分别降低到了-2.57和-8.09℃，低温流动性得到了明显改善，且氧化诱导期略有延长，氧化稳定性有所改善。生物柴油的密度和黏度随着酯基结构的不同而有所变化，但其数值都符合中国生物柴油标准。Abstract: The palm oil biodiesels with different ester alkyls were prepared through transesterification of palm oil with methanol, ethanol, isopropanol and isobutanol. The crystallization behavior and cold flow properties of the palm oil biodiesels were characterized by differential scanning calorimeter (DSC) and stress controlled rheometer; the effect of ester alkyl on certain important properties such as the oxidation stability, kinematic viscosity (40℃) and density (20℃) was then investigated. The results suggested that the palm oil biodiesels with larger ester alkyls exhibit lower crystal precipitation temperature and gelation point than those biodiesels with ester methyl; especially, the crystal precipitation temperature and gelation point for the palm oil biodiesel derived from isobutanol reach -2.57 and -8.09℃, respectively. An increase in the length of ester alkyl chain in alcohol moiety can significantly improve the cold flow properties of the palm oil biodiesels, by slightly prolonging the oxidation induction period and enhancing the oxidative stability. The palm oil biodiesels with different ester alkyls are also different in their kinematic viscosity and density; however, all these values can meet the requirement from the biodiesel standard of China.
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Key words:
- palm oil biodiesel /
- ester alkyl /
- crystallization behavior /
- cold flow properties /
- oxidation stability
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图 1 不同酯基结构棕榈油生物柴油的曲线
Figure 1 DSC curves of palm oil biodiesels derived from different alcohols
图 2 不同酯基结构棕榈油生物柴油的黏弹性参数随温度的变化
Figure 2 Changes of viscolastic parameters of palm oil biodiesel derived from different alcohols as a function of temperature
(a): methyl ester; (b): ethyl ester; (c): isopropyl ester; (d): isobutyl ester
图 3 不同酯基结构棕榈油生物柴油的电导率随时间的变化
Figure 3 Changes of electrical conductivity of palm oil biodiesel derived from different alcohols as a function of time
图 4 不同酯基结构棕榈油生物柴油的运动黏度
Figure 4 Kinematic viscosity of palm oil biodiesels derived from different alcohols
图 5 不同酯基结构棕榈油生物柴油的密度
Figure 5 Density of palm oil biodiesels derived from different alcohols
表 1 不同醇制备生物柴油的实验条件
Table 1 Parameters for the preparation of palm oil biodiesels with different alcohols
Alcohol Molar ratio Catalyst Catalyst quantity*
w/%Reaction temperature
t/℃Reaction time
t/hStirring speed /
(r·min-1)Methanol 6 KOH 1.0 60 1 600 Ethanol 6 KOH 1.0 60 3 600 Isopropanol 9 H2SO4 1.5 84 4 600 Isobutanol 9 H2SO4 1.5 100 4 600 *: weight percentage of the catalyst used on the basis of oil 
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表 2 不同酯基结构棕榈油生物柴油的组成
Table 2 Composition of palm oil biodiesels derived from different alcohols
Fatty acid Composition w/% methyl ester ethyl ester isopropyl ester isobutyl ester C14:0 1.23 1.17 1.15 1.06 C16:0 40.41 39.70 39.25 39.14 C18:0 4.40 4.55 4.26 4.71 C16:1 0.22 0.53 0.55 0.28 C18:1 43.52 43.61 43.66 43.60 C18:2 8.41 8.42 8.25 8.28 C18:3 0.51 0.52 0.45 0.28 Others 1.30 1.50 2.43 2.65
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表 3 不同酯基结构棕榈油生物柴油的特性温度
Table 3 Characteristic temperatures of palm oil biodiesel derived from different alcohols
Ester tco/℃ tp1/℃ t2/℃ tp2/℃ Methyl 11.37 9.48 -41.36 -43.80 Ethyl 5.93 4.90 -42.13 -49.03 Isopropyl -0.28 -2.08 -52.57 -54.81 Isobutyl -2.57 -3.74 -53.56 -57.15
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表 4 不同酯基结构棕榈油生物柴油的tgel，tδ及Δ(tco-tgel)
Table 4 The tgel, tδ and Δ(tco-tgel) of palm oil biodiesels derived from different alcohols
Ester tδ/℃ tgel/℃ Δ(tco-tgel)/℃ Methyl ester 11.30 10.30 1.07 Ethyl ester 4.39 3.39 2.54 Isopropyl ester -2.60 -3.59 3.31 Isobutyl ester -7.60 -8.09 5.52
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