酸性离子液体催化油酸酯化合成生物柴油简

酸性离子液体具有催化活性好、选择性高及易于回收等优点，是一种应用前景非常好的环境友好的酸性催化剂，在生物柴油合成反应中具有重大的理论意义和应用价值. 本文以油酸和甲醇为原料，探讨了7种不同酸性离子液体在生物柴油合成反应中的催化效应. 研究表明，离子液体酸性越强，催化酯化活性越高；引入磺酸基团可大大增强离子液体Brönsted酸性，使其在酯化反应中发挥溶剂/催化剂的双重作用，促进酯化反应向产物方向进行，达到高产率，因而1-丁基磺酸-3-甲基咪唑硫酸氢盐（BHSO₃MIM]HSO₄）催化效果最好. 此外，系统研究了BHSO₃MIM]HSO₄催化油酸与甲醇酯化反应，并采用响应面法优化了反应条件. 结果发现，该反应的最适醇酸摩尔比、催化剂用量、反应温度及反应时间分别为4：1，10%（基于油酸的质量），130 ℃和4 h；在此条件下，生物柴油产率为97.7%. BHSO₃MIM]HSO₄连续使用10批次后，仍能保持初始催化活性的95.6%，表现出极好的操作稳定性. 另外，利用该离子液体催化游离脂肪酸含量为72%的废油脂生产生物柴油，反应6 h可获得产率94.9%. 可见，BHSO₃MIM]HSO₄在酯化生产生物柴油方面具有巨大的应用潜力.

Acidic ionic liquid-catalyzed esterification of oleic acid for biodiesel synthesis

Acidic ionic liquids (ILs) are used as environmentally-friendly and promising acid catalysts for biodiesel synthesis owing to their beneficial characteristics such as high catalytic activity, high selectivity, and ease of recycling. In this paper, seven different acidic ILs were examined as catalysts in the synthesis of biodiesel from the esterification of oleic acid with methanol. It was found that the stronger the acidity of the IL, the higher its esterification activity. The introduction of a SO₃H group into the IL greatly increases its Brönsted acidity and results in a bifunctional nature of the ILs for use as either a catalyst or environmentally-friendly solution in the esterification reaction. All of these effects contribute to product formation. Of all the tested acidic ILs, 1-sulfobutyl-3-methylimidazoliumhydrosulfate (BHSO₃MIM]HSO₄) exhibited the best catalytic performance. The BHSO₃MIM]HSO₄-catalyzed esterification of oleic acid with methanol was systematically explored, and the reaction conditions were optimized using a response surface methodology. The optimum molar ratio of methanol to oleic acid, catalyst amount, reaction temperature, and reaction time were 4:1, 10% (based on the mass of oleic acid), 130 ℃, and 4 h, respectively, under these conditions, and a yield of methyl oleate (biodiesel) of 97.7% was achieved. Furthermore, BHSO₃MIM]HSO₄ retained around 95.6% of its original catalytic activity after 10 successive reuses (4 h per period of use), showing excellent operational stability. In addition, the use of BHSO₃MIM]HSO₄ for biodiesel synthesis from waste oils containing 72% of free fatty acids was examined, and yields as high as 94.9% after 6 h were obtained. Clearly, BHSO₃MIM]HSO₄ shows considerable potential for the synthesis of biodiesel.