Biodiesel Synthesis: Influence of Alkaline Catalysts in Methanol-Oil Dispersion

Biodiesel synthesis from soybean oil using methanol and alkaline catalysts occurs in the following two consecutive steps: dispersion of methanol in the oil and methanolysis. The effect of the alkaline catalysts NaOCH3, KOCH3, NaOH, and KOH in the dispersion step at 30-60 ºC and under mechanical stirring at 400 rpm was evaluated. The dispersion step accounts for 44.6-73.3% of the total synthesis time and was poorly favored compared to methanolysis due to the increase in temperature. The catalysts decreased the dispersion time, although most of them increased the methanol-oil interfacial tension. K-containing catalysts were more active than their Na analogues due to higher adsorption of K+ in the methanol-oil interface and the higher production of methyl esters (which act as emulsifying agents), which promote a more favorable interfacial tension. The alkaline cation effect was more significant in the dispersion step than in the methanolysis step.

以甲醇与碱性催化剂催化大豆油合成生物柴油的过程包含以下两个连续步骤：甲醇在油相中的分散步骤与甲醇醇解反应（methanolysis）。本研究评估了碱性催化剂——甲醇钠（NaOCH3）、甲醇钾（KOCH3）、氢氧化钠（NaOH）与氢氧化钾（KOH）——在30~60℃、400rpm机械搅拌条件下于分散步骤中的作用效果。分散步骤占总合成时长的44.6%~73.3%，且相较于甲醇醇解反应，随着温度升高，分散步骤的反应进程更难得到促进。尽管多数催化剂会提升甲醇-油相界面张力，但它们均能缩短分散步骤的反应时长。含钾催化剂的催化活性优于对应钠基催化剂，原因在于K+在甲醇-油相界面的吸附量更高，且生成的脂肪酸甲酯（可作为乳化剂）更多，从而可形成更利于反应的界面张力。碱性阳离子对反应的影响在分散步骤中相较于甲醇醇解步骤更为显著。