Abstract The continuous biodiesel production process under sub- and supercritical conditions using a trace amount of potassium hydroxide (KOH) as a catalyst has been studied. CO2 was added as a co-solvent to reduce the reaction time and increase biodiesel yield. The proposed procedure enables simultaneous transesterification and esterification of triglycerides and free fatty acid (FFA), respectively. The shorter reaction time and milder reaction conditions may reduce energy consumption due to the simplification of the separation and purification steps. The process variables, including reaction temperature, ethanol to oil molar ratio, catalyst amount, and process pressure, were systematically optimized. The highest biodiesel yield (98.12%) was obtained after a 25-min reaction time using only 0.11% wt. of KOH and a 20:1 ethanol to oil ratio. The process optimum temperature and pressure were 240 °C and 120 bar, respectively. The proposed kinetic model suggested a first-order reaction with an activation energy of 15.7 kJ·mol−1 and a reaction rate constant of 0.0398/min−1. The thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy were calculated as 144.82 kJ·mol−1, 11.4 kJ·mol−1, −0.26 kJ·mol−1 and at 240 °C, respectively.

中文翻译：

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使用乙醇与痕量催化剂和 CO2 共溶剂连续生产生物柴油

摘要 研究了以微量氢氧化钾（KOH）为催化剂在亚临界和超临界条件下连续生产生物柴油的过程。添加 CO2 作为共溶剂以减少反应时间并提高生物柴油产量。所提出的程序能够分别实现甘油三酯和游离脂肪酸 (FFA) 的同时酯交换和酯化。由于分离和纯化步骤的简化，更短的反应时间和更温和的反应条件可以降低能耗。系统地优化了工艺变量，包括反应温度、乙醇与油的摩尔比、催化剂量和工艺压力。仅使用 0.11% wt 的生物柴油在 25 分钟的反应时间后获得最高的生物柴油产量 (98.12%)。KOH 和 20:1 的乙醇油比。工艺最佳温度和压力分别为 240 °C 和 120 bar。所提出的动力学模型表明一级反应的活化能为 15.7 kJ·mol-1，反应速率常数为 0.0398/min-1。热力学参数如吉布斯自由能、焓和熵分别计算为 144.82 kJ·mol-1、11.4 kJ·mol-1、-0.26 kJ·mol-1 和 240 °C。