This study illustrates the purification of end-of-life crude glycerol from a real biodiesel production process and its conversion into triacetin via esterification with acetic acid. Crude glycerol of 50.9 wt% purity was physicochemically treated to 74.3 wt% reducing the content of ashes (16.1 to 9.8 wt%), matter organic non-glycerol (25.6 to 9.8 wt%) and water (7.4 to 6.1 wt%). For esterification, catalyst screening with commercial ion exchange resins and zeolites showed that Amberlyst 36 attained a triacetin yield of 30.1 % and stability after 5 cycles. An increase of temperature, molar ratio, and catalyst loading positively affected the reaction rates and equilibrium, whereas increasing water content in the feedstock only showed effect on the equilibrium leading to lower triacetin yields. After dismissing mass transfer limitations, a thorough study on the reaction kinetics analysed the effect of temperature (100–130 °C), molar excess of acetic acid (6–12) and catalyst loading (2.5–7.5 wt%) on the concentration profiles. Kinetic models based on Langmuir-Hinshelwood-Hougen-Watson and Eley-Rideal equations were formulated to fit the experimental data, where an Eley-Rideal model accounting only for water adsorption fitted best. Deactivation was also contemplated considering the ash content in the substrate, yet the model does not correlate with a loss of catalytic activity. The activation energies for the forward and backward reactions of the in-series esterification reactions are 38.2 – 45.8 kJ mol–1 and 47.0 – 50.3 kJ mol–1, respectively, and the enthalpy for water adsorption is 28.2 kJ mol–1.

中文翻译：

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从工业纯化甘油生产三醋精：概念实验证明、动力学模型推导和验证


这项研究说明了从真实的生物柴油生产过程中纯化报废粗甘油，并通过乙酸酯化将其转化为三醋精。将纯度为 50.9 wt% 的粗甘油进行物理化学处理至 74.3 wt%，从而降低灰分（16.1 至 9.8 wt%）、有机非甘油（25.6 至 9.8 wt%）和水（7.4 至 6.1 wt%）的含量。对于酯化反应，使用商用离子交换树脂和沸石进行的催化剂筛选表明，Amberlyst 36 的三醋精收率为 30.1%，并且在 5 个循环后保持稳定。温度、摩尔比和催化剂负载量的增加对反应速率和平衡产生积极影响，而原料中水含量的增加仅对平衡产生影响，导致三醋精收率降低。在排除传质限制后，对反应动力学进行了彻底的研究，分析了温度 (100–130 °C)、乙酸摩尔过量 (6–12) 和催化剂负载量 (2.5–7.5 wt%) 对浓度曲线的影响。制定了基于 Langmuir-Hinshelwood-Hougen-Watson 和 Eley-Rideal 方程的动力学模型来拟合实验数据，其中仅考虑水吸附的 Eley-Rideal 模型最适合。考虑到底物中的灰分含量，还考虑了失活，但该模型与催化活性的损失无关。串联酯化反应的正向和反向反应的活化能分别为38.2 – 45.8 kJ mol–1和47.0 – 50.3 kJ mol–1，水吸附焓为28.2 kJ mol–1。