【解读】乐军组Chem. Eng. J：双相体系中硫酸选择性催化果糖-葡萄糖混合物中果糖转化制备5-羟甲基糠醛

第一作者和单位：郭文泽 格罗宁根大学

通讯作者和单位：乐军 格罗宁根大学

原文链接：https://doi.org/10.1016/j.cej.2020.128182

关键词：BrØnsted酸，果糖，葡萄糖，5-羟甲基糠醛，动力学，微反应器

Fig. 1. Concept of the integrated process for HMF production from glucose or glucose-rich cellulosic biomass.

1） 研究硫酸催化果糖、葡萄糖和HMF 在水中的动力学行为和反应路径，探明过量甲酸的来源，建立完善的反应网络；

2） 建立果糖-葡萄糖混合物在水-MIBK双相溶剂体系中制备HMF的动力学模型，并进行过程优化和连续反应器设计来实现选择性转化混合糖中的果糖并实现最优HMF收率；

3） 采用微反应器强化选择性转化混合糖（高果糖玉米糖浆）中的果糖制备HMF 的过程。

本工作首先在间歇反应器中通过单相实验研究水中硫酸催化糖类和HMF转化的反应动力学，并比较果糖、葡萄糖及其混合物的反应行为（Fig. 2）。结果表明果糖的反应活性远大于葡萄糖，且在两者混合物的反应中，果糖和葡萄糖分别独立进行反应，两者之间无明显的相互作用。因此，通过调控反应条件来选择性转化混合糖中的果糖是可行的。实验考察了反应温度、底物浓度和硫酸浓度对底物转化率和HMF收率的影响。结果发现升高温度可提高最优的HMF收率，这意味着总体上生成HMF的反应活化能高于HMF的副反应活化能。酸浓度对最优的HMF收率几乎无影响，表明糖转化涉及的各反应步骤对酸浓度具有相似的反应级数。在相同的条件下，底物浓度对转化率（和HMF收率）无明显的影响，表明了糖转化在总体上是对底物的一级反应。

Fig. 2. Results on the conversion of (a) fructose, (b) glucose, (c) fructose-glucose mixture and (d) HMF in water in the laboratory batch reactor. Other reaction conditions: 135 ◦C, 0.05 M H₂SO₄ and 0.1 M substrate (glucose, fructose or HMF). In the figure legend, Glc, Fru, Man, FA and LA denote glucose, fructose, mannose, formic acid and levulinic acid, respectively. Symbols denote the experimental data and lines are for the model values.

Fig. 3. Effect of initial organic to aqueous volume ratio (O/A) on the conversion of fructose-glucose mixture in the water-MIBK biphasic system in the batch reactor: (a) HMF yield as a function of O/A; (b) substrate conversion and product yield at O/A = 4. Other reaction conditions: 135 ◦C, 0.05 M H₂SO₄, 0.1 M glucose and 0.1 M fructose.

Fig. 4. Molar ratio of FA to LA as a function of the conversion of different substrates for all monophasic and biphasic experiments in batch reactors. The insert shows the data of a representative monophasic experiment under a reaction temperature of 135 ᵒC using the aqueous feed with 0.05 M H₂SO₄ and 0.1 M substrate. The unity line (at an FA/LA molar ratio of 1) is included as a reference.

Fig. 5. ESI-MS spectra of the aqueous product sample collected after the reaction of (a) glucose, (b) fructose and (c) HMF in water in the batch reactor. Other reaction conditions: 135 ᵒC, 0.05 M H₂SO₄, 0.1 M substrate (glucose, fructose or HMF), 1 h reaction time. The inset in (a) shows a magnified view of m/z region at 70–100.

Fig. 6. Proposed reaction network for the conversion of fructose-glucose mixture catalyzed by sulfuric acid in monophasic (water) and biphasic (water-MIBK) systems. An additional extraction of HMF (as well as that of FA and LA; not shown for brevity) to the organic phase is present in the biphasic system. Symbol meanings are explained in the text.

Table 1. Kinetic parameter values at 135 ᵒC for the proposed reaction network.

Fig. 7. Modelled glucose conversion and HMF yield in an ideal batch reactor as a function of the fructose conversion in the water-MIBK system by varying (a) the reaction temperature and (b) initial O/A ratio. Other reaction conditions (unless otherwise stated): reaction temperature of 155 ◦C, 0.05 M H₂SO₄, 0.5 M fructose and 0.5 M glucose, O/A = 4 (fed at 20 ◦C).

Fig. 8. (a) Modelled conversions of fructose and glucose in the water-MIBK biphasic system in different continuous flow reactor configurations and (b) the corresponding HMF yield as a function of fructose conversion. Other conditions: reaction temperature of 155 ᵒC, 0.05 M H₂SO₄, 0.5 M fructose and 0.5 M glucose, initial organic to aqueous volumetric flow ratio of 4 (fed at 20 ᵒC).

Fig. 9. Conversion of (a) 10 wt% HFCS-55 (0.26 M fructose and 0.20 M glucose) and (b) 10 wt% HFCS-90 (0.42 M fructose and 0.05 M glucose) in slug flow microreactors. Other reaction conditions: reaction temperature of 155 ᵒC, 0.05 M H₂SO₄ and an initial organic to aqueous volumetric flow ratio of 4 (fed at ca. 20 ᵒC). Error bars represent the standard deviation based on experiments in at least duplicate.

W. Guo, H.J. Heeres, J. Yue, Continuous synthesis of 5-hydroxymethylfurfural from glucose using a combination of AlCl₃ and HCl as catalyst in a biphasic slug flow capillary microreactor, Chem. Eng. J. 381 (2020) 122754.

R.M. Abdilla-Santes, W. Guo, P.C.A. Bruijnincx, J. Yue, P.J. Deuss, H.J. Heeres, High-Yield 5-Hydroxymethylfurfural Synthesis from Crude Sugar Beet Juice in a Biphasic Microreactor, ChemSusChem 12 (2019) 4304-4312.

葡萄糖异构化生产果糖-葡萄糖混合物已经具有成熟的工业化生产背景（如高果糖玉米糖浆、高蔗糖甜菜汁的生产等），然而对混合糖的进一步高价值化转化尚处于初步探索阶段。本工作提出了优先转化混合糖中的果糖来制备HMF，并最大限度保持葡萄糖不转化以利于其回收再异构化，从而提高葡萄糖制备HMF的总体效率的概念。为实现该目标，本工作进行了关于混合糖转化制HMF的实验和动力学建模研究，通过动力学模型对双相体系中混合糖转化的过程参数进行优化并探讨了连续反应器的设计，最终采用双相弹状流微反应器平台强化了工业混合糖转化制备HMF，该过程具有与现有工业混合糖生产链相结合，并对其进行高价值化升级改造的潜力。