固定化磺基离子液体催化合成5-羟甲基糠醛研究

Catalytic Conversion of Fructose into 5-Hydroxymethylfurfural with Sulfonic Group Bearing Ionic Liquid Immobilized on Micro-Ball Silica-Gel

对微球硅胶固定化离子液体(IL3)催化果糖脱水合成5-羟甲基糠醛(HMF)进行了研究。以微球硅胶为载体,通过γ-氯丙基三甲氧基硅烷将磺基功能化离子液体-N-磺丙基咪唑盐(IL2)化学键联到其上制得IL3。用液氮吸附、13C-NMR、元素分析及酸度测定等方法对IL3进行分析与表征,并考察其在果糖脱水合成HMF反应过程中的催化性能。研究结果表明:IL3能有效催化果糖脱水生成HMF。IL2固载量越高,IL3的表面酸度越大、但比表面积和孔体积都下降。当IL2的固载量为45.4%时,所制得的催化剂(45.4-IL3)对果糖脱水生成HMF具有较好的催化性能。过高的反应温度和果糖浓度会使生焦反应加剧,导致HMF收率降低。在115℃、15%～25%(wt)果糖溶液中反应是较合适的,HMF收率维持在80%以上。IL3可方便地循环使用,但随循环使用次数增加,HMF生成速率和收率都呈下降趋势。尤其是催化剂循环使用四次后,HMF收率明显下降,是反应过程中生成的不溶性焦质在催化剂表面覆盖所致。

Synthesis of 5-hydroxymethylfurfural（HMF） from fructose dehydration catalyzed by sulfonic group bearing ionic liquid immobilized on silica-gel（IL3） was studied.The IL3 were prepared by immobilizing different amounts of 1-H-3-（3-sulfonic acid）propylimidazolium chloride（IL2） on micro-ball silica-gels with γ-chloropropyltrimethoxysilane as coupling agent.The prepared IL3 were characterized respectively by N2 adsorption,13C-NMR,elemental analysis and acidity measurement,and their catalytic performance of synthesizing HMF from fructose was investigated.The results indicate that the IL3 are efficient catalyst for fructose dehydration to form HMF.It was observed that,for the prepared IL3,their surface acidity increase,and their specific surface area and pore volume decrease with the increase of IL2 loading.The IL3 catalyst with IL2 loading of 45.4%（45.4-IL3） exhibits the best catalytic performance;too high the hydration reaction temperature and the fructose concentration will cause severe coke formation.Under the condition of 115℃ and with fructose solution of 15%～25%（wt）,using the prepared IL3 as catalyst the yield of HMF keeps over 80%.The IL3 can be reused conveniently,but the yield of HMF drops gradually with the times of reuse;especially after fourth reuse,the yield of HMF decreases obviously.It is caused by coke deposition on the IL3 surface.