Abstract:

Chemoenzymatic epoxidation of olefins is a green and environmental friendly alternative process. However, as an oxidant, hydrogen peroxide leads to the inactivation of lipase and the interphase mass transfer of the reaction system, which needs to be solved urgently. In this work, a stable MOF-immobilized lipase catalyst CALB@Uio-66-NH₂ was successfully synthesized by covalent cross-linking, the structure and crystal form were characterized by scanning electron microscope (SEM) and X-ray diffractometer (XRD). In order to solve the problem of two-phase mass transfer resistance caused by hydrogen peroxide, the effects of polar solvents and ester acyl donors on the reaction were studied. Tert-butanol was finally determined as the solvent and ethyl acetate as the acyl donor. A single-phase reaction system suitable for the chemoenzymatic epoxidation of limonene was constructed to replace the traditional “organic-water” two-phase reaction system. Then, the catalyst addition, hydrogen peroxide concentration and acyl donor concentration were optimized to obtain the optimal reaction efficiency. When the concentration of limonene was 0.1mol/L, the optimized catalyst addition was 20%, and the optimum concentration of hydrogen peroxide and ethyl acetate was 0.5mol/L and 3mol/L, respectively, the yield of 1,2-epoxide was 85.1%, under this condition, CALB@Uio-66-NH₂ can still maintain 90.9% relative activity after 6 times of reuse.

Key words: metal-organic frameworks (MOFs), enzyme immobilization, limonene, epoxidation, solvent

摘要：

化学-酶法催化烯烃环氧化是一种绿色环保的替代工艺，但是作为氧化剂的双氧水造成的脂肪酶失活和反应体系相间传质是亟待解决的难点问题。本文首先采用交联法成功合成了一种稳定的MOF固定化脂肪酶催化剂CALB@Uio-66-NH₂，并用扫描电子显微镜（SEM）与X射线衍射仪（XRD）对其结构与晶型进行了表征。为了克服双氧水的相间传质障碍，考察了极性溶剂与酯类酰基供体对反应的影响，最终确定叔丁醇作为反应溶剂，乙酸乙酯作为酰基供体，构建了适用于柠檬烯化学-酶法环氧化的单相反应体系以取代传统的“有机-水”两相反应体系。通过对体系的催化剂添加量、过氧化氢与酰基供体浓度优化，获得了最佳的反应效率，在柠檬烯浓度为0.1mol/L时，催化剂最适添加量为20%、过氧化氢最适浓度为0.5mol/L、乙酸乙酯最适浓度为3mol/L，40℃下反应40min，柠檬烯-1,2-环氧化物收率可达到85.1%，而且在此条件下，CALB@Uio-66-NH₂重用6次后仍能保持90.9%的相对活力。

关键词: 金属有机骨架, 固定化酶, 柠檬烯, 环氧化, 溶剂