离子液体[BMIM]Cl与H5PV2Mo10O40双效催化降解麦草碱木质素的研究

采用常规合成法制备了杂多酸H₅PV₂Mo₁₀O₄₀，并通过FT-IR、XRD、SEM对其进行表征。研究了BMIM]Cl单催化与{H₅PV₂Mo₁₀O₄₀+BMIM]Cl}双效催化体系中，反应时间、温度以及H₅PV₂Mo₁₀O₄₀用量对麦草碱木质素降解的影响，并初步探讨了木质素的降解机理。结果表明:H₅PV₂Mo₁₀O₄₀中P、V、Mo相对原子质量满足1:2:10关系，并具有典型的Keggin结构；木质素降解反应中，仅离子液体BMIM]Cl降解木质素的最佳条件为140 ℃下反应3 h，降解后固体产物中总羟基由3.49 mol/kg增加到10.92 mol/kg，液体产物中有香草醛与丁香醛生成，分别占2.00%和2.15%；{H₅PV₂Mo₁₀O₄₀+BMIM]Cl}双效催化体系中，最佳反应条件为加入20%的H₅PV₂Mo₁₀O₄₀ 120 ℃下反应6 h，降解后固体产物中总羟基由3.49 mol/kg增加到14.12 mol/kg，摩尔质量由7.691 kg/mol降为1.589 kg/mol；液体产物中无丁香醛生成，香草醛占6.97%。初步认为:当单独BMIM]Cl催化木质素时，H+首先进攻木质素中β-O-4键上的氧原子，正电荷转移到β位，然后水分子中氧原子向带有正电荷的β位进攻，从而催化剂的H+被消除，最后实现了β-O-4键水解断裂，生成愈创木酚，进而侧链发生氧化生成香草醛与丁香醛；当添加H₅PV₂Mo₁₀O₄₀时，PV₂Mo₁₀O₄₀]5-中的VO₂+由V(V)→V(IV)，故使模型化合物得以单电子的氧化，使木质素脱甲氧基，由紫丁香基木质素转变成愈创木基木质素，液体产物中无丁香醛生成，且香草醛质量分数升高。 

Experimental evaluation on the ionic liquid [ BMIM ] Cl and H5PV2Mo10O40 dual function catalytic degradating wheat straw alkali lignin

The H5PV2Mo10O40 heteropoly acid was prepared by the conventional methods and was characterized with FT-IR, XRD and SEM. In{H5PV2Mo10O40+ BMIM ] Cl} dual function catalytic system and BMIM] Cl single function catalytic system, the effects of reaction time, reaction temperature and the amount of H5PV2Mo10O40 on the lignin degradation process were studied, and the degradation mechanism was also discussed preliminarily. The results indicated that the contents of P, V, Mo in the synthesis H5PV2Mo10O40 heteropoly acid accorded with the relationship of 1: 2: 10, and the H5PV2Mo10O40 heteropoly acid had the typical Keggin structure. Under the optimal reaction condition, i. e. , 140℃, 3 hours, the ionic liquids were used as the catalysts, the contents of total hydroxyl of alkali lignin increased from 3. 49 to 10. 92 mol/kg after reaction, and the mass fraction of vanillin and syringaldehyde were 2. 00% and 2. 15% in liquid products, respectively. When 20% H5PV2Mo10O40 was added, the optimal reaction time and temperature were 6 hour and 120 ℃, and the total hydroxyl increased from 3. 49 to 14. 12 mol/kg in solid degradation products. The molar mass reduced from 7. 691 to 1. 589 kg/mol. Only vanillin was found in liquid products, and its mass fraction was 6. 97%. It was believed that H+ attacked oxygen atom on the β-O-4 bond in lignin firstly when BMIM] Cl catalyzed lignin alone. At the same time, the positive charge was transferred to the β position, and then the oxygen atom in the water molecule attacked the β position which had positive charge. As a result, catalyst H+ was eliminated andβ-O-4 bond generated guaiacol due to the hydrolytic cleavage. Then the side chain generated vanillin and syringaldehyde by the oxidation reaction. When H5PV2Mo10O40 was added, PV2Mo10O40 ] 5- released VO2+ and its valencestate was changed from V ( V ) to V ( IV ) . The single electron oxidation model compounds were obtained and the lignin was demethylated. It was thought that the lignin demethoxy group was changed from lignin-type lignin to guaiacol-type lignin, not only without any clove aldehydes were found in the liquid product but also the contents of vanillin were increased.