| Lignin is a unique and abundant natural aromatic polymer compound,but there are several disadvantages such as large molecular weight and low reactivity,making it subject to huge restrictions in industrialization.In this paper,H3PW12O40,ionic liquids[BMIM]Cl and H5PV2Mo10O40 were used as catalysts for the catalytic degradation of wheat straw/enzymatic lignin,and the hydroxyl contents and relative molecular weight of the degradation products were employed as indexes to evaluate the catalytic degradation quality.The results of this study are as follows:H3PW12O40(12-tungstophosphoric acid,TPA)was loaded on ZrO2 framework by impregnation method.The composite material was used to degrade wheat straw lignin and enzymolysis lignin in ethanol-water solvent.The TPA/ZrO2 catalyst were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),nitrogen adsorption/desorption theory(BET),and Fourier transform infrared spectroscopy(FT-IR).The results showed that TPA/ZrO2 had good catalytic activity when the TPA/ZrO2 catalyst loading quantity was 20%and the calcination temperature was 200 ?;The best degradation conditions in the degradation of enzymatic hydrolysis lignin were:reaction time 6 h and the temperature 60 ?,the concentration of lignin was 5%,and the mass fraction of catalyst was 25%.the phenolic hydroxyl group and the total hydroxyl group of the enzymatic hydrolysis lignin degradation products increased significantly.The weight-average molecular weight of lignin decreased after the reaction.The degraded lignin products has a strong antioxidant capacity and increases with the mass concentration increasing.Using ionic liquid[BMIM]Cl as a solvent and catalyst,respectively catalyzed the wheat straw alkali lignin and enzymolysis lignin to catalyze the optimal reaction conditions of wheat straw alkali lignin were:reaction time 3 h,reaction temperature 140 ?,substrate concentration 2.5%,The optimal reaction time for catalytic enzymolysis of lignin is 6 h,the reaction temperature is 120 ?,and the substrate concentration is 5%.In contrast,the enzymolysis of lignin has better solubility in ionic liquids and lignin degradation products contain higher hydroxy compounds under the same reaction conditions.On this basis,the reaction rate and the content of hydroxyl compounds in the degradation product can be increased when the composite catalyst 20TPA/ZrO2-200 with a mass ratio of 1:4 is used.The lignin degraded by {20TPA/ZrO2-200+[BMIM]Cl} showed good oxidation resistance after the straw/enzymatic hydrolysis of lignin.FT-IR and 13C-NMR spectroscopy were used to characterize the structure of the straw lignin lignin and the degradation product of the enzymatic hydrolysis lignin.The structural analysis of the degradation product showed that the basic functional groups did not change before and after the degradation reaction.The main bond was broken and the way is to break the ?-O-4 bond.Heteropoly acid HsPV2Mo10O40was prepared by conventional synthesis method and were analyzed by FT-IR,XRD,and SEM.The results showed that P,V,Mo in the synthesized H5PV2Mo10O40 was correspond to the relationship of 1:2:10,and has a typical Keggin structure.Degradation of wheat straw/enzymatic hydrolysis of lignin with {[BMIM]Cl+ H5PV2Mo10O40}as catalyst.In the reaction of wheat straw lignin catalyzed by {[BMIM]Cl+ H5PV2Mo10O40},The content of total hydroxyl groups and phenolic hydroxyl groups increased to 13.98 mmol/g and 5.86 mmol/g,respectively,and the relative molecular mass decreased from 12691 g/mol to 3589 g/mol when the reaction time is 6 h,the reaction temperature is 120 ?,and the mass ratio of wheat straw lignin to H5PV2Mo10O40 is 5:1,the degradation product after solid degradation.Vanillin was formed in the liquid degradation product and the mass fraction was 6.97%.During the degradation reaction of enzymatic hydrolysis lignin,the reaction time of straw lignin was halved,and vanillin was formed in the liquid degradation product with a mass fraction of 10.32%. |
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