Extraction Of Corn Cob Lignin By Supported Polyoxometalate-deep Eutectic Solvent System

In this study,choline chloride(CC)was used as hydrogen bond acceptor,lactic acid(LA),glycerol(G)and urea(U)were used as hydrogen bond donors,and three kinds of deep eutectic solvents were synthesized according to a certain molar ratio.The effects of types of deep eutectic solvents,molar ratio of hydrogen bond acceptor to hydrogen bond donor,reaction temperature and reaction time on the extraction of lignin from corncob were investigated.The CC-LA reaction system of deep eutectic solvent and the optimal reaction conditions were determined.Three kinds of PMoVn(n=1,2,3)were prepared and loaded on the magnetic carrier Fe₃O₄@Si O₂to synthesize three new types of loaded polyoxometalates PMoVn-Fe₃O₄@Si O₂(n=1,2,3).Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDX),average particle size calculation and X-ray photoelectron spectroscopy(XPS)were used to characterize and analyze the supported polyoxometalates.The results showed that the polyoxometalates was successfully loaded on the magnetic carrier Fe₃O₄@Si O₂.The supported polyoxometalates was added into the CC-LA system as a catalyst for the extraction of lignin from corncob.The effects of single factor conditions such as the type,dosage,reaction temperature,reaction time and oxygen pressure of the loaded polyoxometalates on the lignin extraction rate were investigated,and the orthogonal experiment was designed.The experimental results show that the catalytic effect of PMoV₃-Fe₃O₄@Si O₂is the best.When the dosage is3%,the optimal reaction temperature can be reduced from 150°C to 120°C,and the maximum lignin extraction rate is 98.3%.Compared with the CC-LA system,the CC-LA-PMoV₃system can reduce the activation energy by 65.4%,and reduce the activation energy from 57.91 k J/mol to 20.04 k J/mol.Meanwhile,the supported PMoV₃-Fe₃O₄@Si O₂catalyst has good magnetic properties,safe and simple separation method,and excellent reusability and stability.The purity,weight-average molecular weight and number-average molecular weight of CC-LA lignin and CC-LA-PMoV₃lignin were determined and characterized by FTIR,TGA/DTG and 2D-HSQC.The reaction mechanism of corncob delignification in CC-LA-PMoV₃system was explored.The results showed that compared with CC-LA lignin,CC-LA-PMoV₃lignin had higher purity,higher thermal stability,and lower and narrower molecular weight distribution.At the same time,CC-LA-PMoV₃system had obvious destructive effect on C₂-H₂and C₅-H₅of lignin guaiacol,but did not destroy C?-H?of phenylcoumarin substructure.CC-LA-PMoV₃lignin has a broader industrial application prospect.