Fabrication of Magnetic Catalyst Fe(3)O(4)-SiO(2)-V(3) and Its Application on Lignin Extraction from Corncob in Deep Eutectic Solvent

Fe(3)O(4)-SiO(2)-V(3) was prepared by deposited H(6)PMo(9)V(3)O(40) on Fe(3)O(4)-SiO(2) and employed as a catalyst to extract lignin from corncob in deep eutectic solvent (choline chloride/lactic acid = 1/10). Batch experiments were conducted in an autoclave under the conditions of 500 kPa, 90–130 °C and 15 h, while the dosage of the catalyst was set as a variable. Results indicated that the catalyst could effectively improve the qualities of the lignin, while the characteristics of the lignin showed prominent changes with the participation of the catalyst: the extraction rate increased from 71.65% to 98.13%, the purity was improved from 85.62% to 97.09%, and both the number average molecular weight and the weight average molecular weight also decreased significantly. Besides, the molecular distribution of the lignin achieved from the CC-LA-Fe-Si-V(3) reaction system was found to be more highly concentrated (Polydispersity index = 1.746). Results from 2D NMR HSQC analysis indicated that lignin fractions achieved from the CC-LA-Fe-Si-V(3) system showed distinct destruction involving C(2)-H(2) in guaiacyl units (G), C(5)-H(5) in guaiacyl units (G), and the C(γ)-H(γ) in γ-hydroxylated β-O-4′ substructures, but little changes in the C(γ)-H(γ) in phenylcoumaran substructures.