The effect of Ru/C and MgCl2 on the cleavage of inter- and intra-molecular linkages during cornstalk hydrolysis residue valorization

The cleavage of linkages of lignocellulose is important for its valorization. The linkage cleavage of cornstalk hydrolysis residue was investigated over catalysts (Ru/C + MgCl2) in EtOAc/H2O solvents. The results show that almost hydrogen bonds, C-C bonds, ether and ester bonds in the matrix of lignin and cellulose were broken, accompanying 80.6% of lignin and 98.5% of cellulose conversion, and obtaining 37.5% of aromatic monomers and 28.8% of lignin oligomers. In the reaction system, biphasic EtOAc/H2O solvents exhibited an effect on cleaving the intermolecular linkages between lignin and cellulose. MgCl2 showed limited abilities of breaking the alpha-O-4 and beta-O-4 linkages in lignin and limited beta-1, 4-glycosidic and hydrogen bonds in cellulose were cleaved over Ru/C catalyst. The cleavage of C-O linkages (alpha-O-4, beta-O-4, 4-O-5) and C-C bonds (alpha-beta, beta-5) in lignin were mainly dependent on Ru/C catalyst. Much C-O and the stubborn C-C linkages of beta-5, beta-1 and 5-5 were significantly disrupted by the synergistic effect between MgCl2 and Ru/C. However, MgCl2 exhibited great contribution to breakage of beta-1, 4-glycosidic linkage, hydrogen bonds and sugar ring of cellulose. The linkage of beta-1, 4-glycosidic, hydrogen bonds and C-C in C5/C6 sugars were significantly broken. The increased yield of products was evidently due to the synergistic effect of Ru/C combined with MgCl2.