Study On Catalytic Oxidation Of Lignin By Salen - Porphyrin Complexes

The traditional bleaching using chlorine-containing bleaching agent has a serious impact to the environment. The clean pulping technology is hence needed to develop to solve to the problem caused by chlorine-containing bleaching to the environment. The bioenzyme bleaching of pulp was studied and developed by paper worker. For natural enzymes, due to difficult preparation, harsh reaction conditions, biomimetic enzymes with similar function of natural enzyme have been paid more and more attention by researchers at home and abroad.Biomimetics simulate the activity center of enzyme, therefore, have the advantages of both enzymatic and chemical catalysis. Currently, metal porphyrin and non-porphyrin complexes are used in the bleaching, and metal porphyrin complexes have high catalytic selectivity at mild conditions, the conversion rate is high. We hope salen-porphyrin double center complexes can selectively oxidise hydroxyls of residual lignin in the pulp to become carbonyls, reduce hydrogen bonding and residual lignin is degraded to small molecular units, making pulp easily bleaching.In order to study salen-porphyrin complex catalyzed oxidation of lignin model compound, salen-porphyrin (ZnPSCe) complexes were synthesized. Veratryl alcohol was treated with a catalytic system containing salen-porphyrin, pyridine (2,2’-dipyridyl), hydrogen peroxide, sodium hydroxide. The influence of temperature, catalyst/ligand ratio and pH on the catalytic activity was studied. The GC-MS analysis was used to investigate the degradation product of model compound during the reaction. Results showed that salen-porphyrin type biomimetic system has ability to specifically catalyse veratryl alcohol to veratrylaldehyde. The efficiency of catalytic oxidation was increased first and decreased then as the temperature rised. The conversion of veratryl alcohol was highest when the condition of 80℃, ligand/catalyst 10, pH 12 was used.In order to study salen-porphyrin complex catalyzed oxidation of DBDO (dibenzodioxiaino) lignin model compound, DBDO was synthesized. The structural change and degradation products of DBDO was analyzed by FT-IR,13C-NMR, GC-MS. Salen-porphyrin complex catalyse DBDO to make the Cα-Cβ,α-O-4,β-O-4 linkage break, and methoxy reduced, generating vanillin, phenol, benzene formaldehyde and other degradation products.