Structural Characteristics Of Lignins From Steam-exploded Corn Stalk And Its Enzymatic Hydrolyzed Residue

Lots of cornstalks residue will be produced during the process of fuel alcohol production by lignocellulose. In order to cut down production cost and use lignocellulose more efficiently, the cornstalks residue should be developped and utilized. In this thesis, structural characteristics of cellulolytic enzyme lignins, isolated from virgin cornstalks (CL), steam-exploded cornstalks (SL) and its enzymatic hydrolysis residue (EL), were comparative investigated. Main results could be obtained as followings.1. Three kinds of lignin mentioned above were isolated in optimized enzymatic hydrolysis condition. The yields of lignin samples were 35.1%, 41.8%, and 57.3%, respectively.2. Analysis of the nitrobenzene oxidation products (NOP) shows that chemical structures of the 3 kinds of lignin mainly consisted of guaiacyl unit (G), syringyl unit (S) and p-hydroxyphenyl unit (H). The proportion of the 3 units was between that of the whole cornstalk lignin and the cortex lignin. The content of H was the highest but G and S were close in quantity. The H content in steam-exploded cornstalk and enzymatic hydrolyzed cornstalks residue respectively rised by 8.1% and 6.0%. The NOP yielids of the 3 lignin samples were close.3. Determination of functional groups showed that, CL has a higher content of methoxyl group and lower contents of phenolic hydroxyl and carboxyl groups, compared with those in SL and EL. Functional groups of SL and EL are rather similar. The result means that steam explosion has some effects on the chemical structure of lignin, however, little structural changes occur during the process of enzymatic hydrolysis. The calculated C9 empirical formula of CL, SL and EL were C9H8.81O3.31(OCH3)0.81, C9H9.20O3.54(OCH3)0.74 and C9H9.33O3.62(OCH3)0.74, respectively.4. Molecular weight and molecular weight distribution of 3 lignin samples were tested by GPC. Compared with the molecular weight of CL, both number- and weight-average molecular weight decreased, and the polydispersity increased. It proves that lignin fragmentation happens during the process of steam-explosion which mainly caused by the cleavage ofα-O-4 linkage.