Study On The Structure Changes Of Lignin In Autohydrolysis And Formic Acid Pulping Process Of Neosinocalamus Affinis

The effect of extracting hemicelluloses by autohydrolysis on neosinocalamus affinis alkaline pulping was investigated in the thesis. The chemical composition changes of the milled wood lignin were analyzed under the different conditions. The dissolution of poplar hemicelluloses during pre-hydrolysis in acetic acid-sodium acetate buffer was emphatically discussed. Optimization of a formic acid delignification treatment on neosinocalamus affinis and its influence on the structural characteristics of the formic acid lignins compared with milled wood lignin.Based on the concept of biorefinery, the effect of the autohydrolysis of neosinocalamus affinis with different pretreatment temperature (140-180℃) on hemicelluloses pre-extraction and following alkaline pulping were studied. The soda-AQ pulping and kraft pulping were conducted with pretreated chip samples. The results indicated that autohydrolysis was effective for extracting hemicelluloses hydrolytic sugars. It was observed that both monosaccharides and oligosaccharides contents in pre-hydrolysis liquor increased with the rising of pretreatment temperature, and the yield of pentose in pre-extraction had a same trend. The oligosaccharides content in the autohydrolysis liquor was significantly higher than that of monosaccharides. Compared with the untreated chips, the crystallinity of neosinocalamus affinis increased, and the crystallinity increased with increasing pretreatment temperature. Besides, autohydrolysis can obviously improve the effect of delignification in subsequent alkaline cooking compared with the untreated chips and have a positive effect on the properties of pulp. Considering the biomass utilization of pre-hydrolysis and subsequent pulping performance, at the optimized pretreatment temperature of 170℃, the dissolution of hemicellulose resulted in 8.53 g/L oligosaccharides and 0.99 g/L monosaccharides, and the yield of pentose in pre-extraction is 21%, and this process produced less acetic acid and furfural, the properties of the soda-AQ pulp and kraft pulp are better at the optimized pretreatment.Milled wood lignins from the hydrolyzed neosinocalamus affinis chips with different pretreatment temperature were analyzed using the laser scattering instrument, FTIR and 31P-NMR. The results showed that the average molecular weight of the lignin increased and the lignin polydispersity decreased with increasing pretreatment temperature. The carbon hydrogen bonds and the phenolic hydroxyl in the lignin groups increased, aliphatic hydroxyl decreased, and generated new condensation bonds after hydrolysis. The ether linkage decreased and more phenolic hydroxyl produced, the aliphatic hydroxyl group decreased with increasing pretreatment temperature. The syringyl-type lignin was easier to degrade than the guaiacyl-type lignin. The results indicate that the lignin degradation and condensation reactions occur at the autohydrolysis process.The dissolution of hardwood hemicelluloses during pre-hydrolysis in acetic acid-sodium acetate (AASA) buffer was studied in this work. The results showed that the dissolution of hemicellulose was depended significantly on the buffer pH from 3.0 to 4.2, but was less affected by the buffer strength from 50 mmol/L to 150 mmol/L. It was observed that both total sugar and monosaccharide contents in pre-hydrolysis liquor (PHL) increased with the decreasing pH, and the highest oligosaccharides content was achieved at pH 3.4. Compared to autohydrolysis using water as reaction medium, pre-hydrolysis in AASA buffer promoted the dissolution of the hemicelluloses and inhibited the degradation of carbohydrate, especially monosaccharides, and consequently led to higher yield of oligosaccharides and monosaccharides. At the optimized pH of 3.4 and buffer strength of 100 mmol/L, the dissolution of hemicellulose resulted in 6.47 g/L oligosaccharides and 2.47 g/L monosaccharides, while the degradation products in PHL were remarkably reduced,46% lower for acetic acid and 47% lower for furfural than that of autohydrolysis.Formic acid pulping of neosinocalamus affinis was done with varying cooking tempreture and cooking time. Pulp yield and kappa number decreased with increasing cooking tempreture or cooking time. Compared to the cooking time, the cooking tempreture is more signification for the delignification of neosinocalamus affinis. Cooking time have greater influence than cooking temperature for the decreasing of fine pulp yield. The lignin degradation and condensation reactions between intramolecular and intermolecular occur in the formic acid pulping process. The average molecular weight of the formic acid lignin significantly higher than the milled wood lignin (MWL) of neosinocalamus affinis. The lignin also occur esterification in the formic acid pulping process. Compared to MWL, the ether linkage decreased and more phenolic hydroxyl produced in the formic acid lignin.