Influence of Lignin Structure on Chemical Bioconversion Processes

Lignin is one of the major participants on wood resistance during bioconversion processes where the understanding of its structure in wood and stability during chemical reactions is of main importance to the bioconversion industry.;In chapter 2, comprehensive lignin structure analysis of ten industrially relevant hardwood species is presented. Milled wood lignin (MWL) was isolated from each species and all MWL preparations were analyzed through quantitative 13C NMR spectroscopy, elemental analysis, methoxyl analysis, and nitrobenzene oxidation. A new method to predict the syringyl/guaiacyl (S/G) ratio of total lignin in wood was developed, using a calibration line established by the syringyl/vanillin (S/V) ratio and the S/G ratio of MWL. Significant variations in lignin structures (S/G ratio, beta-O-4, degree of condensation, elemental and methoxyl contents, etc.) were found among the hardwood species studied. However, these structural variations among species appear to be controlled by a single factor, the S/G ratio.;In chapter 3, to explain the variations in delignification behaviors among the different hardwood species, the kraft pulping delignification rate of all species was obtained and correlated with their respective lignin chemical structures. Since H-factor for hardwood is calculated based on the softwood activation energy (Ea) value, a comparison between softwood/hardwood activation energy was also performed. Lignin was isolated by a modified isolation protocol, using alkaline pretreatment of the wood prior to isolation. The lignin preparations were analyzed via quantitative 13C NMR spectroscopy. Substantial variations were found among the hardwood species studied. A linear correlation between the kraft delignification rate and the amount of syringyl was found. Activation energy values obtained for kraft pulping of hardwoods were very similar and almost identical to the value obtained for softwood. Birch was the only species with outlier behavior.;In chapter 4, the kinetics of glucan, xylan and total carbohydrate dissolution during the bulk phase of the kraft pulping process were investigated. A wide range of carbohydrate dissolution rates was obtained and correlated to chemical features and delignification rates for nine different hardwood species. It was determined that carbohydrate dissolution was dependent upon the rate of delignification. Species with high carbohydrate dissolution also presented high lignin removal rates. These results indicate that lignin and carbohydrates (especially hemicelluloses) are strongly associated. Preliminary results also indicate that the presence of lignin carbohydrate complexes (LCCs) significantly influences the pulping process.;In chapter 5, it was investigated the influence of various hardwood characteristics on enzymatic hydrolysis. Hardwood species, comprehensively characterized using quantitative 13C NMR, image analysis and fiber quality analysis were subjected to enzymatic hydrolysis and the hydrolysis efficiency was correlated to the different wood chemical composition and lignin characteristics. Among the key wood components that control enzymatic hydrolysis efficiency, lignin content, enzyme adsorption on substrate and, the ratio of syringyl/guaiacyl (S/G) of the pretreated feedstock were identified as the most important. No wood morphological feature was found to have a significant influence on enzymatic conversion of the pretreated samples.;In chapter 6 we targeted the understanding of the influence using different hardwood species (nine) as feedstock materials on ethanol production yield and costs. It was found that the minimum ethanol revenue (...