KINETIC AND MOLECULAR FEATURES OF GREEN LIQUOR-MODIFIED VERSUS CONVENTIONAL KRAFT PULPING

摘要

Recent work at North Carolina State University has focused on providing a cost effective retro-fit to kraft pulp mills that will improve the energy efficiency and productivity of the mills. It will do this by rerouting a significant portion (20%～30%) of the green liquor (GL) flow from causticization to the pulp digester. Thus, the outcome of our work will be the introduction of a major, yet feasible pulping innovation that has seen installation in Europe, but will be optimized for the US industry to provide major energy savings and increased productivity. Amongst the various research efforts we have undertaken to further promote our understanding of this novel process, is a series of kinetic and mechanistic investigations aimed at fully exploiting this process. GL pretreatment was found to increase the rate of pulping by improving the kinetics at the onset of the bulk delignification stage. Consequently, the GL pretreatment was also found to assist the chemical reactions occurring in the pulping process. Experiments with isolated lignin samples revealed that a significant amount of sulfur uptake takes place when lignin is pretreated with WL and/or GL. The presence of carbonate in GL was found to positively affect such incorporation. As such a correlation between chemical performance and lignin removal was established for GL-modified pulping. The efficiency of reactivity for the hydrosulfide and hydroxide anions in delignification were 2 and 1.6 times higher, respectively, than conventional kraft. Finally, we investigated how the green liquor interacted with an etherified lignin model compound (veratrylglycerol-β-guaiacyl ether) and Enzymatic Mild Acidolysis Lignin (EMAL). The various functional groups of the lignin structure were determined before and after GL treatment by using quantitative 31P-NMR spectroscopy. In addition, the degradation of lignin was followed by gel permeation chromatography (GPC).