Catalytic selectivity in alcohol organosolv pulping of spruce wood

Development of a more efficient and environmentally friendly pulping process is seen as a necessity to cope with problems currently faced by pulp and paper industries. The objectives of this research were to investigate the effect of catalysts on pulping behavior, selectivity, pectin removal and delignification leading to fiber separation in a catalysed alcohol organosolv pulping process.; Under the specified pulping conditions, it was found that not all catalysts used in the organosolv pulping of softwood were able to liberate the fibers. The pulping outcomes were different, depending on the catalyst species.; It is concluded that neither mono- nor trivalent acidic inorganic salts, nor simple organic acids in themselves, except citric acid, can be used as catalysts for effective fiber liberation in organosolv pulping, due largely to the uncontrolled drop of pH below 3.5, at which point delignification becomes significantly retarded. The mystery of the unique neutral alkali earth metal (NAEM) salt catalyst effectiveness is now fully explained and described. Investigation of NAEM catalysed pulps showed total loss of arabinose and galactose from among the carbohydrates of the pulp as if their presence controlled the process of fiber liberation.; Early fiber liberation resulting in high pulp yield and viscosity can only be accomplished with a cooking liquor possessing high chemical and topochemical selectivity for lignin.; Extending the cooking beyond the fiber liberation point provides no benefit at all, because the extent of additional delignification is small and is attained at the expense of carbohydrate degradation and loss, and lignin re-precipitation.; The mechanism of fiber liberation in the NAEM salt catalysed organosolv pulping process can now be described as “versatile” being able to affect both initial removal of the pectin and hemicelluloses (arabinogalactan) followed by bulk and residual delignification. NAEM salt catalysts therefore play a double role: (1) effectively promote the initial pectin removal at pH > 5, and (2) effectively buffer the cooking liquor against uncontrolled pH drops as more and more protons are liberated due to ion exchange with carboxyls and liberation of acetyls. The role of pectin dissolution in controlling effective fiber liberation in organosolv pulping of softwood is described for the first time. The topochemistry of pectin removal from spruce wood was followed by immunolabelling followed by fluorescent microscopy of thin cross-sections. (Abstract shortened by UMI.)...