报告人：Van Heiningen教授（美国缅因大学）
　　题目：Kinetics and Mechanism of Oxygen Delignification of Pulp
　　时间：2008年12月2日上午9：30
　　地点：制浆造纸工程国家重点实验室301会议室

制浆造纸工程国家重点实验室

2008年12月1日

　　内容介绍：
　　Oxygen delignification experiments have been performed in a differentially operated continuous stirred tank reac-tor (CSTR). The rate of delignification at constant dissolved oxygen and alkali concentration was determined from the dissolved lignin concentration in the outflow stream of the reactor. The delignification kinetics were determined at different temperatures, oxygen pressures and caustic concentrations for softwood and hardwood kraft pulps. In all cases the kinetics are first order in residual lignin content (HexA corrected) and follow a Langmuir-type behavi-or for adsorption of oxygen on active aromatic lignin sites. The delignification rate was significantly higher for har-dwood kraft pulp than that for the softwood pulps at the same residual Hexa-corrected lignin content. The first or-der in residual lignin content implies that the active lignin sites are uniformly distributed and have the same reacti-vity. Based on the NaOH concentration reaction order of the kinetics, it is proposed that the active site is the 3 ca-rbon of the aromatic ring where oxygen reacts to form a hydroperoxide with a pKa of almost 2 units higher than t-hat of phenolic lignin. The kinetics of phenolic delignification can be described by assuming that the decomposit-ion of the hydroperoxide anion is rate determining step. The almost uniform presence of aromatic methoxyl groups in residual lignin supports the first order in lignin kinetics. Further supporting evidence is the close relationship be-tween delignification and demethoxylation and the absence of a correlation between phenolic group content of the lignin and rate of delignification. The higher delignification rate for hardwood pulp is consistent with the higher co-ntent of methoxyl groups of hardwood lignin. Implications for further improvement of the oxygen delignification pro-cess are discussed.