工业木素的氧化氨解——机理和动力学

Oxidative Ammonolysis of Technical Lignins——Mechanism and Kinectics

研究了温度、氧压和氢氧化铵浓度对有机溶剂木素 (Repap)氧化氨解速率的影响。动力学实验是在 300ml Parr反应器内进行，反应条件为氢氧化铵浓度 0. 4～ 1. 6mol/L、反应温度 70～ 130℃、氧压 0. 5～ 1. 2MPa。在整个氧化氨解过程中，氮被引入到木素上的反应机理一直不变。大多数氮都是通过芳环裂化被引入到木素分子上的 ,由于酚型木素和非酚型木素的反应性能不一样，因此氮引入的动力学分两个阶段进行，并且在这两个阶段都遵循假一级速率法则。实验结果表明此反应的活化能相当低，大约 35～ 40kJ/mol；氮结合速率与氧压成正比，说明反应与氧的浓度有关。就氢氧化铵浓度而论，反应的级数是一级反应，为 0. 5，说明氢氧化铵参与反应可能阻碍氮的结合。不同来源 (阔叶木有机溶剂木素、麦草有机溶剂木素和碱木素、蓝桉硫酸盐木素、巨桉硫酸盐木素和松木硫酸盐木素 )木素的反应性能与 C9——单元上 S/G(丁香基 /愈疮木基 )的比率成比例。氮的引入与氧的吸收间的线性关系及二氧化碳的生成降低了甲氧基含量，同时总的含碳量也减少了。除了生成二氧化碳之外，这些线性关系均与研究范围内的反应条件无关。在所研究的条件下，氮被引入到木素分子上的机理通常是相同的。然而，反应途径的不同。

The effect of temperature,oxygen pressure and ammonium hydroxide concentration on the rate of oxidative ammonolysis of organosolv lignin(Repap)was studied.The kinetic experiments were conducted in 300 mL Parr's reactor in ammonium hydroxide solutions of 0.4～ 1.6mol/L at the reaction temperature of 70～ 130℃ under oxygen pressure of 0.5～ 1.2MPa.The reaction mechanism of nitrogen incorporation does not change during entire course of oxidative ammonolysis.Most of nitrogen is incorporated into the lignin via cleavage of aromatic rings.The kinetics of nitrogen incorporation has two phases duse to different reactivity of phenolic and non－ phenolic lignin moieties and follows a pseudo－ first order rate law in the both phases.The activation energy was found to be rather low,about 35～ 40 kJ/mole.The rate of nitrogcn incorporation is directly proportional to oxygen pressure indicating the reaction is first order with respect to oxygen concentration.The reaction order with respect to ammonium hydroxide concentration is 0.5 suggesting possible participation of NH4OH in reactions inhibiting nitrogen incorporation.The reactivity of technical lignins of different origin(hardwood organosoly lignin,wheat straw organosoly and soda lignins,Eucalyptus globulus(EGL)， Eucalyptus grandis(EGR) and pine kraft lignins) is proportional to the S/G ratio of C9－ units.Linear relationships between nitrogen incorporation and oxygen uptake and incorporation,CO2 formation,decreases in methoxyl group content and carbon loss were found.Except for CO2 formation,these relationships do not depend on the reaction conditions in the range studied.The mechanism of nitrogen incorporation is generally the same under the conditions studied.However,minor changes in the relation between different reaction pathways are possile.