过渡金属离子对桉木硫酸盐浆氧脱木素的影响

Effect of Transition Metal Ions on the Oxygen Delignification of Eucalyptus Kraft Pulp

为了更好地理解过渡金属离子对纸浆氧脱木素过程的影响和硫酸镁作为纤维素保护剂的作用机制,本研究在桉木硫酸盐纸浆中添加Mn2+、Fe3+、Cu2+等过渡金属离子,考察在桉木硫酸盐浆氧脱木素过程中过渡金属离子对木素脱除率、黏度降低率、脱木素选择性及硫酸镁助剂保护作用的影响。研究结果表明,在桉木硫酸盐浆氧脱木素过程中,不管是否存在硫酸镁助剂,过渡金属离子不影响桉木硫酸盐浆木素的脱除;纸浆中存在的过渡金属离子会加速纸浆纤维素的降解,降低纸浆的黏度;桉木硫酸盐浆中原有的和外部添加的过渡金属离子对纸浆纤维素的降解作用效果相当,且硫酸镁助剂对桉木硫酸盐浆中原有的和外部添加的过渡金属离子的失活作用效果相同;硫酸镁助剂除了和碱反应产生不溶于水的氢氧化镁,通过吸附或形成配位化合物使过渡金属离子失去活性的作用机制之外,还存在着其它作用机理起着保护纤维素的作用。

There is a relationship between the transition metal ions in pulp and the selectivity of oxygen delignifica- tion since the transition metal ions catalyze the decomposition of hydrogen peroxide formed during the reduction of oxygen and lead to generation of hydroxyl and oxyl anion radicals which degrade cellulose. To better understand the effect of the transition metal ions on the oxygen delignification and the possible protective mechanisms of magnesium ions as cellulose protector, in this work, the transition metal ions such as Mn2~ , Fe3＋ , Cu2~ , were added to the eucalyptus kraft pulp during the oxygen delignification to investigate the effect of the transition metal ions on the de- lignification, viscosity reduction, selectivity and protection of MgSQ. The experimental results indicated that the delignification of eucalyptus kraft pulp was not affected by the transition metal ions whether or not the additive of MgSO, was added. The existence of the transition metal ions would accelerate the degradation of cellulose which led to the decrease of pulp viscosity. The added transition metal ions were equivalent to the intrinsic transition metal i- ons on degrading cellulose, and the inactivation of MgSO4 to the intrinsic transition metal ions was also equivalent to the added transition metal ions. MgSO4 reacted with NaOH to produce insoluble Mg（ OH）2, which inactivates the transition metal ions by physically encapsulating them either by adsorption or by the formation of coordination com- plexes to protect pulp cellulose. In addition, there was other protective mechanism working to protect pulp cellulose from degradation.