木质素磺酸盐碱性过氧化氢降解及结构表征

通过表征受碱性过氧化氢降解的木质素磺酸盐,探索高效低耗的木质素降解条件。木质素磺酸盐与含有H2O2的0.5、1.0、2.0 mol/L的NaOH溶液分别在90、170℃下反应2 h。结果表明:碱性过氧化氢处理后木质素磺酸盐的Mw(重均相对分子质量)和Mn(数均相对分子质量)降低,而在170℃,1 mol/L NaOH溶液条件下获得最大程度的降解。木质素磺酸盐的相对分子质量在降解后分布相对集中,这表明木质素磺酸盐可直接用于开发木质素基材料而无需进一步分离。用碱性过氧化氢降解后,甲氧基摩尔分数降低。在170℃、2 mol/L NaOH溶液条件下4步加入过氧化氢,降解得到的木质素甲氧基摩尔分数下降57.4%。碱性硝基苯氧化的结果也表明在170℃下用2 mol/L NaOH溶液和4步添加H2O2处理后会得到最低的香草醛和香草酸产率,表明该条件下非浓缩的木质素结构被有效破坏。FTIR结果显示木质素的芳香结构消失。木质素磺酸盐利用碱性过氧化物降解,最佳条件是在2 mol/L NaOH溶液和170℃条件下,分4步添加H2O2。

Alkaline Hydrogen Peroxide Degradation and Structural Characterization of Lignosulfonates

We characterized the lignosulfonate decomposed with alkaline hydrogen peroxide to gain the better condition of degradation.Lignosulfonates were decomposed with 0.5,1.0,and 2.0 mol/L NaOH containing H2O2 at 90℃and 170℃for 2 h.The Mw and Mn of lignosulfonate were decreased after alkaline hydrogen peroxide treatment,and the maximum degradation was obtained at 170℃in 1 mol/L NaOH.The molecular weight of the lignosulfonate distributes homogeneously after degradation,suggesting that the lignosulfonate could be directly used to develop lignin-based materials without fractionation.The methoxyl content was decreased after degradation with alkaline hydrogen peroxide.Methoxyl content was decreased by 57.4%at 2 mol/L NaOH under 170℃and four-step adding hydrogen peroxide.The alkaline nitrobenzene results also gave lowest yield of vanillin and vanillic acid after treated with 2 mol/L NaOH and fou-step H2O2 addition under 170℃,indicating non condensed lignin structures were destroyed thoroughly.FTIR results showed the disappearance of aromatic structures of lignin.In conclusion,lignosulfonate degraded with alkaline peroxide,and the best condition would be 2 mol/L NaOH and under 170℃,and four-step H2O2 addition.