锌基化合物催化木质素液相解聚研究

Study on Liquid Phase Depolymerization of Lignin Catalyzed by Zinc-based Compounds

关键词:  木质素  解聚  液化率  均相催化剂  催化

Key Words:lignin  depolymerization  liquefaction rate  homogeneous catalyst  catalytic

摘要:采用酸析絮凝法从蔗渣碱法制浆黑液中提取木质素并对其进行理化分析；针对蔗渣木质素反应活性低且难溶的缺点，在NaOH/H₂O₂溶液体系中，研究了Zn、ZnO、Zn(NO₃)₂和ZnAc 4种催化剂催化高浓（质量分数10%）木质素解聚反应的效果。结果表明，蔗渣木质素的酚羟基含量较高（2.81 mmol/g），数均分子质量较大（Mn =11270)；锌及其化合物均可将木质素解聚成酸可溶性化合物，其中，ZnAc的催化效果最显著，木质素液化率达40.9 %，为空白样的2.68倍；添加NH₃·H₂O可使ZnAc转化为相应的锌氨配合物，添加苯酚可减少木质素醌式中间体的重聚，在优化条件下，木质素液化率可进一步提高至84.2%；木质素解聚产生的不溶性物质以焦炭为主，液化产物包括小分子芳香族化合物和木质素分子链段（Mn=3058，分子质量分布为1.570）。

Abstract:Bagasse lignin （BL） was extracted from bagasse soda pulping black liquor by acid precipitation. Aiming at the shortcomings of BL such as low reactivity and solubility in uti1ization， four kinds of catalysts， such as Zn， ZnO， Zn（NO₃）₂， and ZnAc， were used to catalyze BL liquefaction reaction in NaOH/H₂O₂ solution at high lignin concentration （mass fraction of 10%）. The results indicated that BL was oligomers with rich phenolic hydroxyl group content （approximately 2.81 mmol/g） and broad molecular weights （Mn =11270）. The BL could be depolymerized into soluble compounds effectively by zinc and its compounds， and ZnAc had the best catalytic effect， with a BL liquefaction yield of 40.9%， which was 2.68 times that of the blank. The catalytic active center was converted into the corresponding zinc-ammonia complex by adding NH₃·H₂O， and the repolymerization of lignin quinoid intermediates in the NaOH/H₂O₂ solution system could be reduced by adding phenol. The liquefaction yield of BL could be further improved to 84.2% under the optimized conditions. SEM-EDS and GPC showed that the insoluble material produced by depolymerization was mainly coke， and the liquefied products included small molecular aromatic compounds and lignin chain fragments with number average molecular weight and molecular weight distribution of 3058 and 1.570， respectively.