NaOH协同Pd/C选择性解聚木质素β−O−4键

Selective depolymerizationβ−O−4 linkage of lignin over Pd/C and NaOH

β−O−4醚键是木质素结构中含量最丰富的单元间连接键型,研究高效断裂β−O−4的催化体系对木质素解聚制备单酚具有重要意义。本研究以β−O−4型二聚体模型化合物为原料,结合GC-MS、GC-FID、HSQC NMR表征手段,考察炭负载金属催化剂、反应温度、时间、氢气初始压力等因素对二聚体β−O−4键的断键活性以及单体收率的影响。结果表明,NaOH与炭负载金属催化剂存在协同作用,可以增强β−O−4断键活性。其中,NaOH与Pd/C协同效果最佳,二聚体解聚单体产物从44.1%提高至83.4%。机理研究表明,NaOH协同Pd/C能有效抑制二聚体发生C_(α)羟基的脱除,显著提升二聚体β−O−4的断键选择性,从而提高了单体产物的收率。NaOH协同Pd/C催化体系对其他醚键(α−O−4)同样存在优异的断键能力。因此,在所做实验的最佳条件下,NaOH协同Pd/C催化体系能高效解聚碱木质素制备单酚化合物,单体产物收率高达37.5%,苯甲醇类选择性高达48.8%。

β–O–4 is the most abundant linkage in the lignin structure.It is of great significance to convert lignin into monophenols by breaking theβ−O−4 linkage.Therefore,β−O−4 dimer model compound was used as raw materials in this paper.The effects of metal catalysts,temperature,time and hydrogen pressure on the conversion of dimer and yield of monophenols were investigated by GC-MS,GC-FID,HSQC NMR characterization methods.The results show that NaOH and carbon-supported metal catalysts have a synergistic effect which can enhance the breakage ofβ−O−4 linkage,and the best promotion effect is obtained over Pd/C and NaOH with the monomer yield increases from 44.1%to 83.4%.NaOH and Pd/C can inhibit the removal of C_(α)−OH of the dimer and enhance the breakage ofβ−O−4 linkage effectively,leading to the increment in monomers.The NaOH and Pd/C catalytic system also shows excellent performance to the breakage ofα−O−4.Under the best conditions,alkali lignin is converted into monophenols over NaOH and Pd/C with the yield of 37.5%,and the selectivity of benzyl alcohol is as high as 48%.