Influences of 2-ethylanthraquinone on lignin degradation in alkaline cooking of Eucalyptus pellita wood

The impact of 2-ethylanthraquinone (2-EAQ) on alkaline cooking of Eucalyptus pellita wood was examined by analyzing pulp yield, kappa number, the structure and weight-averaged molecular weight (Mw) of dissolved lignin in black liquor and residual lignin in pulp (RL). During soda cooking under 23% of active alkaline (AA) condition, adding 0.06% 2-EAQ reduced the kappa number by 12 points compared to cooking without it. The addition of 0.06% 2-EAQ to kraft cooking increased pulp yield by about 4% at about 19 of kappa number compared to the no addition. The analysis of lignin structure by using semiquantitative heteronuclear single quantum correlation nuclear magnetic resonance (HSQC NMR) showed that the addition of 2-EAQ promoted β-ether cleavage during alkaline cooking and reduced peeling reaction of polysaccharides and prevention of the elimination of γ-OH of lignin to form enol ethers and stilbenes. Overall, the addition of 2-EAQ promoted the degradation of lignin to lower molecular weight compounds, with a more pronounced effect observed in soda cooking than in kraft cooking. Under optimal conditions, the delignification efficiency and pulp yield of soda-EAQ pulping were comparable to kraft cooking.