アルカリ性サルファイト・キノン蒸解におけるリグニンの挙動

Abstract

The sulfite-quinone cooking has been investigated as an alternative to the kraft process in terms of delignification, pulp yields, and pulp qualities. However, behaviors of lignin in this cooking have not been clarified, and there are few studies in which delignification selectivity and pulp qualities were compared at given delignification rates and H-factors with those of the soda-quinone and the kraft-quinone cookings. In this study, yezo spruce/saghalien fir mixed chips and beech chips were cooked by the three kinds of cookings under the conditions where the delignification at a given H-factor (cooking temp. : 170°C cooking time : 2 h) were equal. Pulp yields, handsheet strength properties, and characteristics of lignins in those pulps and black liquors were compared, and behaviors of lignin and mechanism of delignification in the sulfite-quinone pulping were discussed. In these experiments, 1, 4-dihydro-9, 10-dihydroxyanthracene sodium salt (DDA) was used as a quinone additive, and this sulfite-quinone cooking was called the alkaline sulfite-DDA cooking because sodium hydroxide, sodium sulfite, and DDA were used as cooking chemicals. The results are summarized as follows : (1) The alkaline sulfite-DDA cooking of yezo spruce/saghalien fir wood gave pulp of almost the same kappa no. 50 as the soda-DDA and the krart-DDA cookings. At kappa no. 50, the total pulp yields of the former were higher than those of the latter. However, the screened pulp yields of the alkaline sufite-DDA cooking were almost the same as those of the kraft-DDA cooking and slightly lower than those of the soda-DDA cooking because of its higher yields of screen rejects.(2) This cooking of beech wood gave pulp of kappa no. 26.4, but it had no advantage of pulp yields compared with the soda-DDA and the kraft-DDA cookings.(3) The contents of sulfonic acid group of lignin in pulps given by this cooking were about 0.1-0.2/phenyl propane unit.(4) Handsheet strength properties of this cooking were almost the same as those of the kraft-DDA cooking.(5) Gel chromatography indicated that the dissolved lignin of this cooking was richer in low-molucular lignin fractions than those of the other cookings.(6) Alkaline nitrobenzene oxidation of screened pulps and black liquors of this cooking gave higher yields of vanillin (soft wood) or vanillin and syringaldehyde (hard wood) than those of the others.(7) In the alkaline sulfite-DDA cooking, the condensation of lignin was depressed by the addition of sodium sulfite. This must be a reason why delignification is accelerated together with the increase of solubilyty of lignin with the cleavage of β-ether linkages by quinone compounds and the sulfonation by sulfite.