造纸专业英语(1).ppt

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Reaction in Alkaline Cooking During kraft pulping lignin fragmentation is performed by the cleavage of aryl ether bonds and formation of new phenolic groups, which increase the hydrophilicity and solubility of lignin. The reactions of lignin in a kraft cook are complex and still not completely understood, but the main reactions leading to the lignin degradation in alkaline conditions have been well reviewed. The most important delignifying reaction in alkaline conditions is the cleavage of β-aryl ether linkages, which are the most prominent lignin structures. Reaction in Alkaline Cooking In kraft pulping conditions the reaction of hydrosulphide ions with quinone methides leads to the cleavage of β-O-4-linkages, whereas in the absence of hydrosulphide ions, such as in the soda cook, the dominating reaction is the elimination of γ-hydroxymethyl or β-proton, which leads to the formation of formaldehyde and enol ether structures. In addition to hydrosulphide ions, anthraquinone (AQ) and polysulphide (PS) have also been found to enhance the cleavage of β-aryl ether linkages. hydrosulphide 硫氢化物 methide 甲基化合物 hydroxymethyl 羟甲基 formaldehyde 甲醛 aldehyde 醛,乙醛 form- 甲酸,甲酰 enol【化】烯醇 anthraquinone 蒽醌 anthrahydroquinone 蒽氢醌 polysulphide 多硫化物 poly-表示“聚、聚合”之义 Reaction in Alkaline Cooking The cleavage of non-phenolic β-aryl ether bonds is the dominating and rate determining reaction in alkaline lignin degradation. The etherified β-aryl ether linkages are cleaved by hydroxide ions via an oxirane intermediate. This reaction is not affected by sodium sulphide or anthraquinone, but for example α-carbonyls have been shown to accelerate the cleavage of β-aryl ether linkages in non-phenolic lignin units. oxirane -ane -ene -yne 环氧 epoxide 环氧化物 carbonyl【化】羰基 carboxyl 羧基 carboxylic 羧酸的 Reaction in Alkaline Cooking Because the reaction is intramolecular, the stereostructure also affects the reactivity and the erythro form of the β-O-4 structure has been found to be m

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