The delignification of birch chips during kraft pulping was investigated, targeting both the impregnation and cooking steps. Wood chips were impregnated using white liquor, white liquor + NaCl, water or NaCl aqueous solution. Then, the chips were cooked in batch autoclaves applying the same constant composition cooking conditions for all samples. Pulp and two fractions of black liquor (bulk liquor and centrifuged liquor representing the liquor inside the wood chips and fibers) were collected after different pulping times and analyzed for lignin and carbohydrate content. The dissolved wood components were precipitated from selected samples and characterized with respect to composition, molecular weight distribution and structural motifs. Cooking chemicals in the impregnation liquors led to faster delignification and xylan removal during cooking. Higher contents of lignin and xylan were measured in the lumen than in the bulk. The concentration profiles also showed accumulation of dissolved material in the lumen over time, suggesting significant mass transport limitation from lumen to bulk. Further analysis revealed higher fragmentation/degradation of dissolved material with increasing pulping time and in the bulk when compared to the lumen liquor, as demonstrated by the lower molecular weights and the changes in chemical shifts in the NMR spectra.

中文翻译：

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桦木片的硫酸盐蒸煮：孔隙中溶解的有机物质与散装液体之间的差异

研究了牛皮纸制浆过程中桦木片的脱木质素，针对浸渍和蒸煮步骤。使用白液、白液+氯化钠、水或氯化钠水溶液浸渍木片。然后，对所有样品应用相同的恒定成分蒸煮条件，在分批高压釜中蒸煮碎片。在不同制浆时间后收集纸浆和黑液的两部分（散装液和代表木片和纤维内的液的离心液）并分析木质素和碳水化合物含量。从选定的样品中沉淀出溶解的木材成分，并对其成分、分子量分布和结构图案进行表征。浸渍液中的蒸煮化学品导致蒸煮过程中更快的脱木质素和木聚糖去除。在内腔中测得的木质素和木聚糖含量高于本体中的木质素和木聚糖含量。浓度分布还显示随着时间的推移，溶解物质在管腔中积累，表明从管腔到本体的质量传输受到显着限制。进一步的分析表明，与内腔液体相比，随着制浆时间的增加，溶解材料的破碎/降解程度更高，如较低的分子量和 NMR 光谱中化学位移的变化所证明的那样。