Kraft cooking of birch wood chips: differences between the dissolved organic material in pore and bulk liquor

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