Organic matter content in black liquor inside and outside chips during kraft cooking

摘要

The measurement of the organic matter content in the black liquor is a prerequisite for the development of a model which leads to an improved understanding of the driving physical-chemical reactions in a kraft cook. Traditional analytical methods such as total organic carbon or those based on the chemical oxygen demand are flawed because they do not correlate well with the actual organic matter content. This paper presents a new method for the determination of organic matter in black liquors based on the weight loss on ignition. Furthermore the method separates the bound liquor inside the chips from the surrounding free liquor, and it is shown that this distinction is significant as the concentrations of organic matter are not the same in these two regions. Thus, for a given cook, both the volume of the black liquor surrounding the chips, and the volume of the black liquor bound inside the chips, are analysed for organic matter. The total amount of organic matter that could be found in the liquor phase after kraft cooking using the proposed method was validated against the conventional pulp yield determination. For a series of 31 autoclave cooks the comparison resulted in a relationship where the correlation coefficient, r~2, was 0.991. This separation and analytical procedure is to be used as a first step in the development of a mathematical model of the cooking reactions and for calculating pulp yield in both laboratory and industrial environments.