Alkali consumption of aliphatic carboxylic acids during alkaline pulping of wood and nonwood feedstocks

Abstract

The carbohydrate degradation products have been examined, which are formed during the conventional kraft pulping of a softwood, hardwoods, bamboo, and wheat straw as well as soda and soda-anthraquinone pulping of wheat straw. The focus was on “volatile” acids such as formic and acetic acids and “ nonvolatile ” hydroxy monocarboxylic and dicarboxylic acids. The different consumption profiles were obtained for the charged alkali required for the neutralization of these aliphatic acids depending on the feedstock and the cooking method. The relative composition of the acid fraction in the black liquors of softwood and hardwood and nonwood feedstocks showed characteristic variations. However, in the case of wood kraft pulping, the variations in cooking conditions (effective alkali 19 – 21 % and cooking temperature 155 – 170 ° C) had no significant effect on the acid composition. The total amount of volatile and hydroxy acids formed during pulping at a typical target κ number level for each feedstock ranged from 78 to 174 kg ton -1 based on o.d. feedstock. It was highest in birch kraft pulping and lowest in wheat soda-anthraquinone pulping.