Description of an industrial oxygen-alkali delignification process of birch kraft pulp using dissolved material analysis

A detailed description of an industrial oxygen-alkali delignification process of silver birch (Betula pendula) kraft pulp was performed using dissolved material analysis and component material balances. The results revealed that the main reaction products formed in this delignification process are dissolved lignin, hydroxy acids, carbonate and oxidized sulphur-containing compounds. The amount of molecular oxygen and the quality of oxidized white liquor charged to the process both had a clear influence on the composition of the process liquor. The material balances corresponded to a pulp yield of 97-98%. It was estimated that 60% of the dissolved material originated from lignin-derived material. This study indicated that only versatile analysis of the dissolved material offers an appropriate way of clarifying the chemical performance of an industrial oxygen delignification process.