Anthraquinone-alkali pulping

Figure 7-38 illustrates the recovery and conversion of the kraft cooking chemicals. In the case of sulfur-free pulping (soda process, soda-oxygen process, and anthraquinone-alkali pulping) only sodium carbonate is recovered and chemical losses are compensated by adding sodium carbonate. The hydroxide-carbonate and lime cycles are the same as for the kraft process. 

The discovery that small amounts of anthraquinone (0.05-0.25% on wood) added to alkali liquors can enhance delignification and produce kraft quality pulp has been of great interest. Although the price of anthraquinone (AQ) is high and the chemical is not recovered, only small quantities are required, and the benefits outweigh the costs sufficiently that a number of mills around the world now routinely add AQ to the kraft pulp-wood digester. 

Chemical pulping Kraft, polysulfide kraft, prehydrolysis kraft Soda-anthraquinone (AQ) Acid sulfite, bisulfite, alkali sulfite-AQ Multistage sulfite 35-60... 

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