Production of pulp by the soda-anthraquinone process (SAP) with recovery of the cooking chemicals

摘要

A process for the production of cellulose from wood and annual plants is provided where the digesting liquor contains free caustic soda, sodium salts of alkyl benzenesulfonic acids, and of aromatic or aliphatic carboxylic acids. By the addition of anthraquinone or its derivatives to the digesting liquor, the delignification is improved. Anthraquinone is resistant to wet oxidation and can be reintroduced into the digesting process. The solubility and, therefore, the effectiveness of anthraquinone is improved by the use of sulfonic acid salts. For the recovery of the digesting chemicals contained in the black liquor, solubilized liquor is precipitated with mineral acid or carbon dioxide and the hemicelluloses are separated by ultra filtration. The resins are separated by extraction with the residual organic compounds, except for the sulfonates and carboxylics, being burned in an aqueous phase with air and/or oxygen. The solution of chemicals containing no further wood decomposition products can, by caustification of the carbonates, be transformed into caustic soda and after partial crystallization of the aliphatic carboxylics used for the cycle of pulp production. The sodium acetate isolated by crystallization can, by membrane electrolysis, be split into acetic acid and sodium hydroxide. The caustic soda is reintroduced to the digesting process, while the acetic acid is treated separately.