PRODUCTION OF PULP BY THE SODA-ANTHRAQUINONE PROCESS (SAP) WITH RECOVERY OF THE BOILING CHEMICALS

摘要

A process is proposed for the production of cellulose out of wood andannual plants, in which the digesting liquor contains free causticsoda, eventually sodium salts of alkyl benzenesulfonic acids, ofaromatic or aliphatic carboxylic acids.By addition of anthraquinone or its derivatives to the digestingliquor, the delignification is improved. The limitation of quantitiesfor price reasons is eliminated, because anthraquinone is resistant towet oxidation and can be reintroduced into the digesting process. Thesolubility and therefore the effectiveness of anthraquinone isimproved by the use of sulfonic acid salts.For the recovery of the digesting chemicals contained in theblack liquor, it is proposed that the solubilized lignin isprecipitated with mineral acid or carbon dioxide, thateventually the hemicelluloses are separated by ultrafiltrationand the resins by extraction and that the residual organiccompounds, except the sulfonates and the carboxylates, areburned in an aqueous phase with air and/or oxygen. The solutionof chemicals, containing no more wood decomposition products,can by caustification of the carbonates be re-transformed intocaustic soda and after partial crystallization of the aliphaticcarboxylates be used for the cycle of pulp production. Thesodium acetate isolated by crystallization can by means ofmembrane electrolysis be split in acetic acid and sodiumhydroxide. The caustic soda is reintroduced to the digestingprocess, the acetic acid is treated separately.