Abstract: The invention proposes a process which enables separation of aromatic polymers which can be precipitated by acidification, as can be found especially in waste water from cellulose production, from an alkaline solution in a reliable manner and in pure form. To achieve good separation capacity, especially by filtration, it is proposed that the polymers be precipitated by reducing the pH at a relatively low temperature, typically between 15 and 60° C., and the dispersion be subsequently reheated until it passes into filterable form, typically between 50 and 95° C. The product separated in this way for example by filtration can be washed and can be dried at a high temperature, especially up to 110° C., without becoming black.

Abstract: 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.