METHOD OF PREPARING SYNTHETIC TANNER Russian patent published in 2001 - IPC

FIELD: leather industry. SUBSTANCE: invention relates to technology of production of synthetic tanners (syntans) used in leather industry when manufacturing clarified waterproof leathers both for soles and for uppers. Synthetic tanner is prepared by condensation of dihydroxydiphenyl sulfone with formaldehyde and lignosulfonate. Aqueous suspension of dihydroxydiphenyl sulfone is prepared by mixing preliminarily crushed sulfone with water at 60-70 C and stirring suspension for further 15 min to obtain to form homogeneous mixture, which is condensed with formalin fed at flow rate 7-9 l/min in amount 30 l in total. Mixture is heated to 80-85 C and kept for 0.5-1.0 h, after which sodium hydroxide is added at 80-85 C in amount 8-18.5% to the first condensation product until pH 8.2-9.2 is achieved ensuring complete dissolution of dihydroxydiphenyl sulfone. Second condensation is carried out by adding formalin to alkaline product at 80-85 C and flow rate 7-9 l/min in amount 6.1% of the weight of anhydrous dihydroxydiphenyl sulfone, after which temperature is raised to 102-104 C and maintained during 3 h. Second condensation product, phenol-sulfone-formaldehyde resin, is dispersed in lignosulfonate preheated to 40-45 C in amount corresponding to 160-165% of tanning substances based on the weight of anhydrous dihydroxydiphenyl sulfone. Mixture is heated to 96-98 C and kept at this temperature for 2-3 h until resistance of product to sulfuric acid acidification is reached. Dispersion is cooled to 70-80 C and acidified with 15-17% sulfuric acid to pH 3.8-4.5 to give product, which is dried, labeled, and packaged. EFFECT: improved quality of tanner and eliminated presence of free phenol coming with dihydroxydiphenyl sulfone.