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

FIELD: leather industry. SUBSTANCE: synthetic tanner (syntan) is prepared by common condensation of shale phenols with formaldehyde and lignosulfonate followed by dispersing of resulting resin in the same lignosulfonate. In particular, shale phenols are mixed with lignosulfonate in presence of 3-5% sulfuric acid for 2 h at 40 C until pH 2.0- 2.5 is attained. Resulting mass is subjected to polycondensation by gradually adding 5.5% of formaldehyde, stirred at 45-52 C, and kept at this temperature for 1 h to give resin. The latter is dispersed in the same lignosulfonate preheated to 40-50 C. Dispersion is heated to 85-95 C, stirred at this temperature for 4.5 h, and evaporated. Remaining tanner is crushed and packaged. Free phenol level in final product is 0.5%. EFFECT: reduced free phenol level.