Tanning materials and process for their recovery from the waste liquors obtained by the digestion of wood from deciduous trees for the manufacture of chemical woodpulp

摘要

Tanning materials are produced by adding to the waste liquors from the sulphite digestion of the wood of deciduous trees, especially beech, hot concentrated viscose spinning bath wastes containing alkali metal sulphates, separating calcium sulphate, reacting the solution with cation exchangers in the hydrogen form, concentrating and heating to 150 DEG C. the solution now containing free ligneous acids, particularly sulphonic acids, adding stabilizers, e.g. 2 per cent naphthalene sulphonic acids or their homologues, and finally atomizing the solution, when the solids content is 40-60 per cent by weight, e.g. by a rotating disc, in a drying tower to produce a voluminous powder. The hygroscopicity of the powder may be reduced by adding 0.2 per cent turkey red oil. The tanning materials may be dissolved in water and dialyzed through a viscose membrane.