| abstract |
Process of preparation of lignosulfonic acid derivatives, whereby, in a pressure and corrosion resistant closed container, the following steps are carried out: heating for 1 minute to 30 minutes, at temperatures within a range of 115 DEG C. to 160 DEG C., a mixture of a lignosulfonic acid aqueous solution having a pH value lower than 3, containing from 100 g to 600 g of the said acid per liter, with a multivalent-metals free oxidizing agent supplying from 0.5 g to 2 g oxgen per 100 g lignosulfonic acid to form a reaction mixture; neutralizing the reaction mixture with an alkaline solution having a pH value at least equal to 5, in order that the obtained transformed lignosulphonic acid, after concentration or desiccation in powder, may be directly used. |