Process of making sulfonated lignin-based compositions, sulfonated lignin-based compositions so-obtained and their use

A process for preparing a dispersant composition comprising a sulfonated lignin, comprising:

• preparation of a lignin-containing aqueous suspension having a solids content from about 15 wt % to about 45 wt % and a pH from about 6 to about 12, by mixing a lignin with water;
• heating the lignin-containing aqueous suspension to at least about 65° C. and not more than about 95° C. under stirring to obtain a heated lignin-containing aqueous suspension;
• sulfonation of the lignin to obtain a sulfonated lignin-containing mixture, by adding a sulfonating agent to the heated lignin-containing aqueous suspension, the sulfonating agent generating a sulfite ion, a bisulfite ion or a mixture thereof in the aqueous suspension, the sulfonation being performed under stirring at a sulfonation temperature of higher than 100° C. and not more than about 160° C., at a sulfonation pH of from about 8.5 to about 11 and using a molar ratio of the sulfonating agent to the lignin between about 0.1:1 to about 0.6:1 on a sulfite to monomeric lignin sub-unit basis, wherein sulfonation reaction time is between 7 hours and about 12 hours;
• and
• cooling the sulfonated lignin-containing mixture to produce the dispersant composition of sulfonated lignin, wherein the dispersant composition of sulfonated lignin is used in gypsum manufacturing, drilling fluids, coal or agricultural products.