Lignosulphonate, or lignosulfonate, or sulfonated lignin, (CAS No. 8061-51-6) are water-soluble anionic polyelectrolyte polymers: they are byproducts from the production of wood pulp using sulfite pulping. Most delignification in sulfite pulping involves acidic cleavage of ether bonds, which connect many of the constituents of lignin.
Sodium lignosulphonate or calcium lignosulphonate have very broad ranges of molecular mass (they are very polydisperse). A range of from 1000–140,000 da has been reported for softwood lignosulphonates with lower values reported for hardwoods.
Sodium Lignosulphonates, calcium lignosulphonate, megnesium lignosulphonate and ammonium lignosulphonates are recovered from the spent pulping liquids (red or brown liquor) from sulfite pulping.
The most widely used industrial process is the Howard process, in which 90–95% yields of calcium lignosulfonates (CAS number 904-76-3), are precipitated by adding of excess calcium hydroxide. Ultrafiltration and ion-exchange can also be used to separate lignosulfonates from the spent pulping liquid. A list of CAS numbers for the various metal salts of lignosulfonate is available.