Sodium lignosulfonate manufactuering by sulfite pulping

Lignosulfonates stem from sulfite pulping processes, which are typically characterized by the pH of the processes and the bases used. The typical pH of the sulfite pulping process ranges ,neutral sulfite semichemical pulping (NSSC) processes are performed at pH 5–7.

The conditions of pulping processes impart different properties to lignosulfonates. The most commonly used bases are sodium and calcium, although magnesium or ammonium may also be employed.In the sulfite pulping process, the two main reactions that occur to solubilize lignin are sulfonation and hydrolysis.

During this process, the loss of a hydroxyl group or cleavage of the α-ether linkage occurs to form a quinone methide intermediate with either phenolic or nonphenolic substrates via a benzylic cation (hydrolysis).Next, sulfite ions present in solution add to this intermediate structure at the α position to form benzyl sulfonic acid units (sulfonation), which contributes to increasing the solubility of the lignosulfonates.

Alternatively, a condensation reaction may occur between the benzylic carbon of one molecule and the meta-carbon (6th) position of the aromatic ring of another molecule, due to the presence of the benzylic cation; this may prevent the sulfonation reaction because it occurs at the α position.

Sodium carbonate or sodium hydroxide, calcium oxide, or a substituted calcium hydroxide. This method is relatively rare, because sodium carbonate or sodium hydroxide, is usually higher than the price of calcium oxide or calcium hydroxide.

After sulfite pulping, lignosulfonates are removed from pulp through filtration and remain in the spent liquor of the pulping process. In addition to lignosulfonates, the spent liquor of the sulfite pulping process contains hemicelluloses and residual pulping chemicals,wherein lignosulfonates account for 50–80 wt % of the total solids in the mixture, hemicelluloses constitute up to 30 wt % and inorganics represent roughly 10 wt %.

Due to the wide range of conditions under which sulfite pulping can be conducted and, as a result lignosulfonates produced, lignosulfonate structures may vary considerably. However, a full lignosulfonate model structure has also been proposed by Matsushita and may be found elsewhere.

Additional information on lignin and lignosulfonate structures and modification/biological engineering pathways for the purpose of biorefinery valorization has been covered extensively in recent years.

Sodium lignosulfonate Application

Due to their unique properties, lignosulfonates have a wide range of uses, such as animal feed, pesticides, surfactants, additives in oil drilling, stabilizers in colloidal suspensions, and as plasticizers in concrete admixtures.However, the majority of pulp mills employ kraft technology for pulp production, and thus, kraft lignin is more readily available for value-added production. In this regard, the sulfonation of kraft lignin to produce sulfonated kraft lignin has been practiced.