Lignosulfonate Sulfite Lignin

Lignin-SOjH + R,R2R3NH Cl — Lignin-SOJNH RiR2R3 + HQ 

Step 2 Extraction of complex with organic solvent Step 3 Regeneration of lignosulfonate 

Lignin-S03Na + NR,R2R3 + H20, where R, R2, R3 are hydrogen or alkyl groups. 

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Commercial lignosulfonates (also called lignin sulfonates and sulfite lignins) are by-products of the treatment of pulp. One of the methods of isolating and purifying them is to add excess slaked lime to spent sulfite liquor. This precipitates calcium lignosulfonates, which are removed by filtration [32.29]. 

Poly (lignosulfonic acid) Sulfite lignin Definition A metallic sulfonate salt... 

Lignins are most usually employed as various types of sodium lig-nosulfonate and are products of sulfite pulping. (Kraft lignins from the Kraft pulping process are also available.) They are used as dispersants, binders, sequestrants, and emulsifiers. Sodium lignosulfonate product variables include color, MW, and the degree of carboxylation and sulfonation on the lignin backbone. 

The use of the lignin fraction is much more cumbersome currently the best-known chemical of a real commercial importance is vanillin, which is obtained by oxidation of the black liquor. Another example is a product called spray-dried lignosulfonate (as sodium salt) obtained from the older, acidic sulfite pulping process. It is sold as a commercial product primarily as a concrete additive for enhanced strength. Since the cement industry is one of the big contributors of carbon dioxide emissions (due to the production of calcium oxide from calcium carbonate), the use of this renewable, wood-derived product not only is fossil-carbon neutral in itself but also reduces carbon dioxide emission due to the diminished need for cement in large infrastructures made of concrete. 

Lignin derivatives, sulfonated alkali lignin and sulfite lignosulfonates, are being used to increase tertiary oil recovery in pumped out oil wells replacing more expensive synthetic detergents. 

Since the prices of petroleum products have soared, valorization of natural resources has intensively attracted the attention of researchers in different fields. To fully utilize wood, which is a renewable raw material, one must make better use of its 25-30% lignin content which forms the principal dissolved material in the spent liquor of chemical pulping processes. The annual production of sulfite pulp in Canada is approximately 2.6 million tons (data based on 1979), thus, at least one million tons of lignosulfonate is produced, representing a potential resource of raw material for other uses. However, among 35 sulfite mills in Canada, only two or three of them possess a recovery system for spent liquor, that means a very small portion of lignosulfonate has been recovered. The recovered lignin has been... 

The majority of the material in sulfite spent liquors originates from lignin (lignosulfonates) and hemicelluloses (Tables 7-5 and 10-1). A variety of useful products can be isolated and prepared from these liquors (Table 10.-2)... 

Sulfite Process. The sulfite process uses a cooking liquor of sulfurous acid and a salt of the acid. Although calcium was the most widely used base at one time, it has been supplanted by sodium, magnesium, and ammonia. Lignin will react with the bisulfite ion (HSO3") under acidic conditions to form lignosulfonates that are soluble in water. For many years this was the preferred process because it produced pulps of light color that could easily be bleached, it used cheap chemicals in fairly limited amounts so that no recovery was necessary, and it was a relatively simple process to operate. 

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