Kraft lignin production process

A limited amount of lignin is used as the binder for "glass wool" building insulation. It is applied to the hot glass as the ammonium salt solid recovered from the kraft paper production process and allows the glass fibers to bind to one another when the fiber pads are spun or formed. 

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. 

Every year the U.S paper industry produces over 33 million metric tons of kraft lignin (1). Most of this biomass is burned as fuel but small amounts are used as binders, asphalt additives, or cement additives. Larger fractions of this waste would be used in other industrial or commercial processes if an economical way existed to convert lignin into a marketable product with sufficient profit margin to compensate for the loss of the fuel. 

Mild oxidation of kraft lignin dissolved in 1-2N NaOH at 70°C. was studied by Raff and Tomlinson (29) some years ago. By using this process, they observed remarkable changes in the solubilities of the oxidized products in organic solvents (e.g., decrease in acetone solubility) and changes in flow properties. These and other findings indicate that condensation occurs between lignin molecules (/, 77, 22). 

Essentially all of the lignin commercially available is isolated as byproducts from either the sulphite or the kraft process. Table II gives a very conservative idea of annual lignin production in the United States (2) and worldwide 36). 

Knowing that sulfonation of aromatic compounds is a reversible process, can you think of a way to remove the sulfonate groups from Kraft lignin The product would be an analogue of organosolv lignin. 

As a component of whole biomass, lignin is obtained through an isolation process. Various lignins are available commercially. For instance, kraft lignin is a by-product... 

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