Production Kraft lignin

Typical compositions for softwood and hardwood kraft blackhquors are shown in Table 10. Most commercial kraft lignins are sulfonated kraft lignins or lignin amines. A few nonsulfonated products are, however, available. 

Applications of Kraft Lignins. Because of the high fuel value of black Hquor, kraft lignin products are generaUy used in high value... 

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. 

Once lignin is separated from other plant products, it is not now widely used in resource recovery. Extensive studies on the modification of lignin have been made(24) because of the enormous mass of kraft lignin produced each year by the pulp and paper... 

Chaudhari, S.T., Ferdous, D., Dalai, A.K, Bej, S.K, Thring, R.W., and Bakhshi, N.N. (2000). Pyrolysis and Steam Gasification of Westvaco Kraft Lignin for the Production of Hydrogen and Medium Btu Gas, Abstracts Progress in Thermochemical Biomass Conversion, Tyrol, Austria, 17-22 September. 

Experimental evidence has indicated that 7-radiation can also be used to graft styrene onto kraft lignin to give a product with similar solubility properties as polystyrene. The reaction seems to be promoted by methanol... 

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. 

It is becoming apparent that wood components, especially lignin, are chemically modified by solvents during wood dissolution, and that the resulting wood tars or pastes become highly reactive. Attempts have therefore been made to prepare effective adhesives, moldable resins and other products from wood after dissolution in phenols or polyhydric alcohols. This review presents recent progress on wood dissolution, and on the preparation of epoxy and phenol resin adhesives from kraft lignin. 

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). 

Generally, the starting materials used in the commercial production of activated carbons are those with high carbon content, such as wood, lignite, peat, and coal of different ranks [175,176], But, over the last years, growing interest has now shifted to the use of other low-cost, and abundantly accessible, agricultural byproducts, such as coconut shells, rockrose, eucalyptus kraft, lignin, apricot stone, cherry stone, and olive stone to be converted into activated carbons [176],... 

Most of the research on the macromolecular chemistry of lignin has been concentrated on iignosulfonates and kraft lignin because of the insolubility of lignin in its native state. The polymer properties are of importance for the evaluation of the technical applicability of lignin products. For theoretical considerations, see Sections 3.2.2 and 3.2.3. 

The consumption of effective alkali in a kraft cook corresponds to about 150 kilogram sodium hydroxide per ton of wood. As a result of the alkaline degradation of polysaccharides, about 1.6 equivalents of acids are formed for every monosaccharide unit peeled from the chain. Of the charged alkali, 60-70% is required for the neutralization of these hydroxy acids, while the rest is consumed to neutralize uronic and acetic acids (about 10% of alkali) and degradation products of lignin (25-30% of alkali). 

Numerous attempts have been made to produce other low molecular weight products from lignin by subjecting concentrated kraft black liquors directly to various treatments, including hydrogenation, oxidation, or only heating in the presence of excess alkali. 

Large quantities of hydroxy acids as well as acetic and formic acids are formed during kraft pulping (Tables 10-3 and 7-8). Among hydroxy acids from softwood, glucoisosaccharinic acid predominates. Especially when considering that the heat value of these hydroxy acids is only 25-50% of that of kraft lignin, their recovery seems motivated, but adequate markets have not yet been established for these products. Liberation of the aliphatic acids... 

Mathias, A. L. and Rodrigues, A. E., Production of vanillin by oxidation of pine kraft lignins with oxygen. Holzforschung 1995,49 (3), 273-278. 

---