12.2.2.1 Origin and Isolation

Lignosulfonate is the resulting lignin from acid sulfite pulping of wood, which was the dominant process for cellulose production until it was surpassed by the kraft process in the 1940s. Sulfite pulps account now for less than 10% of the total chemical pulp production. In this process, sulfites (SO32-), or bisulfites (HSO3-) are the pulping agents depending on the pH [1, 18]. The counter ion can be sodium, calcium, potassium, magnesium, or ammonium, which could change the behavior of the lignin product. Rather than splitting of b-O-4 structures and lib­eration of hydroxyl phenolic groups, the main reaction during sulfite pulping is the introduction of sulfonic groups in Ca and Cy of C3-alquil lateral chain of ppus

a Values are reported to oven-dry weight of lignin material b Values corrected for ash and sugar content c Values reported to the non-condensed moiety of lignin

d Two distinct fractions of lignosulfonate [63]; the phenolic hydroxyl groups (OHph) per ppu were calculated based on data of the Ref. [63]

LKWest kraft lignin supplied by MeadWestvaco Corp. Indulin AT kraft lignin supplied by MeadWestvaco Corp., Сити 27 IIP kraft lignin supplied by Borregaard Lignoteck, LKBoostS Kraft lignin from softwood isolated by Lignoboost process, supplied by Innventia AB, LSBor Lignotech DP257 (high molecular fraction of a calcium softwood lignosulfonate supplied by Borregaard Lignotech, Norway, LOrgsB organosolv beech wood lignin supplied by Fraunhofer, Germany, Alcell Organosolv lignin from mixed hardwoods (maple, birch, and poplar) produced by Repap Enterprises, Inc, LKEg Eucalyptus globulus kraft lignin obtained from laboratorial kraft pulping (at industrial operating conditions) and isolated by acidification, LKBoostH kraft lignin isolated by Lignoboost process supplied by Innventia AB, LSEg Magnesium lignosulfonate of Eucalyptus globulus’, sulfite liquor provided by Caima, S. A. Portugal and isolated as described in literature [63], LOrgsMxG organosolv lignin from Miscanthus x Giganteus (perennial grass), Sarkanda nonwood lignin obtained from a soda pulping-precipitation process supplied by Granit SA

(Fig. 12.3), the sulfonation, and the cleavage of a-aryl ether linkages (a-O-4) [1, 18]. Sulfonic groups increase the hydrophilicity of the lignin fragments, con­ferring them water solubility, allowing their removal from the polysaccharide matrix. In phenolic b-aryl ether structures, the initial sulfonation in the a-position may be followed by sulfidolytic cleavage of the b-aryl ether bond, but the extension of the reaction is lower than in kraft pulping [18].

Different methods have been developed for the separation of lignosulfonates from the sulfite liquor (namely from the dissolved carbohydrates) and for sepa­rating various molecular weight fractions. The traditional industrial process for recovery lignosulfonates is the Howard process, where lignosulfonate is precipi­tated in different stages from sulfite liquor by addition of lime [23]. Fermentation and yeast growth have been used to remove main sugars, allowing further utili­zation of lignosulfonates for several proposes. For lignin separation and frac­tionation, ultrafiltration [43-46], chromatographic processes [47] as adsorption in chitin [48], extraction with amines [49], liquid membranes [50] and combination of processes [51, 52] have been attempted.