Sulphite lignin

In addition to kraft or sulphite lignins, there are a number of other processes whereby lignin could potentially be recovered (e.g., by acidolysis, steam-explosion, organosolv, biological treatment, etc). The existing and potential processes for lignin recovery are described briefly in the following sections. 

Crude spent sulphite liquor in a concentrated form, or as a powder, is available as a product (Fig. 10.2), but purified forms of sulphite lignin have broader applications and higher value [8]. Such purified lignins are obtained by diverse techniques (sometimes involving the simultaneous recovery of co-products) such as ... 

In the sulphite pulping process wood cut into pieces is subjected to kiering in a calcium bisulphite solution under a pressure of 3-8 kg/cm2, at 120-145°C for 7-30 hr. The higher the temperature, the shorter the time of boiling. Substances accompanying cellulose dissolve in the liquor. Lignin is converted into a soluble lignin sulphonic acid. Cellulose is isolated from the solution, known as sulphite cellulose lye, and washed with water. 

According to the present theory (e.g. Zherebov [1]) most of the hemicelluloses, pentosans and hexosans are removed during sulphitation, because calcium sulphite is capable of forming addition compounds with pentosans. Complete removal of hemicelluloses is only possible however after lignins have been removed, as lignin seems likely to be chemically combined with hemicellulose and thus with pentosans or hexosans. Only rupture of these bonds and the separation of lignins makes it possible to attack the non-cellulosic polysaccharides (Heuser and Haug [2]). 

Gellerstedt, G., "The Reactions of Lignin During Sulphite Pulping", Svensk Paperstidn., 1976, 79, 537. 

Gellerstedt, G., and Gierer, J. (1971). The reactions of lignin during acidic sulphite pulping. Sven. Papperstidn. 74, 117-127. 

Wood, J. R., and Goring, D. A. I. (1973). The distribution of lignin in fibres produced by kraft and acid sulphite pulping of spruce wood. Pulp Pap. Mag. Can. 74, T309-T313. 

Kratzl K, Billek G (1957) Synthesis and testing of lignin precursors Tappi 40 269-285 Kyrklund B, Palenius I (1964) The total lignin content of sulphite pulps and its relation to the kappa number Pap Puu 46 513-520... 

Yang J-M, Goring DAI (1981) The phenolic hydroxyl content of the lignin residual in spruce wood cooked by sulphite and kraft Cellul Chem Technol 15 337-342... 

Beatson RP, Heitner C, Rivest M, Atack D (1985) Sulphite treatment of aspen Factors affecting the formation of carboxylate and sulphonate groups Pap Puu 11 702-708 Brauns FE (1952) The sulfonation of lignin In Brauns FE (ed) The chemistry of lignin Academic Press, New York, 359-393... 

Loras V, Loschbrandt F (1961) Determination of lignin in sulphite pulps Nor Skogind 7... 

Marth DE (1959) Studies on the lignin fraction of aspenwood pulps produced by sulphite-bisulphite cooking liquor systems Tappi 42 301-308... 

Bialski AM, Luthe CE, Fong JL, Lewis NG (1986) Sulphite-promoted delignification of wood identification of paucidisperse lignosulphonates Can J Chem 64 1336-1344 Bourbonnais R, Paice MG (1987) Oxidation and reduction of lignin-related aromatic compounds by Aureobasidium pullulans Appl Microbiol Biotechnol 26 164-169 Braithwaite A, Smith FJ (1985) Chromatographic methods Chapman and Hall, New York, 258-266... 

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). 

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