Alkaline pulp

T. I. Obiaga, "Lignin Molecular Weight and Molecular Weight Distribution during Alkaline Pulping of Wood," Ph.D. thesis. University of Toronto, Canada, 1972. 

Kraft Process. The dominant chemical wood pulping process is the kraft or sulfate process. The alkaline pulping Hquor or digesting solution contains about a three-to-one ratio of sodium hydroxide, NaOH, and sodium sulfide, Na2S. The name kraft, which means strength in German,... 

P. E. Shick, paper presented at TAPPI Conference on Alkaline Pulping and Secondary Fibers, Washiagton, D.C., Nov. 7—10,1977. 

L. D. Starr and co-workers, TAPPI Alkaline Pulping Conference Preprints, 1975, p. 195. 

D. W. Reeve, Pulp and Paper Manufacture, Vol. h. Alkaline Pulping, The Joint Textbook Committee of the Paper Industry, TAPPI Press, Atianta, Ga., 1989, p. 438. 

Quinone methides formed during, for example, alkaline pulping reactions may have other mechanisms for rearomatization. Most commonly, in 8-0-4-, 8-5-, and 8-8-quinone methides QM1-QM3 (Fig. 12.2), retro-aldol elimination of formaldehyde to give styryl aryl ethers or stilbenes is common.40 Retro-aldol reactions using a strong base, for example, diazabicycloundecene (DBU) in CH2CI2 can also provide these compounds conveniently at room temperatures.41 3... 

The quinone methide can also be generated in situ, at least in aqueous NaOH, directly from the peracetate, as hydrolysis of the phenolic acetate is faster than the benzylic acetate (see an example in Section 12.5.3). This method was used to demonstrate the addition of anthrahydroquinone (AHQ) and anthranol to (actual polymeric) lignin quinone methides in studies elucidating the anthraquinone (AQ)-catalyzed 8-0-4-aryl ether cleavage mechanisms in alkaline pulping.64-66... 

Cleavage of 8-0-4-ethers in alkaline pulping is also facilitated by HS as used in kraft pulping.98 The major mechanisms (Fig. 12.8b) are via addition to the quinone methide QM1 to give adduct 19, followed by anchimerically assisted fragmentation via a thioepoxide 20. 

Miksche, G. E. Lignin reactions in alkaline pulping processes (rate processes in soda pulping). In Chemistry of Delignification with Oxygen, Ozone, and Peroxides Nakano, J. Singh, R. P.,Eds. Uni Publishers Co Tokyo, Japan, 1980 pp. 107-120. 

Landucci, L. L. Quinones in alkaline pulping. Characterization of an anthrahydroqui-none-quinone methide intermediate. Tappi 1980, 63, 95-99. 

Cationic flotation of malachite, using mono- and diamines in alkaline pulp, was also examined. Malachite floats readily using mono-amines under laboratory conditions. 

Demecarium bromide, 4 360t Dementholized mint oil (DMO), 24 514 Demerara Sugar, 23 482 Demethanizer overhead expander, 10 616 Demethanizers, 10 613-614 Demethoxylation, during alkaline pulping, 21 23-24... 

Figure 3.15 Mechanism of aryl ether cleavage during alkaline pulping.

In contrast to alkaline pulping, the acetyl groups of the hemicellu-loses are relatively stable at low pH, as are the glucuronic acid residues of the xylans. The main effect of high temperature and low pH is the hydrolysis of the glycosidic linkages in the polysaccharide... 

Kleinert, T. N. Alkaline Pulping Studies VI. Discussion of Results and the Principles of Rapid Delignification. Tappi 48, 477—451 (1965). 

The effect of color production from carbohydrate transformation in an alkaline pulping process, such as kraft pulping, is illustrated in Table III. Cotton linters, which originally had a brightness of 90.5%, were treated for 4 h at 180° with kraft liquor, with and without additives. Brightness was measured on paper made from the resulting, washed pulp. 

One modification that pertains to the present book is the role of anthraquinone (AQ) in the pulping process. Under conditions of alkaline pulping, carbohydrates in the wood reduce AQ into an anion-radical (AQ ). Experiments with lignin quinonemethide as a model compound showed that the AQ anion-radical caused fragmentation of the quinonemethide (Scheme 8.23). 

Other abundant carbohydrates, such as hemicelluloses and pectin, are usually highly branched and thus not very suitable for fiber and film production. Hemicelluloses and some pectins are also acetylated in the native state, which makes them more resistant to enzymatic hydrolysis (20,21) and changes their solubility properties (9-77,75). Branching does not, however, preclude their utilization in such potentially large markets as thickeners and adhesives. Xylans, for example, show such a strong adhesion to cellulose fibers that they are very difficult to remove completely by both acidic and alkaline pulping processes (22). 

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