Kraft pulping conditions

Hansson, J.-A. (1970). Sorption of hemicelluloses on cellulose fibres, Part 3. The temperature dependence on sorption of birch xylan and pine glucomannan at kraft pulping conditions. Sven. Papperstidn. 73,49-53. 

Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide structure. Several representative substitution reactions are illustrated in Fig. 1.5. At moderate temperatures ( 100°C) and under mildly alkaline conditions, benzylic hydroxyl groups in phenolic units are converted to thiols by reaction with bisulfide (Q, Fig. 1.5). At higher temperatures and alkalinities, e.g., under kraft pulping conditions, the mercaptide group undergoes a series of transformations in which the sulfur is ultimately eliminated. 

Kim H (1985) The effect of kraft pulping conditions on molecular weights of kraft lignins. 

Ahvazi, B., and Argyropoulos, D. S., Thermodynamic parameters governing the stereoselective degradation of arylglycerol-P-aryl ether bonds in milled wood lignin under kraft pulping conditions, Nordic Pulp and Paper Res. J. 12(4), 282-288 (1997). 

DA Blythe, LR Schroeder. Degradation of a Nonreducing Cellulose Model, 1,5-Anydro-4-0- 3-D-glucopyranosyl-D-glucitol, under Kraft Pulping Conditions. J Wood Chem Tec/moZ 5 313-334, 1985. 

B C Ahvazi, DS Argyropoulos. Thermodynamic Parameters Governing the Stereoselective Degradation of Arylglycerol-P-aryl Ether Bonds in Milled Wood Lignin under Kraft Pulping Conditions. Nordic Pulp Pap Res J 12 282-288, 1997. 

Mielisch, H.J. Odermatt, J. Kordsachia, O. Patt, R. TCP bleaching of Kraft pulp Investigation of the mixing conditions in an MC ozone stage. Holzforshung 1995, 49, 445-452. 

Jaspers, C.J. Jiminez, G. Penninck, M.J. Evidence for a role of manganese peroxidase in the decolorization of Kraft pulp bleach plant effluent Phanerochaete chrysosporium effects of initial culture conditions on enzyme production. J. Biotechnol. 1994, 37, 229-234. 

Further examination of the results indicated that by invocation of Pearson s Hard-Soft Acid-Base (HSAB) theory (57), the results are consistent with experimental observation. According to Pearson s theory, which has been generalized to include nucleophiles (bases) and electrophiles (acids), interactions between hard reactants are proposed to be dependent on coulombic attraction. The combination of soft reactants, however, is thought to be due to overlap of the lowest unoccupied molecular orbital (LUMO) of the electrophile and the highest occupied molecular orbital (HOMO) of the nucleophile, the so-called frontier molecular orbitals. It was found that, compared to all other positions in the quinone methide, the alpha carbon had the greatest LUMO electron density. It appears, therefore, that the frontier molecular orbital interactions are overriding the unfavorable coulombic conditions. This interpretation also supports the preferential reaction of the sulfhydryl ion over the hydroxide ion in kraft pulping. In comparison to the hydroxide ion, the sulfhydryl is relatively soft, and in Pearson s theory, soft reactants will bond preferentially to soft reactants, while hard acids will favorably combine with hard bases. Since the alpha position is the softest in the entire molecule, as evidenced by the LUMO density, the softer sulfhydryl ion would be more likely to attack this position than the hydroxide. 

Hexenuronic acid (i.e., 4-deoxy-L-threo-hex-4-enopyranosyl-uronic acid) is formed under alkaline conditions by elimination of methanol from side chain residues in xylans [65] (Scheme 10). The reaction is promoted by both increasing alkali concentration and temperature [66,67]. After kraft pulping, only... 

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