Lignin alkaline degradation

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). 

Robert E, Gellerstedt G, Bardet M (1986) Carbon-13 NMR analysis of lignins obtained after sulfonation of steam exploded aspen wood Nord Pulp Pap Res J 3 18-25 Tanaka J, Kondo T (1957) Alkaline degradation products of protolignin Parupu Kami Kogyo Zasshi 11 29-33... 

Fundamental. Figure 14 illustrates a general scheme for the alkaline degradation of hydrolyzable ether units. The reaction of phenolic units (40) is initiated by the phenoxide ion (41) to yield a quinonemethide intermediate (42) with elimination of the a-ether unit R,. This elimination reaction occurs quite readily for an a-aryl ether unit (in 1 M NaOH at 25°C) [326], whereas the a-ether linkage of a lignin-carbohydrate model was shown to be stable under the same conditions [304]. 

Smaller environments can exist even within one of these microenvironments. For example, within one piece of wood associated with metal, there can be regions of an electric field that would cause hydrolytic or alkaline degradation of cellulose or lignin. 

By use of a peroxide under alkaline conditions, Bailey and Dence (129) produced a sharp increase in the carbonyl content of lignin but also induced a 16 to 17 percent loss of methoxyl groups as methanol. Further, production of ethanedioic, 1,3-propanedioic, 1,4-butenedioic, and 2-methor - 1,4-butanedioic acids verified extensive degradation of the lignin. This degradation occurred at... 

Both the sulfite and alkaline (kraft) methods can be modified to produce high purity chemical ceUulose. These pulps, usuaUy in the form of "dissolving pulps," are not only mosdy free of lignin and hemiceUulose, but the molecular weight of the ceUulose is degraded. This increases solubUity in alkah and provides desired viscosity levels in solution. These dissolving pulps are used to make derivatives such as sodium ceUulose xanthate [9051 -13-2] via alkah ceUulose, and various esters and ethers (see Cellulose esters Cellulose ethers). 

Sodium chlorite has also been used for treatment and removal of toxic and odorous gases such as hydrogen sulfide and mercaptans. Chlorine dioxide from chlorite is also useful for microbial and slime control in paper mills and alkaline paper machine systems (164,165). The use of sodium chlorite in textile bleaching and stripping is well known. Cotton is not degraded by sodium chlorite because the oxidation reactions are specific for the hemiceUulose and lignin components of the fibers. 

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