Chemical pulping processes

Table 9. Cooking Conditions for the Kraft Chemical Pulping Process...

Kraft chemical pulp process, 13 94 Kraft lignins, 15 19-20 applications of, 15 19-20 Kraft paper process... 

Wood contains a small proportion (usually less than 5%) of components which are extractable by organic solvents such as ethanol or dichloromethane. The proportion of these extractives varies in hardwoods and softwoods and also between species. Although many of these substances are removed during the chemical pulping process, some may still be retained in the final sheet of paper. Their chemical composition is very varied, and they include alkanes, fatty alcohols and acids (both saturated and unsaturated), glycerol esters, waxes, resin acids, terpene and phenolic components. The proportion which remains in pulp and paper depends upon the pulping process used. In general, acidic components such as the resin and fatty acids are relatively easily removed by alkali by conversion to their soluble... 

The pulping processes in use at present are all relatively old and have generally been evolved from empirical experimentation. Excellent recent books arc available on the chemical technology of pulping 22, 26, 102, 115, 127, 128, 138) and the two major chemical pulping processes have been thoroughly reviewed 150, 151). 

Various modifications have been made to the conventional chemical pulping process to increase the extent and selectivity of delignification. Delignification occurs through the... 

Aho, W. (1983). Advances in chemical pulping processes in progress. In Progress in Biomass Conversion, Vol. 4, Academic Press, New York. 

Since the prices of petroleum products have soared, valorization of natural resources has intensively attracted the attention of researchers in different fields. To fully utilize wood, which is a renewable raw material, one must make better use of its 25-30% lignin content which forms the principal dissolved material in the spent liquor of chemical pulping processes. The annual production of sulfite pulp in Canada is approximately 2.6 million tons (data based on 1979), thus, at least one million tons of lignosulfonate is produced, representing a potential resource of raw material for other uses. However, among 35 sulfite mills in Canada, only two or three of them possess a recovery system for spent liquor, that means a very small portion of lignosulfonate has been recovered. The recovered lignin has been... 

TABLE 15.6 Chemical Pulping Processes Classified by Operating pH, and Pulp End Uses... 

Not generally used as a full chemical pulping process, but may also be used for the production of fine papers. Details of this process are included here to demonstrate the pulping versatility of sulfite ion over the full range of pH conditions. 

The kraft, or sulfate process is today the preeminent chemical pulping process. In Canada alone, 80% of all the chemical pulp produced is by this method, and worldwide some 85% of the total is via this route. The current prominence of this pulping procedure warrants a rather more complete discussion of the details than devoted to the other chemical pulping methods. 

Both pulping and papermaking are energy intensive processes. Mechanical pulp production requires large amounts of eleetrieal energy. Chemical pulping processes on the other hand use principally thermal energy and ehemicals. Semichemical pulps are intermediate in their requirements. 

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