Kappa number

By far the most commonly used oxidation method is the corrected permanganate number test (26) in which the number of mL of 0.1 KMnO consumed by 1 g of oven-dried pulp under specified conditions (kappa number) is deterrnined (TAPPl Historical Method T236 hm-85). Typical kappa numbers for representative pulps are shown in Table 3. 

Technology has been introduced for on-line estimation of the kappa number based on absorption of ultraviolet light (35). This breakthrough ia optical sensor technology permits closed-loop feedback control of digesters from on-line measurement of the kappa number. 

CI2 on pulp = kappa factor x pulp kappa number... 

Dayal, B. S., MacGregor, J. F., Taylor, P. A., Kildaw, R., and Marcikio, S., Application of Feedforward Neural Networks and Partial Least Squares Regression for Modelling Kappa Number in a Continuous Kamyr Digester, Pulp Paper Can., 95(1) 26 (1994)... 

Paulonis, M. A., and Krishnagopalan, A., Kappa Number and Overall Yield Calculation Based on Digester Liquor Analysis, Tappi J., 71(11) 185 (1988)... 

Figure 6.1 The acid group content of pulps expressed as an ion exchange capacity as a function of kappa number (measure of lignin content) for Kraft and sulfite pulps.

In the pulp and paper industry, UV-vis spectroscopy proves helpful in answering many related questions (e.g. around yellowing of pulp), Kappa number monitoring,alkyl xanthate decomposition, etc. 

W. Shen, X. Chen, Online monitoring of kappa number during batch pnlping by visible spectroscopy, Ind. Eng. 

In the enzymatic treatments, enzyme preparations from different origins have been shown to be rather similar with respect to kappa number reduction, yield and brightness. Unpurified enzyme mixtures from strains of Aspergillus and Bacillus have mainly been studied 53). It appears clear that pure endoxylanase brings about a major part of the overall effect in the treatment (Table II). 

Endoxylanase produced by a transformant strain of Escherichia coli has been shown to decrease the kappa number and increase the brightness of pulp in an enzymatic pretreatment followed by chemical extraction (27). Beta-xylosidase, on the other hand, had no effect in the treatment. The mannanase produced by Bacillus suhtilis was found to be equally effective as the xylanase. The specificities of mannanases produced by two different organisms, however, differed considerably 49). Enrichment of the culture broth of Streptomyces olivochromogenes, containing mainly endoxylanase, with different pure enzymes or enzyme mixtures acting on side chains and other hemicelluloses, resulted only in slight increases in brightness and in kappa number reduction (55). 

Table II. Reductions of kappa numbers after peroxide delignification of en matically pretreated pine kraft pulps using of different en me preparations...

A 25-50% charge of hydrogen peroxide to lignin corresponds to ca. 2-4% H2O2 on pulp having a Kappa number of about 50. This is within normal bleaching practice. 

There are many control challenges in this process. These include strong nonlinearity, distributed system, long deadtimes, and a feedstock that varies significantly because of its biological source. The key variable is kappa number (degree of delignifica-tion), which cannot be measured online, so it must be estimated from secondary measurements. 

J Value in parenthesis is kappa number corresponding to lignin content... 

Klason lignin = kappa number x 0 15 Sulfite pulps... 

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