Spent bleach liquor

When bleaching wood pulp in a paper mill, the amount of leftover or residual hydrogen peroxide present in the spent bleach liquor can be important. Sometimes the bleach liquor is used in a second bleach or recycled back to the first bleach. Also, the residual peroxide level can indicate whether the bleach liquor makeup needs adjusting. Laboratory scale bleach tests are performed on the wood pulp, and the residual peroxide levels are checked by titration of the spent bleach liquors using potassium iodide and sodium thiosulfate. By monitoring the residual peroxide levels of these bleaches, the bleach liquor makeup can be adjusted, giving the best level, as needed by each paper mill. 

As far as quantitative chemical derivatization GC analysis is concerned, it is necessary to mention especially the work of Gehrke and his collaborators, who specified the fundamental concepts of quantitative GC analysis combined with the chemical derivatization of sample compounds and applied them to the accurate determination of the twenty natural protein amino acids and other non-protein amino acids as their N-TFA-n-butyl esters [5 ], the urinary excretion level of methylated nucleic acid bases as their TMS derivatives [6], TMS nucleosides [7] and other investigations. Further examples include a computer program for processing the quantitative GC data obtained for seventeen triglyceride fatty acids after their transesterification by 2 NKOH in n-butanol [8], a study of the kinetics of the transesterification reactions of dimethyl terephthalate with ethylene glycol [9] and the GC-MS determination of chlorophenols in spent bleach liquors after isolation of the chlorophenols by a multi-step extraction, purification of the final extract by HPLC and derivatization with diazoethane [10]. 

Although the GC separation of methyl ethers [16] of phenols has been described, these derivatives are nowadays mainly employed only in special instances, e.g., for increasing the sensitivity of the analysis. The determination of chlorinated phenols in spent bleach liquors from paper mills was reported by Lindstrom and Nordin [17]. A water sample was extracted stepwise with diethyl ether at various pH values, after preliminary purification by means of HPLC, phenols were converted into ethyl ethers by reaction with diazoethane in isooctane—ethanol (9 1) and good reproducibility was achieved. 

TABLE 8-4. Composition of the Organic Material in Spent Bleach Liquor from Chlorination and Alkali Extraction Stages (Pine Kraft Pulp)a... 

The spent bleach liquors are complicated mixtures of reaction products, only some of which have been identified. A simple classification according to the type of compounds present has been made in Table 8-4. As can be seen, lignin degradation products dominate in the spent liquors from chlorination and alkali extraction. Because of extensive demethylation of lignin, considerable amounts of methanol are present in the chlorination liquors. The amount of low molecular chlorinated aromatics is very low, but since the most toxic compounds are included in this fraction, clarification of its complicated composition has been the subject of intensive research. 

Pfister, K., and Sjostrom, E. (1979). Characterization of spent bleaching liquors. Part 6. Composition of material dissolved during chlorination and alkali extraction (OCE sequence). Pap. Puu 61, 619-622. 

Lindstrom K, Osterberg F (1984) Characterization of the high molecular mass chlorinated matter in spent bleach liquors (SBL) Part 1 Alkaline SBL Holzforschung 38 201-212 Miksche GE, Yasuda S (1976) Zur Struktur des Lignins der Buche (Fagus silvatica L ) Liebigs Ann Chem 1323-1332... 

Lindstrom K, Nordin J (1976) Gas chromatography-mass spectrometry of chlorophenols in spent bleach liquors J Chromatogr 128 13-26... 

Occurrence of alkyl polychloronaphthalenes (RPCN) in spent bleach liquors was first time reported in 1979 [8], Their structure was deduced to contain one methyl and one isopropyl group [8] which indicates origin from wood. Later analyses indicated that most common RPCNs in kraft pulp mill effluents and sludges were mono- to tetramethyl polychloro naphthalenes (C1-4PCN) [41-45]. In sludges their total contents were 28-72 ng g1 dw and in effluents only trace levels of a few ng 1 1 [42, 45]. Their origin was suggested to be chlorination of alkyl naphthalenes abundant in oil-based defoamers used in pulp mills [42]. 

Tin-119 C Sn) NMR spectroscopy has been used to characterize bis(tri-butyltin) oxide derivatives of various lignin-related phenols and lignin-containing material isolated from spent bleach liquors [9]. Signals of the model derivatives were well resolved, but the broad signals displayed by actual spent liquors limited the utility of the spectra. 

Lindstrom, K. and F. Osterberg. 1980. Synthesis, X-ray structure determination, and formation of 3,4,5-trichloroguaiacol occurring in kraft mill spent bleach liquors. Can. J. Chem. 58 815-822. 

Martinsen, K., A. Kringstad, and G.E. Carlberg. 1988. Methods for determination of sum parameters and characterization of organochlorine compounds in spent bleach liquors from pulp mills and water, sediment and biological samples from receiving waters. Water Sci. Technol. 20[2] 13-24. 

Eklund, G., B. Josefsson and A. Bjdrseth. 1978. Determination of chlorinated and brominated lipophilic compounds in spent bleach liquors from a sulphite pulp mill. Glass capillary column gas chromatography-mass spectrometry-computer ana ys s aad ideuiifkaiion. J. Chromatogr. 150 161-169. 

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