Bleaching spent liquor

Azarniouch and Prahacs have patented an electrochemical recovery procedure for NaOH and other valuable substances (lignin, organic compounds, H2S04, H2, 02 or 02/Cl2 mixtures) from spent liquors and bleach plant effluents [282]. 

Azarniouch MK, Prahacs S (1991) Recovery of NaOH and other values from spent liquors and bleach plant effluents, US 5,061,343 Chem Abstr 116 23226f... 

Table 2 Low-Molecular-Weight Organic Compounds Found in the Spent Liquors from Pulping and Bleaching Processes... 

Kringstad, K.P. Lindstrom, K. Spent liquors from pulp bleaching (critical review). Environ. Set Technol. 1984, 18, 236A-247A. 

Disposal of spent liquors from bleach plants represents a serious environmental problem which so far has defied practical solution. While the effluents from the production of unbleached pulp have been reduced drastically by introduction of a closed pulp washing system, a corresponding... 

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. 

It has been found possible to recycle bleach plant effluents as well as spent liquor from pulping, in the process regaining the chemicals required for pulping and bleaching [27]. 

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. 

KP Kringstad, K Lindstrom. Spent liquors from pulp bleaching. Environ Sci Technol 18(8) 236A-248A, 1984. 

McKague, A. B., M.-C. Kolar, and K. P. Kringstad. 1989. Nature and properties of some chlorinated, lipophilic, organic compounds in spent liquors from pulp bleaching. 2. Environ. Sci. Technol. 23 1126-1129. 

Paper and pulp mill condensate - 189, 206 Paper and pulp mill gas, noncondensable 203 Paper, bleach solutions - 541, 693, 694, 724 Paper, groundwood pulp stocks - 541 Paper machine - 204 Paper mill liquor - 204, 206, 539, 724 Paper, neutral sulfite Cooking liquor - 541 Pulp stocks - 542 Spent liquor - 542 Paper, paperboard waste 542 Paper, parchmentizing - 542 Paper pulp, bleached - 694 Paper pulp slurry 694 Paper, sizing solution - 543 Paper stock 694 Paper, white water Acid - 543 Groundwood - 543 Neutral sulfite - 543 Newsprint - 543 Paperboard 544 Soda - 544 Sulfate - 544 Peracetic acid - 30 Parachloride 230... 

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. 

Elforts have been made to characterize the nature and content of individual components that are present in the low-molecular-mass fraction of the total mill effluents, which include the spent chlorination and alkali extraction stage liquors [2,4]. Approximately 456 types of compounds have been detected in the conventional bleach effluents, of which 330 are chlorinated organic compounds [22]. The compounds may be lumped into three main groups, namely, acidic, phenolic, and neutral (Table 2). Acidic compounds are further divided into the five categories of acids fatty, resin, hydroxy, dibasic, and aromatic acids. The most important fatty acids are formic and acetic acids. The dominant resin acids are abietic and dehydroabietic acids. Among the hydroxy acids identified, glyceric acid predominates. Dibasic acids such as oxalic, malonic, succinic, and mafic acids are derived from the lignin and carbohydrate fraction... 

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