CS258212B1 - A method of accelerating the sedimentation of the caustic sludge in the white liquor - Google Patents

Abstract

The solution relates to a method of accelerating the sedimentation process of caustic sludge in white liquor by adding an aqueous dispersion of cationically modified corn starch ether at an ambient pH above 13 and a temperature of 80 to 90 °C. Cationic modified corn starch is a starch glycidyl ether prepared by a substitution reaction after mixing in 1 to 10% by weight of an etherification agent, whereby 2-hydroxy-3-chloro-propyl-trimethylammonium chloride can be used as the etherification agent.

Description

258212 2

BACKGROUND OF THE INVENTION The present invention relates to a process for accelerating the process of sedimentation of a caustic sludge in white liquor by the addition of an aqueous dispersion of organic polyelectrolyte. Part of the kraft pulp technology is the regeneration of boiling white liquor, resulting in the causticization of green lime by lime. The chemical principle of causticization is sodium re-carbonate to sodium hydroxide by the action of calcium hydroxide. In the causticization process, the sludge, the main component of which is calcium carbonate. The sludge needs to be removed from the white liquor as its presence causes the encrustation of the conduit, and in the delignification process of the species of bituminous-rich woods, one of the factors causing condensation of these substances and thus the contamination of the pulp produced by impurities similar to asphalt impurities. There are a number of principles for removing the caustic sludge, of which sedimentation is most common. Usually, sedimentation takes place in special bulk containers, clarifiers.

The sedimentation process can be accelerated by the addition of various flocculants in aqueous solutions. For economic reasons, it is customary to use native potato starches in aqueous dispersion or thermally modified starches (ANGEVINE PA et al. Pulp & Paper No. 12, (1979) p. 128). Methods have also been described using synthetic polymeric materials, especially cationic in nature. Synthetic flocculants are made on a different chemical base.

These are polyacrylamide-type, modified polyethyleneimine-type polyelectrolytes, and other polymeric materials (G0L1K0VA T.G., SOKOLOVA T.M. et al. Bumažnaya Pramyšlenost No. 2 (1985), p. 18). However, with high alkalinity of the white liquor (pH above 13), ionization of the functional groups of cationic polyelectrolytes is suppressed and the flocculation effect is reduced.

The above mentioned drawbacks are eliminated by the method of accelerating the sedimentation of the caustic sludge by means of an aqueous dispersion of organic polyelectrolyte, characterized in that a dispersion of cationically modified maize starch ether is added to the white liquor in an amount of 10 to 40 g / l at a concentration of 10 to 40 mg / l. temperature of 80 to 90 ° C, at pHnad 13. Residues of unreacted starch in the white liquor also act as a retardant of wood-derived condensation substances in the delignification process.

It has been found that cationically modified corn starch added in an aqueous dispersion concentration of 10 to 40 g / l shows a sedimentation accelerating effect on caustic in the white liquor already at the addition of 10 mg of modified starch per liter of liquor. In addition to the aforementioned effect, the turbidity of the clarified white liquor is reduced, the filterability of the sedimented sludge during their further processing is improved, but mainly the network is not clogged with lime sludge through the filters of unbleached pulp, which directly increases the washing efficiency of the sodium components from the pulp and the increased performance of the washing filters.

By reducing the calcium carbonate content of the white liquor, the incrustation of the inner walls of the evaporators in the black liquor as well as the incrustation of the tubular circulation system of the cookers is substantially prevented, which provides increased time utilization in the boil. By reducing the calcium carbonate content of the cooking liquor, the process of delignification causes the wood to prevent the formation of centers causing precipitation of wood resins, thereby facilitating the action of the anti-inflammatory agent (talc) dosed at the last stage of the unbleached cellulose washing.

Cationically modified starches are used in the papermaking industry to apply fiber re-suspension to increase paper strength characteristics (MOELLER H. W. et al.

Paper Technology No. 4 (1965), p. 279), increased filler retention (RACZYNSKA Z. et. Al., Pegegland Papierniczy No. 3 (1966), p. 69), improved sagging (BURGH L. F. et al.

Pulp Paper Mag. Canada No. 18 (1970), p. 81). It is also known to use them with a nail section of a paper machine. (VOClLKA M., JAAS J. et. Al. Paper and Cellulose No. 10 (1981), p. 207). They are also used for surface sizing in a sizing press (TURNER C. W. et al. Paperboard and Packaging No. 7 (1972), p. 24). The form in which the cationically modified starch is applied varies according to the modification procedure used.

Claims (1)

SUBJECT OF THE INVENTION. Method for accelerating sedimentation of caustic sludge in white liquor by means of an aqueous dispersion of organic polyelectrolyte, characterized in that a dispersion of cationically modified corn starch ether in an amount of 10 to 40 mg / l, at a concentration of 10 to 40 g / l, is added to the white liquor. 80 to 90 ° C, at pH above 13.