FI90573B - Method for improving retention or purification of cellulose fiber suspensions or waste water in the paper, pulp and paperboard industry - Google Patents

Description

1 90573

The present invention relates to a method for improving the retention and / or purification of pulp fiber suspensions or effluents in the paper, pulp or board industry by treating them with a combination of polyol and formaldehyde formaldehyde formaldehyde formaldehyde formaldehyde formaldehyde formulation -10 nioxide and a cationic starch derivative or a cationic cellulose derivative.

Several ways are known in the paper, pulp and board industry to improve retention in the dewatering of pulp fiber suspensions by the addition of various polyelectrolytes such as cationic polyamine, cationic polyacrylamide and cationic cellulose derivative. Pulp fiber suspensions may contain, in addition to the pulp fibers, varying amounts of inorganic fillers, e.g., clay, dolomite lime and gypsum, inorganic and organic binders, lignin and hemicellulose. The addition of polyelectrolytes facilitates the flocculation of the products contained in the pulp suspension and this in turn promotes retention. West German Patent 2,549,089 also discloses the improvement of retention in the dewatering of pulp fiber suspensions using a combination of high molecular weight polyethylene oxide, phenol-formaldehyde resin, alternatively phenol-sulfur resin, and polyamide.

After the water has been removed from the pulp fiber suspension, large amounts of wastewater are obtained, which, even with good retention, contain smaller amounts of fine fiber, the so-called zero fiber, fillers and binder residues, and components dissolved from lignin and hemicellulose. Wastewater treatment is known to flocculate impurities by the addition of inorganic and / or organic polyelectrolytes 2 90S73 such as aluminum sulfate, iron chloride, polyacrylamide, polyacrylate, polyethyleneimine and a cationic starch derivative.

Canadian patent publication CA 1 004 782 5 also discloses the use of phenol formaldehyde in combination with high molecular weight polyethylene oxide to improve retention in the dewatering of pulp fiber suspensions. In both the dewatering of pulp fiber suspensions and the treatment of wastewater, the polyethylene oxide adduct facilitates the agglomeration of Flocks formed with phenol-formaldehyde resin, thereby facilitating retention and purification.

Although the combination of high molecular weight polyethylene oxide and phenol-liformaldehyde resin allows good retention and purification, it has been found that some of the fine fibers and colloidal particles and solute are not retained in the fibrous web or cannot be removed from the wastewater by the proposed procedure. Thus, there is a need for procedures that further improve retention and purification. Such problems occur e.g. when removing water from fiber suspensions obtained from recycled pulp or mechanical pulp or when treating waste water from these pulps or peelings. Thus, there is a need to provide procedures that further improve retention and purification.

It has now been found that retention and purification can be improved if, in addition to formaldehyde resin and high molecular weight polyethylene oxide, a cationic starch derivative or a cationic cellulose derivative is added to the fiber suspension or wastewater. The presence of a cationic starch derivative has been shown to improve the "traceability" of zero fibers and flocculated material present or formed during processing. When water is removed from the fiber suspension, zero fibers, binder particles, flocs, etc. become increasingly bound to the pulp fiber web, which means higher yields, faster dewatering, and cleaner wastewater. In wastewater treatment, it has been found that in the application of the invention, the zero fibers, binder particles, fillers, pigments, lig-5ine and hemicellulose agglomerate to a much greater extent than before into flocs. The flocs are very stable and easy to remove after sedimentation, flotation or centrifugation.

The molecular weight of the oral polyethylene oxide useful in the process of the invention should be greater than 500,000 and preferably greater than 2,000,000. No critical upper limit could be observed and thus good results have been obtained with polyethylene oxide having a molecular weight of 12,000,000. 5 has proved difficult to achieve due to chain shortening in manufacturing. The polyethylene oxide according to the invention is composed mainly of oxyethylene groups, but may have a smaller number of other groups / e.g. oxypropylene groups. The number of non-oxyethylene groups is limited by the condition that the polyethylene oxide must be water-soluble.

The phenol formaldehyde resin of the invention is relatively water soluble, although resins with limited solubility at neutral or basic pH values may be used. The resin usually precipitates at acidic pH values.

The cationic starch derivative used according to the invention is preferably potato, corn or wheat starch substituted with quaternary ammonium groups. The degree of substitution is preferably 0.01 to 0.1.

The cationic cellulose derivative becomes water-soluble by modification. The cationic cellulose derivative must be water-soluble and may contain, in addition to the above-mentioned cationic groups, lower alkyl groups such as methyl or ethyl groups and lower hydroxyalkyl groups such as hydroxyethyl, hydroxypropyl and hydroxybutyl groups. A suitable degree of substitution of the cationic groups of the cellulose derivative, preferably the quaternary ammonium groups, is 0.01 to 0.5 per anhydroglucose unit and the molecular weight is from about 10,000 to about 1,000,000.

The amounts of phenol formaldehyde resin, polyethylene oxide and cationic starch derivative or cationic cellulose derivative are not critical. The amount of addition is preferably adjusted according to the amount and type of zero fibers, fillers, binders-X0 substances, pigments, lignin and hemicellulose. The amount of phenol formaldehyde resin is normally more than 1, preferably more than 5 ppm, the amount of polyethylene oxide is more than 0.1 ppm, preferably more than 1 ppm and the amount of cationic starch derivative is more than 1, preferably more than 5 ppm based on wastewater. Suitable upper limits are about 100, 20 and 200 ppm of wastewater, respectively. Preferred addition amounts for retention are 0.01 to 0.5% by weight of phenol-liformaldehyde resin, 0.001 to 0.1% by weight of polyethylene oxide and 0.01 to 1.0% by weight of cationic starch derivative 20 or cationic cellulose derivative contained in the suspension. calculated on the basis of the ingredients. The ratio of phenol formaldehyde to polyethylene oxide is preferably 1: 5 to 50: 1 and the ratio of cationic starch derivative or cationic cellulose derivative to polyethylene oxide is preferably 1: 5 to 25 to 100: 1, regardless of whether the components are used for water purification or retention.

The three components of the invention may be added in any order. The cationic starch derivative and the cationic cellulose derivative may be added, for example, first, and then the phenol tormaldehyde resin and the polyethylene oxide, respectively. It is also possible to proceed by first adding a phenol formaldehyde resin and then a mixture of polyethylene oxide and a cationic starch derivative or a cationic cellulose derivative.

5,905 ^ 3

The following embodiments illustrate the invention and are not intended to limit the scope of the invention.

Example 1

800 ml of wastewater formed from a mixture of effluents from CTMP and board production was poured into a glass vessel. The pH of the wastewater was 6.5 and the dry matter content was 2.5 g per liter. The effluent was stirred at 500 rpm and a polyelectrolyte was added. After stirring for one minute, pheno-10 liformaldehyde resin was added, and after one additional minute, a high molecular weight ethylene oxide adduct was added with stirring at 500 rpm. After 10 seconds from the last addition, the stirring speed was reduced to 100 rpm and after another 50 se-15 cycles, stirring was stopped. The flocs formed in the effluent were then allowed to settle and then the clear phase was sampled and turbidity was measured nephelometrically. The chemicals added, their amounts and the clarification achieved are shown in Table 1.

It appears from the results that Experiments 2 and 3 of the invention achieved significantly better clarification than Experiment 1, which is in accordance with Canadian Patent CA 1,004,782. Compared to Experiment 1, the addition of polyelectrolytes other than the cationic starch derivative 25 did not improve the results.

Example 2 Wastewater obtained from the bleaching step of unbleached recovered paper was purified at 25 ° C in the same manner as in Example 1. The wastewater had a dry matter content of 2.5 g / l and a pH of 7. The added chemicals, their amounts and results are shown in Table 1. .

The results show that the addition of the cationic starch derivative or the cationic cellulose derivative according to the invention provides a significantly better purification than the conventional combination of phenol formaldehyde resin and high molecular weight polyethylene oxide. No improvement occurred with combinations containing phenol-formaldehyde resin and high molecular weight polyethylene oxide and other polyelectrolytes.

Example 3 5 The effluent from the bleached recovered paper scrubbing step was purified at 25 ° C in the same manner as in Example 1. The effluent had a dry matter content of 4.4 g per liter and a pH of 8. The chemicals added, their amounts and results are shown in Table 3. It appears from the results 10 that the experiments according to the invention achieved a significantly better purification than the use of phenol-formaldehyde resin alone or high molecular weight polyethylene oxide or a combination thereof.

Example 4 Retention tests were performed on a pulp suspension having a pulp fiber concentration of 0.55% by weight and a pH of 7 at 35 ° C. The composition of the pulp fiber was 60% scrubbed pulp, 30% sulfate scrap and 10% bleached sulfate pulp. Retention experiments were performed according to Britt-20. See TAPPI 56 (10), 46 (1973). The chemicals added, their amounts and results are shown in the table below. The results show that the results in the retention according to the invention were substantially better than in the comparative experiments.

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Claims (7)

11. O 5 7 3 • 1. A method of improving the retention and purification of pulp fiber suspensions or effluents in the paper, pulp and board industry by treatment with phenol-formaldehyde resin and high molecular weight polyethylene oxide, characterized in that the treatment with phenol-formaldehyde resin and high molecular weight polyethylene in combination with a cationic starch derivative or a cationic cellulose derivative. Process according to Claim 1, characterized in that the weight ratio of phenol formaldehyde resin to polyethylene oxide is 1: 5 to 50: 1 and the weight ratio of starch derivative or cellulose derivative to polyethylene oxide is 1: 5 to 100: 1. Process according to Claim 1 or 2, characterized in that the cationic groups of the starch derivative and the cellulose derivative are quaternary ammonium groups. Process according to one of the preceding claims, characterized in that the polyethylene oxide has a molecular weight of more than 500,000. Process according to Claims 1 to 4, characterized in that the degree of cationic substitution of the starch derivative is 0.01 to 0.1. Process according to one of the preceding claims 1 to 5, characterized in that the pulp fiber suspension is dewatered in the presence of 0.01 to 0.5% by weight of phenol formaldehyde resin, 0.001 to 0.1% by weight of polyethylene oxide and 0, 01 to 1.0% by weight of a cationic starch derivative or a cationic cellulose derivative. Process according to one of Claims 1 to 6, characterized in that the effluent is treated in the presence of more than 1 ppm of phenol formaldehyde resin, more than 0.1 to 12,575,573 ppm of polyethylene oxide and more than 1 ppm of cationic starch derivative or cationic cellulose derivative, calculated from the effluent. 13 90 573