FI57245C - SAETT ATT RENA AVLOPPSVATTEN INNEHAOLLANDE CELLULOSAFIBRER - Google Patents

Description

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National Board of Patents and Registration (44) Nlhttvlkslpuon ja aud. | Ulk * i * un pvm__

Patent- och registerstyralsen '' An * 6kan utltgd och utl. * Krifi *> published 31.03.80 (32) (33) (31) Pyydetty atuolkau * —Bagird priority 22.02.72

Sweden-Sweden (SE) 2166/72 (71) AB Casco, Box 11010, 100 6l Stockholm 11, Sweden-Sweden (SE) (72) Einar Sigurd Hecktor, Lidingö, Helge Storström, Saltsjöbaden,

Gert Walter Ludwig Eaelböck, Stockholm, Sweden-Sverige (SE) (7 * 0 Oy Borenius & Co Ab (5M

The invention relates to a new way of separating cellulose fibers from waste water. Preferably, the method can be used to treat wastewater from a fibrous industry, e.g. the paper and board industry. These industries produce large amounts of waste water, which contains a fine fibrous material, so-called zero fibers.

Several methods are already known for precipitating various impurities of said type of waste water, e.g. by means of aluminum sulphate, possibly by adding synthetic polyelectrolytes, or by means of natural polymers, e.g. bone glue. U.S. Patent No. 3,141,816 discloses a process for treating papermaking wastewater using polyethylene oxide as a precipitant. DE-A-1,920,590 further discloses a process in which a polymer having a plurality of reactive groups and a polyfunctional crosslinking agent reactive with this polymer is added to the wastewater in combination.

It is known from Swedish patent publication 223,094 to precipitate impurities in wastewater with the aid of phenol-formaldehyde resin. This method has proven to be particularly useful in the manufacture of paperboard, where the precipitated slurry can be returned to the 57245 2 manufacturing process and in which the phenolic resin also acts as a binder for the paperboard.

The process of this patent is carried out by adding a phenol-formaldehyde resin to alkaline wastewater, wherein the phenol-resin is in a water-soluble form. The pH is then lowered, for example by means of an aluminum sulphate solution, until the phenolic resin is no longer soluble in water and the phenolic resin precipitates and other suspended matter is taken up. The formed flocs can then be separated by known methods, e.g. by sedimentation or foaming.

To accelerate sedimentation or foaming, polyelectrolytes such as polyacrylamides, polyacrylates, polyethyleneimines, etc., or cationic starch are usually added, whereby the flocs accumulate.

The efficiency of this method is very variable, which depends on the fact that the organic substances dissolved or suspended in the wastewater vary both quantitatively and qualitatively. Variations in the concentration of metal ions, e.g. aluminum or sodium, in water also affect the result. In addition, aggregation appears to be dependent on water temperature.

Synthetic polyelectrolytes are expensive and often less effective. Cationic starch is difficult to handle because the solution must be prepared every day. The storage stability of such a solution has proven to be 2H per hour. If this time is exceeded, the aggregation effect deteriorates.

According to the method of the present invention, the above-mentioned difficulties are avoided. The method becomes simpler, operational reliability increases, capital costs and chemical costs decrease.

According to the invention, it has surprisingly been found that the aggregation of phenol-formaldehyde flakes is considerably improved if an aqueous solution of a high molecular weight polyether is used together with the phenolic resin.

The method according to the invention means a method which is further defined in the appended claims.

Polyethylene oxide agglomerates the flakes almost instantly into large, very cohesive agglomerations which are particularly well suited for foaming, but which can also be sedimented if desired.

Instant aggregation means that the fibers in the wastewater are separated from the water in a very short time and can thus be removed, resulting in a clear aqueous phase. Since the separation time of the impurities as a whole is very short, the advantage is obtained that the separation equipment can be made relatively small and thus it also becomes cheap.

This surprisingly positive result is explained by the fact that polyethylene oxide together with phenolic resin probably forms a complex, resulting in a rapid increase in the size of the agglomeration. The complexes are relatively very stable, which is why the agglomeration formed can be subjected to relatively high mechanical stresses without decomposing it. In addition, a flocculant is obtained which, despite its mechanical action, is rapidly regenerated, a phenomenon which is often very difficult to achieve by ordinary flocculation with aluminum sulphate and synthetic polyelectrolytes.

The polyethylene oxides used according to the invention are water-soluble polyethylene oxides having a molecular weight greater than 50 ° C. The best results are obtained with polyethylene oxide having a molecular weight greater than 100,000. The upper limit is not decisive. Good results have been obtained with polyethylene oxide having a molecular weight of 10 million,

The polyethylene oxide is suitably added to the effluent to be treated as a very dilute aqueous solution after flocculation has begun. Suitable dosage amounts are about 0.01 to 100 mg / l, preferably 0.1 to 20 mg / l, based on the effluent. Of course, other amounts of additives may also be considered, depending on the amount of wastewater impurities, but this area is often the most practical and economical. The cap is not important, but is chosen for cost reasons.

57245 n

In the process according to the invention, a phenol-formaldehyde resin is added to the effluent, and while the phenol-formaldehyde resin and impurities form flakes, a solution of high-molecular-weight polyether water is added. The agglomerates thus formed are then separated from the water purification technique in a known manner, for example by centrifugation, sedimentation, flotation or filtration.

The addition of the phenol formaldehyde resin can be carried out in various known ways depending on the properties of the water and the resin and is not the main object of the present invention. For example, in the production of a bonded cellulosic material such as paperboard, paper, etc., the effluent is generally acidic, and the addition of phenol formaldehyde resin then causes the resin to precipitate, whereby the impurities flocculate. In the case of alkaline or neutral effluents, such as sawmill effluents containing bark press debris, acidification may be necessary to precipitate the phenol formaldehyde resin.

The phenolic resin used in the process of the invention is a water-soluble resin which precipitates as the pH decreases. The amount of resin added is not essential and can vary within wide limits and is determined in a known manner taking into account the amount of wastewater impurities. The amount of phenolic resin should normally be greater than about 0.03 kg, preferably about 0.1 kg of dry resin per 1 m of wastewater, and is preferably 0.03 to 1 kg of dry resin per 1 m per wastewater. The upper limit is not relevant, but is chosen for cost reasons.

It is also conceivable to use a limited amount of phenol formaldehyde resin, which precipitates on contact with wastewater. The order of addition of the phenol formaldehyde resin and the polyethylene oxide is not relevant in many cases. Thus, it is also conceivable that polyethylene oxide is added before the phenol formaldehyde resin precipitates.

Example 1 Flotation test A. 1 liter of board mill effluent was placed in a cylindrical, graduated beaker. The water had fibers as a dry matter of h. 1% and was cloudy.

5 57245 2 ml of an aqueous solution of phenol formaldehyde resin (Casco 159 * +, Sweden) with a phenolic resin dry matter content of 31% was added with stirring.

Then, 100 ml of air-saturated water and 5 ml of a polyethylene oxide solution (molecular weight 300,000) having a polyethylene oxide dry matter content of 0.1% were added. At the end of the mixing, the now accumulated flocs began to rise to the surface of the liquid, giving clear water to the bottom of the beaker.

The height of the clear water column was measured at various times from the end of mixing. The height as a percentage of the total height of the water column is shown in Table I.

B. For comparison, the procedure described in Example 1A was performed, except that no polyethylene oxide was added. The results are shown in Table I.

C. For comparison, the procedure described in Example 1A was performed, except that the addition of phenol formaldehyde was omitted. The results are shown in Table I.

Table I

% clear water after time

Example. c _1 mxn._5 mm._30 mxn.

1 A 50 90 90 1 B 0 0 x) 1C 0 0 0 x) sedimentation

Example 2 Sedimentation test A. 1 liter of board mill effluent was placed in a graduated cylindrical beaker. The dry matter content of the wastewater, which was fibers, was about 1% and the water was cloudy.

2 ml of an aqueous solution of the same formaldehyde resin used in Example 1A and 5 ml of a polyethylene oxide solution (molecular weight 5,000,000) having a dry matter content of 0.1% were added with stirring. When stirring was stopped, the accumulated flocs began to sediment, resulting in clear water at the top of the beaker.

6 57245

The height of the clear water column was measured at different times after the end of the mixing. The height is expressed as a percentage of the height of the entire water column in Table II.

B. For comparison, the same experiment as in Example 2A was performed, except that no polyethylene oxide was added.

C. For comparison, the same experiment as in Example 2A was performed, except that no phenolic resin was added. The results are shown in Table II.

Table II

% clear water after time

Example *. c ori _1 mxn._5 mm._30 mm.

1 A 25 60 75 i 1 B 5 35 65 1C 0 0 0

As shown in Tables I and II, the combination of phenolic resin and polyether gives much better results for the accumulation of impurities than either component alone. As shown in Examples 1C and 2C, the use of polyether alone as a flocculant does not cause any agglomeration over 30 minutes.