SE440219B - POROS CATALYST, AND PROCEDURE FOR DISTRIBUTING A WATER BASED HYPOCLORITE SOLUTION BY USING THE CATALYST - Google Patents

Description

15 20 25 30 35 8006869-5 this technology has not found any major application. Furthermore, when fixed bed catalysts are exposed to effluent solutions containing both calcium ions and hypochlorite, such as effluents from the manufacture of dry bleaching or decolorizing chemicals, the catalyst rapidly loses activity due to calcium carbonate precipitation in the catalyst pores. Activation of a clogged catalyst is difficult.

It is therefore an object of the present invention to provide an efficient and economically acceptable catalytic method for decomposing hypochlorite contained in aqueous industrial effluents, including those containing dissolved and suspended calcium salts. Another object of the invention is to provide a catalyst for use according to the present invention, which catalyst is effective, non-polluting and has a long service life.

SUMMARY OF THE INVENTION: The present invention relates to catalyst pellets capable of decomposing hypochlorite, which pellets consist of a powdered active catalyst and a resin binder. The catalyst pellets according to the invention are particularly suitable for the treatment of waste water containing hypochlorite in a fixed bed and show improved resistance to disintegration compared with known tableted and extruded catalysts. The use of the present catalyst in the decomposition of hypochlorite in a fixed bed constitutes a second aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION: The aqueous solutions containing hypochlorite which can be treated according to the process of the present invention and with catalyst pellets described herein can be any aqueous solution containing hypochlorite ions, such as subchloric acid or salts of the subchloric acid alkalis, especially the alkalic acids. the earth metal salts. Although in the present description the term "catalyst pellets" is generally used, it is obvious that the catalyst can be used in both particulate form and the preferred pellet form. A common source of aqueous streams containing hypochlorite ions is the wastewater from scrubbing in a chlorine condensing plant, where the non-condensable tail gases are scrubbed with a sodium hydroxide solution to prevent residual chlorine from to get out into the atmosphere. This scrubber stream contains alkali metal hypochlorite, which must decompose before being released into public water. Other sources of aqueous wastewater containing hypochlorite which can be treated by the process of the present invention occur in the manufacture of chlorine-sodium hydroxide and dry bleaching or dry decolorizing chemicals.

The method of treating various chemical streams in a fixed or fixed bed reactor is well known and as such does not form part of the present invention. Correspondingly, a variety of catalytic materials are known which are suitable for the decomposition of hypochlorite ion. The use of these is only a part of the present invention. It is the special form of catalyst and its use in the decomposition of hypochlorite which forms the basis of the invention. According to the present invention, known catalysts for decomposing hypochlorite are combined with an organic thermoplastic resin binder to form a porous catalyst matrix in the form of small particles or pellets, which are used in the known process for decomposing hypochlorite in a solid bed.

Substances suitable for catalyzing the decomposition of hypochlorite include oxides or hydroxides of iron, copper, magnesium, nickel or cobalt. However, any substance which functions in a similar manner can be used in the catalyst pellets in question.

The resin binder, which constitutes the second essential component in the catalyst pellets according to the invention, can be Any of a variety of different organic thermoplastic resins. It is only essential that the resin is relatively stable for long periods of time under contact with hypochlorite and that it exhibits the ability to form a pellet which is relatively stable to mechanical disintegration as well as chemical disintegration in use. In particular, it has been found that polyolefins and halogenated polyolefins, e.g. polyvinylidene halides, are suitable. Representative examples of these materials are polyethylene, polypropylene, polytetrafluoroethylene and polyvinylidene fluoride. QUOSITY QUALITY 10 15 20 25 30 55 8006869-5 4 The ratio of the substance capable of decomposing hypochlorite to the organic resin binder can vary considerably but is usually in the range of 100 to 1:10. A ratio of from 1: 1 to 15: 1 is generally preferred. A weight ratio of about 5: 1 has been found to be suitable when the substance capable of catalyzing the decomposition of hypochlorite is cobalt oxide and the organic resin is one of a variety of thermoplastic polyolefins. The essential criterion for selecting the appropriate ratio is that a sufficient amount of thermoplastic organic resin must be present to obtain a matrix which is stable to mechanical handling, and that the amount of organic resin does not exceed the amount which allows penetration of the hypochlorite solution into the catalyst pellets in question.

The size of the pellets in question is not extremely critical.

What should be considered is ease of handling and the permeability of the said pellets. For this reason, extremely large pellets are undesirable due to the possible difficulty of hypochlorite to penetrate therein and the associated efficient use of the catalyzing component. Pellets in cylindrical shape with a diameter of about 5.2 mm and a length of about 4.8 mm have been found to be suitable for use according to the present invention. Smaller granule-type catalyst particles have also been used with greater efficiency than pellets due to the relatively larger surface area available. The preferred particle size is 18-35 mesh.

Said pellets are prepared so that finely divided catalysts for the decomposition of hypochlorite are intimately dispersed in the organic resin matrix. One way to accomplish this is to grind powdered catalysts and powdered organic resin, e.g. in a ball mill, form the intimately mixed powdered composition into tablets or pellets by compacting them in a conventional machine and then sintering said pellets at or around the softening temperature of the organic resin. It is desirable that heating be carried out at a sufficiently high temperature for sintering to take place, in which case, however, it should not be so high that the physical form of the pellet in question is destroyed. The granule-type catalyst particles have been prepared by crushing the pellets in question and sieving them to a certain size. _. 'I' ”N“ ï "" '--- = - ~ .m 10 15 20 25 30 35 8006869-5 råde. An equivalent catalyst can be prepared directly by extrusion followed by sintering, thus eliminating compaction.

The present invention can be used in the decomposition of hypochlorite effluents containing calcium ions. This poses a particular problem, as the calcium ion appears to contribute to catalyst deactivation by depositing calcium carbonate in the "catalyst pores". According to a particular aspect of the present invention, it has been found advantageous to remove calcium ions by precipitating calcium as an insoluble salt, such as calcium carbonate, which is removed before contacting the hypochlorite solution with the catalyst. However, it is also possible to process hypochlorite solutions containing calcium ions directly and to periodically regenerate the catalyst.

The following examples illustrate in more detail the preparation of the catalyst pellets according to the invention and their use in a fixed bed system for decomposition of hypochlorite solutions.

Example 1 A cobalt oxide powder on a silica support was prepared by slowly precipitating cobalt hydroxide from an aqueous solution of cobalt nitrate containing suspended diatomaceous earth by adding base. The product was washed with water, dried and calcined at M50 ° C for 2 hours. The resulting powder contained 35% by weight of cobalt as cobalt oxide.

To 15 g of the above powder is added 5 g of polyvinylidene fluoride press powder ("Kynar 401"). The mixture is placed in a ball mill of size OOO together with a quarter of the full capacity of ceramic balls and ground for 1 hour. The powdered mixture is tableted into cylindrical tablets about 3.2 mm in diameter and 4.8 mm long at 66 MPa, and the tablets obtained are sintered in an oven at 180 ° C for 1 hour. The polymer matrix tablets are very active in terms of hypochlorite decomposition and maintain their physical integrity indefinitely under the reaction conditions.

100 g of catalyst were charged to a fixed bed catalytic reactor. Simulated industrial effluent containing hypochlorite (prepared as described below) treated to remove soluble calcium (0.499% available chlorine) was passed through the uiMub ~ _.ø-yv ~ - '' V " In the cell at 2.00 ml / min, a starting solution containing 0.058% available chlorine was obtained, which corresponds to 88.4% conversion. of hypochlorite to chloride ion and oxygen.

The simulated industrial wastewater containing hypochlorite was prepared by dissolving 32.4 g of calcium hypochlorite (69.4% available chlorine), 166 g of sodium chloride and 74.1 g of calcium chloride in 1000 ml of distilled water. The resulting solution was clarified by sedimentation, and the hypochlorite content was determined by titration with sodium thiosulfate (-1 -1.25% available chlorine).

Other concentrations were prepared by successive dilutions.

Calcium-free hypochlorite solution was prepared by treating the above simulated industrial wastewater containing hypochlorite with a stoichiometric amount of sodium carbonate (1 mole of carbonate per mole of calcium). The resulting suspension was clarified by sedimentation, and the clear supernatant liquid was treated, after filtration, with the catalyst. šëêmhaliâ This example is identical to Example 1 except that nickel replaces cobalt.

Example 1 This example is identical to Example 1 except that polyethylene powder was used instead of polyvinylidene fluoride powder and the resulting tablets were sintered in an oven at 120 ° C for 1 hour.

The resulting polymer matrix tablets are active with respect to hypochlorite decomposition and maintain their physical integrity indefinitely under the reaction conditions.

Example 4 This example is identical to Example 1 except that the tetrafluoroethylene replaces the polyvinylidene fluoride powder and that the resulting tablets were sintered in an oven at 27,000 for 1 hour.

The resulting polymer matrix tablets are active with respect to hypochlorite decomposition and maintain their physical integrity indefinitely under the reaction conditions.

Catalyst samples prepared according to the procedures described in Examples 1-4 were evaluated using both 1% sodium hypochlorite solution (calcium free) and simulated industrial wastewater containing hypochlorite. With 1% sodium hypochlorite solution, no decreasing catalytic activity was measured during 4 weeks of continuous operation. No disintegration of the catalyst was noted, and the total cobalt content of the effluent was less than 0.5 ppm.

When simulated industrial wastewater containing hypochlorite was used for feed to the reactor, significant catalytic activity was lost in 48 hours. Catalyst deactivation can be attributed to calcium carbonate precipitation in the "catalyst pores". The catalyst activity was restored using the procedure described in Example 5.

Example 5 In a fixed bed catalytic reactor with a cross-sectional area of 2.5 .mu.g, 100 g (-1100 .mu.m) of the cobalt oxide / "Kynar" catalyst used in Example 1 were charged. Simulated industrial effluent containing kypochlorite and calcium (f * 1.25% available chlorine) prepared according to Example 1 was passed through the reactor at a rate of 2.5 ml / min. (2500). After 1 day of continuous operation, 95% of the hypochlorite fed to the reactor was converted to chloride ion and oxygen. After 2 days the conversion was 88%, while after 3 days it was 83% and after 4 days 77%, while the conversion after 5 days was 71%. At this point, the catalyst was regenerated by rinsing with fresh water at a rate of 500 ml / min. for 5 hours. Hypochlorite effluent was again passed over the catalyst at a rate of 2.5 ml / min. The hypochlorite conversion after regeneration was 96.5%.

Continuous operation due to regeneration, when the conversions fell below 80%, was continued for 64 days without any sign that the process can be continued for an infinitely long time without any loss of catalyst efficiency. ÉÉÖRNQUALITY;

Claims (6)

8006869-5 PATENT REQUIREMENTS A porous catalyst matrix in which the catalyst is based on an oxide or hydroxide of a metal selected from the group consisting of iron, copper, magnesium, nickel and cobalt, characterized in that it consists essentially of a mixture of said oxide or hydroxide in powdered form and a powdered thermoplastic resin comprising polyvinylidene fluoride in a weight ratio of metal oxide or hydroxide to resin in the range of from 1: 1 to 15: 1, which mixture of powder has been compacted into pellets and then thermally sintered at or around the softening temperature of the resin. Catalyst matrix according to Claim 1, characterized in that the powdered thermoplastic resin is polyvinylidene fluoride and in that the powdered metal oxide or metal hydroxide is cobalt oxide or cobalt hydroxide. Catalyst matrix according to one of the preceding claims, characterized in that the powdered metal oxide or hydroxide is precipitated on a catalyst support. Catalyst matrix according to any one of the preceding claims, characterized in that said sintered pellets have been crushed and then sieved to a particle size of 0.5-1.0 mm. 5. A process for decomposing an aqueous hypochlorite solution using a metal oxide or metal hydroxide catalyst, wherein the metal is selected from the group consisting of iron, copper, magnesium, nickel and cobalt, characterized in that the aqueous hypochlorite-free the compound is contacted with a porous catalyst matrix consisting essentially of a mixture of said metal oxide or hydroxide in powdered form and a powdered thermoplastic resin comprising polyvinylidene fluoride in a weight ratio of metal oxide or hydroxide to resin in the range of 1 : 1 to 15: 1, which mixture of powder has been compacted into pellets and then thermally sintered at or around the softening temperature of the resin. 7 Process according to Claim 5, characterized in that the powdered thermoplastic resin is polyvinylidene fluoride and that the powdered metal oxide or metal hydroxide is cobalt oxide or cobalt hydroxide.