Method of removing chlorine and halogen-oxygen compounds from water by catalytic reduction

Translation of description of equivalent WO 9607617 A1

A process for removing chlorine and halogen-oxygen compounds from water by catalytic reduction

description

The invention relates to a process for removing water contaminants, in particular of compounds and Ne¬ benprodukten oxidative water treatment.

The known methods for water treatment are häu¬ fig multistage process, where z. B. a thermally-alkali cal, oxidative, biological or adsorptive treatment in different ways can be linked together.

It is known that chenwasser z. B. be used by bank filtration for drinking water surface. For hygienic reasons and to comply with the limit values ​​of drinking water regulation in particular germs and organic substances must be removed.

Likewise, physical processes such. B. Membran¬ are separation processes or known filtration process and also be used.

In the oxidative water treatment, z. B. Des¬ by infection with chlorine, hypochlorite, chlorine dioxide and ozone, in the presence of oxidizable substances also arise Neben¬ products, for. Example, halogen-oxygen compounds such as Chlorsau¬ erstoffVerbindungen or bromates, halogenated Kohlenwasser¬ materials such as trihalo ethane, which must be removed, so that water can be used for drinking water supply, or may be discharged as treated wastewater z. B. in a receiving stream or may be fed as hot water uction process in the Produk¬.

By oxidative treatment for. Example with ozone is halogen halide oxidized as the chloride or bromide as follows Reaktions¬ mechanism.

0₃ + Hai^" → 0₂ + OHal "20₃ + OHal- → 20₂ + Hal0₃^"

This reaction is both pH-dependent oxidant depending on quantity, as well as time-dependent.

Since bromate detectable have carcinogenic, they must be removed from the water. The Weltgesund¬ Health Organization (WHO) requires that the bromate in drinking water 25 ug / 1 must not be exceeded, with the future, a limit of 3μg / l is targeted.

Since chlorate are undesirable in drinking water, it must be removed from the water. Even when disinfecting with chlorine dioxide, undesirable by-products, such as chlorite and chlorate, which should be clear evidence of hemolytic anemia and therefore not included in the drinking water.

But even from water, which should not be used as drinking water, said constituents must be removed because the oxidation potential can be distracting in many cases.

The object of the invention is to provide a process for water treatment is available, with the chlorine and halogen-oxygen compounds are removed economically or their residual concentrations can be minimized.

According to the invention these compounds are reduced to a ge trägerten noble metal catalyst with hydrogen.

The reductive decomposition of bromate given by the following equation:

Kat Br0₃^" + 3H₂ > Br^" + 3H₂0

The reductive decomposition of chlorate given by the following equation:

Kat CIO, - + 3H,> Cl^" + 3H, 0

The catalysts used are noble metal catalysts, the metals of the eighth subgroup of the PSE as an active substance containing z. B. platinum, palladium, iridium, rhodium, preferably palladium or a combination thereof with a metal of the copper group, preferably copper or silver, especially copper, used ,

In a preferred embodiment of the invention, the palladium / copper or palladium catalysts wer¬ set ein¬.

Suitable support materials are inorganic oxides, eg Al₂0₃ vor¬ preferably γ-Al₂0₃, Si0₂, Zr0₂, MgO or Ti0₂ used. Kombi¬ nations of these materials or other support materials such as aluminum silicates, magnesiu-malumosilikate or activated carbon are also suitable. Preferably such anorgani¬ cal materials are used that are waterproof and abrasion resistant. According to the invention is added to the water to be treated Was¬ hydrogen gas and loaded with hydrogen Was¬ ser contacted with the catalyst.

In a preferred embodiment a catalyst is used ver¬ which as metal component, preferably palladium and / - containing or rhodium or palladium and a metal of the copper group, in particular copper. The catalyst support material is impregnated in known manner with the metal component.

Suitable example, an impregnated substrate having an inhomogeneous distribution of the metal or metals with a concentration in the surface area.

Also suitable are materials having a Teilchen¬ diameter in the range from 10 to 5000 microns, preferably 50 to 600 μ.

In the present invention, water and aqueous solutions of any origin can be treated if they are free of substances that are known as poisons for palladium, rhodium or copper-containing catalysts act or attack the substrate. In the present Erfin tion, the term "water" refers to such waters and aqueous solutions.

On the one hand, the process for treatment of water can be used, corresponding to a water in its degree of purity, which has gone through a natural filtration. Such water may contain water-soluble substances, eg. B. an¬ organic salts, in orders of magnitude, such as those found in the groundwater, ie z. B. to several grams per liter. Such waters are z. B. groundwater, well water, spring water, surface water or bank filtrates or be¬ already correspondingly pre-treated waste water, eg. As industrial effluents, such as flue gas scrubbers, but also Ge ​​drinks such as mineral water, soft drinks and fruit juices.

The process is therefore suitable for application in the context of drinking water and the treatment of industrial waters such as industry for the food or Getränkeindu¬.

On the other hand, this method is also suitable halogen-oxygen compounds in highly polluted wastewater (eg chlorate, bromate concentrations> 3 g / l) to reduce.

According to the invention, the hydrogen can be carried out in the water either by direct introduction of hydrogen gas or by means of suitable saturated systems such as static Mi¬ shear, bubble column reactors or through membranes. Other known methods are also suitable for Wasserstoffein¬ support.

In a preferred variant of the process the gassing of the water is carried out with hydrogen in a conventional manner, eg., Via gas saturators, but it is essential that the hydrogen blistering introduced possible feinperlig and without Gas¬ and ver¬ uniformly in the water shares is. Particularly suitable here proves the per se known permeation gassing. Here the Gasein¬ will contract in the water through a solid membrane, for example, an unreinforced or fabric reinforced Silikonkautschukmem¬ bran or a solid support membrane with a 5 to 20 μ dün¬ NEN silicone layer as composite performed. An essential feature of permeation gassing is the blasen¬ free gas entry due to the exclusively on diffusion and solubility processes based transport processes in the non-porous membrane material. Another advantage of Permea¬ tionsbegasung is that the gas entry by simply increasing the gas partial pressure in the membrane system to the pressure-dependent saturation limit of hydrogen in the water, or by increasing the flow rate of the water, thereby reducing the boundary layer at the Phasen¬ border membrane water takes place, can be increased. This proves to be advantageous when large quantities of hydrogen are needed.

The hydrogen can be done either separately or simultaneously with the contacting of the water with the catalyst. In a preferred variant of Was¬ done serstoffeintrag before the actual catalytic reaction.

(Eg trickle) is to catalytic decomposition of high nenkonzentrationen Halogensauerstoffio- advantageously hydrogen simultaneously with the water in a three-phase reactor is brought into contact with the catalyst.

It has proved advantageous, the treatment of water in the presence of such an amount of hydrogen durchzu¬ result which is at least the equivalent amount of about entfer¬ nenden substances, the presence of weite¬ ren reducible substances these are also reduced.

The inventive process can at normal pressure or slight overpressure, eg., Up to 10 atmospheres, work. The solubility of the hydrogen gas in the water is at atmospheric pressure and temperatures between 10 and 25 ° C below 2 mg / 1 and is also doubled each doubling of the pressure. Where hydrogen is needed to reduce large amounts of oxygen compounds correspondingly larger amounts, the use of three-phase reactors has proven itself. Provided that the gassing of the water with hydrogen and the contact with the catalyst occur simultaneously, the water is contacted with the catalyst during such a period of time in contact, which is necessary in order to reduce the present invention to remove substances. The catalytic Behand¬ treatment can be carried out either in a fixed bed and in the fluidized bed or fluid bed reactor.

The treatment can be carried out either continuously or dis¬ continuously.

In one embodiment, water is, the z. B. has already undergone an oxidative treatment stage, in which, however, still halogen-oxygen compounds, and z. B. are residual traces of ozone, with a pH of 4 to 12, preferably 5 to 11 in particular 6.5 to 9.0 in at least one reactor in which the supported Edelmetallkatalysa¬ is tor, initiated and at 0 to 100 ° C, preferably 5 to 40 ° C, especially 10 to 25 ° C and 1 to 10 bar hydrotreated.

It is also a subject of the invention, water, the chlorite, chlorate or bromate ions includes, without having been oxidized pretreated dativ, directly supplying the catalytic reduction.

Thus, it is possible, for example, waste water with a pH value of 3 to 14 and a bromate concentration of, for example 4 g / 1 at temperatures of 5 to 90 ° C and a pressure of Wasserstoff¬ 1 to 10 bar for this method to treat. Here Bromatumsätze can be achieved of over 90%.

If desired, the water several cascaded cascaded, each having a gassing device and containing a reactor reaction units sequentially run through. Here, the pH of the water can at Wei¬ terleiten of a reaction unit in the subsequent action Re¬ unit optionally be re-regulated. In another method embodiment may also include a water des¬ sen content of the present invention to remove substances was not completely removed during a first pass through the gassing and the reactor again be returned to the reaction cycle.

Metallkataly¬ be used catalysts for the novel process, which are formed from an impregnated with the metal component porous support material. As a metal component palladium and / or rhodium can be used. It is also a subject of the invention, palladium complexing combination to use or to use rhodium with a metal of the copper group. As metals of the copper group eig¬ nen particularly copper and silver. Preferably, copper is used.

The proportion of the metal components in the total catalyst may be between 0.1 and 10 wt .-%, preferably between 0.1 and 5, especially between 0.2 and 2.0 wt .-% amount.

As low a palladium content of 0.1 proves to 2.0 wt .-%, preferably 0.1 to 1.0 wt .-%, based on the total weight of the catalyst.

In a preferred variant, a combination of palladium with copper is used as the metal component of the catalyst. The weight ratio of palladium to copper is between 1: 1: 1 and 8: 1, especially 1: 1 and 4. FIG.

In one embodiment of the invention catalysts can be used, whose support a either of porous Materi¬ al, which with a bimodal pore radius distribution at least 20% share based on the Gesamtporenvolu- men of macropores with a radius of at least 2,000 A be¬ sitting, consisting of or comprising a non-homogeneous distribution of the metal with a concentration in the surface area with a layer thickness of 20 to 100 microns, depending on Teilchendurch¬ knife , have, in particular at a particle diameter from 50 to 1000 microns, or those which are present as a powder smaller than 50 microns with a particle diameter.

As porous support materials with a bimodal pore radius distribution materials are having a maximum pore size distribution in the range of small pores with a radius up to about 400 A, for example, between about 50 and 350 A, and a second maximum of Porenradienver¬ distribution in the range of macropores with a radius of minde¬ least about 2,000 A. As low a Trägermate¬ proven material with a maximum of the pore size distribution in the range of small pores having a radius of 50 to 300 Å, more particularly special from 50 to 200 Å. Porenra¬ serving are in the range of about 5,000 for the macropore range to about 20,000 Ä low. The macropore content of the bimodal support materials should ausrei¬ accordingly be high in order to ensure rapid diffusion and can vary depending on the type and size of the carrier particles vary. Be expedient z. B. bimodal Trägermateria¬ prove lien with a macropore content between 20 and 80%, spielsweise 20 and 60%, preferably 40 and 60%, insbeson dere 40 and 50%, based on the total pore volume. For particles with a homogeneous pore distribution mei¬ the first pores should have a radius of 30 to 100 Å. principle for pulverulent particles, the same applies.

In carrying out the process the reagie¬-generating agents should wer¬ quickly removed from the active region to. A fast diffusion of the reacting agents of the catalytically active region of the catalyst may also be promoted by catalysts used wer¬ the in which an inhomogeneous distribution of the metal on the carrier with a concentration in the surface region is vor¬. Be expedient z. B. proves inhomogeneous Me¬ tallverteilung, wherein the metal is concentrated at the surface with a depth between 20 and 100 microns.

A quick diffusion of the reacting agents from the catalyst can also be through the use of powdery catalysts, for example catalyst powders have their particle diameter of below 50 microns, in particular of less than 20 microns can be achieved.

The BET surface areas of support materials, or catalysts Ka¬ with the structures described above kön¬ nen in the range of about 20 to 360, especially 60 to 300 m²/ G vary. Of support materials with a bimodal pore distribution the BET surface areas typically range from 20 to 30 up to 200 m²/ G, wherein powdery Kata¬ catalysts or catalysts with a homogeneous metal distribution in the range of 50 to 200 m²/G.

It can also support materials are used, de¬ ren porosities to differ materially from those described previously. Thus it was found that, for example the application of a porous oxide layer to a practically non-porous core, for example, performs magnesium alumosilicate to a suitable carrier material. It has also been found that magnesium alumosilicate without this porous layer is also suitable.

These carriers have inherent BET surface flat in the range of <1 to 30 m²/G. It can be used support particles of different shapes ver¬. Thus, the carrier can eg., In the form of Pul¬ vern, granules, spheres, beads, cylinders, hollow cylinders or hollow spheres are used.

For applications in the fluidized bed also smaller particle sizes, eg. As powdered catalysts are.

Support materials with a bimodal pore radius distribution can be produced in a manner known per se. Spielsweise can contribute to the production of porous ceramic materials with bimodal pore radius distribution to Träger¬ masses during manufacture substances are added, which washed out during the manufacturing process again or burn out and thereby lead to the formation of macropores. As so-called burnout can combustible organic materials such as wood flour, starch, Sac¬ charose or an ammonium salt of an organic acid such as ammonium acetate, or carbon black, may be added, which in the subsequent firing of the support burn from the Materi¬ al, leaving macropores. This method is particularly suitable for producing bimodal miniumoxidträgern Alu¬. For example, spherical Alumi¬ can be obtained niumoxidträger by the process described in the DE-OS 25 04 463 and 25 46 318, by reacting an aluminum i- niumoxidhydrosol having a hydrolyzable in the heat Ba¬ se, for example hexamethylenetetramine, are mixed and the mixture in water insoluble combustible organic matter or soot and optionally alumina and / or aluminum hydroxide is admixed, then the mixture in a water immiscible liquid-ness at elevated temperature, for example, temperatures between 60 and 100 ° C is added dropwise or is sprayed, the gebilde¬ th gel particles in the water immiscible liquid-speed allowed to age at the precipitation, then washed and dried and then calcined. A bimodal pore radius distribution can also be obtained in known manner by a downstream specific annealing of the carrier materials at temperatures in the range of about 600 to about 1,000 ° C. This method is particularly suitable for pore widening in Si0₂Cost objects. Thus, for. Example, let Si0₂Support materials convict having pore radii zwi¬ 50 and 350 Å by subsequent annealing in bimodal carrier. For example, in Si0₂Beads with pore radius to 215 A by a 5 hour Temperaturbehand¬ treatment at 700 ° C, followed by one-hour annealing at 800 ° C, a 20% sodium proportion of macropores in the range of 5,000 to 50,000 A are generated.

The impregnation of the support eilchen done with the Metallkom¬ component can- by per se conventional catalyst preparation methods. For example, metal salts or complex metal compounds in the impregnation method, spray method or precipitation processes are applied to the carrier material and, after drying and subsequent calcination to be reduced in a conventional manner. Thus spielsweise the carrier particles with a solution or Suspen¬ versions of metal salts or complex metal compounds in water or an organic solvent, for example a lower alcohol such as ethanol, or ketone, or mixtures thereof are impregnated or sprayed, after drying if desired at temperatures be up to 600 ° C, for example between 500 and 600 ° C, calcined, and then with a metal-free reducing agent, preferably hydrogen or optionally under thermal treatment at temperatures ranging up to 550 ° C, for example between about 200 and 550 ° C, or in an aqueous phase with borohydride or sodium formate Natriu be reduced at temperatures between 10 and 50 ° C. The metal distribution on the support material can be varied in known manner by the type of impregnation. Thus, for. Example, when impregnating the carrier with a solution of a soluble metal compound which Eindring¬ deep metal can be controlled in the carrier material by varying the impregnation time, eg., Between 1 and 30 minutes and the solvent, for example water or a faster evaporating organic solvent, for. example, a lower alcohol such as ethanol, or mixtures thereof or by the nature of the metal compound to be impregnated with, or by changing the pH.

The depth of penetration of the metal is therefore dependent on both the time, the pH as well as the metal compound. By short Tränkzeiten is achieved that the metal is principally distributed only in the surface region of the carrier material. An extensive concentration of the metal to the surface area of ​​the support material can also be erzie¬ len in precipitation process, by spraying a solution or suspension of the metal compound or by coating the substrate with a liquid containing metal compound. For catalysts with an inhomogeneous distribution Metall¬ with the metal concentrated in Oberflä¬ surface region, so-called coated catalysts, the Reak¬ will tion expiration of diffusion processes much more independent than in catalysts with a homogeneous metal distribution.

In one embodiment, the method for Trink¬ water treatment is carried out continuously. This disiloxane ferred embodiment is characterized in that continuously entering the water in a dispensing container in which the pH checked and if necessary by Zu¬ rate of acid to a value not exceeding pH 12, preferably between pH 4 and pH 11, especially pH 6.5 and pH 9, is set and then a the Durchflußgeschwin- is speed-regulating pump with variable capacity by one or more reaction units, which each have a Bega¬ detection unit and included a reactor passes, wherein the water is first led into the aeration unit and fumigated it with hydrogen gas, optionally under pressure, followed by a catalyst bed with the Metallka¬ reactor catalytic converter containing is performed, where the water can go through a whole as many reaction units as is not¬ manoeuvrable for reducing the invention to remove substances.

The water obtained can be further processed in a known per se. The water is practically free compounds of oxygen, chlorine, oxygen and Bromsauerstoffverbin¬. It can be used directly for such purposes, where oxygen-free water is required, eg. As water as Brauerei¬. If desired, it can be vented water treatment in a conventional manner for the resumption of oxygen also under the Trinkwas¬, whereby any remaining dissolved small residual amounts are removed to gases.

In the treatment of water containing high concentrations of halogen-oxygen compounds in the three-phase reactor prior pH adjustment is not necessary.

The following examples illustrate the invention erläu¬ tern, but not to limit.

Example 1:

In a stirred reactor, 360 ml of water containing 2 mg / 1 Br0₃^'- Ions contained presented. In stirred reactor is 5 g Pd catalyst {1% Pd content) were. In a hydrogen input of 1 1 / h no more bromate could be detected after a residence time of 12 minutes. Furthermore, an amount of 1.2 mg / 1 bromide formed as a reaction product.

Example 2;

Reaction conditions similar to Example 1:

It is a Pd / Cu catalyst (1% Pd, 0.25% Cu) was used. The water to be treated contained 2 mg / 1 Br0₃^'Ions. After a residence time of 12 minutes no more bromate could be detected. It 1.25mg / 1 bromide were formed as Re¬ action product.

Example 3:

The reaction of the bromate was performed on a catalyst fluid bed. There were 100 g of a Pd-Cu-Trägerkatalsators {1 wt .-% Pd, 0.25 wt .-% Cu).

Water with a Br0₃^'Ion content of 0.5 mg / 1 and a pH of 6,3 was passed at a flow rate of 11 1 / h and at 5 bar through the fluid bed. In water 20 ml / 1 Wasserεtoffgas dissolved. In discharged water which was Br0₃^'Ion concentration on average less than 0.01 mg / 1, the Br' ion concentration was determined to be 0.3 to 0.32 mg /. 1

Example 4:

In a continuous process have been 7m³/ H water with ei¬ ner free chlorine concentration of 0.5 mg / 1 a Fest¬ bedded with 15 kg of Pd-supported catalyst (Pd content 1.0%) tet gelei¬. The treated water contained only <0.05 mg / 1 of free chlorine. Example 5;

In a stirred reactor, 360 ml of water containing 5 mg / 1 C10₃^"- Ion was presented. In stirred reactor is 5 g Pd catalyst were (1% Pd content), at a hydrogen input of 1 1 / h was after a residence time of 15 minutes, the C10₃^_Ion concentration be lowered ge to a value below 0.1 mg /. 1 Furthermore, an amount of 2.1 mg / 1 chloride ions was formed.

Example 6-9;

In a fluidized bed reactor term Alugel-supported catalysts was treated both deionized water (DI water) and tap water in the presence of hydrogen peroxide solution substance at different Pd-hold.

The following operating conditions were set:

Water flow: 71 / h hydrogen entry: 0.3 1 / h (at 20 ° C, Ibar) water temperature: 10 ° C pH value: 7 Print: 5, 8 bar (abs)

The Bromatreduktion scored shows the Table 1 below.

The analysis values ​​account for a bromide Nachweis¬ limit of 20 ug / 1 and a standard deviation of ± 20 ug / 1 or for bromate a detection limit of 2 ug / 1 and a Stan¬ deviation ± 2 g /. 1

Example 10:

In a stirred reactor, 300 ml of water containing 972 mg / 1 chloro- rations submitted. In stirred reactor were 5 g of a Pd / Cu-supported catalyst (0.23% Pd, 0.28% Cu on alumina). There were 2 1 H₂Recorded / h. At a reaction temperature of 90 ° C could after a reaction time of 3 hours, only 35 mg / 1 of chlorate ions, but 406 mg / 1 chloride ions are detected.

Example 11:

In a trickle bed reactor (three-phase fixed bed reactor) be¬ to 1021.6 g of a Pd catalyst [found 0.89% Pd on Zr0₂/ Cordierite (magnesium aluminum silicate)]. Through this reactor, a continuous flow rate of 3.7 1 / h of highly contaminated waste water (pH 11.7) with a Bromationenkonzentration of 3000 was in addition to hydrogen * mg / l. The -Reaktionstemperatur was 60 ° C; in the reactor, a pressure of 4 bar was measured. In the end Bromatkonzen- concentration were measured below 50 mg / 1, ie there was a of catalytic Bromatabbau of over 98% achieved.

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