DE4323085A1 - Process for eliminating the oxygen, nitrite and/or nitrate content from water - Google Patents

Abstract

German Patent Application (P4306875.8) describes a process for producing spherical particles based on inorganic oxides, inter alia aluminium oxide, in which a liquid alkaline component is combined with a liquid acidic component to form a sol, the sol is converted into droplet-shaped sol particles, the sol particles are solidified by contacting with a reaction gas and introduction into a reaction liquid and, in a subsequent work-up stage, aged, washed, dried and, if appropriate, calcined, the sol particles being injected from below into the reaction gas and after passing through a curved flight path are collected in the reaction liquid. It has now been found that such supports, coated with palladium or palladium and copper are outstandingly suitable as catalysts in a process for eliminating or decreasing the oxygen, nitrite and/or nitrate content in aqueous systems.

Description

The present invention relates to the removal or Ver Reduction of the oxygen, nitrite and / or nitrate content in Water using a supported catalyst based on a sprayed carrier.

The in groundwater and surface water in the Federal Republic Germany found nitrite and / or nitrate contents are in increased significantly in recent years. They vary depending on Location considerably and can partially tolerable Exceed limits. For drinking water will be in the new EC Directives, a permissible limit of 50 mg nitrate recommended per liter and for nitrite a limit of 0.1 mg / l. The increasing nitrite and nitrate contents in many basic and Surface waters are increasingly making processes for Ni trit and nitrate removal in the context of drinking water treatment necessary. For this purpose, biological processes and physical / che mixed measures in the field of desalination the. Known disadvantages of these methods are the possible Kon tamination with bacteria or their metabolites or the mere shift of the problem.

The removal of oxygen from water (which gave may also be free of nitrite or nitrate) is in vie len cases desirable. So it is known that oxygen in what the corrosion of metallic components such as cooling systems and Thermal power plants promotes. In the field of foodstuffs tion, for example in the production of beverages such as fruit juices or beer, is preferably an oxygenar or oxygenated water.  

EP-A-0 359 074 (US-A 4,990,266) describes a catalytic table process for the removal of nitrite and / or Nitrate from nitrit- and / or nitrate-contaminated water under selek tive nitrogen formation. One uses a supported catalyst, which is formed from a with a palladium and / or Rhodium or palladium and a metal of the copper group existing metal component impregnated porous support. the This carrier has a bimodal pore radius distribution with a at least 30% of the total pore volume Macropores with a minimum radius of 200 Å and / or a inhomogeneous distribution of the metal component with a concentrate tion in the surface area or it is present as a powder.

Object of the present invention is to provide an improved To provide methods by which the selective Transfer of nitrite and / or nitrate into nitrogen possible is. This object is achieved by that specified in the claims Procedure solved.

Object of the present invention is also a improved, particularly abrasion-resistant bead-shaped Trägerkataly to provide the process implementation. The Particles of this supported catalyst should be in particle size and Composition as low as possible scattering. This up Gabe is by the specified in the claims Trägerkataly solved.

The inventive, continuously feasible Verfah to remove or reduce the oxygen, nitrite and / or nitrate content of oxygenated and / or nitrite and / or nitrate-contaminated water under selective nitrogen formation, wherein the oxygen-containing, nitrite and / or nitrate-laden water introduces hydrogen gas and do it with what hydrogen laden water contacted with a catalyst, wel is formed from one with a palladium and / or Rhodium or palladium and a metal of the copper group existing metal component loaded porous carrier, and man for treating only nitrite-loaded water a cata-  tor, whose metal component of palladium and / or rhodium be and, if the water to be treated also contains nitrate, a catalyst whose metal component is palladium and a metal of the copper group or of rhodium and given if palladium exists, or a mixture of a cata- tor, whose metal component consists of palladium and a metal of Copper group consists, and a catalyst whose Metallkom consists only of palladium, is used, and thereby the pH Value of the water does not rise above pH 8 and the procedural If necessary, it is repeated as often as necessary until the Oxygen content, nitrite content and / or nitrate content of Water removed or reduced to a tolerable level is, provides that one uses a catalyst whose Trä according to patent. , , (Patent Application P 43 06 875.8) under About lead a sol into drop-shaped sol particles by spraying the Solteilchen from below into a reaction gas and catching the Solteilchen after flying through a curved trajectory in the Reaction liquid, and subsequent workup ver solidified sol particles under aging, washing, drying and cal zinieren has been produced.

Of crucial importance of the Verfah inventive rens is thus the use of a catalyst based on special vehicle of the patent. , , (P 43 06 875.8). The manufacturer ment of the carrier will be described below.

The method of the patent. , , (P 43 06 875.8) for the manufacture of spherical particles based on alumina Forces a gel into a gel. As a sol can For example, to use a metastable acid sol, z. B. a nitric acid alumina sol. Alternatively you can do one liquid alkaline component, eg. As water glass, with a their alkaline component, eg. B. Alkalialuminmat solution ver some, as described in DE-OS 29 17 313. The Sol-Her Position also succeeds in that a liquid alkaline Component with a liquid acidic component to a sol united. The sol is converted into drop-shaped sol particles, the sol particles by contacting with a reaction gas and  Incorporating solidified in a reaction liquid and in a aged, washed, ge dries and, with regard to the carrier used here, Calcined, which method is characterized in that one sprays the Solteilchen from below into the reaction gas and the Solteilchen after flying through a curved trajectory in the reaction liquid traps.

As defined in the patent. , , (P 43 06 875.8) He disclosed finding is under a sol so both an unstable sol, which gels immediately after assembly of the components, as well as a metastable sol, which is still some time in the flowable state remains understood.

That method is suitable in principle for the production of Particles formed by gelation of gellable solutions, triggered z. B. by sudden pH change or photoche mixed initiation, can be produced. Very good itself with the inventive method particles on the basis of alumina which is formed by polycondensation form in a sol-gel reaction.

The inventive method can be gelierun for all in which, according to the sol-gel method, an insta Sol by mixing together an alkaline component is obtained with an acidic component.

In known manner for this purpose are acidic aluminum oxidsole as an acidic component with a gaseous alkaline Component such as. B. with gaseous ammonia or the vapors organic amines, for example the vapors of lower alkylamines ne, implemented. Suitable Aluminiumoxidsole can accordingly The prior art of aluminum oxides z. B. from Tonerdehy such as boehmite, pseudo-boehmite, hydrargillite or bayerite, by dispersing in aqueous acid, e.g. In nitric acid, getting produced. In addition, it is also possible to know Way of aluminum hydroxide and aluminum halides, eg. B. AlBr₃, AlCl₃, or metallic aluminum by the action of  dilute acid, e.g. As HCl, aluminum sols or suspensions obtained in the process according to the invention as alumina containing acidic components can be used.

Selbstver ver Sole also be used, which fines everyone Contain known type, amount and particle size. to Improvement of performance characteristics can z. B. in a known manner, as fines additives, z. B. fillers from the group silicas, aluminosilicates, Magnesium compounds, e.g. As MgO, aluminum oxides, titanium dioxide, Kaolin, montmorillonite, bentonite, zeolite, starch, wood flour or Activated carbon be attached. The fillers can be acidic and / or alkaline component in crystalline or amorphous form or in highly dispersed form, as in the DE 42 16 868 is added. Also Feinantei le, which in a known manner the catalytic property The particles can change in a conventional manner be used, as finely divided catalytically active Me talle or their precursors, z. B. metal salts.

Mixing of alkaline component with acidic Component to a gellable unstable sol can on known manner in a suitable mixing device, for. B. a mixing nozzle are performed. Then it will be like this obtained sol directly pumped into a device with the converted it into drop-shaped sol particles and on fiction, be sprayed from below into the reaction gas can. As a spray system, with which the sol from below into the Reak tion gas are introduced in the form of droplet-shaped particles can be laboratory scale from medical practice be knew cannulas or on a larger technical scale per se known spray nozzles, spray disks, ultrasonic nozzles, turbo bells, mechanically driven nozzles or sprayers, as they are used in electrostatic spraying or in jet Printern, z. B. piezo-excited nozzles used, who used the.  

Preferably, according to the inventive method, the sol particles for solidification in the reaction gas from bottom to top at an angle α less than 90 °, as shown in Fig. 1 represents, sprayed. Preferably, the angle α should have a value of 40 to 89 °, in particular a value of 80 to 88 °. The reaction gas is in a container, the so-called precipitation tower, above the verwen for solidifying reaction liquid. In Fig. 1, the structure of the front direction for carrying out the method according to the invention is shown cal diagrammatically. By a spray system, the gellable sol is sprayed from bottom to top at an angle α less than 90 ° in the felling tower, wherein the liquid jet after the United spray system is torn open shortly after entering the Fallenurm in about the same size Soltropfen. The sol drops thus obtained then pass through a parabolic-like trajectory in the reaction gas before they are collected by the reaction liquid introduced below the reaction gas. By the Soltropfen must pass through a trajectory curved to a parabola trajectory, their residence time in the reaction gas is maximized. Due to the longer residence time in the reaction gas, the reaction gas can contribute particularly long time to solidify the particles before they hit the reaction liquid on. Here, the curved trajectory of the sol particles is of particular advantage, as a result, the speed of the sol particles goes through a minimum, so that in particular sol particles with larger diameters undamaged can be collected tion liquid in the presented Reak.

As reaction gases and reaction liquids in the he inventive method all according to the sol-gel method übli chen acidic or alkaline reaction gases or liquids are used, as they usually for solidification of particles based on alumina after the sol-gel Ver drive to be used. As alkaline reaction gases can so z. As the vapors of organic amines or ammonia, as a reaction liquid, the solution of an organic amine or an aqueous Ammonia solution can be used. Particular preference is given to setting as alkaline reaction gas ammonia and as reaction liquid  speed corresponding to an aqueous ammonia solution, for. B. a 5 to 10% aqueous ammonia solution, a. As acid reaction gases can z. As the vapors of organic acids, eg. B. the vapors of Formic acid, acetic acid or acetic anhydride or chlorine hydrogen, sulfur dioxide or nitrogen oxides are used. the Correspondingly, the acidic reaction liquid is then added to equivalent acids. Preference is given as an acid Re Hydrogen chloride, sulfur dioxide or nitrogen oxides and as the acidic reaction liquids preferred to the equivalent aqueous acids, ie hydrochloric acid, sulfuric acid or nitric acid re, z. B. in a concentration of 1 to 5%. On the corresponding reaction liquids, the used Reaction gases in the tower as a closed container light being held. Fresh reaction gas can constantly through a separate gas supply as needed in the Fallen tower refilled become. The sol-gel method can be used at ambient temperature as well be carried out at elevated temperature.

The process of the invention can be kugelför produce miges particles whose average diameter after drying in the range of 0.001 mm to 5 mm kön NEN. The particle size can be over the used Sprühvor be varied.

Al₂O₃ contained particles with a diameter of approx. 0.05 mm to 1 mm can by the method according to the invention z. Example, be prepared by adding a Alkalialuminatlösung in a manner known per se with an aqueous sulfuric acid oil in a mixing nozzle or by mixing emanating from a metastable sol, immediately afterwards in a Spraying system pumps and into the defensive tower from bottom to top in an angle α of about 87 ° sprayed as a sol particle, so that in an alkaline reaction gas, eg. As ammonia, under Fixation of the spherical shape can be preconsolidated and finally in the submitted alkaline reaction solution, for. B. aqueous Am moniaklösung, be caught and geliert. Subsequently the particles are then still dehydrated, if desired with treated with an alcohol or ketone (see below), and calcined.  

Drying usually takes place at temperatures in the range from 100 ° C to 200 ° C for a period of 1 to 24 hours. to closing the particles may be on be be knew manner at temperatures of 400 to 1200 ° C, preferably 550 to 900 ° C, in particular 590 to 650 ° C are calcined. The temperature used depends on which Porösi degree is desired. At low temperature you get Carrier with small pore diameter and high surface area, at higher temperature carrier with a larger pore diameter at smaller surface.

It is preferable to use catalysts with palladium or Palladium and copper as a catalytic component.

The content of such metals is usually in Be rich from 0.1 to 5 wt .-%, based on the finished cata- torträger. The preparation of the catalysts of the invention can be done in a known manner. For example, can Metal salts or complex metal compounds in the impregnating method, spray method or precipitation method on the part apply and after drying and calcination desired if reduce. The metals are preferred by an imprä standard procedure, eg. B. with a solution or suspension of Me tallsalts or complex metal compounds in water or an organic solvent applied to the particles. It can be stated that produced according to the invention Particles in this impregnation to an edge enrichment nei gen, d. h., That the metals used in the impregnation process stronger in the peripheral areas than in the interior of the particles deposit. This is particularly advantageous, as this is for the Production of the catalysts according to less metal turned must be set. The catalytically active metals are at Scha directing catalysts by short diffusion paths more accessible. Another advantage of based on the invention Herge Particles obtained catalysts is their überra Shearing high abrasion resistance.  

In a variant of the method according to the invention the obtained spherical particles after solidification in the reaction liquid and before drying and calcination nor a treatment with a lower alkyl alcohol, esp dere a C₁-C₄-alcohol, such as. As methanol, ethanol, propanol or isopropanol or a treatment with acetone. Preference is given to isopropanol, which is anhydrous as possible should be, for this treatment of the particles. By the Treatment of the particles with a lower alkyl alcohol or Acetone can be achieved two different effects: Zum one can by treatment advantageously an Ver sticking of the obtained particles, in particular particles an average diameter smaller than 1 mm avoided who on the other hand, this treatment can reduce the pore volume the particles obtained are increased. For this purpose, the Particles in particular for a period of 1 minute to 24 hours, suitably 2 to 3 hours, of this treatment subjected. In particular, it is with the Ver invention drive the pore volume of alumina for the first time possible to change particles through this treatment. That's how it is z. B. the pore volume of the inventive method produced aluminum oxide particles after treatment with a lower alkyl alcohol before drying in the range of 0.4 to 1.2 ml / g (determined after drying). Appropriately be for this z. B. produced by the process according to the invention Aluminum oxide particles then with isopropanol for one to treated eight times 2 hours before drying. Carrier in the form of Spherical particles based on alumina, which a diameter in the range of 0.05 to 1 mm, preferably 0.4 to 0.6 mm, are particularly suitable. A specific surface in the range of 5 to 250 m² / g, preferably 100 to 200 m² / g especially advantageous. A bulk density in the range of 0.3 to 1.2 g / ml, in particular 0.3 to 0.7 g / ml, and a pore volume in the Range of 0.6 to 1.2 ml / g is advantageous. The middle butt rendurchmesser lies in the range of 100 to 200 Å.

By the method of the patent. , , (P 43 06 875.8) is it advantageously possible, supported catalysts in the form of  Aluminum oxide-based particles with a very similar moderate spherical shape and a very narrow grain spectrum to he hold. Here, the accumulation of larger amounts of sub- Oversize grain are largely avoided. So they point to that Process obtainable particles with those in the following Table given diameter following narrow grain spectrum on:

Diameter of particles [mm] Grain spectrum [mm] 1.0-5.0 ± 1.0 0.1-1.0 ± 0.1 0.01-0.1 ± 0.02 0.001-0.01 ± 0.004

In the process, no molding oil needs to be used, so that the particles thus produced are also free of further Ver impurities or discoloration. Also can be after Particles produced by the process according to the invention a treatment with acetone or a lower alkyl alcohol the drying increase the pore volume in an advantageous manner. In addition, the supported catalysts on supports in Form of ku produced by the process according to the invention gel particles have a surprisingly high abrasion resistance, what they especially in connection with the narrow grain spectrum suitable for use as catalyst or catalyst carrier ger in fluidized bed reactors.

In the context of the present invention can oxygenhal or nitrite or nitrate contaminated waters and aqueous Lösun be treated of any origin. In the present Application, the term "water" means such waters and aqueous solutions. Contains the water to be purified among the Reduce reaction conditions of the process according to the invention other substances are also reduced. If it is desirable, one removes such reducible others Substances previously from the water to be purified.  

Another object of the present invention is a special carrier used in the process according to the invention talysator. To reduce the oxygen content, the Ni trit and / or nitrate content comprises suitable supported catalyst Palladium, rhodium or palladium and a metal of the copper group pe on a support based on alumina, the support according to patent. , , (German Patent Application P 43 06 875.8) by Transfer a sol into droplet-shaped sol particles by one spray the sol particles from below into a reaction gas and up catch the sol particles after flying through a curved flight train in a reaction liquid work up the solidified Sol particles by aging, washing, drying and calcining, with the proviso that the carrier has a specifi should have a surface area in the range of 5 to 250 m² / mg.

Particularly suitable are supported catalysts he meadows whose support before the application of the catalytically active Metal component at a temperature of 600 to 1200 ° C kal has been ziniert. Supported catalysts with a bulk density from 0.3 to 1.2 g / ml and a pore volume of 0.4 to 1.2 ml / g deliver particularly good process results. Further preferred Embodiments of the supported catalyst of the invention ent speak the one described above as being preferably used Supported catalysts. Particularly advantageous are supported catalysts Although they have a completely homogeneous structure of the carrier, but an inhomogeneous distribution of the catalytically active component namely, in which the concentration of the catalytic active component increases from the center to the periphery (shells catalysts).

The preparation of such supported catalysts is according to known methods possible. For the production of palladium or rhodium-containing supported catalysts are impregnated expedient the carrier with an aqueous solution of a soluble Palladium or rhodium compound with subsequent drying and glowing. For the production of palladium and copper enthal supported catalysts is suitably so that one the carrier first with an aqueous solution of a palladium  compound, preferably Na₂PdCl₄ solution, impregnated, then ßend dries and optionally glows (calcined) and give if necessary, and then the palladium-containing carrier impregnated with an aqueous solution of a copper compound and then again calcined and reduced. Especially advantageous, palladium and copper-containing catalysts were prepared by using the palladium-containing carrier with a basic solution, for example aqueous sodium carbonate Solution, was contacted, and then the impregnation with a copper compound was made. Of course you can do that Apply metals to the carrier at the same time.

Supported catalysts based on Alugel carriers have the Advantageous that they have a high uniformity, and on the one hand in terms of their external shape (spherical shape, en spectrum of size distribution) as well as in terms of Material quality of the carrier material for all particles. you have a high mechanical stability and are characterized in preferred embodiments, by a concentration of catalytically active components on the surface. from that results in a high selectivity and a high degradation rate of Catalyst particles.

Using supported catalysts with a high Oberflä (<140 m² / g) and correspondingly small pore diameters, In the case of shell catalysts, the mass diffusion becomes less limited as compared to catalysts of the prior art.

The nitrite and / or nitrate content and the Sauerstoffge halt, which removed by the method according to the invention or can be reduced to a tolerable concentration vary within a wide range. So can be with the invent According to the invention water with a nitrite and / or nitrate load between 0.1 mg / l and a few grams per liter spindles. In particular, the present method is suitable for Removal of nitrite and / or nitrate content from water with a low nitrite and / or nitrate pollution, for example in Be rich from 0.1 mg to 2 g / l nitrite and / or 1 mg to 10 g / l nitrate.  

For the expert it is clear that the Verfah inventive be used to remove oxygen from water can, which contains neither nitrite nor nitrate. The procedure Of course, it can also be used to remove nitrite and / or nitrate be applied from water, which contains no oxygen. Finally, one can the method according to another variant also for the removal of nitrite and / or nitrate from simultaneously Apply oxygen-containing water. In this case will In addition to nitrite or nitrate and the oxygen removed.

In particular, the inventive method for treating ment of water used, which in its purity ei Nem water, which is a natural filtration through has run. Such water can be water-soluble substances, z. As inorganic salts, in orders of magnitude, as in the reason water are found, so z. B. up to a few grams per Liters included. Examples of the Ver drive to be treated water are z. B. groundwater, wells water, spring water or bank filtrate or already accordingly Pre-cleaned other wastewater z. Industrial wastewater, for example, from flue gas scrubbing, in which the content of Oxygen, nitrite and / or nitrate can be reduced. Wei Tere examples of water, with the Verfah There are drinks like mineral waters, Limona and fruit juices and water used to produce Ge soak like mineral waters, sodas, fruit juices or beer manufacture, to be used.

The method is suitable, for example, for use in Framework of drinking water treatment and reprocessing of Water or service water for the food or beverage industry and for other purposes where an oxygen, nitrite and / or nitrate-poor or -free water is needed.

Contains the water only nitrite and possibly sour fabric, so you can use a supported catalyst whose Metal component of palladium and / or rhodium. contains the water to be treated also nitrate, so you use one  Supported catalyst whose metal component of palladium and egg metal of the copper group or of rhodium and optionally Palladium exists. If the water to be treated is also nitrate contains, you can also the catalyst system of the invention use, advantageously the catalyst system of palladium only catalyst particles containing metal component and Palla dium and a metal of the copper group, in particular copper as Metal component-containing supported catalyst particles. The Weight ratio of palladium-containing to palladium / copper containing catalyst particles may, depending on the nitrate and Ni Tritgehalt of the water and the amount and composition of Metal components of the catalysts vary and may vary between 1: 5 and 5: 1, preferably between 1: 2 and 2: 1. The un Different particles are appropriate separate from each other in front. Then you lead the water to be treated only through the Palladium / copper group metal-containing particles and then by the particles containing only palladium, preferably in each case the fluidized bed.

Suitably, the pH of the water is regulated so that the reaction-induced increase does not lead to values above pH 8. The adjustment of the pH can, for example, by adding an aqueous solution of an acid, preferably a dilute one inorganic acid such as hydrochloric acid or CO₂ take place.

The introduction of the hydrogen gas into the water and a If necessary, necessary pH regulation can, if desired take place while the water is in contact with the catalyst. However, the hydrogen gas is useful in a separate Device introduced into the water before this with the Ka is contacted. If you want you can do the Adjust the pH of the water to be treated so that the subsequent pH increase remains within the desired range.

The pH of the water to be treated should be in one Range of about 4 to 8, in particular 6 to 8 are.  

Usually contains water whose nitrite and / or Ni trated content can be reduced with the method according to the invention should, also dissolved oxygen. For complete removal of the Nitrite and / or nitrate content of the water is therefore total requires such an amount of hydrogen gas, which at least the to reduce the oxygen content and the nitrite and / or Nitrate content of the water stoichiometrically necessary amount equivalent. Thus, for the reduction of 100 mg of nitrate theoretically about 9 mg of hydrogen required to remove 8 mg Oxygen about 1 mg of hydrogen. Unless the thing to be treated it contains only minor amounts of nitrite and / or nitrate, he it is useful to include such an amount of hydrogen which at least the stoichiometrically calculated Amount and at most a 20% excess of these calculated Quantity corresponds.

The fumigation of the water with hydrogen is preferred wise on the type of Permeationsbegasung. Here, the Gas entry into the water via a solid membrane, for example a silicone rubber membrane. Particularly suitable are mem Branches with an integral asymmetric structure and in particular Kom membranes here. These membranes comprise a porous, watery permanent support structure and at least one layer of water resistant, non-porous polymer, at which the Flüs to be gassed is passed. This non-porous layer, z. B. off Silicone polymer is very thin, it has for example one Thickness of 0.5 to 10 microns. Such membranes are in EP-A 291 679 (US Pat. No. 4,933,085). Other methods z. B. on gas saturator, are also suitable for H₂ entry.

The inventive method can at atmospheric pressure or slight overpressure, z. B. up to 10 atmospheres or more The solubility of the hydrogen gas in the water is at atmospheric pressure and temperatures between 10 and 25 ° C below 1.7 mg / l and increases in proportion to the working pressure. Where to Reduction of higher amounts of nitrite and / or nitrate accordingly Higher amounts of hydrogen are needed, it is recommended therefore, to do the fumigation under pressure. In the treatment  of water that only contains oxygen is working at Ambient pressure very possible.

The process according to the invention is preferably operated as expanded bed, fluidized bed, suspension or fluidized bed.

With high content of oxygen, nitrite or nitrate one can the inventive method if necessary several times in succession or increase the working pressure until a sufficient Reduction z. B. also for drinking water tolerable values or a complete distance is reached. You can do this one Return part of the already treated water to the reactor or you can see several reaction units with Begasungseinrich tion and reactor before. About the used amount of hydrogen or Multiple treatment of the water can take any rest concentration of the original content of oxygen or Adjust nitrite or nitrate in the treated water.

The temperature during the treatment can be between 5 ° C and 95 ° C, preferably between 8 ° C and 25 ° C.

The nitrite and / or nitrate degradation performance may vary depending on the Nitrite and / or nitrate initial concentration, the pH of the Hydrogen gas concentration or fumigation rate and the temperature vary. With a palladium catalyst with 1 or 2 wt .-% palladium can in the batch laboratory test at For example, nitrite removal efficiencies of over 40 mg nitrite per Hour and grams of catalyst can be achieved. With a pal ladium and copper doped catalyst with 1.0 wt% palladium and 0.25 wt.% copper on alumina may be, for example Nitrate removal efficiencies of 15 mg nitrate per hour and gram Ka be achieved.

A continuously feasible fixed bed process and a system which can be used for this purpose are described in EP-A-0 359 074 wrote. The water is first ge in a dosing conducts, in which the pH can be measured, then by a degermination device, finally via a pump through  one or more reaction units from hydrogen fumigation container and fixed bed reactor. The plant can be even more custom facilities, for example flowmeters, Pressure gauges, pH meters, temperature gauges. The treat te water can then be subjected to a pH adjustment become.

For carrying out the method according to the invention in the fluidized bed or suspension layer is as follows described plant particularly well suited. It includes one Pressure booster equipped with a hydrogen entry The device is connected to the water in a vortex stratified bed, suspension bed or fluidized bed reactor which conducts the above-described special alumina supported catalyst contains. Preferably, the plant has two filter devices on, before the pressure booster or after the reactor are arranged. The system can still have a dosing tank Have pH measuring and control device, the front and / or behind Pressure increasing device is arranged. If desired NEN in the pipes or system parts nor measuring points be appropriate for the determination of analytical data of the water, For example, pressure measuring devices, Druckflußmeßeinrichtungen and / or temperature measuring devices.

The gassing unit preferably has a permeation membrane for hydrogen entry. Very well suited too Permeation membranes, which consist of a porous, water-resistant Polymer formed carrier structure and at least one Layer of water-resistant, non-porous polymer, wherein the zu treating water on the side of the layer of wasserbeständi gem, pore-free polymer with the membrane in contact. Very For example, integrally asymmetric membras are well suited nen, z. B. of polyetherimide. Very well suited Membranes additionally with water-resistant, hydrophobic, nonporous polymer, preferably silicone polymer are. Such membranes are known as composite membranes. The Gassing unit can, for example, out as a hollow fiber module forms his.  

The inventive method has considerable advantages on. Due to the high selectivity of the carrier to be used Catalysts do not give rise to environmental pollution because of its high mechanical stability and abrasion resistance Stigkeit of these catalysts, the Verfah inventive over a long time without loss of catalyst activity and without the need for catalyst replacement be written. Particularly advantageous both in economic As well as hygiene, the implementation of the inventive method using a spherical Supported catalyst in the fluidized bed.

The carrier catalyst to be used preferably contains Palladium or palladium and copper as the catalytically active com component. The palladium content is preferably 0.1 to 4 wt .-%, in particular 0.5 to 2.5 wt .-%, based on the total weight the finished supported catalyst. Consists of the metal component from palladium and copper, the weight ratio of Pal preferably between 2: 1 and 8: 1, preferably 3: 1 and 5: 1, in particular 4 ± 0.1: 1.

The invention will be elucidated by the following examples tert, without limiting their scope.

Fig. 1

Schematic representation of the process for carrier production:
( 1 ): sol, ( 2 ): pump, ( 3 ): spray device, ( 4 ): sol jet, ( 5 ): sol drop, ( 6 ): precipitation tower, ( 7 ): reaction gas supply, ( 8 ): receiver tank with reaction liquid, ( 9 ): sieve for separating the particles from the reaction liquid, ( 10 ): catching container for the particles, ( 11 ): pump, ( 12 ): returning the reaction liquid to the receiver, α: angle α.

The sol ( 1 ) to be processed is pressurized via the pump ( 2 ) and the cannula ( 3 ) or cannulas ( 3 '), ( 3 ''),. , , sprayed in a sol beam ( 4 ) in the precipitation tower ( 6 ) in such a way that the sol beam ( 4 ) after entering the precipitation tower ( 6 ) in Soltropfen ( 5 ) torn. After passing through a curved trajectory through the reaction gas in the precipitation tower ( 6 ), the Soltropfen ( 5 ) were collected in the filled with reaction liquid storage tank ( 8 ). The reaction gas used was ammonia gas, which was constantly replenished via the reaction gas feed ( 7 ) into the precipitation tower ( 6 ). As the reaction liquid, an ammonia solution was used. The particles were then aged in the aqueous ammonia solution and then separated via the screen ( 9 ) from the reaction liquid and transferred to the collecting container ( 10 ). The reaction liquid was pumped via the pump ( 11 ) through the return ( 12 ) back into the Vorlagebehäl ter ( 8 ).

The resulting particles were then known per se Base-exchanged, dried and tempered.

Examples

The following Examples 1 to 3 describe the preparation of the Alugel carrier. They were carried out in a device according to FIG .

example 1 Production of Alugel particles

Spherical particles based on alumina were prepared as follows:
A metastable acid Aluminiumoxidsol (Condea Disperal® 30/2) with a composition of 14,19 wt .-% Al₂O₃ and 85.81 wt .-% water was in a device according to Fig. 1 by means of the pump ( 2 ) at a pressure of 6 bar over 10 cannulas (diameter: 0.70 mm, length: 3.2 cm) with a throughput of 0.75 l / minute sprayed from bottom to top.

The Solstrahlen tore after a flight distance of a total of about 75 cm in the same size Soltröpfchen on, and they arrived after about 25 cm in the filled with ammonia gas Fallen tower. The following reaction conditions are given below:
Original: 5% ammonia solution
Aging: 1 h
Drying: 8 h 120 °
Annealing: 4 h 600 °
Diameter: 0.4-0.6 mm
Bulk weight: 0.71 g / m²
specific surface area: 287 m² / g
Pore volume: 0.44 ml / g

Example 2

Spherical particles based on alumina were like in Example 1, prepared. In addition, these were Particles still a treatment with anhydrous isopropanol (Density: 0.785 g / ml). For a period of 2 hours for that, the obtained particles were each dried before drying 1 liter of isopropanol per 1 liter of particles. At egg In addition to the particles, the isopropanol treatment also became more performed by adding the particles from the isopropanol solution were decanted and then again for the same time were overlaid in an identical manner with isopropanol. This isopropanol treatment was up to several particles performed eight times in a row. After drying and cal zinieren, as already described in Example 3, was obtained Particles having the properties given in the table below companies.

From Table 4 shows that the pore volume, the bulk weight and the mean pore diameter of the inventions alumina particles produced according to the invention process itself through the additional alcohol treatment in wide ranges vary.  

Table 1

Properties of the process according to Example 2 obtained process products

Example 3

Spherical particles based on alumina were prepared as follows:
A metastable acid Aluminiumoxidsol (Condea Disperal® 30/1) with a composition of 18.00 wt .-% Al₂O₃ and 82.00 wt .-% water was in an apparatus according to FIG. 1 by means of an electrically driven spray gun (Bullcraft N, Bullcraft N, 80W) with egg nem throughput of 0.060 l / minute sprayed from bottom to top in the filled with ammonia gas tower. The following reaction conditions and the properties of the particles obtained are given below:
Original: 5% ammonia solution
Aging: 0.5 h
Alcohol treatment: twice 2 h, isopropanol
Drying: 8 h 120 °
Annealing: 4 h 600 °
Diameter: 0.02-0.05 mm
Bulk weight: 0.43 g / ml
specific surface area: 291 m² / g
Pore volume: 1.19 ml / g

Example 4

Spherical particles based on alumina were prepared as follows:
A metastable nitric acid Aluminiumoxidsol (Kondea Disper ral® 30/1) was sprayed as described in Example 1 via 4 cannulas in the apparatus of FIG. 1 in the filling tower filled with ammonia gas. The following reaction conditions are indicated below:
Original: 3% ammonia solution
Alcohol treatment: 3 times 2 h, isopropanol
Drying: 8 h 120 °
Annealing: 4 h 900 ° C
Diameter: 0.4 to 0.6 mm
Bulk weight: 0.58 g / ml
specific surface area: 180 m² / g
Pore volume: 0.68 ml / g

Example 5 Preparation of Palladium-Containing Alugel-Trägerkatalysato reindeer

General manufacturing instructions:

5.1 .: Preparation of a 1% by weight Pd-containing Trägerkataly crystallizer

10 kg of intended for occupancy carrier were in Washed 60 l of deionized water. After pouring off the water was the pretreated substrate with 50 L of deionized Added water in which 168.21 g of PdCl₂ and 109.85 g of NaCl ver puts. The soaking time was usually about 45 minutes.  

After the palladium salt had entered the carrier material, the supernatant clear liquid was poured off, the damp one soaked carrier material washed with water and then mixed with a reduction solution. For the preparation of this Re were 18.24 g of NaBH₄ in 60 l of deionized water been dissolved. After about a quarter of an hour of contact between Supported catalyst and reducing solution, this was poured off, the supported catalyst was washed and dried.

Microprobe testing revealed that the palladium metal was in the Concentrated surface area of the carrier. The one penetration depth was up to about 50 microns.

5.2. Preparation of a 1.5 wt .-% palladium-containing carrier catalyst

Example 5.1. was repeated. This time became an impregnation solution used, which contained 252.32 g of PdCl₂ and 164.78 g of NaCl. The Reduction solution consisted of 67.36 g NaBH₄ dissolved in 60 l entio water.

The microprobe investigation showed that even in such Trä gerkatalysatoren the palladium metal in the surface area kon centered.

Palladium was used to cover the spherical alumina Particles of Examples 1 to 4. Application experiments showed that the thus prepared palladium-Alugel carrier catalysts for the removal of oxygen from aqueous solutions with addition of hydrogen are suitable as a reducing agent. They are suitable also for continuous nitrite reduction in water. The Nitrite degradation performance of supported palladium-supported catalysts with 1 wt .-% Pd was in the continuous process between about 8 and about 10 mg of nitrite per gram of catalyst and hour, the Ammonium formation was usually less than 5 mol%.  

Example 6 Preparation of a Pd / Cu supported Alugel catalyst 6.1. Preparation of the supported catalyst without base pretreatment lung 6.1.1. Preparation of the supported catalyst with 1 wt .-% Pd and 0.25% by weight of Cu

The carrier prepared according to Example 4 which was used in By analogy with Example 5 had been occupied with 1 wt .-% Pd. 5 kg this palladium-containing carrier were 24.5 l with a Copper impregnation solution, which by dissolving 39.28 g Copper acetate monohydrate in deionized water was. The soak time was about 45 minutes. The supernatant was then poured off. The copper-impregnated carrier was then washed several times with deionized water. Subsequently was the still moist carrier mixed with a reducing solution, the by dissolving 27.36 g of NaBH₄ in 30 liters of deionized water had been generated. After about 15 minutes contact between carriers and reducing solution, the supernatant was poured off. The wet one Supported catalyst was then dried at 120 ° C.

6.1.2. Preparation of a supported catalyst with 1.5% by weight of Pd and 0.375 wt% Cu

Example 6.1.1. was repeated analogously. This time was for 5 kg of the palladium-containing support 24.5 l of a Kupferränklö obtained by dissolving 58.91 g of copper acetate-Mo hydrate in deionized water. As Re A solution of 41.04 g NaBH₄ in 30 l entio used water.

6.2. Preparation of a Pd and Cu-containing Alugel Trägerkata lysators with base pretreatment 6.2.1. Preparation of a supported catalyst with 1 wt .-% Pd and 0.25% by weight of Cu

5 kg (dry weight) of the Example 6.1.1. used Palla dium-containing supported catalyst were first entio with entio washed with water. Then the support material was with about 6 l of an ammonium carbonate solution (concentration of ammonium carbonate: 5 g / l) and allowed to stand overnight. there the ammonium carbonate solution covered the support material.

Subsequently, the supernatant solution was poured off and the pretreated substrate washed briefly.

To prepare the copper dipping solution, 47.5 g of copper oxide were used tri-dihydrate dissolved in 10 l of deionized water and then ßend by means of ammonium carbonate to a pH of 5.3 ge introduced; while a flocculation is to be omitted. In these Solution became that with ammonium carbonate as described above treated palladium-containing Alugelmaterial introduced and 2 hours left in it. The supernatant solution was depleted sen, the material washed several times with deionized water and dried at 120 ° C for 15 hours. Subsequently was annealed for 4 hours at 230 ° C in a nitrogen stream to the convert resulting copper carbonate into copper oxide. subsequently, ßend took place as in 6.1.1. described the reduction of the Copper oxide with NaBH₄ solution.

6.2.2. Preparation of a 1.5 wt .-% Pd and 0.375 wt .-% Cu ent holding supported catalyst

Example 6.2.1. was repeated. As a copper dipping solution was This time a solution of 71.3 g of Cu (NO₃) ₂-trihydrate in 10 l used deionized water. The reduction of the finally produced copper oxide as described in 6.1.2. with NaBH₄ solution.

The investigation with a microprobe (electron backscatter Auf assumption) that the palladium and copper-containing Ka a concentration of the deposited metal at the  Surface had. The metal penetration depth was up to about 50 μm.

Example 7 Application of supported Pd / Cu-Alugel catalysts to nitrate reduct tion

100 g of the according to Example 6.2.1 were used. produced Palladium-copper-supported Alugel catalyst with 1 wt .-% Pd and 0.25% by weight of Cu. Water containing 60 mg / l nitrate was at a flow rate of about 11 liters per hour and what hydrogen pressure of 5 bar at a pH of 6.3 through the Trä gerkatalysator fixed bed out. The nitrate decomposition performance was 0.7 to 1.4 mg per gram of catalyst per hour.

Claims (12)

1. Continuously feasible process for the removal or reduction of the oxygen content, the nitrite and / or nitrate content of oxygenated and / or nitrite and / or nitrate-polluted water under selective nitrogen formation, where in the oxygen-containing, nitrite and / or nitratbela Stete Water introduces hydrogen gas and contacted with the hydrogen-laden water with a catalyst which forms ge from a loaded with a consisting of palladium and / or rhodium or palladium and a metal of the copper group metal component porous carrier, and to treat ment only nitrite loaded Water a catalyst whose metal component consists of palladium and / or rhodium and, if the water to be treated also contains nitrate, a Ka catalyst whose metal component consists of palladium and a Me tall the copper group or rhodium and optionally Palla dium, or a mixture from a catalyst, desse n metal component consists of palladium and a metal of the copper group, and a catalyst whose metal component consists only of palladium, and thereby does not raise the pH of the water above pH 8 and optionally the process is carried out so often in succession until the oxygen content , The nitrite content and / or the nitrate content of the water is removed or reduced to a tolerable value, characterized in that one uses a supported catalyst, the Trä ger according to patent. , , (Patent Application P 43 06 875.8) under lead a sol in drop-shaped sol particles by spraying the Solteilchen from below into a reaction gas and collecting the Solteilchen after flying through a curved trajectory in the reaction liquid, and subsequent workup of the soled BEFE sol particles under aging, washing, drying and calcination has been produced. 2. The method according to claim 1, characterized in that Palladium or palladium and copper as the catalytically active com component is used.   3. The method according to claim 1 or 2, characterized net, that one uses a supported catalyst, the carrier was calcined at a temperature of 400 to 1200 ° C. 4. The method according to any one of the preceding claims, characterized in that verwen use a supported catalyst det, whose grain size in the range of 0.05 mm to 1 mm, preferably in the range 0.4 to 0.6 mm and its pore volume in Be rich from 0.4 to 1.2 ml / g. 5. The method according to any one of the preceding claims, characterized in that verwen use a supported catalyst det, whose pore diameter is in the range of 50 to 1500 Å, before preferably 100 to 200 Å. 6. The method according to any one of the preceding claims, characterized in that in the water such a quantity What is introduced, which at least the reduction the predetermined content of oxygen and nitrite and / or Nitrate stoichiometrically necessary amount of hydrogen and hoch at least equal to a 20 wt .-% excess of this amount. 7. The method according to any one of the preceding claims, characterized in that one uses water, which with 0.1 mg / l to 2 g / l nitrite and / or 1 mg / l to 10 g / l nitrate be is lasted. 8. The method according to any one of the preceding claims, characterized in that it is in a fluidized bed or an expanded bed performs. 9. To reduce the oxygen content, nitrite and / or nitrate content of a suitable supported catalyst comprising Palladium, rhodium or palladium and a metal of the copper group pe on a support based on alumina, the support according to patent. , , (German Patent Application P 43 06 875.8) by Transfer a sol into droplet-shaped sol particles by one Say the sol particles from below into a reaction gas and up  catch the sol particles after flying through a curved flight train in a reaction liquid work up the solidified Sol particles by aging, washing, drying and calcining, with the proviso that the carrier has a specifi cal surface in the range of 5 to 250 m² / g, preferably in Range of 100 to 200 m² / g. 10. Supported catalyst according to claim 9, characterized gekennzeich net, that the carrier before the application of the catalytically active Metal component at a temperature of 400 to 1200 ° C kalzi was renamed. 11. Supported catalyst according to one of claims 9 or 10, characterized in that the bulk density 0.3 to 1.2 g / ml and the pore volume is 0.4 to 1.2 ml / g. 12. Supported catalyst according to one of claims 9 to 11, characterized by a content of palladium or rhodium in the Range from 0.5% to 5% by weight and, if copper is included, by a content of copper in the range of 0.1 to 2 wt .-%.