DE3939480A1 - METHOD, ADSORPTION AGENT AND DEVICE FOR DENICKING NOXES CONTAINING NOX BY ADSORPTION - Google Patents

Description

The invention relates to a method for removing nitrogen oxides (NOx). relatively low concentration of gases, such as those caused by the Ventilation systems for tunnels such as motorway tunnels, mountain tunnels, Sea tunnels, underground or built roads and the like be, as well as an adsorbent and a device for cleaning of gases containing nitrogen oxides.

For road tunnels that are long in length and high in traffic have, it is necessary to air out with considerable throughput vacuum the tunnel to ensure adequate ventilation and Health risks for drivers and passengers and an impairment to avoid the view. Even with relatively short tunnels in urban areas Areas or suburban areas, it is common to ventilate the tunnel to air pollution by concentrated at the entrance and exit of the tunnel released carbon monoxide (CO), nitrogen oxides (NOx) and the like to reduce.

However, if the gas extracted by the ventilation is near the tunnel is released, the polluted gas leads to environmental pollution in the affected area. Especially in city centers and suburbs where that was caused by emissions from motor vehicles If pollution spreads two-dimensionally, it then happens a greater spread of severe environmental pollution. The same problem also occurs when road tunnels or road superstructures are created to reduce the environmental impact of existing roads.

The invention relates to a method, a device and an adsorbent to remove low NOx concentrations from the gas released by the ventilation system for such tunnels.

Characteristic of that extracted from tunnels by the ventilation system Gas is a relatively low NOx concentration on the order of 5 ppm, depending on the traffic in a wide range fluctuates, and a relatively low, the normal outside temperature corresponding temperature.  

So far there are methods for removing those generated from solid sources Nitrogen oxides have been investigated, with which the exhaust gas from burners is cleaned leaves. Basically, the following three can be used in these processes Differentiate types.

(1) Catalytic reduction

In this process, ammonia is used as the reducing agent NOx contained in the exhaust gas selectively to harmless nitrogen and water vapor reduced. This process is commonly used for the denitrification of the exhaust gases used by burners. The gas to be cleaned must be used in this process however, have a temperature of at least 200 ° C. For this The reason this process is uneconomical when cleaning gas from road tunnels, because that in large quantities at normal ambient temperature resulting gas must be heated using a lot of energy.

(2) Wet absorption process

This process takes advantage of the fact that nitrogen dioxide (NO₂) and nitrogen trioxide (N₂O₃) are relatively easy in a liquid absorbent such as water or an aqueous alkali solution. The NO contained in the gas to be treated is oxidized by one injects an oxidation catalyst or ozone into the absorbent, and the resulting NO₂ and N₂O₃ is in the absorbent absorbed. However, this process is relatively complex because the NOx is in enriched the absorbent in the form of nitrates and nitrites, so that a renewal and post-treatment of the absorbent, d. H. a treatment the waste liquid. Furthermore, this procedure economic disadvantages because the cost of the oxidizing agent per mole are higher than the cost of the reducing agent NH₃, which in the selective catalytic reduction is used.

(3) Dry adsorption process

In this process, NOx is removed using a suitable adsorbent removed from the exhaust. Various methods of this type have been investigated been before the selective catalytic reduction process for denitrification  of burner gases has become common. However, since the burner exhaust gas is high Has NOx concentrations and a high temperature as well as a high Has water content, the dry adsorption process is the catalytic Reduction process economically inferior and therefore not in the practice has been introduced.

However, as the dry adsorption process in terms of cleaning of gases from the ventilation systems of road tunnels re-examined this procedure proved to be in contrast to that used in the treatment results found from burner exhaust gases as simple and economical.

The studies on denitrification by adsorption include a study carried out by the Japanese Industrial Development Research Institute on the adsorptive removal of NOx with low concentration from combustion gases ("Research on Development of New Denitration System with Use of Special Adsorptive Oxidizing Catalysts", May 1978). In this study, experiments were carried out with an air H₂O-NO test gas (initial concentration of NO: 100-120 ppm, dry gas (dew point -17 ° C), space velocity 3270 h ^-1 ), and it was reported that a metallic Copper (oxide) containing adsorbent on a natural tuff support has been found to be useful.

The NOx concentration in the gas from road tunnels is up to 5 ppm estimated. In the area there is no information as to whether NOx has a low Concentration of 5 ppm with the adsorbent used in this study can be effectively adsorbed. (In the study, the NOx concentration 100 ppm).

To date, there are no reports of absorbents with which one effective adsorption of NOx even at low concentrations of approx 5 ppm is possible.

The invention is therefore based on the object of an adsorption process specify with which that in the gas from ventilation systems of road tunnels NOx contained in low concentration can be effectively removed can.  

Another object of the invention is to carry out an adsorbent of this procedure.

In conventional devices for denitrification of exhaust gases in general between fixed bed and moving bed devices Bed can be distinguished.

A fixed bed device has a plurality of ones arranged parallel to one another Adsorber on. If the concentration of the substance to be removed at the outlet of one of the adsorbers has reached a limit after one certain amount of the substance contained in the adsorber Adsorbent has been adsorbed, it is switched to another adsorber, and the adsorbed substance is desorbed to the adsorbent to regenerate. If large quantities of gas have to be treated, then so the adsorber is reduced with regard to the flow resistance Amount of adsorbent loaded, making the adsorber more common must be switched. Taking into account that desorption or regeneration takes a certain amount of time, the device must in this case have a larger number of adsorbers arranged in parallel, so that overall relatively large dimensions of the device result.

In the case of a device with a moving bed, on the other hand, the one to be treated Gas in an adsorber is generally countercurrent with the adsorbent brought into contact. The adsorbent that's a big one The amount of substance to be removed has been added for the purpose of Regeneration continuously removed by desorption, and fresh or Regenerated adsorbent is continuously fed to the adsorber. This device can thus be operated continuously and it is no switching required, so the overall dimensions of the device can be smaller than with a device with a fixed bed.

In order to explain the conventional NOx removing device described in the above-mentioned publication of the research institute, reference should already be made here to Fig. 10 of the drawing.

A dryer 48 in the upper part of a drying tower 47 contains silica gel (silica gel), which serves as a drying agent and adsorbs water from the exhaust gas supplied via a line 41 (NOx + air + H₂O). When water is adsorbed, the desiccant moves downward into a regenerator 49 due to gravity. In the regenerator 49 , the drying agent is brought into contact with a regenerating drying gas (from the outlet of an adsorber 51 in an adsorption tower 50 ), which is supplied via a line 43 , whereby the desiccant is freed from the adsorbed water. In this way, the desiccant is regenerated and transported upward into the dryer 48 by the drying gas so that it circulates in the drying tower 47 .

While the silica gel serving as the drying agent circulates in the drying tower 47 , water is thus repeatedly adsorbed by the silica gel and released again (during regeneration). The exhaust gas supplied via line 41 is dried and flows through line 42 into adsorber 51 in the upper part of adsorption tower 50 . The regenerating dry gas, which was introduced through line 43 into the regenerator 49 of the drying tower 47 , takes up water there and is released into the atmosphere as purified gas (air + H 2 O).

A NOx adsorbent is contained in the adsorber 51 of the adsorption tower 50 and adsorbs NOx from the dry exhaust gas (air + NOx) from the drying tower 47 . After the uptake of NOx, the adsorbent moves downward into a desorption regenerator 52 by the action of gravity. In the regenerator 52 , the NOx adsorbent is heated to 400 ° C by means of a heater 46 , brought into contact with a dry purge gas described below so that it is regenerated by releasing NOx, and returned to the upper part of the adsorption tower 50 .

Part of the gas emerging from the adsorber 51 serves as a regenerating dry gas which is introduced into the desorption regenerator 52 via a line 44 . This gas takes up NOx from the adsorbent in the regenerator 52 and is discharged as a desorption gas from the system via a line 45 . The out of the dryer 48 via the line 42 entering the adsorber 51 dry exhaust gas (NOx + air) is denitrified in the adsorber 51, and the greater part of the thus obtained purified and dried air is fed via line 43 into the regenerator 49 of the drying tower 47 initiated and serves as a drying gas for the regeneration of the drying agent. The remaining part of the air is introduced as dry gas for the regeneration of the NOx adsorbent in the regenerator 52 of the adsorption tower 50 .

The desorption gas discharged from the system via line 45 contains the NOx absorbed by the adsorbent. It has therefore been proposed to remove the NOx from the gas by absorbing the NOx in an aqueous alkali solution or the like (wet absorption). In practice, however, the wet absorption process is complex and costly since the NOx enriched in the liquid absorbent in the form of nitrates and nitrites requires renewal and aftertreatment of the absorbent (aftertreatment of the waste liquid).

To rid the desorption gas of pollutants and into the atmosphere To be able to deliver, a procedure has already been proposed in which an adsorbent with adsorbed NOx for the purpose of regeneration is treated with air containing NH₃ (unexamined Japanese patent publication No. 15 593/88). In this process, the absorbed NOx selectively reduced to harmless N₂ and H₂O with NH₃. If the NOx adsorbent is regenerated only by heating, so the adsorbent heated to 400 ° C, as already mentioned. If against a copper salt with a denitrifying catalytic as NOx adsorbent Effect on zeolite is used as a carrier material, so can the adsorbent can be regenerated by using it at a low Temperature of 100 to 300 ° C with air containing NH₃ (regeneration gas) in contact (Japanese Patent Application No. 133 446/88).

In the method described above, in which a gas containing NH₃ is used to regenerate the NOx adsorbent high probability that the NOx does not react completely with NH₃ and remains in the desorption gas, or that excess NH₃ in the Desorption gas remains. To a free of excess NH₃ desorption gas to obtain the amount of the regeneration gas added  NH₃ be carefully controlled. The NOx adsorbent is reversed not fully regenerated when the amount of NH₃ supplied is too small. Operation of the desorption regenerator for the NOx adsorbent therefore causes extraordinary difficulties.

If a little too large amount of NH₃ added to the regeneration gas to achieve complete regeneration of the NOx adsorbent, so the desorption gas contains excess NH₃, and this gas must be introduced into another denitrification reactor and through the denitrification reaction of NOx with NH₃ or by oxidation-decomposition of the NH₃ be made harmless. In the conventional one described above Device with a NOx adsorber with a moving bed and one Drying device, the lines must have a large cross-section, thus the flow resistance counteracting the gas flows is reduced when large amounts of exhaust gas have to be processed. On the other hand, to improve the effectiveness of the adsorption process, it is required, particles of the adsorbent from the lines intercept and discharge, the particles evenly over the line cross-section are distributed, and the particles must also be in a similar form the system will be introduced. In practice, this results in considerable Difficulties. Furthermore, moving in the adsorption tower Gravity used to move the adsorbent, and the regenerated adsorbent is raised with the help of dry air transported through the tower. This leads to abrasion on the adsorbent and for breaking up the adsorbent particles and for abrasion on the inner surfaces of the tower and risers. Result from this themselves significant disadvantages. The adsorption tower has a complex one Set up and the device is difficult to operate.

The invention is therefore also based on the object of providing a simple, effective and easy to use device for cleaning To create gases containing NOx.

According to the invention, the above-mentioned objects are achieved by the in Method specified in claim 1, the adsorbent according to claim 3 and the device according to claim 6.  

According to the invention, the gas contains NOx in low concentration brought into contact with an adsorbent containing a copper salt Contains zeolite as a carrier material.

The inventive method enables effective adsorption and Removal of NOx, especially in ventilation systems for road tunnels resulting exhaust gases that have a low NOx concentration of about 5 ppm and have normal ambient temperatures and at which the pollutant content and the temperature depending on traffic and environmental conditions varied in a wide range.

The absorbent used in the process according to the invention comprises at least one copper salt, which is based on a natural or synthetic Zeolite is present as a carrier. Examples of preferred copper salts as Adsorbents are copper chloride, copper chloride double salts and that Ammine complex salt of copper chloride.

The device according to the invention for cleaning gases containing NOx includes an adsorption dryer for drying the gas and for Regeneration of a drying agent with a cleaned gas and a Adsorption denitrification unit for denitrification of the dried gas. The denitrification unit has an adsorbent regeneration zone on that with a gas recirculation line for recirculating an NH₃ containing regeneration gas and provided with a gas extraction line is through which part of the regeneration gas from the recirculation line branched off, passed through a denitrification reactor and after denitrification is released into the atmosphere.

The adsorption dryer and the adsorption denitrification unit have preferably each have a rotatable adsorber for continuous transport of the drying agent or the NOx adsorbent perpendicular to Gas flow on, resulting in continuous withdrawal, regeneration and Allows supply of the drying agent or the NOx adsorbent becomes.

In the device according to the invention, the gas in the adsorbent Regeneration zone have an excess of NH₃. This will  a sufficient supply of NH₃ ensured to the reaction zone, so that the NOx bound by the adsorbent is completely reduced by reduction removed and the adsorbent completely regenerated can. This eliminates the need to carefully control the supply of NH₃.

Preferred exemplary embodiments of the invention are described below of the drawings explained in more detail.

Show it:

Fig. 1 to 5 are graphical representations of the time course of the NOx concentration at the outlet;

Fig. 6 is a graph showing the relationship between the amount of copper bonded to carriers and the breakthrough time;

Fig. 7 is a flowchart of an embodiment of the invention;

Fig. 8 is a perspective view of a rotary dryer;

Fig. 9 is a perspective view of a rotary NOx adsorber; and

Fig. 10 is a flowchart of a conventional method for removing NOx.

The adsorbent according to the invention becomes more natural or synthetic Zeolite used as a carrier material. For shaping the adsorbent or the carrier can be used as a binder or extender substances other than zeolite may also be present, for example alumina Sol, alumina, silica sol, silica alumina and the like.

The carrier for the adsorbent according to the invention can be a natural one or synthetic zeolite. Suitable natural zeolites are faujasite, Mordenite and the like. Synthetic faujasite, synthetic mordenite  and the like can be used as synthetic zeolites. To the Synthetic faujasites include, for example, zeolite type A (SiO₂ / Al₂O₃ Molar ratio: 1.85 ± 0.5), zeolite type-X (SiO₂ / Al₂O₃ molar ratio: 2.5 ± 0.5) and zeolite type-Y (SiO₂ / Al₂O₃ molar ratio: 4.5 ± 1.5). To the synthetic Mordenites include, for example, zeolite type L (SiO₂ / Al₂O₃ Molar ratio: 6.4 ± 0.5) and zeolites manufactured by Norton Co. will. Zeolites in which the SiO₂ / Al₂O₃ are particularly suitable Molar ratio is at least 2.

Another feature of the adsorbent according to the invention is in that there is at least one special copper salt on the carrier. Examples of suitable copper salts are copper chloride (CuCl₂), copper chloride Double salts such as ammonium copper (II) chloride (CuCl₂ · 2 NH₄Cl) and Ammine complex salt of copper chloride. The amount of copper salt on the Carrier is about 0.1 to 20 percent by weight, preferably about 0.5 to 10% by weight, calculated as metallic copper in relation to the as End product obtained adsorbent.

The copper salt is generally applied to the support by the Zeolite in a solution of the copper salt in a suitable solvent is immersed.

The amount of copper salt absorbed by the carrier is, for example adjusted by adjusting the concentration of the copper salt or the temperature of the solution or the immersion time varies.

After immersion in the copper salt solution, the carrier is released from the solution pulled out, washed with water and in air at about 110 to 120 ° C. dried. If necessary, the dried product in air baked at about 300 to about 500 ° C. If the adsorbent is continuous with repeated adsorption and desorption processes is used for regeneration, it is recommended that the adsorbent To undergo heat treatment at a temperature slightly higher is considered the highest temperature when using the adsorbent occurs.

There are no restrictions on the shape of the adsorbent.  The shape is preferably chosen so that there is a large contact area results with the gas and an even gas flow is made possible. For example, the adsorbent can be more solid in shape Have cylinders, balls, Raschig rings or honeycombs.

The method described here for removing NOx by adsorption is among those commonly found in dry adsorption processes Conditions executed.

A device for cleaning the exhaust air from ventilation systems for road tunnels will be described below with reference to the flowchart shown in FIG. 7.

The exhaust air contaminated with nitrogen oxides or the exhaust gas is introduced with the aid of a ventilation line 8 into an adsorption dryer 1 in order to remove water from the gas by means of a desiccant by adsorption and to dry the gas. The gas is then introduced into an adsorption denitrification unit 2 in order to remove NOx from the gas by adsorption, so that a purified gas results. The drying agent in the dryer 1 is regenerated with the help of the cleaned gas. The adsorbent, on which the nitrogen oxides were adsorbed in the denitrification unit 2 , is regenerated with the help of a NH₃-containing regeneration gas.

According to an essential feature of the invention, a larger part of the regeneration gas, the NH₃ was added with the help of an NH₃ source 3 , returned by means of a blower 4 arranged in a gas recirculation line 9 and in an adsorbent regeneration zone of the denitrification unit 2 for regeneration of the NOx Adsorbent used, while another part of the regeneration gas as purge gas branches off via a gas extraction line 10 , passed through a denitrification reactor 5 and then released into the atmosphere.

If the NOx adsorbent is to be regenerated with the aid of the NH 3 -containing gas, it is expedient to heat the adsorbent to be regenerated and the recycled regeneration gas with the aid of a heating device 6 to a suitable temperature (100 to 300 ° C.), so that the NOx Adsorbent can react effectively with the NH₃.

If in the conventional method described at the beginning the NOx Adsorbent is to be regenerated, so NH₃ must be carefully in lower Concentration in the regeneration gas can be distributed so that the amount of NH₃ corresponds to the amount of NO₃ bound by the adsorbent. That is, the amount of NH₃ must be just enough to eliminate of NOx through reduction. To set this amount of NH₃ correctly to be able to, the amount of adsorbed NOx would have to be measured accurately will. A continuous measurement of the amount of NOx that is Adsorbent is bound, however, is not possible in practice. The conventional method for regeneration of the NOx adsorbent is therefore very likely to lead to the release of excess NH₃ or for incomplete regeneration of the adsorbent due to insufficient supply of NH₃.

In contrast, excess can occur in the device proposed here NH₃ be present in the adsorbent regeneration zone. The supply of a sufficient amount of NH₃ in the regeneration zone allows it to completely remove the adsorbed NOx by reduction and thus to fully regenerate the adsorbent. This will enables simple and economical operation of the device.

While the recycled regeneration gas is partially discharged as a purge gas, the excess NH 3 contained in the purge gas and the NOx which has not reacted and has passed into the gas by desorption of the adsorbent can be rendered harmless with the aid of the denitrification reactor 5 arranged downstream of a heating device 7 . The amount of in the Entstickungsreaktors 5 to be treated purge gas is very small. The reactor 5 therefore only needs to be of a small size, and yet the purge gas can be freed of pollutants effectively and at a low cost.

In the arrangement shown in FIG. 7, there is an impairment of the cleaning effect when a leakage flow of the recirculated regeneration gas into the clean gas freed from NOx occurs. If a degree of denitrification of at least 60% is aimed for, the leakage flow of the regeneration gas into the clean gas is a serious problem.

According to FIG. 9, the adsorption Entstickungseinheit 2 is formed as a rotatable adsorbent in which an adsorbent rotor in sliding contact with the nozzle for the exhaust gas and the regeneration gas is. Complete sealing of the parts sliding past one another is difficult. For this reason, a lower operating pressure is set in the regeneration part (cooling, regeneration and preheating) than in the NOx adsorption part, so that the impairment of the cleaning action by gas leakage currents is prevented. In this case, gas passes from the adsorption part into the regeneration part. The amount of gas corresponding to this leakage flow is taken from the recirculation line 9 for the regeneration gas and discharged. The NOx adsorbent adsorbs NOx as well as a small amount of water that has been desorbed in the regeneration part and has accumulated in the regeneration gas returned. In order to limit the water content of the recirculated regeneration gas to a certain value, the recirculation line 9 is supplied with a suitable amount of dry air via the sliding connection point, and the recirculation gas containing water is partially discharged from the recirculation channel 9 .

Thus, the device is designed such that the leakage gas on the sliding Junction the main source for supplying dry air to the recirculated Regeneration gas forms.

A cleaning device in which rotatable adsorber as adsorption dryer and as a denitrification unit serve.

The rotatable adsorbers shown in the flow chart in Fig. 7 are designed so that the desiccant and the NOx adsorbent are continuously removed, regenerated and fed again. The mode of operation of the device corresponds to the mode of operation of the conventional device described at the outset, but the device according to the invention is characterized by a simpler construction and by a lower gas flow resistance.

An example of a rotating dryer will be described below with reference to FIG. 8. In the dryer 1 , the exhaust gas to be cleaned is dried with the aid of a drying agent which is regenerated with the aid of the denitrified, dry clean gas.

The amount of dry gas used to regenerate the desiccant corresponds approximately to the amount of exhaust gas to be cleaned. The dryer 1 has a rotor 11 with drying agent. Expedient embodiments of the rotor 11 are an arrangement of adsorption plates which contain silica gel as water-adsorbing agent and are arranged in layers with the interposition of suitable spacers between two adjacent plates, an arrangement of flat plates and corrugated adsorbing plates which contain silica gel as water-adsorbing agent and in one alternating layer sequence are arranged, or a water adsorber made of silica gel in the form of a uniform honeycomb structure. The ventilation line 8 , via which the exhaust gas containing NOx is supplied, is arranged so that the exhaust gas flows through a zone 11 a, which has a semicircular cross-section and is formed in the axial direction of the rotor through its right or left half. A clean gas line 13 is arranged so that the dry regenerating gas from the series gas line flows through a zone 11 b, which also has a semicircular cross section and forms the other half of the rotor 11 . The rotor 11 is rotated in the direction of arrow A, so that the exhaust air is continuously dried.

An example of a rotating adsorber of the denitrification unit will be explained below with reference to FIG. 9. The denitrification unit 2 serves to adsorb the NOx contained in the dried exhaust gas and thus to convert the exhaust gas into a dry clean gas (air). At the same time, the denitrification unit is used to regenerate the NOx adsorbent with the circulating regeneration gas containing NH₃. The denitrification unit 2 has a rotor 12 made of NOx adsorbent. Advantageous embodiments of the rotor 12 are an arrangement of plates of copper salt on an adsorbent containing zeolite support, which are arranged in layers with the interposition of suitable spacers between two adjacent plates, an arrangement of flat adsorbent plates and corrugated adsorbent plates, which in are arranged in an alternating layer sequence and are produced from an adsorbent containing copper salt on a zeolite carrier, or an adsorber made of copper salt on a zeolite carrier designed as a uniform honeycomb structure. The ventilation line 8 is arranged so that the dried exhaust gas flows through a zone 12 a, which has a semicircular cross section and is formed in the axial direction of the rotor 12 through its right or left half. On the rotor 12 , the recirculation line 9 is further arranged such that the NH₃-containing regeneration gas flows successively through zones 12 b, 12 c and 12 d of the rotor, each of which has a sector-shaped cross section and is formed by third sectors of the other half of the rotor 12 will. Consequently, the NOx is adsorbed in zone 12 a and the rotor 12 is cooled in zone 12 b, regenerated in zone 12 c and preheated in zone 12 d.

example 1

Zeolite Type-Y, (a product of the company Nishio Kogyo Co., Ltd. (SiO₂ / Al₂O₃ = 4.7), Manufacturer's designation SK-40, 1/16 inch extrudate) is milled to by sieving a fraction with a particle size of 1.4-2.00 mm (10 to 14 mesh). The granular carrier thus obtained becomes at room temperature 16 hours in an aqueous copper (II) chloride solution a concentration of 1 mol / liter immersed, the volume of which is three times of the carrier volume is. The carrier is washed with water, then dried at 110 to 120 ° C for 2 hours and finally 3 hours baked at a temperature of 400 ° C, so that an adsorbent (CuCl₂-Y) receives (the bound amount of copper is 6.5 weight percent).

The adsorbent (7 g, about 12 cm³) was placed in a stainless steel reaction tube with an inner diameter of 22 mm, dried at about 235 ° C for one hour by blowing dry air (dew point about -35 ° C) with a throughput of 5 Liters / min passed through the reaction tube and then allowed to cool the adsorbent to room temperature. After cooling, the air flow was stopped and dry air containing 4.48 ppm nitrogen monoxide was passed through the reaction tube at a rate of 5 liters / min and the NOx concentration of the gas flowing out of the densely packed layer of the adsorbent became immediately after the introduction of the air continuously measured via that of a chemiluminescence detector. Fig. 1 shows the change with time of the NOx concentration is measured at the gas outlet. As can be seen from the graph, the time in which the NOx concentration at the outlet rose to 10% of the concentration at the inlet, ie to 0.45 ppm, was 49.7 minutes. (This time will hereinafter be referred to as the "breakthrough time").

Comparative Example 1

Fig. 2 shows the change in the NOx concentration at the outlet, which was measured under the same conditions as in Example 1, except that the granular carrier material prepared according to Example 1 was used instead of the adsorbent and that the NOx concentration at the inlet Was 4.67 ppm. As can be seen from FIG. 2, the breakthrough time in this case was only 0.8 minutes. This shows that the use of only the zeolite carrier material without copper salt bound thereon leads to less adsorption of NOx.

Comparative Examples 2 and 3

An adsorbent containing copper (II) chloride supported by impregnation was prepared in the same manner as in Example 1, except for the γ-alumina (Comparative Example 2) or diatomaceous earth (Comparative Example 3) in place of the zeolite Type-Y was used as the carrier material. Fig. 3 shows the temporal changes in the NOx concentration (C) at the outlet, which were determined under the same conditions as in Example 1, except that the adsorbent described above was used and that the NOx concentration at the inlet (C₀ ) Was 4.6 ppm. The diagram shows that the adsorbent produced using γ-aluminum oxide or kieselguhr as the carrier material does not adsorb a sufficient amount of NOx.

Comparative Examples 5-6

Adsorbents were prepared in the same manner as in Example 1, except that an aqueous solution of iron (III) chloride, FeCl₃ (comparative example) instead of the aqueous solution of copper (II) chloride of 1 mol / liter as aqueous metal salt solutions 4), an aqueous solution of cobalt chloride, CoCl₂ (comparative example 5) or an aqueous solution of chromium (III) chloride, CrCl₃ (comparative example 6) were used. The solutions had the same concentration as the copper (II) chloride solution. Fig. 4 shows the temporal changes in the NOx concentration at the outlet, which were determined under the same conditions as in Example 1, except that the above-mentioned adsorbents were used and the NOx concentration at the inlet 4.5 to 4, Was 6 ppm. The diagram shows that the use of base metal salts other than copper salt leads to an insufficient adsorption of NOx.

Examples 2 and 3 and Comparative Examples 7-10

Adsorbents were prepared in the same manner as in Example 1 with the exception that instead of the aqueous solution of copper (II) chloride, of 1 mol / liter an aqueous solution of 1 mol / liter of copper nitrate, Cu (NO) ₃ (Comparative Example 7), an aqueous solution of 1 mol / liter of Copper sulfate, CuSO₄ (Comparative Example 8), an aqueous solution of 0.5 mol / liter of copper bromide, CuBr₂ (Comparative Example 9), an aqueous solution of 0.5 mol / liter of copper acetate, Cu (CH₃COO) ₂ (comparative example 10), an aqueous solution of 1 mol / liter of ammonium copper (II) chloride, CuCl₂ · 2 NH₄Cl (Example 2) and a solution was used by adding from ammonia water to an aqueous solution of 1 mol / liter of copper (II) - Preserved chloride until a copper (II) ammonia complex was formed (Example 3).

Fig. 5 shows the changes in the NOx concentration at the outlet measured under the same conditions as in Example 1, except that the above adsorbents were used and the NOx concentration at the inlet was 4.6 to 4, Was 8 ppm.

As can be seen from the diagram, the adsorbents that Ammonium copper (II) chloride or an amine complex salt of copper (II) - chloride contained, achieved excellent adsorption properties.  

Example 4

Adsorbents containing different amounts of copper were produced in the same manner as in Example 1, the zeolite carrier being the same zeolite type Y (SiO₂ / Al₂O₃ molar ratio: 4.7) as in Example 1 or "Zeolite 1 "(SiO₂ / Al₂O₃ molar ratio: 2.4) with a smaller SiO₂ content or" Zeolite 2 "(SiO₂ / Al₂O₃ molar ratio: 10) with a higher SiO₂ content was used and that aqueous solutions of copper (II) chloride or Ammonium copper (II) chloride in different concentrations were used. Table 1 and FIG. 6 show the amounts of copper bound in these adsorbents and the associated breakthrough times, which were measured under the same conditions as Example 1.

It turns out that adsorbents with excellent adsorption properties are obtained when using zeolite supports in which the SiO₂ / Al₂O₃ molar ratio is not less than about 2.

Referring to FIG. 6, the preferred amount of copper (II) chloride or a double salt thereof, that is, ammonium copper (II) chloride, about 0.5 to about 10 weight percent, calculated as the weight ratio of copper to the total adsorbent , but the amount of copper varies depending on the type of carrier used.

Table 1

Claims (11)

1. A process for the denitrification of gases containing NOx in a low concentration by adsorption, characterized in that the gas is brought into contact with an adsorbent which contains at least one copper salt on a carrier made of natural or synthetic zeolite. 2. The method according to claim 1, characterized in that the copper salt is selected from a group consisting of copper chloride, copper chloride Double salts and amine complex salts of copper chloride. 3. Adsorbent for adsorbing NOx, characterized by at least a copper salt on a carrier made of natural or synthetic Zeolite. 4. Adsorbent according to claim 3, characterized in that the Copper salt is selected from a group consisting of copper chloride, Copper chloride double salts and amine complex salts of copper chloride. 5. Adsorbent according to claim 3 or 4, characterized in that the amount of copper salt deposited on the zeolite 0.1 to 20% by weight metallic copper based on the total weight of the adsorbent is. 6. Device for the denitrification of NOx-containing gases, with an adsorption dryer ( 1 ), in which the gas is dried with the aid of a desiccant and the desiccant is regenerated with purified gas, and with an adsorption denitrification unit ( 2 ) with a denitrification zone ( 12 a) for denitrification of the dried gas and an adsorbent regeneration zone ( 12 c), characterized in that a recirculation line ( 9 ) is connected to the adsorbent regeneration zone ( 12 c), in which a regeneration gas containing NH₃ circulates, and that the recirculation line ( 9 ) is connected to a gas extraction line ( 10 ), via which a portion of the regeneration gas is branched off from the recirculation line ( 9 ), passed through a denitrification reactor ( 5 ) and released to the atmosphere as a denitrified gas. 7. The device according to claim 6, characterized in that the denitrification unit ( 2 ) and preferably also the dryer ( 1 ) has a rotating adsorber ( 12; 11 ) in which the NOx adsorbent or the drying agent is continuously moved transversely to the gas flow . 8. The device according to claim 7, characterized in that the rotating adsorber ( 11 ) of the dryer ( 1 ) is formed by layers by means of spacers spaced-apart dryer plates which contain silica gel as a water-adsorbing drying agent, alternately arranged in a layer sequence flat and corrugated dryer plates that contain silica gel as a drying agent, or by a one-piece honeycomb structure that contains silica gel as a drying agent. 9. Apparatus according to claim 7 or 8, characterized in that a gas line ( 8 ) for the gas containing NOx is arranged on the rotating adsorber ( 11 ) of the dryer such that the undried gas flows through part ( 11 a) of the adsorber, and that a clean gas line ( 13 ) is arranged on the rotating adsorber ( 11 ) in such a way that dry gas supplied via the clean gas line flows through another part ( 11 b) of the adsorber for regeneration of the adsorber. 10. The device according to one of claims 7 to 9, characterized in that the rotating absorber ( 12 ) of the denitrification unit ( 2 ) is formed by layers of spacer plates spaced apart from one another of an adsorbent which contains a copper salt on a carrier made of zeolite, by an alternating layer sequence of flat and corrugated plates made of an adsorbent that contains copper salt on a zeolite carrier, or by a one-piece honeycomb structure of an adsorbent that contains copper salt on a zeolite carrier. 11. The device according to one of claims 7 to 10, characterized in that a gas line ( 8 ) for supplying the NOx-containing dry gas is arranged on the rotating adsorber ( 12 ) of the denitrification unit that the gas is a part ( 12 a) Flows through adsorber, and that the recirculation line ( 9 ) is arranged on the rotating adsorber such that the NH₃-containing regeneration gas flows through another part ( 12 c) of the adsorber.