WO1996012552A1

WO1996012552A1 - Process, device and catalyst for cleaning used air

Info

Publication number: WO1996012552A1
Application number: PCT/DE1995/001504
Authority: WO
Inventors: Joachim Kunze; Rainer Plenz; Holger Kryk; Torsten Kerl; Torsten Kühn
Original assignee: Joachim Kunze; Rainer Plenz; Holger Kryk; Torsten Kerl; Kuehn Torsten
Priority date: 1994-10-19
Filing date: 1995-10-19
Publication date: 1996-05-02
Also published as: AU3800595A

Abstract

The invention relates to a process, a device and a catalyst for cleaning used air of oxidisable impurities. The purpose is to provide a process and device making it possible economically and highly effectively to clean the air of oxidisable pollutants by burning without giving rise to problems in the disposal of the products used. This purpose is attained in that the used air to be cleaned is intensively mixed in a pre-reaction or reaction vessel with a finely divided aqueous phase containing oxidising agents and surface-active substances. At the same time or thereafter the used air to be cleaned and the aqueous phase are brought into contact on a large-area solid catalytically active phase while the temperatures at the point of contact are kept below 105 °C.

Description

Process, device and catalyst for cleaning exhaust air

description

The invention relates to a method, a device and a catalyst for purifying exhaust air according to the preambles of claims 1, 4 and 17.

Methods and devices for cleaning exhaust air from oxidizable pollutants, in particular pollutants from the groups of hydrocarbons, alcohols, aldehydes, acids and acid anhydrides, esters, halogenated hydrocarbon compounds, inorganic and organic gases, of conventional design, generally have an air inlet for those to be cleaned and an air outlet for the cleaned air. Various elements are arranged between the inlet and outlet, which, in accordance with the respective process, guide the incoming air so that it optimally comes into contact with other media. In addition, screens and filters can be arranged that mechanically separate the contaminants.

When cleaning the air from gaseous constituents such as solvent vapors, it is customary to bring the air into contact with other media in order to remove these gaseous contaminants by means of adsorption, absorption, chemisorption or a to carry out catalytic post-combustion or combustion at higher temperatures.

Due to the stricter requirements regarding the content of impurities in the exhaust air released into the atmosphere, post-combustion of oxidizable pollutants in promisingly designed devices appears promising.

So far, however, it has been found that the known methods and devices repeatedly cause problems caused by the products formed in the oxidation reaction, which have an extremely unfavorable effect on the service life of the devices with regard to the products formed as a result of the oxidation reaction. This increases operating costs and creates new disposal problems.

It is also known that contaminated exhaust air is passed through distribution devices through a bed of special zeolite granules into which a mixture of hydrogen peroxide and deionized water is fed. In addition, ozone can be added to the zeolite bed in order to increase the oxidizing capacity. This method has the major disadvantage that the zeolite granules are completely saturated with water within a short time after starting up the plant and the hydrogen peroxide contained therein cannot develop its oxidation effect, which consists in particular in that OH radicals can be released from the hydrogen peroxide.

The recycling of desalinated water is disadvantageous for cost reasons. In addition, the gaseous ozone that may also be used in this process can cause ecological problems.

The invention is based on the object of a method and a device with which it is possible to inexpensively and highly effectively purify the exhaust air from oxidizable pollutants such as hydrocarbons, alcohols, aldehydes, acids, acid anhydrides, esters, halogenated hydrocarbon compounds and others to achieve inorganic and organic gases by incineration without causing disposal problems with regard to the resulting reaction products.

The solution to this problem results from the characterizing features of claims 1, 16 and 22.

The invention has several advantages.

The oxidizable pollutants are not collected and transferred to another medium, but are destroyed in accordance with the method and the device according to the invention and converted into compounds such as water, carbon dioxide, organic acids which are ecologically harmless. In this way, a residue of substances that should be sent to a landfill is almost completely avoided. It has been shown that the air can be cleaned extremely cost-effectively by means of the invention. In particular, solvents, such as those found in the paint processing industry, can be converted almost completely oxidatively and removed from the exhaust air by means of the device. The result is a high degree of purity in the treated air achieved that goes far beyond the existing standards.

A further advantage of the invention is that in particular substances which are difficult to oxidize, as are often used in solvents, such as hydrocarbons, halogenated hydrocarbons,

Alcohols, ketones, are broken down.

When contacting the solid support material with a large surface area, in particular in the presence of catalytically active materials according to the invention, there is a particularly rapid release of atomic oxygen and OH radicals from peroxidic oxidizing agents.

The carrier materials used according to the invention are particularly effective when they are combined or mixed with catalytically active compositions. It was shown that oxidic compounds of the subgroups of the periodic table in cooperation with oxidizing agents at the solid / liquid phase boundary make a catalytic conversion of the pollutants possible, which is almost quantitative. The catalytically active coating is applied here by impregnating or coating the solid, inert carrier material with a salt solution or with salt or oxide melts, followed by intensive heat treatment. The guantative and qualitative composition of the catalyst can be varied within wide limits and enables an optimal adaptation to the composition of the exhaust air. According to the invention, an optimal oxidation temperature is also set at this location via heat exchangers.

As oxygen-releasing compounds, in particular peroxidic nature, water-soluble substances such as Hydrogen peroxide preferred. According to the invention, ozone can also be used alternatively or additionally. However, the prerequisite for this is that the ozone is completely dissolved in the aqueous phase.

In a further development, the finely divided aqueous phase according to the invention, which is intensively mixed with the exhaust air, contains surface-active substances which favor the formation of an oil-in-water emulsion. This leads to an extremely advantageous solution-mediating absorption, in particular of the organic impurities which are less soluble in water into the aqueous phase, in which the pollutants can then be oxidized.

The surfactants preferably used according to the invention are low molecular weight emulsifiers and high molecular weight emulsifiers which promote the formation of oil-in-water emulsions. These include anionic substances such as soaps

(Na, K, NH ₄ , morpholine, triethanolamine), sodium lauryl sulfate, sodium cetyl sulfate, sodium mersolate,

Sodium 2-ethylhexyl sulfate, sodium xylene sulfonate, sodium naphthalenesulfonate, sodium alkylnaphthalenesulfonate, sodium sulfosuccinate, RCOOC ₂ H ₄ S0 ₃ sodium, RCONHC ₂ H ₄ S0 ₃ sodium (R = C ₁₇ H ₃₃ ), oleyl lysyl prinic acid sodium, oleyl sodium balsa Turkish red oil, natural solfonated oils, sodium salt of sulfonosuccinic acid dialkyl ester, bile acid Salts, resin soaps; cationic substances such as laurylpyridinium chloride, lauryltrimethylammonium chloride, lauryl-colamin-formyl-methyl-pyridinium chloride and nonionic substances such as polyoxyethylene fatty alcohol ether, polyoxyethylene fatty acid esters and high molecular weight emulsifiers such as casein, gelatin, protein degradation agar products, glue arabic, glue) , Moss, carrageen, gum, saponin, cellulose ether and ester, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone.

The wetting agents present according to the invention result in a particularly light and intensive contact of the aqueous phase with the solid inert phase, which leads to the fact that the release of atomic oxygen is extremely favored. Compounds from the group of alkylbenzenesulfonates are particularly suitable as wetting agents.

The device according to the invention also has important advantages over the prior art.

For example, the use of heat exchangers is provided in the area of the solid support material with a large surface area.

Another heat exchanger is located in the pre-reaction tank. This makes it possible to either heat or cool the exhaust gas to be cleaned to the required temperature. The heat exchanger can perform a synergetic function if the exothermic heat generated in the packed bed of the reaction container is supplied to the exhaust gas to be cleaned in the pre-reaction container. In turn, it is possible to use the heat exchanger in the packed bed of the reaction container dissipate any exothermic heat and if necessary supply it to the exhaust gas to be cleaned via the heat exchanger in the pre-reaction tank in order to achieve a required exhaust gas temperature. Through these possibilities of heat dissipation or heat supply, the device according to the invention can be used practically anywhere, even if the exhaust gas temperature there is not optimal. The exhaust gas to be cleaned is brought to the appropriate temperature in the reaction zone by means of the device. The presence of a heat exchanger in the reaction area of the reaction vessel has the additional advantage that the temperature of the reaction zone can be limited to a maximum of 105 ° C. in the case of strongly exothermic reactions. This is of considerable importance for the safe operation of the system.

The series connection of several reaction vessels provided according to subclaim 18 enables e.g. Advantageously, on the one hand, the combination of acidic and alkaline stages for removing pollutant components that can be oxidized in different environments and, on the other hand, an increase in the residence time in confined spaces and in the disposal of contaminants that are difficult to oxidize.

The development of claim 19, according to which a parallel connection of the reaction vessels is provided, increases the system flexibility with large or time-changing exhaust air volumes.

The invention is explained in more detail with reference to the drawings. Show it 1 shows a flow diagram of an exhaust air purification system with a pre-reaction container and a reaction container;

2 shows a flow diagram of an exhaust air purification system with a pre-reaction container and two separate reaction containers,

3 shows a flow diagram of an exhaust air purification system with a pre-reaction container and a reaction container with subchambers

1 consists of a pre-reaction container 1 and a reaction container 2. Above a raw gas inlet 5, the exhaust air is introduced into the pre-reaction container 1 through an exhaust air inlet 36. At the same time, an aqueous phase is atomized via nozzles 15. The finely divided aqueous phase and the exhaust gas mix intensively. The mixed aqueous phase and the exhaust air are passed in cocurrent via a heat exchanger 16, which brings the exhaust gas to the required oxidation temperature. Air is used as the heat transfer medium. This air enters a cooling air inlet 11 and is guided through the heat exchanger 16 via a fan 12 and fed back into the atmosphere via the heat transfer medium outlet 13. A part of the aqueous phase supplied via the nozzles 15 collects in the lower part of the pre-reaction container 1. A level control 17 controls the discharge of the aqueous phase from the lower region of the pre-reaction container 1. The aqueous solution of an oxidizing agent is introduced via a reaction solution inlet 18 and brought to the required reaction concentration with the water entering via a water inlet 19. Those collecting in the lower area of the reaction container 1 aqueous phase is discharged via a waste water outlet 20 or fed back into the system via the nozzles 15. The exhaust gas to be cleaned is passed into the reaction container 2 via the gas outlet 31. A temperature measurement is carried out in a temperature control 7. After the exhaust air has entered the reaction vessel 2 via the gas inlet 32, the exhaust air is passed on through the packed bed 23. Here and in the space above, there is intimate contact with the aqueous phase which is atomized into the reaction container 2 via nozzles 22. A water separator 24 arranged in the upper part of the reaction container 2 likewise contains packing elements which not only bring about water separation, but also make post-oxidation of the pollutants which have not yet been implemented possible. A clean gas outlet 10 guides the cleaned exhaust air through a pollutant concentration control 8, from which the cleaned exhaust air is conveyed into the atmosphere via the clean gas outlet 39 by means of a fan 9. A reaction solution inlet 26 enables the addition of an aqueous solution of the oxidizing agent, which is then brought to the required oxidation concentration with the water supplied via the water inlet 27. The aqueous phase thus set is then atomized via the nozzles 22 in the reaction container 2. In the lower part of the reaction container 2, the aqueous phase collects, which is either fed to the nozzles 22 by means of a pump 21 or, in the case of high consumption of oxidizing agent, is discharged via a waste water outlet 28. The reaction solution, which is fed into the system via the reaction solution inlet 26, is removed from a storage container for reaction solution 3. Not more usable wastewater, ie used aqueous phase is fed via a wastewater outlet 28 to a container for wastewater 4.

The device for exhaust air purification according to FIG. 2 has two reaction vessels 2 and 34 compared to the device of FIG. If the clean gas leaving the reaction container 2 via the clean gas outlet 10a does not yet have the required low levels of pollutants, this clean gas is passed into the reaction container 34 via the gas inlet 33. Here again there is intensive contact with the aqueous phase. A heat exchanger 30 enables the heat dissipation of the exothermic heat generated in the reaction areas of the packed bed 23. This limits the heat development and the temperature does not rise above 105 ° C. The heat dissipated there can be used to heat the incoming exhaust air in the pre-reaction container 1 to a required reaction temperature. This heating then takes place via the heat exchanger 16 in the pre-reaction container 1.

The device for exhaust air purification according to FIG. 3 differs from the device according to FIG. 2 in that the devices in FIG. 2 are arranged separately

Reaction containers 2 and 34 are combined in one container and are separated from one another by vertical dividing walls. This enables a compact design. The one provided in the pre-reaction container 1

Conveying the exhaust air and the atomized aqueous phase in cocurrent can also be easily switched to countercurrent. The exhaust air inlet 36 would then be arranged in the lower region of the pre-reaction container 1. A flow switch 35 enables after Determination of the pollutant concentration in the pollutant concentration control 8a the passage of the not yet sufficiently cleaned exhaust gas into a sub-chamber 2b. This sub-chamber 2b is structurally identical to the sub-chamber 2a. The aqueous phase collecting in the lower regions of the subchambers 2a and 2b is removed by controlling the aqueous phase 37. Unused aqueous phase is returned to the system and used aqueous phase is transferred to the waste water container 4.

example 1

An exhaust gas volume flow of 650 m ³ / h must be disposed of in the drying stage of a printing house. A methanol / ethanol mixture (450 mg / m ³ ) and an aldehyde mixture (100 mg / m ³ ) occur as pollutants at a temperature of 25 ° C. The gas first passes into the pre-reaction container 1 and then into the reaction container 2 (FIG. 1). A 1.5% hydrogen peroxide solution is used as the washing solution and as the oxidative reaction liquid. The packed bed 23 in the sprinkling zone of the reaction container 2 consists of a mixture of oxidation-active manganese dioxide (MnO ² ) and poroton granules. For water separation, post-adsorption or post-oxidation and gas drying, a further brown stone and poroton layer on a ceramic packing bed is used in the water separator 24 above the atomization zone.

The clean gas leaving the plant has a pollutant concentration of 30 mg / m ³ alcohol and 12 mg / m ³ aldehyde. The clean gas temperature is 40 ° C Example 2

In the paint booth of a conveyor system operation during the drying process 550m ³ / h exhaust gas with a pollutant concentration of 200 mg / m3 xylene and 250 mg / m3 alcohols (methanol, ethanol, propanol, butano dan) fall. The exhaust gas temperature is 30 ° C. The exhaust gases are in a cleaning system 3 (plant with recirculation of the clean gas stream and 2-stage reactor) disposed of.

The exhaust gas is passed into the pre-reaction tank 1 for prewashing. A 1.5% hydrogen peroxide solution is used as the washing liquid. This process reduces the alcohol concentration to 50 mg / m3.

Then the pre-cleaned exhaust gas reaches the subchamber 2a of the reaction container 2. A 1.5% hydrogen peroxide solution is used as the reaction solution, which is added as a phase transfer catalyst surfactant in a concentration of 0.1% to solubilize the xylene. A mixture of manganese dioxide, zeolite and porcelain granules impregnated with potassium permanganate and ceramic fillers serves as the reactive packing. Above the nebulization zone is a poroton and brown fill for droplet separation and post-adsorption or post-oxidation. The clean gas has a concentration of 15 mg / m ³ xylene and 10 mg / m ³ alcohol. The clean gas temperature is 45 ° C. As a result of an accident in the paint supply line, the pollutant concentration in the exhaust gas increases to 350 mg / m ³ xylene and 440 mg / m ³ alcohol, which results in a clean gas concentration to 25 mg / m ³ xylene. By responding to the control device, the Gas flow into the sub-chamber 2b of the second reaction stage, whereby the pollutant concentration is reduced to 10 mg / m ³ xylene.

Example 3

In a one-stage laboratory test facility with a diameter of 15 mm, an air volume flow of 200 l / h was cleaned with the method according to the invention. The air was contaminated with methanol at a concentration of 500 mg / m ³ .

30 ml of an iron-copper-platinum mixed catalyst were used as the catalytically active fixed bed. The carrier material was γ-aluminum oxide in the form of extrusions (diameter approx. 1.5 mm). 300 ml of a 1% hydrogen peroxide solution, which was circulated, were used as washing liquid and oxidizing agent. The clean gas concentration was 10-15 mg / m ³ .

Example 4

In a one-stage test facility (diameter 45 mm), the cleaning of 2m ³ / h was carried out with odor-intensive contaminants such as phenol, mercaptans and aldehydes contaminated exhaust air (concentration approx. 100 mg / m ³ ). 500 ml of a porous clay mineral with an increased Fe (III) content on the surface (diameter approx. 6 mm) were used as the catalyst. 1 liter of a 1% hydrogen oxide solution was used as the reaction liquid. Reference list

Pre-reaction tank 18 reaction solution inlet

Reaction tank 19 Water inlet a partial chambers 20 Waste water outlet b partial chambers 21 Pump

Storage container for 22 nozzles

Reaction solution 22a nozzles

Waste water tank 23 Packing material

Raw gas inlet 24 water separators

Temperature control 24a water separator

Temperature control 25 level control

Pollutant concentration control

27 Water inlet a pollutant concentration control 28 Waste water outlet

Fan 29 control

0 Clean gas outlet 30 heat exchangers

0a Clean gas outlet 31 Gas outlet

0b Clean gas outlet 32 Gas inlet 1 Cooling air inlet 33 Gas inlet

2 fan 34 post-reaction tank

3 Heat transfer outlet 35 flow switching

4 Pump 36 exhaust air inlet

5 nozzles 37 control of the aqueous

Phase 6 heat exchanger

38 Air inlet 7 level control

39 Clean gas outlet

Claims

claims

1. A method for purifying exhaust air from oxidizable pollutants by bringing the exhaust air into contact with an aqueous phase containing an oxidizing agent, characterized in that the aqueous phase is finely divided, the aqueous phase containing oxidizing agents that the exhaust air with the finely divided aqueous phase is intensively mixed, that a mixing or contacting of the exhaust air and the aqueous phase with a solid, inert and / or catalytically active and / or with a catalytically active coating provided inert or catalytically active carrier material with a large surface area and that at the place of Mixing or contacting the temperature is kept below 105 ° C.

2. The method according to claim 1, characterized in that oxygen-releasing compounds are introduced into the aqueous and / or gaseous phase as the oxidizing agent.

3. The method according to any one of claims 1 or 2, characterized in that that oxygen-releasing compounds such as peroxides and / or ozone are used as oxidizing agents.

4. The method according to any one of claims 1 to 3, characterized in that surfactants such as low molecular weight and / or high molecular weight emulsifiers (O / W) and / or wetting aids are added to the aqueous phase.

5. The method according to any one of claims 1 to 4, characterized in that fillings, moldings and / or powder are used as the solid carrier material with a large surface.

6. The method according to any one of claims 1 to 5, characterized in that the inert support material and catalytically active material are mixed together.

7. The method according to any one of claims 1 to 6, characterized in that the exhaust air is cleaned of oxidizable pollutants in several stages.

Method according to one of claims 1 to 7, characterized in that the supply of the oxidizing agent takes place in correlation with the pollutant concentration.

9. The method according to any one of claims 1 to 8, characterized in that the supply of the aqueous phase takes place in correlation with the exhaust air volume flow.

10. The method according to any one of claims 1 to 9, characterized in that the solid, powdery carrier material is brought into contact with the exhaust air as an aqueous suspension.

11. The method according to any one of claims 1 to 10, characterized in that the pH of the aqueous phase is adjusted to a value from 1 to 12.

12. The method according to any one of claims 1 to 11, characterized in that the pH of the aqueous phase is adjusted to a value of 5 to 8.

13. The method according to any one of claims 1 to 12, characterized in that the temperature at the site of mixing or contacting is set to 20 ° C to 80 ° C.

14. The method according to any one of claims 1 to 13, characterized in that the catalytically active material contains metal oxides and / or mixtures which are assigned to the subgroups IB, IIB, IVB, VB, VIB, VIIB and / or VIII of the periodic table.

15. The method according to any one of claims 1 to 14, characterized in that the catalytically active material contains Mn, Pt, Fe, Pd, Co, Ag, Ni and / or Cu.

16. Device for cleaning exhaust air from oxidizable pollutants by bringing the exhaust air into contact Air containing an aqueous oxidizing agent solution, characterized in that a pre-reaction vessel (1) and a reaction vessel (2) are connected to one another via exhaust air pipelines, the pre-reaction vessel (1) having a raw gas inlet (5), nozzles (15 ) for atomizing an aqueous phase, has a gas outlet (31) and a heat exchanger (16) is arranged above the gas outlet (31), which is connected to a further heat exchanger (30) in the reaction vessel (2), and the reaction vessel (2) having nozzles (22) in the central region, below which solid support material with a large surface area, below the solid support material a gas inlet (32) and above the nozzles (22) water separator (24) and a clean gas outlet (10).

17. The apparatus according to claim 16, characterized in that no pre-reaction container (l) is provided.

18. The apparatus according to claim 16 or 17, characterized in that a plurality of reaction vessels (2) are switched one after the other ge.

19. The apparatus according to claim 16 or 17, characterized in that a plurality of reaction vessels (2 \ are connected in parallel.

20. Device according to one of claims 16 to 19, characterized in that the reaction container contains at least two Teilkam¬ mern (2a, 2b).

21. Device according to one of claims 16 to 20, characterized in that instead of the nozzles (15) distributor plates are provided for the direct introduction of the aqueous phase.

22. A catalyst for carrying out the process according to claim 1, consisting of a solid, inert support material and an oxide or an oxide mixture of the metals which are assigned to the subgroups IB, IIB, IVB, VB, VIB, VIIB and / or VIIIB of the periodic table.

23. A catalyst according to claim 22, characterized in that 21

that the catalytically active oxide composition is applied as a layer on the inert support material.

24. A catalyst according to claim 22 or 23, characterized in that the catalytically active oxide composition is mixed as granules with the solid, inert support material.

25. Catalyst according to one of claims 22 to 24, characterized in that the content of the catalytically active oxide composition is 1 to 15 mass percent.

26. A process for the preparation of the catalyst according to claim 22, characterized in that one or more salt solutions or

Salt melting or oxide melting on the inert

Carrier material are applied, a drying treatment is carried out and then calcined.