Adsorption-catalytic system for treating gases to remove toxic impurities

FIELD: gas treatment.

SUBSTANCE: invention relates to novel catalysts, which can be, in particular, used in automobile engine exhaust treatment, in processes of deep oxidation of toxic organic impurities in industrial emission gases, and in other applications. Adsorption-catalytic system, including granules of sorbent capable of sorbing at least one of reagents and catalyst, represents geometrically structured system wherein catalyst is made in the form of microfibers 5-20 μm in diameter, sorbent granules are disposed inside catalyst, and size ratio of sorbent granules to catalyst microfibers is at least 10:1. Catalyst microfibers are structured in the form of woven, knitted, or pressed material. Gas treatment process involving use of such system is based on that gaseous reaction mixture to be treated is passed through above-defined system while periodically varying temperature of mixture, in particular raising it, to accomplish or regeneration of sorbent.

EFFECT: enhanced process simplicity and reliability (simple process government system, absence of mechanical stream switching devices, reduced power consumption, and enabled continuous gas treatment.

2 cl, 2 ex

 

The invention relates to the field of chemical industry, new catalysts that can be used, in particular, in the processes for purification of exhaust gases of automotive engines in the deep oxidation of toxic organic pollutants in industrial waste gases and in other areas.

Famous traditional heterogeneous catalytic system, representing the layers of the solid catalyst formed in the form of granules, blocks, etc. through which pass the gaseous reaction mixture.

Thus, the known catalytic system in the form of a stationary layer of granulated catalyst used in the method of cleaning exhaust gases of industrial enterprises from toxic organic impurities [Thermal methods of waste disposal - L.: Chemistry, 1975, p.25-40]. The method is based on the reaction of oxidation of exhaust gases with oxygen by passing the purified gas through a fixed bed of granular catalyst.

A disadvantage of the known catalytic system is that although it allows to carry out the method with a high cleaning efficiency, however, requires constant heating the purified gas before feeding them into the catalyst bed to a temperature of reaction of the oxidation - up to 200-400°that explains the high intensity of this method, in which bennoti when cleaning gases with low content of toxic impurities. Such defects are manifested, in particular, catalytic purification of dilute gas emissions from industrial enterprises, such as the ventilation of gases having, as a rule, low content of toxic impurities and low temperature, insufficient for the implementation of the oxidation reactions of impurities. Similar weaknesses catalytic system is manifested in its use in catalytic converters of exhaust gases of internal combustion engines, in which at the time of starting the engine temperature is also high enough for the effective carrying out catalytic reactions.

Known adsorptive-catalytic system used in the method of cleaning exhaust gases from toxic organic impurities in a fixed bed of granular material that combines the properties of the catalyst and adsorbent (U.S. Patent No. 4234549, IPC 01 D 53/42, priority 29.06.79, publ. 18.11.80). The method is based on the cyclic process of purification, and the cycle includes two successive stages. The first stage of the cycle (adsorption) is in the preliminary accumulation available in the cleaned gas toxic impurities in the layer of the catalyst-adsorbent. Accumulation occurs due to adsorption and/or chemisorption by passing the purified gas through the catalyst bed at a temperature lower is the characteristic temperature of the beginning of oxidation of these impurities. The second stage of the cycle (regeneration) is adsorbed in the oxidation catalyst layer of toxic impurities. Oxidation occurs when passing through the catalyst layer of air heated to a temperature above the characteristic temperature of the beginning of deep oxidation of adsorbed impurities. This method provides a high degree of purification of exhaust gases with low initial concentrations of impurities, while it is significantly less energy intensive compared to the above method, since the temperature rise of the catalyst used heat flowing catalytic reactions.

A disadvantage of the known adsorption-catalytic system is that the energy consumption when carrying out the second stage of the cycle is large enough, as the temperature in the adsorption-catalytic system at the level typical of the reaction of oxidation of adsorbed impurities, you want to keep for a long, up to 10 hours of time. Also, the use of such a system determines the frequency of cleaning of exhaust gases, because it occurs only on the first stage of the cycle, and at the time of implementation of the second stage is interrupted. In addition, when heated described adsorption-catalytic system in the process of regeneration possible desorption of unreacted reagent that can there is i.i.d. reduce the overall efficiency of the catalytic conversion, or require technological sophistication catalytic systems, for example, the installation of an additional reactor to remove the desorbed substances.

The authors sought to develop an adsorption-catalytic system, different technological simplicity, low power consumption and high efficiency of purification of gas emissions, in particular, providing a minimum level of emissions of unreacted reagents when carrying out regeneration of the adsorbent-catalyst.

The problem is solved in that the adsorption-catalytic system for gas purification from toxic impurities, comprising granules of adsorbent, can absorb at least one of the reactants and the catalyst is a geometrically structured framework in which the catalyst is made in the form of microfibers with a diameter of 5-20 μm, the sorbent pellets placed inside the catalyst, the ratio of the amount of sorbent granules and microfibers of the catalyst is at least 10:1. Moreover, microfiber catalyst is structured in the form of woven, braided or extruded material.

The technical effect of the claimed invention is to improve the efficiency of gas cleaning, in particular, to reduce emissions of toxic compounds, the reduction of energy consumption and possibilities about what edenia cleaning in continuous mode.

This is due to the following. During heating of the adsorption-catalytic system for the regeneration of the adsorbent-catalyst heated by the gas flow, the temperature of sorbent granules and fibers of the catalyst occurs at different speeds due to different intensity of heat exchange granules and fibers with gas. Because of the much smaller characteristic size of the fiber catalyst have significantly higher specific heat transfer surface per unit volume than granules, and therefore heat up much faster. As a result, when the pellets are heated to a temperature at which it begins appreciable desorption of previously adsorbed impurities, catalyst already has a temperature sufficiently high to perform the reaction. Due to this effect desorbed impurities effectively oxidized in the layer microfiber catalyst and the concentration in the purified gas mixture is small or equal to zero during the entire regeneration cycle. Heat flowing reactions due to the intensive heat exchange with microfibers of the catalyst is effectively used for further heating systems and complete regeneration, which can significantly reduce energy consumption in the process of purification of gas emissions. The regeneration system can be performed without stopping delivery of the cleaned gas is a mixture, i.e. gas purification can be carried out in a continuous mode.

Adsorption-catalytic system for heterogeneous reactions contains granules of adsorbent located in a geometrically structured layer microbolometer catalyst, and the amount of sorbent granules exceeds the characteristic size of the microfibers of the catalyst is at least 10 times. This microfiber catalyst can be structured in the form of woven, braided or extruded material.

The process of cleaning gases with the use of such systems is based on the fact that the purified gaseous reaction mixture is passed through this system, periodically changing the temperature of the mixture, in particular, periodically increasing its for carrying out the regeneration of the sorbent.

The advantages of the proposed adsorption-catalytic system are: technological simplicity and reliability (simple process control system, no mechanical switching devices flow), reduced power consumption for performing the cleaning process, the possibility of gas purification in a continuous mode.

Examples of use of the inventive adsorptive-catalytic system

Example 1

Adsorption-catalytic system includes a spherical granules of alumina sorbent capable of adsorbing article is rol. Granules are microfiber inside layer of catalyst (platinum, deposited on a metal microfiber). The amount of sorbent granules of about 1 mm, the characteristic diameter of the microfibers of the catalyst is about 20-50 microns. Microfiber is structured in the form of extruded material of the flat layer, and the flue gases are in the direction perpendicular to the surface layer. Cleaning serves vent gas emissions, representing the air containing styrene at a concentration of 50 mg/m3with a temperature of 25°C. These emissions are passed through the inventive adsorptive-catalytic system.

At the stage of adsorption of the gas to be cleaned is passed through the system described without heating, while flowing the cleaning gas by adsorption of styrene on the sorbent granules, so the concentration in the vent purified gas does not exceed 0.1-0.5 mg/m3.

After 20 hours the early stage of adsorption, the concentration of styrene in the purified gas is increased to 1 mg/m3. After this stage adsorption finish and begin phase oxidation of adsorbed styrene and regeneration of the sorbent. For this purpose, the purified gas is heated in the space between the parts of the catalyst layer from the electrical heat source. After reaching the temperature of the catalyst on the olo 250-300° Since there is heating of the sorbent granules to a temperature of 60-100°, which begins intensive desorption of styrene pellets of the sorbent. Eye-catching styrene is oxidized in the catalyst layer emitting a large amount of heat. Heating of the gases cease at the beginning of the reaction of oxidation, and further regeneration occurs due to the heat of the reaction. During regeneration, the concentration of styrene in the purified gas at the outlet of the catalyst layer does not exceed 1-2 mg/m3the maximum temperature in the catalyst bed reaches 550°C. the Average degree of purification for the cycle is over 99%. After regeneration, the temperature is automatically reduced to the original (25°).

Next, the process is conducted in a continuous mode cyclically, sequentially repeating the first and second stages.

In similar conditions during the cleaning gas using granular adsorbent-catalyst used in the method described in U.S. Patent No. 4234549, during regeneration of the adsorbent-catalyst is a real concentration of styrene in the exhaust gas can reach 50-100 mg/m3and the average for a series of purification does not exceed 96-98%.

Example 2

Cleaning exposed to diesel engine exhaust containing toxic impurities (CO, hydrocarbons, nitrogen oxides) in concentrations of 200-1000 ppm Adsorption-catalytic system, includes a combination of granulated sorbent with a granule size of about 1-2 mm and fiberglass platinum catalyst, structured in the form of a woven material (fiberglass), and the threads of the woven cloth are made of microfibers catalyst with a characteristic size of about 10 microns. Thus the cloth is fiberglass twisted in a multilayer cylinder, wherein between the layers are evenly placed sorbent granules. Exhaust gases are passed through the adsorption-catalytic system for the Transmission of emissions is carried out in directions perpendicular to the surface of the cylinder.

In the initial period of treatment (when starting the engine) exhaust gas temperature is low and thus there is adsorption of toxic impurities on the sorbent granules. As the growth temperature of the gases is heated catalytic fiberglass to a temperature of 300-350°C, while the temperature of the adsorbent reaches 100-150°and begins the desorption of the impurities. Deformirovaniya impurities effectively neutralized in the layers of fiberglass, in General, the starting period of the engine, the average degree of purification of the exhaust gases is more than 90% of CO and hydrocarbons and about 30-40% of the nitrogen oxides. After completion of the heating system works in a purely catalytic mode.

Traditional catalytic converters o opov in similar conditions in the starting period of engine operation is practically not provide gas cleaning.

1. Adsorption-catalytic system for gas purification from toxic impurities, comprising granules of adsorbent, can absorb at least one of the reactants and catalyst, characterized in that it is a geometrically structured framework in which the catalyst is made in the form of microfibers with a diameter of 5-20 μm, the sorbent pellets placed inside the catalyst, the ratio of the amount of sorbent granules and microfibers of the catalyst is at least 10:1.

2. The catalytic system according to claim 1, characterized in that the fibers of the structured catalyst in the form of woven, braided or extruded material.



 

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