RU2543168C2 - Composition of adsorbent for removal of toxic substances from automobile exhaust gases and method of manufacturing thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: group of inventions relates to adsorbents for the removal of hydrocarbons from automobile exhaust gases in the period of cold start of an internal combustion engine. The adsorbent represents zeolite of the ZSM-5 type or BETA type, into which an alkali metal, selected from the group K, Na, Li or their mixture, is introduced with a specified component ratio. The method of the adsorbent manufacturing consists in the impregnation of initial zeolites with salts of the said alkali metals to a specified content at room temperature. After that, thermal processing is carried out in air medium in two stages: at 100-150°C and at 500-600°C.

EFFECT: invention provides obtaining the adsorbent with high temperature resistance and stable characteristics in case of long-lasting cyclic hydrothermal influence, as well as provides the continuous retention of hydrocarbons when the temperature increases with heating of the engine to higher than 300°C.

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Description

The proposed group of inventions relates to the field of engineering, mainly to the automotive industry, and in particular to adsorbents for removing hydrocarbons from the exhaust gases of a car in the cold start mode of the engine and can be used as an absorber to capture environmentally hazardous emissions into the environment by devices using hydrocarbon fuel.

The urgency of the problem of reducing the toxicity of automobile transport used is based on the fact that the exhaust system of the internal combustion engine used in it emits ~ 60% of the total volume of hydrocarbons released into the environment, in addition, a significant amount of CO and NO _{x is released} . At the same time, about 80% of the car’s hydrocarbon emissions occur during the cold start period, when the catalytic converter is not heated to a working temperature of 300 ° C.

One of the methods to reduce the toxicity of exhaust gases of an internal combustion engine is the use of absorbers of harmful substances - adsorbents. Adsorbents are used in fuel-air systems to prevent fuel vapors from entering the environment, as well as in engine exhaust systems to prevent unburned hydrocarbons from being released into the atmosphere within 60 seconds after starting the engine when the catalytic converter has not yet reached operating temperature. According to www.defa.com, Fig. 1 shows hydrocarbon emissions for a Renault Laguna 1.6L car with a cold start (element 1 of the diagram - at an ambient temperature of -20 ° C, element 2 of the diagram - at an ambient temperature of -10 ° C, element 3 of the diagram - at an ambient temperature of 0 ° C), and also after warming up and the catalytic converter reaches an operating temperature of 300 ° C (element 1a of the diagram - at an ambient temperature of -20 ° C, element 2a of the diagram - at a temperature ambient temperature -10 ° C, element 3a of the diagram - at temperatures e environment 0 ° C).

Known methods and compositions of adsorbents used to capture toxic substances from vehicle exhaust gases (RF patent No. 2406558, IPC B01D 53/04, published December 20, 2010), in which an adsorbent is used, which is an organometallic frame structure of the MOF-5 type allowing efficient removal of hydrocarbons in the "cold start" mode.

The advantage of using adsorbents in the “cold start” mode is based on the “regenerative principle”, which consists in the capture of hydrocarbons by the adsorbent during a cold start and their recovery after the catalytic converter reaches operating temperature. The adsorbent absorbs hydrocarbons during the startup period as long as the structure remains cold.

In addition to high absorption capacity, a necessary condition for the effectiveness of the use of adsorbents in the exhaust tract of an internal combustion engine is the ability to selectively trap unburned hydrocarbons at a low temperature and hold them until the catalytic converter reaches a working temperature of 300 ° C.

Adsorbents are known, for example, based on zeolite of the ZSM-5 type, and methods for their preparation (RF patent No. 1610777, IPC C01B 39/36, publ. June 27, 1995), in which the problem of increasing the efficiency of hydrocarbon absorption is solved, which was achieved , in particular, by increasing the crystallinity of the finished sorbent.

However, the known invention does not provide the ability of the absorber to selectively trap unburned hydrocarbons at low temperature and retain them until the operating temperature of the catalytic converter (at least 300 ° C) is reached.

As the closest in technical essence to the claimed one, an adsorbent is known for removing hydrocarbons from automobile exhaust gases (RF patent No. 2213230, IPC B01D 53/04, publication September 27, 2003), which is a matrix on a porous basis from a carbon mixture, metallized with alloys from various metals and a catalyst bed. The known invention improves the efficiency of the converter during cold start of the engine.

The disadvantages of the known solutions include the insufficiently high temperature stability of the absorber and the stability of characteristics during prolonged cyclic hydrothermal exposure, as well as the inability to continuously retain hydrocarbons from exhaust gases when the temperature rises until the internal combustion engine is heated above 300 ° C.

In the patent US 7981834 B2 (publication of July 19, 2011) an adsorbent for purifying exhaust gases based on a mixture of beta-type zeolites with a SiO ₂ / Al ₂ O ₃ module of more than 10, but less than 200 and beta with a SiO ₂ / Al ₂ O ₃ module, is presented. from 200 to 1000. This adsorbent absorbs hydrocarbons well, but desorbs them at a temperature of less than 300 ° C, when the afterburning catalyst does not work yet, i.e. does not solve the problem of a cold start.

Patent RU 2438777 C2 (published September 27, 2010) describes a particulate filter for a diesel engine exhaust gas that contains an adsorbent for absorbing hydrocarbons — zeolite, for example mordenite, silicate, Y-zeolite, ZSM-5 — zeolite and beta-zeolite, or mixtures thereof. However, in the patent it is noted that these zeolites desorb hydrocarbons at a temperature of more than 200 ° C, therefore, catalysts are introduced to burn them. This adsorbent also does not retain hydrocarbons during a cold start until the afterburning catalyst reaches 300 ° C.

The task of the authors of the invention is to develop an adsorbent composition for removing hydrocarbons from the exhaust gases of a vehicle and a method for its manufacture, providing high temperature stability of the absorber and stability characteristics during prolonged cyclic hydrothermal exposure, as well as ensuring the retention of hydrocarbons of exhaust gases when the temperature rises until the catalytic converter is heated above 300 ° C.

A new technical result when using the proposed adsorbent and the method for its production is to provide high parameters of the temperature stability of the absorber and stability of characteristics during prolonged cyclic hydrothermal exposure, as well as to ensure prolonged retention of hydrocarbons with increasing temperature until the catalytic converter is heated above 300 ° C.

These tasks and a new technical result are ensured by the fact that the developed adsorbent for removing hydrocarbons from the exhaust gases of a vehicle based on a hydrocarbon-absorbing material according to the invention is a ZSM-5 type zeolite or beta zeolite, the SiO ₂ / Al ₂ O ₃ module is 38, 0 (Beta-38), in which one of the alkali metals K, Na or Li was introduced by the method of impregnation in terms of moisture capacity in the following ratio, wt.%:

- either sodium - 2.0-3.5, or potassium - 3-5, or lithium - 4.5-5.5, or a mixture of sodium + potassium in a ratio of 1:99 to 99: 1 - 2.0-5.0, either a mixture of sodium + lithium in a ratio of 1:99 to 99: 1 - 2.0-5.5, or a mixture of potassium + lithium in a ratio of 1:99 to 99: 1 - 3.0-5.5, or a mixture of sodium + potassium + lithium for each metal in a mixture from 1 to 99% - 2.0-5.5;

- zeolite ZSM-5 or Beta-38 - the rest.

These tasks and a new technical result are ensured by the fact that in the known method for producing an adsorbent for removing toxic substances from vehicle exhaust gases, including modifying the initial zeolite, according to the proposed method, the processing of the initial zeolite of the ZSM-5 or Beta-38 type is carried out by the method of impregnation of reagent, which is used as a metal-containing compound from the group of water-soluble salts of K, Na or Li at room temperature, followed by heat treatment in air with In two stages: at a temperature of 120 ° C and at a temperature of 500-600 ° C.

The proposed adsorbent for removing toxic substances from the exhaust gases of the car during the cold start of the engine and the method of its manufacture are explained as follows on the example of zeolite type ZSM-5, in which Na is introduced.

The initial zeolite of the ZSM-5 type is an aluminosilicate with a frame structure (Fig. 2, http://izasc.ethz.ch/fmi/xsl/IZA-SC) having a silica module SiO ₂ / Al ₂ O ₃ equal to 35.0 . At the nodes of the lattice are atoms of silicon or aluminum, which are connected through oxygen. The ZSM-5 zeolite structure contains two systems of intersecting channels: sinusoidal channels running along the “a” axis and straight channels parallel to the “b” axis. The pores of zeolite ZSM-5 are formed by 10-membered oxygen rings (O-10) and their size is about 0.6 nm. Windows O-10 can be round or ellipsoidal, their diameters vary in the range of 0.6-0.65 nm.

The proposed adsorbent based on zeolite ZSM-5 is obtained by treating the initial zeolite ZSM-5 by impregnation with a modifying reagent until the zeolite powder is completely impregnated with sodium ions from an aqueous solution of sodium salts, for example sodium carbonate, at room temperature, followed by heat treatment in air in two stages: at a temperature of 120 ° C until complete removal of water and at a temperature of 500-600 ° C.

When conducting studies to obtain an adsorbent capable of retaining hydrocarbons during the cold start of an internal combustion engine, the modification of ZSM-5 type zeolites by impregnation with Mn, Cr, Cs, Ni, Li, Co, Zn, K, and Na ions was verified. To study the nature of hydrocarbon desorption, the obtained adsorbents were saturated with toluene, then the thermal desorption curves of toluene were taken for the adsorbents, which show the amount of hydrocarbons released depending on the desorption temperature. Toluene was used as a model substance for hydrocarbons. Figure 3 shows the thermal desorption curves of toluene from adsorbents based on zeolite type ZSM-5, modified with Cr ions (curve 1), Ni (curve 2), Cs (curve 3), Mn (curve 4), Co (curve 5), Zn (curve 6) and Li (curve 7), the mass fraction of the introduced elements was 5%. It was shown that the most optimal results of the absorption and retention of hydrocarbons up to 300 ° C were manifested when zeolite was modified with Li ion. Figure 4 shows the thermal desorption curves of toluene from adsorbents based on ZSM-5 zeolite, the original (curve 1) and modified with K ions, which was introduced in a mass fraction of 3% (curve 2) and 5% (curve 3). It was shown that the introduction of K into zeolite of the ZSM-5 type leads to an increase in the temperature of toluene desorption to 300 ° C. Figure 5 shows the curves of thermal desorption of toluene from an adsorbent based on zeolite ZSM-5, modified with Na ions, the mass fraction of the element is 2.5%. It was shown that a high-temperature desorption peak (peak 1a) appears on the toluene thermal desorption curve (curve 1). This indicates that environmentally hazardous hydrocarbons in the exhaust gases that are formed during the cold start of the internal combustion engine are retained by an adsorbent based on ZSM-5 zeolite modified with Na ions until the catalytic converter is heated and reaches 300 ° C, which leads to to reduce emissions of unburned hydrocarbons into the environment. The positive point is that during sorption and desorption of toluene under hydrothermal conditions, in an atmosphere of 10% water vapor (which corresponds to the composition of the exhaust gases), only the high-temperature desorption peak is present on the thermal desorption curve (curve 2, Fig. 5). The peak of high-temperature desorption is maintained after 8 cycles of sorption-desorption and a total test time of 28 hours (Fig.6).

Similar results were obtained when modifying a BETA-38 type zeolite with alkali metals of either K or Na, Figs. 7-10. It was shown that complete desorption of toluene from the original, not modified zeolite occurs at temperatures up to 300 ° C (curve in Fig.7). When introduced into the zeolite type Beta-38 K in a mass fraction of 2.5, 3.2. 3.3 and 3.9% (Fig. 8, curves 1, 2, 3, and 4, respectively) and Na in the mass fraction of 3.1% (Fig. 9, curve 1) a high-temperature desorption peak appears. It was shown for the adsorbent based on Beta-38 zeolite with introduced Na in a mass fraction of 3.1% that the high-temperature peak of toluene desorption is also retained during the sorption and desorption of toluene in the atmosphere of 10% water vapor (which corresponds to the composition of the exhaust gases) (Fig. 9, curve 2). A similar result was obtained when testing zeolite with K introduced in a mass fraction of 2.5% in an atmosphere of 10% water vapor (Fig. 10, curve 1), the peak of high-temperature desorption persists after 7 sorption-desorption cycles and a total test time of 40 h (Fig. 10, curve 2).

The obtained experimental data for the developed adsorbents testify in favor of the fact of reducing the amount of toxic components of exhaust gases during a cold start of an internal combustion engine.

When an adsorbent is obtained during the heat treatment of a zeolite impregnated with the indicated compounds, either K, Na, or Li, in the second stage at a temperature below 500 ° C the necessary thermal decomposition of metal compounds does not occur and the required spatial arrangement of metal ions in the structure of the converted zeolite is not realized. Heat treatment above 600 ° C leads to a sharp decomposition of metal compounds and an uneven distribution of metal ions in the structure of the modified zeolite.

In the finished adsorbent, either K, Na, or Li ions should be uniformly distributed in the zeolite structure.

The experimentally selected conditions for the treatment of the initial zeolite with a modifying reagent from the group of water-soluble salts of K, Na or Li and the heat treatment of the modified zeolite made it possible to absorb hydrocarbons during the cold start of the internal combustion engine and to keep them until the catalytic converter reaches its operating temperature (300 ° C).

Thus, adsorbents based on zeolites of type ZSM-5 or type Beta-38, into which one of the alkali metals K, Na or Li is introduced in the following ratio, wt.%: Either sodium - 2.0-3.5, or K is 3-5, or Li is 4.5-5.5; either a mixture of sodium + potassium in a ratio of 1:99 to 99: 1 - 2.0-5.0, or a mixture of sodium + lithium in a ratio of 1:99 to 99: 1 - 2.0-5.5, or a mixture of potassium + lithium in a ratio of 1: 99 to 99: 1 - 3.0-5.5, or a mixture of sodium + potassium + lithium with a content of each metal in the mixture from 1 to 99% - 2.0-5.5, zeolite ZSM-5 or Beta-38 - the rest are good hydrocarbon adsorbents for cold start of the internal combustion engine, however, preference should be given to adsorbents based on zeolite type ZSM-5, modified Na, and on the basis of zeolite type Beta-38 modified K.

The use of the proposed adsorbents to remove toxic substances from the exhaust gases of a car and the method of their manufacture provides the necessary parameters for the temperature stability of the absorber and stability of characteristics during prolonged cyclic hydrothermal exposure, as well as the long-term retention of toluene with increasing temperature until the catalyst is heated to 300 ° C.

The possibility of industrial implementation of the proposed adsorbents for the removal of toxic substances from vehicle exhaust gases and the method of their manufacture is confirmed by the following specific examples.

Example 1. In laboratory conditions, the proposed method is implemented on the layout of the installation to obtain an adsorbent based on zeolites. Na in a zeolite of type ZSM-5 was introduced Na in a mass fraction of 2.5% by processing the zeolite in powder form by impregnation with a modifying reagent - an aqueous solution of Na ₂ CO ₃ salt. A 5 g sample of zeolite was taken and 2.5 ml of Na ₂ CO ₃ solution was poured, to obtain which 294.69 mg of Na ₂ CO _{3 was} dissolved in 2.5 ml of water. The zeolite was thoroughly mixed with a solution of Na ₂ CO ₃ grinding. The heat treatment was carried out in two stages: in a drying cabinet at a temperature of 120 ° C for 4 hours, then in a laboratory setup with a furnace in an air stream at a temperature of 500-600 ° C for 2 hours. In the second stage, the air flow rate was 200-300 ml / min.

Example 2. Under the conditions of Example 1, the proposed method is implemented using a beta-type zeolite adsorbent (BETA-38) as an initial component, into which Na was introduced in a mass fraction of 3.1% by impregnation. A 5 g sample of zeolite was taken and 2.5 ml of Na ₂ CO ₃ solution was poured, to obtain which 367.69 mg of Na ₂ CO _{3 was} dissolved in 2.5 ml of water.

The obtained samples of transformed zeolites of the ZSM-5 type, with Na introduced in a mass fraction of 2.5%, and of Beta-38 type with Na introduced in a mass fraction of 3.1%, were subjected to tests of sorption and desorption of toluene under hydrothermal conditions, in an atmosphere of 10% water vapor (which corresponds to the composition of the exhaust gases), the results of which are graphically illustrated in figure 5, curve 2 and figure 9, curve 2, respectively.

Example 3. In the conditions of example 1, the proposed method is implemented using as an initial component to obtain an adsorbent of zeolite type ZSM-5, into which K was introduced in a mass fraction of 3% by impregnation. A 5 g sample of zeolite was taken and 2.5 ml of KNO ₃ solution was poured, to obtain which 400.48 mg of KNO _{3 was} dissolved in 2.5 ml of water.

Example 4. Under the conditions of Example 1, the proposed method is implemented using a zeolite type ZSM-5 adsorbent as an initial component, into which Li was introduced in a mass fraction of 5% by the method. A 5 g sample of zeolite was taken and 2.5 ml of LiHCO ₃ solution was poured, to obtain which 2652.1 mg of LiHCO ₃ -H ₂ O was dissolved in 2.5 ml of water.

The obtained samples of the converted zeolite of the ZSM-5 type, with K introduced in a mass fraction of 3% and Li introduced in a mass fraction of 5%, were subjected to tests of sorption and desorption of toluene, the results of which are presented in Fig. 4, curve 2 and in Fig. 3, curve 7, respectively.

Example 5. In the conditions of example 1, the proposed method is implemented using as an initial component to obtain an adsorbent of a zeolite of the Beta-38 type, into which K was introduced in a mass fraction of 2.5% by impregnation. In this case, a 5 g sample of zeolite was taken and 1.5 ml of a solution of K ₂ CO ₃ was added, to obtain which 136.09 mg of Na ₂ CO _{3 was} dissolved in 1.5 ml of water.

The obtained sample of the transformed zeolite type beta with K introduced in a mass fraction of 2.5% was subjected to tests of sorption and desorption of toluene in an atmosphere of 10% water vapor (which corresponds to the composition of exhaust gases) for 40 hours and 7 sorption-desorption cycles, the results are presented in figure 10, curve 2

As shown by experimental studies, the proposed adsorbents based on zeolite type ZSM-5 or Beta-38, into which one of the alkali metals K, Na or Li was introduced by impregnation with the following ratio of mass fractions,%: - or sodium - 2.0- 3.5, or potassium - 3-5, or lithium - 4.5-5.5, or a mixture of sodium + potassium in a ratio of 1:99 to 99: 1 - 2.0-5.0, or a mixture of sodium + lithium in a ratio of 1:99 to 99: 1 - 2.0-5.5, or a mixture of potassium + lithium in a ratio of 1:99 to 99: 1 - 3.0-5.5, or a mixture of sodium + potassium + lithium with each metal in the mixture from 1 to 99% - 2.0-5.5, zeolite ZSM-5 or Beta-38 - remained Noe, and methods for their preparation allow obtaining the required parameters of the temperature stability of the adsorbent and toluene prolonged retention by increasing the temperature until the warming of the internal combustion engine and the exit of the catalyst to operating conditions of 300 ° C.

Claims (2)

1. The composition of the adsorbent for removing toxic substances from the exhaust gases of a car based on a hydrocarbon-absorbing material, characterized in that the adsorbent is a zeolite of the type ZSM-5 or type BETA-38, into which one of the alkali metals K, Na or Li is introduced in the following ratio, wt.%: sodium - 2.0-3.5, or K - 3-5 or Li - 4.5-5.5, or a mixture of sodium + potassium in a ratio of 1:99 to 99: 1 in quantity 2.0-5.0, or a mixture of sodium + lithium in a ratio of from 1:99 to 99: 1 in an amount of 2.0-5.5, or a mixture of potassium + lithium in a ratio of from 1:99 to 99: 1 in an amount 3.0-5.5, or a mixture of sodium + feces d + Li at a content of each metal in the mixture of from 1 to 99% in an amount of 2.0-5.5. 2. A method of manufacturing an adsorbent for removing toxic substances from the exhaust gases of a vehicle described in claim 1, comprising treating a zeolite of type ZSM-5 or type BETA-38 with a modifying reagent selected from the group of potassium, lithium or sodium-containing water-soluble salts at room temperature followed by heat treatment in air in two stages: at a temperature of 100-150 ° C and at a temperature of 500-600 ° C.

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