JP2018079428A - Hydrocarbon adsorbent and hydrocarbon removal method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrocarbon adsorbent in which a decrease in the desorption temperature of adsorbed hydrocarbon is suppressed as compared with a conventional hydrocarbon adsorbent. A hydrocarbon adsorbent containing a LEV-type zeolite containing copper. The copper content of the LEV-type zeolite is preferably 1.0 to 7.0% by weight in terms of the weight ratio of copper to the LEV-type zeolite. Preferably, the hydrocarbon adsorbent has an average particle size of 0.5 μm of the LEV-type zeolite and a molar ratio of silica to alumina of the LEV-type zeolite of 10 to 50. [Selection diagram] None

Description

  The present invention relates to a hydrocarbon adsorbent and a hydrocarbon adsorption method. In particular, it relates to hydrocarbon adsorbents suitable for application to exhaust gas purification systems.

  Exhaust gas discharged from an internal combustion engine used for moving bodies such as automobiles and ships contains a large amount of hydrocarbons. In order to remove hydrocarbons from exhaust gas discharged from a moving body, an exhaust gas treatment system in which a catalyst or the like is provided after an internal combustion engine has been put into practical use. Three-way catalysts containing precious metals are widely used as hydrocarbon removal catalysts in exhaust gas treatment systems. However, in order for the three-way catalyst to function, a temperature environment of 250 ° C. or higher is necessary. Therefore, the three-way catalyst cannot decompose hydrocarbons at a low temperature, such as when the internal combustion engine is started. The hydrocarbons discharged from the engine are discharged out of the moving body as they are.

  Therefore, when the exhaust gas treatment system combines a three-way catalyst and a hydrocarbon adsorbent, the hydrocarbon adsorbent is adsorbed to the hydrocarbon adsorbent before the three-way catalyst functions, and the temperature at which the three-way catalyst functions is reached. The hydrocarbons adsorbed in the above are desorbed from the hydrocarbon adsorbent and decomposed and removed with a three-way catalyst to suppress the release of hydrocarbons into the atmosphere (for example, Patent Document 1). Since it is difficult to adsorb and desorb hydrocarbons having a small number of carbon atoms, improvement of adsorption and desorption characteristics of hydrocarbons having a small number of carbon atoms has been studied for hydrocarbon adsorbents in exhaust gas purification systems.

  For example, Patent Document 1 discloses an exhaust gas purification system for a gasoline engine in which two types of zeolites having different silica / alumina ratios are combined downstream of a three-way catalyst. Furthermore, Patent Document 1 describes that it is preferable to use ZSM-5 to adsorb lower hydrocarbons. Patent Document 2 discloses that ferrierite, mordenite, ZSM-5, and β-type zeolite ion-exchanged with silver can be used as an adsorbent for ethylene. Furthermore, Patent Document 3 discloses that proton-type SUZ-4 is excellent in propylene adsorption performance.

JP-A-11-192427 Special table 2009-518162 Patent 2011-062664

  The hydrocarbon adsorbent applied to the exhaust gas treatment system is required to have a function of desorbing hydrocarbons adsorbed at 200 to 300 ° C. in addition to the hydrocarbon adsorption function. In addition to this, the hydrocarbon adsorbent of the exhaust gas treatment system is exposed to exhaust gas at a temperature of 600 ° C or higher, more preferably 900 ° C or higher, while it is exposed to room temperature and further to zero when the internal combustion engine is stopped. Big.

  However, the conventionally reported hydrocarbon adsorbents did not have particularly stable hydrocarbon desorption characteristics because the temperature at which hydrocarbons are desorbed significantly decreases due to heat load due to heat load. .

  In view of such problems, an object of the present invention is to provide a hydrocarbon adsorbent in which a decrease in the desorption temperature of adsorbed hydrocarbons is suppressed as compared with conventional hydrocarbon adsorbents.

  The inventors of the present invention repeatedly studied a hydrocarbon adsorbent suitable for application as an exhaust gas treatment system for an internal combustion engine. As a result, it has been found that the inclusion of a metal in a small pore zeolite having a specific structure reduces the change in the desorption characteristics of hydrocarbons after heat load, and has completed the present invention.

That is, the gist of the present invention is as follows.
[1] A hydrocarbon adsorbent containing LEV-type zeolite containing copper.
[2] The hydrocarbon adsorbent according to [1], wherein the copper content of the LEV-type zeolite is 1.0% by weight or more and 7.0% by weight or less as a weight ratio of copper with respect to the LEV-type zeolite.
[3] The hydrocarbon adsorbent according to any one of [1] or [2] above, wherein the molar ratio of silica to alumina in the LEV-type zeolite is 10 or more and 50 or less.
[4] The hydrocarbon adsorbent according to any one of [1] to [3], wherein the LEV-type zeolite has an average particle size of 0.5 μm or more.
[5] A method for treating a hydrocarbon-containing gas, wherein the hydrocarbon adsorbent according to any one of [1] to [4] is used.
[6] A hydrocarbon adsorption method using the hydrocarbon adsorbent according to any one of [1] to [4].

  According to the present invention, it is possible to provide a hydrocarbon adsorbent in which a change in the desorption temperature of the adsorbed hydrocarbon is small as compared with a conventional hydrocarbon adsorbent.

  Hereinafter, the hydrocarbon adsorbent of the present invention will be described.

  The hydrocarbon adsorbent of the present invention contains LEV-type zeolite containing copper. LEV-type zeolite is a crystalline aluminosilicate having a LEV structure. The LEV structure is an IUPAC structure code defined by the Structure Commission of the International Zeolite Association (hereinafter referred to as “IZA”), and is a LEV structure. The crystalline aluminosilicate has a structure (hereinafter also referred to as “network structure”) in which aluminum (Al) and silicon (Si) are formed by repeating a network through oxygen (O).

  The LEV-type zeolite containing copper (hereinafter, also referred to as “copper-containing LEV-type zeolite”) contained in the hydrocarbon adsorbent of the present invention contains copper. Since copper is cheaper than noble metals such as silver and palladium, the hydrocarbon adsorbent of the present invention containing copper tends to increase the amount of hydrocarbon adsorption per price as compared with these. Copper is preferably contained in at least LEV type pores.

  The copper-containing LEV-type zeolite has a copper content of 1.0% by weight or more and 7.0% by weight or less, more preferably 2.0% by weight or more and 5.0% by weight or less as a weight ratio of copper to the LEV-type zeolite. It is preferable. As the copper content increases, the desorption temperature of the adsorbed hydrocarbon tends to increase. The copper content in the present invention is the weight ratio of copper to the copper-containing LEV-type zeolite.

The copper-containing LEV-type zeolite contained in the hydrocarbon adsorbent of the present invention has a silica to alumina molar ratio (hereinafter also referred to as “SiO ₂ / Al ₂ O ₃ molar ratio”) of 10 or more and 50 or less, and further It is preferably 30 or more and 40 or less. Tend to heat resistance is high by SiO ₂ / _Al 2 _{O 3} molar ratio is _higher, the adsorption amount of hydrocarbon SiO 2 / _Al 2 _{O 3} molar ratio is too high tends to be low. By setting the SiO ₂ / Al ₂ O ₃ molar ratio to 10 or more and 50 or less, it has practical resistance to a heat load and shows a practical amount of adsorbing hydrocarbons.

  The copper-containing LEV-type zeolite contained in the hydrocarbon adsorbent of the present invention preferably has an average crystal diameter of 0.5 μm or more, more preferably 0.8 μm or more. When the average crystal diameter is 0.5 μm or more, a decrease in the amount of adsorbed hydrocarbon after the thermal history is easily suppressed.

  The crystal diameter in the present invention is the particle diameter of primary particles, and is the diameter of independent minimum unit particles observed with an electron microscope. The average crystal diameter is a value obtained by arithmetically averaging the crystal diameters of 30 or more primary particles randomly extracted with an electron microscope. Therefore, the secondary particle diameter and average secondary particle diameter, which are the diameters of secondary particles in which a plurality of primary particles are aggregated, are different from the crystal diameter and average crystal diameter. The shape of the primary particles may be at least one selected from the group consisting of a cubic shape, a tetragonal shape, and a twin shape in which a cubic shape or a tetragonal shape is combined.

  The shape of the hydrocarbon adsorbent of the present invention is arbitrary, and may be any shape of a powder or a molded body. When the hydrocarbon adsorbent of the present invention is used in powder form, it may be used as a catalyst member coated or wash coated on a substrate such as a honeycomb. When the hydrocarbon adsorbent of the present invention is used as a molded body, it is at least one shape selected from the group consisting of a spherical shape, a substantially spherical shape, an elliptical shape, a disc shape, a cylindrical shape, a polyhedral shape, an indefinite shape, and a petal shape, and other uses. The shape may be suitable for the case.

  When the hydrocarbon adsorbent of the present invention is used as a molded article, the hydrocarbon adsorbent of the present invention is a group consisting of silica, alumina, kaolin, attapulgite, montmorillonite, bentonite, allophane and sepiolite in addition to the copper-containing LEV-type zeolite. The at least 1 sort (s) of clay may be included.

  The hydrocarbon adsorbent of the present invention can be used in a hydrocarbon-containing gas treatment method, a hydrocarbon adsorption method, a hydrocarbon adsorption-desorption method, etc., and a hydrocarbon adsorbent from a hydrocarbon-containing gas, In particular, it is suitable for use as an adsorbent for hydrocarbons having a small number of carbon atoms (hereinafter also referred to as “lower hydrocarbons”). In the case of adsorbing hydrocarbons using the hydrocarbon adsorbent of the present invention, a hydrocarbon-containing gas may be used as the gas to be treated and brought into contact with the hydrocarbon adsorbent of the present invention. When the hydrocarbon adsorbent of the present invention is brought into contact with the hydrocarbon-containing gas, the hydrocarbon can be adsorbed by setting the temperature to -30 ° C or higher and lower than 250 ° C. Moreover, the adsorbed hydrocarbon can be desorbed by setting the hydrocarbon adsorbent adsorbing hydrocarbon to 250 ° C. or higher. Furthermore, the hydrocarbon adsorbent of the present invention has a hydrocarbon desorption start temperature of 250 ° C. or higher, more preferably 260 ° C. or higher. In particular, the hydrocarbon adsorbent of the present invention has a hydrocarbon desorption start temperature of 250 ° C. or higher, more preferably 260 ° C. or higher, even after being exposed to high temperature and high humidity. The temperature difference between the desorption start temperatures of the hydrocarbons before and after exposure is as small as 50 ° C. or less, and further 30 ° C. or less. Even when used as an exhaust gas treatment system for a moving internal combustion engine, it exhibits a high hydrocarbon adsorption capacity. The temperature at which the hydrocarbon desorption amount increases, so-called desorption peak temperature, is usually higher than the desorption start temperature. Thus, the hydrocarbon adsorbent of the present invention can also be used as a hydrocarbon adsorption / desorption material that adsorbs hydrocarbons at less than 250 ° C. and desorbs hydrocarbons at 250 ° C. or more.

The hydrocarbon-containing gas may be any gas containing hydrocarbons, and specifically includes exhaust gas from an internal combustion engine, and further exhaust gas from a diesel engine or a gasoline engine. The hydrocarbon-containing gas may contain at least one member selected from the group consisting of carbon monoxide, carbon dioxide, hydrogen, oxygen, nitrogen, nitrogen oxides, sulfur oxides, and water in addition to hydrocarbons. The following composition can be illustrated as a hydrocarbon containing gas.
Hydrocarbon: 0.001 to 5% by volume, further 0.005 to 3% by volume (in terms of methane)
Carbon monoxide: 0 to 1% by volume
Carbon dioxide: 0 to 10% by volume
Oxygen: 0 to 20% by volume
Nitrogen oxide: 0 to 1% by volume
Sulfur oxide: 0 to 0.05% by volume
Water _(H 2 O): _0~15% by volume
Nitrogen: balance

  The hydrocarbon adsorbed by the hydrocarbon adsorbent of the present invention is not particularly limited, but the lower hydrocarbon is a hydrocarbon having 1 to 3 carbon atoms, and at least one member selected from the group consisting of methane, ethane, ethylene, propane and propylene. Can be mentioned.

  In the present invention, the hydrocarbon desorption start temperature can be determined by quantitatively analyzing hydrocarbons in the gas after passing through the hydrocarbon adsorbent of the present invention using a hydrogen ionization detector (FID). . The hydrocarbon concentration of the hydrocarbon-containing gas before passing through the hydrocarbon adsorbent of the present invention (hereinafter referred to as “the hydrocarbon concentration before adsorption”) and the carbonization of the hydrocarbon-containing gas after passing through the hydrocarbon adsorbent of the present invention Measure the hydrogen concentration (hereinafter referred to as “post-adsorption hydrocarbon concentration”), the state where the pre-adsorption hydrocarbon concentration is higher than the post-adsorption hydrocarbon concentration, and the post-adsorption hydrocarbon concentration from the pre-adsorption hydrocarbon concentration. A high state is regarded as a desorption stage, and the temperature at which the adsorption stage and the desorption stage are switched may be used as the hydrocarbon desorption start temperature.

  Next, the manufacturing method of the hydrocarbon adsorbent of this invention is demonstrated.

The hydrocarbon adsorbent of the present invention can be produced by any method as long as it includes the above-described copper-containing LEV-type zeolite. Examples of the method for producing the hydrocarbon adsorbent of the present invention include a production method having a copper-containing step in which a LEV-type zeolite whose cation type is either H-type or NH ₄ -type and a copper compound are brought into contact with each other.

As the LEV-type zeolite (hereinafter also referred to as “raw material zeolite”) whose cation type is either H-type or NH ₄ -type used in the copper-containing step, those obtained by a known method can be used. .

  As a known method for producing LEV, for example, a crystallization step of crystallizing a composition containing a silica source, an alumina source, an alkali source, an organic structure directing agent and water (hereinafter also referred to as “raw material composition”). The manufacturing method of the LEV type zeolite which has can be mentioned. In addition to the above-described various raw materials, a production method may further include a crystallization step of crystallizing a raw material composition containing a copper source.

When the cation type of the LEV type zeolite is Na type or K type, it can be mixed with an ammonium chloride aqueous solution to obtain a raw material zeolite whose cation type is NH ₄ type, and the cation type is NH ₄ type. By calcining the type LEV-type zeolite, it is possible to obtain a raw material zeolite whose cation type is H-type.

  In the copper-containing step, the raw material zeolite and the copper compound are brought into contact. Thereby, copper is inserted into the pores of the raw material zeolite. As a contact method between the raw material zeolite and the copper compound, at least one selected from the group consisting of an ion exchange method, an impregnation support method, an evaporation to dryness method, a precipitation support method and a physical mixing method, and at least an ion exchange method or an impregnation support method. Either can be mentioned.

  As long as the copper source and the copper compound to be used for the copper-containing process are any compounds, and are at least one copper compound in the group consisting of nitrate, sulfate, acetate, chloride, complex salt, oxide and complex oxide It is preferable that it is at least one member selected from the group consisting of chlorides, nitrates and oxides.

  In the copper-containing step, it is preferable to heat-treat the copper-containing LEV-type zeolite after being brought into contact with the copper compound at 500 ° C. or more and 900 ° C. or less. Thereby, copper existing on the surface of the copper-containing LEV-type zeolite or the like is easily taken into the pores in a highly dispersible state.

  Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these examples.

Example 1
A copper-containing LEV-type zeolite was obtained by impregnating NH ₄ -type LEV-type zeolite with an aqueous copper nitrate solution. That is, after adding 4.5 mL of 1 mol / L copper nitrate aqueous solution to 10 g of NH ₄ type LEV type zeolite, the mixture was kneaded in a mortar. After kneading, it was dried in air at 110 ° C. overnight, and further heated in air at 800 ° C. for 5 hours to disperse copper in the pores. The obtained copper-containing LEV-type zeolite had a SiO ₂ / Al ₂ O ₃ molar ratio of 31, a copper content of 2.7% by weight, and an average crystal grain size of 1.0 μm.

  The copper-containing LEV type zeolite light was used as the hydrocarbon adsorbent of this example.

Example 2
A copper-containing LEV-type zeolite of this example was obtained in the same manner as in Example 1 except that the temperature of the heat treatment after kneading with the aqueous copper nitrate solution was 600 ° C. The obtained copper-containing LEV-type zeolite had a SiO ₂ / Al ₂ O ₃ molar ratio of 31, a copper content of 2.8% by weight, and an average crystal grain size of 1.0 μm.

  The copper-containing LEV type zeolite light was used as the hydrocarbon adsorbent of this example.

Example 3
A copper-containing LV zeolite of this example was obtained in the same manner as in Example 1 except that 6.5 mL of a 1 mol / L aqueous copper nitrate solution was used as the aqueous copper nitrate solution. The obtained copper-containing LEV-type zeolite had a SiO ₂ / Al ₂ O ₃ molar ratio of 31, a copper content of 4.0% by weight and an average crystal grain size of 1.0 μm.

  The copper-containing LEV type zeolite light was used as the hydrocarbon adsorbent of this example.

Example 4
Anhydrous copper sulfate, pure water, ethylenediamine, precipitated silica, sodium aluminate, 1-adamantylamine and chabazite-type zeolite were crystallized at 180 ° C. for 72 hours, then in air, at 600 ° C., 2 The LEV-type zeolite containing copper in the pores was obtained by calcining with time. The obtained copper-containing LEV-type zeolite had a SiO ₂ / Al ₂ O ₃ molar ratio of 22, a copper content of 3.6% by weight, and an average crystal grain size of 5.1 μm.

  The copper-containing LEV type zeolite light was used as the hydrocarbon adsorbent of this example.

Example 5
Anhydrous copper sulfate, pure water, triethylenetetramine precipitated silica, sodium aluminate, 1-adamantylamine and chabazite-type zeolite were crystallized at 180 ° C. for 135 hours, then in air, at 600 ° C., Calcination was performed for 2 hours to obtain LEV-type zeolite containing copper in the pores. The obtained copper-containing LEV-type zeolite had a SiO ₂ / Al ₂ O ₃ molar ratio of 33, a copper content of 1.8% by weight, and an average crystal grain size of 4.5 μm.

  The copper-containing LEV type zeolite light was used as the hydrocarbon adsorbent of this example.

Comparative Example 1
NH ₄ type LEV-type zeolite was obtained in the same manner as in Example 1. Silver ion exchange was performed by adding 10 g of the obtained NH4 type LEV type zeolite to 60 mL of 0.3 mol / L silver nitrate aqueous solution and stirring at 60 ° C. for 4 hours.

After the silver ion exchange, silver-containing LEV-type zeolite was obtained by solid-liquid separation, washing, and drying in air at 110 ° C. overnight. The obtained silver-containing LEV-type zeolite had a SiO ₂ / Al ₂ O ₃ molar ratio of 31, a silver content of 4.2% by weight, and an average crystal grain size of 1.0 μm.

  The copper-containing LEV type zeolite light was used as the hydrocarbon adsorbent of this comparative example.

Comparative Example 2
Similar to Example 1 except that NH ₄ type CHA type zeolite was used instead of NH ₄ type LEV type zeolite, and kneading with an aqueous copper nitrate solution was followed by heating in air at 600 ° C. for 2 hours. A copper-containing CHA-type zeolite was obtained by this method. The obtained copper-containing CHA-type zeolite had a SiO ₂ / Al ₂ O ₃ molar ratio of 31 and a copper content of 3.0% by weight.

  The copper-containing CHA-type zeolite light was used as the hydrocarbon adsorbent of this comparative example.

Comparative Example 3
The same as in Example 1 except that NH ₄ type MFI type zeolite was used instead of NH ₄ type LEV type zeolite, and the mixture was kneaded with an aqueous copper nitrate solution and then heated in air at 600 ° C. for 2 hours. A copper-containing CHA-type zeolite was obtained by this method. The obtained copper-containing CHA-type zeolite had a SiO ₂ / Al ₂ O ₃ molar ratio of 31 and a copper content of 3.0% by weight.

  The copper-containing CHA-type zeolite light was used as the hydrocarbon adsorbent of this comparative example.

Measurement example 1
The hydrocarbon desorption start temperature was evaluated using a hydrocarbon-containing gas having the following composition.
Propylene: 1000 ppm by volume (concentration in terms of methane)
Water: 10% by volume
Nitrogen: balance

(Preparation and pretreatment of measurement sample)
The hydrocarbon adsorbents obtained in Examples and Comparative Examples were respectively pressure-molded and pulverized to obtain indefinitely formed bodies having an aggregate diameter of 20 to 30 mesh. The molded hydrocarbon adsorbent was filled into an atmospheric pressure fixed bed flow type reaction tube, pretreated at 500 ° C. for 1 hour under nitrogen flow, and then cooled to 50 ° C.
(Measurement of hydrocarbon desorption temperature)
After the pretreatment, the nitrogen gas was switched to a hydrocarbon-containing gas, and the hydrocarbon desorption temperature was measured while flowing the hydrocarbon-containing gas through the hydrocarbon adsorbent under the following conditions.
Measurement temperature: 50-600 ° C
Temperature increase rate: 10 ° C / min
Flow rate of hydrocarbon-containing gas: 200 mL / min

  The hydrocarbon in the gas after passing through the hydrocarbon adsorbent was continuously quantitatively analyzed by a hydrogen ionization detector (FID). The hydrocarbon concentration of the hydrocarbon-containing gas on the inlet side of the normal pressure fixed bed flow type reaction tube (hereinafter referred to as “inlet hydrocarbon concentration”) and the hydrocarbon content on the outlet side of the normal pressure fixed bed flow type reaction tube The gas hydrocarbon concentration (hereinafter referred to as “exit hydrocarbon concentration”) is measured, and the state where the inlet hydrocarbon concentration is higher than the outlet hydrocarbon concentration is the adsorption stage, and the outlet hydrocarbon concentration is higher than the inlet hydrocarbon concentration. Was regarded as the desorption stage, and the temperature at which the adsorption stage and the desorption stage were switched was defined as the hydrocarbon desorption start temperature. The results are shown in Table 1.

Measurement example 2
After subjecting the hydrocarbon adsorbents obtained in the examples and comparative examples to hydrothermal durability treatment, the hydrocarbon desorption start temperature was measured in the same manner as in Measurement Example 1. The results are shown in Table 1.

  Hydrothermal endurance treatment is performed by filling aggregated particles into a 20-30 mesh agglomerated diameter obtained by pressure-molding and pulverizing a hydrocarbon adsorbent into a normal pressure fixed bed flow type reaction tube, and circulating the mixed gas under the following conditions: It was done by doing.

Process gas: Propylene 3000ppmC (Methane equivalent concentration)
10% by volume of water
Nitrogen remainder Flow rate: 200 mL / min Processing temperature: 900 ° C.
Processing time: 5 hours

  From Table 1, the hydrocarbon adsorbents of the examples did not decrease the hydrocarbon desorption temperature before and after being exposed to a high-temperature and high-humidity atmosphere, and further, the hydrocarbon desorption start temperature tends to increase. there were. On the other hand, the hydrocarbon adsorbent composed of LEV-type zeolite containing silver and the hydrocarbon adsorbent composed of zeolite other than LEV-type zeolite are both greatly reduced in desorption start temperature when exposed to a high-temperature and high-humidity atmosphere. I was able to confirm.

  The hydrocarbon adsorbent composed of the Cu-supported LEV-type zeolite with little deterioration in adsorption performance even after the hydrothermal durability treatment of the present invention can be used as an adsorbent for purifying hydrocarbons contained in automobile exhaust gas.

Claims (6)

  A hydrocarbon adsorbent comprising a LEV-type zeolite containing copper.   2. The hydrocarbon adsorbent according to claim 1, wherein the copper content of the LEV-type zeolite is 1.0% by weight or more and 7.0% by weight or less as a weight ratio of copper to the LEV-type zeolite.   3. The hydrocarbon adsorbent according to claim 1, wherein a molar ratio of silica to alumina in the LEV-type zeolite is 10 or more and 50 or less.   The hydrocarbon adsorbent according to any one of claims 1 to 3, wherein the LEV-type zeolite has an average particle size of 0.5 µm or more.   A method for treating a hydrocarbon-containing gas, wherein the hydrocarbon adsorbent according to any one of claims 1 to 4 is used.   A hydrocarbon adsorption method according to any one of claims 1 to 4, wherein the hydrocarbon adsorption method is used.