JP2023039939A - Hydrocarbon adsorbent, adsorption method of hydrocarbon - Google Patents

Abstract

The present invention provides a hydrocarbon adsorbent that exhibits high hydrocarbon adsorption properties even after exposure to a high-temperature, high-humidity atmosphere. The hydrocarbon adsorbent is characterized by having a structure that includes 8-membered oxygen ring pores with a major axis of less than 4.8 Å as framework pores, and also by containing silver-containing zeolite. [Selected Figures] None

Description

The present disclosure relates to hydrocarbon adsorbents and methods of adsorbing hydrocarbons.

Exhaust gases emitted from internal combustion engines used in moving bodies such as automobiles and ships contain a large amount of hydrocarbons. Hydrocarbons emitted from an internal combustion engine are purified by a three-way catalyst. A temperature environment of 200° C. or higher is required for the three-way catalyst to function. Therefore, in the temperature range where the three-way catalyst does not function, such as at the so-called cold start, hydrocarbons are adsorbed on the hydrocarbon adsorbent, and in the temperature range where the three-way catalyst starts to function, hydrocarbons are released from the adsorbent, resulting in carbonization. Hydrogen is decomposed and purified by a three-way catalyst.

A composition containing zeolite is generally used as a hydrocarbon adsorbent, and the higher the hydrocarbon desorption starting temperature of the composition, the higher the activity of the three-way catalyst, and the more hydrocarbons are released. be able to. Since the purification efficiency of hydrocarbons is increased, a composition having a high desorption start temperature of hydrocarbons is desired. Furthermore, a practical hydrocarbon adsorbent is required to have a composition that adsorbs a large amount of hydrocarbons and exhibits a high purification rate. In addition, the exhaust gas temperature of automobile exhaust gas reaches 900° C. or higher depending on the operating conditions of the engine, so the hydrocarbon adsorbent is required to have high heat resistance.

Patent Document 1 proposes an adsorbent for purifying hydrocarbons in exhaust gas prepared using a silver-supported molecular sieve. Patent Document 2 proposes a hydrocarbon adsorbent made of zeolite containing an alkali metal.

In any of these methods of adsorbing and removing hydrocarbons using a hydrocarbon adsorbent, the hydrocarbons contained in the exhaust gas are once adsorbed by the hydrocarbon adsorbent in a low temperature range when the engine is started, and the exhaust gas purifying catalyst is It catalytically purifies hydrocarbons desorbed from the hydrocarbon adsorbent above its operating temperature. However, all of the conventional hydrocarbon adsorbents have insufficient durability in a high-temperature, high-humidity atmosphere.

JP-A-06-126165 JP-A-2001-293368

The present disclosure aims to provide a hydrocarbon adsorbent that exhibits high hydrocarbon adsorption properties, particularly for lower hydrocarbons, even after exposure to high temperature and high humidity atmospheres.

The present inventors investigated the hydrocarbon adsorption properties of compositions containing zeolites. As a result, the present inventors have found that zeolite having a specific structure among so-called small pore zeolites is excellent in adsorbing hydrocarbons, especially lower hydrocarbons, by containing silver.

That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows.
[1] A hydrocarbon adsorbent characterized by having a structure containing 8-membered oxygen ring pores with a long axis of less than 4.8 Å as skeleton pores and containing silver-containing zeolite.
[2] The hydrocarbon adsorbent according to [1] above, wherein the skeleton pores included in the structure are the oxygen eight-membered ring pores and skeleton pores smaller than the eight-membered ring pores.
[3] The structure is ABW, AEI, AFT, AFV, AFX, ANA, ATN, AWW, BIK, CAS, CDO, CHA, DDR, EEI, ESV, IFY, IHW, KFI, LTA, MRT, MTF, MWF , PAU, PHI, PWN, RHO, RTE, SAS, SFW and UFI, the hydrocarbon adsorbent according to the above [1] or [2].
[4] The hydrocarbon adsorbent according to any one of [1] to [3] above, wherein the structure is one selected from the group consisting of AEI, AFX, CHA and DDR.
[5] The hydrocarbon adsorbent according to any one of [1] to [4] above, wherein the mass ratio of silver to the zeolite is 1.0% by mass or more and 10.0% by mass or less.
[6] The hydrocarbon adsorbent according to any one of [1] to [5] above, wherein the zeolite has a peak top temperature of 404° C. or higher in H ₂ -TPR measurement.
[7] The hydrocarbon adsorbent according to any one of [1] to [6] above, wherein the zeolite has a silica to alumina molar ratio of 5 or more and 75 or less.
[8] The hydrocarbon adsorbent according to any one of [1] to [7] above, wherein the silver includes at least a silver ion state.
[9] The hydrocarbon adsorbent according to any one of [1] to [8] above, wherein the proportion of silver ions in the silver is 75% or more.
[10] A hydrocarbon adsorption system comprising the hydrocarbon adsorbent according to any one of [1] to [9].
[11] A method for adsorbing hydrocarbons using the hydrocarbon adsorbent according to any one of [1] to [9].

The present disclosure can provide hydrocarbon adsorbents that exhibit high hydrocarbon adsorption properties, particularly for lower hydrocarbons, even after exposure to high temperature and high humidity atmospheres.

Hereinafter, the hydrocarbon adsorbent of the present disclosure will be described by showing an example of an embodiment. The terms used in this embodiment are as follows.

"Zeolite" is a compound having a regular structure in which skeleton atoms (hereinafter also referred to as "T atoms") are interposed with oxygen (O), and T atoms are metal atoms, metalloid atoms and other atoms. It is a compound consisting of at least one. Examples of metal atoms include one or more selected from the group consisting of iron (Fe), aluminum (Al), gallium (Ga), tin (Sn) and titanium (Ti), and other transition metal elements. (B), one or more selected from the group of silicon (Si), germanium (Ge), arsenic (As), antimony (Sb) and tellurium (Te) can be exemplified, and phosphorus (P) is exemplified as other atoms can. Specific zeolites include metallosilicates in which the T atom is composed of a metal atom and silicon, such as one or more selected from the group of aluminosilicates, ferrosilicates and gallosilicates, aluminophosphates (AlPO) and silicoaluminophosphates (SAPO) can be exemplified by metal phosphates such as at least one of The zeolite contained in the hydrocarbon adsorbent of the present embodiment is preferably zeolite containing no phosphorus as a T atom.

The zeolite contained in the hydrocarbon adsorbent of the present embodiment is preferably metallosilicate, more preferably crystalline aluminosilicate. A crystalline aluminosilicate is a compound having a crystal structure consisting of a repeating network of aluminum (Al) and silicon (Si) via oxygen (O). The crystalline aluminosilicate may have a structure in which at least a portion of at least one of aluminum and silicon in T atoms is replaced with at least one of metal atoms and metalloid atoms of aluminum and silicon.

The framework structure of zeolite (used interchangeably with crystal structure or crystal phase, hereinafter also referred to as "zeolite structure") is defined by the Structure Commission of the International Zeolite Association (hereinafter also referred to as "IZA"). The XRD pattern of each zeolite structure described in Collection of simulated XRD powder patterns for zeolites, Fifth revised edition (2007) (hereinafter also referred to as "reference pattern") and the XRD pattern of the target zeolite for identification.

In this embodiment, XRD patterns include those obtained from XRD measurements under the following conditions.

Accelerating current/voltage: 40mA/40kV
Radiation source: CuKα ray (λ = 1.5405 Å)
Measurement mode: step scan
Scan condition: 40°/min
Measurement time: 3 seconds
Measurement range: 2θ = 3° to 43°
Divergence longitudinal limiting slit: 10mm
Divergence/Entrance Slit: 1°
Light receiving slit: open
Receiving solar slit: 5°
Detector: Semiconductor detector (D/teX Ultra)
Filter: Ni filter In the present embodiment, a zeolite having a zeolite structure indicated by a specific structure code is also referred to as "-type zeolite". For example, "CHA structure" or "CHA type" means a zeolite structure specified by the structure code "CHA", and CHA type zeolite means zeolite having a CHA structure, particularly zeolite consisting of a CHA structure.

A “skeletal pore” (channel) is a pore formed by a ring structure composed of a T atom and an oxygen atom bonded thereto (hereinafter also referred to as “skeletal oxygen”). The pore size of the framework pores is determined based on the number of T atoms and framework oxygen forming the pores. "Oxygen n-membered ring pore" is a skeletal pore formed by a ring structure consisting of a T atom and n skeletal oxygens (where n is a positive integer other than 0), For example, an "oxygen 8-membered ring pore" is a skeletal pore formed by a ring structure consisting of a T atom and 8 skeletal oxygens. Also, the "long axis" of a skeletal pore is the maximum length of the skeletal pore.

Skeletal pores included in each zeolite structure and their long axes can be confirmed from the Framework and Reference Material of each structure code posted on the IZA homepage. For example, the Ring sizes are 8, 6 and 4 in the Framework of AEI structure. From this, it can be confirmed that the skeleton pores included in the AEI structure are oxygen eight-membered ring pores, oxygen six-membered ring pores and oxygen four-membered ring pores. In the Reference Material of the AEI structure, Channels are [100] 8 3.8×3.8<->[110] 8 3.8×3.8<->[001] 8 3.8×3.8 is. From this, it can be confirmed that the oxygen 8-membered ring pore in the AEI structure consists of 3.8 Å×3.8 Å, and the long axis (and short axis) is 3.8 Å. From this, it can be confirmed that the AEI structure has an oxygen 8-membered ring with a major axis diameter of 3.8 Å and a structure containing the following skeletal pores.

"Hydrocarbon purification rate" and "desorption start temperature" are values measured by the following method.

<Measurement sample>
Shape: Agglomeration diameter 20-30 mesh, amorphous hydrocarbon adsorbent Manufacturing method: Pressure molding and pulverization <Pretreatment>
Atmosphere: Nitrogen atmosphere Temperature: 500°C
Time: 30 minutes <Hydrocarbon adsorption and desorption conditions>
A measurement sample is packed in a normal pressure fixed bed flow type reaction tube, and a hydrocarbon-containing gas is passed under the following conditions.

Hydrocarbon-containing gas: Propylene 1000 volume ppmC (methane equivalent concentration)
Water 3% by volume
Nitrogen balance Gas flow rate: 200 mL/min Measurement temperature: 50 to 600°C
Heating rate: 10°C/min <Hydrocarbon purification rate>
Hydrocarbon concentration of the hydrocarbon-containing gas on the inlet side of the atmospheric pressure fixed bed flow reaction tube (methane conversion concentration; hereinafter also referred to as "inlet concentration"), and the outlet side of the atmospheric pressure fixed bed flow reaction tube The hydrocarbon concentration of the hydrocarbon-containing gas (methane equivalent concentration; hereinafter also referred to as "outlet concentration") is measured using a hydrogen ionization detector (FID), and the integral value of the inlet concentration is transferred to the hydrocarbon adsorbent. The hydrocarbon content of the gas to be treated before circulation (hereinafter also referred to as "HC amount before circulation") [μmolC], and the integrated value of the outlet concentration is the hydrocarbon content of the gas to be treated after circulation to the hydrocarbon adsorbent. The amount (hereinafter also referred to as “the amount of HC after distribution”) is [μmolC]. The hydrocarbon purification rate is calculated from the HC amount before distribution and the HC amount after distribution in the measurement temperature range of 50° C. to 200° C. using the following formula.

Hydrocarbon purification rate [%] =
{(HC amount before distribution−HC amount after distribution)/HC amount before distribution}×100
<Desorption start temperature>
The change in the amount of desorption of hydrocarbons per mass of the hydrocarbon adsorbent is measured as the measurement temperature rises, and the lowest temperature at which the amount of desorption is 0 μmol C/g may be taken as the desorption start temperature. The amount of hydrocarbons desorbed per mass of the hydrocarbon adsorbent is the difference between the amount of HC before circulation and the amount of HC after circulation (= HC amount before circulation - HC amount after circulation) [ μmol C].

The hydrocarbon adsorbent of the present embodiment has a structure containing an oxygen eight-membered ring pore with a long axis of less than 4.8 Å as a skeleton pore, and further contains a zeolite containing silver. hydrogen adsorbent.

The hydrocarbon adsorbent of the present embodiment is a zeolite having a structure containing oxygen 8-membered ring pores with a long axis of less than 4.8 Å (hereinafter also referred to as “maximum 8-membered ring pores”) as skeleton pores. include. When the zeolite having such oxygen 8-membered ring pores contains silver, it becomes easier to adsorb hydrocarbons, especially lower hydrocarbons. The long axis of the maximum 8-membered ring pore is less than 4.8 Å, preferably 4.6 Å or less, 4.4 Å or less, or 4.0 Å or less, and preferably 3.0 Å or more, or 3.6 Å or more .

Since the purifying properties of lower hydrocarbons are particularly high, the zeolite contained in the hydrocarbon adsorbent of the present embodiment has a skeleton pore contained in its structure with a maximum of 8-membered ring pores and a maximum of 8-membered ring pores. Smaller framework pores are preferred.

In the hydrocarbon adsorbent of this embodiment, the skeleton pores included in the structure are oxygen 8-membered ring pores (maximum 8-membered ring pores) with a long axis of less than 4.8 Å, and the 8-membered ring pores It is preferable to include a zeolite having only smaller skeleton pores and containing silver (hereinafter also referred to as "silver-containing small pore zeolite"). That is, in the zeolite contained in the hydrocarbon adsorbent of the present embodiment, the skeleton pores included in the structure are pores larger than eight-membered ring pores (oxygen 10-membered ring pores, oxygen 12-membered ring pores, etc. , pores in which the number of oxygen atoms constituting the pores is greater than 8) and oxygen eight-membered ring pores with a long axis of 4.8 Å or more are preferably not included. The skeletal pores smaller than the eight-membered ring pores include one or more selected from the group consisting of six-membered oxygen ring pores, five-membered oxygen ring pores, and four-membered oxygen ring pores, and six-membered oxygen ring pores. At least one of pores and oxygen 4-membered ring pores can be exemplified.

The silver-containing small pore zeolite is a zeolite having only pores with a maximum of 8-membered rings and pores smaller than the maximum of 8-membered ring pores, and is a so-called small pore zeolite. Compared to zeolites with LEV structures that are similarly small pore zeolites and have eight-membered ring pores with a long axis of 4.8 Å, and FER-type zeolites that have skeleton pores exceeding oxygen eight-membered ring pores, these Zeolites have high adsorption properties for hydrocarbons, especially lower hydrocarbons, in a high-temperature atmosphere.

The structures of silver-containing small pore zeolites are ABW, AEI, AFT, AFV, AFX, ANA, ATN, AWW, BIK, CAS, CDO, CHA, DDR, EEI, ESV, IFY, IHW, KFI, LTA, MRT, Preferably any structure selected from the group of MTF, MWF, PAU, PHI, PWN, RHO, RTE, SAS, SFW and UFI, and any structure selected from the group of AEI, AFX, CHA and DDR is more preferable.

As specific zeolites, silver-containing small-pore zeolites include ABW-type zeolite, AEI-type zeolite, AFT-type zeolite, AFV-type zeolite, AFX-type zeolite, ANA-type zeolite, ATN-type zeolite, AWW-type zeolite, BIK-type zeolite, CAS-type zeolite, CDO-type zeolite, CHA-type zeolite, DDR-type zeolite, EEI-type zeolite, ESV-type zeolite, IFY-type zeolite, IHW-type zeolite, KFI-type zeolite, LTA-type zeolite, MRT-type zeolite, MTF-type zeolite, MWF-type zeolite It is preferably one or more selected from the group of zeolite, PAU-type zeolite, PHI-type zeolite, PWN-type zeolite, RHO-type zeolite, RTE-type zeolite, SAS-type zeolite, SFW-type zeolite and UFI-type zeolite, AEI-type zeolite, It is more preferably one or more selected from the group of AFX-type zeolite, CHA-type zeolite and DDR-type zeolite, and more preferably one or more selected from the group of AEI-type zeolite, CHA-type zeolite and DDR-type zeolite, At least one of AEI zeolite and CHA zeolite is even more preferable, and CHA zeolite is particularly preferable.

The molar ratio of silica to alumina in the silver-containing small-pore zeolite (hereinafter also referred to as “SiO ₂ /Al ₂ O ₃ ratio”) is preferably 5 or more, 10 or more, 15 or more, or 18 or more. Also, the SiO ₂ /Al ₂ O ₃ ratio may be 75 or less, 50 or less, 40 or less, or 30 or less.

The BET specific surface area of the silver-containing small-pore zeolite is preferably 200 m ² /g or more, or 300 m ^{2 /g or more, and preferably 800 m 2 /} g or less, or 700 m ² /g or less.

The crystal grain size of the silver-containing small-pore zeolite is preferably 0.01 μm or more, or 0.1 μm or more, and preferably 50 μm or less, or 20 μm or less.

The silver-containing small pore zeolite contains silver, preferably ion-exchanged with or loaded with silver.

The silver content of the silver-containing small-pore zeolite is 1.0% by mass or more, 4.0% by mass or more, or 6.0% by mass or more, and is 10.0% by mass or less and 9.5% by mass or less. Alternatively, it may be 9.0% by weight or less. The silver content is calculated by converting the silicon (Si) of the silver-containing small pore zeolite into SiO ₂ , the aluminum (Al) into Al ₂ O ₃ , and the silver (Ag) into Ag ₂ O, with respect to the total mass of Ag ₂ It is the mass ratio [% by mass] of silver (Ag) in terms of O.

Silver contained in the silver-containing small-pore zeolite is preferably in one or more states selected from the group consisting of silver ions, silver clusters and metallic silver. More preferably, silver is in at least one of silver ions and silver clusters, and more preferably includes at least silver ions. Silver is preferably in the form of silver ions, which is the form with the greatest number of adsorption points, because it serves as adsorption points for hydrocarbons when used as a hydrocarbon adsorbent.

The ratio of silver ions to the silver contained in the silver-containing small-pore zeolite (hereinafter also referred to as "silver ion ratio") is preferably 75% or more, 80% or more, or 90% or more. As a result, the adsorption rate of hydrocarbons, particularly the adsorption rate of lower hydrocarbons, tends to increase. When all the silver contained in the silver-containing small-pore zeolite becomes ions, the silver ion rate becomes the maximum value (100%). The silver ion rate may be 100% or less, 99% or less, and further 95% or less.

The silver ion ratio can be obtained from the peak area of silver in each state obtained by correcting the UV spectrum measured under the following conditions, performing KM conversion, and separating the waveform.
<UV spectrum measurement conditions>
Measurement method: Diffuse reflection method
Wavelength: 200-700nm
Temperature: room temperature
Slit width: 5 nm
BG: barium sulfate <silver ion rate>
Silver ion rate [%] = {S _P1 / (S _P1 + S _P2 + S _P3 )} × 100
where _SP1 is the area of the UV peak (P1) corresponding to silver ions after waveform separation, _SP1 is the area of the UV peak (P2) corresponding to silver clusters after waveform separation, and _SP1 is the waveform Area of the UV peak (P3) corresponding to metallic silver after separation. In addition, P1 is a UV peak having a peak top at a wavelength of 200 nm or more and 240 nm or less, P2 is a UV peak having a peak top at a wavelength of 240 nm or more and 350 nm or less, and P1 is a UV peak having a peak top at a wavelength of 350 nm or more and 700 nm or less. be.
<Amount of silver ions>
The silver ion content [mass%] of the silver-containing small-pore zeolite is preferably 1.0 mass% or more, 2.0 mass% or more, 3.0 mass% or more, 4.0 mass% or more, 5 0% by mass or more, or preferably 6.0% by mass or more. Moreover, the amount of silver ions can be exemplified to be 10.0% by mass or less, 9.5% by mass or less, or 9.0% by mass or less. The amount of silver ions can be calculated by multiplying the silver ion rate [%] obtained above and the silver content [% by mass].

The silver-containing small-pore zeolite preferably has a peak top temperature of 404° C. or higher in H ₂ -TPR measurement. The peak top temperature is the temperature indicated by the peak top of the peak having the maximum peak height among the peaks of 200° C. or higher in the TPR spectrum obtained by H ₂ -TPR measurement.

When the peak top temperature is 404° C. or higher, the resistance to reduction is increased, and the adsorption performance of the silver-containing small-pore zeolite after hydrothermal treatment is further improved. More specifically, in a high-temperature environment, silver ions are aggregated and reduced to metallic silver accompanied by sintering. The hydrocarbon adsorbent of the present embodiment has small pores in a small pore zeolite containing an oxygen 8-membered ring pore structure with a long axis of less than 4.8 Å and has a moderate size that can accommodate silver ions. contains silver. As a result, the silver ions in each pore are likely to be kept dispersed, and sintering in a high-temperature environment is suppressed. Therefore, it is considered that the resistance to reduction is increased. In this embodiment, the peak top temperature is more preferably 420° C. or higher, 430° C. or higher, 450° C. or higher, or 500° C. or higher. Also, the peak top temperature is 910° C. or lower, 700° C. or lower, or 600° C. or lower.

Conditions for H ₂ -TPR measurement in this embodiment include the following conditions.

Measurement atmosphere: Argon atmosphere containing 5% by volume of hydrogen
Flow rate: 30 mL/min
Heating rate: 10°C/min
Measurement temperature: 50 to 910°C
Sample amount: 0.2g
Pretreatment conditions for H ₂ -TPR measurement include the following conditions.

Pretreatment atmosphere: Helium atmosphere
Flow rate: 50 mL/min
Heating rate: 15°C/min
Pretreatment temperature: 300°C
Pretreatment time: 30 minutes The silver-containing small-pore zeolite preferably has few defects in the skeleton structure, and the amount of SiOH groups, which is one of the indicators of the amount of defects, should be 3.00 × 10 ²⁰ /g or less. is preferred. Since the amount of defects in the zeolite is small, the hydrocarbon desorption starting temperature of the hydrocarbon adsorbent of the present embodiment is further improved. More preferably, the amount of SiOH groups is 2.00×10 ²⁰ /g or less, 1.50×10 ²⁰ /g or less, or 1.00×10 ²⁰ /g or less. Also, the amount of SiOH groups is 0.10×10 ²⁰ groups/g or more, or 0.30×10 ²⁰ groups/g or more.

The amount of SiOH groups can be determined by ¹ H-MAS-NMR spectrum measurement. The amount of SiOH groups can be calculated by a calibration curve method from the area intensity of the peak (2.0±0.5 ppm peak) attributed to SiOH groups in the ¹ H-MAS-NMR spectrum of the silver-containing zeolite.

A calibration curve may be prepared using benzene as a standard substance. A calibration curve is prepared from standard samples (eg, 0 mmol, 0.01 mmol, and 0.02 mmol) at three or more points (eg, 3 to 5 points) with different amounts of benzene in the range of 0 mmol to 0.02 mmol. Perform NMR measurement on each standard sample under the following conditions, plot the correlation between the proton amount of each standard sample obtained and the area intensity of the spectrum, and prepare a calibration curve for converting the area intensity and the proton amount.

Prior to ¹ H-NMR spectrum measurement, the silver-containing small-pore zeolite is heat-treated under the following conditions for dehydration, then nitrogen is introduced, and the temperature is lowered to room temperature in a nitrogen atmosphere for pretreatment. preferable.

Pretreatment atmosphere: vacuum
Heating rate: 0.25°C/min
Pretreatment temperature: 400°C
Pretreatment time: 5 hours Conditions for ¹ H-MAS-NMR spectrum measurement in this embodiment include the following conditions.

Equipment used: Nuclear magnetic resonance equipment (equipment name: VNMRS-400, manufactured by Varian)
Observation nucleus: ^1H (399.8MHz)
Pulse width: π/2
Measurement waiting time: 10 seconds
Accumulated times: 32 times
Rotation frequency: 15kHz
Shift standard: TMS
The obtained ¹ H-NMR spectrum is assigned to SiOH groups by baseline correction and waveform separation by Gaussian function using a spectrum data analysis program (eg, trade name: GRAMS/AI, manufactured by Thermo Fisher Scientific). A peak (2.0±0.5 ppm peak) and its area intensity may be detected and analyzed.

The hydrocarbon purification rate of the hydrocarbon adsorbent of this embodiment is preferably 20% or more, 25% or more, or 30% or more. The hydrocarbon purification rate is, for example, 100% or less, 99% or less, or 95% or less.

The desorption start temperature of the hydrocarbon adsorbent of this embodiment is preferably 200° C. or higher, 250° C. or higher, or 300° C. or higher. The desorption start temperature may be about the same as the temperature at which a purification catalyst such as a three-way catalyst functions, and may be, for example, 500° C. or less or 400° C. or less.

The hydrocarbon adsorbent of the present embodiment preferably has high hydrocarbon purification properties after exposure to a high temperature and high humidity atmosphere, and the above hydrocarbon purification rate and desorption start temperature are values after hydrothermal treatment. is preferred. Hydrothermal treatment is a treatment that exposes a hydrocarbon adsorbent to a hot and humid atmosphere.
The following conditions can be illustrated as conditions of hydrothermal treatment.

Processing gas: 10% by volume of water
Dry air balance Gas flow rate: 200 mL/min Space velocity: 4000 hr ^-1
Processing temperature: 900°C
Treatment time: 1 hour The hydrocarbon adsorbent of the present embodiment can be used in any shape according to the application, and is not particularly limited, but for example, in the shape of powder, compact, or adsorption member. can be used. Specific shapes of the molded body include one or more selected from the group of spherical, substantially spherical, elliptical, disk-like, columnar, polyhedral, irregular and petal-like.

From the viewpoint of use as a slurry, the hydrocarbon adsorbent of this embodiment may contain a solvent. The solvent can be exemplified by at least one of water and alcohol, and water.

From the viewpoint of use as a molded body, the hydrocarbon adsorbent of the present embodiment may contain a binder. As the binder, one or more selected from the group of silica, alumina, kaolin, attapulgite, montmorillonite, bentonite, allophane and sepiolite may be used.

The hydrocarbon adsorbent of this embodiment can be used in a method for adsorbing hydrocarbons. The hydrocarbon adsorption method using the hydrocarbon adsorbent of the present embodiment is arbitrary, but for example, a hydrocarbon adsorption method comprising the step of flowing a hydrocarbon-containing fluid through the hydrocarbon adsorbent of the present embodiment, is mentioned.

The hydrocarbon adsorbent to be subjected to the step of contacting the hydrocarbon-containing fluid with the hydrocarbon adsorbent of the present embodiment (hereinafter also referred to as the "HC removal step") may include the hydrocarbon adsorbent of the present embodiment. may be two or more hydrocarbon adsorbents containing silver-containing small-pore zeolites that are different in at least one of composition and zeolite structure; and a hydrocarbon adsorbent comprising zeolites other than small pore zeolites.

The hydrocarbon-containing fluid to be subjected to the HC removal step may be at least one of a hydrocarbon-containing liquid and a gas, and may be a hydrocarbon-containing gas.

The hydrocarbon-containing fluid preferably contains at least lower hydrocarbons, and more preferably contains hydrocarbons having from 1 to 10 carbon atoms, such as methane, ethane, ethylene, propylene, butane, It is more preferable to contain one or more selected from the group of linear paraffins having 5 to 10 carbon atoms and linear olefins having 5 to 10 carbon atoms, and methane, ethane, ethylene, propylene and butane. It is even more preferable to contain one or more selected from the group, and it is particularly preferable to contain at least propylene. Also, the hydrocarbon-containing gas may contain aromatic hydrocarbons and one or more selected from the group consisting of benzene, toluene and xylene.

The hydrocarbon content of the hydrocarbon-containing fluid is arbitrary, but can be exemplified by 100 volume ppmC (methane equivalent concentration) or more, or 200 volume ppmC (methane equivalent concentration) or more.

Further, the hydrocarbon-containing fluid may contain one or more selected from the group consisting of carbon monoxide, carbon dioxide, hydrogen, oxygen, nitrogen, nitrogen oxides, sulfur oxides and water.

Specific examples of hydrocarbon-containing fluids include combustion gas, exhaust gas from internal combustion engines, and one or more selected from the group consisting of ship exhaust gas and automobile exhaust gas.

The flow in the HC removal step may be any correspondence that allows hydrocarbons to be adsorbed by the hydrocarbon adsorbent of the present embodiment. As a flow method, it is possible to circulate the hydrocarbon-containing fluid through the hydrocarbon adsorbent of the present embodiment at a temperature of −30° C. to 300° C. and a space velocity of 1000 h ⁻¹ to 100000 h ⁻¹ .

The hydrocarbon adsorbent of this embodiment can be used as a hydrocarbon adsorption system comprising the same. A hydrocarbon adsorption system may comprise the hydrocarbon adsorbent of the present embodiment, one or more selected from the group consisting of a nitrogen oxide reduction catalyst, a three-way catalyst, an oxidation catalyst and a hydrocarbon decomposition catalyst, may be provided.

Next, a method for producing the hydrocarbon adsorbent of this embodiment will be described.

The hydrocarbon adsorbent of the present embodiment may be produced by any method as long as the hydrocarbon adsorbent satisfying the above constitution is obtained.

As a method for producing the hydrocarbon adsorbent of the present embodiment, for example, zeolite having a structure containing oxygen 8-membered ring pores (maximum 8-membered ring pores) with a long axis of less than 4.8 Å as skeleton pores, mixing a silver source.

Silver is contained in the zeolite, and more specifically, silver is supported on the zeolite by the process of adding silver to the zeolite having the above structure (hereinafter also referred to as "silver-containing process").

The zeolite subjected to the silver-containing step is a zeolite having a structure containing an oxygen 8-membered ring pore (a maximum 8-membered ring pore) with a long axis of less than 4.8 Å as a skeleton pore, preferably a zeolite having a skeleton pore with a maximum of 8 members. Zeolites, ABW, AEI, AFT, AFV, AFX, ANA, ATN, AWW, BIK, CAS, CDO, CHA, DDR, EEI, ESV, which are ring pores and framework pores smaller than maximum 8 ring pores , IFY, IHW, KFI, LTA, MRT, MTF, MWF, PAU, PHI, PWN, RHO, RTE, SAS, SFW and UFI, preferably AEI, AFX, CHA. And zeolite having one or more structures selected from the group of DDR, more preferably zeolite having one or more structures selected from the group of AEI, AFX, CHA and DDR (hereinafter also referred to as "raw zeolite"). Just do it. Furthermore, the starting zeolite preferably does not contain silver.

Raw material zeolite is ABW type zeolite, AEI type zeolite, AFT type zeolite, AFV type zeolite, AFX type zeolite, ANA type zeolite, ATN type zeolite, AWW type zeolite, BIK type zeolite, CAS type zeolite, CDO type zeolite, CHA type zeolite. Zeolite, DDR type zeolite, EEI type zeolite, ESV type zeolite, IFY type zeolite, IHW type zeolite, KFI type zeolite, LTA type zeolite, MRT type zeolite, MTF type zeolite, MWF type zeolite, PAU type zeolite, PHI type zeolite, One or more selected from the group of PWN-type zeolite, RHO-type zeolite, RTE-type zeolite, SAS-type zeolite, SFW-type zeolite and UFI-type zeolite, and the group of AEI-type zeolite, AFX-type zeolite, CHA-type zeolite and DDR-type zeolite One or more selected from can be exemplified. The starting zeolite is preferably one or more selected from the group consisting of AEI zeolite, CHA zeolite and DDR zeolite, more preferably at least one of AEI zeolite and CHA zeolite. From the viewpoint of obtaining a hydrocarbon adsorbent with a higher hydrocarbon purification rate, the starting zeolite is preferably AEI zeolite. On the other hand, from the viewpoint of obtaining a hydrocarbon adsorbent that easily retains adsorbed hydrocarbons in a higher temperature range, the raw material zeolite is preferably a CHA-type zeolite, and N,N,N-trialkyladamantane ammonium cations and trialkylcyclohexyl More preferably, the composition containing at least one of the ammonium cations is crystallized CHA-type zeolite, and it is even more preferable that the composition containing trialkylcyclohexylammonium cations is crystallized CHA-type zeolite.

The raw material zeolite may have physical properties similar to those of the zeolite contained in the hydrocarbon adsorbent of the present embodiment. The raw zeolite can be exemplified by having the following physical properties.

SiO ₂ /Al ₂ O ₃ ratio: 5 or more, 10 or more, 15 or more, or 18 or more,
75 or less, 50 or less, 40 or less, or 30 or less BET specific surface area: 200 m ² /g or more, 300 m ² /g or more, or 400 m ² /g or more,
800 m ² /g or less, 700 m ² /g or less, or 600 m ² /g or less Crystal grain size: 0.01 μm or more, 0.1 μm or more, or 0.3 μm or more,
50 µm or less, 20 µm or less, or 10 µm or less The silver source to be subjected to the silver-containing step may be at least one of a silver-containing compound and a complex, and preferably at least one of a silver complex and a water-soluble silver compound. Specific silver sources include one or more selected from the group of silver fluoride, silver chloride, silver nitrate and silver cyanide, preferably one or more selected from the group of silver fluoride, silver nitrate and silver cyanide, more preferably fluorine. At least one of silver halide and silver nitrate can be exemplified.

The mixing method in the silver-containing step may be any method as long as the raw material zeolite and the silver source are brought into sufficient contact, and at least one of wet mixing and dry mixing can be exemplified. This gives a silver-containing small pore zeolite. A preferable mixing method is a method of mixing an aqueous solution containing a raw material zeolite and a silver source, and one or more selected from the group of ion exchange, impregnation support and evaporation to dryness, preferably selected from the group of ion exchange, impregnation support and evaporation to dryness. One or more, more preferably at least one of ion exchange and impregnation support, and more preferably ion exchange can be exemplified.

Mixing can be exemplified by contacting the starting zeolite and the aqueous solution containing the water-soluble silver source at 10° C. or higher and 100° C. or lower for 10 seconds or longer and 10 hours or shorter.

As a specific mixing method, there is a method of circulating an aqueous solution containing a silver source in raw material zeolite.

In the production method of the present embodiment, small-pore zeolite containing silver (hereinafter also referred to as "silver-containing small-pore zeolite"). A step of washing the silver-containing small-pore zeolite (hereinafter also referred to as a “washing step”), a step of drying the silver-containing small-pore zeolite (hereinafter also referred to as a “drying step”), and a step of drying the silver-containing small-pore zeolite It may have one or more steps selected from the group of a step of calcining the pore zeolite (hereinafter also referred to as an "activation step"), preferably has at least a washing step, and a washing step and It may have a drying step.

Any washing method may be used as long as impurities and the like can be removed from the silver-containing small-pore zeolite. As a washing method, washing the silver-containing small-pore zeolite with a sufficient amount of pure water can be exemplified.

Any drying method may be used as long as the moisture remaining on the surface and pores of the silver-containing small-pore zeolite can be removed. As a drying method, it can be exemplified by treating in the atmosphere at 100° C. or higher and 200° C. or lower, preferably 110° C. or higher and 190° C. or lower.

The activation step may be any heat treatment as long as the organic matter can be removed from the silver-containing small-pore zeolite. Examples of the heat treatment method include treatment at 400° C. to 700° C. in air, and further treatment at 500° C. to 600° C. in air.

When the hydrocarbon adsorbent of the present embodiment is applied to a substrate, the production method of the present embodiment may include a step of mixing silver-containing small-pore zeolite and a solvent (hereinafter, “slurry step”). preferable.

The slurrying step obtains a silver-containing small pore zeolite slurry. Any method of mixing the silver-containing zeolite and the solvent can be used as long as a zeolite slurry suitable for coating the desired substrate is obtained. As a mixing method in the slurrying step, at least one of water and alcohol, preferably silver-containing small-pore zeolite may be added and mixed with water.

When the hydrocarbon adsorbent of the present embodiment is used as a molded body, it is preferable to include a step of molding the silver-containing small-pore zeolite (hereinafter referred to as "molding step").

The shaping step shapes the silver-containing small pore zeolite into the desired shape. The molding method in the molding step may be any method as long as a molded article having a desired shape can be obtained, and is selected from the group of rolling dynamic granulation molding, press molding, extrusion molding, injection molding, slip casting, and sheet molding. 1 or more.

In the molding step, a composition mixed with a binder in addition to the silver-containing small-pore zeolite may be molded. As the binder, one or more selected from the group of silica, alumina, kaolin, attapulgite, montmorillonite, bentonite, allophane and sepiolite may be used.

In this embodiment, the long axis of the maximum 8-membered ring pore, SiO ₂ /Al ₂ O ₃ ratio, BET specific surface area, crystal grain size, silver content, silver ion rate, peak top temperature, SiOH group amount, hydrocarbon The purification rate, desorption start temperature, time, temperature, etc. may be any upper limit, lower limit, or combination of the values described above.

The present disclosure will be described in detail below using examples. However, the disclosure is not limited to these examples.

(Identification of crystal structure)
A sample was subjected to XRD measurement using a general X-ray diffractometer (device name: UltimaIV Protectus, manufactured by Rigaku Corporation). The measurement conditions are as follows.

Accelerating current/voltage: 40mA/40kV
Radiation source: CuKα ray (λ = 1.5405 Å)
Measurement mode: Continuous scan
Scan condition: 40°/min
Measurement range: 2θ = 3° to 43°
Divergence longitudinal limiting slit: 10mm
Divergence/Entrance Slit: 1°
Light receiving slit: open
Detector: D/teX Ultra
Using Ni filter The XRD pattern obtained was compared with a reference pattern to identify the crystal structure of the sample.

(composition analysis)
A sample solution was prepared by dissolving the sample in a mixed aqueous solution of hydrofluoric acid and nitric acid. Using a general ICP device (device name: OPTIMA5300DV, manufactured by PerkinElmer), the sample solution was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). From the obtained measured values of Si, Al and Ag, the SiO ₂ /Al ₂ O ₃ molar ratio of the sample and the mass % of Ag were determined.

(Calculation of silver ion rate)
The hydrocarbon adsorbents obtained in the following examples and comparative examples were each pressure-molded to form irregular-shaped compacts with aggregate diameters of 20 to 30 mesh. 3 mL of the obtained compact was charged into a normal pressure fixed bed flow reaction tube and pretreated by heat treatment under the following conditions.

Processing gas: 10% by volume of water
Dry air balance Gas flow rate: 200 mL/min Space velocity: 4000 hr ^-1
Processing temperature: 900°C
Processing time: 1 hour A general ultraviolet-visible spectrophotometer (device name: UV-visible near-infrared spectrophotometer V-770, manufactured by JASCO Corporation and integrating sphere unit ISN-923, manufactured by JASCO Corporation) UV-vis measurement was performed on the sample after pretreatment, and a UV-vis spectrum was obtained. The measurement conditions are as follows.

Measurement method: Diffuse reflection method
Wavelength: 200-700nm
Temperature: room temperature
Slit width: 5 nm
BG: barium sulfate The resulting UV-vis spectrum was corrected, KM-converted, and waveform-separated by the method described above, and from the UV-vis spectrum after waveform separation, the silver ion rate was determined using the following formula. .

Silver ion rate [%] = {S _P1 / (S _P1 + S _P2 + S _P3 )} × 100
where _SP1 is the area of the UV peak (P1) corresponding to silver ions after waveform separation, _SP1 is the area of the UV peak (P2) corresponding to silver clusters after waveform separation, and _SP1 is the waveform Area of the UV peak (P3) corresponding to metallic silver after separation. In addition, P1 is a UV peak having a peak top at a wavelength of 200 nm or more and 240 nm or less, P2 is a UV peak having a peak top at a wavelength of 240 nm or more and 350 nm or less, and P1 is a UV peak having a peak top at a wavelength of 350 nm or more and 700 nm or less. be.

(Calculation of amount of silver ions)
In each example and comparative example, the silver ion content [% by mass] was calculated by multiplying the silver ion rate [%] obtained above by the silver content [% by mass].

(H ₂ -TPR measurement)
Hydrocarbon adsorbents obtained in the following examples and comparative examples were subjected to H ₂ -TPR measurement using a general catalyst analyzer (device name: BELCATII, manufactured by MicrotracBEL). Heat treatment was performed under the following conditions, and pretreatment was performed by lowering the temperature to 50°C.

Pretreatment atmosphere: Helium atmosphere
Flow rate: 50 mL/min
Heating rate: 15°C/min
Pretreatment temperature: 300°C
Pretreatment time: 30 minutes
Sample amount: 0.2g
The samples after pretreatment were measured under the following conditions.

Measurement atmosphere: Argon atmosphere containing 5% by volume of hydrogen
Flow rate: 30 mL/min
Heating rate: 10°C/min
Measurement temperature: 50 to 910°C
Sample amount: 0.2 g
The temperature at which the peak top of the peak having the maximum peak height among the peaks of 200° C. or higher from the H ₂ -TPR spectrum obtained was taken as the peak top temperature in the H ₂ -TPR measurement.

( ¹ H-NMR measurement)
¹ H-NMR measurements of the hydrocarbon adsorbents obtained in the following examples were carried out using a general NMR spectrometer (VNMRS-400, manufactured by Varian). After the treatment under the following conditions, nitrogen was introduced and the temperature was lowered to room temperature in a nitrogen atmosphere for pretreatment.

Pretreatment atmosphere: vacuum
Heating rate: 0.25°C/min
Pretreatment temperature: 400°C
Pretreatment time: 5 hours
Sample amount: 70 mg
The samples after pretreatment were measured under the following conditions.

Observation nucleus: ^1H (399.8MHz)
Pulse width: π/2
Measurement waiting time: 10 seconds
Accumulated times: 32 times
Rotation frequency: 15 kHz
Shift standard: TMS
Sample amount: 40 mg
The resulting NMR spectrum was analyzed using a spectral data analysis program (eg, trade name: GRAMS/AI, manufactured by Thermo Fisher Scientific), baseline correction, waveform separation by Gaussian function, and peaks attributed to SiOH groups. (2.0±0.5 ppm peak) and its area intensity were detected and analyzed. A calibration curve was constructed using benzene as a standard. From the area intensity of the obtained NMR spectrum attributed to the silanol groups, the amount of protons derived from the silanol groups in the sample was determined by the calibration curve method, and the amount of SiOH was determined from the amount of protons and the mass of the weighed sample.

Example 1
CHA-type zeolite obtained by crystallizing a composition containing N,N,N-dimethylethylcyclohexylammonium cations, having a SiO ₂ /Al ₂ O ₃ ratio of 19.2, and having a proton-type cation type as a starting zeolite used as

After the starting zeolite was mixed with pure water to form a slurry, the slurry was suction-filtered to obtain a starting zeolite cake. An aqueous solution of silver nitrate having a silver concentration of 1.3% by mass was passed through the resulting cake at room temperature to cause silver to be supported on the CHA-type zeolite. In distribution, the silver nitrate aqueous solution was used in such an amount that the ratio of the Ag content [mol] of the silver nitrate aqueous solution to the Al content [mol] of the raw material zeolite (hereinafter also referred to as "prepared Ag/Al") was 1.0. . Then, after washing with a sufficient amount of pure water, it was dried in the air at 110° C. to obtain silver-containing CHA-type zeolite (silver-supported CHA-type zeolite), which was used as the hydrocarbon adsorbent of this example.

The obtained silver-containing CHA-type zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 19.8, a silver content of 8.9% by mass, and a silver ion rate of 92%.

Example 2
An AEI zeolite obtained by crystallizing a composition containing a 1,1,3,5-tetramethylpiperidinium cation, having a SiO ₂ /Al ₂ O ₃ ratio of 24.6 and a proton type cation type AEI zeolite containing silver (AEI zeolite supporting silver) was obtained in the same manner as in Example 1, except for using AEI as the starting zeolite, and this was used as the hydrocarbon adsorbent of this example.

The obtained silver-containing AEI zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 24.6 and a silver content of 8.7% by mass.

Example 3
A DDR-type zeolite obtained by crystallizing a composition containing 1-adamantaneamine, having a SiO ₂ /Al ₂ O ₃ ratio of 31.0 and having an ammonium-type cation type was used as a starting zeolite; A silver-containing DDR-type zeolite (silver-loaded DDR-type zeolite) was obtained in the same manner as in Example 1, except that the silver nitrate aqueous solution was circulated so that Ag/Al was 2, and this was used as the hydrocarbon of this example. used as an adsorbent.

The obtained silver-containing DDR type zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 31.6 and a silver content of 4.6% by mass.

Example 4
An AFX-type zeolite obtained by crystallizing a composition containing a 1,3-bis-(1-adamantyl)imidazolium cation, having a SiO ₂ /Al ₂ O ₃ ratio of 23.1 and a proton type cation type AFX-type zeolite containing silver (AFX-type zeolite supporting silver) was obtained in the same manner as in Example 1, except that AFX-type zeolite was used as the raw material zeolite, and this was used as the hydrocarbon adsorbent of this example.

The obtained silver-containing AFX-type zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 23.1 and a silver content of 7.5% by mass.

Comparative example 1
LEV-type zeolite obtained by crystallization of a composition containing 1-adamantaneamine, having a SiO ₂ /Al ₂ O ₃ ratio of 31.2 and having an ammonium-type cation type was used as a raw material zeolite; Silver-containing LEV-type zeolite (silver-supporting LEV-type zeolite) was obtained in the same manner as in Example 1 except that the silver nitrate aqueous solution was circulated so that Ag/Al was 2, and this was used as the hydrocarbon of this comparative example. used as an adsorbent.

The obtained silver-containing LEV-type zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 31.4 and a silver content of 6.1% by mass.

Comparative example 2
A CHA-type zeolite obtained by crystallization of a composition containing an N,N,N-dimethylethylcyclohexylammonium cation, having a SiO ₂ /Al ₂ O ₃ ratio of 24.0 and having a proton-type cation type was compared. Example hydrocarbon adsorbent.

Comparative example 3
Except that FER-type zeolite having a SiO ₂ /Al ₂ O ₃ ratio of 17.5 and an ammonium cation type was used as the raw material zeolite, and that an aqueous solution of silver nitrate was circulated so that Ag/Al was 2. obtained a silver-containing FER-type zeolite (silver-supporting FER-type zeolite) in the same manner as in Example 1, and used this as a hydrocarbon adsorbent of a comparative example.

The obtained silver-containing FER-type zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 17.5, a silver content of 9.0% by mass, and a silver ion rate of 66%.

Comparative example 4
Except that MFI type zeolite having a SiO ₂ /Al ₂ O ₃ ratio of 39.0 and an ammonium cation type was used as the raw material zeolite, and that an aqueous solution of silver nitrate was circulated so that the charge Ag/Al was 2. A silver-containing MFI zeolite (silver-supporting MFI zeolite) was obtained in the same manner as in Example 1, and this was used as a hydrocarbon adsorbent for Comparative Example.

The obtained silver-containing MFI zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 39.0 and a silver content of 8.0% by mass.

Measurement example (preparation of hydrocarbon adsorbent measurement sample)
The hydrocarbon adsorbents obtained in Examples and Comparative Examples were pressure-molded and pulverized to obtain irregular-shaped compacts with aggregate diameters of 20 to 30 mesh.

(hydrothermal treatment)
3 mL of the obtained compact was charged into a normal pressure fixed bed flow reaction tube and hydrothermally treated under the following conditions to obtain a hydrothermally treated compact.

Processing gas: 10% by volume of water
Dry air balance Gas flow rate: 200 mL/min Space velocity: 4000 hr ^-1
Processing temperature: 900°C
Processing time: 1 hour (pretreatment of hydrocarbon adsorbent measurement sample)
0.1 g of the molded body obtained in the preparation of the hydrocarbon adsorbent measurement sample and 0.1 g of the molded body after the hydrothermal treatment were each charged in a normal pressure fixed bed flow reaction tube and heated at 500° C. for 30 minutes under nitrogen flow. After the treatment, the temperature was lowered to 50°C for pretreatment.

(Hydrocarbon adsorption of hydrocarbon adsorbent)
A hydrocarbon-containing gas was passed through each hydrocarbon adsorbent that had undergone the above pretreatment, and the adsorbed hydrocarbons were measured between 50° C. and 600° C. to determine the amount of adsorbed hydrocarbons. The composition and measurement conditions of the hydrocarbon-containing gas are shown below.

Hydrocarbon-containing gas: Propylene 1000 volume ppmC (methane equivalent concentration)
Water 3% by volume
Nitrogen balance Gas flow rate: 200 mL/min Measurement temperature: 50 to 600°C
Heating rate: 10°C/min (hydrocarbon purification rate and desorption start temperature)
Hydrocarbon-containing gas was passed through each hydrocarbon adsorbent in the same manner as in (Hydrocarbon adsorption of hydrocarbon adsorbent). The inlet concentration and the outlet concentration were measured using FID, and the integrated value of the inlet concentration was taken as the HC amount before circulation [μmol C], and the integrated value of the outlet concentration was taken as the HC amount after circulation [μmol C]. The hydrocarbon purification rate was calculated using the following formula from the amount of HC before distribution and the amount of HC after distribution in the measurement temperature range of 50°C to 200°C.

Hydrocarbon purification rate [%] =
{(HC amount before distribution−HC amount after distribution)/HC amount before distribution}×100
In addition, the change in the amount of desorption of hydrocarbons per mass of the hydrocarbon adsorbent was measured as the measurement temperature increased, and the lowest temperature at which the amount of desorption was 0 μmol C/g was taken as the desorption start temperature. The amount of hydrocarbons desorbed per mass of the hydrocarbon adsorbent is the difference between the amount of HC before circulation and the amount of HC after circulation (= HC amount before circulation - HC amount after circulation) [ μmol C].

Table 1 shows the results. In Table 1, "skeletal pore" indicates the type (n) of the oxygen n-membered ring pore contained in each zeolite structure for convenience, for example, "8" means "oxygen 8-membered ring pore" Equivalent to. In addition, "major axis" in Table 1 is the length of the major axis of the maximum eight-membered ring pore.

Example 5
CHA-type zeolite obtained by crystallizing a composition containing N,N,N-dimethylethylcyclohexylammonium cations, having a SiO ₂ /Al ₂ O ₃ ratio of 24.0, and having a proton-type cation type as a starting zeolite The silver-containing CHA-type zeolite (silver-supporting CHA-type zeolite) of this example was prepared in the same manner as in Example 1, except that the silver nitrate aqueous solution was circulated so that the charged Ag/Al was 2. This was used as the hydrocarbon adsorbent of this example.

The obtained silver-containing CHA-type zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 23.2, a silver content of 6.8% by mass, and a silver ion rate of 92%.

Example 6
A CHA-type zeolite obtained by crystallization of a composition containing an N,N,N-trimethyladamantane ammonium cation, having a SiO ₂ /Al ₂ O ₃ ratio of 24.0 and having an ammonium cation type is used as a starting zeolite. Silver-containing CHA-type zeolite (silver-supporting CHA-type zeolite) of this example was prepared in the same manner as in Example 1, except that the silver nitrate aqueous solution was circulated so that Ag/Al was 0.6. was obtained, and this was used as the hydrocarbon adsorbent of this example.

The obtained silver-containing CHA-type zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 24.0, a silver content of 6.5% by mass, and a silver ion rate of 79%.

Example 7
CHA-type zeolite obtained by crystallizing a composition containing N,N,N-dimethylethylcyclohexylammonium cations, having a SiO ₂ /Al ₂ O ₃ ratio of 24.0, and having a proton-type cation type as a starting zeolite The silver-containing CHA-type zeolite of this example ( A silver-supported CHA-type zeolite) was obtained and used as the hydrocarbon adsorbent of this example.

The obtained silver-containing CHA-type zeolite had a SiO ₂ /Al ₂ O ₃ ratio of 24.4, a silver content of 8.0% by mass, and a silver ion rate of 94%.

The evaluation results of the hydrocarbon adsorbents of Examples and Comparative Examples are shown in the table below.

In Table 1, the columns of silver ion rate, silver ion amount, hydrocarbon purification rate after hydrothermal treatment, desorption start temperature after hydrothermal treatment, H ₂ -TPR measurement peak top temperature, and SiOH amount are indicated with "-". Those marked with are not measured. As shown in Table 1, the hydrocarbon adsorbents of Examples had a high desorption start temperature of 200° C. or higher and a hydrocarbon purification rate of 30% or higher after the hydrothermal treatment. In addition, it was confirmed that the hydrocarbon adsorbents of Examples had a higher desorption start temperature, that is, a higher holding power for adsorbed hydrocarbons, by hydrothermal treatment. On the other hand, the hydrocarbon adsorbent made of LEV-type zeolite containing silver in Comparative Example 1 had a hydrocarbon purification rate of 10% after the hydrothermal treatment, despite being a small-pore zeolite. was significantly lower than

In addition, it can be confirmed that the hydrocarbon adsorbent of Comparative Example 2, which is made of CHA-type zeolite containing no silver, has a low desorption start temperature before the hydrothermal treatment, and cannot retain the adsorbed hydrocarbons. Furthermore, the hydrocarbon adsorbent of Comparative Example 2 made of FER zeolite, which is not small-pore zeolite, had a hydrocarbon purification rate of 10% after the hydrothermal treatment, which was about the same as in Comparative Example 1. Furthermore, the hydrocarbon adsorbent of Comparative Example 3 made of MFI-type zeolite has a desorption start temperature after hydrothermal treatment of less than 200°C, and it can be confirmed that hydrothermal treatment reduces the retention of adsorbed hydrocarbons. .

In addition, it can be confirmed that compared with the hydrocarbon adsorbent composed of the silver-containing LEV-type zeolite of Comparative Example 1, the hydrocarbon adsorbent composed of any silver-containing CHA-type zeolite has a high hydrocarbon purification rate.

Furthermore, the silver contents of the hydrocarbon adsorbents of Examples 1, 5 and 7 were 6.8% by mass, 8.0% by mass and 8.9% by mass, and the desorption start temperature after hydrothermal treatment was 301 C., 306.degree. C., and 324.degree. Further, the hydrocarbon purification rate of Example 5 was 57%, and the hydrocarbon purification rate of Example 7 was 52%.

In addition, Example 3 shows the same silver ion rate as Comparative Example 4, but when looking at the hydrocarbon desorption starting temperature before and after the hydrothermal treatment, Comparative Example 4, which does not have oxygen eight-membered ring pores, is significantly lower. In contrast, Example 3 is improved. Similarly, Example 7 shows the same silver ion rate as Comparative Example 1, but when looking at the hydrocarbon purification rate before and after the hydrothermal treatment, Comparative Example 1, which has a long axis of 4.8 Å, greatly decreased. In contrast, Example 7 maintains a high purification rate even after the hydrothermal treatment. A hydrocarbon adsorbent composed of a silver-containing small-pore zeolite having a structure containing oxygen eight-membered ring pores with a long axis of less than 4.8 Å is compared with a hydrocarbon adsorbent composed of a silver-containing zeolite that does not have such a structure. Therefore, it was confirmed that the hydrocarbon adsorption performance was improved.

Furthermore, in Examples 1 to 5 and 7, in which the peak top temperature in H ₂ -TPR measurement was 404°C or higher, both the hydrocarbon purification rate and the desorption start temperature maintained high levels even after the hydrothermal treatment. was confirmed.

Claims (11)

A hydrocarbon adsorbent comprising a zeolite containing silver and having a structure containing oxygen eight-membered ring pores with a long axis of less than 4.8 Å as skeleton pores. 2. The hydrocarbon adsorbent according to claim 1, wherein the skeletal pores included in the structure are the oxygen 8-membered ring pore and the skeletal pore smaller than the 8-membered ring pore. The structure is ABW, AEI, AFT, AFV, AFX, ANA, ATN, AWW, BIK, CAS, CDO, CHA, DDR, EEI, ESV, IFY, IHW, KFI, LTA, MRT, MTF, MWF, PAU, 3. The hydrocarbon adsorbent according to claim 1 or 2, having any structure selected from the group of PHI, PWN, RHO, RTE, SAS, SFW and UFI. 3. The hydrocarbon adsorbent according to claim 1 or 2, wherein said structure is any structure selected from the group of AEI, AFX, CHA and DDR. 3. The hydrocarbon adsorbent according to claim 1, wherein the mass ratio of silver to said zeolite is 1.0% by mass or more and 10.0% by mass or less. 3. The hydrocarbon adsorbent according to claim 1, wherein the zeolite has a peak top temperature of 404° C. or higher in H ₂ -TPR measurement. The hydrocarbon adsorbent according to claim 1 or 2, wherein the zeolite has a silica to alumina molar ratio of 5 or more and 75 or less. 3. The hydrocarbon adsorbent according to claim 1 or 2, wherein the silver includes at least the state of silver ions. 3. The hydrocarbon adsorbent according to claim 1, wherein the proportion of silver ions in said silver is 75% or more. A hydrocarbon adsorption system comprising the hydrocarbon adsorbent according to claim 1 or 2. A method for adsorbing hydrocarbons using the hydrocarbon adsorbent according to claim 1 or 2.