Hydrocarbon adsorbent and hydrocarbon adsorption method

Abstract

To provide a hydrocarbon adsorbent exhibiting a high hydrocarbon adsorption rate even in a high temperature environment, or a method of adsorbing a hydrocarbon using the hydrocarbon adsorbent.SOLUTION: A hydrocarbon adsorbent includes: zeolite represented by YO2-X2O3, and containing copper, and a rare earth, where Y is a tetra-valent element, X is a tri-valent element, the content of copper is 0.5 mass% or more and 4 mass% or less relative to 100 mass% of the zeolite, and the mole ratio of the rare earth to X is 0.005 or more and 0.1 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to hydrocarbon adsorbents and methods for adsorbing hydrocarbons. [Background technology]

[0002] Exhaust gases emitted from internal combustion engines used in mobile vehicles such as automobiles and ships contain a large amount of hydrocarbons. These hydrocarbons are purified using a three-way catalyst. Because a three-way catalyst requires a temperature environment of 200°C or higher to function, hydrocarbons are adsorbed onto a hydrocarbon adsorbent at temperatures where the three-way catalyst does not function, such as during cold starts. The hydrocarbons are then released from the adsorbent at temperatures where the three-way catalyst begins to function, and are then decomposed and purified by the three-way catalyst. Zeolite-containing compositions are commonly used as hydrocarbon adsorbents, but the higher the hydrocarbon desorption initiation temperature, the more active the three-way catalyst will be in releasing hydrocarbons, which is advantageous for purifying hydrocarbons. Therefore, a composition with a high hydrocarbon desorption initiation temperature is desired.

[0003] Patent Document 1 proposes a composition containing copper-containing FAU-type zeolite as a composition having a high hydrocarbon desorption initiation temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-150822 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the zeolite described in Patent Document 1 was insufficient in durability in a hydrothermal atmosphere, particularly at high temperatures of around 900°C. It is generally known that zeolites lose some of their framework atoms, such as aluminum, in a high-temperature, high-humidity environment, reducing their crystallinity and resulting in a decrease in the amount of hydrocarbons they adsorb and desorb. As a result, the hydrocarbon adsorption rate tends to decrease in high-temperature environments such as those found in automobile exhaust systems.

[0006] An object of the present disclosure is to provide a hydrocarbon adsorbent that exhibits a high hydrocarbon adsorption rate even in a high-temperature environment, or a method for adsorbing hydrocarbons using the hydrocarbon adsorbent. [Means for solving the problem]

[0007] The present inventors have discovered the following hydrocarbon adsorbent that exhibits a high hydrocarbon adsorption rate even in a high-temperature environment.

[0008] That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows.

[0009] [1] A hydrocarbon adsorbent comprising a zeolite represented by the formula YO2-X2O3 and containing copper and a rare earth element, wherein Y is a tetravalent element and X is a trivalent element, the content of the copper is 0.5% by mass or more and 4% by mass or less relative to 100% by mass of the zeolite, and the molar ratio of the rare earth element to X is 0.005 or more and 0.1 or less.

[0010] [2] The hydrocarbon adsorbent according to [1], wherein the molar ratio of YO2 to X2O3 (YO2 / X2O3 ratio) of the zeolite is 2 or more and 100 or less.

[0011] [3] The hydrocarbon adsorbent according to [1] or [2], wherein the rare earth is at least one selected from the group consisting of scandium, yttrium, lanthanum, cerium, neodymium, samarium, gadolinium, terbium, thulium, ytterbium, and lutetium.

[0012] [4] The hydrocarbon adsorbent according to any one of [1] to [3], wherein the zeolite has a ring structure of 10 or more members.

[0013] [5] The hydrocarbon adsorbent according to any one of [1] to [4], wherein the zeolite has one or more structures selected from the group consisting of a BEA structure, an MFI structure, an MOR structure, a YFI structure, and an FAU structure.

[0014] [6] A method for adsorbing hydrocarbons using the hydrocarbon adsorbent according to any one of [1] to [5] above. [Effects of the Invention]

[0015] An object of the present disclosure is to provide a hydrocarbon adsorbent that exhibits a high hydrocarbon adsorption rate even in a high-temperature environment, or a method for adsorbing hydrocarbons using the hydrocarbon adsorbent. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a graph showing the relationship between the molar ratio of cerium to aluminum in a hydrocarbon adsorbent and the hydrocarbon adsorption rate. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, the hydrocarbon adsorbent of the present disclosure will be described with reference to an example embodiment.

[0018] The hydrocarbon adsorbent of this embodiment is a hydrocarbon adsorbent containing a zeolite represented by YO-XO, which contains copper and a rare earth element, wherein Y is a tetravalent element and X is a trivalent element, the copper content is 0.5% by mass or more and 4% by mass or less relative to 100% by mass of the zeolite, and the molar ratio of the rare earth element to X is 0.005 or more and 0.1 or less.

[0019] The hydrocarbon adsorbent of this embodiment exhibits a high hydrocarbon adsorption rate even in a high temperature environment based on its constituent requirements.

[0020] (Zeolite) In this embodiment, zeolite is a compound having a regular structure in which skeleton atoms (hereinafter also referred to as "T atoms") are connected via oxygen (O), and the T atoms are at least one of metal atoms, metalloid atoms, and other atoms. 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), as well as boron (B) and other transition metal elements. Examples of metalloid atoms include one or more selected from the group consisting of boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te), and examples of other atoms include phosphorus (P).

[0021] The zeolite contained in the hydrocarbon adsorbent of this embodiment is a crystalline aluminosilicate. Crystalline aluminosilicate has a crystal structure consisting of a repeating network of aluminum (Al) and silicon (Si) via oxygen (O). That is, the zeolite contained in the hydrocarbon adsorbent of this embodiment contains SiO2 as YO2 and Al2O3 as X2O3, where Y is Si and X is Al. In addition to aluminosilicate, the zeolite contained in the hydrocarbon adsorbent of this embodiment may be composed of metallosilicates such as ferrosilicate and gallosilicate, or zeolite-related substances such as SAPO (silicoaluminophosphate) and AlPO (aluminophosphate).

[0022] In the following description, the zeolite contained in the hydrocarbon adsorbent of this embodiment will be described as a crystalline aluminosilicate.

[0023] The skeletal structure of a zeolite (used interchangeably with the crystalline structure, and hereinafter also referred to as the "zeolite structure") is a skeletal structure specified by the structure code (hereinafter also referred to simply as the "structure code") established by the Structure Commission of the International Zeolite Association, and can be identified by comparing the XRD pattern of the target zeolite with the XRD pattern of each zeolite structure (hereinafter also referred to as the "reference pattern") described in Collection of simulated XRD powder patterns for zeolites, Fifth revised edition (2007).

[0024] In this embodiment, the XRD pattern can be obtained by XRD measurement under the following conditions.

[0025] Acceleration current / voltage: 40mA / 40kV Radiation source: CuKα radiation (λ=1.5405Å) Measurement mode: Continuous scan Scan condition: 40° / min Measurement range: 2θ=3° to 43° Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Receiving solar slit: 5° Detector: D / teX Ultra Ni filter used The molar ratio of silica to alumina in the zeolite contained in the hydrocarbon adsorbent of this embodiment (hereinafter also referred to as the "SiO2 / Al2O3 ratio") preferably has a lower limit of 5, and upper limits of 35, 20, 18, 15, and 10, in that order, are more preferable, in terms of the high hydrocarbon desorption initiation temperature.

[0026] The zeolite contained in the hydrocarbon adsorbent of this embodiment has a high hydrocarbon desorption starting temperature and a lower limit of the BET specific surface area of ​​200 m 2 / g, 300m2 / g, with the upper limit at 700m 2 / g or less, 800m 2 / g, the order of preference becomes higher.

[0027] The zeolite contained in the hydrocarbon adsorbent of this embodiment may have, for example, one or more zeolite structures selected from the group consisting of a BEA structure, an MFI structure, an FAU structure, an FER structure, and an MOR structure. In terms of a high hydrocarbon desorption initiation temperature, it is preferable to have one or more zeolite structures selected from the group consisting of a BEA structure, an MFI structure, an FAU structure, and an MOR structure. In this embodiment, a zeolite having a specific zeolite structure is also referred to as a "-type zeolite." For example, a zeolite having an FAU structure is also referred to as an FAU-type zeolite. Examples of FAU-type zeolites include zeolite X, zeolite LSX, zeolite Y, and zeolite USY, with at least one of zeolite Y and zeolite USY being preferred. The zeolite contained in the hydrocarbon adsorbent of this embodiment may be composed of an intergrowth having two or more of the above zeolite structures.

[0028] The zeolite contained in the hydrocarbon adsorbent of this embodiment has an average crystal size of 0.1 μm or more, preferably 0.3 μm or more. Because the hydrocarbon adsorption properties tend to improve not only after exposure to a reducing atmosphere but also to a high-temperature, high-humidity oxidizing atmosphere, the average crystal size of the zeolite is more preferably 0.4 μm or more, and even more preferably 0.5 μm or more.

[0029] From the viewpoint of improving operability such as the ease of application to the adsorbent carrier, the average crystal size of the zeolite is preferably 2.5 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less. In order to exhibit high hydrocarbon adsorption properties even after exposure to both a reducing atmosphere and an oxidizing atmosphere, a high-temperature, high-humidity atmosphere, the average crystal size of the zeolite is preferably 0.4 μm or more and 2.0 μm or less, and particularly preferably 0.6 μm or more and 0.9 μm or less.

[0030] In this embodiment, the average crystal size of zeolite is the average particle size of primary particles. The particle size of primary particles is the particle size of primary particles confirmed in SEM observation images obtained by observation with a scanning electron microscope (hereinafter also referred to as "SEM"), and the average crystal size is the average value of the particle sizes of the primary particles. One method for measuring the average crystal size is to extract 80 to 150 primary particles observed at a magnification of 3,000 to 20,000 times, measure the particle sizes of the primary particles, and use the average value as the average crystal size. When extracting primary particles for particle size measurement, the number of SEM observation images used may be one or more.

[0031] (copper rare earth-containing zeolite) The zeolite contained in the hydrocarbon adsorbent of this embodiment contains copper and rare earths. Zeolite containing copper and rare earths (hereinafter also referred to as "copper-rare earth-containing zeolite") has superior hydrocarbon retention and adsorption rate after hydrothermal durability compared to zeolite not containing copper or rare earths. It is thought that the inclusion of copper and rare earths in the zeolite stabilizes the Al framework of the zeolite, thereby maintaining crystallinity and suppressing copper sintering during hydrothermal durability.

[0032] The zeolite contained in the hydrocarbon adsorbent of this embodiment contains copper. Copper-containing zeolite (hereinafter also referred to as "copper-containing zeolite") has superior hydrocarbon retention power compared to copper-free zeolites. Most hydrocarbons adsorbed in a hydrocarbon adsorbent containing copper-free zeolite are easily released as the temperature of the hydrocarbon adsorbent increases. It is believed that the inclusion of copper in the zeolite strengthens the interaction between the hydrocarbons and the zeolite, making it more difficult for hydrocarbons adsorbed in a hydrocarbon adsorbent containing such copper to be released from the hydrocarbon adsorbent.

[0033] In this embodiment, the state of copper contained in the zeolite is divalent copper (Cu 2+ ), and more preferably, divalent copper with high dispersibility (hereinafter also referred to as "dispersed copper"). 2+ions and / or CuO clusters, and Cu 2+ Preferably, it is an ion.

[0034] The copper content of the zeolite contained in the hydrocarbon adsorbent is preferably such that the lower limit is 0.5 mass%, 1.0 mass%, or 1.5 mass%, and is more preferably such that the upper limit is 4.0 mass%, 3.0 mass%, or 2.8 mass%, in that order.

[0035] In this embodiment, the copper content of the zeolite contained in the hydrocarbon adsorbent is the mass ratio of copper to the mass of metals and metalloids other than rare earths contained in the zeolite, calculated as oxides. For example, the copper content of a hydrocarbon adsorbent containing copper (Cu) and an alkali metal (M) can be calculated using the following formula:

[0036] Copper content (mass%) = W' Cu / (W Al +W Si +W M +W Cu ) x 100 In the above equation, W' Cu is the copper (Cu) content in the zeolite contained in the hydrocarbon adsorbent. Al , W Si , W M and W Cu are the mass of aluminum (Al) in the zeolite contained in the hydrocarbon adsorbent converted into its oxide (Al2O3), the mass of silicon (Si) converted into its oxide (SiO2), the mass of alkali metal (M) converted into its oxide (MO), and the mass of copper converted into its oxide (CuO), respectively.

[0037] The zeolite contained in the hydrocarbon adsorbent of this embodiment contains rare earths. In this embodiment, the rare earths contained in the zeolite are preferably tetravalent or pentavalent rare earths, and more preferably highly dispersible rare earths (hereinafter also referred to as "dispersed rare earths"). Examples of dispersed rare earths include at least one of rare earth ions and rare earth oxide clusters, and rare earth ions are preferred.

[0038] The rare earth contained in the zeolite contained in the hydrocarbon adsorbent of this embodiment refers to scandium, yttrium, lanthanum, cerium, neodymium, samarium, gadolinium, terbium, thulium, ytterbium, and lutetium, and preferably contains at least one selected from this group, more preferably at least one of cerium and thulium. In terms of improving the hydrocarbon adsorption rate, it is increasingly preferable that the molar ratio of the rare earth contained relative to X in the zeolite contained in the hydrocarbon adsorbent be 0.005 to 0.1, 0.01 to 0.09, 0.02 to 0.08, or 0.03 to 0.06, in that order.

[0039] The zeolite contained in the hydrocarbon adsorbent of this embodiment may contain an alkali metal. The alkali metal is not particularly limited, and examples thereof include at least one selected from the group consisting of sodium, potassium, rubidium, and cesium. As an example, the zeolite contained in the hydrocarbon adsorbent may contain an alkali metal that is derived from the raw material composition and contained in the zeolite during hydrothermal synthesis.

[0040] The hydrocarbon adsorbent of this embodiment may contain components other than those described above. The components other than those described above are not particularly limited, but examples thereof include a binder.

[0041] (Method of manufacturing hydrocarbon adsorbent) Next, a method for producing the hydrocarbon adsorbent of this embodiment will be described.

[0042] The hydrocarbon adsorbent of this embodiment can be obtained by a production method including a copper-incorporating step of incorporating copper into zeolite, and a rare earth-incorporating step of incorporating rare earth into the zeolite after the copper-incorporating step.

[0043] (Zeolite manufacturing method) The method for producing the zeolite used in this embodiment is not particularly limited. For example, the zeolite may be obtained by a production method including a crystallization step of hydrothermally treating a composition containing a silica source, an alumina source, an alkali source, and water (hereinafter also referred to as a "raw material composition") to obtain a crystallized product.

[0044] The silica source may be at least one of a silicon-containing salt and compound, for example, at least one selected from the group consisting of colloidal silica, amorphous silica, sodium silicate, tetraethyl orthosilicate, and aluminosilicate gel, and among these, at least one of colloidal silica and amorphous silica is preferred.

[0045] The alumina source may be at least one of an aluminum-containing salt and compound, and examples thereof include at least one selected from the group consisting of aluminum nitrate, aluminum sulfate, sodium aluminate, aluminum hydroxide, aluminum chloride, aluminosilicate gel, and metallic aluminum. Of these, at least one of aluminum hydroxide and aluminum sulfate is preferred.

[0046] The alkali source may be, for example, one or more selected from the group consisting of various salts such as hydroxides, halides and carbonates of sodium, potassium and ammonium.

[0047] The raw material composition may contain a structure directing agent (hereinafter also referred to as "SDA") as needed. Examples of the structure directing agent include N,N,N-trimethyl-(+)-cis-myrtanylammonium cation, hexamethonium cation, 1,1-dialkyl-4-alkylcyclohexylpiperazin-1-ium cation, 1,1-dialkyl-4-cyclohexylpiperazin-1-ium cation, 1,1'-((3as,6as)-octahydropentalen-2,5-diyl)bis(1-methylpiperidin-1-ium) cation, 1,1'-(buthyl)- ... 1,1'-(pentane-1,4-diyl)bis(1-methylpiperidin-1-ium) cation, 1,1'-(pentane-1,5-diyl)bis(1-methylpiperidin-1-ium), 1,1'-(hexane-1,6-diyl)bis(1-methylpiperidin-1-ium) cation, 3-hydroxy-1-(4-(1-methylpiperidin-1-ium-1-yl)butyl)quinukikudzin-1-ium cation, 3-hydroxy-1-(5-(1-methylpiperidin-1- (Ium-1-yl)pentyl)quinucuzin-1-ium cation, N,N,N,N-tetraethylbicyclo[2.2.2]-oct-7-ene-dipyrrolidinium, N,N-dimethyl-N'-cyclohexylpiperazinium cation, dimethyldipropylammonium cation, tetraethylammonium cation, 1,6-bis(N-cyclohexylpyrrolidinium)hexane dication, 1,4-bis(N-cyclohexylpiperidinium)butane Examples of the SDA include one or more selected from the group consisting of dication, 1,4-bis(N-cyclohexylpyrrolidinium)butane dication, 1,4-bis(N-cyclopentylpiperidinium)butane dication, 1,5-bis(N,N-dimethylcyclohexylammonium)pentane dication, N,N,N-trimethyltricyclo[5.2.1.0]-decaneammonium, and (6R,10S)-6,10-dimethyl-5-azoniaspiro[4.5]decane cation. SDA may be contained in the raw material composition as a salt paired with one or more anions selected from the group consisting of fluoride, chloride, bromide, iodide, and hydroxide (hereinafter, the salt of SDA may be referred to as "SDAX"). Preferably, the raw material composition has the following molar composition:In the following compositions, SDAX is a salt of SDA, and X is an anion other than fluorine.

[0048] SiO2 / Al2O3 ratio =2 or more and 500 or less SDAX / SiO2 ratio = 0.00 or more and 0.80 or less Na / SiO2 ratio = 0.00 or more and 0.80 or less K / SiO2 ratio = 0.00 or more and 0.80 or less X / SiO2 ratio = 0.00 or more and 2.0 or less HF / SiO2 ratio = 0.00 or more and 1.0 or less H2O / SiO2 ratio = 2 or more and 100 or less In the method for producing a zeolite according to the present embodiment, the raw material composition preferably contains seed crystals. By including the seed crystals, the crystallization rate of the zeolite increases, the time required for producing the zeolite can be shortened, and the yield can be improved.

[0049] The zeolite seed crystals are preferably zeolite having at least one structure selected from the group consisting of an LTL structure, an LTA structure, an MOR structure, an MFI structure, an *BEA structure, an FAU structure, a CHA structure, and a YFI structure.

[0050] The SiO2 / Al2O3 molar ratio of the seed crystals is preferably 2 or more and 100 or less, and more preferably 3 or more and 60 or less.

[0051] The content of the seed crystals is preferably small, but in consideration of the reaction rate and the effect of suppressing impurities, it is preferably 0.1 to 60 mass %, more preferably 0.5 to 40 mass %.

[0052] The content of the seed crystals in the raw material composition (hereinafter also referred to as "seed crystal content") can be calculated from the mass of silicon (Si) contained in the raw material composition converted into SiO by the formula: Seed crystal content (mass%) = (SiO mass of zeolite) / (SiO mass in the entire raw material composition) × 100.

[0053] (crystallization process) In the crystallization step, the raw material composition is crystallized by hydrothermal treatment. The conditions for the hydrothermal treatment are not particularly limited, but the following conditions can be mentioned, for example.

[0054] Temperature: 80℃ or higher and 200℃ or lower Time: 1 hour to 10 days Pressure: Autogenous pressure The hydrothermal treatment crystallizes the raw material composition to obtain zeolite. The obtained zeolite may be subjected to any of the steps of recovery, washing, drying, and calcination, and may further be subjected to dealumination treatment to adjust the SiO / AlO ratio to any value.

[0055] When the zeolite contains SDA, the hydrocarbon desorption starting temperature tends to be high, so it is preferable to calcinate the zeolite after crystallization to remove the SDA from the zeolite. The calcination conditions are arbitrary, but examples of the calcination conditions include an oxidizing atmosphere, a calcination temperature of 400°C to 800°C, and a calcination time of 0.5 hours to 12 hours.

[0056] (Copper addition process) The copper addition step includes a copper source contacting step of contacting the zeolite with a copper source, and a calcining step of calcining the zeolite after the copper source contacting step.

[0057] In the copper source contacting step, the copper source is a compound containing copper (Cu), preferably a copper salt, more preferably at least one selected from the group consisting of copper-containing nitrates, sulfates, acetates, chlorides, complex salts, oxides, and composite oxides, and even more preferably at least one selected from the group consisting of copper nitrate, copper sulfate, and copper acetate.

[0058] The lower limit of the copper content of the zeolite is preferably 0.5 mass %, 1.0 mass %, or 1.5 mass %, and the upper limit is preferably 4.0 mass %, 3.0 mass %, or 2.8 mass %, in that order.

[0059] The method for contacting the zeolite with the copper source can be a known method, and examples thereof include at least one method selected from the group consisting of an ion exchange method, an impregnation method, an evaporation-to-dryness method, a precipitation method, and a physical mixing method. At least one method of the ion exchange method and the impregnation method is preferred, and the impregnation method is more preferred.

[0060] After contacting the zeolite with the copper source, the zeolite may be washed and dried by any method. An example of a washing method is washing with a sufficient amount of water, and an example of a drying method is treatment in air at 100°C to 150°C or lower for 5 to 30 hours.

[0061] The firing conditions in the firing step are arbitrary, but the following conditions can be mentioned.

[0062] Firing atmosphere: Oxidizing atmosphere, preferably air Firing temperature: 400℃ to 600℃ Baking time: 30 minutes to 5 hours The firing step is preferably carried out under air flow, and the air flowing preferably has a low moisture content. Firing in air with a low moisture content tends to strengthen the interaction between copper and the aluminum that constitutes the framework of the crystal structure, making it easier to improve heat resistance. The moisture content of the air flowing is preferably 0.7% by volume or less, more preferably 0.5% by volume or less, and even more preferably 0.3% by volume or less.

[0063] (Rare earth addition process) The rare earth adding step includes a rare earth source contacting step of contacting the zeolite after the copper adding step with a rare earth source, and a calcining step of calcining the zeolite after the rare earth source contacting step.

[0064] In the rare earth source contacting step, the rare earth source is a compound containing a rare earth, preferably a rare earth salt, more preferably at least one selected from the group consisting of nitrates, sulfates, acetates, chlorides, complex salts, oxides, and composite oxides containing a rare earth, and even more preferably at least one selected from the group consisting of nitrates, sulfates, and acetates.

[0065] In terms of improving the hydrocarbon adsorption rate, it is increasingly preferable that the molar ratio of the rare earth element to X in the zeolite contained in the hydrocarbon adsorbent be 0.005 or more and 0.1 or less, 0.01 or more and 0.09 or less, 0.02 or more and 0.08 or less, or 0.03 or more and 0.06 or less.

[0066] The method for contacting the zeolite with the rare earth source can be a known method, and examples thereof include at least one method selected from the group consisting of ion exchange, impregnation, evaporation to dryness, precipitation, and physical mixing. At least one method of the ion exchange and impregnation is preferred, and the impregnation is more preferred.

[0067] After contacting the zeolite with the rare earth source, the zeolite may be washed and dried by any method. An example of a washing method is washing with a sufficient amount of water, and an example of a drying method is treating the zeolite in air at 100°C to 150°C or lower for 5 to 30 hours.

[0068] The firing conditions in the firing step are arbitrary, but the following conditions can be mentioned.

[0069] Firing atmosphere: Oxidizing atmosphere, preferably air Firing temperature: 400℃ to 600℃ Baking time: 30 minutes to 5 hours The firing step is preferably carried out under air flow, and the air flowing preferably has a low moisture content. Firing in air with a low moisture content tends to strengthen the interaction between copper and the aluminum that constitutes the framework of the crystal structure, making it easier to improve heat resistance. The moisture content of the air flowing is preferably 0.7% by volume or less, more preferably 0.5% by volume or less, and even more preferably 0.3% by volume or less.

[0070] (hydrocarbon adsorbent) The hydrocarbon adsorbent of this embodiment may have any shape depending on the application, and may be at least one of a powder and a molded body. Specific molded body shapes include at least one selected from the group consisting of spherical, approximately spherical, ellipsoidal, disk-like, cylindrical, polyhedral, irregular, and petal-like shapes.

[0071] When the hydrocarbon adsorbent is used as a powder, the hydrocarbon adsorbent can be mixed with a solvent such as water or alcohol to form a slurry, and the slurry can be coated on a substrate to form an adsorption member.

[0072] When the hydrocarbon adsorbent of this embodiment is formed into a molded body, the hydrocarbon adsorbent may be mixed with a binder as needed and molded by any method. The binder may preferably be at least one selected from the group consisting of silica, alumina, kaolin, attapulgite, montmorillonite, bentonite, aloene, and sepiolite. The molding method may preferably be at least one selected from the group consisting of rolling granulation molding, press molding, extrusion molding, injection molding, slip casting, and sheet molding.

[0073] The hydrocarbon adsorbent of the present embodiment can be used in a method for adsorbing hydrocarbons, preferably in a method for adsorbing hydrocarbons in an environment in which the hydrocarbon adsorbent is exposed to high temperatures, more preferably in a method for adsorbing hydrocarbons from the exhaust gas of an internal combustion engine, and even more preferably in a method for adsorbing hydrocarbons from the exhaust gas of an internal combustion engine of a mobile body.

[0074] The hydrocarbon adsorbent of this embodiment can adsorb hydrocarbons by a method including a step of contacting a hydrocarbon-containing fluid with the hydrocarbon adsorbent of this embodiment (hereinafter also referred to as a "contact step"). Examples of the hydrocarbon-containing fluid include a hydrocarbon-containing gas and a hydrocarbon-containing liquid.

[0075] The hydrocarbon-containing gas that comes into contact with the hydrocarbon adsorbent of this embodiment is a gas containing at least one type of hydrocarbon. The hydrocarbon-containing gas is not particularly limited, but is preferably a combustion gas such as exhaust gas from a general internal combustion engine such as an automobile engine.

[0076] The hydrocarbons to be adsorbed contained in the hydrocarbon-containing gas are not particularly limited, but examples of those contained in the combustion gas include at least one selected from the group consisting of paraffins, olefins, and aromatic hydrocarbons. The number of carbon atoms in the hydrocarbons may be 1 or more, and is preferably 1 to 15. The hydrocarbon adsorbent of this embodiment has a high adsorption capacity for aromatic hydrocarbons, olefins, and paraffins, in that order, due to the strength of the interaction between the hydrocarbons and the zeolite.

[0077] Specific examples of hydrocarbons to be adsorbed include at least one selected from the group consisting of methane, ethane, ethylene, propylene, butane, linear paraffins having 5 or more carbon atoms, linear olefins having 5 or more carbon atoms, benzene, toluene, and xylene. In particular, since toluene is a hydrocarbon contained in large amounts in combustion gases and has a strong electrical interaction with zeolite, it is preferable to apply the hydrocarbon adsorbent of this embodiment to a hydrocarbon-containing gas containing at least toluene as the hydrocarbon to be adsorbed.

[0078] The hydrocarbon-containing gas may further comprise at least one member of the group consisting of carbon monoxide, carbon dioxide, hydrogen, oxygen, nitrogen, nitrogen oxides, sulfur oxides, and water. [Example]

[0079] The hydrocarbon adsorbent of this embodiment will be described in more detail below with reference to examples, but this embodiment is not limited to these examples.

[0080] (Identification of crystal structure) Using a general X-ray diffractometer (device name: Ultima IV Protectus, manufactured by Rigaku Corporation), XRD measurements of the samples were carried out under the following conditions.

[0081] Acceleration current / voltage: 40mA / 40kV Radiation source: CuKα radiation (λ=1.5405Å) Measurement mode: Continuous scan Scan condition: 40° / min Measurement range: 2θ=3° to 43° Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Receiving solar slit: 5° Detector: D / teX Ultra Ni filter used The zeolite structure was identified by comparing the obtained XRD pattern with a reference pattern.

[0082] (composition analysis) A sample solution was prepared by dissolving the sample in a mixed aqueous solution of hydrofluoric acid and nitric acid. The sample solution was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using a general ICP device (device name: OPTIMA5300DV, manufactured by PerkinElmer). From the measured values ​​of Si, Al, Cu, and Ce, the SiO2 / Al2O3 molar ratio, Ce / Al molar ratio, and copper mass% of the sample were calculated.

[0083] Example 1 (copper addition) To a mass ratio of 1 part FAU zeolite (product name: HSZ-341NHA, manufactured by Tosoh Corporation), 0.097 parts copper nitrate trihydrate and 0.38 parts pure water were added and mixed, and then dried overnight in air at 110°C. The dried FAU zeolite was calcined for 2 hours at 550°C in a stream of air with a water content of 0.1% by volume, yielding a copper-containing FAU zeolite. The obtained copper-containing FAU zeolite had a SiO2 / Al2O3 molar ratio of 7.2 and a copper content of 2.42% by mass.

[0084] (Addition of rare earth (Ce)) To the obtained copper-containing FAU zeolite (mass ratio: 1), cerium acetate (mass ratio: 0.0079) and pure water (mass ratio: 0.38) were added and mixed, and then dried overnight in air at 110°C. The dried FAU zeolite contained the entire amount of cerium acetate added. The dried FAU zeolite was further calcined at 550°C for 2 hours in a stream of air with a water content of 0.1% by volume, thereby desorbing acetate ions from the cerium acetate, thereby obtaining copper- and cerium-containing FAU zeolite, which was used as the hydrocarbon adsorbent of Example 1. Calculated from the amount of cerium acetate added, the molar ratio of cerium to aluminum (Ce / Al molar ratio) in the obtained hydrocarbon adsorbent was 0.011.

[0085] Example 2 An adsorbent for hydrocarbons of Example 2 was obtained in the same manner as in Example 1, except that the mass ratio of the cerium acetate added in Example 1 was set to 0.022.

[0086] Example 3 An adsorbent for hydrocarbons of Example 3 was obtained in the same manner as in Example 1, except that the mass ratio of the cerium acetate added in Example 1 was set to 0.034.

[0087] Example 4 An adsorbent for hydrocarbons of Example 4 was obtained in the same manner as in Example 1, except that the mass ratio of the cerium acetate added in Example 1 was set to 0.045.

[0088] Example 5 An adsorbent for hydrocarbons of Example 5 was obtained in the same manner as in Example 1, except that the mass ratio of the cerium acetate added in Example 1 was set to 0.067.

[0089] Comparative Example 1 An adsorbent for hydrocarbons of Comparative Example 1 was obtained in the same manner as in Example 1, except that cerium acetate was not added.

[0090] Comparative Example 2 An adsorbent for hydrocarbons of Comparative Example 2 was obtained in the same manner as in Example 1, except that the mass ratio of the cerium acetate added in Example 1 was set to 0.089.

[0091] The Ce / Al molar ratios in Examples 1 to 5 and Comparative Examples 1 and 2 are shown in Table 1.

[0092] Example 6 An adsorbent for hydrocarbons of Example 6 was obtained in the same manner as in Example 1, except that thulium acetate n-hydrate was added in a mass ratio of 0.046 to 1 mass of zeolite instead of cerium acetate.

[0093] Example 7 An adsorbent for hydrocarbons of Example 7 was obtained in the same manner as in Example 1, except that yttrium acetate tetrahydrate was added in a mass ratio of 0.042 to 1 mass of zeolite instead of cerium acetate.

[0094] The rare earth / Al molar ratios in Examples 6 and 7 are shown in Table 2.

[0095] (Preparation and pretreatment of measurement samples) The hydrocarbon adsorption rates of the hydrocarbon adsorbents obtained in Examples 1 to 7 and Comparative Examples 1 and 2 were measured as follows.

[0096] The hydrocarbon adsorbents according to Examples 1 to 7 and Comparative Examples 1 and 2 were each pressure-molded and pulverized to form irregularly shaped bodies with an aggregate size of 20 to 30 mesh, and the resulting molded bodies were each used as measurement samples.

[0097] 1 g of each measurement sample was packed into an atmospheric pressure fixed-bed flow-type reactor tube, treated at 500°C for 1 hour under nitrogen flow, and then cooled to 50°C as a pretreatment.

[0098] (Measurement of hydrocarbon adsorption rate) A hydrocarbon-containing gas was passed through each of the hydrocarbon adsorbents that had been pretreated as described above, and the amount of hydrocarbon adsorbed was measured between 50°C and 200°C, and this was taken as the amount of hydrocarbon adsorption. The composition of the hydrocarbon-containing gas and the measurement conditions are shown below.

[0099] Hydrocarbon-containing gas: Toluene 3000 ppmC by volume (methane equivalent concentration) Water 3% by volume Nitrogen Remainder Gas flow rate: 200 mL / min Measurement temperature: 50~600℃ Heating rate: 10°C / min Using a hydrogen ionization detector (FID), the hydrocarbons in the gas after passing through the hydrocarbon adsorbent were continuously quantitatively analyzed. The hydrocarbon concentration of the hydrocarbon-containing gas at the inlet side of the atmospheric pressure fixed-bed flow reactor (methane equivalent concentration; hereinafter referred to as "inlet concentration") and the hydrocarbon concentration of the hydrocarbon-containing gas at the outlet side of the atmospheric pressure fixed-bed flow reactor (methane equivalent concentration; hereinafter referred to as "outlet concentration") were measured. The ratio of the integral of the outlet concentration (methane equivalent concentration) to the integral of the inlet concentration was calculated as the hydrocarbon adsorption efficiency (also referred to as the "hydrocarbon purification efficiency").

[0100] (Hydrothermal durability test) The hydrocarbon adsorbent was treated hydrothermally in the same manner as in (Measurement of hydrocarbon adsorption rate), except that the treatment gas was passed through the pretreated hydrocarbon adsorbent under the following conditions.

[0101] Treated gas: 10% water by volume Nitrogen Remainder Gas flow rate: 300mL / min Space velocity: 6000hr -1 Processing temperature: 900℃ Processing time: 1 hour The hydrocarbon adsorption rate of each measurement sample after the hydrothermal treatment is shown in Table 1. The difference between the hydrocarbon adsorption rate of each example and the hydrocarbon adsorption rate of Comparative Example 1 (hydrocarbon adsorption rate of each example - hydrocarbon adsorption rate of Comparative Example 1) is shown in the graph of Figure 1.

[0102] [Table 1]

[0103] As shown in Table 1, the hydrocarbon adsorbents of Examples 1 to 5 exhibit hydrocarbon adsorption rates up to higher temperatures than the hydrocarbon adsorbents of Comparative Examples 1 and 2.

[0104] 1, the hydrocarbon adsorption rate reached a maximum when the Ce / Al molar ratio was around 0.04, suggesting the existence of a preferable range of the Ce / Al molar ratio. Furthermore, Examples 1 to 5, in which the Ce / Al molar ratio was 0.005 or more and 0.08 or less, exhibited higher hydrocarbon adsorption rates than Comparative Example 1, which contained only Cu without Ce, and Comparative Example 2, in which the Ce / Al molar ratio was 0.106.

[0105] Table 2 shows the hydrocarbon adsorption rates after hydrothermal treatment for Example 6, which contains thulium, and Example 7, which contains yttrium, both of which have the same rare earth / Al molar ratio as Example 3.

[0106] [Table 2]

[0107] As shown in Table 2, the hydrocarbon adsorbents of Examples 6 and 7, like those of Examples 1 to 5, maintain their hydrocarbon adsorption rates up to higher temperatures than the hydrocarbon adsorbent of Comparative Example 1. Since Ce, Tm, and Y are rare earth elements with similar chemical properties, it is believed that similar effects can be obtained by adding a rare earth element.

Claims

1. YO ２ -X ２ O ３ A hydrocarbon adsorbent comprising a zeolite containing copper and a rare earth element, Y is Si and X is Al; The zeolite has an FAU structure, The copper content is 0.5% by mass or more and 4% by mass or less relative to 100% by mass of the zeolite, a molar ratio of the rare earth to X is 0.005 or more and 0.1 or less, A hydrocarbon adsorbent that adsorbs at least one of the group consisting of paraffins, olefins, and aromatic hydrocarbons.

2. X of the zeolite ２ O ３ YO ２ The molar ratio (YO ２ / X ２ O ３ 2. The hydrocarbon adsorbent according to claim 1, wherein the ratio (R) is 2 or more and 100 or less.

3. 3. The hydrocarbon adsorbent according to claim 1, wherein the rare earth element is at least one element selected from the group consisting of scandium, yttrium, lanthanum, cerium, neodymium, samarium, gadolinium, terbium, thulium, ytterbium, and lutetium.

4. A hydrocarbon adsorbent described in any one of claims 1 to 3, wherein the rare earth is at least one of cerium and thulium.

5. The hydrocarbon adsorbent according to claim 1, wherein the molar ratio of the rare earth to X is 0.03 or more and 0.06 or less.

6. A method for adsorbing at least one of the group consisting of paraffins, olefins, and aromatic hydrocarbons, using the hydrocarbon adsorbent according to any one of claims 1 to 5.

Images