JP7540167B2 - Hydrophobic MFI zeolite, its production method, and its uses - Google Patents

Description

The present invention relates to a hydrophobic MFI zeolite, its manufacturing method, and its applications. The hydrophobic MFI zeolite of the present invention is useful, for example, for selectively adsorbing and removing organic compounds from mixed gases containing water vapor, or for adsorbing and recovering them, and as a catalyst for use in competitive reaction processes with water.

Organic compounds emitted from painting equipment, printing equipment, industrial product cleaning equipment, etc. are considered to be a cause of air pollution such as suspended particulate matter and photochemical oxidants, and there is a demand to reduce emissions. In order to reduce these organic compounds, various organic compound adsorbents have been developed.

In recent years, organic compound adsorbents using zeolite have been proposed. Generally, zeolites with low _SiO2 / _{Al2O3 molar} ratios have a high water adsorption capacity, so that the adsorption capacity of organic compounds is relatively low, and a lot of energy is required to heat and remove the adsorbed organic compounds and water to regenerate the adsorbent. For this reason, zeolites with low water adsorption capacity, i.e., high _SiO2 / _{Al2O3 molar} ratios, which are generally considered to be highly hydrophobic, are used.

As a highly hydrophobic MFI zeolite, Patent Document 1 proposes a method for hydrophobizing an MFI zeolite having a SiO ₂ /Al ₂ O ₃ molar ratio of 100 to 1500. However, in order to obtain an MFI zeolite having a SiO ₂ /Al ₂ O ₃ molar ratio of 100 to 1500, it has been necessary to synthesize the zeolite using an expensive organic structure-directing agent, or to increase the SiO ₂ /Al ₂ O ₃ molar ratio of an MFI zeolite having a low SiO ₂ /Al ₂ O ₃ molar ratio by treating it with an acid.

JP 2017-114755 A

An object of the present invention is to provide a hydrophobic MFI zeolite that combines high hydrophobicity and high organic compound adsorption capacity, which could not be obtained with conventional zeolites having a low SiO ₂ /Al ₂ O ₃ molar ratio.

As a result of intensive research into solving the above problems, the inventors discovered that a specific hydrophobic MFI zeolite can solve the above problems, and thus completed the present invention.

That is, the present invention provides
The present invention relates to a hydrophobic MFI zeolite having a water adsorption amount of not more than 8 g/100 g of zeolite at 25°C and a relative humidity (hereinafter also referred to as "RH") of 60%, a toluene adsorption amount of not less than 5 g/100 g of zeolite at 25°C and 0.01 kPa, and a _SiO2 / _{Al2O3 molar} ratio in the range of 20 to 100, a method for producing the same, and uses thereof.

The present invention will be described in detail below.

One embodiment of the present invention is a hydrophobic MFI zeolite having a water adsorption amount of not more than 8 g/100 g of zeolite at 25°C and RH 60%, a toluene adsorption amount of not less than 5 g/100 g of zeolite at 25°C and 0.01 kPa, and a SiO ₂ /Al ₂ O ₃ molar ratio in the range of 20 to 100.

In the present invention, the water adsorption amount is the equilibrium water adsorption amount at a temperature of 25° C., equilibrium pressure P/P ₀ =0.6, and P=1.90 kPa (RH 60%), converted into a mass per 100 g of zeolite, and the toluene adsorption amount is the equilibrium adsorption amount at a temperature of 25° C., equilibrium pressure P=0.01 kPa, converted into a mass per 100 g of zeolite. The lower the water adsorption amount, the higher the "hydrophobicity" can be evaluated, and the higher the toluene adsorption amount, the higher the "organic compound adsorption ability". The present invention is characterized by having both high hydrophobicity and high organic compound adsorption ability, with the water adsorption amount at 25° C., RH 60% being (8 g/100 g of zeolite) or less and the toluene adsorption amount at 25° C., 0.01 kPa being (5 g/100 g of zeolite) or more. Furthermore, the water adsorption amount at 25°C and RH 60% is preferably 6g/100g zeolite or less, more preferably 5g/100g zeolite or less. There is no lower limit to the water adsorption amount, but the lower the limit, the better. The toluene adsorption amount at 25°C and 0.01 kPa is preferably 6g/100g zeolite or more, more preferably 7g/100g zeolite or more. There is no upper limit to the toluene adsorption amount, but the higher the limit, the better.

The hydrophobic zeolite of the present invention is a zeolite having a structure classified as an MFI structure by the International Zeolite Association.

The hydrophobic MFI zeolite of the present invention has a SiO ₂ /Al ₂ O ₃ molar ratio in the range of 20-100, preferably 20-80, from the viewpoints of improving productivity and reducing waste acid.

The hydrophobic MFI zeolite of the present invention may contain one or more metals selected from the group consisting of sodium, potassium, cesium, iron, copper, silver, platinum, ruthenium, rhodium, palladium, and iridium, from the viewpoints of higher adsorption selectivity and heat resistance when used as an organic compound adsorbent, and from the viewpoint of imparting functions such as oxidative decomposition of adsorbed organic compounds.

The method for incorporating the metal component is not particularly limited, and ion exchange, impregnation, evaporation to dryness, etc. can be used. Ion exchange methods include contacting zeolite with a solution containing the desired ions until the amount of ions in the zeolite reaches the desired concentration. Common ion exchange methods such as the batch method and flow method can be used.

In the present invention, when manufacturing an organic compound adsorbent in the form of a molded body or honeycomb structure, it is possible to either incorporate metal into zeolite powder and then mold it into a molded body or honeycomb structure, or to incorporate metal into zeolite powder and then mold it into a molded body or honeycomb structure.

Next, we will explain the method for producing the hydrophobic MFI zeolite of the present invention.

The manufacturing method is not particularly limited as long as it can produce the hydrophobic MFI zeolite of the present invention, but examples include a manufacturing method in which the base zeolite is brought into contact with steam at a temperature of 500°C to 900°C. The manufacturing method aims to increase the hydrophobicity of the base zeolite by treating it with steam. The hydrophobic MFI zeolite obtained by this manufacturing method is characterized in that its water adsorption amount at 25°C and RH 60% is less than the water adsorption amount of the base zeolite.

As the zeolite base material, a synthetic zeolite having a SiO ₂ /Al ₂ O ₃ molar ratio of 20 to 100 can be suitably used.

One method for producing zeolite as the base material is, for example, to add an organic structure directing agent to a mixture of a silica source, an alumina source, and an alkali source (hereinafter also referred to as the "raw material mixture") as necessary, and then to crystallize the raw material mixture under hydrothermal conditions.

Examples of silica sources include colloidal silica, amorphous silica, sodium silicate, tetraethyl orthosilicate, and aluminosilicate gel.

Examples of alumina sources include aluminum sulfate, sodium aluminate, aluminum hydroxide, aluminum chloride, aluminosilicate gel, metallic aluminum, etc. The silica source and alumina source are preferably in a form that can be mixed sufficiently uniformly with other raw materials.

Examples of alkali sources include various salts such as hydroxides, halides, sulfates, nitrates, and carbonates of sodium, potassium, and ammonium, as well as alkali components in aluminates, silicates, and aluminosilicate gels.

Examples of organic structure directing agents include tetrapropylammonium hydroxide and tetrapropylammonium bromide.

Zeolite can be crystallized using an autoclave, and the crystallization temperature (temperature under hydrothermal treatment) can be 100°C to 250°C, preferably 110°C to 200°C, and more preferably 120°C to 190°C. The crystallization time can be 12 hours to 84 hours, preferably 14 hours to 72 hours, and more preferably 16 hours to 48 hours. Crystallization can be performed either by leaving it to stand or by stirring.

After crystallization is complete, solid-liquid separation is performed, and the excess alkaline solution can be washed off with pure water, warm water, or the like. After washing, the product can be dried. The drying temperature can be, for example, 80°C or higher and 200°C or lower, and preferably 90°C or higher and 190°C or lower. If an organic structure-directing agent is included, it can be removed by a thermal decomposition treatment after drying.

As the base material, zeolites synthesized without adding organic structure-directing agents (OSDA-free synthesis), zeolites synthesized by structural transformation of zeolites with other structures, and zeolites synthesized by dry gel conversion, etc. can be suitably used. It is economically preferable to use MFI-type zeolites synthesized without adding expensive organic structure-directing agents.

In the present invention, as the zeolite base material, a zeolite containing the structure-directing agent obtained after the crystallization can be used, or a zeolite from which the structure-directing agent used during the production has been removed can be used. Alternatively, a zeolite from which the structure-directing agent has been removed and which has been dealuminated to have a SiO ₂ /Al ₂ O ₃ molar ratio of 20 to 100 by contacting with an acidic solution can be used.

The hydrophobic MFI zeolite of the present invention can be suitably produced by contacting the base zeolite with steam of preferably 10 to 100% by volume, more preferably 10 to 80% by volume, at a temperature of 500°C to 900°C, more preferably 600 to 850°C, for a period of 30 minutes to 5 hours. When the steam concentration is 10% by volume to 80% by volume, better hydrophobicity can be exhibited. Also, when the contact temperature is 600°C to 850°C, better hydrophobicity and higher crystallinity can be exhibited.

When the base zeolite is a zeolite crystallized using an organic structure-directing agent, the hydrophobic MFI zeolite of the present invention can be produced by contacting the zeolite with water vapor under the above-mentioned conditions after the organic structure-directing agent is thermally decomposed or during the process of thermally decomposing the organic structure-directing agent.

The zeolite used as the base material is preferably a proton-type or ammonia-type zeolite from which the alkali metals present during synthesis have been removed in order to maintain the pore structure. When using a zeolite containing an alkali metal, it is preferable to contact the zeolite with steam at a lower temperature, with a lower steam concentration, or for a shorter time among the steam contact conditions described above.

The organic compound adsorbent containing the hydrophobic MFI zeolite of the present invention has excellent effects, particularly as an adsorbent for volatile organic compounds. The organic compound adsorbent makes it possible to adsorb and remove or adsorb and recover organic compounds in a humid atmosphere or in water while reducing the influence of moisture. Therefore, the organic compound adsorbent is useful as a method for removing organic compounds by contacting with a fluid containing at least one organic compound and removing the organic compound from the fluid. For example, it can be useful as an adsorbent used for adsorbing and removing/recovering exhaust gases or organic compounds in wastewater discharged from painting equipment, printing equipment, industrial product cleaning equipment, etc., or as an adsorbent for adsorbing and removing organic hydrocarbon components in automobile exhaust gases.

The catalyst containing the hydrophobic MFI zeolite of the present invention can be useful as a catalyst that reduces reaction inhibition caused by water in a reaction in which the adsorption process of the reactants on the zeolite catalyst is competitive with water when reacting hydrocarbons in a reaction system in which water coexists or is produced as a by-product.

The hydrophobic MFI zeolite of the present invention can be used as an organic compound adsorbent or catalyst in the powder state as produced, but it can also be used as a molded body formed into a desired shape such as beads, pellets, or a trefoil shape, or it can be used as a honeycomb structure in which the hydrophobic MFI zeolite powder of the present invention is made into a slurry and applied to a honeycomb-shaped substrate.

The hydrophobic MFI zeolite of the present invention can be mixed with other zeolites when used as an organic compound adsorbent or catalyst.

It is possible to provide a hydrophobic MFI zeolite that has both high hydrophobicity and high organic compound adsorption capacity, which could not be obtained with conventional zeolites, and also has a low SiO ₂ /Al ₂ O ₃ molar ratio.

Water adsorption isotherms at 25°C for the Examples and Comparative Examples Adsorption isotherm of toluene at 25°C in the examples

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these.

<Measurement of water adsorption amount and toluene adsorption amount>
The amount of adsorption was measured using a constant volume adsorption measuring device (BELSORP MAXII, manufactured by Microtrackbel Co., Ltd.). The samples used in each of the examples and comparative examples were pretreated at 350°C for 2 hours under a vacuum of 10 Pa or less. The adsorption temperature was 25°C.

Example 1
The hydrophobic MFI zeolite of the present invention was obtained by heat treating (contacting with water vapor) 10 g of a commercially available ammonia-type MFI zeolite (HSZ-820NHA: manufactured by Tosoh Corporation, SiO ₂ /Al ₂ O ₃ molar ratio 23) for 2 hours in a 20% by volume water vapor atmosphere at 700°C. The SiO ₂ /Al ₂ O ₃ molar ratio was 23. The water adsorption amount and toluene adsorption amount at 25°C are shown in Figures 1 and 2, and Table 1, respectively.

Example 2
The hydrophobic MFI zeolite of the present invention was obtained by heat treating (contacting with water vapor) 10 g of a commercially available ammonia-type MFI zeolite (HSZ-840NHA: manufactured by Tosoh Corporation, SiO ₂ /Al ₂ O ₃ molar ratio 39) for 2 hours in a 20% by volume water vapor atmosphere at 650°C. The SiO ₂ /Al ₂ O ₃ molar ratio was 39. The water adsorption amount and toluene adsorption amount at 25°C are shown in Figures 1 and 2, and Table 1, respectively.

Comparative Example 1
The amount of water adsorption at 25° C. of the commercially available ammonia-type MFI zeolite (HSZ-820NHA: manufactured by Tosoh Corporation, SiO ₂ /Al ₂ O ₃ molar ratio 23) used as the raw material in Example 1 is shown in FIG.

Comparative Example 2
The amount of water adsorption at 25° C. of the commercially available ammonia-type MFI zeolite (HSZ-840NHA: manufactured by Tosoh Corporation, SiO ₂ /Al ₂ O ₃ molar ratio 39) used as the raw material in Example 2 is shown in FIG.

As is clear from Figures 1, 2 and Table 1, the hydrophobic MFI zeolite of the present invention has both high hydrophobicity and high organic compound adsorption performance.

Claims (8)

A hydrophobic MFI zeolite (excluding ZSM-5 zeolite having a composite _of boron-containing micropores and mesopores in the framework) characterized in that the water adsorption amount at 25°C and a relative humidity of 60% is not more than ( ₈ g/100 g of zeolite), the toluene adsorption amount at 25°C and 0.01 kPa is not less than (5 g/100 g of zeolite), and the SiO 2 /Al 2 O ₃ molar ratio is in the range of 20 to 39. The hydrophobic MFI zeolite according to claim 1, characterized in that it contains one or more metals selected from the group consisting of sodium, potassium, cesium, iron, copper, silver, platinum, ruthenium, rhodium, palladium and iridium. A method for producing a hydrophobic MFI zeolite according to claim 1 or 2, characterized in that the base material zeolite is contacted with steam at a temperature of 500°C to 900°C, and the base material zeolite is an ammonia type. The method for producing hydrophobic MFI zeolite according to claim 3, characterized in that the base zeolite is a zeolite crystallized without using an organic structure-directing agent. The method for producing hydrophobic MFI zeolite according to claim 3, characterized in that the base zeolite is a zeolite crystallized using an organic structure-directing agent, and the method of contacting with steam at a temperature of 500°C to 900°C is a method of contacting with steam during the process of thermally decomposing the organic structure-directing agent. An organic compound adsorbent containing the hydrophobic MFI zeolite according to claim 1 or 2. A method for removing organic compounds, comprising contacting the organic compound adsorbent according to claim 6 with a fluid containing at least one organic compound, and removing the organic compound from the fluid. An organic compound conversion catalyst containing the hydrophobic MFI zeolite according to claim 1 or 2.