JP7725862B2 - Catalyst for converting pyrolysis products of hydrocarbon-based plastics and method for producing lower hydrocarbons using the same - Google Patents

Description

The present invention relates to a catalyst for converting pyrolysis products of hydrocarbon-based plastics into useful products, particularly a catalyst for converting aliphatic hydrocarbons, such as paraffins, olefins, and diolefins with 1 to 30 carbon atoms (hereinafter sometimes referred to as C), which are the main components of the pyrolysis products of hydrocarbon-based plastics, into olefins, paraffins, aromatic hydrocarbons with 2 to 8 carbon atoms, which are useful as petrochemical products, in a highly efficient, well-balanced and stable manner, and to a method for producing lower hydrocarbons using the catalyst.

In recent years, issues such as global warming and marine plastic pollution have come into sharp focus, and chemical recycling, in which waste plastic is chemically broken down and reused as raw materials for petrochemical products, has been attracting attention. Among these, oil-to-plastic technology through thermal decomposition converts thermoplastic polyolefins (polyethylene, polypropylene), which account for half of waste plastic, into hydrocarbon oil. This hydrocarbon oil can then be used as a raw material for naphtha crackers and other processes, making it an important technology that essentially enables the recycling of plastics.

The technology of converting waste plastics into oil through thermal decomposition has been known for a long time, and when thermal decomposition is carried out under oxygen-free and catalyst-free conditions, a wide range of carbon number distributions, from C1 to C30, is obtained, i.e., hydrocarbon oils. Of these, light oils from C5 to C10 can be used as feedstock for naphtha crackers, but kerosene, diesel, heavy oil, and waxes with C11 and above are used as fuel and do not offer high added value to the product.

As a method for increasing the added value of products, a method has been proposed in which polyolefin (waste) plastics are thermally decomposed and the products generated by the thermal decomposition are brought into contact with a catalyst layer such as zeolite to recover hydrocarbon oils (see, for example, Patent Document 1 and Non-Patent Document 1).

In addition, a method for treating waste plastics has been proposed in which waste plastics are vaporized by pyrolysis, and the resulting pyrolysis product is brought into contact with a boron-containing silicate catalyst to recover hydrocarbon oil (see, for example, Patent Document 2). Furthermore, a method for treating waste plastics using a gallium-containing silicate catalyst (see, for example, Patent Document 3) has also been proposed.

Japanese Unexamined Patent Publication No. 178195/1983 Patent No. 4341162 Patent No. 4103198

Polymer, Vol. 45, p. 311 (1996)

However, in the method proposed in Patent Document 1, while the carbon number distribution of hydrocarbon oils is lowered from C5-C38 to C5-C21 by using a ZSM-5 catalyst, there is still an issue of a large proportion of low-value-added kerosene, light oil, and heavy oil fractions of C11 and above. In the method proposed in Non-Patent Document 1, thermal cracking is carried out using HY, REY, and Ni/ReY catalysts in addition to ZSM-5, and selectivity to C5-C11 gasoline fractions is particularly high when a REY catalyst is used, but these Y-type zeolites have poor thermal stability and still produce a large proportion of low-value-added fractions of C9 and above, making them insufficient as industrial catalysts.

In the method proposed in Patent Document 2, the use of a boron-containing silicate catalyst significantly reduced the molecular weight of hydrocarbon oils, particularly increasing the total selectivity for C3 and C4 olefins and paraffins. However, the production of biased components made it difficult to use in conjunction with existing plants. For example, the load on a specific distillation column in an ethylene plant (naphtha cracker) increased, necessitating an excessive reduction in the naphtha cracker's operating rate or the construction of a new specific distillation column, making the method economically unreasonable. Furthermore, the synthesis of boron-containing silicates is difficult, making them difficult to obtain, and their coking resistance is insufficient, leaving no satisfactory investigation into catalyst life. Furthermore, in the method proposed in Patent Document 3, the use of a gallium-containing silicate catalyst increases the selectivity for carbon number distributions of C1 to C13, particularly benzene (C6), toluene (C7), and xylene (C8), and promotes balanced reduction in molecular weight. However, with gallium-containing silicates, particularly gallosilicates, it is difficult to insert Ga metal into the silicate framework, making them difficult to synthesize reproducibly and industrially. In addition, coking resistance is insufficient, leaving room for improvement in terms of catalyst life.

Therefore, there has been a need for a catalyst for converting the pyrolysis products of hydrocarbon plastics that can efficiently convert the pyrolysis products of hydrocarbon plastics into C2 to C8 hydrocarbons, which are useful as petrochemical products, and a method for producing lower hydrocarbons using the same.

As a result of extensive research to solve the above problems, the inventors discovered that a conversion catalyst containing a specific 10-membered ring pore zeolite exhibits excellent coking resistance and catalyst life when using pyrolysis products of hydrocarbon-based plastics as raw materials, and also has improved selectivity for paraffins, olefins, and aromatic hydrocarbons with 2 to 8 carbon atoms, which are useful as petrochemical products, resulting in a catalyst that exhibits excellent performance, leading to the completion of the present invention.

That is, the present invention relates to a catalyst for converting pyrolysis products of hydrocarbon-based plastics, characterized in that the catalyst contains a zeolite that satisfies the following characteristics (i) to (iii), and to a method for producing lower hydrocarbons using the catalyst:
(i) The average particle size is 100 nm or less.
(ii) 10-ring pore zeolites of MFI type or MEL type.
(iii) The Bronsted acid amount of the outer surface is 0.1 to 10.0 μmol/g.

The present invention is described in detail below.

The pyrolysis product conversion catalyst of the present invention is a catalyst that enables highly selective conversion of pyrolysis products of hydrocarbon-based plastics, which have traditionally been difficult to use as raw materials due to the wide variety of components they contain, into lower hydrocarbons useful as petrochemical products, particularly lower hydrocarbons such as olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms. The catalyst contains a zeolite that satisfies all of the following requirements: (i) an average particle diameter (hereinafter sometimes referred to as PD) of 100 nm or less; (ii) a 10-membered ring pore zeolite of the MFI or MEL type; and (iii) Bronsted acid sites on the outer surface of 0.1 to 10.0 μmol/g.

The zeolite that constitutes the pyrolysis product conversion catalyst of the present invention has (i) a PD of ≦100 nm, and since this catalyst has particularly excellent thermal stability, it is desirable for the zeolite to have a PD of 5 nm ≦ PD ≦ 100 nm. However, if the PD exceeds 100 nm, the efficiency of converting the pyrolysis products of hydrocarbon-based plastics into lower hydrocarbons will be poor.

The PD in the present invention may be measured by any method without any limitation, and examples thereof include a method in which 100 or more particles are arbitrarily selected from a photograph taken with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and the average diameter of the particles is determined, and a method in which the PD is calculated from the external surface area of the zeolite using the following formula (1).
PD=6/S×(1/(2.29×10 ⁶ )+0.18×10 ⁻⁶ ) (1)
(Here, S represents the external surface area (m ² /g).)
The external surface area (S (m ² /g)) in formula (1) can be determined by the t-plot method using a general nitrogen adsorption method at liquid nitrogen temperature. For example, when t is the thickness of the adsorption amount, measurement points in the range of 0.6 to 1 nm for t are linearly approximated, and the external surface area of the zeolite is determined from the slope of the resulting regression line.

Among these, SEM or TEM methods are preferred because they allow for simple measurements.

The zeolite constituting the pyrolysis product conversion catalyst of the present invention is (ii) an MFI-type or MEL-type 10-membered ring pore zeolite. Examples of MFI-type zeolites include aluminosilicate compounds that belong to the structure code MFI defined by the International Zeolite Association. Zeolites other than MFI-type or MEL-type 10-membered ring pore zeolites will result in less efficient conversion reactions of pyrolysis products of hydrocarbon plastics.

The zeolite constituting the pyrolysis product conversion catalyst of the present invention (iii) has an outer surface Bronsted acid amount (hereinafter sometimes referred to as B acid amount) of 0.1 to 10.0 μmol/g, and by having an outer surface B acid amount within a specific range, it exhibits particularly excellent catalytic performance. Here, if the outer surface B acid amount is less than 0.1 μmol/g, the production efficiency and catalytic performance when converting the pyrolysis products of hydrocarbon-based plastics will be inferior. On the other hand, if it is greater than 10.0 μmol/g, side reactions and coking will easily occur on the catalyst surface, resulting in insufficient catalytic performance.

The zeolite constituting the pyrolysis product conversion catalyst of the present invention is a catalyst that exhibits excellent conversion efficiency for pyrolysis products of hydrocarbon-based plastics, particularly selectivity to lower hydrocarbons such as olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms. Therefore, (iv) the amount of B acid is preferably 0.01 to 1.0 mmol/g, and more preferably 0.1 to 1.0 mmol/g.

Here, the B acid amount of a zeolite refers to the number of Bronsted acid sites (hereinafter sometimes referred to as B acid sites), and indicates the acidic OH groups present in the zeolite. Typically, zeolites have B acid sites on their outer surface and within their (micro)pores. Having only a small number of B acid sites on the outer surface means that most of the B acid sites are present within the (micro)pores.

Any method that can confirm the amount of B acid on the outer surface of the zeolite can be used. For example, it can be confirmed by adsorption of 2,4-dimethylquinoline, which has adsorption properties for B acid sites. 2,4-Dimethylquinoline has the ability to adsorb to B acid sites (acidic OH groups) present in zeolite (including within the pores). However, when the (micro)pore diameter of the zeolite is smaller than the 2,4-dimethylquinoline molecule, as in the case of MFI-type zeolite, it cannot penetrate the (micro)pores and cannot adsorb to the B acid sites within the (micro)pores. In other words, it only adsorbs to the B acid sites on the outer surface of the zeolite. Therefore, the amount of B acid on the outer surface can be quantified by determining the amount of 2,4-dimethylquinoline adsorbed to the B acid sites on the outer surface of MFI-type zeolite.

More specifically, the zeolite is pretreated by degassing and dehydrating it for two hours at 400°C, and then its infrared absorption spectrum is measured at 150°C. Then, 2,4-dimethylquinoline gas is introduced into the degassed and dehydrated zeolite and adsorbed for 30 minutes. The excess 2,4-dimethylquinoline is removed by evacuation at 150°C to prepare 2,4-dimethylquinoline-adsorbed zeolite, and its infrared absorption spectrum is measured at 150°C. That is, the amount of B acid on the outer surface can be determined by quantifying the difference (decrease) in infrared absorption in the range of 3600 to 3650 cm ^-1 in the difference spectrum of infrared absorption before and after 2,4-dimethylquinoline adsorption. Note that 2,4-dimethylquinoline also adsorbs to silanol sites on the zeolite surface, and absorption due to the O-H stretching vibration of silanol is observed at 3700 to 3800 cm ^-1 . On the other hand, absorption due to the O-H stretching vibration of the acid sites B on the outer surface of the zeolite was observed in the range of 3600 to 3650 cm ⁻¹ , and the decrease in the infrared absorption spectrum in the range of 3600 to 3650 cm ⁻¹ due to the O-H stretching vibration of the acid sites B upon adsorption of 2,4-dimethylquinoline indicates that 2,4-dimethylquinoline was adsorbed onto the acid sites B on the outer surface of the zeolite.

The amount of B acid in the zeolite (the B acid sites present on the outer surface and within the (micro)pores) can be measured by any method that allows such measurement. For example, it can be confirmed by adsorption of pyridine, which has adsorption properties for B acid sites. Pyridine has the ability to adsorb B acid sites (acidic OH groups) present in zeolite (including within the pores). If the (micro)pore diameter of the zeolite is larger than that of pyridine, it can penetrate into the (micro)pores and adsorb to the B acid sites on the outer surface and within the (micro)pores. Therefore, it is possible to quantify the amount of all B acid present in the zeolite, including the B acid sites present within the pores of MFI zeolite.

More specifically, the zeolite is pretreated by degassing and dehydrating it for two hours at 400°C, and then its infrared absorption spectrum is measured at 150°C. Pyridine gas is then introduced into the degassed and dehydrated zeolite and adsorbed for 10 minutes, and the excess pyridine is removed by evacuation at 150°C to prepare pyridine-adsorbed zeolite, which is then subjected to infrared absorption spectrum measurement at 150°C. That is, the amount of B acid, including that within the pores, can be obtained by quantifying the difference (decrease) in infrared absorption in the range of 1515 to 1565 ^cm-1 in the difference spectrum of infrared absorption before and after pyridine adsorption.

The zeolite that constitutes the pyrolysis product conversion catalyst of the present invention is a catalyst that is particularly excellent in conversion efficiency for pyrolysis products of hydrocarbon-based plastics and selectivity for olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms. Therefore, it is preferable that the zeolite has a small number of B acid sites on its outer surface, with most of the B acid sites being present within its (micro)pores. It is preferable that the B acid sites present on the outer surface account for 1 to 10% of all B acid sites. The proportion of B acid sites on the outer surface is calculated by dividing the amount of B acid on the outer surface of the zeolite described above by the amount of B acid present in the zeolite (including within its pores).

Any method can be used to produce this zeolite, as long as it can produce a zeolite that satisfies the characteristics (i) to (iii) above. Furthermore, a method for selectively removing B acid sites from the zeolite surface, that is, a zeolite that has a specific, minute amount of B acid sites on its outer surface, can be produced by hydrothermal (steam) treatment for part or all of the calcination treatment (heat treatment) when producing a zeolite that satisfies the characteristics (i) to (ii), and adding an ion exchange treatment before or after the calcination treatment.

Zeolites satisfying the characteristics (i) and (ii) can be synthesized using commonly known methods to produce zeolites with a PD≦100 nm, MFI or MEL 10-ring pore framework structure. Specifically, they can be produced by mixing a compound containing an alkali metal and/or alkaline earth metal as a cation, an organic structure-directing agent, and an aluminosilicate gel, and then calcining the resulting crystals. Examples of compounds containing alkali metals and alkaline earth metals include sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide, with sodium hydroxide being preferred. Examples of organic structure-directing agents include tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and tetraethylammonium hydroxide. Examples of aluminosilicate gels include amorphous aluminosilicate gels.

Furthermore, zeolites satisfying the characteristics (i) to (iii) can be produced by a method in which the crystalline material obtained as described above is subjected to ion exchange before being calcined, and then part or all of the calcination is hydrothermal treated, followed by further ion exchange; or by a method in which the crystalline material obtained as described above is calcined and then ion exchanged to form proton-type zeolite, followed by calcination in a hydrothermal atmosphere.

The firing conditions are preferably a treatment temperature of 300 to 900°C, and more preferably 400 to 700°C. The treatment time is preferably 5 minutes to 25 hours from an industrial perspective. Examples of the atmosphere include nitrogen, air, oxygen, argon, and other inert gases, or a combination of two or more of these. Part or all of the firing process is hydrothermal (steam) treatment, which removes aluminum from the B acid site. The hydrothermal treatment temperature is preferably 400 to 750°C, and more preferably 500 to 650°C. The steam concentration is preferably 5 to 100%, and more preferably 10 to 80%.

Ion exchange is carried out before or after the calcination process, and may be carried out in multiple separate steps. Examples of ion exchange include ion exchange using acids such as ammonium chloride, hydrochloric acid, and nitric acid, with hydrochloric acid and nitric acid being preferred. Ion exchange can also be performed by washing with water.

The zeolite that constitutes the pyrolysis product conversion catalyst of the present invention exhibits high catalytic performance as is, but to further enhance coking resistance and catalyst life, it may contain (v) at least one metal selected from sodium, potassium, calcium, silver, and zinc, with a metal-containing zeolite having a content of 0.05 to 5.0 wt% being preferred. Of these metals, zinc- and/or calcium-containing zeolite is even more preferred, as this enhances selectivity to olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms. Furthermore, there are no limitations on the method for incorporating the metal, and any of methods such as impregnation, ion exchange, physical mixing, and vapor deposition are possible.

When used as a catalyst for converting pyrolysis products, it is preferable to mold the zeolite into a molded body, as this provides excellent handleability and catalytic performance. Any molding method can be used to mold the zeolite powder directly into a desired shape, such as by compression molding; mixing a predetermined proportion of binder with the zeolite, optionally with additional additives, and molding the mixture into a desired shape; or sintering the resulting molded body. Particularly when used as a catalyst for converting pyrolysis products of hydrocarbon plastics, a molded body consisting of the zeolite and a binder is preferred, as it not only provides excellent moldability as a molded body but also exhibits high crushing strength, ease of handling, and excellent catalyst life. A molded body consisting of the zeolite and silica is even more preferred, as it provides even better catalytic performance. The silica used in this case may be any type that falls within the category known as silica, and may have a specific crystalline structure or be amorphous. Furthermore, there are no restrictions on the particle size or agglomeration size of the silica. The blending ratio of the zeolite and silica is optional, but a zeolite:silica ratio of 50-95:50-5 (weight ratio) is preferred, with a ratio of 60-90:40-10 being particularly preferred, as this results in a conversion catalyst that exhibits particularly excellent catalytic performance, ease of handling, and catalyst life.

The pyrolysis product conversion catalyst may be of any shape, including, for example, a cylindrical shape, a polygonal prism such as a triangular prism, a square prism, a pentagonal prism, or a hexagonal prism, a hollow polygonal prism, or a spherical shape. Among these, a cylindrical shape is preferred, as it provides a catalyst with excellent continuous productivity and high crushing strength. Furthermore, its size (diameter, width, length, etc.) and density (bulk density, true density, etc.) can be selected as desired, taking into account factors such as packing efficiency. A cylindrical shape with a diameter of 1.0 to 10 mm or a thickness of 0.5 to 5.0 mm is preferred, as it provides a catalyst that can effectively produce olefins, paraffins, aromatic hydrocarbons, and other compounds with 2 to 8 carbon atoms, which are particularly useful as petrochemical products.

The pyrolysis product conversion catalyst of the present invention enables the highly selective production of hydrocarbons, particularly lower hydrocarbons useful as petrochemical products, i.e., olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms, by contacting hydrocarbons, which are pyrolysis products of hydrocarbon-based plastics, as a raw material. The pyrolysis products of hydrocarbon-based plastics used as the raw material can be any product obtained by pyrolysis of hydrocarbon-based plastics. Among these, hydrocarbon-based plastics that exhibit thermoplasticity and do not contain oxygen or nitrogen atoms in their structure, as well as pyrolysis products of used waste plastics and/or waste products generated during the production and processing of hydrocarbon-based plastics, are preferred, since recycling plastic waste as a resource can contribute to resolving social issues in both resource conservation and waste disposal. Examples of hydrocarbon-based plastics include polyethylene, polypropylene, ethylene-propylene rubber, and polystyrene. Further examples include vinyl chloride resin, vinylidene chloride resin, and plastics obtained by separating and removing the chlorine atoms from chlorinated plastics such as chlorinated polyethylene.

The pyrolysis products of hydrocarbon-based plastics are not particularly limited, as long as they are hydrocarbons produced by the thermal decomposition of hydrocarbon-based plastics. For example, they can be products obtained by melting polyolefins such as polyethylene or polypropylene under oxygen-free and catalyst-free conditions and then thermally decomposing the melt. Pyrolysis products of hydrocarbon-based plastics are generally mixtures of aliphatic hydrocarbons consisting of paraffins, olefins, and diolefins with carbon numbers ranging from C1 to C30, and the blend ratios can be selected appropriately depending on the hydrocarbon-based plastic and its thermal decomposition conditions.

The pyrolysis product conversion catalyst of the present invention, when contacted with the pyrolysis products of hydrocarbon-based plastics, can highly selectively produce lower hydrocarbons, particularly olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms. The reaction temperature is not particularly limited; a range of 350 to 650°C is preferred because it results in a more efficient production method, and a range of 500 to 600°C is more preferred because it increases the selectivity of useful components. There is also no restriction on the reaction pressure; for example, operation is possible within a pressure range of approximately 0.05 MPa to 5 MPa. The supply of pyrolysis products is not particularly limited as a ratio of the volume of the raw pyrolysis product gas to the catalyst volume; for example, a space velocity of approximately 1 h ^-1 to 50,000 h ^-1 can be used. In this case, the catalyst can be diluted with a single or mixed gas selected from an inert gas such as nitrogen, hydrogen, carbon monoxide, and carbon dioxide.

The lower hydrocarbons produced using the thermal cracking product conversion catalyst of the present invention are preferably olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms, such as paraffins such as ethane, propane, butane, pentane, hexane, heptane, and octane; olefins such as ethylene, propylene, butene, pentene, hexene, heptene, and octene; and benzene, toluene, xylene, trimethylbenzene, ethylbenzene, and ethyltoluene.

The pyrolysis product conversion catalyst of the present invention efficiently reduces the molecular weight of pyrolysis products of hydrocarbon-based plastics and promotes cyclodehydrogenation, enabling the highly selective production of lower hydrocarbons useful as petrochemical products, namely, olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms, with selectivity of 60% or more. Furthermore, because the components of olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms are produced in a well-balanced manner, efficient combined operation with an existing plant is possible without the need to install new distillation columns. Specifically, because the distillation columns for each component in the ethylene plant can be fully utilized, the ethylene plant can be operated efficiently without excessively reducing the operating rate of the naphtha cracker.

While the pyrolysis product conversion catalyst of the present invention is excellent in selectivity, efficiency, catalyst life, and coking resistance, in the production of lower hydrocarbons using the pyrolysis products of hydrocarbon-based plastics as raw materials, coke forms on the catalyst as the catalytic reaction progresses, and the coke deposition inevitably reduces catalytic performance. While there are no particular limitations on the method for regenerating a catalyst with reduced catalytic performance, for example, combustion removal with oxygen is a preferred method. Coke deposited on the pyrolysis product conversion catalyst of the present invention can be efficiently removed by contacting the catalyst with a gas containing 2 to 25% oxygen by weight at 380 to 530°C, thereby restoring catalytic performance. Contact with a gas containing 5 to 25% oxygen by weight at 400 to 450°C is particularly preferred due to its excellent regeneration efficiency.

Examples of gases with an oxygen content of 2 to 25% by weight include those prepared by mixing air or oxygen with an inert gas such as nitrogen, argon, or neon. There are no particular restrictions on the amount of gas supplied or the regeneration time during regeneration, as long as the catalyst can be regenerated. In particular, since this allows for efficient removal of coke that has accumulated on the pyrolysis product conversion catalyst of the present invention, it is preferable to supply the gas at a gas volume/catalyst volume ratio of 200 to 700 per hour, and the regeneration time is preferably 30 to 65 hours.

The pyrolysis product conversion catalyst of the present invention has high coking resistance and a long catalyst life, even when used with pyrolysis products of hydrocarbon-based plastics. This enables stable, long-term production of paraffins, olefins, and aromatic hydrocarbons with 2 to 8 carbon atoms, which are useful as petrochemical products, with high selectivity, and is therefore expected to be industrially useful.

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

The 10-membered ring pore zeolite used in the examples and comparative examples was prepared based on Japanese Patent No. 6070336. The zeolite and the catalyst for converting pyrolysis products were evaluated and measured using the following methods.

~Measuring average particle size~
The average particle size was measured using a transmission electron microscope (hereinafter sometimes referred to as TEM) and a scanning electron microscope (hereinafter sometimes referred to as SEM). TEM was performed using a transmission electron microscope (manufactured by JEOL Ltd., (trade name) JEM-2100, acceleration voltage 200 kV, observation magnification 30,000 times). A sample was lightly crushed in a mortar, ultrasonically dispersed in acetone, dropped onto a plastic support film, and air-dried to serve as a microscopic sample, which was then photographed. For each primary particle in the photograph, the longest diameter and the average diameter in the perpendicular direction at its midpoint were measured, and the average of a total of 300 particles was taken as the average particle size.

SEM was performed using a scanning electron microscope (Keyence Corporation, product name VE-9800, accelerating voltage 20 kV, observation magnification 2000x). A sample lightly crushed in a mortar was placed on a sample stage, gold was vapor-deposited on it, and a photograph was taken. The side length of 150 particles in the photograph was measured, and the average value was taken as the average crystal diameter.

~2,4-dimethylquinoline adsorption infrared absorption spectroscopy measurement (amount of outer surface B acid)~
Infrared absorption spectroscopy was measured by the transmission method using an FT-IR measurement device (product name FT/IR-6700, manufactured by JASCO Corporation). An MCT detector was used to obtain a spectrum with 256 integration times. The sample was molded into a 13 mm diameter disk and then placed in a disk holder inside a quartz vacuum degassing cell, thereby being positioned perpendicular to the infrared light path. As a pretreatment for the sample, the temperature was raised to 400°C at 10°C/min under vacuum evacuation and maintained at that temperature for 2 hours. After cooling to 150°C, the infrared absorption spectrum before 2,4-dimethylquinoline adsorption was measured. 2,4-dimethylquinoline gas was introduced and allowed to adsorb for 30 minutes. After evacuation at 150°C for 1 hour, the infrared absorption spectrum after 2,4-dimethylquinoline adsorption was measured. The difference between the infrared absorption spectrum after 2,4-dimethylquinoline adsorption and the spectrum before adsorption was calculated, and the change in infrared absorption due to adsorption was measured. In this difference spectrum, the peak near 3600 cm ⁻¹ is the peak of the absorption spectrum of 2,4-dimethylquinoline adsorbed to the Brønsted acid. After determining this integrated intensity, the amount of outer surface B acid was calculated using the Lambert-Beerr law according to the following formula (2):
Amount of B acid (μmol/mg) = A・S/(W・ε) (2)
(Here, A is the peak area intensity (cm ⁻¹ ) of the peak of interest, S is the sample cross-sectional area (cm ² ), W is the sample weight (mg), and ε is the integrated extinction coefficient, which is 3.7 cm·μmol ⁻¹ .)
~ Pyridine adsorption infrared absorption spectroscopy measurement (total amount of B acid) ~
The same apparatus and method were used in the above 2,4-dimethylquinoline adsorption infrared absorption spectroscopy measurement, except that pyridine gas was introduced and allowed to adsorb for 10 minutes.

The peak near 1545 cm ⁻¹ in the difference spectrum was used as the peak of the absorption spectrum of pyridine adsorbed to the Bronsted acid, and the total amount of B acid was calculated from the above formula (2) using an integrated absorption coefficient of 1.67 cm μmol ⁻¹ .

～Outer surface B acid rate～
The ratio of the amount of B acid on the outer surface divided by the total amount of B acid was defined as the outer surface B acid ratio.

~ Powder X-ray diffraction measurement ~
Measurements were taken in air using an X-ray diffraction measurement device (Spectris, product name: X'pert PRO MPD) with a tube voltage of 45 kV, a tube current of 40 mA, and CuKα1. The range of 0.04 to 5 degrees was analyzed at 0.08 degree/step and 200 seconds/step. In addition, background correction based on the absorption rate of the direct beam was removed.

The crystal structure was identified by visually checking for the presence or absence of peaks. Alternatively, a peak search program can be used. Any common peak search program can be used. For example, when the measurement results, with 2θ (degrees) on the horizontal axis and intensity (a.u.) on the vertical axis, are smoothed using the SAVITSKY & GOLAY equation and a sliding polynomial filter, and then second-order differentiation is performed, if three or more consecutive negative values are found, it can be determined that a peak is present.

~Measurement of SiO ₂ /Al ₂ O ₃ molar ratio and amount of metal introduced~
The SiO ₂ /Al ₂ O ₃ molar ratio of the zeolite and the amount of transition metal incorporated were determined by dissolving the zeolite in a mixed aqueous solution of hydrofluoric acid and nitric acid and measuring the resultant solution by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using an ICP apparatus (product name: OPTIMA 3300DV, manufactured by PerkinElmer).

-Production equipment for lower hydrocarbons and its production method-
Using the catalysts obtained in the Examples and Comparative Examples, lower hydrocarbons were produced by the following method, and their performance as catalysts for converting pyrolysis products of hydrocarbon plastics was evaluated.

The lower hydrocarbon production equipment used consisted of a fixed-bed gas-phase flow reactor connected to a stainless steel autoclave (internal volume 200 ml) for melting and thermally decomposing hydrocarbon plastics, and a stainless steel reaction tube (inner diameter 16 mm, length 600 mm) for converting the pyrolysis products into lower hydrocarbons. The stainless steel reaction tube was packed in the middle with a molded catalyst body, and a thermal pretreatment was carried out at 530°C in a dry air flow.

High-density polyethylene (HDPE), a waste product from the production process of a low-pressure polyethylene manufacturing facility, was placed in a stainless steel autoclave and purged with nitrogen. The HDPE was melted by slowly raising the temperature to 180°C, and then heated to 450°C under a nitrogen gas flow (40 ml/min) to undergo thermal decomposition, producing a hydrocarbon mixture called a pyrolysis product. The pyrolysis product was fed into a stainless steel reaction tube using nitrogen gas, where it came into contact with a pyrolysis product conversion catalyst and reacted. The temperature of the catalyst (molded body) layer was controlled using a ceramic tubular furnace.

The reaction outlet gas and reaction liquid were collected and analyzed separately using a gas chromatograph. The gas components were analyzed using a gas chromatograph (Shimadzu Corporation, product name GC-1700) equipped with a TCD detector and packing material (Waters, product name PorapakQ or GL Sciences, product name MS-5A). The liquid components were analyzed using a gas chromatograph (Shimadzu Corporation, product name GC-2015) equipped with an FID detector and a capillary column (GL Sciences, product name TC-1) as a separation column.

The reaction conditions were set as follows:

(Catalytic reaction conditions for producing lower hydrocarbons)
Catalyst weight: 3.8g.
Flow gas: nitrogen 40 ml/min.
Reaction temperature: 530°C or 585°C.
Reaction time: 24 hours.

- Catalyst activity testing method as an indicator of catalyst life -
After the performance evaluation of the catalyst for converting hydrocarbon plastics into pyrolysis products in the above-mentioned lower hydrocarbon production equipment was completed, the stainless steel autoclave was separated from the stainless steel reaction tube, and the activity of the catalyst for converting pyrolysis products packed in the stainless steel reaction tube was tested using the following C4 fraction. The conversion rate of the C4 fraction one hour after the start of the reaction was used as an index of catalyst life.

(Catalytic reaction conditions in catalytic activity test)
C4 fraction: isobutane 2 Nml/min, normal butane 5 Nml/min, trans-2-butene 8 Nml/min, 1-butene 15 Nml/min, isobutene 3 Nml/min, propane 7 Nml/min, propylene 2 Nml/min. Diluent gas: nitrogen 42 Nml/min.
Reaction temperature: 530°C.
Reaction time: 1 hour.

Example 1
Amorphous aluminosilicate gel was added to an aqueous solution of tetrapropylammonium hydroxide and sodium hydroxide and suspended. MFI zeolite was added as seed crystals to the resulting suspension to prepare a raw material composition. The amount of seed crystals added was 0.7 wt % relative to the weight of Al ₂ O ₃ and SiO ₂ in the raw material composition. The composition of the raw material composition is as follows:
_SiO2 / _{Al2O3 molar} ratio=48, TPA/Si molar ratio=0.05, Na/Si molar ratio=0.16, OH/Si molar ratio=0.21, _H2O /Si molar ratio=10.

The resulting raw material composition was sealed in a stainless steel autoclave and crystallized for four days while stirring at 115°C, yielding a slurry-like mixture. After crystallization, the slurry-like mixture was subjected to solid-liquid separation using a centrifugal settler, and the solid particles were washed with a sufficient amount of pure water and dried at 110°C to yield a dry powder.

The resulting dry powder was dispersed in 1 mol/L hydrochloric acid at room temperature, filtered, and the solid particles were washed with a sufficient amount of pure water. After filtering again, the powder was dried overnight at 100°C. It was then calcined in air at 550°C for 1 hour and then treated with 30% water vapor at 600°C for 2 hours.

The resulting powder was dispersed in 1 mol/L hydrochloric acid at room temperature, filtered, and the solid particles were washed with a sufficient amount of pure water. After filtering again, zeolite was obtained.

The physical properties of the obtained zeolite are shown in Table 1. The zeolite was a 10-ring pore zeolite with an MFI-type zeolite framework structure, and the average particle diameter measured using TEM was 25 nm.

100 parts by weight of the zeolite prepared above was mixed with 25 parts by weight of silica (product name Snowtex N-30G, manufactured by Nissan Chemical Industries, Ltd.), 5 parts by weight of cellulose, and 40 parts by weight of pure water, and the mixture was then kneaded. The kneaded mixture was then formed into a cylindrical molded body with a diameter of 1.5 mm and a length of 1.0 to 7.0 mm (average length 3.5 mm). This was dried overnight at 100°C. The dried molded body was calcined in an air stream at 600°C for 2 hours to obtain a molded body, which was used as a catalyst for converting pyrolysis products of hydrocarbon plastics.

Using the resulting catalyst for converting pyrolysis products from hydrocarbon plastics, lower hydrocarbons were produced at a temperature of 585°C, and the catalytic reaction was evaluated. The results are shown in Table 1. Useful components such as olefins, paraffins, and aromatic hydrocarbons with carbon numbers of 2 to 8 were obtained with high selectivity. Furthermore, high catalytic performance was maintained even after the reaction was completed, enabling stable production and exhibiting excellent coking resistance.

Example 2
The crystallization of zeolite in an autoclave, washing, and drying operations were carried out in the same manner as in Example 1. The obtained dry powder was dispersed in 1 mol/L hydrochloric acid at room temperature and filtered, after which the solid particles were washed with a sufficient amount of pure water, filtered again, and dried overnight at 100°C. After calcining in air at 550°C for 1 hour, the mixture was treated with 45% steam at 600°C for 3 hours.

The obtained powder was dispersed in 1 mol/L hydrochloric acid at 40°C, filtered, and the solid particles were washed with a sufficient amount of pure water. After filtering again, the mixture was dried overnight at 100°C to obtain MFI zeolite. The physical properties of the obtained MFI zeolite are shown in Table 1.

100 parts by weight of the MFI zeolite prepared above was mixed with 25 parts by weight of silica (product name Snowtex N-30G, manufactured by Nissan Chemical Industries, Ltd.), 5 parts by weight of cellulose, and 40 parts by weight of pure water, and the mixture was then formed into a cylindrical molded body with a diameter of 1.5 mm and a length of 1.0 to 7.0 mm (average length 3.4 mm). This was dried overnight at 100°C. The dried molded body was calcined in an air stream at 600°C for 2 hours to obtain a molded body, which was used as a catalyst for converting pyrolysis products of hydrocarbon plastics.

The resulting molded body was used to produce lower hydrocarbons at a temperature of 585°C using a catalyst for converting pyrolysis products from hydrocarbon plastics, and the catalytic reaction was evaluated. The results are shown in Table 1. Useful components such as olefins, paraffins, and aromatic hydrocarbons with carbon numbers of 2 to 8 were obtained with high selectivity. Furthermore, high catalytic performance was maintained even after the reaction was completed, enabling stable production and exhibiting excellent coking resistance.

Example 3
The procedures for crystallization of zeolite in an autoclave, washing, and drying were carried out in the same manner as in Example 1.

The resulting dried powder was calcined in air at 550°C, dispersed in 1 mol/L hydrochloric acid at room temperature, filtered, and the solid particles were washed with a sufficient amount of pure water. After filtering again, the powder was dried overnight at 100°C.

The resulting powder was calcined in air at 550°C for 1 hour, and then treated with 20% steam at 600°C for 60 minutes. The physical properties of the resulting MFI zeolite are shown in Table 1.

100 parts by weight of the MFI zeolite prepared above was mixed with 25 parts by weight of silica (product name Snowtex N-30G, manufactured by Nissan Chemical Industries, Ltd.), 5 parts by weight of cellulose, and 40 parts by weight of pure water, and the mixture was then kneaded. The kneaded mixture was then formed into cylindrical molded bodies with a diameter of 1.5 mm and lengths of 1.0 to 7.0 mm (average length 3.5 mm). These were dried overnight at 100°C. The dried molded bodies were calcined in an air stream at 600°C for 2 hours to obtain a molded body, which was used as a catalyst for converting pyrolysis products of hydrocarbon plastics.

Using the resulting catalyst for converting pyrolysis products from hydrocarbon plastics, lower hydrocarbons were produced at a temperature of 585°C, and the catalytic reaction was evaluated. The results are shown in Table 1. Useful components such as olefins, paraffins, and aromatic hydrocarbons with carbon numbers of 2 to 8 were obtained with high selectivity. Furthermore, high catalytic performance was maintained even after the reaction was completed, enabling stable production and exhibiting excellent coking resistance.

Comparative Example 1
The procedures for crystallization of zeolite in an autoclave, washing, and drying were carried out in the same manner as in Example 1.

The resulting dried powder was calcined in air at 550°C, dispersed in 1 mol/L hydrochloric acid at room temperature, filtered, and the solid particles were washed with a sufficient amount of pure water. After filtering again, the mixture was dried overnight at 100°C to obtain zeolite. The physical properties of the resulting zeolite are shown in Table 1.

100 parts by weight of the zeolite prepared above was mixed with 25 parts by weight of silica (Nissan Chemical Industries, Ltd., product name Snowtex N-30G), 5 parts by weight of cellulose, and 40 parts by weight of pure water, and the mixture was then formed into a cylindrical molded body with a diameter of 1.5 mm and a length of 1.0 to 7.0 mm (average length 3.6 mm). This was dried overnight at 100°C. The dried molded body was then calcined in an air stream at 600°C for 2 hours to obtain a molded body.

The resulting molded product was used as a catalyst to produce lower hydrocarbons at 585°C, and the catalytic reaction was evaluated. The results are shown in Table 1. The selectivity for olefins, paraffins, and aromatic hydrocarbons with 2 to 8 carbon atoms was low, and the catalytic activity decreased significantly, indicating poor performance as a catalyst for converting thermal cracking products.

Comparative Example 2
100 parts by weight of proton-type MFI zeolite powder (manufactured by Tosoh Corporation, product name: HSZ-840HOA) were mixed with 40 parts by weight of silica (manufactured by Nissan Chemical Industries, Ltd., product name: Snowtex N-30G), 5 parts by weight of cellulose, and 40 parts by weight of pure water, and the mixture was kneaded. The kneaded mixture was then formed into a cylindrical molded body having a diameter of 1.5 mm and a length of 1.0 to 7.0 mm (average length 3.5 mm). This was dried overnight at 100°C. The dried molded body was calcined at 600°C for 2 hours in an air stream to obtain a molded body.

The resulting molded product was used as a catalyst to produce lower hydrocarbons at a temperature of 585°C, and the catalytic reaction was evaluated. The results are shown in Table 1. The selectivity for useful components, such as olefins, paraffins, and aromatic hydrocarbons with 2 to 8 carbon atoms, was low, and catalytic activity declined significantly, indicating poor performance as a catalyst for converting pyrolysis products.

Example 4
100 g of the MFI zeolite molded body obtained in Example 1 was immersed for 30 minutes in 109.9 g of a 0.75 mol/L aqueous zinc acetate solution. The molded body was separated by filtration, dried overnight at 110°C, and then calcined for 5 hours at 550°C in an air stream to obtain zinc-containing MFI zeolite. The zinc content of the obtained zinc-containing MFI zeolite was 2.6 wt%.

The zinc-containing MFI zeolite had a 10-membered ring pore structure, and the average particle size measured using TEM was 25 nm, the amount of B acid on the outer surface was 2.8 μmol/g, the total amount of B acid was 0.06 mmol/g, and the outer surface B acid ratio was 4.7%.

Zinc-containing MFI-type zeolite was used as a catalyst for converting pyrolysis products from hydrocarbon plastics, and lower hydrocarbons were produced at a temperature of 530°C, and the catalytic reaction was evaluated. The results are shown in Table 2. Paraffins, olefins, and aromatic hydrocarbons with carbon numbers of 2 to 8, which are useful as petrochemical products, showed high selectivity, and each component was produced in a balanced manner.

Example 5
240 g of the MFI zeolite shaped body obtained in Example 1 was packed into a polyvinyl chloride tube with an inner diameter of 10 mm (packing length: 2.0 m). A 12.1 mmol/L aqueous calcium hydroxide solution was circulated for 6 hours at a linear flow velocity of 26 cm/min. Thereafter, pure water was circulated at the same linear flow velocity, and washing was repeated until the pH fell within the range of 8 to 10. The shaped body was separated by filtration, dried overnight at 110°C, and then calcined for 5 hours at 550°C in an air stream, yielding a calcium-containing MFI zeolite. The calcium content of the resulting calcium-containing MFI zeolite was 0.23 wt%.

The calcium-containing MFI zeolite had a 10-membered ring pore structure, and the average particle size measured using TEM was 25 nm, the amount of B acid on the outer surface was 2.8 μmol/g, the total amount of B acid was 0.13 mmol/g, and the outer surface B acid ratio was 2.2%.

Calcium-containing MFI zeolite was used as a catalyst for converting pyrolysis products from hydrocarbon plastics, and lower hydrocarbons were produced at a temperature of 585°C, and the catalytic reaction was evaluated. The results are shown in Table 2. They demonstrate high selectivity for paraffins, olefins, and aromatic hydrocarbons with carbon numbers of 2 to 8, which are useful as petrochemical products, and the production of each component was well balanced.

Example 6
The catalytic reaction evaluation was carried out in the same manner as in Example 1, except that low-density polyethylene (LDPE) was used instead of HDPE as the hydrocarbon-based plastic and lower hydrocarbons were produced at a temperature of 530°C. The results are shown in Table 2. Useful components, such as olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms, were obtained with high selectivity. Furthermore, high catalytic performance was maintained even after the reaction was completed, enabling stable production and exhibiting excellent coking resistance.

The pyrolysis product conversion catalyst of the present invention and the method for producing lower hydrocarbons using the same exhibit excellent catalytic performance when converting hydrocarbon plastics, particularly the pyrolysis products of waste plastics, into lower hydrocarbons, and are of extremely high industrial value as catalysts.

Claims (9)

A catalyst for converting pyrolysis products of polyolefins , comprising:
A catalyst for converting pyrolysis products, characterized in that it is a conversion catalyst containing a zeolite that satisfies the following characteristics (i) to (iii):
(i) The average particle size is 100 nm or less.
(ii) 10-ring pore zeolites of MFI type or MEL type.
(iii) The Bronsted acid amount of the outer surface is 0.1 to 10.0 μmol/g. The thermal decomposition product conversion catalyst according to claim 1, further characterized in that (iv) the Bronsted acid amount is 0.01 to 1.0 mmol/g. The pyrolysis product conversion catalyst according to claim 1 or 2, further comprising (v) at least one metal selected from sodium, potassium, calcium, silver, and zinc, the content of which is 0.05 to 5.0 wt %. A pyrolysis product conversion catalyst according to any one of claims 1 to 3, further comprising silica and having a cylindrical shape with a diameter of 1.0 to 10 mm or a thickness of 0.5 to 5.0 mm. A method for producing lower hydrocarbons, which comprises contacting a thermal decomposition product of a polyolefin with the thermal decomposition product conversion catalyst according to any one of claims 1 to 4. 6. The method for producing lower hydrocarbons according to claim 5, wherein the polyolefin is at least one selected from the group consisting of polyethylene, polypropylene, and ethylene propylene rubber. 7. The method for producing lower hydrocarbons according to claim 5 or 6, wherein the polyolefin is a waste plastic and/or a waste product generated during the production and processing of polyolefin . 8. The method for producing lower hydrocarbons according to any one of claims 5 to 7, wherein the lower hydrocarbons are olefins, paraffins, or aromatic hydrocarbons having 2 to 8 carbon atoms. 9. The method for producing lower hydrocarbons according to claim 5, wherein the selectivity for lower hydrocarbons is 60% or more.