JP7703909B2 - Method for simultaneous production of lower aliphatic and aromatic hydrocarbons - Google Patents

Description

The present invention relates to a method for producing lower hydrocarbons and aromatic hydrocarbons from hydrocarbon-based plastics, and more specifically, to a method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons that enables highly efficient, well-balanced and stable conversion of aliphatic hydrocarbons consisting of paraffins, olefins, diolefins, etc. having 1 to 30 carbon atoms (hereinafter sometimes written as C), which are the main components of the thermal decomposition products of hydrocarbon-based plastics, into olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms, which are useful as petrochemical products, through a specific process using two specific types of zeolite catalysts.

In recent years, issues such as global warming and marine plastic pollution have come into the spotlight, and chemical recycling, in which waste plastic is chemically broken down and reused as raw materials for petrochemical products, has been attracting attention. In particular, oil-making technology using thermal decomposition is an important technology that can essentially recycle plastics by converting thermoplastic polyolefins (polyethylene, polypropylene), which make up half of waste plastics, into hydrocarbon oil, which can then be used as raw material for naphtha crackers, etc.

The technology of converting waste plastic 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 products with carbon numbers from C1 to C30, that is, hydrocarbon oils, is obtained. Of these, light oils from C5 to C10 can be used as feedstock for naphtha crackers, but kerosene, diesel, heavy oil, and wax with carbon numbers of C11 and above are used as fuel and do not add much value to the product.

As a method for increasing the added value of products, a method has been proposed in which polyolefin-based (waste) plastics are thermally decomposed, and the product generated by the thermal decomposition is 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).

A method for treating waste plastics has also been proposed in which waste plastics are vaporized by thermal decomposition, and the resulting thermal decomposition 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, although the carbon number distribution of the hydrocarbon oil is reduced from C5-C38 to C5-C21 by using a ZSM-5 catalyst, there is still a problem that there is a large amount of low added value kerosene, light oil, and heavy oil fractions of C11 and above. In the method proposed in Non-Patent Document 1, in addition to ZSM-5, HY, REY, and Ni/ReY catalysts are used for thermal cracking, and the selectivity of C5-C11 gasoline fraction is particularly high when a REY catalyst is used, but these Y-type zeolites have poor thermal stability and still contain a large amount of low added value fractions of C9 and above, so they are not sufficient 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, and in particular increased the total selectivity of 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 tower in an ethylene plant (naphtha cracker) increased, forcing the naphtha cracker's operating rate to be excessively reduced, or requiring the construction of a new specific distillation tower, making the method economically unreasonable. In addition, the synthesis of boron-containing silicate is difficult, making it difficult to obtain, and the catalyst's lifespan has not been satisfactorily examined due to its insufficient coking resistance. Furthermore, in the method proposed in Patent Document 3, the use of a gallium-containing silicate catalyst increases the selectivity of carbon number distributions of C1 to C13, particularly benzene (C6), toluene (C7), and xylene (C8), and the reduction in molecular weight proceeds in a well-balanced manner. However, with gallium-containing silicates, particularly gallosilicates, it is difficult to insert Ga metal into the silicate skeleton, making it difficult to synthesize reproducibly and industrially, and the coking resistance is insufficient, leaving room for improvement in terms of catalyst life.

Therefore, there has been a demand for a manufacturing method that can convert the pyrolysis products of hydrocarbon plastics into lower aliphatic hydrocarbons and aromatic hydrocarbons that are useful as petrochemical products with high efficiency and selectivity at the same time.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that when producing lower hydrocarbons and aromatic hydrocarbons from the pyrolysis products of hydrocarbon-based plastics, a specific process using two specific types of zeolite catalysts can be used to simultaneously produce lower aliphatic hydrocarbons and aromatic hydrocarbons that are useful as petrochemical products in high yields, and that this production method has an excellent catalyst life, leading to the completion of the present invention.

That is, the present invention relates to a method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons using hydrocarbon plastics as a raw material, the method being characterized by going through at least the following steps (1) to (3):
Step (1): A step of heating and melting a hydrocarbon-based plastic.
Step (2): A step of thermally decomposing a heat-molten hydrocarbon-based plastic in the presence of a zeolite having an acid amount (solid acid amount by the NH ₃ -TPD method) of 200 μmol/g or less, determined from the high-temperature desorption amount in an ammonia temperature programmed desorption spectrum, to obtain a thermal decomposition product.
Step (3): A step of contacting the thermal cracking product with a catalyst containing a zeolite satisfying the following characteristics (i) to (iv) under heated conditions to simultaneously produce lower aliphatic hydrocarbons and aromatic hydrocarbons:
(i) The average particle size is 100 nm or less.
(ii) 10-ring pore zeolites of the MFI or MEL type.
(iii) the Bronsted acid amount of the outer surface is 0.1 to 10.0 μmol/g.
(iv) the total Bronsted acidity is 0.01 to 1.0 mmol/g.

The present invention is described in detail below.

The production method of the present invention is a method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons that are useful as petrochemical products, even from hydrocarbon-based plastics that have traditionally been difficult to use as raw materials due to the wide variety of components they contain, and involves the following steps: (1) heat-melting the hydrocarbon-based plastic; (2) heat-decomposing the heat-molten hydrocarbon-based plastic in the presence of a zeolite having an acid amount (solid acid amount as determined by the NH ₃ -TPD method) of 200 μmol/g or less, as determined from the high-temperature desorption amount in an ammonia temperature-programmed desorption spectrum, to produce a thermal decomposition product; and (3) contacting the thermal decomposition product under heating conditions with a catalyst containing a zeolite that satisfies the following characteristics: (i) an average particle size of 100 nm or less, (ii) an MFI-type or MEL-type 10-membered ring fine pore zeolite, (iii) an outer surface Bronsted acid amount of 0.1 to 10.0 μmol/g, and (iv) a total Bronsted acid amount of 0.01 to 1.0 mmol/g, to simultaneously produce lower aliphatic hydrocarbons and aromatic hydrocarbons. A schematic diagram of a preferred embodiment in this case is shown in FIG.

The manufacturing method of the present invention uses hydrocarbons, which are the thermal decomposition products of hydrocarbon-based plastics, as a raw material through steps (1) to (3) to enable the simultaneous highly selective production of hydrocarbons, particularly lower hydrocarbons useful as petrochemical products, i.e., lower aliphatic hydrocarbons and aromatic hydrocarbons having 2 to 8 carbon atoms. The thermal decomposition products of the hydrocarbon-based plastics used as the raw material are not limited as long as they are obtained by thermal decomposition of the hydrocarbon-based plastics. In particular, since plastic waste can be used again as a resource to contribute to solving social issues in terms of both resource conservation and waste disposal, it is preferable to use hydrocarbon-based plastics that do not have oxygen atoms or nitrogen atoms in the plastic structure and exhibit thermoplasticity, and furthermore, the thermal decomposition products of used waste plastics and/or waste products during the production and processing of hydrocarbon-based plastics. Examples of hydrocarbon-based plastics include polyethylene, polypropylene, ethylene propylene rubber, polystyrene, etc., and further include plastics obtained by separating and removing chlorine atoms that are composed of polyvinyl chloride resin, vinylidene chloride resin, and chlorinated polyethylene chlorinated plastics.

Step (1) of the manufacturing method of the present invention is a step of heating and melting a hydrocarbon-based plastic. As long as the hydrocarbon-based plastic can be heated and melted and the molten plastic can be supplied to the subsequent step (2), the apparatus and method are not particularly limited. For example, a single-screw or twin-screw extrusion melter heated by a heat medium jacket or heater, or a stirring autoclave, etc. can be used. The temperature during heating and melting is not particularly limited as long as the hydrocarbon-based plastic can be heated and melted. For example, 140°C to 300°C is preferable, and 160°C to 250°C is even more preferable.

The step (2) constituting the manufacturing method of the present invention is a step of thermally decomposing a heat-molten hydrocarbon-based plastic in the presence of a zeolite having a solid acid amount of 200 μmol/g or less as measured by the _NH 3 -TPD method to obtain a thermal decomposition product, and the process and the apparatus are not particularly limited as long as the thermal decomposition product, a mixture of aliphatic hydrocarbons consisting of paraffins, olefins, and diolefins having a carbon number distribution of C1 to C30, can be made lower in molecular weight and can be supplied to the step (3). For example, a method in which a heat-molten hydrocarbon-based plastic is brought into contact with a zeolite having a solid acid amount of 200 μmol/g or less as measured by the NH ₃ -TPD method can be mentioned. Specifically, a method in which a heat-molten hydrocarbon-based plastic is supplied to a thermal decomposition device such as a single-screw or twin-screw extrusion melter heated by a heat medium jacket or heater, or an agitation autoclave, and a zeolite having a solid acid amount of 200 μmol/g or less as measured by the NH ₃ -TPD method is supplied, and further the steps (1) and (2) can be carried out simultaneously or sequentially in the same device.

The shape of the zeolite in step (2) is not particularly limited, with a powder shape being preferred due to ease of handling. There is no particular limit to the reaction temperature, with a range of 200 to 600°C being preferred as this allows for more efficient thermal decomposition, and a range of 250 to 500°C being more preferred as this allows for more efficient molecular weight reduction. There is also no limit to the reaction pressure, with operation possible within a pressure range of, for example, normal pressure to approximately 5 MPa. When supplying the heated and melted hydrocarbon plastic and zeolite, they can also be used after dilution with an inert gas such as nitrogen.

The zeolite used in the step (2) is a zeolite having an acid amount of 200 μmol/g or less, determined from the high-temperature desorption amount in an ammonia temperature programmed desorption spectrum. Here, the solid acid amount of zeolite by the NH ₃ -TPD method is a value measured by the NH ₃ -TPD method according to "Measurement of Solid Acidity by Ammonia Temperature Programmed Desorption Method, Catalyst, vol. 42, p. 218 (2000)". In other words, the solid acid amount of zeolite by the NH ₃ -TPD method in the present invention is a value obtained by measuring the amount of ammonia desorbed at 100° C. or more and 500° C. or less from a sample saturated with ammonia at room temperature. Specifically, it is measured by the measurement of solid acid amount by the NH ₃ -TPD method described later.

The zeolite used in step (2) has a solid acidity of 200 μmol/g or less as measured by the NH ₃ -TPD method, and within this range, the yield of relatively low aliphatic hydrocarbons (olefins, paraffins, diolefins) having a carbon number distribution of C1 to C20 is high, and by supplying these aliphatic hydrocarbons to step (3), it becomes possible to carry out a catalytic reaction using a catalyst containing the zeolite in step (3), i.e., to efficiently produce lower aliphatic hydrocarbons and aromatic hydrocarbons simultaneously by further lowering and cyclization of the aliphatic hydrocarbons. The framework structure of the zeolite is not particularly limited, and examples of the framework structure that can be used include, as structure codes consisting of three capital letters defined by the International Zeolite Society, ABW, AFG, ANA, ^* BEA, BIK, BOG, BRE, CAN, CAS, CFI, CHA, DAC, DDR, EAB, EDI, EMT, EPI, ERI, ESV, EUO, FAU, FER, FRA, GIS, G ME, GOO, HEU, IFR, ITE, JBW, KFI, LAU, LEV, LIO, LOS, LTA, LTL, LTN, MAZ, MEI, MEL, MER, MFI, MFS, MON, MO R, MSO, MTF, MTN, MTT, MTW, MWW, NAT, NES, NON, OFF, -PAR, PAU, PHI, RHO, RTS, RUT, SFE, SFF, SFG, SOD, SST, STF, STI, STT, TER, THO, TON, TSC, UFI, VET, VFI, WEN, YUG and the like are included, and from the viewpoints of high catalytic activity and easy availability, ^* BEA, FAU, FER, LTA, LTL, MFI, MOR and MWW are preferred, and FAU and MFI are more preferred.

The composition of the zeolite is not particularly limited, and examples thereof include aluminosilicates; metalloaluminosilicates such as boroaluminosilicate, titanoaluminosilicate, vanadium aluminosilicate, manganese aluminosilicate, iron aluminosilicate, zinc aluminosilicate, gallium aluminosilicate, and tin aluminosilicate; and metallosilicates such as borosilicate, titanosilicate, vanadium silicate, manganese silicate, iron silicate, zinc silicate, gallium silicate, and tin silicate. Of these, aluminosilicates are preferably used because they are easily available on an industrial level.

Here, the _above -mentioned aluminosilicate is generally represented by a composition of M2 _{/nO.Al2O3.xSiO2.yH2O (} n represents the valence of the _cation M, x represents a number equal to or greater than 2, and y represents the amount _of adsorbed water), and an aluminosilicate in which the cation M is a proton type is preferably used. In addition, x is called the _SiO2 / _{Al2O3 ratio} , and is a numerical value that serves as an index of the heat resistance, acid resistance, solid acidity, and reactivity of the zeolite. There is no particular limitation on the range as long as the solid acid amount measured by the _NH3 -TPD method is 200 μmol/g or less, and since the yield of relatively low aliphatic hydrocarbons having a carbon number distribution of C1 to _C20 is increased, the _SiO2 / _Al2O3 ratio is preferably 100 or more, and more preferably 200 or more, and is a proton type aluminosilicate. In this case, the method for producing the proton type aluminosilicate having a SiO ₂ /Al ₂ O ₃ ratio of 100 or more is not particularly limited, and for example, the aluminosilicate is synthesized by a hydrothermal synthesis method in which a mixture of a silica source, an alumina source, an alkali source, and water is heated in a closed system. Since the hydrothermal synthesis method often produces a structurally stable alumina silicate having a SiO ₂ /Al ₂ O ₃ ratio of 5 to 50, a desired alumina silicate having a SiO ₂ /Al ₂ O ₃ ratio of 100 or more is synthesized by various techniques such as hydrothermal (steam) treatment and acid treatment. Since the cation M of the alumina silicate produced by hydrothermal synthesis is an alkali metal, conversion to the proton type is easily performed by a method of ion-exchanging the alumina silicate into the ammonium type, followed by heating or an acid treatment.

The zeolite shows high catalytic performance as it is, but since the solid acid amount by the NH ₃ -TPD method can be efficiently adjusted, it is preferable that the cation M contains at least one metal selected from metals belonging to Groups IA and IIA of the periodic table. The content is not particularly limited as long as the solid acid amount by the NH ₃ -TPD method is 200 μmol/g or less, and it is preferable that the zeolite has a content of 0.05 to 5.0 wt%. Among these metals, calcium and sodium are more preferable because they have a high yield of relatively low aliphatic hydrocarbons with a carbon number distribution of C1 to C20 and are also highly heat-resistant. The method for producing an aluminosilicate containing at least one metal selected from metals belonging to Groups IA and IIA of the periodic table is not particularly limited, and a method of introducing a metal by ion exchange using the above-mentioned proton-type alumina silicate is used. In addition, the amount of metal to be ion-exchanged may be appropriately selected so that the metal content is the desired content.

Furthermore, since the solid acidity of the zeolite can be precisely adjusted by the NH ₃ -TPD method, it is preferable that the zeolite is one in which some or all of the surface OH groups have been silylated. The silylation treatment of the zeolite is not particularly limited, and the zeolite can be easily treated, for example, by using the above-mentioned proton-type aluminosilicate and appropriately treating it with a silylating agent such as hexamethylsilazane, trimethylsilyl chloride, t-butyldimethylchlorosilane, or butylchlorodimethylsilane.

In addition, as an embodiment of the step (2), since it enables particularly efficient decomposition, it is preferable to have a process that includes at least step (A), a first decomposition step in which the heated and molten hydrocarbon plastic is decomposed without oxygen and without a catalyst, and step (B), a second decomposition step in which the heated and molten hydrocarbon plastic is contacted with zeolite and decomposed by heat after step (A), to obtain a decomposition product. A schematic diagram of a preferred embodiment is shown in Figure 2. Here, the device for step (A) is not particularly limited, and a thermal decomposition device such as a single-screw or twin-screw extrusion melter heated by a heat medium jacket or a heater, or an agitation autoclave is preferably used. The temperature is not particularly limited, and a range of 200 to 600 ° C is preferable because the thermal decomposition proceeds more efficiently, and a range of 250 to 500 ° C is more preferable because the molecular weight is further reduced. There is no limit to the reaction pressure, and operation is possible within a pressure range of, for example, normal pressure to about 5 MPa. In addition, when supplying the heated and melted hydrocarbon plastic and zeolite, they can also be diluted with an inert gas such as nitrogen.

The apparatus for step (b) is not particularly limited, and a fixed-bed flow-type catalytic reaction process is preferably used. The shape of the zeolite may be any, and is preferably granular because it is easy to handle, and examples of such shapes include a cylindrical shape, a cylindrical shape, a polygonal prism shape such as a triangular prism shape, a square prism shape, a pentagonal prism shape, and a hexagonal prism shape, a hollow polygonal prism shape, and a spherical shape. Among these, a cylindrical shape or a cylindrical shape is preferable because it is excellent in continuous productivity and has a high crushing strength. The size such as the diameter, width, and length, and the density such as the bulk density and true density can be arbitrarily selected in consideration of the packing efficiency, and the catalyst is preferably one having a cylindrical shape with a diameter of 1.0 to 10 mm or a cylindrical shape with a thickness of 0.5 to 5.0 mm, because it is capable of supplying aliphatic hydrocarbons with a carbon number distribution suitable for step (3). The temperature is not particularly limited, and is preferably in the range of 200 to 600°C because the thermal decomposition proceeds more efficiently, and more preferably in the range of 250 to 500°C because the molecular weight reduction proceeds more efficiently. There is no restriction on the reaction pressure, and operation is possible within a pressure range of, for example, normal pressure to about 5 MPa. The supply of the pyrolysis product is not particularly restricted in terms of the ratio of the volume of the pyrolysis product gas to the volume of the zeolite catalyst, and can be, for example, a space velocity of about 1 h ^-1 to 50,000 h ^-1 . In this case, the pyrolysis product can be used after being diluted with a single or mixed gas selected from an inert gas such as nitrogen, hydrogen, carbon monoxide, and carbon dioxide.

In addition, a more preferred embodiment of the process includes a step between steps (A) and (B) of separating the pyrolysis product into high-boiling and low-boiling components by distillation, in which step (B) brings the high-boiling component into contact with zeolite and pyrolyzes it, and further includes a step (D) of mixing the low-boiling component from step (A) with the decomposition product from step (B) to obtain a pyrolysis product, as shown in a schematic diagram in Figure 3. Here, any ordinary distillation method can be used as long as it can separate the aliphatic hydrocarbons, which have a wide carbon number distribution of C1 to C30 and are produced by pyrolyzing the heat-molten hydrocarbon plastic without oxygen or catalyst, into high-boiling and low-boiling components.

In step (A), the heat-molten hydrocarbon plastic is pyrolyzed without oxygen and without a catalyst, so that aliphatic hydrocarbons with a wide carbon number distribution of C1 to C30 are produced. Of these, the relatively low aliphatic hydrocarbons of C1 to C15, i.e., the low boiling point components, are separated by distillation and used as part of the pyrolysis product to be supplied to step (D). On the other hand, the relatively high aliphatic hydrocarbons of C16 to C30, i.e., the high boiling point components, are contacted with a zeolite having a solid acidity of 200 μmol/g or less by the NH ₃ -TPD method, and the pyrolysis product produced by contact and pyrolysis is also used as part of the pyrolysis product to be supplied to step (D). By adding a step of separating the pyrolysis product into high boiling point components and low boiling point components by distillation between steps (A) and (B), the burden on the zeolite having a solid acidity of 200 μmol/g or less by the NH ₃ -TPD method is reduced, and there is an advantage in that the deterioration of the zeolite catalyst can be suppressed.

The step (3) constituting the production method of the present invention is a step in which the pyrolysis product is contacted under heating conditions with a catalyst containing a zeolite that satisfies the characteristics (i) to (iv) above, thereby making it possible to simultaneously produce lower aliphatic hydrocarbons and aromatic hydrocarbons, particularly olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms, with high selectivity. The reaction temperature at this time is not particularly limited, and is preferably in the range of 350 to 650 ° C. because it is a more efficient production method, and more preferably in the range of 500 to 600 ° C. because it increases the selectivity of useful components. There is also no limit to the reaction pressure, and operation is possible within a pressure range of, for example, about 0.05 MPa to 5 MPa. The supply of the pyrolysis product is not particularly limited as the ratio of the volume of the raw pyrolysis product gas to the volume of the catalyst, and can be, for example, a space velocity of about 1 h ^-1 to 50,000 h ^-1 . In this case, it can also be used after dilution with a single or mixed gas selected from an inert gas such as nitrogen, hydrogen, carbon monoxide, and carbon dioxide. The reaction apparatus used in this case is not limited, and examples thereof include a single-screw or twin-screw extruder melter heated by a heat medium jacket or heater, and a thermal decomposition apparatus such as an agitator autoclave.

The zeolite contained in the catalyst in step (3) has (i) an average particle diameter (hereinafter sometimes referred to as PD) ≦100 nm, and since it is a catalyst with particularly excellent thermal stability, it is desirable that 5 nm ≦ PD ≦ 100 nm. Here, if the PD exceeds 100 nm, the conversion efficiency of the thermal decomposition products of the hydrocarbon-based plastic to lower aliphatic hydrocarbons and aromatic hydrocarbons will be poor.

The method for measuring PD in the present invention is not limited, and any method can be used, such as a method of randomly selecting 100 or more particles from a photograph taken with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and determining the average diameter thereof, or a method of calculating PD from the external surface area of the zeolite using PD = 6/S x (1/(2.29 x 10 ⁶ ) + 0.18 x 10 ^-6 ) (S represents the external surface area (m ² /g)).

The external surface area (S (m ² /g)) can be determined by a 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 can be determined from the slope of the obtained regression line.

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

The zeolite is (ii) an MFI or MEL type 10-membered ring pore zeolite. Here, MFI type zeolites include aluminosilicate compounds that belong to the structure code MFI defined by the International Zeolite Association, and MEL type zeolites include aluminosilicate compounds that belong to the same structure code MEL. Here, if the zeolite contains a zeolite other than MFI or MEL type 10-membered ring pore zeolites, the conversion reaction of the pyrolysis products of hydrocarbon plastics will be less efficient.

The zeolite (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, the zeolite 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 thermal decomposition products of hydrocarbon-based plastics will be inferior. On the other hand, if it is more than 10.0 μmol/g, side reactions and coking will easily occur on the catalyst surface, resulting in insufficient catalytic performance.

The zeolite is a catalyst with excellent conversion efficiency for pyrolysis products of hydrocarbon-based plastics, particularly excellent selectivity to lower aliphatic and aromatic hydrocarbons having 2 to 8 carbon atoms, so (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.

The B acid amount of a zeolite refers to the amount of Bronsted acid sites (hereinafter sometimes referred to as B acid sites), and indicates the acidic OH groups present in the zeolite. Normally, a zeolite has B acid sites on its outer surface and within its (micro)pores. And when a zeolite has only a few B acid sites on its outer surface, this means that most of the B acid sites are present within the (micro)pores.

The amount of B acid on the outer surface of the zeolite can be confirmed by any method that allows such confirmation. For example, it can be confirmed by adsorption of 2,4-dimethylquinoline, which has an adsorption property to B acid sites. 2,4-dimethylquinoline has an adsorption property 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, it cannot enter the (micro)pore and cannot be adsorbed to the B acid sites within the (micro)pore. In other words, it is only adsorbed 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.

As a more specific method, the infrared absorption spectrum of zeolite that has been subjected to degassing and dehydration treatment at 400°C for 2 hours as a pretreatment of the zeolite is measured at 150°C. Then, 2,4-dimethylquinoline gas is introduced into the degassed and dehydrated zeolite and adsorbed for 30 minutes, and the excess 2,4-dimethylquinoline is removed by evacuation at 150°C to prepare 2,4-dimethylquinoline-adsorbed zeolite, and the infrared absorption spectrum is measured at 150°C. That is, the amount of B acid on the outer surface can be obtained by quantifying the difference (reduction) 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 is also adsorbed to the OH site on the zeolite surface, but the absorption due to the O-H stretching vibration of OH is observed at 3700 to 3800 cm ^-1 . On the other hand, absorption due to the O-H stretching vibration of the acid site B on the outer surface of the zeolite was observed at 3600 to 3650 cm ^-1 , and a 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 site B upon adsorption of 2,4-dimethylquinoline was observed, which indicates that 2,4-dimethylquinoline was adsorbed to the acid site B on the outer surface of the zeolite.

The amount of B acid in the zeolite (B acid sites present on the outer surface and in 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 an adsorption property for B acid sites. Pyridine has an adsorption property with B acid sites (acidic OH groups) present in the zeolite (including in the pores), and when the (micro)pore diameter of the zeolite is larger than that of pyridine, it can also enter the (micro)pores and adsorb to the B acid sites on the outer surface and in 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 in the pores of MFI-type zeolite.

In a more specific method, the zeolite is pretreated by degassing and dehydrating it for 2 hours at 400° C., and then infrared absorption spectroscopy is performed at 150° C. Then, pyridine gas is 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, and infrared absorption spectroscopy is performed at 150° C. In other words, the amount of B acid, including that in the pores, can be obtained by quantifying the difference (reduction) 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 in step (3) is a catalyst that is particularly excellent in conversion efficiency of pyrolysis products of hydrocarbon-based plastics and selectivity to lower aliphatic 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 (micro)pores, and it is preferable that the B acid sites present on the outer surface account for 1 to 10% of the total B acid sites. The proportion of B acid sites on the outer surface is calculated by taking the amount of B acid on the outer surface of the zeolite described above as the proportion of the amount of B acid present in the zeolite (including within the pores).

As a method for producing the zeolite, any method can be used as long as it is possible to produce a zeolite that satisfies the characteristics described in (i) to (iv) above. As a method for selectively removing B acid sites from the zeolite surface, that is, a zeolite that has a specific amount of B acid sites on its outer surface, a method in which part or all of the calcination treatment (heat treatment) when producing a zeolite that satisfies the characteristics (i) to (ii) is performed as a hydrothermal (steam) treatment, and an ion exchange treatment is added before or after the calcination treatment, can be mentioned.

As a method for synthesizing a zeolite satisfying the characteristics (i) to (ii), a zeolite having a PD≦100 nm, MFI type or MEL type 10-membered ring pore framework structure can be obtained by using a general known method. Specifically, the zeolite 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 firing the resulting crystals. In this case, examples of the compound containing an alkali metal or alkaline earth metal include sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, etc., and among these, sodium hydroxide is preferred. Examples of the organic structure directing agent include tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium hydroxide, etc. In addition, examples of the aluminosilicate gel include amorphous aluminosilicate gel, etc.

Furthermore, when making a zeolite that satisfies the characteristics (i) to (iv), it is possible to produce it by a method in which ion exchange is performed before calcining the crystals obtained by the above method, and then a part or all of the calcination is hydrothermal treated, and then further ion exchange is performed, or a method in which ion exchange is performed after calcining the crystals obtained by the above method to make a proton-type zeolite, and then calcining in a hydrothermal atmosphere.

The calcination 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. The atmosphere may be, for example, one or a combination of two or more of nitrogen, air, oxygen, argon, and other inert gases. A part or all of the calcination process is subjected to hydrothermal (steam) treatment, which causes aluminum at the B acid site to be desorbed. The treatment temperature for the hydrothermal treatment 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 step, and may be divided into multiple ion exchanges. Examples of ion exchange include ion exchange using an acid such as ammonium chloride, hydrochloric acid, or nitric acid, with hydrochloric acid and nitric acid being preferred. Ion exchange can also be substituted by washing with water.

The zeolite used in step (3) exhibits high catalytic performance as is, but may contain at least one metal selected from (v) sodium, potassium, calcium, silver, and zinc to provide a catalyst with even higher coking resistance and catalytic life, and is preferably a metal-containing zeolite with a metal content of 0.05 to 5.0 wt %. Of these metals, zinc- and/or calcium-containing zeolite is more preferable because it enhances the selectivity for lower aliphatic and aromatic hydrocarbons having 2 to 8 carbon atoms. The method of introducing the metal is not limited, and any method such as impregnation, ion exchange, physical mixing, and vapor deposition is possible.

When the catalyst is used in the (3) step, it is preferable to give the zeolite a shape as a molded body, since the catalyst has excellent handling properties and catalytic performance. When giving the shape, any method may be used for molding, such as a method of molding the zeolite powder into a predetermined shape by compression molding, a method of mixing a predetermined ratio of a binder with the zeolite, and optionally mixing further additives in a predetermined ratio, and molding the mixture into a predetermined shape to give a molded body, and a method of sintering the mixture to give a molded body. In addition to excellent moldability as a molded body, it is preferable to use a molded body made of the zeolite and a binder, as it has high crushing strength and is easy to handle and has excellent catalytic life, and it is more preferable to use a molded body made of the zeolite and silica, as it shows better catalytic performance. The silica in this case may be any type that belongs to the category called silica, and may have a specific crystal structure or may be non-crystalline. Furthermore, there is no restriction on the particle size or agglomeration size of the silica. The mixing ratio of the zeolite and silica is arbitrary, but since this produces a zeolite catalyst that exhibits particularly excellent catalytic performance, ease of handling, and catalyst life, it is preferable for the zeolite:silica ratio to be 50-95:50-5 (weight ratio), and it is particularly preferable for the ratio to be 60-90:40-10.

The zeolite catalyst may have any shape, for example, a cylindrical shape, a cylindrical shape, a polygonal prism shape such as a triangular prism shape, a square prism shape, a pentagonal prism shape, a hexagonal prism shape, a hollow polygonal prism shape, a spherical shape, etc., and among them, a cylindrical shape or a cylindrical shape is preferable because it is a catalyst with excellent continuous productivity and high crushing strength. In addition, the size such as the diameter, width, length, etc., and the density such as the bulk density and true density can be arbitrarily selected in consideration of the packing efficiency, etc., and it is preferable that the zeolite catalyst has a cylindrical shape with a diameter of 1.0 to 10 mm or a cylindrical shape with a thickness of 0.5 to 5.0 mm, because it is a catalyst that can effectively produce lower aliphatic hydrocarbons and aromatic hydrocarbons having 2 to 8 carbon atoms, which are particularly useful as petrochemical products. The zeolite catalyst in the step (3) has a solid acidity of preferably 10 to 150, more preferably 20 to 100, as determined by the NH ₃ -TPD method, because it has high catalytic activity and can extend the catalyst life.

In the step (3), the pyrolysis product is contacted under heating conditions with a catalyst containing a zeolite that satisfies the characteristics (i) to (iv), whereby it is possible to highly selectively produce lower hydrocarbons and aromatic hydrocarbons, particularly olefins, paraffins, and aromatic hydrocarbons having 2 to 8 carbon atoms. The reaction temperature is not particularly limited, and is preferably in the range of 350 to 650°C since it is a more efficient production method, and more preferably in the range of 500 to 600°C since it increases the selectivity of useful components. There is also no restriction on the reaction pressure, and operation is possible within a pressure range of, for example, about 0.05 MPa to 5 MPa. The supply of the pyrolysis product is not particularly limited as the ratio of the volume of the raw pyrolysis product gas to the volume of the catalyst, and can be, for example, a space velocity of about 1 h ^-1 to 50,000 h ^-1 . In that case, it can also be used after dilution with a single or mixed gas selected from an inert gas such as nitrogen, hydrogen, carbon monoxide, and carbon dioxide.

In the production method of the present invention, the lower aliphatic hydrocarbons and aromatic hydrocarbons produced 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 aromatic hydrocarbons such as benzene, toluene, xylene, trimethylbenzene, ethylbenzene, and ethyltoluene.

The manufacturing method of the present invention efficiently reduces the molecular weight of the pyrolysis products of hydrocarbon-based plastics and causes cyclization dehydrogenation reactions, making it possible to produce lower aliphatic hydrocarbons and aromatic hydrocarbons useful as petrochemical products with high selectivity, particularly at a selectivity of 60% or more. In addition, because olefins, paraffins, and aromatic hydrocarbons with carbon numbers of 2 to 8 are produced in a well-balanced manner, it becomes possible to efficiently operate the plant in combination with an existing plant without the need to install a new distillation tower. Specifically, because the distillation towers for each component of the ethylene plant can be fully utilized, it becomes possible to operate the ethylene plant efficiently without excessively reducing the operating rate of the naphtha cracker.

The method of the present invention for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons uses specific processes using two specific types of zeolite catalysts to simultaneously produce lower hydrocarbons and aromatic hydrocarbons from the thermal decomposition products of hydrocarbon plastics. This process produces paraffins, olefins, and aromatic hydrocarbons with carbon numbers of 2 to 8, which are useful as petrochemical products, in high yields, and has an excellent catalyst life, making it an expected industrially useful method.

FIG. 2 is a schematic diagram showing an example of a process for the simultaneous production of lower aliphatic and aromatic hydrocarbons. (2) A schematic diagram showing an example of a method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons through steps (a) and (b). FIG. 2 is a schematic diagram showing an example of a process for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons, which further includes step (d) between steps (a) and (b).

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

- Measurement of solid acidity by NH ₃ -TPD method -
The amount of acid was measured by a method conforming to the ammonia-TPD method (see Measurement of solid acidity by ammonia temperature-programmed desorption method, Catalyst, vol. 42, p. 218 (2000)). The device used was a catalyst analyzer (manufactured by Microtrack Bell, product name: BELCATII), and after pretreatment at 500°C for 1 hour under helium flow, ammonia was adsorbed at 100°C for 30 minutes. Thereafter, the mixture was treated at 125°C for 60 minutes under helium flow containing water vapor by passing through a bubbler, and the ammonia adsorbed at the weak acid site was removed. Thereafter, the mixture was purged at 100°C under helium flow, and then the temperature was raised at 10°C/min under helium flow to measure the amount of thermal desorption. A quadrupole mass spectrometer (product name: BELMASS, manufactured by Microtrack Bell) was used as a detector. The peak derived from the acid site near the desorption temperature of 370° C. in the obtained temperature-programmed desorption curve was fitted with a Gaussian function, and the amount of ammonia desorbed was calculated from the area, thereby obtaining the amount of acid.

-Measurement of average particle diameter (PD)-
The average particle size was measured by a transmission electron microscope (hereinafter, sometimes referred to as TEM) and a scanning electron microscope (hereinafter, sometimes referred to as SEM). For the TEM, a transmission electron microscope (manufactured by JEOL Ltd., product name: JEM-2100, acceleration voltage 200 kV, observation magnification 30,000 times) was used, and a sample lightly crushed in a mortar was ultrasonically dispersed in acetone, dropped onto a plastic support film, and naturally dried to prepare 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.

For the SEM, a scanning electron microscope (Keyence Corporation, product name: VE-9800, accelerating voltage 20 kV, observation magnification 2000x) was used, and a sample that had been lightly crushed in a mortar was placed on the sample stage, gold was vapor-deposited on it to serve as a specimen for microscopic examination, and a photograph was taken. The length of one side of 150 particles in the photograph was measured, and the average value was taken as the average crystal diameter.

~ Powder X-ray diffraction measurement ~
The measurements were performed in air using an X-ray diffraction measurement device (Spectris, product name: X'pert PRO MPD) with a tube voltage of 45 kV and a tube current of 40 mA, using CuKα1. The range of 0.04 to 5 degrees was analyzed at 0.08 degrees/step and 200 seconds/step. In addition, the background corrected for 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 may be used. A common peak search program can be used. For example, when the measurement results, with the horizontal axis being 2θ (degrees) and the vertical axis being intensity (a.u.), are smoothed using the SAVITSKY & GOLAY formula and a sliding polynomial filter, and then the second derivative is taken, if there are three or more consecutive negative values, it can be determined that a peak is present.

~2,4-Dimethylquinoline adsorption infrared absorption spectroscopy measurement (amount of outer surface B acid)~
The infrared absorption spectroscopy was measured by a transmission method using an FT-IR measuring device (product name: FT/IR-6700, manufactured by JASCO Corporation). The spectrum was obtained by 256 integration times using an MCT detector. The sample was molded into a disk with a diameter of 13 mm, and then placed in a disk holder in a quartz vacuum degassing cell, so that it was placed vertically on the infrared light path. As a pretreatment of the sample, the temperature was raised to 400°C at 10°C/min under vacuum evacuation and held 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 adsorbed for 30 minutes, and 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 taken, and the change in infrared absorption due to adsorption was measured. In this difference spectrum, the peak near 3600 cm ^-1 is the absorption spectrum peak of 2,4-dimethylquinoline adsorbed to Brønsted acid. After determining this area intensity, the amount of outer surface B acid was calculated according to the Lambert-Beerr law, using the equation: Amount of B acid (μmol/mg) = A·S/(W·ε) (where A is the peak area intensity of the target peak (cm ^-1 ), S is the cross-sectional area of the sample (cm ² ), W is the sample weight (mg), and ε is the integrated extinction coefficient, 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 according to the Lambert-Beerr law using an integrated absorption coefficient of 1.67 cm·μmol ⁻¹ .

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

Measurement of _SiO2 / _{Al2O3 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 introduced were determined by dissolving the zeolite in a mixed aqueous solution of hydrofluoric acid and nitric acid and measuring the results by inductively coupled plasma atomic emission spectrometry (ICP-AES) using an ICP apparatus (product name: OPTIMA3300DV, manufactured by PerkinElmer).

~(3) Method for testing catalyst activity as an indicator of catalyst life including zeolite used in step ~
After conducting an experiment in which hydrocarbon plastics were used as a raw material to convert them into lower aliphatic hydrocarbons and aromatic hydrocarbons, a catalytic activity test was conducted using the following C4 fraction in order to grasp the catalytic performance of the zeolite in step (3). The conversion rate of the C4 fraction one hour after the start of the reaction was used as an index of the 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.

Catalyst Preparation Example 1
Proton-type MFI zeolite powder (manufactured by Tosoh Corporation, product name: HSZ-840HOA) was calcined in air at 550° C. for 1 hour, and then treated with 30% water vapor at 600° C. Then, it was calcined in air at 550° C. for 2 hours to obtain a powder.

Catalyst Preparation Example 2
The zeolite powder obtained in Catalyst Preparation Example 1 was immersed in distilled water to prepare a suspension. A 0.2 mol/L aqueous solution of sodium nitrate was gradually added to this suspension at room temperature, and the suspension was stirred at 80° C. for 2 hours to perform Na ion exchange. After cooling to room temperature, the suspension was filtered, washed with distilled water, and dried in this order, and then calcined in air at 550° C. for 4 hours to obtain a zeolite powder partially exchanged with Na ions.

100 parts by weight of this powder was mixed with 40 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. 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 3.5 mm). This was dried overnight at 100°C. The dried molded body was fired at 600°C for 2 hours in air circulation to obtain a molded body.

Catalyst Preparation Example 3
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. The 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 fired at 600°C for 2 hours under air circulation to obtain a molded body.

Catalyst Preparation Example 4
100 g of the molded body obtained in Catalyst Preparation Example 3 was immersed in distilled water. It was then immersed in a 0.12 mol/L aqueous calcium hydroxide solution. The molded body was filtered, washed with water, and then immersed again in a 0.2 mol/L aqueous sodium nitrate solution. It was dried overnight at 110°C, and then calcined for 5 hours at 550°C in an air stream to obtain a zeolite (molded body) in which calcium ions were partially exchanged with sodium ions.

Catalyst Preparation Example 5
Amorphous aluminosilicate gel was added to an aqueous solution of tetrapropylammonium hydroxide and sodium hydroxide and suspended. MFI type 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% by weight based on the weight of _Al2O3 and _SiO2 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 obtained raw material composition was sealed in a stainless steel autoclave and crystallized for 4 days while stirring at 115°C to obtain a slurry mixture. After the crystallization, the slurry mixture was separated into solid and liquid using a centrifugal settler, and the solid particles were washed with a sufficient amount of pure water and dried at 110°C to obtain 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, filtered again, and dried overnight at 100°C. It was calcined in air at 550°C for 1 hour, and then treated with 30% water vapor at 600°C for 2 hours.

The obtained 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 and filtered again to obtain zeolite.

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 were added to 100 parts by weight of the zeolite prepared above and 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 fired at 600°C for 2 hours in air circulation to obtain a molded body.

Catalyst Preparation Example 6
100 g of the MFI zeolite molded body obtained in Catalyst Preparation Example 5 was immersed in 109.9 g of a 0.75 mol/L aqueous zinc acetate solution for 30 minutes. The molded body was filtered off, dried overnight at 110° C., and then calcined for 5 hours at 550° C. in an air stream to obtain a zeolite (molded body) partially containing zinc ions.

Example 1
The apparatus used was a fixed-bed gas-phase flow-type reactor having a stainless steel autoclave (inner volume 200 ml) for carrying out step (1) of melting the hydrocarbon plastic and step (2) of thermal decomposition, and a stainless steel reaction tube (inner diameter 16 mm, length 600 mm) for carrying out step (3) of converting the thermal decomposition product into lower hydrocarbons. The stainless steel reaction tube was packed in the middle with a zeolite catalyst molded body, and was subjected to a thermal pretreatment at 530° C. under a dry air flow.

A stainless steel autoclave was charged with high density polyethylene (HDPE) that had been lost during the production process of a low pressure polyethylene manufacturing facility and 5 g of the zeolite catalyst (powder) prepared in Catalyst Preparation Example 1, and the contents were replaced with nitrogen. The temperature was slowly raised to 180°C to melt the HDPE, and then the temperature was raised to 450°C under a nitrogen gas flow (40 ml/min), and the resulting hydrocarbons were subjected to thermal decomposition and used as thermal decomposition products. The thermal decomposition products were fed to a stainless steel reaction tube by nitrogen gas, and reacted with the zeolite catalyst (molded body) prepared in Catalyst Preparation Example 5 (catalyst weight: 3.8 g, flow gas: nitrogen 40 ml/min, reaction temperature: 585°C, reaction time: 24 hours). A ceramic tubular furnace was used to control the temperature of the stainless steel reaction tube.

The reaction outlet gas and reaction liquid were collected, and the gas and liquid components were 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 a 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 results are shown in Table 1. Useful components, lower aliphatic hydrocarbons and aromatic hydrocarbons with carbon numbers of 2 to 8, were obtained in high yields. In addition, even after the reaction was completed, the zeolite catalyst prepared in Catalyst Preparation Example 5 maintained high catalytic performance, allowing for stable production and also exhibiting excellent coking resistance.

Example 2
The apparatus used was a combination of a stainless steel autoclave (capacity 200 ml) for carrying out step (1) of melting hydrocarbon plastics and step (2) of thermal decomposition, and a fixed-bed gas-phase flow-type reactor having a stainless steel reaction tube (inner diameter 16 mm, length 600 mm) for carrying out step (3) of converting the thermal decomposition products into lower hydrocarbons. The stainless steel reaction tube was packed with the zeolite catalyst (molded body) prepared in Catalyst Preparation Example 2 in the front stage and the zeolite catalyst (molded body) prepared in Catalyst Preparation Example 6 in the rear stage, and was subjected to a heat pretreatment at 530° C. under a dry air flow.

High density polyethylene (HDPE) that was lost during the manufacturing process of a low pressure polyethylene manufacturing facility was placed in a stainless steel autoclave and purged with nitrogen. The temperature was slowly raised to 180°C to melt the HDPE, and then the temperature was raised to 450°C under a nitrogen gas flow (40 ml/min) to perform thermal decomposition, producing a thermal decomposition product that is a hydrocarbon mixture. The thermal decomposition product was fed into a stainless steel reaction tube by nitrogen gas and reacted in contact with two types of zeolite catalysts (molded bodies) (catalyst weight: 3.8 g for each, flow gas: nitrogen 40 ml/min, reaction temperature: 530°C, reaction time: 24 hours).

The product was analyzed in the same manner as in Example 1, and the results are shown in Table 1.

Example 3
A stainless steel autoclave was filled with high density polyethylene (LDPE) that had become a waste product during the manufacturing process of a high pressure polyethylene manufacturing facility, and the atmosphere was replaced with nitrogen. The temperature was slowly raised to 180°C to melt the LDPE, and then the temperature was raised to 450°C under a nitrogen gas flow (40 ml/min) to perform thermal decomposition. Gas components and liquid components at room temperature and pressure were collected separately as thermal decomposition products.

The liquid components were distilled (pressure 2.6 kPa, reflux ratio 20) using a packed distillation column (Shibata Scientific, product name: HP-1000) with 35 theoretical plates equipped with a mantle heater type still, a thermometer, a reflux valve, and an effluent receiver, and the distillation was terminated when the component with a top temperature of 150°C flowed out.

A fixed-bed gas-phase flow reactor with a stainless steel reaction tube (inner diameter 16 mm, length 600 mm) was used to convert the thermal decomposition products into lower hydrocarbons. The stainless steel reaction tube was filled with the zeolite catalyst (formed body) prepared in Catalyst Preparation Example 2 in the front stage and the zeolite catalyst (formed body) prepared in Catalyst Preparation Example 5 in the rear stage, and a heating pretreatment was performed at 530°C under a dry air flow.

The liquid components collected in the effluent receiver were analyzed using a liquid delivery pump, and the gas components were analyzed using a gas chromatograph. Based on the analysis results, simulated gas components were prepared using reagents, and the liquid and gas components were fed into a stainless steel reaction tube using a mass flow controller, where they were contacted with a zeolite catalyst (molded body) and reacted (catalyst weight: 3.8 g for each, gas flow: nitrogen 40 ml/min, reaction temperature: 530°C, reaction time: 24 hours).

The product was analyzed in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1
The thermal decomposition of hydrocarbon-based plastics and the reaction evaluation with the zeolite catalyst were carried out in the same manner as in Example 2, except that the zeolite catalyst (molded body) prepared in Catalyst Preparation Example 2 was not used, and the zeolite catalyst (molded body) prepared in Catalyst Preparation Example 3 was used instead of the zeolite catalyst (molded body) prepared in Catalyst Preparation Example 6. The results are shown in Table 1.

The method for producing lower aliphatic hydrocarbons and aromatic hydrocarbons of the present invention makes it possible to convert hydrocarbon plastics, particularly the pyrolysis products of waste plastics, with high selectivity into paraffins, olefins, and aromatic hydrocarbons with 2 to 8 carbon atoms, which are useful as petrochemical products, and the industrial value of this production method is extremely high.

Claims (11)

A method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons from thermal decomposition products of hydrocarbon plastics, the method comprising at least the following steps (1) to (3):
Step (1): A step of heating and melting a hydrocarbon-based plastic.
Step (2): A step of thermally decomposing a heat-molten hydrocarbon-based plastic in the presence of a zeolite having an acid amount (solid acid amount by the NH ₃ -TPD method) of 200 μmol/g or less, determined from the high-temperature desorption amount in an ammonia temperature programmed desorption spectrum, to obtain a thermal decomposition product.
Step (3): A step of contacting the thermal cracking product with a catalyst containing a zeolite satisfying the following characteristics (i) to (iv) under heated conditions to simultaneously produce lower aliphatic hydrocarbons and aromatic hydrocarbons:
(i) The average particle size is 100 nm or less.
(ii) 10-ring pore zeolites of the MFI or MEL type.
(iii) the Bronsted acid amount of the outer surface is 0.1 to 10.0 μmol/g.
(iv) the total Bronsted acidity is 0.01 to 1.0 mmol/g. The method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to claim 1, characterized in that the zeolite in step (2) is a proton-type aluminosilicate. The method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to claim 1 or 2, characterized in that the zeolite in step (2) is a proton-type aluminosilicate and contains at least one metal selected from metals belonging to Groups IA and IIA of the periodic table. The method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to any one of claims 1 to 3, characterized in that the zeolite in step (2) is a proton-type aluminosilicate, and is a zeolite in which some or all of the surface OH groups have been silylated. 5. The method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to any one of claims 1 to 4, wherein the step (2) comprises at least the following steps (a) and (b):
Step (A): A first decomposition step in which a heat-molten hydrocarbon plastic is thermally decomposed in the absence of oxygen and without a catalyst.
Step (b): A second decomposition step in which the product is contacted with zeolite and decomposed by heating after step (a) to obtain a thermal decomposition product. The method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to claim 5, characterized in that between steps (a) and (b), there is a step of separating the thermal decomposition product into high-boiling components and low-boiling components by distillation, in which step (b) involves contacting and thermally decomposing the high-boiling components with zeolite, and in step (d), mixing the low-boiling components from step (a) with the decomposition product from step (b) to obtain a thermal decomposition product. A method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to any one of claims 1 to 6, characterized in that the zeolite in step (3) contains at least one metal selected from sodium, potassium, calcium, silver, and zinc, and has a metal content of 0.05 to 5.0 wt %. A method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to any one of claims 1 to 7, characterized in that the hydrocarbon-based plastic is at least one selected from the group consisting of polyethylene, polypropylene, ethylene propylene rubber, and polystyrene. A method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to any one of claims 1 to 8, characterized in that the hydrocarbon plastics are used waste plastics and/or waste products during the production and processing of hydrocarbon plastics. A method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to any one of claims 1 to 9, characterized in that the total selectivity of lower aliphatic hydrocarbons and aromatic hydrocarbons is 60% or more. A method for simultaneously producing lower aliphatic hydrocarbons and aromatic hydrocarbons according to any one of claims 1 to 10, characterized in that the lower aliphatic hydrocarbons are one or more of olefins having 2 to 8 carbon atoms and paraffins having 2 to 8 carbon atoms, and the aromatic hydrocarbons are one or more of aromatic hydrocarbons having 6 to 8 carbon atoms.