JP2011079815A - Method of producing p-xylene - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing p-xylene with high p-xylene selectivity, from ethylene, i.e., a starting material by causing ethylene to contact a catalyst. <P>SOLUTION: The method of producing p-xylene by allowing a raw material composed of ethylene as its main component to contact a catalyst in a reactor, preferably in a gas phase, is characterized in that the active component of the catalyst is a zeolite and the amount of acids present on the outer surface of the zeolite is not higher than 1% relative to the amount of the acids present in the whole zeolite. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing p-xylene by bringing a raw material containing ethylene into contact with a catalyst.

Of the xylene isomers, p-xylene is the most important in that it is used as a raw material for terephthalic acid, which is a monomer of polyester.
p-Xylene is usually subjected to aromatic extraction or fractionation of C8 aromatic hydrocarbon mixture obtained by reforming naphtha, followed by aromatic extraction or fractionation, or cracked gasoline by-produced by thermal decomposition of naphtha. It is produced from a C8 aromatic hydrocarbon mixture obtained in this way. The composition of the C8 aromatic hydrocarbon mixture raw material varies widely, and usually 10 to 40% by weight of ethylbenzene, 12 to 25% by weight of p-xylene, 30 to 50% by weight of m-xylene, and 12 to 20% of o-xylene. The desired p-xylene content is 25% by weight, and the content in the mixture raw material is low. Therefore, there is a drawback that the efficiency of the subsequent purification and separation process is low.

On the other hand, techniques for producing aromatic hydrocarbons from hydrocarbon raw materials other than aromatic hydrocarbons such as aliphatic hydrocarbons have been studied. For example, those using paraffin as the main raw material, those using olefins having 3 or more carbon atoms such as propylene and butene, methanol, dimethyl ether obtained from hydrogen / carbon monoxide mixed gas obtained by reforming natural gas Various materials have been studied.
However, these aromatic hydrocarbon production methods are difficult to procure raw materials or have low practicality such as a low aromatic yield, and are not suitable as a method for producing p-xylene.

As a method for producing p-xylene, a method using ethylene as a raw material has been studied. As a method of using ethylene as a raw material, a technique for producing p-xylene using a zeolite whose surface is treated with a compound containing silicon as a catalyst has been studied.
However, in most cases, p-xylene is obtained as a secondary product in the methylation reaction of toluene with methanol, or the disproportionation reaction of toluene, rarely the alkylation reaction of ethylbenzene, or the disproportionation reaction of ethylbenzene. Only.
As a method for producing p-xylene using ethylene as a raw material, Non-Patent Documents 1 and 2 use Ga-ZSM-5 as a catalyst, and the ethylene concentration in the reaction mixture gas is very low at 5 mol%. The examination result of is described. However, in the region where the aromatic yield is high, the selectivity of m-xylene is high, the selectivity of p-xylene is low, and the practicality is still poor.

Journal of Catalysis, 205 (2002), p398-403 Microporous and Mesoporous Materials 51 (2002), p203-210

  As described above, in the conventional technology, the aromatic hydrocarbon yield and p-xylene selectivity from the ethylene raw material are not sufficient, and the selectivity of p-xylene decreases with the increase of the aromatic hydrocarbon yield. Therefore, a high p-xylene yield could not be achieved.

  An object of the present invention is to provide a production method in which ethylene is used as a starting material and p-xylene selectivity is high, in which the disadvantages of the prior art are solved.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies, and as a result, zeolite having a small amount of acid on the outer surface relative to the total amount of acid is used as an active component of the catalyst. It has been found that p-xylene can be produced from a raw material containing ethylene in a yield, and has led to the present invention.

  That is, the first gist of the present invention is a process for producing p-xylene by bringing a raw material mainly composed of ethylene into contact with a catalyst in a reactor, wherein the active component of the catalyst is zeolite, and the zeolite The p-xylene production method is characterized in that the acid amount of the outer surface of the zeolite is 1% or less with respect to the acid amount of the whole zeolite.

  The second gist lies in the method wherein the zeolite is a crystalline silicate containing at least one element selected from the group consisting of elements belonging to Group IIIb of the periodic table.

The third gist lies in a method in which the element belonging to Group IIIb of the periodic table is Al and / or Ga in the production method.
The fourth gist lies in a method in which the zeolite has a pore diameter of 0.5 nm or more and 0.75 nm or less in the production method.

The fifth gist lies in a method in which, in the production method, the zeolite has an oxygen 10-membered ring channel structure.
The sixth gist lies in a method in which the zeolite has an MFI structure in the production method.

The seventh gist lies in a method in which the zeolite contains Al as an element and the SiO ₂ / Al ₂ O ₃ molar ratio is 5 or more and 1000 or less in the production method.
The eighth gist resides in a method in which, in the production method, the zeolite contains Ga as an element and the SiO ₂ / Ga ₂ O ₃ molar ratio is 5 or more and 1000 or less.

  The ninth gist lies in a method in which, in the production method, the zeolite is obtained by silylated the outer surface of the zeolite.

  According to the present invention, p-xylene can be produced with high selectivity and high yield by bringing a raw material containing ethylene into contact with a catalyst in a reactor.

  Below, the typical aspect for implementing this invention is demonstrated concretely, However, This invention is not limited to the following forms, unless the summary is exceeded.

  In the method for producing p-xylene of the present invention, a catalyst containing zeolite as an active component (hereinafter sometimes referred to as “zeolite catalyst”) is brought into contact with a raw material containing ethylene, preferably in the gas phase. -In the reaction for producing xylene, the zeolite is characterized in that the zeolite has an outer surface acid amount described below of 1% or less of the acid amount of the entire zeolite described later.

Here, when a raw material containing ethylene is brought into contact with the zeolite catalyst, an aromatic compound is generated with a carbocation as an intermediate. Specifically, the following reactions (i) to (iv) occur continuously. It is estimated that
(I) Ethyl cations are generated by adsorption of ethylene to the acid sites of the zeolite catalyst, and the cations and ethylene cause a dimerization reaction.
(Ii) C8 olefin is produced by the subsequent trimerization reaction and further the tetramerization reaction.
(Iii) A C8 diene and a ring closure reaction accompanied by a dehydrogenation reaction occur from a C8 olefin, and a C8 aromatic hydrocarbon (for example, xylene isomer mixture or ethylbenzene) is generated.
(Iv) Benzene, toluene, C9 aromatic hydrocarbons and the like are produced from C8 aromatic hydrocarbons by disproportionation and dealkylation reactions.
Although it is estimated, the zeolite catalyst used in the present invention in which the amount of acid on the outer surface is reduced at this time produces C8 aromatic hydrocarbons due to the shape selectivity characteristic of the zeolite pores (iii), and further the acid on the outer surface. It is considered that p-xylene is selectively obtained with high yield by suppressing the side reaction (iv) occurring on the spot.

  First, the catalyst (1) used in the present invention will be described in detail, and then the xylene production method (2) of the present invention will be described in detail.

(1) Catalyst The catalyst used in the present invention means a catalyst having zeolite as an active component and capable of generating p-xylene from ethylene.
Zeolite, which is an active component, may be used as it is as a catalyst in the reaction, or may be used in the reaction by granulating and molding using a substance or binder that is inert to the reaction, or by mixing them. Examples of the substance or binder inert to the reaction include alumina or alumina sol, silica, silica gel, quartz, and a mixture thereof.
Mixing with these substances is effective in reducing the cost of the entire catalyst and acting as a heat sink for heat shielding assist during catalyst regeneration, and is also effective in increasing the density of the catalyst and increasing the catalyst strength.
The zeolite used in the present invention has the following physical properties.

(1-1) Zeolite Zeolite is a tetrahedral structure of TO ₄ units (T is the central atom) that share O atoms and connect three-dimensionally to form open regular micropores. Refers to crystalline material. Specifically, silicates, phosphates, germanates, arsenates, etc. described in the data collection of the Structure Committee of the International Zeolite Association (hereinafter referred to as “IZA”) Is included.

(1-2) Structure The pore diameter of the zeolite used in the present invention is not particularly limited, but is usually 0.5 nm or more, usually 0.75 nm or less, preferably 0.65 nm or less. It has something.
The term “pore diameter” as used herein refers to a crystallographic free diameter of the channels defined by the International Zeolite Association (IZA). The shape of the pore is not particularly limited, but when the cross-sectional shape is a perfect circle, it means the average diameter, and when the shape is an ellipse, it means the major axis.

  When the pore diameter of the zeolite is less than the lower limit, the diffusion barrier of the generated aromatic hydrocarbons to the outer surface crystals of the zeolite becomes high, and it may be difficult to desorb into the gas phase. It may be difficult to produce aromatic hydrocarbons including xylene at a high rate.

  When the pore diameter of the zeolite exceeds the upper limit, by-products such as aromatics having 9 or more carbon atoms and polycyclic aromatics having a plurality of aromatic rings tend to increase. It may be difficult to produce p-xylene at a high rate.

The number of oxygen constituting the pores of the zeolite used in the present invention is not particularly limited, but usually, one having a structure containing a 10-membered or 12-membered ring of oxygen is preferable, and among them, a 10-membered ring is preferable. What has a structure containing is preferable.
Here, the structure containing an oxygen 10-membered ring or 12-membered ring means that the zeolite has 10 or 12 pores of TO ₄ units (where T represents Si, P, Ge, Al, Ga, etc.). A ring structure consisting of
Further, the type of pores possessed by the zeolite is not particularly limited, and pores having different oxygen numbers may be mixed, and even if there are one type of pores having the same oxygen number and size, Two or more kinds of pores having the same oxygen number but different sizes may be mixed.
As a zeolite containing only a 10-membered oxygen ring and having only pores of 10-membered oxygen ring or less, specifically expressed by a code defined by the International Zeolite Association (IZA), for example, AEL, AFO, EUO, FER, MEL, MFI, MTT, MWW, TON and the like can be mentioned. Among them, MFI and MWW are preferable, and MFI is more preferable.
Examples of the zeolite containing a 12-membered oxygen ring and having only pores of 12-membered oxygen or less include AFI, ATO, BEA, CON, FAU, GME, LTL, MOR, MTW, OFF, and the like.

  The element constituting the zeolite used in the present invention is not particularly limited, but crystallinity containing Si and at least one element selected from elements belonging to Group IIIb of the periodic table in its skeleton. Silicates are preferred. The element belonging to Group IIIb of the periodic table is preferably Al or Ga, and more preferably contains both Al and Ga.

The framework density of the zeolite is not particularly limited, and is preferably 18 or less, more preferably 17 or less, and the lower limit is usually 13 or more, preferably 14 or more.
Here, the framework density (unit: T / nm ³ ) is the number of T atoms (atoms other than oxygen among the atoms constituting the skeleton of the zeolite) present per unit volume (1 nm ³ ) of the zeolite. This means that this value depends on the structure of the zeolite.

(1-3) Composition In the vicinity of the element belonging to Group IIIb of the periodic table in the zeolite skeleton, cations such as Na + are present in order to maintain the charge balance. This cation can be easily exchanged with another cation, and the place where it exists is called an ion exchange site.
As the zeolite used in the present invention, a proton exchange type in which the ion exchange site is a proton is usually used, but some of the elements of the ion exchange site are alkali metals such as Na and K, and alkaline earth metals such as Mg and Ca. It may be exchanged for a metal or other metal element. In the crystalline aluminosilicates, a part of Al atoms constituting the aluminosilicate may be substituted with other metal atoms.

  Besides replacing part of the ion exchange site with a metal element, alkali metals such as Na and K; alkaline earth metals such as Mg and Ca; Cr, Cu, Ni, Fe, Mo, W, Pt, Re, etc. These transition metals may be metal-supported. Here, the metal loading can be usually performed by an impregnation method such as an equilibrium adsorption method, an evaporation to dryness method, or a pore filling method.

When the zeolite is a crystalline silicate, SiO ₂ / M ₂ O ₃ (where M represents a trivalent element such as Al, Ga, Fe, Ti, and B. Hereinafter, it may be referred to as a hetero element) molar ratio. Is preferably 5 or more, more preferably 10 or more, and the upper limit is usually 1000 or less. If this value is too low, the durability of the catalyst tends to decrease, and if it is too high, the catalytic activity tends to decrease.

When the crystalline silicate is a crystalline aluminosilicate containing Al, the molar ratio of SiO ₂ / Al ₂ O ₃ is such that a part of the Al atoms constituting this is removed by steaming, acid treatment, etc. A material having a SiO ₂ / Al ₂ O ₃ ratio can also be used.
Usually, the molar ratio of SiO ₂ / Al ₂ O ₃ is 5 or more, preferably 10 or more, more preferably 30 or more, and usually 1000 or less, preferably 500 or less, more preferably 150 or less. In addition to the above method, the molar ratio of SiO ₂ / Al ₂ O ₃ can be adjusted by controlling the amount of Al during synthesis.

When the SiO ₂ / Al ₂ O ₃ molar ratio of the crystalline aluminosilicate is less than the lower limit, the durability of the catalyst tends to decrease. On the other hand, if the SiO ₂ / Al ₂ O ₃ molar ratio exceeds the upper limit, the catalytic activity tends to decrease.

When the crystalline silicate is a crystalline gallosilicate containing Ga, the SiO ₂ / Ga ₂ O ₃ molar ratio is usually 5 or more, preferably 10 or more, more preferably 30 or more, and usually 1000 or less, preferably 500 Below, more preferably 150 or less.
When the SiO ₂ / Ga ₂ O ₃ molar ratio of the crystalline gallosilicate as the catalyst active component is less than the lower limit, the durability of the catalyst is lowered, which may not be preferable. On the other hand, if the SiO ₂ / Ga ₂ O ₃ molar ratio exceeds the upper limit, the catalytic activity may be lowered.

  The method of containing Ga is not particularly limited, and a Ga compound raw material is added at the time of crystalline silicate synthesis, or a part or all of the Al atoms constituting the crystalline aluminosilicate are replaced with Ga element, or Ga can be contained by a known method such as impregnation or support in crystalline silicates.

(1-4) Acid amount The acid amount of the outer surface of the zeolite used in the present invention (hereinafter sometimes referred to as the outer surface acid amount) is sometimes referred to as the total acid amount of the zeolite (hereinafter referred to as the total acid amount). ) To 1% or less. Preferably it is 0.8% or less, More preferably, it is 0.7% or less, More preferably, it is 0.6% or less. The lower limit is not particularly limited, and the lower the better, the more usually 0.01% or more.

  When the outer surface acid amount exceeds the above upper limit with respect to the total acid amount, there are many acid points on the outer surface of the zeolite (hereinafter sometimes referred to as outer surface acid points), so a high selection from the pores of the zeolite P-xylene produced at a high rate reacts again on the acid surface on the outer surface, resulting in a distribution of aromatic hydrocarbons having 6 to 8 carbon atoms close to the thermal equilibrium composition, and the selectivity for p-xylene decreases. Therefore, it is not preferable. In order to suppress the side reaction occurring at the outer surface acid point, it is necessary to adjust the outer surface acid amount to 1% or less with respect to the total acid amount.

Here, the amount of acid on the outer surface of the zeolite indicates the total amount of acid sites present on the outer surface of the zeolite. The amount of acid on the outer surface is the amount of 4-methylquinoline per catalyst weight when 4-methylquinoline is adsorbed on the acid sites on the zeolite surface and then the adsorbed 4-methylquinoline is released from the catalyst. The value obtained by measuring. Specifically, the amount of acid on the outer surface is a pretreatment of drying at 500 ° C. for 1 hour under vacuum, then contacting and adsorbing with 4-methylquinoline vapor under reduced pressure at 200 ° C., exhausting at 200 ° C., and helium Desorption amount of 4-methylquinoline per unit weight of zeolite at 30 to 900 ° C. determined by the temperature rising desorption method of the zeolite obtained by removing excess 4-methylquinoline by circulation at a temperature rising rate of 10 ° C./min Say.
4-Methylquinoline is a probe molecule with a size that does not enter the zeolite pores. Therefore, since it is adsorbed only at the acid points on the outer surface, the amount of acid on the outer surface can be measured.
The outer surface acid amount is not particularly limited, and the smaller the better, the lower limit is not particularly limited.

  The total acid amount of zeolite is to measure the amount of pyridine per catalyst weight when pyridine is adsorbed on acid sites on both the zeolite surface and inside the zeolite, and then the adsorbed pyridine is desorbed from the catalyst. The value obtained by Specifically, the total amount of acid is obtained by pre-drying at 500 ° C. for 1 hour under vacuum as a pretreatment, and contact-adsorbing with pyridine vapor under a reduced pressure condition of 200 ° C., and removing excess pyridine by flowing helium at 200 ° C. The amount of pyridine desorbed per unit weight of zeolite at 30 to 800 ° C. determined by the temperature rising desorption method of the obtained zeolite at a temperature rising rate of 10 ° C./min.

Pyridine is a probe molecule with a size that also enters the zeolite pores. Therefore, since it is adsorbed on both the outer surface and the acid sites in the pores, the total acid amount can be measured.
The total acid amount is usually 4.8 mmol / g or less, preferably 2.8 mmol / g or less. Moreover, a minimum is 0.15 mmol / g or more normally, Preferably it is 0.30 mmol / g or more. When the amount of acid is too large, deactivation due to coke adhesion is accelerated, and Al constituting the zeolite easily escapes from the skeleton, so that the acid strength per acid point tends to be weakened. If the amount of acid is too small, the number of active sites of the reaction decreases, and the ethylene conversion tends to decrease.

(1-5) Method for reducing the ratio of the external surface acid amount to the total acid amount The method for decreasing the ratio of the external surface acid amount to the total acid amount is not particularly limited, but is a commonly used method known per se, for example, zeolite Is treated with a substance that has a size that does not enter the zeolite pores and reacts with the surface acid sites, specifically, a method of treating with a compound such as a silylating agent (silylation), ethylenediamine, etc. The method etc. which process with amines are mentioned. In addition, a method of synthesizing a zeolite with a large amount of acid inside the zeolite crystal and a small amount of acid outside the zeolite crystal by controlling the gel composition and the like at the time of synthesizing the zeolite is also included. Hereinafter, the treatment method will be described in detail with silylation as an example, but the present invention is not limited to the following description.

(Silylation)
By performing silylation on the outer surface of the zeolite, the ratio of the outer surface acid points to the total acid amount can be reduced. The method of silylation is not particularly limited, and a method known per se may be used, but liquid phase silylation using alkoxysilane or gas phase silylation using chlorosilane is used.

  Specific examples of silylating agents include quaternary alkoxysilanes such as tetramethoxysilane and tetraethoxysilane, tertiary silanes such as trimethoxymethylsilane and triethoxymethylsilane, dimethoxydimethylsilane, diethoxydimethylsilane and the like. Secondary alkoxysilanes, primary alkoxysilanes such as methoxytrimethylsilane and ethoxytrimethylsilane. Further, chlorosilanes such as tetrachlorosilane, dimethyldichlorosilane, and trimethylchlorosilane can be used. Of these, tetraethoxysilane is preferable for alkoxysilane, and tetrachlorosilane is preferable for chlorosilane.

In the case of silylation in the liquid phase, it is preferable to use alkoxysilane, and it is more preferable to use tetraethoxysilane.
The solvent used in the liquid phase silylation method is not particularly limited, and examples thereof include organic solvents such as benzene, toluene, hexamethyldisiloxane, and water.

  In the liquid phase silylation method, the amount ratio (mol / mol) of silylating agent / zeolite in the treatment solution is usually 5 or less, preferably 3 or less, and the lower limit is usually 0.05 or more, preferably 0.8. 1 or more. If this value is too high, pores tend to be blocked due to excessive silylation, and if it is too low, silylation may be insufficient and the external surface acid amount may not be reduced.

  The temperature of silylation depends on the type of silylating agent and solvent, but is usually 140 ° C. or lower, preferably 120 ° C. or lower, and the lower limit is usually 20 ° C. or higher, preferably 40 ° C. or higher. If the treatment temperature is too high, silylation may not occur efficiently due to evaporation of the liquid, and if the temperature is too low, the reaction rate of silylation tends to be slow.

The treatment time for silylation is usually 0.5 hours or more, preferably 2 hours or more, and there is no particular upper limit for the treatment time. When the treatment time is too short, sufficient silylation does not occur, and the decrease in the acid amount on the outer surface may be insufficient.
Specifically, the method of silylating in the liquid phase is preferably a method using tetraethoxysilane. To the zeolite, the solvent hexamethyldisiloxane and the silylating agent tetraethoxysilane are added and stirred at 100 ° C., 6 A time-reflux treatment is performed, and after the treatment, a solid-liquid is separated by filtration, and dried at 100 ° C. for 6 hours to obtain a silylated zeolite.

  In the gas phase silylation method, the deposited silica is generally 20 wt% or less, preferably 18 wt% or less, based on the zeolite. The lower limit of the deposition amount is usually 0.1% by weight or more, preferably 1% by weight or more. If this value is too high, pores tend to be clogged due to excessive silylation, and if it is too low, silylation may be insufficient and the amount of acid on the outer surface may not be reduced.

  The temperature of the gas phase silylation is usually 20 ° C. or higher, preferably 100 ° C. or higher, and the upper limit is usually 500 ° C. or lower, preferably 400 ° C. or lower. If the temperature is too high, decomposition of the silylating agent and collapse of the skeleton of the zeolite tend to occur, and if the treatment temperature is too low, the silylation reaction may not proceed easily.

The treatment time is usually 0.5 hours or more, preferably 3 hours or more, and there is no particular upper limit for the treatment time. When the treatment time is too short, sufficient silylation does not occur, and the decrease in the acid amount on the outer surface may be insufficient.
Specifically, a method using chlorosilane is preferred as a method for silylation in the gas phase, and the zeolite can be treated with chlorosilane as a silylating agent at 300 ° C. for 3 hours under a helium flow to obtain a silylated zeolite.

(1-6) Method for Preparing Zeolite The above-mentioned zeolite is a commonly used method known per se, such as a hydrothermal synthesis method, that is, a crystal containing a silica raw material, a hetero element source, and an alkali (earth) metal element source. A precursor aqueous gel can be prepared and synthesized by a method such as heating. Further, after the hydrothermal synthesis, as described above, the composition can be changed by modification of acid amount reduction, impregnation, loading, etc., as necessary.
The zeolite used in the present invention is not limited as long as it has the above physical properties and composition, and may be prepared by any method. Commercially available zeolite can also be used.

(2) Method for Producing p-Xylene The method for producing p-xylene according to the present invention is characterized in that p-xylene is produced from ethylene using the above catalyst containing zeolite. In this production method, p-xylene can be produced by a method known per se, that is, a method in which a raw material containing ethylene is contacted with the catalyst in a suitable reactor under suitable reaction conditions.

(2-1) Raw material containing ethylene The raw material used in the present invention is not particularly limited as long as it contains ethylene. For example, those produced by catalytic cracking or steam cracking from petroleum sources, those obtained by performing Fischer-Tropsch synthesis using hydrogen / carbon monoxide mixed gas obtained by coal gasification as raw materials, ethane Obtained by dehydrogenation or oxidative dehydrogenation of propylene, obtained by metathesis reaction and homologation reaction of propylene, obtained by contact reaction with a solid acid catalyst from oxygenate raw materials such as methanol and / or dimethyl ether, Those obtained by various known methods such as those obtained from the dehydration reaction of the corresponding alcohol (ethanol) can be arbitrarily used. At this time, a state in which components other than ethylene resulting from various production methods are arbitrarily mixed may be used as they are, purified ethylene may be used, or purified ethylene may be used.

  Examples of the alcohol obtained by dehydration of alcohol include those obtained by a modification reaction of plant-derived alcohols, those obtained by fermentation, and those obtained from organic substances such as recycled plastic and municipal waste. In addition, since ethanol is easily dehydrated and converted into ethylene due to acid sites in the zeolite, the case where ethanol is directly introduced into the reactor is also included in the present invention.

  Further, when p-xylene is produced by the method of the present invention, ethylene contained in the reactor outlet gas may be recycled. The component to be recycled is usually ethylene, but the olefin and paraffin after separation of other aromatic hydrocarbons may be recycled to serve as an ethylene source.

(2-2) Reaction conditions (2-2-1) Substrate concentration There is no particular limitation on the concentration of ethylene in all feed components fed to the reactor (ie, substrate concentration), but usually 1 volume in all feed components. % Or more, preferably 5% by volume or more, usually 90% by volume or less, preferably 50% by volume or less.
If the substrate concentration is less than the lower limit, the reaction rate becomes slow, so a large amount of catalyst is required, and the reactor tends to be too large. On the other hand, if the substrate concentration exceeds the above upper limit, the load on the catalyst becomes too high and the activity tends to be difficult to obtain. Therefore, it is preferable to dilute ethylene with a diluent described below as necessary so as to obtain such a substrate concentration.

  In addition to ethylene, components to be supplied into the reactor include helium, argon, nitrogen, carbon monoxide, carbon dioxide, hydrogen, water, methane, hydrocarbons such as paraffins and olefins, and mixtures thereof. A gas inert to the reaction can optionally be present.

(2-2-2) Reaction temperature The reaction temperature in the method of the present invention is not particularly limited, but is usually 200 ° C or higher, preferably 300 ° C or higher, and usually 700 ° C or lower, preferably 600 ° C or lower. is there. When the reaction temperature is less than the lower limit, the reaction rate tends to decrease, and the yield of the target product also tends to decrease. On the other hand, when the reaction temperature exceeds the upper limit, xylene in aromatics, and further, p-xylene selectivity in xylene tends to decrease, yield of the target product tends to decrease, and catalyst stability decreases. There is a case.

(2-2-3) Reaction pressure
The reaction pressure in the method of the present invention is not particularly limited, but is usually 0.1 kPa (absolute pressure, hereinafter the same) or more, preferably 7 kPa or more, more preferably 50 kPa or more, usually 10 MPa or less, preferably 5 MPa. It is as follows. If the reaction pressure is less than the lower limit, the reaction rate tends to be slow, and if the reaction pressure exceeds the upper limit, the amount of undesirable by-products such as high-boiling aromatic hydrocarbons having 9 or more carbon atoms increases, The yield of the desired product tends to decrease.

(2-2-4) but are not a space velocity space velocity particularly limited, and usually between 0.01 hr ^-1 for 500HR ^-1, preferably in the range from 0.1 hr ^-1 to 100 Hr ^-1. If the space velocity is too high, ethylene in the reactor outlet gas increases, and the aromatic hydrocarbon yield may be lowered. On the other hand, if the space velocity is too low, m-xylene in xylene increases and the target p-xylene yield may decrease.

  The space velocity referred to here is the flow rate of ethylene (weight per unit time) as the reaction raw material per weight of the catalyst (catalytic active component), where the weight of the catalyst is used for the granulation / molding of the catalyst. It is the weight of the catalyst active component (zeolite) which does not contain the inactive component and binder used.

(2-2-5) Conversion The ethylene conversion is not particularly limited and is usually 20% or more, preferably 40% or more, more preferably 50% or more, and the upper limit is not particularly limited, but is usually 80% or more. Yes, the higher the better.

The reaction conditions such as the reaction temperature and WHSV (weight space velocity) in the production method of the present invention can be arbitrarily set according to known methods. However, when a large amount of unreacted ethylene is present in the effluent component from the reaction system, In order to increase the utilization rate of ethylene, it is necessary to recycle at least a part of the reactor to the reactor and to recycle the recycled ethylene as a reaction raw material, which requires equipment and costs. Therefore, it is preferable to employ conditions for reacting raw material ethylene at a high conversion rate as the various reaction conditions.
(2-2-6) Selectivity The selectivity of p-xylene in the C8 aromatic component obtained by the production method of the present invention is preferably higher, but usually 30% or more, preferably 40% or more, more preferably Is 50% or more.

(2-3) Other reaction conditions (2-3-1) Reaction mode The reaction mode in the production method of the present invention is not particularly limited, but the feedstock is preferably a gas phase in the reaction zone, Specifically, a known gas phase reaction process using a fluidized bed reactor, a moving bed reactor, or a fixed bed reactor can be applied. Further, it can be carried out in any form of batch, semi-continuous or continuous, but is preferably carried out continuously, and the method may be a method using a single reactor, or in series or in parallel. A method using a plurality of arranged reactors may also be used.

(2-3-2) Catalyst regeneration As the method of the present invention is continued, the catalyst causes coking in the reactor and the reaction activity decreases. In this case, the catalyst can be removed from the reactor and, for example, the coke accumulated in the oxygen-containing atmosphere can be oxidized to remove all or a part of the catalyst, thereby regenerating the catalyst. The catalyst regenerated in this way is introduced again into the reactor. From the viewpoint of extraction and reintroduction of such a catalyst, a process using a moving bed reactor or a fluidized bed reactor from a fixed bed. The operation is simple and preferable.

(2-3-3) Reaction product
As the reactor outlet gas (reactor effluent), a mixed gas containing the reaction product p-xylene, unreacted ethylene, by-products and a diluent is obtained. The concentration of p-xylene in the mixed gas is usually 1% by weight or more, preferably 2% by weight or more, and the upper limit is usually 95% by weight or less, preferably 80% by weight or less.
When the target aromatic compound is isolated from the reactor outlet gas (reactor effluent), it is introduced into a known separation / purification facility and recovered, purified, recycled, discharged according to each component. What is necessary is just to receive a process.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

The measurement of the amount of acid was performed using TP5500 manufactured by Nippon Bell Co., Ltd. based on the following conditions.
(Measurement method of acid amount on the outer surface)
1. (Pretreatment of sample)
The sample is vacuum degassed at 500 ° C. for 60 minutes and treated at 10 Pa.
2. (Adsorption of 4-methylquinoline)
4-Methylquinoline is introduced in four portions at 200 ° C. and 10 Pa, and adsorbed for 15 minutes at a saturated vapor pressure.
3. (Physical adsorption removal)
In order to remove 4-methylquinoline physically adsorbed outside the acid sites, vacuum degassing is performed at 200 ° C. for 60 minutes. At this time, the pressure of the system is 0.8 Pa or less.
4). (Temperature desorption)
While circulating about 0.013 MPa of helium at 50 mL / min, the temperature was increased from 30 ° C. to 900 ° C. at 10 ° C./min, and the mass spectrum of desorbed 4-methylquinoline (m / z = 78) was measured. .
5). (Analysis and derivation of acid amount)
The outer surface acid amount (mmol / g) per catalyst weight is determined from the area of the mass intensity chart obtained by the measurement.

  When there is one peak in the spectrum, the entire area is used for calculating the external surface acid amount, but when there are two or more peaks, the acid amount is calculated using only the area of the peak on the highest temperature side. (This is because the peak on the low temperature side includes physical adsorption that could not be removed in the above physical adsorption removal step.) The area of the peak on the highest temperature side is a spectrum using the Davidson-Fletcher-Powell method (DFP method). Is divided into waveforms having a Gaussian distribution. As a coefficient for converting the peak area into the acid amount, a value calibrated by mass intensity (m / z = 78) measured when a certain amount of pyridine is pulsed into the apparatus is used.

(Measurement method of total acid amount)
1. (Pretreatment of sample)
The sample is vacuum degassed at 500 ° C. for 60 minutes and treated at 10 Pa.
2. (Adsorption of pyridine)
Pyridine is introduced in four portions at 200 ° C. and 10 Pa, and adsorbed for 15 minutes each under saturated vapor pressure.
3. (Physical adsorption removal)
In order to remove pyridine physically adsorbed to other than the acid sites, helium is circulated at 50 mL / min for 30 minutes at 200 ° C.
4). (Temperature desorption)
While circulating about 0.013 MPa of helium at 50 mL / min, the temperature is increased from 30 ° C. to 800 ° C. at 10 ° C./min, and the mass spectrum (m / z = 79) of desorbed pyridine is measured.
5). (Analysis and derivation of acid amount)
The total acid amount (mmol / g) per catalyst weight is determined from the area of the mass intensity chart obtained by the measurement.

The acid amount is calculated using only the area of the peak on the high temperature side excluding the peak of 200 ° C. or lower in the spectrum. (Because the peaks below 200 ° C include physical adsorption that could not be removed even in the above physical adsorption removal step.) The peak area excluding the peaks below 200 ° C uses the Davidson-Fletcher-Powell method (DFP method). The spectrum is obtained by separating the spectrum into waveforms having a Gaussian distribution. As a coefficient for converting the peak area into the acid amount, a value calibrated by mass intensity (m / z = 78) measured when a certain amount of pyridine is pulsed into the apparatus is used.
In the following Examples and Comparative Examples, the conversion rate and selectivity of each hydrocarbon are values calculated from the measured values according to the following formula. In the following formulas, “derived carbon molar flow rate (mol / Hr)” of each hydrocarbon means the molar flow rate of carbon atoms constituting each hydrocarbon.

Ethylene conversion (%) = [[reactor inlet ethylene flow rate (mol / Hr) −reactor outlet ethylene flow rate (mol / Hr)] / reactor inlet ethylene flow rate (mol / Hr)] × 100
Aromatic total selectivity (%) = [reactor outlet aromatic-derived carbon molar flow rate (mol / Hr) / [reactor outlet total carbon molar flow rate (mol / Hr) −reactor outlet ethylene-derived carbon molar flow rate (mol / Hr)]] × 100
C8 aromatic total selectivity (%) = [reactor outlet C8 aromatic-derived carbon molar flow rate (mol / Hr) / [reactor outlet total carbon molar flow rate (mol / Hr) −reactor outlet ethylene-derived carbon molar flow rate ( mol / Hr)]] × 100
Ethylbenzene selectivity (%) = [reactor outlet ethylbenzene-derived carbon molar flow rate (mol / Hr) / reactor outlet C8 aromatic-derived carbon molar flow rate (mol / Hr)] × 100
p-xylene selectivity (%) = [reactor outlet p-xylene-derived carbon molar flow rate (mol / Hr) / reactor outlet C8 aromatic-derived carbon molar flow rate (mol / Hr)] × 100
m-xylene selectivity (%) = [reactor outlet m-xylene-derived carbon molar flow rate (mol / Hr) / reactor outlet C8 aromatic-derived carbon molar flow rate (mol / Hr)] × 100
o-xylene selectivity (%) = [reactor outlet o-xylene-derived carbon molar flow rate (mol / Hr) / reactor outlet C8 aromatic-derived carbon molar flow rate (mol / Hr)] × 100

<Catalyst preparation>
<Preparation Example 1>
A solution A in which 12.8 g of tetrapropylammonium bromide was dissolved in 106 ml of distilled water was added to 103 g of water glass 3 (manufactured by Kishida Chemical Co., Ltd.) with stirring. Subsequently, 7.65 g of aluminum nitrate and nitric acid were added to 100 ml of distilled water. Liquid B in which 8.00 g of gallium and 7.1 g of concentrated sulfuric acid were dissolved was also added with stirring. After stirring for 2 hours, the mixture was transferred to an autoclave, heated to 180 ° C. in 2 hours, and then kept at 180 ° C. for 40 hours. After allowing to cool, the solid was taken out, filtered and washed with water. The crystalline zeolite obtained by drying was calcined at 550 ° C. under air flow. In order to replace the cation with NH 4, it was immersed in a 1M ammonium nitrate aqueous solution, heated and stirred at 80 ° C. for 1 hour, cooled, filtered and washed. This ion exchange was repeated twice to convert to NH4 type zeolite. Furthermore, it was made a proton type by baking at 500 ° C. in an air stream. The obtained zeolite was analyzed by XRD (X-ray diffraction) and elemental analysis by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Confirm that the diameter is 0.55 nm and 0.56 nm) aluminogallosilicate (SiO ₂ / Al ₂ O ₃ = 50 (molar ratio), SiO ₂ / Ga ₂ O ₃ = 52 (molar ratio)). did.

<Preparation Example 2>
Silylated with tetraethoxysilane for proton type aluminogallosilicate (SiO ₂ / Al ₂ O ₃ = 50 (molar ratio), SiO ₂ / Ga ₂ O ₃ = 52 (molar ratio)) having MFI structure It was. To 0.42 g of aluminogallosilicate, 4.2 ml of a solvent hexamethyldisiloxane and 1.05 ml of a silylating agent tetraethoxysilane were added and refluxed for 6 hours with stirring at 100 ° C. After the treatment, the solid and liquid were separated by filtration, and the obtained aluminogallosilicate was dried at 100 ° C. for 6 hours.

<Acid amount measurement>
With respect to the aluminogallosilicates of Preparation Examples 1 and 2, the external surface acid amount and the total acid amount were measured by a 4-methylquinoline-TPD (temperature-programmed desorption) method and a pyridine-TPD method, respectively. The measurement was performed according to the method described above.
The values of (outer surface acid amount) / (total acid amount) derived as described above are shown in Table 1.

Example 1
The reaction was carried out using an atmospheric pressure fixed bed flow reactor, and a mixture of 100 mg of the catalyst of Preparation Example 2 and 400 mg of quartz sand was packed in a quartz reaction tube having an inner diameter of 6 mm. A mixed gas of 13% ethylene and 87% nitrogen was supplied to the reactor so that the space velocity of ethylene was 2.0 Hr ^−1, and the reaction was performed at 425 ° C. and 0 MPaG (gauge pressure). 0.25 hours after the start of the reaction, the product was analyzed by gas chromatography. The results are shown in Table 1.

(Comparative example)
The reaction was performed in the same manner as in Example 1 except that the catalyst of Preparation Example 1 was used. The obtained results are shown in Table 1.
As described above, p-xylene could be synthesized with high selectivity by setting the outer surface acid amount to 1% or less with respect to the total acid amount.

  According to the production method of the present invention, the most important p-xylene among the xylene isomers as a raw material for producing terephthalic acid can be produced from a raw material containing ethylene with high selectivity. Moreover, it is useful at the point which can improve the efficiency of a refinement | purification separation process by the manufacturing method with high p-xylene selectivity in a C8 aromatic compound.

Claims (9)

  In a method for producing p-xylene by bringing a raw material mainly composed of ethylene into contact with a catalyst in a reactor, the active component of the catalyst is zeolite, and the amount of acid on the outer surface of the zeolite A method for producing p-xylene, characterized by being 1% or less with respect to the acid amount.   The method for producing p-xylene according to claim 1, wherein the zeolite is a crystalline silicate containing at least one element selected from the group consisting of elements belonging to Group IIIb of the periodic table.   The method for producing p-xylene according to claim 2, wherein the element belonging to Group IIIb of the periodic table is Al and / or Ga.   The method for producing p-xylene according to any one of claims 1 to 3, wherein the pore diameter of the zeolite is 0.5 nm or more and 0.75 nm or less.   The method for producing p-xylene according to any one of claims 1 to 4, wherein the zeolite has an oxygen 10-membered ring channel structure.   The method for producing p-xylene according to any one of claims 1 to 5, wherein the zeolite has a MFI structure. Zeolite contains Al as the element, and _SiO 2 / _Al 2 _{O 3} molar ratio of 5 or more, the production method of p- xylene according to any one of claims 1 to 6, is 1000 or less. Zeolite containing Ga as the element, and _SiO 2 / _Ga 2 _{O 3} molar ratio of 5 or more, the production method of p- xylene according to any one of claims 1 to 6, is 1000 or less.   The method for producing p-xylene according to any one of claims 1 to 8, wherein the zeolite is obtained by silylated the outer surface of the zeolite.