MFI molecular sieve, preparation method thereof, preparation method of xylene isomerization reaction catalyst and xylene isomerization reaction

Abstract

The present application relates to a kind of MFI molecular sieve and preparation method, the preparation method of xylene isomerization reaction catalyst and xylene isomerization reaction, the preparation method of MFI molecular sieve includes: (1) make alkyl cycloalkyl amine and halogenated hydrocarbon R1X in alcohol solvent contact reaction, obtain the first mixture material containing template agent;Wherein, R m It is linear alkylene with carbon number 4~8, R1And R2Each is independently selected from linear alkyl with carbon number 1~8, X is selected from chlorine or bromine;(2) the first mixture material, boron source, silicon source and water are mixed, then hydrothermal reaction is carried out, and MFI molecular sieve is obtained.The self-made cyclic structure quaternary ammonium salt template agent of the present application, the MFI molecular sieve of high crystallinity and uniform growth is prepared, and xylene isomerization reaction catalyst is prepared, ion exchange is carried out by specific ion exchanger, and by single quaternary ammonium salt template agent aqueous solution, steam treatment is carried out, so that catalyst acid function is better optimized, reduce isomerization reaction temperature while improving xylene yield.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalyst technology, in particular to a MFI molecular sieve, a preparation method thereof, a preparation method of a xylene isomerization reaction catalyst and a xylene isomerization reaction. BACKGROUND

[0002] Paraxylene (PX) is an important chemical raw material, mainly used for producing terephthalic acid, terephthalate, etc., in addition to being applied in the fields of coatings, dyes, pesticides and medicines, etc. With the development of these industries, the demand for PX is rapidly increasing. At present, the main process technology for increasing PX production is xylene isomerization, which is an important means for converting low-value meta-xylene and ortho-xylene into PX.

[0003] Through xylene isomerization reaction, the content of paraxylene in the product reaches or approaches the thermodynamic equilibrium value, and the PX product can be separated out by a separation device, and a small amount of light non-aromatic hydrocarbons, benzene, toluene and C9 + heavy aromatic hydrocarbons are separated out, and the remaining C8 aromatic hydrocarbons can be recycled as isomerization raw materials.

[0004] So far in industrial production, gas phase isomerization is generally used, and the PX-lean raw material is heated by heat exchange and heating furnace to vaporize and heat the reaction material to 350 degrees or above, which is then introduced into the xylene isomerization reactor to contact with the catalyst bed, so that the three isomers of xylene reach or approach the thermodynamic equilibrium.

[0005] Since the cost of separating ethylbenzene from xylene is high, ethylbenzene must be converted during xylene isomerization. There are two different target directions for ethylbenzene conversion, which are ethylbenzene conversion to xylene and ethylbenzene de-ethylation to benzene. These two directions are suitable for different market conditions. Among them, the method of converting ethylbenzene to benzene by using de-ethylation catalyst has the advantages of high single-pass conversion rate of ethylbenzene, less material circulation, and high PX content in adsorption feed, etc. In recent years, the production capacity of aromatic hydrocarbon combined devices using this method has increased rapidly.

[0006] The comprehensive performance of the existing de-ethylation catalyst still has room for improvement, which is specifically manifested in that high-activity catalysts usually also lead to high side reactions, resulting in decreased process selectivity and loss of xylene yield. Modification of the acid component of the molecular sieve is an important means to improve the performance of the catalyst. At present, there are many methods for modifying the acid component of the catalyst, and the most commonly used is hydrothermal modification or adding rare earth elements to the molecular sieve. The effect of modification is to optimize the acid distribution of the molecular sieve and weaken the side reaction acid sites.

[0007] Patent CN200710178230.7 discloses a kind of β zeolite containing boron as boron source, is added into synthesis system, thus preparation contains boron composite molecular sieve, with good acid catalytic performance.But the preparation process of composite molecular sieve is complex, must have β zeolite containing boron as boron source, therefore, it is not simple and efficient means for preparing boron-containing molecular sieve.

[0008] Patent CN201480015750.4 discloses the synthesis of a boron aluminosilicate molecular sieve and its use in a xylene isomerization reaction, which provides a higher selectivity than conventional commercial catalysts, resulting in a reduction in the formation of methyl transfer by-products and simultaneously providing a high degree of xylene isomerization. However, this method requires the introduction of an aluminum source, and is not a pure boron-substituted MFI molecular sieve. This results in the presence of at least two types of acid centers on the molecular sieve, one formed by silicon-aluminum bridging oxygen bonds and one formed by silicon-boron bridging oxygen bonds. It is generally believed that the acid centers formed by silicon-boron bridging oxygen bonds are more suitable for aromatic conversion reactions.

[0009] In summary, how to develop a synthesis method of MFI molecular sieve completely substituted by boron atoms, and make targeted modification treatment, so as to make it suitable for preparing xylene isomerization catalyst is a technical problem to be solved at present. SUMMARY

[0010] The purpose of the present application is to prepare a MFI molecular sieve and a catalyst by preparing a template agent with better structure-guided function, so as to reduce the temperature of isomerization reaction and improve the yield of xylene.

[0011] In one aspect, the present application relates to a preparation method of a MFI molecular sieve, which comprises the following steps: (1) allowing an alkyl cycloalkyl amine having the following formula I to react with a halogenated hydrocarbon R1X in an alcohol solvent to obtain a first mixture containing a template agent; wherein, R m is a linear alkylene group with a carbon number of 4-8, R1 and R2 are each independently selected from a linear alkyl group with a carbon number of 1-8, and X is selected from chlorine or bromine;

[0012]

[0013] (2) mixing the first mixture, a boron source, a silicon source and water, and then performing a hydrothermal reaction to obtain the MFI molecular sieve.

[0014] Optionally, R m is butylene or pentylene.

[0015] Optionally, in step (1), the molar ratio of the alkyl cycloalkyl amine, the halogenated hydrocarbon R1X and the alcohol solvent is 1:(0.5-1.5):(3-20); the temperature of the contact reaction is 35-150℃, and the time is 2-24 hours.

[0016] Optionally, in step (1), the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol; preferably, the alcohol solvent is ethanol.

[0017] Optionally, in step (2), the boron source is selected from sodium borate or boric acid, and the silicon source is selected from water glass, silica sol, solid silica gel or white carbon black; preferably, the boron source is sodium borate, and the silicon source is water glass; further preferably, the silicon source is water glass with a molar ratio of SiO2 to Na2O of (2-4):1.

[0018] Optionally, in step (2), the molar ratio of the silicon source calculated as SiO2 to the boron source calculated as B2O3 is (30-70):1, and the molar ratio of water, the template agent and the silicon source calculated as SiO2 is (20-50):(0.01-0.22):1.

[0019] Optionally, in step (2), the hydrothermal reaction comprises a first temperature control stage, a second temperature control stage and a third temperature control stage, and the temperature of the second temperature control stage is lower than that of the first temperature control stage and the third temperature control stage.

[0020] Optionally, the temperature of the first temperature control stage is 105-135℃, and the time is 6-18 hours; the temperature of the second temperature control stage is 45-85℃, and the time is 6-18 hours; the temperature of the third temperature control stage is 155-185℃, and the time is 12-48 hours; and the heating or cooling rate in the first temperature control stage, the second temperature control stage and the third temperature control stage is 0.5-2 degrees / minute.

[0021] In another aspect, the present application relates to the MFI molecular sieve prepared according to the preparation method; preferably, the MFI molecular sieve is a nanocrystal molecular sieve with a crystal size of 20-60 nm; further preferably, the MFI molecular sieve is distributed with pores with a pore size of 30-80 nm.

[0022] In still another aspect, the present application relates to a preparation method of a catalyst for xylene isomerization reaction, which comprises the following steps: (a) mixing the MFI molecular sieve or the MFI molecular sieve prepared according to the preparation method with a binder and a peptizing agent to form a shaped carrier; (b) calcining the shaped carrier and then ion exchanging it in an aqueous solution of a quaternary ammonium salt to obtain an ion-exchanged shaped carrier; wherein the quaternary ammonium salt is selected from a compound with a structural formula of N(R E )4X1, R E each independently selected from an alkyl group with a carbon number of 1-4, and X1 is selected from halogen; and (c) steam treating the ion-exchanged shaped carrier.

[0023] Optionally, the binder in step (a) is selected from alumina or titania, and the peptizing agent is selected from nitric acid or hydrochloric acid; preferably, the binder is alumina and the peptizing agent is nitric acid; in the shaped carrier, the MFI molecular sieve accounts for 40-70% by mass, and the balance is alumina, based on the total mass of the shaped carrier.

[0024] Optionally, R E are each independently selected from ethyl or propyl, and X1 is selected from chlorine or bromine.

[0025] Optionally, in step (b), the concentration of the aqueous quaternary ammonium salt solution is 0.04-0.06 mol / L, the liquid-to-solid ratio during ion exchange is 5-30 mL / g, the ion exchange temperature is 50-90°C, and the number of ion exchange times is 2-4.

[0026] Optionally, step (b) further comprises the following step after ion exchange: washing the ion-exchanged shaped carrier with water until no halide anion is detected in the washing liquid, the pH value of the washing liquid is 6-8, and the molar content of Na2O in the ion-exchanged shaped carrier after water washing is 0.05-0.20%.

[0027] Optionally, the steam treatment in step (c) uses an aqueous solution of the template agent as a steam source.

[0028] Optionally, the concentration of the aqueous solution of the template agent is 0.01-0.08 mol / L, the amount of the aqueous solution of the template agent is 5-30 mL / g based on the mass of the ion-exchanged shaped carrier, the temperature of the steam treatment is 150-500°C, and the time of the steam treatment is 3-6 hours; preferably, the concentration of the aqueous solution of the template agent is 0.04-0.06 mol / L, and the temperature of the steam treatment is 200-450°C.

[0029] In still another aspect, the present application relates to a xylene isomerization reaction, in which a xylene isomerization raw material is subjected to a xylene isomerization reaction under the catalysis of the xylene isomerization reaction catalyst prepared by the above preparation method; preferably, the xylene isomerization reaction is carried out under hydrogenation conditions, the reaction temperature is 250-350°C, the reaction pressure is 0.5-2.0 MPa, the weight hourly space velocity of the xylene isomerization reaction catalyst is 6-20 h -1 , and the molar ratio of hydrogen to hydrocarbon is 0.8-2.8.

[0030] Advantages:

[0031] The application is self-made quaternary ammonium salt template agent containing cyclic structure, which makes boron grow into MFI molecular sieve with high crystallinity and uniformity in the preparation of molecular sieve, optimizes the preparation of xylene isomerization catalyst based on the molecular sieve, exchanges ions by specific ion exchanger, and optimizes the acid function of the catalyst by steam treatment with aqueous solution of single quaternary ammonium salt template agent, thereby reducing the temperature of isomerization reaction and improving the yield of xylene. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the XRD spectrum of Na type raw powder ZD-1 prepared in Comparative Example 1;

[0033] Figure 2 is the XRD spectrum of molecular sieve sample Z-1 prepared in Example 9;

[0034] Figure 3 is the SEM electron micrograph of molecular sieve sample Z-1 prepared in Example 9;

[0035] Figure 4 is the SEM electron micrograph of molecular sieve sample ZD-1 prepared in Comparative Example 1. DETAILED DESCRIPTION

[0036] The application will be further described in detail below by means of the accompanying drawings and examples. Through these descriptions, the features and advantages of the application will become more apparent.

[0037] The special word "exemplary" here means "serving as an example, embodiment or illustration". Any embodiment described as "exemplary" here is not necessarily to be construed as superior or better than other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0038] In addition, the technical features involved in different embodiments of the application described below can be combined with each other as long as there is no conflict.

[0039] In a first aspect, the application relates to a preparation method of MFI molecular sieve, which comprises the following steps: (1) contacting and reacting alkylcycloalkylamine with halogenated hydrocarbon R1X in alcohol solvent to obtain a first mixture containing template agent, wherein R m is a linear alkylene group with carbon number of 4-8, R1and R2are each independently selected from linear alkyl group with carbon number of 1-8, and X is selected from chlorine or bromine;

[0040]

[0041] (2) mixing the first mixture, boron source, silicon source and water, and then performing hydrothermal reaction to obtain the MFI molecular sieve.

[0042] It should be noted that in the preparation method of the first aspect of the present application, step (1) synthesizes a template agent in a low-carbon alcohol solvent, which can be referred to as a monoquaternary ammonium cation salt template agent. The monoquaternary ammonium cation salt can be represented as N(R1R2R m )X. The synthesis of the quaternary ammonium salt template agent, i.e., the monoquaternary ammonium cation salt template agent (SDA), can use an alkyl cycloalkyl amine of the form N(R2R m ), which undergoes an addition reaction with a halogenated hydrocarbon of the form R1X (X is a chlorine or bromine atom) in a low-carbon alcohol solvent to obtain an alcohol solution of the corresponding monoquaternary ammonium cation salt template agent. In the process of synthesizing the monoquaternary ammonium cation salt template agent (SDA), the alkyl cycloalkyl amine and the halogenated hydrocarbon R1X are preferably added slowly into the low-carbon alcohol solvent, respectively, and the mixture is stirred for 0.1-12 hours to make the materials uniformly mixed.

[0043] The monoquaternary ammonium cation in the quaternary ammonium salt template agent is a monovalent cation of the form N(R1R2R m ) + , in which R m is connected to N at both ends to form a ring, and R1 and R2 are respectively connected to N at one end, and N is a nitrogen atom.

[0044] It should be noted that the first mixture obtained in step (1) is a mixture containing the quaternary ammonium salt template agent, the alcohol solvent, and part of the raw material substances, such as the remaining alkyl cycloalkyl amine or halogenated hydrocarbon. The first mixture can also be referred to as a low-carbon alcohol solution of the quaternary ammonium salt template agent. In step (2), preferably, the low-carbon alcohol solution of the quaternary ammonium salt template agent (the first mixture) is first uniformly mixed with water to form a mixed solution; then the boron source is slowly added under stirring, and the mixture is stirred for 2-12 hours; then the silicon source is slowly added to form a liquid sol, and the sol is stirred for 6-18 hours to make the sol phase uniform, and then the hydrothermal reaction is performed.

[0045] In the template agent of the present application, R m and N together form a ring, so that in the process of preparing the molecular sieve, the template agent can maintain a direction, so that the boron B grows in a direction that is more conducive to the formation of the silicon-boron MFI molecular sieve, and the grown MFI molecular sieve structure is more uniform, has high crystallinity, and the catalyst prepared based on the molecular sieve has higher catalytic activity.

[0046] According to an embodiment of the first aspect of the present application, R m is butylene or pentylene.

[0047] It should be noted that R m is not limited to the above two, and the number of carbons in R m may also be 5, 6, or 7.

[0048] According to an embodiment of the first aspect of the present application, in step (1), the molar ratio of the alkylcycloalkylamine, the halogenated hydrocarbon R1X and the alcohol solvent is 1:(0.5-1.5):(3-20); the temperature of the contact reaction is 35-150℃, and the time is 2-24 hours.

[0049] It should be noted that the reaction conditions in the process of synthesizing the quaternary ammonium salt template, i.e. the monoquaternary ammonium cation salt template (SDA), should be controlled as described above.

[0050] According to an embodiment of the first aspect of the present application, in step (1), the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol; preferably, the alcohol solvent is ethanol.

[0051] It should be noted that the alcohol solvent can be a mixture of two or more of the above-mentioned alcohols in any proportion, and the alcohol solvent is preferably ethanol.

[0052] According to an embodiment of the first aspect of the present application, in step (2), the boron source is selected from sodium borate or boric acid, and the silicon source is selected from water glass, silica sol, solid silica gel or white carbon black; preferably, the boron source is sodium borate, and the silicon source is water glass; further preferably, the silicon source is water glass with a molar ratio of SiO2 to Na2O of (2-4):1.

[0053] According to an embodiment of the first aspect of the present application, in step (2), the molar ratio of the silicon source (calculated based on SiO2) to the boron source (calculated based on B2O3) is (30-70):1, and the molar ratio of water, the template and the silicon source (calculated based on SiO2) is (20-50):(0.01-0.22):1.

[0054] It should be noted that in step (2), when mixing the first mixture, the boron source, the silicon source and water, the mass ratio of the quaternary ammonium salt template in the first mixture (calculated based on the amounts of the alkylcycloalkylamine, the halogenated hydrocarbon R1X and the alcohol solvent in step (1)) is determined, then the molar amount of the quaternary ammonium salt template is calculated according to the molar ratio of water, the quaternary ammonium salt template and the silicon source (calculated based on SiO2) in step (2), and thus the amount of the first mixture required in step (2) can be calculated.

[0055] According to an embodiment of the first aspect of the present application, in step (2), the hydrothermal reaction includes a first temperature control stage, a second temperature control stage and a third temperature control stage, and the temperature of the second temperature control stage is lower than that of the first temperature control stage and the third temperature control stage.

[0056] It should be noted that, in the synthesis of the molecular sieve based on the self-prepared template agent, the second temperature control stage is arranged between the first temperature control stage and the third temperature control stage, and the temperature of the intermediate stage is lower than that of the two stages before and after, so that the performance of the molecular sieve is improved, and the performance of the subsequent prepared dimethylbenzene isomerization reaction catalyst is improved.

[0057] According to an embodiment of the first aspect of the present application, the temperature of the first temperature control stage is 105-135 DEG C, and the time is 6-18 hours; the temperature of the second temperature control stage is 45-85 DEG C, and the time is 6-18 hours; the temperature of the third temperature control stage is 155-185 DEG C, and the time is 12-48 hours; and the temperature increasing or decreasing rate in the first temperature control stage, the second temperature control stage and the third temperature control stage is 0.5-2 DEG C / min.

[0058] It should be noted that, in the synthesis of the molecular sieve based on the self-prepared template agent, the second temperature control stage is arranged between the first temperature control stage and the third temperature control stage, and the temperature of the intermediate stage is lower than that of the two stages before and after, so that the performance of the molecular sieve is improved, and the performance of the subsequent prepared dimethylbenzene isomerization reaction catalyst is improved. Figure 3 As can be seen from the electron micrograph of the MFI structure multi-level hole nanometer molecular sieve, the pore sizes between the molecular sieve crystal grains are different, and a multi-level hole distribution is presented.

[0059] The MFI structure multi-level hole nanometer molecular sieve raw powder can be washed several times with excess deionized water after synthesis until the pH of the washing liquid is 6-8. The MFI structure multi-level hole nanometer molecular sieve raw powder after sufficient washing is dried at 120 DEG C for 8-24 hours, and the drying can be carried out in a static atmosphere without air flow or in a dynamic atmosphere with a volume space velocity of 50-500 h-1. -1 The dried molecular sieve can be mixed with an alumina binder and formed according to a conventional method.

[0060] In the second aspect, the MFI molecular sieve is prepared according to the preparation method of the first aspect of the present application; preferably, the MFI molecular sieve is a nanometer crystal grain molecular sieve, and the crystal grain size is 20-60 nm; and further preferably, the MFI molecular sieve is distributed with pores with a pore size of 30-80 nm.

[0061] It should be noted that, in the MFI molecular sieve prepared according to the preparation method of the first aspect of the present application, the silicon-boron molar ratio can be (30-70):1 (molar ratio of SiO2 and B2O3).

[0062] Thirdly, the present invention relates to a method for preparing a xylene isomerization reaction catalyst, the method comprising the following steps: (a) mixing the MFI molecular sieve described in the second aspect of the present invention or the MFI molecular sieve prepared by the method described in the first aspect with a binder and a solvent to form a molded support; (b) calcining the molded support and then subjecting it to ion exchange in a quaternary ammonium salt aqueous solution to obtain an ion-exchanged molded support; wherein the quaternary ammonium salt is selected from the structure N(R E Compounds of 4X1, R E Each is independently selected from alkyl groups having 1 to 4 carbon atoms, and X1 is selected from halogens; (c) the ion-exchanged molded carrier is subjected to steam treatment.

[0063] It should be noted that step (a) includes at least one MFI molecular sieve prepared by the preparation method described in the first aspect.

[0064] It should be noted that the molded carrier is dried at 120℃ for 8–24 hours and then calcined in air at 540℃ for 2–24 hours. Calcination can be carried out in a static atmosphere without airflow, or at a volume hourly space velocity (VHSV) of 50–500 h⁻¹. -1 It takes place in a dynamic atmosphere.

[0065] It should be noted that, in step (b), compared with the existing method of using inorganic ammonium salts such as ammonium chloride and ammonium bromide for ion exchange, the catalyst preparation method of the present invention uses the compound N(R) for ion exchange. E A 4X1 aqueous solution is used for ion exchange on the molded carrier. E Each ion is independently selected from a straight-chain alkyl group having 1 to 4 carbon atoms, preferably ethyl or propyl, so that the volume of the N-containing ion is larger than that of the ammonium ion. This allows the acidic sites on the molecular sieve surface to be exchanged for N(R) during ion exchange. E )4 + Meanwhile, acidic sites existing inside the molecular sieve channels can be retained without being exchanged because N(R) E )4 + Large ions cannot enter the molecular sieve pores or the amount entering is significantly reduced. Therefore, the ion exchange energy of the present invention is controlled within a certain range, thereby optimizing the acid function distribution of the exchanged molecular sieve.

[0066] According to one embodiment of the third aspect of the present invention, the binder in step (a) is selected from alumina or titanium dioxide, and the adhesive solvent is selected from nitric acid or hydrochloric acid; preferably, the binder is alumina and the adhesive solvent is nitric acid; in the molding carrier, the mass ratio of the MFI molecular sieve is 40-70%, and the balance is alumina, based on the total mass of the molding carrier.

[0067] The application uses the MFI structure multi-level hole nanometer molecular sieve containing boron as the acidic active component in the catalyst, and provides the acidic site of the xylene isomerization reaction.

[0068] According to an embodiment of the third aspect of the application, R E are each independently selected from ethyl or propyl, and X1 is selected from chlorine or bromine.

[0069] It should be noted that when the ion exchange of step (b) is performed, the ion exchange is preferably performed by using a solution of the quaternary ammonium salt as the ion exchange solution. E and X1 can further better optimize the acid function distribution of the molecular sieve, so as to obtain a catalyst with more optimized acid function distribution.

[0070] According to an embodiment of the third aspect of the application, in step (b), the concentration of the aqueous quaternary ammonium salt solution is 0.04-0.06 mol / L, the liquid-solid ratio during the ion exchange is 5-30 mL / g, the exchange temperature during the ion exchange is 50-90°C, and the exchange times are 2-4 times.

[0071] It should be noted that after the shaped carrier obtained in step (a) is dried and calcined before the ion exchange of step (b) is performed, the liquid-solid ratio during the ion exchange is based on the mass of the shaped carrier after the drying and calcination.

[0072] According to an embodiment of the third aspect of the application, step (b) further comprises the following steps after the ion exchange: the shaped carrier after the ion exchange is washed with water until no halogen anion is detected in the washing liquid, the pH value of the washing liquid is 6-8, and the molar content of Na2O of the shaped carrier after the water washing is 0.05-0.20%.

[0073] According to an embodiment of the third aspect of the application, the steam treatment in step (c) uses an aqueous solution of the template agent as the steam source.

[0074] It is to be noted that in the prior art, water vapor is used for steam treatment to eliminate excessively active boron B or aluminum (such as Al-H) on the molecular sieve of the catalyst, thereby reducing the number of acid sites and further optimizing the acid function distribution. When water vapor is used for steam treatment, the structure of the molecular sieve collapses in some places and the crystallinity is reduced while the boron B or aluminum is eliminated. In the preparation method of the catalyst of the present application, the elimination of the acid sites is performed by using the aqueous solution of the quaternary ammonium salt template as a steam source. While the excessively active B is eliminated, the quaternary ammonium salt template can play a certain supporting role on the structure of the molecular sieve to prevent the structure from collapsing and thereby avoid the reduction of the crystallinity. In addition, because the amount of the quaternary ammonium salt template introduced by steam treatment in step (c) is very small, it is not necessary to perform the step of calcination and film removal, and the obtained catalyst can be directly used for isomerization reaction.

[0075] According to an embodiment of the third aspect of the present application, the concentration of the aqueous solution of the template is 0.01-0.08 mol / L; the amount of the aqueous solution of the template is 5-30 mL / g based on the mass of the ion-exchanged shaped carrier; the temperature of the steam treatment is 150-500°C and the time is 3-6 hours; preferably, the concentration of the aqueous solution of the template is 0.04-0.06 mol / L and the temperature of the steam treatment is 200-450°C.

[0076] In a fourth aspect, the present application relates to a xylene isomerization reaction. The xylene isomerization raw material is subjected to xylene isomerization reaction under the catalysis of the xylene isomerization reaction catalyst prepared by the preparation method of the third aspect of the present application. Preferably, the xylene isomerization reaction is performed under hydrogenation conditions, the reaction temperature is 250-350°C, the reaction pressure is 0.5-2.0 MPa, the weight hourly space velocity of the xylene isomerization reaction catalyst is 6-20 h -1 , and the hydrogen hydrocarbon molar ratio is 0.8-2.8.

[0077] It is to be noted that the current industrial isomerization temperature is generally 360-380°C, and the xylene isomerization reaction of the present application can be well performed at 250-350°C when the catalyst prepared by the preparation method of the present application is used for isomerization reaction, which can reduce the isomerization reaction temperature and improve the xylene yield.

[0078] The preparation of the catalyst includes the synthesis of the template (quaternary ammonium salt template, i.e. monoquaternary ammonium salt template), the optimized synthesis, washing, drying and calcination of the boron-containing MFI structure multi-level pore nanomolecular sieve, and the synthesis of the catalyst, and the ion exchange and acid function distribution optimization treatment after the shaping of the catalyst. The catalyst prepared by the above method can be used for xylene isomerization reaction, and compared with the existing catalyst, the reaction temperature can be reduced and the xylene yield of the catalyst can be improved.

[0079] The present application is further explained in detail by the following examples, but the present application is not limited to them.

[0080] The reagents used in the following examples are all commercially available reagents.

[0081] Example 1

[0082] Into a 500 mL three-necked flask with condensing reflux, 9.6 g of methanol, 5.33 g of 1-chloropentane, and 11.3 g of N-propylpyrrolidine were added, and after the mixture was stirred thoroughly for 0.1 hour, it was heated to 120°C under pressurized reflux, and after 8 hours of synthesis time, it was cooled to room temperature to obtain 10.27 g of the monocationic quaternary ammonium template S-1 (a mixture containing the template).

[0083] Example 2

[0084] The monocationic quaternary ammonium template S-2 was prepared according to the method of Example 1, except that 30.0 g of isopropanol, 14.9 g of 1-bromohexane, and 9.9 g of N-ethylpyrrolidine were added, and after the mixture was stirred thoroughly for 0.5 hour, it was heated to 80°C, and after 16 hours of synthesis time, it was cooled to room temperature to obtain 22.49 g of the monocationic quaternary ammonium template S-2 (a mixture containing the template).

[0085] Example 3

[0086] The monocationic quaternary ammonium template S-3 was prepared according to the method of Example 1, except that 59.2 g of n-butanol, 9.26 g of 1-chlorobutane, and 8.5 g of N-methylpyrrolidine were added, and after the mixture was stirred thoroughly for 3 hours, it was heated to 35°C, and after 24 hours of synthesis time, it was cooled to room temperature to obtain 17.7 g of the monocationic quaternary ammonium template S-3 (a mixture containing the template).

[0087] Example 4

[0088] The monocationic quaternary ammonium template S-4 was prepared according to the method of Example 1, except that 60.0 g of n-propanol, 16.5 g of 1-bromohexane, and 9.9 g of N-methylpiperidine were added, and after the mixture was stirred thoroughly for 8 hours, it was heated to 150°C under pressurized reflux, and after 2 hours of synthesis time, it was cooled to room temperature to obtain 24.9 g of the monocationic quaternary ammonium template S-4 (a mixture containing the template).

[0089] Example 5

[0090] The monocationic template S-5 was prepared according to the method of Example 1, except that isobutyl alcohol 148.0 g, 1-bromo octane 25.1 g, N-methyl piperidine 9.9 g were added, the mixture was stirred thoroughly for 12 hours, then the temperature was raised to 90°C, the synthesis time was 15 hours, and the temperature was cooled to room temperature. 27.8 g of the monocationic template S-5 (a mixture containing the template) was obtained.

[0091] Example 6

[0092] The monocationic template S-6 was prepared according to the method of Example 1, except that ethanol 69.0 g, 1-chloroheptane 20.2 g, N-ethyl piperidine 11.3 g were added, the mixture was stirred thoroughly for 6 hours, then the temperature was raised to 60°C, the synthesis time was 21 hours, and the temperature was cooled to room temperature. 23.3 g of the monocationic template S-6 (a mixture containing the template) was obtained.

[0093] Table 1 Summary of template synthesis of Examples 1-6

[0094]

[0095] Comparative Example 1

[0096] Na-type raw powder of MFI structure boron-containing hierarchical pore nanomolecular sieve was synthesized using a conventional template.

[0097] In a 1 L reaction kettle, the template tetrapropyl ammonium bromide was added in an amount of 2.7 g, water 72.0 g was added, and the mixture was thoroughly dissolved. Then, the boron source (sodium borate) 0.95 g was added, and stirred for 4 hours. Then, the silicon source (water glass, silicon dioxide mass concentration 24 mass%, modulus 3.1) 50 g was added, and stirred for 12 hours. The first stage temperature was 105°C, and maintained for 12 hours. The second stage temperature was 70°C, and maintained for 9 hours. The third stage temperature was 170°C, and maintained for 35 hours. The temperature variation rate was 0.8°C / min.

[0098] The Na-type eutectic molecular sieve of the comparative example was obtained, and was recorded as ZD-1, with a silicon-boron ratio of 40. The raw powder was dried at 120°C for 8 hours, and the drying was completed in a flow of air with an air volume space velocity of 100.

[0099] Comparative Example 2

[0100] The molecular sieve was prepared according to the method of Comparative Example 1, using N-methyl piperidine as the template, and other preparation process conditions were shown in Table 2-1. The prepared catalyst was recorded as ZD-2.

[0101] Examples 7-16

[0102] In a 1L reaction kettle, template agent was added, water was added, and after being dissolved thoroughly, boron source (sodium borate decahydrate) was added, stirred, and then silicon source (water glass, silicon dioxide mass concentration 24 mass%, modulus 3.1) was added, stirred; one-stage or multi-stage synthesis was performed.

[0103] The molecular sieve was prepared, and the raw powder was dried at 120 degrees.

[0104] The raw materials and synthesis temperature procedures used in the synthesis of the molecular sieve in Examples 7-16 are listed in Tables 2-1 and 2-2.

[0105] Table 2-1

[0106]

[0107]

[0108] Table 2-2

[0109] Example 11 12 13 14 15 16 Sample Z-3 Z-4 Z-5 Z-6 Z-7 Z-8 Templating agent S-3, 0.5 g S-4, 4.1 g S-5, 13.5 g S-6, 9.7 g S-1, 3.0 g S-4, 0.5 g Water / g 113.4 202.5 151.2 144 54 113.4 Silica to boron ratio 70 40 60 45 50 70 Boron source / g 0.49 1.19 0.67 0.68 0.57 0.49 Stirring time / hour 2 4 12 6 12 8 Silica source / g 45 62.5 52.5 40 37.5 45 Stirring time / hour 12 10 6 9 6 9 Temperature of first stage / °C 125 110 120 125 135 135 Time of first stage / hour 12 15 9 10 18 18 Temperature of second stage / °C 45 55 75 60 50 50 Time of second stage / hour 16 12 18 12 9 9 Temperature of third stage / °C 185 160 170 166 180 180 Time of third stage / hour 12 24 18 36 48 36 Temperature ramp rate, °C / min 1 1.5 2 0.9 1.2 1.2 Drying time / hour 8 18 24 15 12 15 Drying, air volume space velocity 350 450 500 50 240 360

[0110] Comparative Example 3

[0111] The xylene isomerization catalyst was prepared according to a conventional method.

[0112] After 10 g of the dried raw powder of the molecular sieve ZD-1 prepared in Comparative Example 1 was mixed with 10 g of alumina, 20 mL of 5 mass% nitric acid aqueous solution was added to prepare a viscous mixture, which was extruded into a strip shape. The strip-shaped product was dried at 120°C for 12 hours, then pelletized, and calcined at 540°C for 24 hours. Ion exchange was performed at 60°C for 2 hours x 4 times using 0.05 mol / L tetraethylammonium bromide aqueous solution, and the solution amount was 15 mL / g of the carrier. After washing until there was no chloride ion in the mother liquor, the Na2O molar content of the mixed crystal molecular sieve after washing was 0.06%.

[0113] The exchanged carrier was subjected to hydrothermal treatment using tetrapropylammonium bromide aqueous solution as a steam source, the solution concentration was 0.04 mol / L, the solution amount was 25 mL / g of the carrier, and the steam treatment temperature was 300°C, and the treatment time was 3 hours. The treated sample was the finished catalyst CD-1.

[0114] Comparative Example 4

[0115] The xylene isomerization catalyst was prepared according to the method of Comparative Example 3, and the molecular sieve ZD-2 prepared in Comparative Example 2 was used as the molecular sieve raw material. The raw materials and conditions are listed in Table 3-1.

[0116] Examples 17-32

[0117] The molecular sieve powder was mixed with alumina (total mass of 20 g) and dried. A 20 ml solution of 5 mass% nitric acid was added to the mixture to form a paste, which was extruded into a strip. The strip was dried at 120°C for 12 hours, then cut into pellets and calcined at 540°C for 24 hours. The catalyst was ion exchanged with an aqueous solution of an ion exchange agent and washed until the mother liquor was free of halide anions.

[0118] The ion-exchanged support was subjected to hydrothermal treatment (steam treatment) using an aqueous solution of a steam treatment agent as a steam source to produce the catalyst.

[0119] Examples 17 to 32 were prepared according to the above-described method. The specific parameters of the molecular sieve, ion exchange solution and steam treatment solution used, and the operating procedures, etc. are shown in Tables 3-1 to 3-3. The Na2O mole fraction (%) was determined by XRF (X-ray fluorescence).

[0120] Table 3-1 Catalysts and reaction performance

[0121]

[0122]

[0123] Table 3-2

[0124]

[0125] Table 3-3

[0126]

[0127]

[0128] Test Example 1

[0129] The catalysts prepared in Examples 17 to 32, Comparative Example 3 and Comparative Example 4 were evaluated in a continuous flow fixed bed micro-hydrogen unit. Two grams of catalyst was loaded and an industrial xylene isomerization feedstock was used to evaluate the catalyst. The feedstock composition used in the reaction is shown in Table 4, and the evaluation process parameters and reaction results for each catalyst are shown in Tables 3-1 to 3-3. The reaction conditions included: hydrogenation, temperature of 330°C, pressure of 1.0 MPa, weight hourly space velocity of 10 h -1 , hydrogen / hydrocarbon molar ratio of 1.5.

[0130] The catalyst performance was evaluated using the following calculation method:

[0131] Isomerization equilibrium achievement rate:

[0132] Xylene yield:

[0133] Table 4 Raw material composition

[0134]

[0135] Test Example 2

[0136] The molecular sieve prepared in Example 9 and Comparative Example 1 was subjected to XRD detection.

[0137] The XRD diffraction spectrum of the Na-type raw powder ZD-1 prepared in Comparative Example 1 is shown in Figure 1. Figure 1 In the range of 5-35 degrees, there are characteristic peaks of MFI molecular sieve.

[0138] The spectrum of the molecular sieve Z-1 sample synthesized in Example 9 is shown in Figure 2. Figure 2 The spectrum of the molecular sieve Z-1 sample synthesized in Example 9 is shown in Figure 2.

[0139] Test Example 3

[0140] The molecular sieve sample Z-1 prepared in Example 9 and Comparative Example 1 was subjected to scanning electron microscope analysis.

[0141] The SEM spectrum of the molecular sieve sample Z-1 prepared in Example 9 is shown in Figure 3. Figure 3 , which has the characteristics of multi-level pore nanocrystal structure.

[0142] The SEM spectrum of the molecular sieve sample ZD-1 prepared in Comparative Example 1 is shown in Figure 4. Figure 4 , which has the characteristics of ordinary molecular sieve crystal structure.

[0143] From the above example results, it can be seen that the activity and selectivity of the catalyst prepared from the molecular sieve synthesized by using the conventional template agent or constant temperature method are not as good as those of the sample synthesized by using the single quaternary ammonium cation template agent and variable temperature hydrothermal synthesis. The activity and selectivity can be further improved by ion exchange with the quaternary ammonium salt aqueous solution and hydrothermal treatment using the single quaternary ammonium cation template agent aqueous solution as the vapor source. From the scanning electron microscope photos of the molecular sieve sample Z-1 prepared in Example 9 and the molecular sieve sample ZD-1 prepared in Comparative Example 1, it can be seen that the molecular sieve prepared in Example 9 is more uniform and further it is inferred that the crystallinity is higher, and a catalyst with better activity can be prepared.

[0144] ​In the description of the present application, it needs to be explained that the terms "upper", "lower", "inner", "outer", "front", "back", "left", "right" and the like indicate the orientation or positional relationship based on the working state of the present application, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0145] In the description of the present application, it needs to be explained that the terms "installation", "connection", "connection" should be understood broadly unless otherwise explicitly specified and limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0146] The above describes the present application in combination with the preferred embodiments, but these embodiments are only exemplary and serve only to illustrate. On this basis, various substitutions and improvements can be made to the present application, which all fall within the scope of protection of the present application.

Claims

1. A method for preparing an MFI molecular sieve, characterized in that, The preparation method comprises the following steps: (1) contacting an alkylcycloalkylamine having the following formula I with a halogenated hydrocarbon R1X in an alcoholic solvent to form a first mixture material containing a template; wherein R m is a linear alkylene group having a carbon number of 4 to 8, R1and R2are each independently selected from a linear alkyl group having a carbon number of 1 to 8, and X is selected from chlorine or bromine; Formula I; (2) mixing the first mixture, a boron source, a silicon source and water, and then performing a hydrothermal reaction to obtain the MFI molecular sieve.

2. The production method according to claim 1, characterized by, R m is ethylene or pentylene.

3. The production method according to claim 1, characterized by, In step (1), the molar ratio of the alkylcycloalkylamine, the halogenated hydrocarbon R1X and the alcohol solvent is 1:(0.5-1.5):(3-20). The temperature of the contact reaction is 35-150°C, and the time is 2-24 hours.

4. The method of claim 1, wherein, In step (1), the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol.

5. The preparation method according to claim 4, characterized in that, The alcohol solvent is ethanol.

6. The method of claim 1, wherein, In step (2), the boron source is selected from sodium borate or boric acid, and the silicon source is selected from water glass, silica sol, solid silica gel or white carbon black.

7. The production method according to claim 6, wherein The boron source is sodium borate, and the silicon source is water glass.

8. The preparation method according to claim 7, wherein the silicon source is water glass with a molar ratio of SiO2 to Na2O of (2-4):

1.

9. The preparation method according to claim 6, characterized in that, In step (2), the molar ratio of the silicon source calculated based on SiO2 to the boron source calculated based on B2O3 is (30-70):1, and the molar ratio of water, the template agent and the silicon source calculated based on SiO2 is (20-50):(0.01-0.22):

1.

10. The method of claim 1, wherein, In step (2), the hydrothermal reaction comprises a first temperature control stage, a second temperature control stage and a third temperature control stage, and the temperature of the second temperature control stage is lower than that of the first temperature control stage and the third temperature control stage.

11. The method of claim 10, wherein, The temperature of the first temperature control stage is 105-135°C, the time is 6-18 hours, the temperature of the second temperature control stage is 45-85°C, the time is 6-18 hours, and the temperature of the third temperature control stage is 155-185°C, the time is 12-48 hours. The temperature increasing or decreasing rate in the first temperature control stage, the second temperature control stage and the third temperature control stage is 0.5-2°C / min.

12. The MFI molecular sieve prepared by the preparation method according to any one of claims 1-11.

13. The MFI molecular sieve of Claim 12, wherein, The MFI molecular sieve is a nanocrystal molecular sieve, and the crystal grain size is 20-60 nm.

14. The MFI molecular sieve of Claim 13, wherein, The MFI molecular sieve is distributed with pores with a pore size of 30-80 nm.

15. A process for preparing a catalyst for xylene isomerization reaction, characterized by, The preparation method comprises the following steps: (a) mixing the MFI molecular sieve according to any one of claims 12-14 or the MFI molecular sieve prepared by the preparation method according to any one of claims 1-11 with a binder and a peptizing agent to form a shaped carrier; (b) ion-exchanging the shaped support after calcination in an aqueous solution of a quaternary ammonium salt to obtain an ion-exchanged shaped support; wherein the quaternary ammonium salt is selected from compounds of the structural formula N(R E )4X1, R E each independently is selected from alkyl groups having a carbon number of 1 to 4, and X1is selected from halogens; and (b) ion-exchanging the shaped support after calcination in an aqueous solution of a quaternary ammonium salt to obtain an ion-exchanged shaped support; wherein the quaternary ammonium salt is selected from compounds of the structural formula N(R E )4X1, R E each independently is selected from alkyl groups having a carbon number of 1 to 4, and X1is selected from halogens; and (c) performing steam treatment on the shaped carrier after ion exchange.

16. The method of claim 15, wherein, In step (a), the binder is selected from alumina or titanium dioxide, and the peptizing agent is selected from nitric acid or hydrochloric acid. In the shaped carrier, the mass fraction of the MFI molecular sieve is 40-70%, and the balance is alumina, based on the total mass of the shaped carrier.

17. The method of claim 16, wherein the method further comprises, In step (a), the binder is alumina, and the peptizing agent is nitric acid.

18. The method of claim 15, wherein, R E each independently selected from ethyl or propyl, and X1is selected from chlorine or bromine.

19. The method of claim 15, wherein, In step (b), the concentration of the aqueous quaternary ammonium salt solution is 0.04-0.06 mol / L, the liquid-solid ratio during ion exchange is 5-30 mL / g, the ion exchange temperature is 50-90°C, and the exchange times are 2-4.

20. The method of claim 15, wherein, The step (b) further comprises the following steps after the ion exchange: The ion-exchanged shaped carrier is washed with water until no halogen anion is detected in the washing liquid, the pH value of the washing liquid is 6-8, and the molar content of Na2O of the ion-exchanged shaped carrier after the water washing is 0.05-0.20%.

21. The method of claim 15, wherein, The steam treatment in the step (c) uses an aqueous solution of the template agent as the steam source.

22. The method of claim 21, wherein, The concentration of the aqueous solution of the template agent is 0.01-0.08 mol / L; the amount of the aqueous solution of the template agent is 5-30 mL / g based on the mass of the ion-exchanged shaped carrier; the temperature of the steam treatment is 150-500 ℃, and the time is 3-6 hours.

23. The preparation method according to claim 22, characterized in that, The concentration of the aqueous solution of the template agent is 0.04-0.06 mol / L, and the temperature of the steam treatment is 200-450 ℃.

24. A xylene isomerization reaction characterized by, The xylene isomerization raw material is subjected to xylene isomerization reaction under the catalysis of the xylene isomerization reaction catalyst prepared by the preparation method of any one of claims 15-23.

25. The xylene isomerization reaction of claim 24, wherein, The xylene isomerization reaction is carried out under hydrogenation conditions, the reaction temperature is 250-350℃, the reaction pressure is 0.5-2.0MPa, the weight hourly space velocity of the xylene isomerization reaction catalyst is 6-20h -1 , and the hydrogen / hydrocarbon molar ratio is 0.8-2.8.

Images