A method for modifying the outer surface of a molecular sieve

Abstract

The application discloses a method for modifying the outer surface of a molecular sieve, comprising the following steps: 1) treating the initial molecular sieve with an organic species to perform channel filling pretreatment, so as to obtain a micropore-clogged low-micropore molecular sieve; 2) performing chemical treatment on the molecular sieve obtained in step 1); and 3) performing calcination treatment on the molecular sieve obtained in step 2), so as to obtain a molecular sieve with a modified outer surface. In step 1), the organic species is a compound containing at least C and H, and comprises one or more of hydrocarbons or organic amines. The method can realize the directional modification of the outer surface of the molecular sieve, and can protect the internal structure and properties of the crystal well and is not affected by the treatment conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of molecular sieve technology, and particularly relates to a method for modifying the outer surface of a molecular sieve. BACKGROUND

[0002] Molecular sieve is an important active component or catalyst carrier in the field of petroleum and chemical industry. It is usually composed of [SiO4], [AlO4], [PO4] and other tetrahedrons as structural units, and has regular microporous channels and high specific surface area. The [AlO4] tetrahedron in the framework of the molecular sieve has a negative charge, so it needs to be neutralized by additional framework cations. These cations are free in the framework around the framework, and different cations can be used for replacement. Different cations exhibit different properties in the framework, thereby reflecting different chemical reaction properties of the molecular sieve. Due to the narrow microporous channels of the molecular sieve, it also exhibits different shape-selective properties in different reactions. For example, Y molecular sieve has large pores with a twelve-membered ring, so it is suitable for cracking reactions of large molecular diesel components; ZSM-5 molecular sieve has mesopores with a ten-membered ring, so it is suitable for cracking gasoline components to produce propylene or converting methanol to produce aromatic hydrocarbons; and SAPO-34 molecular sieve has small pores with an eight-membered ring, so it is suitable for converting methanol to produce ethylene and propylene.

[0003] The outer surface of the molecular sieve lacks channel restriction, and the element distribution is different from that in the crystal, so it exhibits different chemical properties from the microporous channels. For example, the outer surface lacks shape-selective properties, and at the same time retains acidic properties, leading to the occurrence of side reactions on the outer surface to generate by-products; or the outer surface has pore blockage, causing the diffusion rate of reactants and products into and out of the micropores to decrease; or the outer surface has weak acidic sites such as Si-OH, which adsorb reaction molecules, leading to a decrease in molecular diffusion rate, which is not conducive to the reaction. Therefore, the outer surface of the molecular sieve needs to be modified by a certain method.

[0004] The existing methods for modifying the outer surface mainly include acid treatment, alkali treatment, chemical deposition and metal modification.

[0005] CN 102050463 A discloses a Beta molecular sieve containing mesopores and a siliconization preparation method thereof. The Beta molecular sieve after calcination is first subjected to acid treatment to remove aluminum, and then subjected to liquid-phase surface deposition of a silicon source to form a surface silicon-rich layer. In this method, the acid treatment may affect the microporous properties of the molecular sieve.

[0006] ZL200610047961 uses a gas-phase / liquid-phase deposition method to deposit tetraethoxysilane on the molecular sieve, and removes the organic groups by calcination. However, it can only be deposited on the outer surface and the pore mouth, and in order to achieve good results, multiple deposition modifications are needed, which is easy to cause channel blockage. SUMMARY

[0007] Therefore, the main purpose of the present application is to provide a method for modifying the outer surface of a molecular sieve, which can change the acid properties of the outer surface without affecting the original properties of the inner surface of the molecular sieve and without blocking the pores.

[0008] To achieve the above-mentioned purposes, the present application adopts the following technical solutions: a method for modifying the outer surface of a molecular sieve, comprising the following steps:

[0009] 1) treating the initial molecular sieve with an organic species to perform pore filling pretreatment, thereby obtaining a micropore-clogged low-micropore molecular sieve;

[0010] 2) performing chemical treatment on the molecular sieve obtained in step 1);

[0011] 3) performing calcination treatment on the molecular sieve obtained in step 2), thereby obtaining a molecular sieve with a directionally modified outer surface;

[0012] In the step 1), the organic species is a compound containing at least C and H, and contains one or more of hydrocarbons or organic amines, and the molecular diameter is 0.30-0.70 nm.

[0013] The hydrocarbon organic species meeting the above requirements can achieve the purpose of the present application. In a specific embodiment of the present application, the hydrocarbon organic species is one or more of benzene and its substituted derivative, naphthalene and its substituted derivative, and cycloalkane and its substituted derivative. The substituted derivative is preferably methyl and ethyl.

[0014] The hydrocarbon organic species meeting the above requirements can achieve the purpose of the present application. In a specific embodiment of the present application, the hydrocarbon organic species is a compound with a molecular formula of C i H 2i (i=4-8), C i H 2i+2 (i=4-8), C i H 2i-2 (i=4-8).

[0015] The hydrocarbon organic species meeting the above requirements can achieve the purpose of the present application. In a specific embodiment of the present application, the hydrocarbon organic species is a carbon deposition compound generated in a methanol-to-olefin reaction.

[0016] The organic amine meeting the above requirements can achieve the purpose of the present application. In a specific embodiment of the present application, the organic amine is selected from one or more of triethylamine, diethylamine, di-n-propylamine, diisopropylamine, morpholine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and n-butylamine.

[0017] According to the method of the present application, the organic species is preferably one or more of benzene, toluene, carbon deposition species, triethylamine, and morpholine. The above-mentioned preferred organic species can diffuse into the micropore channels of the molecular sieve and simultaneously not easily escape, thus playing the roles of plugging the pores and supporting the framework, and the selected organic species only contains carbon, hydrogen, and nitrogen elements, which can be completely removed through calcination treatment in the later stage.

[0018] According to the method of the present application, the pore filling pretreatment in step 1) is one or more of gaseous molecular diffusion, liquid molecular diffusion, or organic species transformation treatment caused by chemical reaction in the pores. In the gaseous molecular diffusion treatment, the organic species is in a gaseous form and contacts the molecular sieve; in the liquid molecular diffusion treatment, the organic species is in a liquid form and contacts the molecular sieve; and in the organic species transformation treatment caused by chemical reaction in the pores, the organic species undergoes chemical reaction under certain specific conditions in the micropore channels of the molecular sieve to generate carbon deposition species, for example, after methanol contacts the molecular sieve at 400-500 ℃, chemical reaction occurs and the methanol is converted into carbon deposition species.

[0019] According to the method of the present application, the micropore volume of the low-micropore molecular sieve in step 1) is less than 0.05 cm 3 g -1 , and preferably, the micropore volume is less than 0.03 cm 3 g -1 .

[0020] According to the method of the present application, the chemical treatment in step 2) is one or more of acid treatment, alkali treatment, hydrothermal treatment, silanization treatment, silicon tetrachloride gas isomorphous replacement treatment, ammonium fluosilicate liquid isomorphous replacement treatment, aluminum chloride gas isomorphous replacement, or secondary crystallization treatment; preferably, one or more of acid treatment, alkali treatment, and silanization treatment. The specific treatment methods can refer to the corresponding treatment technologies of the existing molecular sieves.

[0021] According to the method of the present application, the calcination in step 3) is performed at 500-800 ℃ for 1-6 h.

[0022] According to the method of the present application, the initial molecular sieve can be selected from the conventional molecular sieves in the industry, including but not limited to ZSM-5 molecular sieve, SAPO-34 molecular sieve, Y-type molecular sieve, Beta molecular sieve, and the like.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] The application discloses a method for selectively modifying the outer surface of a molecular sieve. The method comprises the following steps: firstly, performing channel filling pretreatment on the molecular sieve by using the aforementioned organic species; secondly, performing secondary chemical treatment on the molecular sieve, for example, but not limited to, acid treatment, alkali treatment, silanization treatment, crystallization treatment and the like; and finally, performing calcination treatment, so as to restore the blocked internal channels, achieve the purpose of modifying the outer surface properties of the molecular sieve, and meanwhile, not affect the internal surface properties of the molecular sieve. Therefore, the method can realize directional modification of the outer surface of the molecular sieve, and plays a good protective role on the internal structure and properties of the crystal, and is not affected by the treatment conditions. Meanwhile, the selected organic species is not easy to escape after diffusing into the microporous channels of the molecular sieve, and can play a role in blocking the channels. DETAILED DESCRIPTION

[0025] The application will be further described below in combination with examples, but the application is not limited to the listed examples, and should also include equivalent improvements and modifications of the technical solutions defined in the claims attached to the application.

[0026] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited. The ranges and values should be interpreted as being approximate. For numeric values, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with one another to form one or more new numeric ranges, which should be considered as being specifically disclosed herein.

[0027] In the following examples and comparative examples:

[0028] (1) Main raw material source explanation

[0029] The ZSM-5 molecular sieve is purchased from Nankai Catalyst Factory, and the pore opening diameter is 0.55 nm;

[0030] The SAPO-34 molecular sieve is purchased from Shandong Jiangyue Technology Co., Ltd., and the pore opening diameter is 0.38 nm;

[0031] The sources of other reagents are shown in Table 1:

[0032] Table 1

[0033]

[0034]

[0035] (2) Characterization and test means explanation

[0036] The crystal structure of the molecular sieve is characterized by XRD. The XRD tester used is a D8 ADVANCE X-ray diffractometer of Bruker Company, Germany. The test conditions are as follows: Cu Kα ray source, tube voltage 40 kV, tube current 40 mA; scanning at 5-50°, scanning rate 4° / min.

[0037] The relative crystallinity calculation method is as follows: the molecular sieve is characterized by XRD to obtain corresponding characteristic diffraction peaks. The characteristic diffraction peaks of ZSM-5 molecular sieve are 7.9°, 8.9°, 23.1°, 23.3° and 23.9°, and the characteristic diffraction peaks of SAPO-34 molecular sieve are 9.5°, 15.9°, 20.5°, 26° and 31°. After the XRD instrument measures each sample, first, the sum of the characteristic diffraction peak areas of Comparative Example 1 and Comparative Example 2 is calculated. Comparative Example 1 is taken as the ZSM-5 molecular sieve benchmark, and it is specified that the sum of the characteristic diffraction peak areas of Comparative Example 1 corresponds to 100%. The ZSM-5 molecular sieve crystallinity calculation formula is: sum of measured diffraction peak areas / sum of characteristic diffraction peak areas of Comparative Example 1*100%. Comparative Example 2 is taken as the SAPO-34 molecular sieve benchmark, and it is specified that the sum of the characteristic diffraction peak areas of Comparative Example 2 corresponds to 100%. The SAPO-34 molecular sieve crystallinity calculation formula is: sum of measured diffraction peak areas / sum of characteristic diffraction peak areas of Comparative Example 1*100%.

[0038] The pore structure of the molecular sieve in the application is determined by low-temperature N2 physical adsorption characterization, and the instrument is Micromeritics ASAP 2460 (USA). He is used as the inert gas to measure the dead volume of the sample tube, and nitrogen is used as the adsorbent to measure the pore structure properties of the sample. The specific surface area is calculated by the BET formula, and the micropore specific surface area and the micropore volume are calculated by the t-plot method.

[0039] Total acid amount determination: NH3-TPD test is performed on a Micromeritics AutoChem II 920 / AutoChem HP 2950 type chemisorption instrument. 0.2 g of sample is heat-treated at 550℃ for 0.5 h in a He atmosphere, then cooled to 100℃, then NH3-He mixed gas with φ(NH3) of 10% is introduced, the sample is subjected to NH3 adsorption for 80 min, then He is used for purging for 20 min to remove physically adsorbed NH3, and finally, the temperature is raised from 100℃ to 600℃ at a rate of 10℃ / min in a He atmosphere for programmed temperature NH3 desorption.

[0040] Surface acid amount determination: The surface acid density was characterized by TGA-Py method. Pyridine molecules, 0.60 nm, cannot enter the mouth of SAPO-34 molecular sieve (0.38 nm), so they can only be adsorbed by the surface acid sites. The molecular sieve sample was heated to 500 ℃ for 1 h to remove the water and other impurity gases adsorbed by the sample. The sample was cooled to 50 ℃, pyridine was injected and adsorbed for 2 h. To remove the physically adsorbed pyridine, the temperature was raised to 150 ℃ and maintained for 1 h. Then the temperature was raised from 150 ℃ to 500 ℃, and maintained at 500 ℃ for 1 h. The amount of external surface acid was the amount of pyridine desorbed after 150 ℃.

[0041] The following examples are used to illustrate the method for modifying the external surface of the molecular sieve of the present application.

[0042] Example 1

[0043] The ZSM-5 molecular sieve was calcined at 650 ℃ for 5 h to remove the original template in the pores. 10 g of the calcined ZSM-5 molecular sieve was loaded into a quartz tube reactor with an inner diameter of 1 cm, the reactor was placed horizontally in a heating furnace, the temperature was controlled at 100 ℃, and benzene was introduced from one end of the quartz tube at a flow rate of 0.05 ml / min for 5 h. Nitrogen was used to purge for 1 h to obtain a benzene-filled molecular sieve. Nitrogen physical adsorption characterization showed that the micropore volume was 0.01 cm 3 g -1 ;

[0044] The benzene-filled molecular sieve 5 g was dissolved in 100 g of 0.1 mol / L hydrochloric acid solution, stirred at 65 ℃ for 2 h, filtered, washed, dried, and calcined at 650 ℃ for 5 h to obtain the ZSM-5 molecular sieve with modified external surface.

[0045] Example 2

[0046] The ZSM-5 molecular sieve was calcined at 650 ℃ for 5 h. 10 g of the calcined ZSM-5 molecular sieve was mixed with a toluene solution, sealed, and left to stand at room temperature for 24 h. Centrifugal separation was performed to obtain a toluene-filled molecular sieve. Nitrogen physical adsorption characterization showed that the micropore volume was 0.01 cm 3 g -1 ;

[0047] The toluene-filled molecular sieve 5 g was dissolved in 100 g of 0.1 mol / L sodium hydroxide solution, stirred at 65 ℃ for 1 h, filtered, washed, dried, and calcined at 650 ℃ for 5 h to obtain the ZSM-5 molecular sieve with modified external surface.

[0048] Example 3

[0049] Take SAPO-34 molecular sieve at 650 ℃ calcination treatment 5h, take calcined SAPO-34 molecular sieve 10g, is loaded into the inner diameter of 1cm quartz reaction tube, the quartz tube is placed vertically, the molecular sieve is supported by the quartz cotton at the lower end, the heating furnace is wrapped and heated, the temperature is controlled at 500℃, 80% concentration methanol aqueous solution is introduced from the lower end of the quartz tube by plunger pump, the flow rate is 0.1ml / min, the treatment is 2h, the chromatographic detection catalyst is completely deactivated (methanol conversion rate is less than 99%), the carbon filled molecular sieve is obtained, the nitrogen physical adsorption characterization determines that the micropore volume is 0.02cm 3 g -1 ;

[0050] The carbon filled molecular sieve 5g is dissolved in 0.2mol / L oxalic acid solution 100g, stirred at room temperature for 5h, filtered, washed, dried, and calcined at 650℃ for 5h to obtain the SAPO-34 molecular sieve with outer surface modification.

[0051] Example 4

[0052] The toluene filled molecular sieve obtained in example 2 is dissolved in a mixed tetraethyl orthosilicate n-hexane solution (tetraethyl orthosilicate 30wt%) 100g, stirred at 80℃ for 4h, filtered, washed, dried, and the above stirring treatment process is carried out for 2 more times, after washing and drying, calcined at 650℃ for 5h to obtain the ZSM-5 molecular sieve with silicon deposition on the outer surface.

[0053] Example 5

[0054] Take SAPO-34 molecular sieve at 650 ℃ calcination treatment 5h, take calcined SAPO-34 molecular sieve 10g, mix with triethylamine solution (99%), seal, stand at room temperature for 24h, centrifugal separation, obtain triethylamine filled molecular sieve, nitrogen physical adsorption characterization determines that the micropore volume is 0.02cm 3 g -1 ;

[0055] The triethylamine filled molecular sieve 5g is dissolved in 0.2mol / L oxalic acid solution 100g, stirred at 90℃ for 1h, filtered, washed, dried, and calcined at 650℃ for 5h to obtain the SAPO-34 molecular sieve with outer surface modification.

[0056] Example 6

[0057] Take SAPO-34 molecular sieve at 650 ℃ calcination treatment 5h, take calcined SAPO-34 molecular sieve 10g, mix with morpholine solution (99%), seal, stand at room temperature for 24h, centrifugal separation, obtain morpholine filled molecular sieve, nitrogen physical adsorption characterization determines that the micropore volume is 0.03cm 3 g -1 ;

[0058] The toluene-filled ZSM-5 molecular sieve 5 g obtained in Example 2 was loaded into a quartz tube reactor with an inner diameter of 1 cm, the reactor was placed horizontally in a heating furnace, the temperature was controlled at 400 ℃, SiCl4 solution was introduced from one end of the quartz tube at a flow rate of 0.05 ml / min using a plunger pump, and the treatment was performed for 4 h, then the nitrogen blowing was switched for 1 h, then the product was filtered, washed, dried, and calcined at 650 ℃ for 5 h to obtain a ZSM-5 molecular sieve with an enriched silicon element on the outer surface.

[0059] Example 7

[0060] The toluene-filled ZSM-5 molecular sieve 5 g obtained in Example 2 was loaded into a quartz tube reactor with an inner diameter of 1 cm, the reactor was placed horizontally in a heating furnace, the temperature was controlled at 400 ℃, SiCl4 solution was introduced from one end of the quartz tube at a flow rate of 0.05 ml / min using a plunger pump, and the treatment was performed for 4 h, then the nitrogen blowing was switched for 1 h, then the product was filtered, washed, dried, and calcined at 650 ℃ for 5 h to obtain a ZSM-5 molecular sieve with an enriched silicon element on the outer surface.

[0061] Comparative Example 1

[0062] The ZSM-5 molecular sieve was calcined at 650 ℃ for 5 h.

[0063] Comparative Example 2

[0064] The SAPO-34 molecular sieve was calcined at 650 ℃ for 5 h.

[0065] Comparative Example 3

[0066] The ZSM-5 molecular sieve was calcined at 650 ℃ for 5 h, and then 5 g of the calcined molecular sieve was dissolved in 100 g of a 0.1 mol / L sodium hydroxide solution, the mixture was stirred at 65 ℃ for 1 h, then the product was filtered, washed, dried, and calcined at 650 ℃ for 5 h to obtain a ZSM-5 molecular sieve treated with alkali.

[0067] Comparative Example 4

[0068] The SAPO-34 molecular sieve was calcined at 650 ℃ for 5 h, and then 5 g of the calcined molecular sieve was dissolved in 100 g of a 0.2 mol / L oxalic acid solution, the mixture was stirred at room temperature for 5 h, then the product was filtered, washed, dried, and calcined at 650 ℃ for 5 h to obtain a SAPO-34 molecular sieve treated with acid.

[0069] The micropore volume, relative crystallinity, and acid amount characterization results of the products of the above examples and comparative examples are shown in Table 2.

[0070] Table 2

[0071]

[0072]

[0073] From the data in Table 2 of the examples and comparative examples, it can be concluded that, compared with the same type of molecular sieve, the primary filling of organic species and the secondary chemical treatment in Examples 1-7 can significantly reduce the acid amount on the outer surface of the original molecular sieve, while the total acid amount of the molecular sieve remains essentially unchanged. In Comparative Examples 1-4, no organic species is filled, and the secondary chemical reaction is directly performed, which greatly destroys the structure of the original molecular sieve, greatly reduces the crystallinity, and significantly reduces the total acid amount, but the acid amount on the outer surface does not decrease significantly.

[0074] Obviously, the above examples of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can also be made by those of ordinary skill in the art. It is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application are within the scope of the spirit of the present application.

Claims

1. A method for modifying the external surface of a molecular sieve, characterized by: The method comprises the following steps: 1) treating the initial molecular sieve with an organic species to perform channel filling pretreatment, to obtain a micropore-clogged low-micropore molecular sieve; 2) performing chemical treatment on the molecular sieve obtained in step 1); 3) performing calcination treatment on the molecular sieve obtained in step 2), to obtain a molecular sieve with an outer surface directionally modified; In step 1), the organic species is a compound containing at least C and H, and comprises one or more of hydrocarbons or organic amines, and the molecular diameter is 0.30-0.70 nm.

2. The method of modifying the external surface of a molecular sieve of claim 1 wherein: The hydrocarbon organic species is one or more of benzene and substituted derivatives thereof, naphthalene and substituted derivatives thereof, and cycloalkanes and substituted derivatives thereof.

3. The method of modifying the external surface of a molecular sieve of claim 1 wherein: The hydrocarbon organic species is a compound of formula C i H 2i , CiH 2i+2 , CiH 2i-2 , wherein i = 4-8.

4. The method of modifying the external surface of a molecular sieve of claim 1 wherein: The hydrocarbon organic species is a carbon deposition compound generated in a methanol-to-olefin reaction.

5. The method of modifying the external surface of a molecular sieve of claim 1 wherein: The organic amine is selected from one or more of triethylamine, diethylamine, di-n-propylamine, diisopropylamine, morpholine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and n-butylamine.

6. The method of modifying the external surface of a molecular sieve of any one of claims 1-5, wherein: The organic species is selected from one or more of benzene, toluene, carbon deposition species, triethylamine, and morpholine.

7. The method of modifying the external surface of a molecular sieve of claim 1 wherein: In step 1), the channel filling pretreatment is selected from one or more of gaseous molecular diffusion, liquid molecular diffusion, or organic species conversion treatment caused by chemical reaction in the channel.

8. The method of modifying the external surface of a molecular sieve of claim 1 wherein: The micropore volume of the microporous molecular sieve in step 1) is less than 0.05 cm 3 g -1 .

9. The method of modifying the external surface of a molecular sieve of claim 8, wherein: The micropore volume of the microporous molecular sieve in step 1) is less than 0.03 cm 3 g -1 .

10. The method of modifying the external surface of a molecular sieve of claim 1 wherein: In step 2), the chemical treatment is selected from one or more of acid treatment, alkali treatment, hydrothermal treatment, silanization treatment, silicon tetrachloride gas isomorphous replacement treatment, ammonium fluorosilicate liquid isomorphous replacement treatment, aluminum chloride gas isomorphous replacement, or secondary crystallization treatment.

11. The method of modifying the external surface of a molecular sieve of claim 10 wherein: In step 2), the chemical treatment is selected from one or more of acid treatment, alkali treatment, and silanization treatment.

12. The method of modifying the external surface of a molecular sieve of claim 1 wherein: In step 3), the calcination conditions are 500-800 DEG C, and the calcination time is 1-6 h.

Images