CN109569718B - Preparation method of melem modified microporous molecular sieve shape-selective catalyst - Google Patents

Preparation method of melem modified microporous molecular sieve shape-selective catalyst Download PDF

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CN109569718B
CN109569718B CN201811476877.2A CN201811476877A CN109569718B CN 109569718 B CN109569718 B CN 109569718B CN 201811476877 A CN201811476877 A CN 201811476877A CN 109569718 B CN109569718 B CN 109569718B
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molecular sieve
melem
microporous molecular
shape
selective catalyst
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CN109569718A (en
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薛冰
刘佳宝
柳娜
徐瑞诚
管啸天
许杰
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Changzhou University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
    • B01J31/0234—Nitrogen-, phosphorus-, arsenic- or antimony-containing compounds
    • B01J31/0235—Nitrogen containing compounds
    • B01J31/0244—Nitrogen containing compounds with nitrogen contained as ring member in aromatic compounds or moieties, e.g. pyridine
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/26—Catalysts comprising hydrides, coordination complexes or organic compounds containing in addition, inorganic metal compounds not provided for in groups B01J31/02 - B01J31/24
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C6/00—Preparation of hydrocarbons from hydrocarbons containing a different number of carbon atoms by redistribution reactions
    • C07C6/08—Preparation of hydrocarbons from hydrocarbons containing a different number of carbon atoms by redistribution reactions by conversion at a saturated carbon-to-carbon bond
    • C07C6/12—Preparation of hydrocarbons from hydrocarbons containing a different number of carbon atoms by redistribution reactions by conversion at a saturated carbon-to-carbon bond of exclusively hydrocarbons containing a six-membered aromatic ring
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2231/00—Catalytic reactions performed with catalysts classified in B01J31/00
    • B01J2231/40—Substitution reactions at carbon centres, e.g. C-C or C-X, i.e. carbon-hetero atom, cross-coupling, C-H activation or ring-opening reactions
    • B01J2231/42—Catalytic cross-coupling, i.e. connection of previously not connected C-atoms or C- and X-atoms without rearrangement
    • B01J2231/4205—C-C cross-coupling, e.g. metal catalyzed or Friedel-Crafts type
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2531/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • C07C2531/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2531/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • C07C2531/26—Catalysts comprising hydrides, coordination complexes or organic compounds containing in addition, inorganic metal compounds not provided for in groups C07C2531/02 - C07C2531/24
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Abstract

The invention relates to a preparation method of a melem modified microporous molecular sieve shape-selective catalyst, which takes microporous molecular sieves MCM-22 and ZSM-5 as matrixes and disperses melem on the outer surface of the microporous molecular sieves by a liquid-phase ultrasonic dispersion method. The shape-selective catalyst obtained by the invention has good shape-selective catalytic performance in the process of synthesizing paraxylene by disproportionation of toluene.

Description

Preparation method of melem modified microporous molecular sieve shape-selective catalyst
Technical Field
The invention relates to the field of preparation of shape-selective catalysts, in particular to a preparation method of a modified microporous molecular sieve shape-selective catalyst used in a process of synthesizing paraxylene by toluene disproportionation.
Background
Paraxylene is an important chemical raw material, and the traditional synthetic method is mainly obtained through a toluene disproportionation process. The catalyst used in the toluene disproportionation process is ZSM-5 or MCM-22 microporous molecular sieve, and the alkylation reaction can simultaneously obtain the isomers of ortho-xylene, meta-xylene and para-xylene, and the main reason is that the para-xylene generated in the reaction process can easily generate the isomerization reaction on the outer surface of the catalyst to generate the ortho-xylene and the meta-xylene. Therefore, to increase the selectivity to para-xylene during disproportionation, i.e., to increase the shape selectivity of the catalyst, the molecular sieve must be modified. The purpose of modification is mainly two points: firstly, the number of acid sites on the outer surface of the catalyst is reduced, and the isomerization reaction of the product p-xylene on the outer surface of the molecular sieve is reduced; secondly, the size of the molecular sieve pore is adjusted, and the diffusion resistance of o-xylene and m-xylene is increased. Common methods of modification are chemical vapor silicon deposition, chemical liquid silicon deposition, pre-carbon deposition and metal oxide modification. Although the shape-selective performance of the molecular sieve catalyst can be effectively improved by the silicon deposition method, the acting force between the hydroxyl on the surface of the molecular sieve and the deposit is very weak, and 3-4 times of deposition is usually needed to achieve a good effect, so that the operation is complex and the energy consumption is high. The pre-carbon deposition can also improve the shape-selective performance of the molecular sieve catalyst, but the regenerated catalyst also needs to be pre-deposited again, so the operation is troublesome, and the laboratory research is limited at present. The operation of covering the acid sites on the outer surface of the molecular sieve by using metal oxide modification is very simple, and a good covering effect can be achieved at one time.
Therefore, the preparation method of the high-efficiency modified microporous molecular sieve shape-selective catalyst is found to have important application value in the process of synthesizing paraxylene.
Disclosure of Invention
The invention aims to solve the technical problems of complicated preparation operation, high cost, low catalytic efficiency and the like of a shape-selective catalyst in the process of synthesizing p-xylene by disproportionation of toluene, and provides a preparation method of the shape-selective catalyst, which has the advantages of simple synthesis method, low cost and high shape-selective performance.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a preparation method of a melem modified microporous molecular sieve shape-selective catalyst is characterized by comprising the following steps:
(1) adding a microporous molecular sieve into deionized water, and ultrasonically dispersing for 30min at room temperature, wherein the mass ratio of the microporous molecular sieve to the deionized water is 1:20-1: 50;
(2) gradually adding melem powder into the mixture obtained in the step (1), wherein the adding amount of the melem powder is 1 percent of the mass of the microporous molecular sieve in the solution each time, and performing ultrasonic treatment for 30min after each time of adding; adding for 5-10 times;
(3) and (3) filtering the mixture obtained in the step (2), drying the filter cake at 80 ℃ for 12h, heating to 120 ℃, keeping the temperature for 2h, and then cooling to room temperature to obtain the required melem modified microporous molecular sieve shape-selective catalyst.
As a limitation to the invention, the microporous molecular sieve of the invention is ZSM-5 or MCM-22.
As a limitation to the invention, the catalyst of the invention can be used in the process of synthesizing paraxylene by toluene disproportionation.
The preparation method of the microporous molecular sieve MCM-22 comprises the following steps:
dissolving 13.3g of sodium hydroxide in 443mL of deionized water; then adding 4g of sodium metaaluminate and 38mL of hexamethyleneimine into the solution, and stirring vigorously; 195mL of silica sol was slowly added dropwise to the above solution under vigorous stirring, and vigorous stirring was continued for 30 min. Transferring the obtained white gel into a crystallization kettle with a polytetrafluoroethylene lining, and crystallizing for 7 days in an oven at 150 ℃; then filtering, washing until the pH value is 8.0, drying for 24h at 110 ℃, and then roasting for 8h at 550 ℃ in a muffle furnace to obtain the microporous molecular sieve MCM-22.
The preparation method of the microporous molecular sieve ZSM-5 comprises the following steps:
firstly, dissolving 12.5g of sodium hydroxide in 288mL of deionized water; 3.7g of NaAlO were then added to the solution2And 195mL of tetrapropylammonium hydroxide solution, and vigorously stirred; 195mL of silica gel solution was slowly added dropwise to the solution with vigorous stirring, and vigorous stirring was continued for 30 min. Then transferring the white gel into a crystallization kettle with a polytetrafluoroethylene lining, and crystallizing for 3 days in an oven at 160 ℃; filtering, washing to pH 9.0,110 deg.C, oven drying for 24h, and calcining in muffle furnace at 550 deg.C for 8h to obtain microporous molecular sieve ZSM-5.
In order to improve the shape-selective performance of the microporous molecular sieve in the synthesis process of paraxylene, the covering of the acid sites on the outer surface of the microporous molecular sieve is key. SiO is mostly adopted in the conventional method for covering the outer surface of the microporous molecular sieve2MgO, etc. The dispersion of the substances on the outer surface of the microporous molecular sieve is mainly Van der Waals force, so that the substances are not firmly adsorbed and are not uniformly dispersed, and the stability and shape-selective performance of the catalyst are reduced. The invention takes melem as an adsorbate, and can effectively solve the problems.
Melem is a compound with a large molecular size, and the structure of the melem is shown as follows:
Figure BDA0001892380270000031
the melem is an alkaline substance with larger molecular size, and the preparation process adopts an ultrasonic dispersion mode, so that not only can layered melem be effectively stripped, but also the dispersion uniformity of the melem on the outer surface of the microporous molecular sieve can be enhanced. In addition, due to the alkalinity of the melem molecules, the melem molecules and the acid sites on the outer surfaces of the microporous molecular sieves MCM-22 and ZSM-5 are subjected to acid-base reaction and are firmly adsorbed on the outer surfaces of the molecular sieves. Therefore, the modified molecular sieve catalyst shows excellent stability and shape-selective performance in the toluene disproportionation process.
Drawings
FIG. 1 is an FT-IR spectrum of MCM-22 and Cat 2;
wherein A is the FT-IR spectrum of MCM-22; b is FT-IR spectrum of Cat 2; c is the C-N vibration peak of melem;
FIG. 2 is an FT-IR spectrum of 2, 4-dimethylquinoline adsorption of MCM-22 and Cat 2; wherein A is the FT-IR spectrum of MCM-22; b is FT-IR spectrum of Cat 2; c is an outer surface acid site;
as can be seen from FIG. 1, the C-N vibration peak of melem is clearly seen on Cat2, and it can be seen that the method can effectively support the melem on the surface of MCM-22.
As can be seen in FIG. 2, the acidic sites on the external surface of Cat2 have been significantly reduced compared to MCM-22 molecular sieve, which is the primary reason for the shape-selective nature of Cat 2.
Detailed Description
The invention will be further described in the following examples, but it is to be understood that these examples are for illustrative purposes only and are not to be construed as limiting the practice of the invention.
Example 1
Adding 2g of microporous molecular sieve MCM-22 into 40mL of deionized water, and ultrasonically dispersing for 30min at room temperature; gradually adding melem powder 0.02g each time into the mixture, and continuously adding for 5 times, and performing ultrasonic treatment for 30min after each addition; and filtering the obtained mixture, drying the filter cake at 80 ℃ for 12h, heating to 120 ℃, keeping the temperature for 2h, and then cooling to room temperature to obtain the required melem modified microporous molecular sieve shape-selective catalyst, which is recorded as Cat 1.
Example 2
Adding 2g of microporous molecular sieve MCM-22 into 100mL of deionized water, and ultrasonically dispersing for 30min at room temperature; gradually adding melem powder 0.02g each time into the mixture, continuously adding for 10 times, and performing ultrasonic treatment for 30min after each addition; and filtering the obtained mixture, drying the filter cake at 80 ℃ for 12h, heating to 120 ℃, keeping the temperature for 2h, and then cooling to room temperature to obtain the required melem modified microporous molecular sieve shape-selective catalyst, which is recorded as Cat 2.
Example 3
Adding 2g of microporous molecular sieve MCM-22 into 60mL of deionized water, and ultrasonically dispersing for 30min at room temperature; adding melem powder gradually into the mixture, adding 0.02g each time, continuously adding for 7 times, and performing ultrasonic treatment for 30min after each addition; and filtering the obtained mixture, drying the filter cake at 80 ℃ for 12h, heating to 120 ℃, keeping the temperature for 2h, and then cooling to room temperature to obtain the required melem modified microporous molecular sieve shape-selective catalyst, which is recorded as Cat 3.
Example 4
Adding 2g of microporous molecular sieve ZSM-5 into 40mL of deionized water, and ultrasonically dispersing for 30min at room temperature; gradually adding melem powder 0.02g each time into the mixture, and continuously adding for 8 times, and performing ultrasonic treatment for 30min after each addition; and filtering the obtained mixture, drying the filter cake at 80 ℃ for 12h, heating to 120 ℃, keeping the temperature for 2h, and then cooling to room temperature to obtain the required melem modified microporous molecular sieve shape-selective catalyst, which is recorded as Cat 4.
Example 5
Adding 2g of microporous molecular sieve ZSM-5 into 50mL of deionized water, and ultrasonically dispersing for 30min at room temperature; adding melem powder gradually into the mixture, adding 0.02g each time, continuously adding for 9 times, and performing ultrasonic treatment for 30min after each addition; and filtering the obtained mixture, drying the filter cake at 80 ℃ for 12h, heating to 120 ℃, keeping the temperature for 2h, and then cooling to room temperature to obtain the required melem modified microporous molecular sieve shape-selective catalyst, which is recorded as Cat 5.
Example 6
Adding 2g of microporous molecular sieve ZSM-5 into 70mL of deionized water, and ultrasonically dispersing for 30min at room temperature; gradually adding melem powder 0.02g each time into the mixture, and continuously adding for 6 times, and performing ultrasonic treatment for 30min after each addition; and filtering the obtained mixture, drying the filter cake at 80 ℃ for 12h, heating to 120 ℃, keeping the temperature for 2h, and then cooling to room temperature to obtain the required melem modified microporous molecular sieve shape-selective catalyst, which is recorded as Cat 6.
When the melem modified microporous molecular sieve obtained in the above embodiment is used in the process of synthesizing paraxylene by toluene disproportionation, the typical reaction conditions are as follows: the reaction temperature is 400 ℃, and the mass space velocity of the raw material is 0.8h-1And continuously evaluating for 8 h. The catalytic performance of each catalyst is shown in table 1:
TABLE 1 catalytic Properties of the catalysts
Catalyst and process for preparing same Toluene conversion (%) P-xylene selectivity (%)
Cat 1 27.4 65.3
Cat 2 19.1 83.6
Cat 3 25.9 77.4
Cat 4 22.8 75.2
Cat 5 20.7 78.5
Cat 6 24.3 69.0
As can be seen from the results in Table 1, the oxide modified microporous molecular sieve catalyst prepared by the invention has good catalytic performance in the process of synthesizing paraxylene by alkylation of toluene, not only realizes higher toluene conversion rate, but also obtains good shape-selective performance.
In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims (2)

1. A preparation method of a melem modified microporous molecular sieve shape-selective catalyst is characterized by comprising the following steps:
(1) adding a microporous molecular sieve into deionized water, and ultrasonically dispersing for 30min at room temperature, wherein the mass ratio of the microporous molecular sieve to the deionized water is 1:20-1: 50;
(2) gradually adding melem powder into the mixture obtained in the step (1), wherein the adding amount of the melem powder is 1 percent of the mass of the microporous molecular sieve in the solution each time, and carrying out ultrasonic treatment for 30min after each time of addition, and adding the mixture for 5-10 times;
(3) filtering the mixture obtained in the step (2), drying the filter cake at 80 ℃ for 12h, then heating to 120 ℃, keeping the temperature for 2h, and then cooling to room temperature to obtain the required melem modified microporous molecular sieve shape-selective catalyst, wherein the microporous molecular sieve is ZSM-5 or MCM-22.
2. The method of claim 1, wherein the melem-modified microporous molecular sieve shape-selective catalyst is used in the disproportionation of toluene to para-xylene.
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