CN100457266C - Manufacturing method of faujasite coated phosphorus heteropoly tungstic acid catalyzer - Google Patents

Abstract

An octa zeolite covering PTA heteropoly acid catalyst preparation method, which makes tungstate and phosphate as material, the octa zeolite is the matrix of covering PTA heteropoly acid, with adopting ''bottle shipbuilding'' method, react in a microwave reactor in situ synthesis. The invention has short synthesis time, high synthesis efficiency and the crystal structure of the octa zeolite keep complete in the acidification synthesis.

Description

Preparation method of faujasite-coated phosphotungstic heteropolyacid catalyst

technical field

The invention relates to a novel and highly efficient preparation method of a novel solid acid-faujasite-coated phosphotungstic heteropolyacid.

Background technique

Solid acids (such as molecular sieves, oxides, mixed oxides, phosphates, etc.) are very important catalysts in the production of petrochemicals and many chemicals. So far, more than 180 industrial processes have used the above-mentioned solid acid catalysts. However, there are still many acid-catalyzed reactions (for example: esterification reaction, hydrolysis reaction and hydration reaction, etc.) that need to be carried out under the action of a large amount of inorganic acid (sulfuric acid, hydrochloric acid, etc.) or _AlCl3 , and these reaction processes are accompanied by severe toxicity, corrosion There are a series of problems such as safety, product separation and waste liquid treatment difficulties. Therefore, the use of safe, non-corrosive and easy-to-separate solid acid to replace liquid acid as a catalyst is of great significance for environmental protection.

There is always water in the raw materials or products of many organic reactions (for example: hydrolysis reaction, hydration reaction, esterification reaction and Prins reaction, etc.), because the water in the reaction system is very easy to make the active center of solid acid catalyst (such as molecular sieves, etc.) Poisoning and inactivation, only a very small number of solid acids (such as heteropoly acids) have a certain degree of activity and stability.

酸的特性等。这些性质可使杂多酸用作均相和多相氧化型催化剂和酸催化剂。杂多酸作为一种新型的酸催化剂被广泛应用在酯分解反应、烷基化反应、环氧化物开环反应、缩合反应和醚化反应等。Heteropolyacids have many excellent characteristics, such as: simple components, definite structure, and structural characteristics of general complexes and metal oxides; it is both a multi-electron oxidant and a strong protonic acid, and its oxidative and acidic properties can be changed by changing It is modulated by its composition method; it is easily soluble in water and polar organic solvents, and its solution is generally relatively stable; among them, the heteropolyacid with Keggin structure has a strong and uniform

Acid properties, etc. These properties allow heteropolyacids to be used as homogeneous and heterogeneous oxidation-type catalysts and acid catalysts. As a new type of acid catalyst, heteropolyacid is widely used in ester decomposition reaction, alkylation reaction, epoxide ring opening reaction, condensation reaction and etherification reaction.

However, heteropolyacids also have defects such as small specific surface area (less than 10m ² /g), low thermal stability, difficult recovery, and easy loss when dissolved in water. Therefore, the impregnation method is usually used to load heteropolyacids on the carrier to improve Its specific surface area, thermal stability, catalytic activity and repeated use performance. In recent years, various carriers, such as: activated carbon, amorphous silica, molecular sieve, etc., have been used to support heteropolyacid compounds. However, because heteropolyanions are easy to transfer electrons to the carrier, the acidity of heteropolyacids decreases after loading; at the same time, in practical applications, there are still problems such as easy dissolution and loss of heteropolyacids, and low selectivity of target products in complex reactions. .

At the same time, another type of commonly used solid acid catalyst, molecular sieve, has low catalytic activity for reactions that require strong acid catalysis due to its few defects in the skeleton network and weak acidity. However, there are uniform pores in the molecular sieve structure. When the molecular size of the reactants and products is close to the pore size in the crystal, the selectivity of the reaction often depends on the relative size of the molecule and the pore size. When they match each other, they often have a high target product. selective. Therefore, if the strong acidity of heteropolyacids is combined with the pore characteristics of molecular sieves, it is possible to produce new solid acid catalysts with both strong acidity and high product selectivity. Since the pores of Y-type molecular sieves are generally 0.74×0.78 nanometers, and the diameter of phosphotungstic heteropolyacids with Keggin structures is about 1.0-1.2 nanometers, it is difficult to directly introduce heteropolyacids into the pores of molecular sieves through traditional impregnation processes. middle. However, Y-type molecular sieve has a supercage structure, and the size of its internal spherical cavity is 1.3 nanometers. If the raw materials for the synthesis of phosphotungstic heteropolyacid are introduced into the molecular sieve supercage in advance, and then synthesized in situ by the "ship-in-a-bottle" method , the final heteropolyacid will be fixed inside the Y-type molecular sieve. The faujasite-coated phosphotungstic heteropoly acid catalyst prepared by this method can, on the one hand, adjust the acidity of the catalyst by adjusting the load of the heteropoly acid, make up for the weak acidity of molecular sieves, and improve its catalytic performance; On the other hand, the shape-selective performance of the product can also be increased by virtue of the pore characteristics of the molecular sieve. At the same time, due to the limitation of the pores of the molecular sieve, it can effectively overcome the problems such as the loss of heteropolyacids during use.

In 1996, B.Sulikowski et al first proposed the synthesis of phosphotungstic heteropolyacid in the supercage of Y-type molecular sieve. They used the Y-type molecular sieve dealuminated by H ₄ EDTA as the parent material, and the prepared catalyst was tested by infrared and ³¹ P-NMR characterization Phosphotungstic heteropolyacids have been formed in the supercages of Y-type molecular sieves and applied to the disproportionation reaction of m-xylene. (Catalysis Letters 1996, 39, 27)

In 1996, B.Sulikowski et al first proposed the synthesis of phosphotungstic heteropolyacid in the supercage of Y-type molecular sieve. They used the Y-type molecular sieve dealuminated by H ₄ EDTA as the parent material, and the prepared catalyst was tested by infrared and ³¹ P-NMR characterization Phosphotungstic heteropolyacid has been formed in the supercage of Y-type molecular sieve, but the synthesis efficiency is very low. (Catalysis Letters 1996, 39, 27)

In their later work, they performed cesium ion exchange on the molybdophosphopolyacid synthesized in situ in the Y-type molecular sieve supercage to increase the stability of the molybdophosphopolyacid. It was found that the retained amount of the partially exchanged phosphomolybdenum heteropolyacid in the supercage increased, but the catalytic effect in the esterification reaction decreased due to the decrease of the amount of the heteropolyacid after the exchange. (Reaction Kinetics and Catalysis Letters 2000, 69, 253)

In addition, they also studied the effect of the silicon-aluminum ratio in the molecular sieve matrix on the synthesis efficiency, and found that a moderate aluminum content is beneficial to the synthesis. The raw materials for the synthesis of phosphomolybdenum heteropolyacid can be induced by aluminum atoms, and exchange with aluminum atoms first, thereby promoting the synthesis. However, excessive aluminum content affects the acid content of phosphomolybdenum heteropolyacid. (Chemical Engineering Science 2001, 56, 799)

The above literature reports all adopt high-temperature hydrothermal acidification process, the synthesis medium has high acidity (pH=1.5-2), the solution temperature is high (95 degrees Celsius), and the synthesis time is long (0.5-3 hours), which is very easy to form the parent molecular sieve The collapse of the structure makes it difficult to obtain a catalyst with a complete faujasite crystal form.

In order to eliminate these adverse effects above, S.R.Mukai et al. attempted to use ion-exchange membrane technology in 2003 to achieve effective coating of heteropolyacids. However, their research shows that although the use of electrode reaction is helpful to the synthesis of phosphomolybdenum heteropoly acid, the amount fixed in the molecular sieve supercage is very small. Therefore, they still used the traditional hydrothermal method to synthesize, by adding tetrabutanol to stabilize phosphomolybdic acid, and obtained catalysts coated with heteropolyacids at different temperatures of 60-150 degrees Celsius. (Applied Catalysis A: General 2003, 256, 107).

According to the method reported in the above-mentioned literature, the skeleton of the molecular sieve has collapsed during the synthesis process, and an amorphous silicon dioxide-coated phosphorus tungsten heteropolyacid is obtained. Therefore, it is difficult to successfully synthesize this new solid-acid catalytic material by conventional hydro-synthesis processes, and new synthesis processes need to be explored and developed.

Contents of the invention

The purpose of the present invention is to provide a method that can overcome the problems of relatively high acidity of the synthesis medium, high temperature, and long synthesis time in the process reported in the literature, without adding a stabilizer; simultaneously, the faujasite crystal form can be obtained The synthesis process of complete phosphotungstic heteropolyacid catalyst.

The preparation method of the faujasite-coated phosphotungstic heteropolyacid catalyst mainly includes: using tungstate and phosphate as raw materials, faujasite as the matrix of the coated phosphotungstic heteropolyacid, and adopting "shipbuilding in a bottle" Method, reaction in situ synthesis in a microwave reactor, detailed preparation steps are as follows:

1. According to the weight ratio of tungstate and phosphate is 5-15:1, completely dissolve the two kinds of salts in deionized water to make a mixed solution of tungstate and phosphate, in which tungstate and deionized water The weight to volume ratio is 1:5-10;

2. Put the faujasite precursor in a vacuum reactor, and heat through the outer wall to help desorb the water vapor and other gases attached to the molecular sieve channels;

3. According to the weight ratio of faujasite matrix and tungstate: 1:1-2, add dropwise the mixed solution of tungstate and phosphate obtained in step 1 to the faujasite matrix to make it completely infiltrated, so that the tungsten Acid ions and phosphate ions enter the supercage of the molecular sieve. After the solution is added dropwise, transfer the suspension to a beaker and stir for 12-24 hours;

4. Add an acidifying agent dropwise to the suspension obtained in step 3 until pH = 1, then quickly transfer it to a round bottom flask, and put it into a microwave reactor for reaction. The microwave reaction time is 3-10 minutes, and the power is 650 watts. After the reaction is completed, cool, filter, and completely elute the phosphotungstic acid on the surface of the molecular sieve with hot water, then dry the catalyst and roast at 250 degrees Celsius for 2 hours to obtain the catalyst of the present invention.

The synthesis process of the novel faujasite-coated phosphotungstic heteropolyacid catalyst provided by the present invention uses faujasite as the matrix for coating phosphotungstic heteropolyacid.

Phosphate raw materials for preparing phosphotungstic acid in the faujasite-coated phosphotungstic heteropoly acid catalyst of the present invention are disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate and phosphoric acid Potassium, tungstate raw materials are sodium tungstate, potassium tungstate and ammonium tungstate. The preferred raw materials for synthesizing phosphotungstic acid are sodium tungstate and disodium hydrogen phosphate. The acidulant is selected from concentrated hydrochloric acid or phosphoric acid, preferably concentrated hydrochloric acid.

The microwave heating adopted in the present invention uses microwaves to accelerate the internal movement of the heated material to generate heat. Since the heat conduction process is not required, the inside of the material can reach the heating temperature in an instant. Compared with conventional heating methods, microwave heating has the characteristics of uniform heating of the reaction system, the ability to promote the collision probability between reaction molecules, shorten the reaction time, and increase the reaction yield. Therefore, in the process of synthesizing a new type of faujasite-coated phosphotungstic heteropolyacid catalyst by using the "boat-in-a-bottle" method, in-situ synthesis assisted by microwave heating can shorten the synthesis reaction time and reduce the amount of faujasite itself in the synthesis process. Possibility of structural damage.

The synthesis process provided by the invention can obtain a complete faujasite crystal structure when the microwave-assisted reaction time is appropriate. The acid strength and acid content of the catalyst obtained by this process are equivalent to those directly obtained by the equal-volume impregnation method, and the phosphotungstic acid will not be lost during the reaction.

Detailed ways

Example 1

Dissolve 15 grams of sodium tungstate and 1.5 grams of disodium hydrogen phosphate in 50 ml of deionized water at the same time, add 10 grams of faujasite, and stir thoroughly for 24 hours. Put the suspension into hot water at 95 degrees Celsius, slowly add concentrated hydrochloric acid dropwise under stirring, stop adding when pH=1 is controlled with an acidity meter, and continue to react for half an hour to generate phosphotungstic acid. After cooling, filter with suction, wash with 100 ml of deionized water at 80 degrees Celsius for several times each time, completely elute the phosphotungstic acid attached to the surface of the molecular sieve, collect the filtrate, and detect the filtrate with ultraviolet spectroscopy to determine whether the attached Phosphotungstic acid was completely eluted. After the phosphotungstic acid on the surface of the molecular sieve is completely eluted, the catalyst is dried and calcined at 250 degrees Celsius for 2 hours. The samples synthesized by this method are labeled PW@USY (hydrothermal method). The structures of the above samples were detected by means of X-ray diffraction, nitrogen adsorption and ammonia temperature-programmed desorption, and the results are shown in Tables 1 and 2.

Example 2

Completely dissolve 15 grams of sodium tungstate and 1.5 grams of disodium hydrogen phosphate in 50 milliliters of deionized water for later use. Put 10 grams of faujasite in a round bottom flask to evacuate, and heat on the outer wall to help the desorption of water vapor and other gases attached to the molecular sieve channels. Then add a mixed solution of sodium tungstate and disodium hydrogen phosphate dropwise to the faujasite to make it completely infiltrated, so as to help tungstate ions and hydrogen phosphate ions enter the supercage of the molecular sieve. After the dropwise addition of the solution, the suspension was transferred to a beaker and stirred for 12 hours, then concentrated hydrochloric acid was added dropwise at room temperature until pH = 1, and it was quickly transferred to a round bottom flask and placed in a microwave reactor for reaction. Microwave reaction times range from 3 to 9 minutes at a power of 650 watts. After the reaction is complete, cool, filter, and use hot water to completely elute the phosphotungstic acid on the surface of the molecular sieve, then dry the catalyst and roast at 250 degrees Celsius for 2 hours. The samples synthesized by this method are labeled PW@USY (X minutes) (X represents the microwave reaction time). The structures of the above samples were detected by means of X-ray diffraction, nitrogen adsorption and ammonia temperature-programmed desorption, and the results are shown in Tables 1 and 2.

Example 3

Add 10 grams of faujasite into an aqueous solution dissolved with 4 grams of phosphotungstic heteropolyacid for equal volume impregnation, leave the catalyst at room temperature for 24 hours, dry the catalyst, and roast at 250 degrees Celsius for 2 hours. Samples synthesized in this way are labeled PW/USY. The structures of the above samples were detected by means of X-ray diffraction, nitrogen adsorption and ammonia temperature-programmed desorption, and the results are shown in Tables 1 and 2.

Example 4

Completely dissolve 15 grams of sodium tungstate and 1.7 grams of sodium phosphate in 50 milliliters of deionized water for later use. Put 10 grams of faujasite in a round bottom flask to evacuate, and heat on the outer wall to help the desorption of water vapor and other gases attached to the molecular sieve channels. Then drop the mixed solution of sodium tungstate and sodium phosphate into the faujasite to make it completely infiltrated, so as to help the tungstate ions and phosphate ions enter the supercage of the molecular sieve. After the dropwise addition of the solution, the suspension was transferred to a beaker and stirred for 12 hours, then concentrated hydrochloric acid was added dropwise at room temperature until pH = 1, and it was quickly transferred to a round bottom flask and placed in a microwave reactor for reaction. The microwave reaction time is 7 minutes and the power is 650 watts. After the reaction is complete, cool, filter, and use hot water to completely elute the phosphotungstic acid on the surface of the molecular sieve, then dry the catalyst and roast at 250 degrees Celsius for 2 hours. The samples synthesized by this method were labeled PW@USY (sodium phosphate). The structures of the above samples were detected by means of X-ray diffraction, nitrogen adsorption and ammonia temperature-programmed desorption, and the results are shown in Table 1.

Example 5

Completely dissolve 15 grams of sodium tungstate and 1.2 grams of sodium dihydrogen phosphate in 50 milliliters of deionized water for later use. Put 10 grams of faujasite in a round bottom flask to evacuate, and heat on the outer wall to help the desorption of water vapor and other gases attached to the molecular sieve channels. Then add a mixed solution of sodium tungstate and sodium dihydrogen phosphate dropwise to the faujasite to make it completely infiltrated, so as to help tungstate ions and dihydrogen phosphate ions enter the supercage of the molecular sieve. After the dropwise addition of the solution, the suspension was transferred to a beaker and stirred for 12 hours, then concentrated hydrochloric acid was added dropwise at room temperature until pH = 1, and it was quickly transferred to a round bottom flask and placed in a microwave reactor for reaction. The microwave reaction time is 7 minutes and the power is 650 watts. After the reaction is complete, cool, filter, and use hot water to completely elute the phosphotungstic acid on the surface of the molecular sieve, then dry the catalyst and roast at 250 degrees Celsius for 2 hours. The samples synthesized by this method are labeled EPW@USY (sodium dihydrogen phosphate). The structures of the above samples were detected by means of X-ray diffraction, nitrogen adsorption and ammonia temperature-programmed desorption, and the results are shown in Table 1.

Example 6

Completely dissolve 15 grams of potassium tungstate and 1.5 grams of disodium hydrogen phosphate in 50 milliliters of deionized water for later use. Put 10 grams of faujasite in a round bottom flask to evacuate, and heat on the outer wall to help the desorption of water vapor and other gases attached to the molecular sieve channels. Then add a mixed solution of potassium tungstate and disodium hydrogen phosphate dropwise to the faujasite to make it completely infiltrated, so as to help tungstate ions and hydrogen phosphate ions enter the supercage of the molecular sieve. After the dropwise addition of the solution, the suspension was transferred to a beaker and stirred for 12 hours, then concentrated hydrochloric acid was added dropwise at room temperature until pH = 1, and it was quickly transferred to a round-bottomed flask and placed in a microwave reactor for reaction. The microwave reaction time is 7 minutes and the power is 650 watts. After the reaction is complete, cool, filter, and use hot water to completely elute the phosphotungstic acid on the surface of the molecular sieve, then dry the catalyst and roast at 250 degrees Celsius for 2 hours. The samples synthesized by this method were labeled PW@USY (potassium tungstate). The structures of the above samples were detected by means of X-ray diffraction, nitrogen adsorption and ammonia temperature-programmed desorption, and the results are shown in Table 1.

Example 7

Completely dissolve 13 grams of ammonium tungstate and 1.5 grams of disodium hydrogen phosphate in 50 milliliters of deionized water for later use. Put 10 grams of faujasite in a round bottom flask to evacuate, and heat on the outer wall to help the desorption of water vapor and other gases attached to the molecular sieve channels. Then add a mixed solution of ammonium tungstate and disodium hydrogen phosphate dropwise to the faujasite to make it completely infiltrated, so as to help tungstate ions and hydrogen phosphate ions enter the supercage of the molecular sieve. After the dropwise addition of the solution, the suspension was transferred to a beaker and stirred for 12 hours, then concentrated hydrochloric acid was added dropwise at room temperature until pH = 1, and it was quickly transferred to a round bottom flask and placed in a microwave reactor for reaction. The microwave reaction time is 7 minutes and the power is 650 watts. After the reaction is complete, cool, filter, and use hot water to completely elute the phosphotungstic acid on the surface of the molecular sieve, then dry the catalyst and roast at 250 degrees Celsius for 2 hours. The samples synthesized by this method were labeled PW@USY (ammonium tungstate). The structures of the above samples were detected by means of X-ray diffraction, nitrogen adsorption and ammonia temperature-programmed desorption, and the results are shown in Table 1.

Example 8

Dissolve 15 grams of sodium tungstate completely in 50 milliliters of deionized water for later use. Put 10 grams of faujasite in a round bottom flask to evacuate, and heat on the outer wall to help the desorption of water vapor and other gases attached to the molecular sieve channels. Then add sodium tungstate solution dropwise to the faujasite to make it completely infiltrated, so as to help the tungstate ions enter the supercage of the molecular sieve. After the solution was added dropwise, the suspension was transferred to a beaker and stirred for 12 hours, then phosphoric acid was added dropwise at room temperature until pH = 1, then quickly transferred to a round bottom flask, and placed in a microwave reactor for reaction. The microwave reaction time is 7 minutes and the power is 650 watts. After the reaction is complete, cool, filter, and use hot water to completely elute the phosphotungstic acid on the surface of the molecular sieve, then dry the catalyst and roast at 250 degrees Celsius for 2 hours. Samples synthesized in this way were labeled PW@USY (phosphoric acid). The structures of the above samples were detected by means of X-ray diffraction, nitrogen adsorption and ammonia temperature-programmed desorption, and the results are shown in Table 1.

Table 1. Structures of samples obtained by different synthesis methods

Catalyst Specific surface area (m2/g) Super cage volume (ml/g) Catalyst crystal form USY 693.6 0.25 Faujasite PW@USY (hydrothermal method) 171.1 0.07   Amorphous silica PW@USY(9 minutes) 331.4 0.10   Amorphous silica PW@USY(7 minutes) 324.5 0.11 Faujasite PW@USY(5 minutes) 383.3 0.13 Faujasite PW@USY(3 minutes) 542.8 0.22 Faujasite PW/USY 476.7 0.21 Faujasite PW@USY (Sodium Phosphate) 351.3 0.12 Faujasite PW@USY (sodium dihydrogen phosphate) 362.4 0.11 Faujasite PW@USY (potassium tungstate) 321.2 0.12 Faujasite PW@USY (Ammonium Tungstate) 341.3 0.11 Faujasite PW@USY (phosphoric acid) 375.3 0.14 Faujasite

Table 2: Acid properties of samples obtained by different synthesis methods

A: Amount of strong acid produced by faujasite B: Amount of strong acid produced by phosphotungstic acid

Claims (5)

1, a kind of preparation method of faujasite coated phosphorus heteropoly tungstic acid catalyzer, with tungstates and phosphate is raw material, and faujasite is the parent of coated phosphorus heteropoly tungstic acid, adopts the direct in-situ synthetic method, the reaction original position is synthetic in microwave reactor, and preparation process is as follows:

1) be 5-15 by tungstates and phosphate weight ratio: 1, two kinds of salt are dissolved in the deionized water fully, make tungstates and phosphatic mixed solution, wherein the volume ratio of the weight of tungstates and deionized water is 1: 5-10;

2) place reactor to vacuumize the faujasite parent, at outer wall heating steam and other desorbing gas to help to adhere in the molecular sieve pore passage;

3) by faujasite parent and tungstates weight ratio be: 1: 1-2, in the faujasite parent, drip tungstates and the phosphatic mixed solution that step 1 obtains, make it to soak into fully, tungstate ion and phosphoric acid hydrogen radical ion are entered in the supercage of molecular sieve, after treating that solution dropwises, suspension is transferred to beaker stirred 12-24 hour;

4) in the suspension of step 3 gained, drip acidulant to pH=1, be transferred to rapidly in the round-bottomed flask then, put into microwave reactor and react, 3-9 minute microwave reaction time, 650 watts of power, after reaction finished, cooling was filtered, water is with the complete wash-out of the phosphotungstic acid on molecular sieve surface, again with catalyst oven dry, 250 degrees centigrade of roastings 2 hours can obtain the faujasite coated phosphorus heteropoly tungstic acid catalyzer.

2, the preparation method of faujasite coated phosphorus heteropoly tungstic acid catalyzer according to claim 1 is characterized in that described raw material tungstates is a kind of in sodium tungstate, potassium tungstate and the ammonium tungstate.

3, the preparation method of faujasite coated phosphorus heteropoly tungstic acid catalyzer according to claim 1 is characterized in that described raw material phosphate is a kind of in sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate and the potassium phosphate.

4, the preparation method of faujasite coated phosphorus heteropoly tungstic acid catalyzer according to claim 1 is characterized in that described tungstates and phosphatic raw materials are respectively sodium tungstate and sodium hydrogen phosphate.

5, the preparation method of faujasite coated phosphorus heteropoly tungstic acid catalyzer according to claim 1 is characterized in that described acidulant selects concentrated hydrochloric acid or phosphoric acid for use.