CN109569600B - Catalyst for synthesizing methyl methacrylate and preparation method thereof - Google Patents

Abstract

The invention discloses a preparation method of a catalyst for synthesizing methyl methacrylate. The catalyst is prepared by a polymer protection method. The catalyst comprises an active center and a carrier, the active center comprises gold and two lanthanide metals, and the carrier comprises two One of silica, alumina, and alkali or alkaline earth metals, which are present in the catalyst as oxides. The catalyst of the invention has the advantages of low Au loading, simple preparation process, convenient operation, excellent activity and good stability, low catalyst price, high conversion rate of methacrolein and high selectivity of MMA, and is suitable for industrial production.

Description

Catalyst for synthesizing methyl methacrylate and preparation method thereof

technical field

The invention belongs to the technical field of catalyst preparation, and particularly relates to a catalyst for synthesizing methyl methacrylate and a preparation method and application thereof.

Background technique

Methyl methacrylate (MMA) is an important organic polymer monomer, and polymethyl methacrylate (PMMA, also known as plexiglass) prepared from it is widely used in national defense and military industries, construction , transportation, advertising and decoration, culture, education, health, instrumentation, daily necessities and other fields; in addition, it also has many applications in water-soluble coatings, latex paints, etc.

At present, the production processes of MMA in the world mainly include acetonitrile alcohol method (ACH method), isobutylene method and ethylene method. In the global MMA production capacity, the acetone cyanohydrin method accounts for 83%, the isobutylene method accounts for 16%, and the ethylene method accounts for 1%. The ACH method has the characteristics of simple process and high maturity, but the raw material hydrocyanic acid used in this method is highly toxic, and hydrocyanic acid and sulfuric acid are highly corrosive, which requires high reaction equipment and large waste acid discharge. May cause great harm to the environment.

The methacrylic acid-methanol oxidative esterification method was first industrialized by Mitsubishi Rayon Company after more than 20 years of research and development in Japan. The process is two-step oxidation of isobutene and oxygen under the action of molybdenum-based catalyst, that is, isobutene is first oxidized to methacrolein, methacrolein is then oxidized to methacrylic acid, and methacrylic acid is finally esterified with methanol to form MMA. The method is relatively simple and only needs three steps of reaction, but methacrylic acid is highly corrosive, requires higher equipment, and increases the production cost.

Directly using air or oxygen as the oxidant to directly oxidize methacrolein and methanol into the target product MMA in one step is undoubtedly a simple, green and economically competitive process route, because there is no generation of methacrylic acid in the middle, and there is no follow-up. The esterification process of methylpropionic acid and methanol can greatly save production costs, and at the same time, the by-product of this process is water, which is environmentally friendly. However, the difficulty of this process lies in the preparation of the catalyst. Therefore, many efforts have been made to solve this problem. For example, Japan's Asahi Kasei developed the oxidation of isobutene to methacrolein, and methacrolein was oxidatively esterified with methanol under the action of Pd-Pb catalyst to prepare MMA. The process does not involve highly corrosive methacrylic acid, and does not require high reaction equipment. In addition, the process is very simple, requiring only two-step reactions. The by-product is only water, which is green and environmentally friendly. Compared with the original MMA preparation process, the process requires lower cost of raw materials, high product purity, compact equipment, and significantly reduced construction costs, but requires high catalyst design and preparation. The selectivity of the first-generation Pd-Pb catalyst to MMA is not high, about 84%, which will increase the cost of subsequent separation and affect the quality of the product.

Subsequently, Japan's Asahi Kasei found in the follow-up research that the core-shell structure of gold nanocatalysts (Au@NiOx) can efficiently catalyze the co-oxidation of methacrolein and methanol to MMA. The process is simple and the catalyst shows excellent stability. However, the catalyst has high technical requirements for preparation, and when the conversion rate of methacrolein is 65%, the selectivity of MMA is about 95%, and in practical application, it is often necessary to ensure high activity (usually based on high conversion rate) At the same time, the high selectivity of the target product can be maintained; in addition, the cost of the catalyst is also relatively high, with a cost of about 6 million/ton, which will also limit its industrial application to a certain extent.

Chinese Patent Publication No. CN107107034A discloses a gold-based catalyst for oxidative esterification of aldehydes to obtain carboxylic acid esters. Gold is used as an active component, and oxidized silicon, aluminum and other elements are used as carriers, and the other elements are selected from Alkali metals, alkaline earth metals, rare earth metals, Ti, Zr, Cu, Mn, Pb, Sn or Bi, forming catalysts in particle form which can be used for the oxidative esterification of aldehydes to carboxylates over a long period of time, especially in the presence of water and mixtures containing carboxylic acids. However, the catalyst catalyzes the conversion of methacrolein into MMA, the catalytic conditions are harsh and the active center is single, so the conversion rate of methacrolein and the selectivity of MMA are not ideal, especially the selectivity to MMA in the industrial expansion test Not high, affecting product quality.

SUMMARY OF THE INVENTION

In order to make up for the deficiencies of the prior art, the present invention provides a method for preparing a catalyst for synthesizing methyl methacrylate and a method for synthesizing methyl methacrylate. The catalyst has simple preparation process, convenient operation, excellent activity and good performance. Stability, high conversion rate of methacrolein and selectivity of MMA, suitable for industrial production.

The present invention is achieved through the following technical solutions:

One aspect of the present invention provides a catalyst for synthesizing methyl methacrylate, the catalyst is prepared by a polymer protection method; the catalyst includes an active center and a carrier; the active center includes gold and two lanthanide metals; the The carrier includes silica, alumina and one of alkali metals or alkaline earth metals; the alkali metals or alkaline earth metals exist in the form of oxides in the catalyst; the gold and lanthanide metals exist in the form of elemental substances; the catalyst , the mass ratio of the active center to the carrier is 0.51-3.96:99.49-96.04.

Based on the above technical solutions, preferably, the two lanthanide metals are any two of La, Ce, Pr, and Nd

Based on the above technical solutions, it is further preferred that in the active center, the mass fraction of lanthanide metals is in the range of 50-96%, and preferably in the range of 55-95%. The addition of lanthanide metals as active centers can greatly improve the selectivity of methyl methacrylate, and the addition of two lanthanide metals as active centers can effectively improve the selectivity of methyl methacrylate while changing the selectivity of methyl methacrylate. The conversion rate also has a certain impact on the stability of the catalyst; lanthanide metals include elements with atomic numbers 57-71, but not all lanthanide metals can effectively improve the selectivity of methyl methacrylate. In this application, La The combination of any two lanthanide metals among Ce, Pr, and Nd can synergistically catalyze with the Au active center, maximize the selectivity of methyl methacrylate, and improve the conversion rate of methacrolein and the stability of the catalyst. have a positive effect.

Based on the above technical solutions, preferably, in the carrier, the mass fraction of SiO ₂ is in the range of 55-95%, and the preferred range is 60-85%; the mass fraction of A1 ₂ O ₃ is in the range of 4-44%, and the preferred range is 15- 30%; the mass fraction of alkali metals and alkaline earth metals ranges from 1 to 25%.

Based on the above technical solutions, preferably, the alkali metal or alkaline earth metal is one of Rb, Cs, Mg, and Sr; as a carrier, the alkali metal or alkaline earth metal can increase the activity of the catalyst, improve the stability of the catalyst, and protect the Au particles from reunion.

Another aspect of the present invention provides a preparation method of the above-mentioned synthetic methyl methacrylate catalyst, the method comprising the following steps:

(1) Preparation of oxide carrier:

Under stirring conditions, the alkali metal or alkaline earth metal precursor, the silica precursor and the alumina precursor aqueous solution are mixed uniformly at 10-90°C (preferably 40-80°C), and a certain amount of acid is added to adjust the pH value. to 0.5-5.5 (preferably 1.5-4.0), continue to stir for 1-24h to obtain a mixture, spray-dry the mixture to obtain spherical particles with a particle size of 50-100 μm, and roast the spherical particles in an air atmosphere to obtain an oxide carrier;

(2) Preparation of catalyst by polymer protection method:

Under stirring conditions, the gold precursor, reducing agent and deionized water are fully mixed to obtain a stable, uniform and single gold sol with high dispersion state. Add the precursors of two lanthanide metals and the oxide carrier obtained in step (1), continue to stir for 1-24 hours and slowly heat up to 60-80°C, after stirring, drop to room temperature, stand for filtration, use deionized water Washing until no chloride ion can be detected, drying and calcining in air to obtain the catalyst.

As a preferred solution, the acid described in step (1) is one of nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid, and may be more preferably nitric acid.

As a preferred solution, in step (1), the precursors of alkali metals or alkaline earth metals are simple substances, oxides, hydroxides, other compounds or composites of the corresponding metals, and the silica precursors are silica sol, solid silica gel, One of the white carbon blacks, preferably silica sol; the alumina precursor is one of aluminum nitrate, aluminum sulfate, aluminum phosphate, aluminum acetate or aluminum oxide powder, preferably aluminum nitrate, which can be based on actual conditions in industrial production to make a selection.

As a preferred solution, in the catalyst obtained in step (2), the precursor of Au is selected from but not limited to gold cyanide (Au(CN) ₃ ), potassium gold cyanide, gold chloride (AuCl), chloride One or more of gold (AuC1 ₃ ), chloroauric acid, chloroauric acid salt, sodium gold sulfite or Ragkin.

As a preferred solution, in the catalyst prepared in step (2), the precursors of lanthanide metals are selected from but not limited to sulfates, nitrates, phosphates, carbonates and acetates of the corresponding metals.

As a preferred solution, in the catalyst prepared in step (2), the reducing agent is selected from but not limited to sodium citrate, tetrahydroxymethylphosphorus chloride (THPC), oxalic acid (H ₂ C ₂ O ₄ ) and sodium borohydride.

As a preferred solution, in the catalyst prepared in step (2), the macromolecular protective agent is selected from but not limited to polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), tetramethylolphosphorus chloride (THPC), Methyldipropylene ammonium chloride (PDDA), sodium citrate, thiols.

As a preferred solution, in the catalyst prepared in step (2), the mass ratio of lanthanide metal element: gold element: reducing agent: macromolecular protective agent: carrier: water is 1: (0.02-0.98): (0.2-0.5) :(0.2～0.5):(50～200):(200～400).

Another aspect of the present invention provides the application of a catalyst for synthesizing methyl methacrylate, and relates to a method for synthesizing methyl methacrylate. As the reaction raw material, methyl methacrylate was catalyzed and synthesized by one-step oxidation.

Based on the above technical solutions, preferably, the method for synthesizing methyl methacrylate comprises the following steps: adding the reaction raw materials into the reactor to fully mix, adding the above catalyst for synthesizing methyl methacrylate into the reactor; sealing the reactor , turn on the stirring, feed air and inert gas at the rate of 0.8-1.3L/min and 2.5-3.2L/min respectively at the bottom of the reactor, and use a liquid constant flow pump to add reaction to the reactor at a rate of 8-12ml/min Raw material, the reacted product is stored in the storage tank at the same rate as the reaction raw material addition rate; the mass concentration of methanol in the reaction mixture is 50-70%, the reaction raw material and the catalyst form a reaction system; the catalyst is in the reaction The mass concentration in the system is 15-20%.

Based on the above technical solutions, preferably, the materials in the reactor start to react at 80°C, and the product in the storage tank can be taken out at regular intervals for gas chromatography analysis, and the conversion rate and target of methacrolein can be calculated. Selectivity of the product methyl methacrylate. The reaction indexes obtained after 150-200 hours of reaction are: conversion of methacrolein ≥97%, selectivity of methyl methacrylate ≥98%, and no loss of active centers on the catalyst after continuous reaction for 4000 hours.

beneficial effect

The beneficial effects of the invention are as follows: the invention adopts the polymer protection method to prepare the catalyst of the multi-metal active center. The supported catalyst prepared by the polymer protection method has low requirements on the carrier and a wide range of options, and the obtained active center has high activity and stable performance. The gold active center and the two lanthanide metal active centers cooperate in catalysis, which not only improves the catalyst activity, but also improves the conversion rate of methacrolein and the selectivity of methyl methacrylate. Gold-based catalysts. Moreover, the active center Au and lanthanide metals still exist stably on the catalyst after the continuous reaction for 4000 h, and there is no loss. The particle size of the active center Au prepared by the polymer protection method is small and uniform, and the activity is high. The catalyst preparation process is simple, the operation is convenient, the production cost is low, the stability is good, and the service life is long. The low loading makes the catalyst low in price and suitable for large-scale industrialization. Production.

Description of drawings

Accompanying drawing 1 is the electron microscope picture of the catalyst prepared in Example 6.

Detailed ways

The present invention will be described in further detail below in conjunction with specific embodiments to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solutions of the present invention. The protection scope of the present invention includes but is not limited to the following examples , any modifications made to the details and forms of the technical solutions of the present invention without departing from the spirit and scope of the present application fall within the protection scope of the present invention.

Example 1

Under stirring conditions, weigh 50kg of silica sol (30wt%), add 9kg of aluminum nitrate during the stirring process, add 7kg of magnesium nitrate after dissolving, mix well at 50°C, add 250ml of concentrated nitric acid to adjust the pH value, and continue at 50°C Stir for 24h, cool down to room temperature, and then spray dry. The spray conditions are: 10ml/min feed rate, inlet temperature 200-220°C, outlet temperature 80-100°C, to obtain spherical SiO ₂ -Al ₂ O ₃ with a particle size of about 70 μm -MgO powder, and the powder was calcined at 700°C for 6 hours in an air atmosphere, and then cooled to room temperature for later use.

Under stirring conditions, 250g of chloroauric acid, 275g of sodium citrate and 60L of deionized water were fully mixed to obtain a stable, uniform and single gold sol with a relatively high dispersion state. Under stirring conditions, 280g of polyvinylpyrrolidone (PVP, Molecular weight 8000-10000), then add 940g lanthanum nitrate, 935g cerium nitrate successively, add 30kg of the SiO ₂ -Al ₂ O ₃ -MgO powder prepared above after being completely dissolved, continue to stir and slowly heat up to 75 ° C, continue to stir at this temperature After 14 hours, it was lowered to room temperature. After standing, the upper layer liquid was poured out. The lower layer precipitate was washed with deionized water until no chloride ions were detected in the solution. After drying at 100 °C for 24 hours, it was calcined in air at 300 °C for 24 hours to obtain the catalyst La-Ce- Au/ _{SiO2 - Al2O3} -MgO. The mass percentages of La, Ce, and Au in the catalyst are 1%, 1%, and 0.48%, respectively.

Example 2

The carrier molding conditions are the same as those in Example 1, wherein the magnesium nitrate is replaced with rubidium nitrate under the same mass fraction of the metal to obtain spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm. calcined for 6 h in an air atmosphere, and then cooled to room temperature for later use.

The catalyst preparation conditions were the same as those in Example 1, and the catalyst La-Ce-Au/SiO ₂ -Al ₂ O ₃ -RbO was obtained, wherein the mass percentages of La, Ce, and Au in the catalyst were 1%, 1%, and 0.48%, respectively. .

Example 3

The carrier molding conditions are the same as those in Example 1, in which the magnesium nitrate is replaced with cesium nitrate under the same mass fraction of the metal to obtain spherical SiO ₂ -Al ₂ O ₃ -CsO powder with a particle size of about 70 μm. calcined for 6 h in an air atmosphere, and then cooled to room temperature for later use.

The catalyst preparation conditions were the same as those in Example 1, and the catalyst La-Ce-Au/SiO ₂ -Al ₂ O ₃ -CsO was obtained, wherein the mass percentages of La, Ce, and Au in the catalyst were 1%, 1%, and 0.48%, respectively. .

Example 4

The carrier molding conditions are the same as those in Example 1, in which the magnesium nitrate is replaced with strontium nitrate under the same mass fraction of the metal to obtain spherical SiO ₂ -Al ₂ O ₃ -SrO powder with a particle size of about 70 μm, and then the powder is heated at 700 μm. calcined for 6 h in an air atmosphere, and then cooled to room temperature for later use.

The catalyst preparation conditions were the same as those in Example 1, and the catalyst La-Ce-Au/SiO ₂ -Al ₂ O ₃ -SrO was obtained, wherein the mass percentages of La, Ce, and Au in the catalyst were 1%, 1%, and 0.48%, respectively. .

Example 5

The carrier molding conditions were the same as those in Example 2, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. for 6 hours in an air atmosphere, and then cooled to room temperature for use.

The catalyst preparation conditions are the same as those in Example 2, wherein lanthanum nitrate is replaced with praseodymium nitrate under the same mass fraction of metals to obtain a catalyst Pr-Ce-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein Pr, Ce, Au The mass percentages in the catalyst are 1%, 1%, and 0.48%, respectively.

Example 6

The carrier molding conditions were the same as those in Example 2, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. for 6 hours in an air atmosphere, and then cooled to room temperature for use.

The catalyst preparation conditions are the same as those in Example 2, wherein lanthanum nitrate is replaced with neodymium nitrate under the same mass fraction of metals to obtain a catalyst Nd-Ce-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein Nd, Ce, Au The mass percentages in the catalyst are 1%, 1%, and 0.48%, respectively. It can be seen from the electron microscope image in Fig. 1 that the obtained catalyst has a very good sphericity and a very smooth surface.

Example 7

The carrier molding conditions were the same as those in Example 2, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. for 6 hours in an air atmosphere, and then cooled to room temperature for use.

The catalyst preparation conditions are the same as those in Example 2, wherein the cerium nitrate is replaced with praseodymium nitrate under the same conditions of the mass fraction of metals to obtain a catalyst La-Pr-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein La, Pr, Au The mass percentages in the catalyst are 1%, 1%, and 0.48%, respectively.

Example 8

The carrier molding conditions were the same as those in Example 2, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. for 6 hours in an air atmosphere, and then cooled to room temperature for use.

The catalyst preparation conditions are the same as those in Example 2, wherein cerium nitrate is replaced with neodymium nitrate under the same conditions of the mass fraction of metals to obtain a catalyst La-Nd-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein La, Nd, Au The mass percentages in the catalyst are 1%, 1%, and 0.48%, respectively.

Example 9

The carrier molding conditions were the same as those in Example 2, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. for 6 hours in an air atmosphere, and then cooled to room temperature for use.

The catalyst preparation conditions are the same as those in Example 2, wherein lanthanum nitrate is replaced with praseodymium nitrate and cerium nitrate is replaced with neodymium nitrate under the same mass fraction of metals to obtain catalyst Pr-Nd-Au/SiO ₂ -Al ₂ O ₃ -RbO , wherein the mass percentages of Pr, Nd, and Au in the catalyst are 1%, 1%, and 0.48%, respectively.

Example 10

The carrier molding conditions were the same as in Example 6, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. in an air atmosphere for 6 hours, and then cooled to room temperature for use.

The catalyst preparation conditions are the same as those in Example 6, the precursor of the Au component is replaced by Au(CN) ₃ , the reducing agent is replaced by tetramethylolphosphorus chloride (THPC), and the polymer protective agent is replaced by polydimethyldipropylene chloride ammonium chloride (PDDA) to obtain a catalyst Nd-Ce-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein the mass percentages of Nd, Ce, and Au in the catalyst are 1%, 1%, and 0.48%, respectively.

Example 11

The carrier molding conditions were the same as in Example 6, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. in an air atmosphere for 6 hours, and then cooled to room temperature for use.

The preparation conditions of the catalyst are the same as those in Example 6, the precursor of the Au component is replaced with potassium aurous cyanide, the reducing agent is replaced with oxalic acid (H ₂ C ₂ O ₄ ), and the macromolecular protective agent is replaced with polyvinyl alcohol (PVA) to obtain The catalyst is Nd-Ce-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein the mass percentages of Nd, Ce and Au in the catalyst are 1%, 1% and 0.48% respectively.

Example 12

The carrier molding conditions were the same as in Example 6, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. in an air atmosphere for 6 hours, and then cooled to room temperature for use.

The catalyst preparation conditions are the same as those in Example 6, the precursor of the Au component is replaced with gold sodium sulfite, the reducing agent is replaced with sodium borohydride, and the macromolecular protective agent is replaced with tetramethylolphosphorus chloride (THPC) to obtain the catalyst Nd- Ce-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein the mass percentages of Nd, Ce, and Au in the catalyst are 1%, 1%, and 0.48%, respectively.

Comparative Example 1

Using the method and preparation process in Example 20 of CN 107107034 A, the catalyst Au/SiO ₂ -Al ₂ O ₃ -MgO was prepared. The mass percentage content of Au in the catalyst is 0.48% respectively, and the performance of the catalyst is shown in the table.

Comparative Example 2

The carrier molding conditions were the same as in Example 6, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. in an air atmosphere for 6 hours, and then cooled to room temperature for use.

The catalyst preparation conditions were the same as those in Example 6, but no neodymium nitrate was added to obtain a catalyst Ce-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein the mass percentages of Ce and Au in the catalyst were 1% and 0.48%, respectively.

Comparative Example 3

The carrier molding conditions were the same as in Example 6, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. in an air atmosphere for 6 hours, and then cooled to room temperature for use.

The catalyst preparation conditions were the same as those in Example 6, but no cerium nitrate was added to obtain a catalyst Nd-Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein the mass percentages of Nd and Au in the catalyst were 1% and 0.48%, respectively.

Comparative Example 4

The carrier molding conditions were the same as in Example 6, and spherical SiO ₂ -Al ₂ O ₃ -RbO powder with a particle size of about 70 μm was obtained, and the powder was calcined at 700° C. in an air atmosphere for 6 hours, and then cooled to room temperature for use.

The catalyst preparation conditions were the same as those in Example 6, but cerium nitrate and neodymium nitrate were not added to obtain the catalyst Au/SiO ₂ -Al ₂ O ₃ -RbO, wherein the mass percentage of Au in the catalyst was 0.48% respectively.

Comparative Example 5

Under stirring conditions, 750g of chloroauric acid, 775g of sodium citrate and 60L of deionized water were fully mixed to obtain a stable, uniform and single gold sol with a relatively high dispersion state. Under stirring conditions, 780g of polyvinylpyrrolidone (PVP, Molecular weight 8000-10000), then add 940g lanthanum nitrate, 935g cerium nitrate successively, add 30kg of the SiO ₂ -Al ₂ O ₃ -MgO powder prepared above after being completely dissolved, continue to stir and slowly heat up to 75 ° C, continue to stir at this temperature After 14 hours, it was lowered to room temperature. After standing, the upper layer liquid was poured out. The lower layer precipitate was washed with deionized water until no chloride ions were detected in the solution. After drying at 100 °C for 24 hours, it was calcined in air at 300 °C for 24 hours to obtain the catalyst La-Ce- Au/ _{SiO2 - Al2O3} -MgO. The mass percentages of La, Ce, and Au in the catalyst are 1%, 1%, and 1.4%, respectively.

Example 13

The catalysts described in Examples 1-12 and Comparative Examples 1-5 were respectively applied to the synthesis reaction of methyl methacrylate under the same conditions, and the reaction conditions were:

2000mL of methacrolein and methanol mixture were fully mixed in a 3L stainless steel autoclave, 280g of catalyst was added, and the mixture was fully mixed, wherein the concentration of methacrolein was 30wt%, the reaction kettle was sealed, stirring was started, and the system was heated to 80°C When the reaction started, air and nitrogen were introduced at the bottom of the reactor at a rate of 1L/min and 3L/min respectively, and a liquid constant-flow feed pump was used to add the reaction raw materials to the reactor at a rate of 10ml/min to generate The product is continuously discharged to the storage tank, the feed liquid is taken out at regular intervals, and the discharge liquid is analyzed by gas chromatography, and n-decane is used as the internal standard to calculate the conversion rate of methacrolein and methyl methacrylate. Ester selectivity, reaction 200h.

Example 14

2000mL of methacrolein and methanol mixture were fully mixed in a 3L stainless steel autoclave, 280g of the catalyst in Example 1 was added, and the mixture was fully mixed, wherein the concentration of methacrolein was 30wt%, the reaction kettle was sealed, and stirring was started, The reaction was started when the system was heated to 80°C. Air and nitrogen were introduced at the bottom of the reactor at a rate of 1L/min and 3L/min respectively, and a liquid constant-flow feed pump was used to feed the system into the reactor at a rate of 10ml/min. The reaction raw materials are added, the generated product is continuously discharged to the storage tank, the feed liquid is taken out at regular intervals, the discharge liquid is analyzed by gas chromatography, and n-decane is used as the internal standard to calculate the conversion rate of methacrolein and methyl methacrylate selectivity, the reaction 4000h. The results are shown in the following table. As can be seen from the table, the catalyst prepared by the present invention has better conversion rate of methacrolein and selectivity of methyl methacrylate. It can be seen that the addition of lanthanide metals improves the activity of the catalyst, so that the Conversion and selectivity are improved. The performance of the catalyst in the comparative example is lower than that of the catalyst prepared by the present invention, and the performance of the catalyst decreases after the loading of Au is increased. The catalytic performance of adding only one lanthanide metal in the catalyst preparation process is lower than that of adding two metals.

Claims (15)

1. A catalyst for synthesizing methyl methacrylate, which is characterized in that: the catalyst comprises an active center and an oxide carrier; the active center comprises gold and two lanthanide metals; the oxide support comprises silica, alumina and one of an alkali metal or an alkaline earth metal; the alkali metal or alkaline earth metal is present in the catalyst in the form of an oxide; in the catalyst, the mass ratio of the active center to the carrier is 0.51-3.96: 99.49-96.04;

the gold and lanthanide metals are present in elemental form;

the two lanthanide metals are any two of La, Ce, Pr and Nd.

2. The catalyst for the synthesis of methyl methacrylate according to claim 1, characterized in that: in the carrier, SiO₂The mass fraction of A1 is 55-95%₂O₃The mass fraction of the components is 4-44%; the mass fraction of alkali metal and alkaline earth metal is 1-25%.

3. The catalyst for the synthesis of methyl methacrylate as claimed in claim 1, wherein: the alkali metal or alkaline earth metal is one of Rb, Cs, Mg and Sr.

4. The catalyst for the synthesis of methyl methacrylate according to claim 2, characterized in that: in the active center, the mass fraction of lanthanide metal is 55-95%.

5. A method for preparing the catalyst for synthesizing methyl methacrylate according to any one of claims 1 to 4, characterized in that: the catalyst is prepared by adopting a macromolecule protection method, and specifically comprises the following steps:

(1) preparation of oxide support

Under the condition of stirring, uniformly mixing an alkali metal or alkaline earth metal precursor, a silicon dioxide precursor, an alumina precursor and water at the temperature of 10-90 ℃, adding a certain amount of acid to adjust the pH value to 0.5-5.5, continuously stirring for 1-24h to obtain a mixture, carrying out spray drying and forming on the mixture to obtain spherical particles with the particle size of 50-100 mu m, and roasting the spherical particles in an air atmosphere to obtain the oxide carrier;

(2) preparation of the catalyst

Under the condition of stirring, adding a gold precursor and a reducing agent into deionized water, mixing to obtain a gold sol, sequentially adding two lanthanide series metal precursors and the carrier prepared in the step (1) into the gold sol in the presence of a high-molecular protective agent, and heating to 60-80 DEG^oAnd C, continuously stirring for 1-24h, cooling to room temperature after stirring, standing, filtering, washing with deionized water until no chloride ion is detected, drying, and roasting in the air to obtain the catalyst.

6. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (1), the acid is one of nitric acid, sulfuric acid, hydrochloric acid and phosphoric acid.

7. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (1), the precursor of the alkali metal or the alkaline earth metal is a simple substance, an oxide, a hydroxide or a compound of the corresponding metal.

8. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (2), the Au precursor is gold cyanide (Au (CN)₃) Potassium aurous cyanide, aurous chloride (AuC1), gold chloride (AuC1)₃) Chloroauric acid, chloroauric acid salt, sulfurous acidOne or more than two of sodium gold sulfate or gold.

9. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (2), the precursor of the lanthanide metal is sulfate, nitrate, phosphate, carbonate or acetate of the corresponding metal.

10. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (2), the reducing agent is selected from sodium citrate, tetrakis (hydroxymethyl) phosphonium chloride, oxalic acid and sodium borohydride; the polymer protective agent is polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), tetrakis (hydroxymethyl) phosphonium chloride (THPC), poly (dimethyl-ammonium chloride) (PDDA), sodium citrate, and thiol.

11. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: the mass ratio of the lanthanide metal, gold, the reducing agent, the polymer protective agent, the carrier and water is 1: 0.02-0.98: 0.2-0.5: 50-200: 200-400.

12. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: the precursor of the silicon dioxide is one of silica sol, solid silica gel and white carbon black.

13. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: the precursor of the aluminum oxide is one of aluminum nitrate, aluminum sulfate, aluminum phosphate, aluminum acetate or aluminum oxide powder.

14. A method for synthesizing methyl methacrylate is characterized in that: the catalyst for synthesizing methyl methacrylate according to any one of claims 1 to 4 is used for catalytically synthesizing methyl methacrylate by a one-step oxidation method by using methacrolein and methanol as reaction raw materials.

15. The method for synthesizing methyl methacrylate according to claim 14, wherein: the method comprises the following steps: adding reaction raw materials into a reactor for full mixing, then adding the catalyst for synthesizing the methyl methacrylate into the reactor, sealing the reactor, and starting stirring; introducing air and inert gas at the bottom of the reactor at the speed of 0.8-1.3L/min and 2.5-3.2L/min respectively, adding reaction raw materials at the speed of 8-12ml/min by adopting a liquid constant flow pump, and storing the reacted product at the same speed as the reaction raw materials; the mass concentration of methanol in the reaction mixture is 50-70%, and the reaction raw material and the catalyst form a reaction system; the mass concentration of the catalyst in a reaction system is 15-20%.

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