CN110075835B

CN110075835B - Catalyst for preparing methyl methacrylate by one-step oxidation esterification method and preparation method and application thereof

Info

Publication number: CN110075835B
Application number: CN201910438644.1A
Authority: CN
Inventors: 陈秉辉; 许梦东; 郑进保; 宗子厚; 吴钊男; 王明亮
Original assignee: Xiamen University
Current assignee: Xiamen University
Priority date: 2019-05-24
Filing date: 2019-05-24
Publication date: 2022-03-29
Anticipated expiration: 2039-05-24
Also published as: CN110075835A

Abstract

The invention discloses a catalyst for preparing methyl methacrylate by a one-step oxidation esterification method, a preparation method and an application thereof, wherein the catalyst takes a material containing an electron-rich oxide as a composite carrier, takes metal palladium as an active component, takes rare earth metal as an auxiliary active component, takes a surfactant as an auxiliary agent, and has a chemical general formula which can be expressed as follows: x_aPd_bY_c/M_d-N, wherein Pd is palladium, X is a surfactant, Y is one of the rare earth elements scandium, yttrium, lanthanum or cerium, M is an electron-rich oxide, and N is a carrier. The catalyst can be applied to the reaction for producing Methyl Methacrylate (MMA) in one step by oxidizing methacrolein and esterifying the methacrolein and methanol. The catalyst forms a special electron supply structure among the active component, the carrier and the surfactant, overcomes some defects of the existing oxidation esterification catalyst, and has the characteristics of simple preparation process and mild reaction conditions besides the advantages of high conversion rate and good selectivity when applied to the reaction for producing MMA by the one-step oxidation esterification method.

Description

Catalyst for preparing methyl methacrylate by one-step oxidation esterification method and preparation method and application thereof

Technical Field

The invention belongs to the technical field of catalysis, and particularly relates to a catalyst for preparing methyl methacrylate by a one-step oxidation esterification method, and a preparation method and application thereof.

Background

MMA is an organic chemical raw material widely used in industry, and the synthesis method mainly uses an acetone cyanohydrin method (ACH method) in the past, and the industrial application technology is mature and reliable, but the method has the defects of high toxicity of hydrocyanic acid serving as a raw material, difficulty in treatment of reaction by-products, poor atom economy, environmental protection limitation and the like, and is gradually replaced by an environment-friendly process, wherein a carbon four synthesis process is mainly used. The carbon four synthesis process is mainly divided into the following 4 process routes: isobutylene (IB)/Tertiary Butanol (TBA) three-step oxidation, isobutylene/tertiary butanol two-step oxidation, isobutylene/tertiary butanol direct esterification and isobutane oxidation; the method is characterized in that the industrialization of an Isobutene (IB)/tert-butyl alcohol (TBA) three-step oxidation method is respectively realized in 1982 by Japan catalytic chemical company and Mitsubishi rayon company, the process is complex and long in flow, more production equipment is needed, and the comprehensive yield is low; the research on the synthesis of MMA by two-step oxidation of isobutylene/tert-butanol by the Asahi formation company since 1995, and the direct esterification of isobutylene/tert-butanol, which is also a process developed and industrially applied by the Asahi formation company in 1984, do not use hydrocyanic acid, a highly toxic chemical, but produce a large amount of ammonium bisulfate as a by-product, and need to solve a series of problems such as waste acid treatment, environmental pollution and equipment corrosion, and the yield of MMA is not as high as that of the direct oxidation method, so that the Asahi formation company modifies the process into a two-step apparatus for direct oxidation of isobutylene/tert-butanol in 1999. The American Lomhas company uses heteropolyacid catalyst to catalyze isobutane to directly oxidize and dehydrogenate to prepare MAA, and then uses MAA to esterify and prepare MMA, namely an isobutane oxidation method.

The two-step method for directly oxidizing isobutene/tert-butanol is to integrate the last two steps of the three-step method into one step, i.e. IB/TBA is directly oxidized into MAL, and then MAL, MeOH and O₂The methyl methacrylate is obtained by the next step of oxidative esterification under the action of a catalyst. The two-step method is an environment-friendly process route with very wide prospect, compared with an Isobutene (IB)/tert-butyl alcohol (TBA) three-step oxidation method, the two-step method greatly simplifies the process flow, has higher atom economy, lower energy consumption, lower investment cost and operation cost, does not generate intermediate product methacrylic acid, reduces the corrosion of acid substances to equipment, simultaneously reduces the polymerization side reaction of the methacrylic acid, can recycle the raw material methanol, and is the most competitive production method at present. Pd is the main catalyst in the production of MMA by the direct oxidative esterification reaction of methacrolein, methanol and molecular oxygenActive components, but the result of single metal catalysis is low conversion, high by-products and poor selectivity (US 3772381). Subsequent patents have improved this by, for example, Pd-Pb system catalysts proposed in Japanese patents JP-B-57-35856, JP-A-57-50545 and JP-A-61-243044, Pd-Bi systems proposed in Japanese patents JP-B-61-60820, JP-B-62-7902 and JP-A-5-148184, Pd-Te systems proposed in Japanese patent JP-A-61-243044, Pd-Tl-Hg systems proposed in Japanese patent JP-B-57-35860, Pd-alkaline earth-Zn-Cd systems proposed in Japanese patent JP-B-57-19090, etc., but the improvement methods disclosed in these Japanese patents are limited only to the addition of many other metal components to improve this defect, and the catalyst has complicated preparation process and poor reproducibility. Subsequent studies on single metal catalysts, such as Au-based catalysts proposed in Japanese patent JP-2000154164 and JP-2003192632, have high production cost and are not easy to regenerate, active components are easy to run off, Pt-based catalysts proposed in Japanese patent JP-57048937 have low activity and are expensive, and Ru-based catalysts proposed in Japanese patent JP-2003260357 still have a large difference between catalytic activity and noble metal catalysts. Since then, there has been no much investigation into the monometallic Pd catalyzed direct oxidative esterification of aldols to the corresponding carboxylic acid esters. Therefore, it is challenging but promising to improve Pd-based single metal catalysts and use them for producing MMA.

Disclosure of Invention

A catalyst for preparing methyl methacrylate by a one-step oxidation esterification method takes a material containing an electron-rich oxide as a composite carrier, takes metal palladium as an active component, takes rare earth metal as an auxiliary active component, takes a surfactant as an auxiliary agent, and has a chemical general formula which can be expressed as follows: x_aPd_bY_c/M_d-N, wherein Pd is palladium, X is one of polyvinyl alcohol (PVA) or polyethylene glycol (PEG) as a surfactant, Y is one of scandium, yttrium, lanthanum or cerium as a rare earth element, M is one of MgO, ZnO and CaO as an electron-rich oxide, and N is Al as a carrier₂O₃、SiO₂、TiO₂、CeO₂、ZrO₂Kaolin, SBA-15, SBA-16, MCM-41, ZSM-5, silica-alumina, active carbon, carbon black, carbon nano tube or graphene, wherein the a is substitutedThe mass ratio of the surface active agent to the metal palladium is 0.001-10.0, preferably 2.5-4.0; b represents the mass ratio of the metal Pd to the carrier, and b is 0.1-10.0, preferably 4.0-7.0; c represents the mass ratio of the rare earth element to the palladium, wherein c is 0-1.0, and preferably 0.4-0.6; d represents the mass ratio of M to the carrier, and d is 1.0-99.0, preferably 2.0-20.0.

A preparation method of a catalyst for preparing methyl methacrylate by a one-step oxidation esterification method comprises the following specific steps:

1) dissolving an electron-rich oxide precursor salt and a rare earth precursor salt, adding a carrier, heating and stirring until the solvent is evaporated to dryness, drying the obtained solid, grinding into powder, roasting the powder in a nitrogen atmosphere at 350-550 ℃ for 2-5 h, and cooling to room temperature to obtain a composite carrier;

2) dissolving metal palladium precursor salt and a surfactant in water, adding the solution into the composite carrier prepared in the step 1), stirring the obtained mixture, adding a reducing agent for reduction, washing the obtained solid for 3 times respectively by deionized water and absolute ethyl alcohol after filtering, and drying the washed solid for 3-24 hours at 25-80 ℃ to obtain the catalyst for preparing the methyl methacrylate by the one-step oxidative esterification method.

Preferably, the rare earth metal precursor salt in step 1) is selected from one of lanthanum nitrate, scandium nitrate, yttrium nitrate and cerium nitrate.

Preferably, the metal palladium precursor salt in step 2) is selected from one of palladium chloride or palladium nitrate.

Preferably, the reducing agent in step 2) is selected from one of HCHO, hydrazine hydrate or sodium borohydride; preferably 5 wt% HCHO-5 wt% NaOH solution, in an amount such that the molar ratio of HCHO to Pd is 1: 10-30: 1; the reduction reaction temperature is 20-100 ℃, and preferably 60-80 ℃; the reduction reaction time is 15min to 4h, preferably 25 to 40 min.

The application of the catalyst for preparing the methyl methacrylate by the one-step oxidation esterification method comprises the following specific steps: adding the catalyst for preparing methyl methacrylate by the one-step oxidation esterification method into a mixed solution consisting of methacrolein, methanol and a polymerization inhibitor, and then introducing oxygen to carry out oxidation esterification reaction to prepare the methyl methacrylate.

Preferably, the molar ratio of the methanol to the methacrolein is 1 to 100, preferably 30 to 50.

Preferably, the polymerization inhibitor is one selected from hydroquinone, methyl hydroquinone, p-hydroxyanisole, tert-butyl catechol and 2-tert-butyl hydroquinone.

Preferably, the flow rate of the oxygen is 10ml/min to 30ml/min, preferably 18ml/min to 22 ml/min.

Preferably, the conditions of the oxidative esterification reaction are: the reaction temperature is 45-85 ℃, preferably 55-70 ℃, the reaction pressure is 0.1-0.5 MPa, preferably 0.1-0.2 MPa, and the reaction time is 2-8 h, preferably 3-5 h.

The principle of the invention is as follows: the catalyst for preparing methyl methacrylate by the one-step oxidation esterification method provided by the invention is a novel composite catalyst which is composed of main active components of metal palladium, rare earth, a surfactant and a carrier; wherein, the carrier is an electron-rich material, and the surfactant is a protective agent containing electron-rich groups such as hydroxyl, amino, alkoxy and the like. In the catalytic reaction process, both the carrier and the surfactant can provide electrons for the active component Pd, so that the Pd is in an electron-rich state, and the capability of activating methacrolein, methanol and molecular oxygen is improved (Diao YY, Yan RY, Zhang SJ, ethanol. effects of Pb and Mg doping in Al)₂O₃-supported Pd catalyst on direct oxidative esterification of aldehydes with alcohols to esters[J]Journal of Molecular Catalysis A Chemical 2009,303: 35-42); in addition, Pd is partially wrapped by surfactant, which can mask the active site of surface part of Pd, thus weakening the hydrogenation and oxidation capability of Pd, effectively inhibiting the side reaction of excessive hydrogenation and deep oxidation of reaction substrate (P.D. Scholes, A.G.A. Coombes, L.Illum, et. detection and determination of surface levels of polar and PVA surfactant on biologically degradable surfactants using SSIMS and XPS [ J.]Journal of Controlled Release,1999,59: 261-; in addition, the aggregation of the metallic palladium among each other is restricted due to the steric hindrance of the surfactant, so that high dispersion and stability are obtainedThe palladium nanoparticles of (a); and the addition of a proper amount of rare earth elements can not only improve the thermal stability of the catalyst, but also enhance the alkalinity of the catalyst and neutralize partial acid centers on the surface of the catalyst, thereby improving the activity.

Compared with the existing catalyst for preparing MMA and the preparation method thereof, the invention has the following advantages:

(1) the catalyst provided by the invention uses an active component palladium, and is added with a surfactant and rare earth metal. The special electron supply structure formed among the active component, the carrier and the surfactant overcomes the defects of low conversion rate and selectivity and the like of the existing oxidation esterification catalyst.

(2) The preparation method of the catalyst provided by the invention has the advantages of simple and convenient operation, easy control and uniform distribution of the particle size of the active component, high utilization rate of the noble metal Pd, small dosage, low cost and the like.

(3) The catalyst prepared by the invention is applied to the reaction of preparing methyl methacrylate by a one-step oxidation esterification method, and has the advantages of high conversion rate and good selectivity, as well as simple preparation process and mild reaction conditions.

Drawings

FIG. 1 shows catalyst PVA₃-Pd₅/MgO-Al₂O₃An infrared spectrum of (1);

FIG. 2 shows catalyst PVA₃-Pd₅/MgO-Al₂O₃XPS spectra of (A).

Detailed Description

The present invention will be described in further detail with reference to examples. It is also to be understood that the following examples are intended to illustrate the present invention and are not to be construed as limiting the scope of the invention, and that the particular materials, reaction times and temperatures, process parameters, etc. listed in the examples are exemplary only and are intended to be exemplary of suitable ranges, and that insubstantial modifications and adaptations of the invention by those skilled in the art in light of the foregoing description are intended to be within the scope of the invention. The examples, where specific techniques or conditions are not indicated, are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by manufacturers, and are all conventional products which can be purchased in the market.

Example 1 PVA₃-Pd₅/MgO₁₀-Al₂O₃Catalyst and process for preparing same

PVA₃-Pd₅/MgO₁₀-Al₂O₃The preparation method of the catalyst comprises the following steps:

(1) mixing 6.4g Mg (NO)₃)₂·6H₂Dissolving O in 200ml deionized water, adding carrier 10g gamma-Al₂O₃Heating and stirring until the solvent is evaporated to dryness, drying the obtained solid, grinding the dried solid into powder, roasting the powder at 350-550 ℃ for 2-5 h in a nitrogen atmosphere, and cooling to room temperature to obtain the composite carrier MgO₁₀-Al₂O₃；

(2) 0.225g of PVA and 0.125g of PdCl were taken₂Dissolving in 9ml deionized water, adding 0.0825g NaCl, magnetically stirring at room temperature for complete dissolution, and adding 1.5g MgO prepared in step (1)₁₀-Al₂O₃A carrier, and then adding 10ml of 5 wt% NaOH-5 wt% HCHO solution into the obtained mixture after stirring to perform reduction reaction at the temperature of 60 ℃ for 15 min; after the reduction reaction is finished, carrying out suction filtration, washing the obtained solid for 3 times by using deionized water and ethanol respectively, and finally drying in a vacuum drying oven at the temperature of 80 ℃ for 3 hours to obtain the PVA₃-Pd₅/MgO₁₀-Al₂O₃The catalyst of (1). For the prepared PVA₃-Pd₅/MgO₁₀-Al₂O₃The catalyst was characterized by an infrared appearance and XPS: the infrared spectrum result is shown in figure 1, and the result shows that: at 3000cm^-1Has weak vibration peak of methyl or methylene species at 3600cm^-1The infrared absorption peak of hydroxyl exists, which shows that organic PVA remains on the surface of the catalyst and contains a large amount of hydroxyl. XPS characterization results are shown in figure 2: after the surface active agent PVA treatment, the binding energy of active metal Pd in the catalyst is shifted, and the Pd₅/MgO₁₀-Al₂O₃3d of_5/2Pd of the track⁰Has a binding energy of 336.22V (FIG. 2a), and after PVA treatment has become 335.78eV (FIG. 2b)Pd of the sample₅/MgO₁₀-Al₂O₃3d of_3/2Pd of the track⁰、3d_5/2Pd of the track²⁺、3d_3/2Pd of the track²⁺The binding energy of the Pd is less than that of the catalyst treated by the surfactant, which shows that an electron transfer phenomenon occurs between the Pd and the surfactant PVA, and the PVA transfers part of electrons to the Pd so that the binding energy of each orbit of the Pd shifts towards the direction of low binding energy, so that the Pd is in an electron-rich state, and the catalytic activity of the Pd on the preparation of carboxylic ester by one-step oxidation esterification of aldol is greatly improved.

Using PVA₃-Pd₅/MgO₁₀-Al₂O₃The reaction steps of the catalyst for preparing the methyl methacrylate by the one-step oxidation esterification method are as follows: carrying out catalytic reaction in a pressure-resistant reaction bottle at 60 deg.C under 0.1Mpa, catalyst charge of 0.4g, polymerization inhibitor HQ charge of 100ppm, reaction substrate MeOH charge of 20ml, MAL charge of 1ml, O₂The flow rate is 20ml/min, the product content is detected by sampling after 4 hours of continuous reaction, the conversion rate of the reaction substrate and the selectivity of the product are calculated, and the results are shown in Table 1.

Example 2 PVA_0.001-Pd₁₀/MgO_1.0-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1 except that Mg (NO) in example 1 was used₃)₂·6H₂The mass of O was changed to 0.64g, the mass of PVA was changed to 0.00015g, PdCl₂The mass of (1) was changed to 0.25g, the mass of NaCl was changed to 0.165g, and the amount of the reducing agent, 5 wt% NaOH to 5 wt% HCHO, was changed to 20ml, and the other conditions were the same.

Example 3 PVA_2.5-Pd₄/MgO_2.0-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1 except that Mg (NO) in example 1 was used₃)₂·6H₂The mass of O was changed to 1.28g, the mass of PVA was changed to 0.15g, PdCl₂The mass of (b) is changed to 0.1g, the mass of NaCl is changed to 0.066g, and the mass of reducing agent is 5 wt% NaOH-5 wt% HCHOThe amount was changed to 8ml, and the rest of the conditions were the same.

Example 4 PEG_4.0-Pd₇/MgO₂₀-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1 except that Mg (NO) in example 1 was used₃)₂·6H₂The mass of O was changed to 12.8g, PVA to 0.42g PEG, PdCl₂The mass of (A) was changed to 0.175g, the mass of NaCl was changed to 0.1155g, and the amount of the reducing agent, 5 wt% NaOH-5 wt% HCHO, was changed to 14ml, and the other conditions were the same.

Example 5 PEG_10.0-Pd_0.1/MgO₉₉-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1 except that Mg (NO) in example 1 was used₃)₂·6H₂The mass of O is changed to 12.8g, gamma-Al₂0₃The mass of (A) was changed to 2.02g, PVA was changed to 0.015g PEG, PdCl₂The mass of (1) was changed to 0.0025g, the mass of NaCl was changed to 0.0017g, and the amount of the reducing agent 5 wt% NaOH to 5 wt% HCHO was changed to 0.2ml, and the other conditions were the same.

Example 6 PVA₃-Pd₅La_0.4/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1, except that 0.1263g of La (NO) was added in step (1) of example 1₃)₃·6H₂O and 6.4g of magnesium nitrate hexahydrate are dissolved in 200ml of deionized water, and then 10g of gamma-Al is added to the solution₂O₃The other conditions were the same.

Example 7 PVA₃-Pd₅La_0.6/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1, except that 0.1894g of La (NO) was added in step (1) of example 1₃)₃·6H₂O and 6.4g of magnesium nitrate hexahydrate are dissolved in 200ml of deionized water, and then 10g of gamma-Al is added to the solution₂O₃The other conditions were the same.

Example 8 PVA₃-Pd₅La_1.0/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1, except that 0.3156g of La (NO) was added in step (1) of example 1₃)₃·6H₂O and 6.4g of magnesium nitrate hexahydrate are dissolved in 200ml of deionized water, and then 10g of gamma-Al is added to the solution₂O₃The other conditions were the same.

Example 9 PVA₃-Pd₅Sc_0.4/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1, except that 0.2259g of Sc (NO) was added in step (1) of example 1₃)₃·6H₂O and 6.4g of magnesium nitrate hexahydrate are dissolved in 200ml of deionized water, and then 10g of gamma-Al is added to the solution₂O₃The other conditions were the same.

Example 10 PVA₃-Pd₅Y_0.4/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1, except that 0.1291g Y (NO) was added in step (1) of example 1₃)₃·6H₂O and 6.4g of magnesium nitrate hexahydrate are dissolved in 200ml of deionized water, and then 10g of gamma-Al is added to the solution₂O₃The other conditions were the same.

TABLE 1 catalytic Properties of catalysts obtained in examples 1 to 10

The data are shown in table 1, as the Pd content increases, the conversion of MAL increases continuously, and the selectivity of MMA increases and then decreases; the more the surfactant is added, the better, but there is a suitable value that when the amount is 0.001 wt%, PVA provides insufficient number of electron-rich hydroxyl groups to completely activate Pd; at 10 wt%, the organic polymer is more coated around Pd to cover too many active sites. In addition, the addition of an appropriate amount of rare earth metal can improve the selectivity of the target product, as shown in example 7, the conversion of MAL is 98.0%, and the selectivity of MMA is 87.5%.

Example 11 PVA₃-Pd₅/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The same procedure as in example 1 was followed except that the reducing agent 5 wt% NaOH-5 wt% HCHO solution was used in an amount of 0.05ml, the reduction reaction temperature was 20 ℃ and the reduction time was 4 hours in step (2) in example 1, and the other conditions were the same.

PVA₃-Pd₅/MgO₁₀-Al₂O₃The reaction conditions of the catalyst for catalyzing the methyl methacrylate preparation by the one-step oxidation esterification method are as follows: the reaction temperature is 45 ℃, the reaction pressure is 0.2Mpa, the catalyst charge is 0.4g, the polymerization inhibitor methyl hydroquinone charge is 100ppm, the reaction substrate MeOH charge is 5ml, the MAL charge is 10ml, O₂The flow rate is 10ml/min, the product content is detected by sampling after continuous reaction for 8h, the conversion rate of the reaction substrate and the selectivity of the product are calculated, and the results are shown in Table 2.

Example 12 PVA₃-Pd₅/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The same procedure as in example 1 was followed except that 13.5ml of a 5 wt% NaOH-5 wt% HCHO solution as the reducing agent in step (2) in example 1 was used, that the reduction reaction temperature was 80 ℃ and that the reduction time was 25min, and that the other conditions were the same.

PVA₃-Pd₅/MgO₁₀-Al₂O₃The reaction conditions of the catalyst for catalyzing the methyl methacrylate preparation by the one-step oxidation esterification method are as follows: the reaction temperature is 55 ℃, the reaction pressure is 0.5Mpa, the catalyst charge is 0.4g, the polymerization inhibitor p-hydroxyanisole charge is 100ppm, the reaction substrate MeOH charge is 14.7ml, and the MAL charge1ml of material, O₂The flow rate is 18ml/min, the product content is detected by sampling after continuous reaction for 3h, and the conversion rate of the reaction substrate and the selectivity of the product are calculated, and the results are shown in Table 2.

Example 13 PVA₃-Pd₅/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The same procedure as in example 1 was followed except that the reducing agent used in step (2) in example 1 was replaced with 80% by weight of hydrazine hydrate in an amount of 0.3ml, and the remaining conditions were the same.

PVA₃-Pd₅/MgO₁₀-Al₂O₃The reaction conditions of the catalyst for catalyzing the methyl methacrylate preparation by the one-step oxidation esterification method are as follows: the reaction temperature is 70 ℃, the reaction pressure is 0.5Mpa, the catalyst charge is 0.4g, the polymerization inhibitor tert-butyl catechol charge is 100ppm, the reaction substrate MeOH charge is 24.5ml, the MAL charge is 1ml, O₂The flow rate is 22ml/min, the product content is detected by sampling after continuous reaction for 3h, and the conversion rate of the reaction substrate and the selectivity of the product are calculated, and the results are shown in Table 2.

Example 14 PVA₃-Pd₅/MgO₁₀-Al₂O₃Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1 except that the reducing agent required in step (2) in example 1 was replaced with sodium borohydride in an amount of 0.16 g: the reduction reaction temperature is 100 ℃, the reduction time is 40min, and the rest conditions are the same.

PVA₃-Pd₅/MgO₁₀-Al₂O₃The reaction conditions of the catalyst for catalyzing the methyl methacrylate preparation by the one-step oxidation esterification method are as follows: the reaction temperature is 85 ℃, the reaction pressure is 0.5Mpa, the catalyst charge is 0.4g, the polymerization inhibitor charge is 100ppm, the reaction substrate charge is 24.5ml MeOH, the MAL charge is 0.5ml, O₂The flow rate is 30ml/min, the product content is detected by sampling after 2 hours of continuous reaction, the conversion rate of the reaction substrate and the selectivity of the product are calculated, and the results are shown in Table 2.

TABLE 2 catalytic performances of the catalysts obtained in examples 11 to 14

The data are shown in table 2, in example 11, the concentration of the reducing agent is low, the reduction conditions are mild, the particle size of the reduced Pd particles is larger, the active sites are significantly less than those of the Pd particles obtained in example 1, and when the reaction time is prolonged to 8 hours, the conversion rate of methacrolein reaches 100%. When the molar ratio of the reducing agent HCHO to Pd in example 12 is 30: 1, the molar ratio of the alcohol to the aldehyde is 30: at 1, the selectivity of methyl methacrylate is significantly improved. Noble metal Pd is obtained by reduction with a liquid phase chemical reduction method, and similar effects can be achieved by reducing agents formaldehyde, hydrazine hydrate and sodium borohydride. For the one-step oxidation esterification reaction, the reaction time is prolonged, and the conversion rate of the methacrolein is increased; the molar ratio of the alcohol to the aldehyde is improved, which is beneficial to increasing the selectivity of the methyl methacrylate. In example 14, when the molar ratio of aldol is 100: at 1, the selectivity of methyl methacrylate reaches 91.7%, but too high a ratio of aldol has no practical value for practical industrial production.

Example 15 PVA₃-Pd₅/MgO₁₀-TiO₂Catalyst and process for preparing same

The catalyst was prepared by the same procedure as in example 1, except that γ -Al was used in step (2) in example 1₂O₃Substituted by TiO₂The amount used was 10g, and the other conditions were the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 16 PVA₃-Pd₅/MgO₁₀-CeO₂Catalyst and process for preparing same

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃Replacement by CeO₂The amount used was 10g, and the other conditions were the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 17 PVA₃-Pd₅/MgO₁₀-ZrO₂Catalyst and process for preparing same

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃Substituted by ZrO₂The amount used was 10g, and the other conditions were the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 18 PVA₃-Pd₅/MgO₁₀-SBA-15 catalyst

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃The molecular sieve SBA-15 is replaced, the using amount is 10g, and the other conditions are the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 19 PVA₃-Pd₅/MgO₁₀-MCM-41 catalyst

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃The molecular sieve MCM-41 is replaced, the dosage is 10g, and the rest conditions are the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 20 PVA₃-Pd₅/MgO₁₀-ZSM-5 catalyst

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃The molecular sieve ZSM-5 was replaced, the amount was 10g, and the other conditions were the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 21 PVA₃-Pd₅/MgO₁₀Kaolin catalysts

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃The kaolin was replaced with 10g and the other conditions were the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 22 PVA₃-Pd₅/MgO₁₀-silica alumina catalyst

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃The amount of the silica was 10g instead of the amount of the silica-alumina, and the other conditions were the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 23 PVA₃-Pd₅/MgO₁₀-activated carbon catalyst

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃The activated carbon was replaced with 10g of activated carbon, and the other conditions were the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 24 PVA₃-Pd₅/MgO₁₀-carbon nanotube catalyst

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃The carbon nanotubes were replaced with 10g of carbon nanotubes, and the other conditions were the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

Example 25 PVA₃-Pd₅/MgO₁₀-graphene catalyst

The same procedure as in example 1 was used except that Al in step (2) in example 1 was used₂O₃The graphene is replaced by 10g, and the other conditions are the same. The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 3.

TABLE 3 catalytic Performance of catalysts obtained in examples 15 to 25

The data are shown in table 3, after the electron-rich oxide MgO modified carrier is obtained as the composite carrier, the catalytic activity is obviously improved, and the activity improvement degrees of different carriers are different. The catalyst synthesized by the composite carrier obtained by modifying the electron-rich carbon material, particularly graphene, has the selectivity of methyl methacrylate of 88.7 percent under the same reaction evaluation conditions as those in the example 1. The carrier SBA-15 is a better choice in consideration of the influence of the practical engineering application of the catalyst, such as the manufacturing cost of the carrier, the wear resistance, the bulk density of the catalyst, the service life and the like. The catalyst obtained after modification of SBA-15 in example 18 exhibited a methacrolein conversion of 93.3% and a methyl methacrylate selectivity of 84.9% under the same reaction evaluation conditions as in example 1.

Comparative example 1 CTAB₃-Pd₅/MgO-Al₂O₃Catalyst and process for preparing same

A catalyst was prepared by following the same procedure as in example 1, except that PVA in example 1 was changed to CTAB of the same mass, to obtain CTAB of the composition₃-Pd₅/MgO-Al₂O₃The catalyst of (1).

The catalytic reaction was evaluated under the same conditions as in example 1, and the evaluation results are shown in Table 4.

Comparative example 2 SDBS₃-Pd₅/MgO-Al₂O₃Catalyst and process for preparing same

A catalyst was prepared by following the same procedure as in example 1, except that the PVA in example 1 was changed to SDBS of the same quality, to obtain a catalyst having the composition of SDBS₃-Pd₅/MgO-Al₂O₃The catalyst of (1).

Comparative example 3 PVA₁-Pd₅/MgO-Al₂O₃Catalyst and process for preparing same

A catalyst was prepared by following the same procedure as in example 8, except that the mass of PVA in example 1 was changed from 0.225g to 0.075g, to obtain a PVA having the composition₁-Pd₅/MgO-Al₂O₃The catalyst of (1).

Comparative example 4 PVA₅-Pd₅/MgO-Al₂O₃Catalyst and process for preparing same

A catalyst was prepared by following the same procedure as in example 1, except that the mass of PVA in example 1 was changed from 0.25g to 0.375g, to obtain a PVA having the composition₅-Pd₅/MgO-Al₂O₃The catalyst of (1).

Comparative example 5 Pd₅/MgO-Al₂O₃Catalyst and process for preparing same

A catalyst was prepared by following the same procedure as in example 1, except that the mass of PVA in example 1 was changed from 0.25g to 0g, to thereby obtain a catalyst having a composition of Pd₅/MgO-Al₂O₃The catalyst of (1).

TABLE 4 catalytic performance of catalysts obtained in comparative examples 1 to 5

The data are shown in Table 4, when selecting the hydroxyl rich surfactant PVA, the catalytic activity is compared to Pd₅/MgO-Al₂O₃The improvement is greatly improved; when selected to contain Br^-CTAB and Na-containing surfactant of⁺The surfactant SDBS of (a) cannot provide electrons to Pd to activate Pd, resulting in very low catalytic activity. Further, the more the surfactant PVA is added, the better is not the more, but there is a suitable value that when the amount is 1% by weight, the PVA provides an insufficient number of electron-rich group hydroxyl groups to completely activate Pd; when the addition amount is 5 wt%, the organic polymer PVA wrapped around Pd is more and covers excessive effective active sites; when the addition amount is 3 wt%, the amount of the electron-rich group hydroxyl provided by the PVA is just proper, so that a proper amount of electrons are provided for the Pd, and the capability of activating a reaction substrate by the Pd is improved; secondly, Pd is partially wrapped by the surfactant to cover partial active sites on the surface of Pd, so that the hydrogenation and oxidation capabilities of Pd are weakened, and side reactions of excessive hydrogenation and deep oxidation of reaction substrates are inhibited; in addition, aggregation of palladium particles with each other is restricted due to steric hindrance by the surfactant, and high molecular weight is obtainedDivergence and stable palladium nanoparticles. Thus, the obtained monometallic Pd catalyst had good reaction activity, as shown in example 1, with a conversion of MAL of 97.9% and a selectivity of MMA of 85.8%.

Claims

1. The catalyst for preparing methyl methacrylate by a one-step oxidation esterification method is characterized in that the catalyst takes a material containing an electron-rich oxide as a composite carrier, metal palladium as an active component, rare earth metal as an auxiliary active component and a surfactant as an auxiliary agent, and the chemical general formula of the catalyst can be expressed as follows:

wherein Pd is palladium, X is surfactant selected from one of polyvinyl alcohol or polyethylene glycol, Y is rare earth element selected from one of scandium, yttrium, lanthanum or cerium, M is electron-rich oxide selected from one of MgO, ZnO and CaO, N is carrier selected from Al₂O₃、TiO₂、CeO₂、ZrO₂The metal palladium catalyst comprises one of kaolin, SBA-15, SBA-16, MCM-41, ZSM-5, silica-alumina, activated carbon, carbon black, carbon nano tubes or graphene, wherein a represents the mass ratio of a surfactant to metal palladium, and a is 2.5-4.0; b represents the mass ratio of metal Pd to the carrier, and b is 4.0-7.0; c represents the mass ratio of the rare earth element to the palladium, and c is 0.4-0.6; d represents the mass ratio of M to the carrier, and d is 2.0-20.0.

2. The preparation method of the catalyst for preparing the methyl methacrylate by the one-step oxidative esterification method according to claim 1, which is characterized by comprising the following steps:

3. The method according to claim 2, wherein the precursor salt of rare earth metal element in step 1) is selected from lanthanum nitrate, scandium nitrate, yttrium nitrate, and cerium nitrate.

4. The method for preparing a catalyst used in the preparation of methyl methacrylate by the one-step oxidative esterification method according to claim 2, wherein the metal palladium precursor salt in the step 2) is selected from one of palladium chloride and palladium nitrate.

5. The method for preparing a catalyst for preparing methyl methacrylate by a one-step oxidative esterification method according to claim 2, wherein the reducing agent in the step 2) is one selected from HCHO, hydrazine hydrate or sodium borohydride; the reduction reaction temperature is 20-100 ℃; the reduction reaction time is 15 min-4 h.

6. The method for preparing a catalyst for preparing methyl methacrylate by a one-step oxidative esterification process according to claim 5, wherein the reducing agent in the step 2) is

Solution added in an amount such that the molar ratio of HCHO to Pd is 1: 10-30: 1; the reduction reaction temperature is 60-80 ℃; the reduction reaction time is 25-40 min.

7. The application of the catalyst for preparing methyl methacrylate by the one-step oxidative esterification method according to claim 1 is characterized by comprising the following specific steps: adding the catalyst for preparing methyl methacrylate by the one-step oxidation esterification method into a mixed solution consisting of methacrolein, methanol and a polymerization inhibitor, and then introducing oxygen to carry out oxidation esterification reaction to prepare the methyl methacrylate.

8. The use of the catalyst for preparing methyl methacrylate by the one-step oxidative esterification method according to claim 7, wherein the molar ratio of the methanol to the methacrolein is 1 to 100.

9. The use of the catalyst for preparing methyl methacrylate by the one-step oxidative esterification method according to claim 8, wherein the molar ratio of the methanol to the methacrolein is 30 to 50.

10. The use of the catalyst for preparing methyl methacrylate by the one-step oxidative esterification process as claimed in claim 7, wherein the polymerization inhibitor is selected from one of hydroquinone, methyl hydroquinone, p-hydroxyanisole, tert-butyl catechol, and 2-tert-butyl hydroquinone.

11. The use of the catalyst for preparing methyl methacrylate by the one-step oxidative esterification method according to claim 7, wherein the flow rate of the oxygen is 10mL/min to 30 mL/min.

12. The use of the catalyst for preparing methyl methacrylate by the one-step oxidative esterification method according to claim 11, wherein the flow rate of the oxygen is 18mL/min to 22 mL/min.

13. The use of a catalyst for the preparation of methyl methacrylate by a one-step oxidative esterification process according to claim 7, wherein the oxidative esterification reaction is carried out under the following conditions: the reaction temperature is 45-85 ℃, the reaction pressure is 0.1-0.5 MPa, and the reaction time is 2-8 h.

14. The use of a catalyst for the preparation of methyl methacrylate by the one-step oxidative esterification process according to claim 13, wherein the oxidative esterification reaction is carried out under the following conditions: the reaction temperature is 55-70 ℃, the reaction pressure is 0.1-0.2 MPa, and the reaction time is 3-5 h.