Process for preparation of catalyst for supported gold nanoparticles (np) for production of methyl methacrylate by oxidative esterification, catalyst thus obtained and method of oxidative esterification (oe)

Abstract

A process for preparing a catalyst for the oxidative esterification of methacrolein to methyl methacrylate, the process comprising providing a support selected from the group consisting of oxides of silicon, carbides of silicon, metal oxides, and metal carbides. Particles of at least one oxide of a metal are provided on the support. The support is brought into contact with a gold salt and heated at a temperature in the range of 50 DEG C to 600 DEG C for a time in the range of at least 0.1 hours to 48 hours to convert the gold salt into gold nanoparticles having an average diameter of less than 12 nm and a standard deviation of + / -4 nm. Wherein at least 75% by number of the gold nanoparticles are located within 20 nm of the particles of the oxide of the metal.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method for preparing a catalyst for the production of methyl methacrylate by oxidative esterification of methacrolein.

[0002] Heterogeneous catalysts for the production of carboxylic acid esters (including methyl methacrylate) from aldehydes are known.

[0003] U.S. Patent 8,461,373 discloses a catalyst comprising nickel oxide and at least one element selected from nickel, palladium, platinum, ruthenium, gold, silver, and copper. The diameter of the catalyst ranges from 10 μm to 200 μm.

[0004] WO 2016 / 113106 discloses a catalyst comprising gold, silica, alumina, and an oxide of at least one element selected from alkali metals, alkaline earth metals, lanthanide elements having an atomic number from 57 to 71, Y, Sc, Ti, Zr, Cu, Mn, Pb, and Bi. The average diameter of the catalyst ranges from 10 μm to 200 μm.

[0005] However, there is a need for an improved catalyst and a method for producing a catalyst that can increase selectivity and / or reduce the formation of by-products. SUMMARY OF THE INVENTION

[0006] One aspect of the present invention relates to a method for preparing a catalyst for the oxidative esterification of methacrolein to methyl methacrylate. The method includes providing a support selected from oxides of silicon, carbides of silicon, metal oxides, and metal carbides. Particles of at least one oxide of a metal are provided on the support. The metal of the at least one oxide of the metal is selected from the group consisting of aluminum, titanium, lanthanide elements, zirconium, nickel, cobalt, zinc, tellurium, antimony, bismuth, alkali metals, and alkaline earth metals. The support is contacted with a gold salt and then heated at a temperature in the range of 50°C to 600°C for a time in the range of at least 0.1 hour to 48 hours to convert the gold salt into gold nanoparticles having an average diameter of less than 12 nm and a standard deviation of + / - 4 nm. At least 75% by number of the gold nanoparticles are located within 20 nm of the particles of the oxide of the metal. DETAILED DESCRIPTION

[0007] Unless otherwise specified, all percentage compositions are by weight (wt%), and all temperatures are in °C. Unless otherwise specified, the average value is the arithmetic mean. "Catalyst center" is the centroid of the catalyst particle, i.e., the average position of all points in all coordinate directions. The diameter is any linear dimension passing through the catalyst center, and the average diameter is the arithmetic mean of all possible diameters. The aspect ratio is the ratio of the longest diameter to the shortest diameter. Unless otherwise specified, the average diameter of the particles refers to the average diameter of the particles after the catalyst is prepared and before the catalyst is used. An aged catalyst is a catalyst that has been used.

[0008] The catalyst of the present invention comprises a support having nickel oxide and gold particles disposed thereon.

[0009] The present invention relates to a method for preparing a catalyst for the oxidative esterification of methacrolein to methyl methacrylate.

[0010] The method includes providing a support and providing particles of at least one oxide of a metal on the surface of the support, contacting the support with a gold salt, and heating the support at a temperature in the range of 50 °C to 600 °C for a time in the range of at least 0.1 hour to 48 hours to convert the gold salt into gold nanoparticles having an average diameter of less than 12 nm and a standard deviation of + / - 4 nm. Wherein at least 75% of the gold nanoparticles by number are located within 20 nm of the particles of the oxide of the metal.

[0011] The support comprises a material selected from oxides of silicon, carbides of silicon, metal oxides, and metal carbides. The metals of the metal oxides and metal carbides can be selected from, for example, aluminum, titanium, zirconium, zinc, and magnesium. Preferably, the support is capable of withstanding long-term use in an oxidative esterification reactor. Materials capable of long-term use can avoid being crushed or pulverized during use.

[0012] In one embodiment, the support can have an average diameter in the range of 50 nm to 500 μm, preferably 100 nm to 400 μm, and more preferably 150 nm to 300 μm. In this embodiment, the catalyst can be suitable for a reactor in which the catalyst is maintained in suspension, such as a slurry reactor or a continuous stirred tank reactor. When the support is less than 500 μm, the support can be formed directly by: being a reaction product and then dried, spray drying the support, filtering and / or centrifuging after precipitation, or pulverizing larger materials to form the desired size. Alternatively, the support can be prepared by classifying the particles to select the desired average particle size.

[0013] In another embodiment, the carrier may have an average diameter greater than 500 μm, such as from 500 μm to 10 mm. In embodiments where the average diameter of the carrier is greater than 500 μm, the catalyst can be used in a reactor including a fixed bed, for example, a fixed bed reactor, a trickle bed reactor, or a packed bubble column reactor. For carriers having an average diameter greater than 500 μm, the carriers can be produced by extrusion or granulation or any other known method. When the carrier is formed by extrusion or granulation, the carrier can be formed in the presence or absence of a binder.

[0014] Particles of at least one metal oxide are provided on the carrier, wherein the metal is selected from aluminum, titanium, lanthanides, zirconium, alkali metals, alkaline earth metals, nickel, cobalt, zinc, magnesium, tellurium, antimony, rhenium, tungsten, and bismuth. The particles of at least one metal oxide can be formed on the carrier by the following steps: first contacting the carrier with a salt of the metal and then oxidizing the metal in an environment containing an oxygen-containing gas (e.g., air or oxygen).

[0015] Preferably, the carrier comprises an oxide of silicon, consists of an oxide of silicon, or consists essentially of an oxide of silicon. More preferably, the carrier comprises an oxide of silicon modified with particles of titanium oxide or nickel oxide, consists of an oxide of silicon modified with particles of titanium oxide or nickel oxide, or consists essentially of an oxide of silicon modified with particles of titanium oxide or nickel oxide. As used herein with respect to the carrier, the phrase "consists essentially of" excludes the presence of materials that would reduce the mechanical strength of the carrier. Alternatively, "consists essentially of" means that the carrier comprises at least 95% by weight of the said material relative to the total weight of the carrier.

[0016] Preferably, the surface area of the carrier is greater than 10 m 2 / g, preferably greater than 30 m 2 / g, preferably greater than 50 m 2 / g, preferably greater than 100 m 2 / g, preferably greater than 120 m 2 / g.

[0017] Preferably, the aspect ratio of the catalyst particles is not greater than 10:1, preferably not greater than 5:1, and preferably not greater than 3:1. Although the shape is not limited, the preferred shapes of the catalyst particles include spherical, cylindrical, rectangular solid, annular, multi-lobed (e.g., alfalfa leaf cross-section), shapes with multiple holes, and "wagon wheel"; preferably spherical. Irregular shapes can also be used.

[0018] To form gold nanoparticles on a support, the support is contacted with a gold salt, which is preferably in the form of an aqueous solution containing the gold salt. The gold salt is then converted into particles of metallic gold by heating the support at a temperature in the range of 50 °C to 600 °C for a time in the range of 0.1 hour to 48 hours.

[0019] In one embodiment, the step of heating the support to convert the gold salt into metallic gold can be carried out in the presence of an oxygen-containing gas (such as air or oxygen) to calcine the catalyst. The calcination can be carried out at a temperature in the range of 150 °C to 500 °C, preferably 200 °C to 450 °C. Calcination is the preferred method for converting the gold salt into metallic gold because it can simultaneously form particles of metal oxide from the metal salt.

[0020] In an alternative embodiment, the step of heating the support to convert the gold salt into metallic gold can be carried out in the presence of a reducing gas containing at least 0.1 vol% of a reducing agent.

[0021] In another alternative embodiment, the step of heating the support to convert the gold salt into metallic gold can be carried out in the presence of an inert atmosphere, in which case the inert gas allows the gold salt to self-reduce to metallic gold.

[0022] In yet another alternative embodiment, the step of heating the support to convert the gold salt into metallic gold can be carried out in the liquid phase in the presence of a solvent and a reducing agent, where the ratio of the reducing agent to the solvent is at least 0.01. In this embodiment, the support is heated at a temperature in the range of 50 °C to less than the boiling point of the solvent.

[0023] The contact of the support with the gold salt can be carried out by several different methods. For example, the contact of the support with the gold salt can be carried out by impregnating the support with an aqueous solution containing the gold salt, dip-coating the support with a solution containing the gold salt, spraying the support with a solution containing the gold salt, or by sequentially impregnating the support with a first solution (aqueous or organic) to fill at least 80 vol% of any pores that may be present in the support and then impregnating the support with a second solution containing the gold salt. When the support is contacted with a solution or aqueous solution of the gold salt, the support can first be dried and then heated to convert the gold salt into particles of metallic gold.

[0024] Preferably, the catalyst is produced by precipitating gold and the metal (i.e., the metal of the metal oxide) from an aqueous solution of a metal salt in the presence of a support. In a preferred embodiment, the catalyst is produced by contacting an aqueous solution of a suitable gold precursor salt and a nickel salt with a porous inorganic oxide such that the pores are filled with the solution, and then removing the water by drying. The resulting material is then converted into the finished catalyst by calcination or reduction to decompose the gold salt and the metal salt into gold and the metal oxide. Preferably, a C2-C 18 thiol containing at least one hydroxyl or carboxylic acid substituent is present in the solution. Preferably, a C2-C 18 thiol has 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, preferably 3 to 6 carbon atoms. Preferably, the thiol compound contains no more than 4, preferably no more than 3, preferably no more than 2 total hydroxyl and carboxylic acid groups. Preferably, the thiol compound has no more than 2, preferably no more than 1 thiol group. If the thiol compound contains a carboxylic acid substituent, they may be present in acid form, conjugate base form, or a mixture thereof. Particularly preferred thiol compounds include thiomalic acid, 3-mercaptopropionic acid, mercaptoacetic acid, 2-mercaptoethanol, and 1-thioglycerol, including their conjugate bases.

[0025] The metal oxide and the gold particles are preferably disposed on the outer surface of the support material. Preferably, at least 75 wt% of the gold particles are within the outer 25% of the volume of the catalyst. More preferably, at least 80 wt%, still more preferably at least 85 wt% of the gold particles are within the outer 25% of the volume of the catalyst.

[0026] The metal oxide disposed on the support is preferably in the form of nanoparticles.

[0027] Preferably, at least 75% of the gold particles by number are within at least 20 nm of the metal oxide nanoparticles. As used herein, the phrase "within at least X nm" means that the edge of the gold particle is within X nm of the edge of the metal oxide nanoparticle closest to the gold particle. Preferably, at least 75% of the gold particles are within at least 15 nm of the metal oxide nanoparticles, more preferably within at least 12 nm of the metal oxide nanoparticles, and even more preferably within at least 10 nm of the metal oxide nanoparticles.

[0028] More preferably, at least 75% of the gold particles, by number of gold particles, are within at least 20 nm of two metal oxide nanoparticles, i.e., the edges of the gold particles are within at least 20 nm of the edges of the two metal oxide nanoparticles closest to the gold particles. Preferably, at least 75% of the gold particles are within at least 15 nm of two metal oxide nanoparticles, more preferably within at least 12 nm of two metal oxide nanoparticles, and even more preferably within at least 10 nm of two metal oxide nanoparticles.

[0029] Even more preferably, at least 75% of the gold particles, by number of gold particles, are within at least 20 nm of at least three metal oxide nanoparticles, i.e., the edges of the gold particles are within at least 20 nm of the edges of the at least three metal oxide nanoparticles closest to the gold particles. Preferably, at least 75% of the gold particles are within at least 15 nm of at least three metal oxide nanoparticles, more preferably within at least 12 nm of at least three metal oxide nanoparticles, and even more preferably within at least 10 nm of at least three metal oxide nanoparticles.

[0030] The gold particles have an average diameter of less than 12 nm, preferably less than 10 nm, and more preferably less than 8 nm. The standard deviation of the average diameter of the gold particles is + / - 4 nm, preferably + / - 2.5 nm. As used herein, the standard deviation is calculated by the following equation:

[0031]

[0032] where x is the size of each particle, is the average of n particles, and n is at least 500.

[0033] The metal oxide nanoparticles preferably have an average diameter less than 5 times the average diameter of the gold particles, more preferably an average diameter less than 4 times the average diameter of the gold particles, even more preferably an average diameter less than 3 times the average diameter of the gold particles, still more preferably an average diameter less than 2 times the average diameter of the gold particles, and additionally more preferably an average diameter less than 1.5 times the average diameter of the gold particles. Preferably, the metal oxide nanoparticles have an average diameter at least half of the average diameter of the gold particles, and more preferably at least the same as the average diameter of the gold particles.

[0034] The amount of gold particles by weight relative to the amount of metal oxide nanoparticles can range from 1:1 to 1:20. Preferably, the weight ratio of gold particles to metal oxide nanoparticles ranges from 1:2 to 1:15, more preferably 1:3 to 1:10, and even more preferably 1:3 to 1:.

[0035] The amount by weight of the metal oxide relative to the amount by weight of the gold particles may range from 0.1:1 to 10:1, preferably from 0.2:1 to 5:1, more preferably from 0.33:1 to 3:1, and still more preferably from 0.5:1 to 2:1.

[0036] Preferably, the gold particles are uniformly distributed in the metal oxide nanoparticles. As used herein, the term "uniformly distributed" means that the gold particles are randomly dispersed in the metal oxide nanoparticles with substantially no agglomeration of the gold particles. For example, based on the total weight of the gold particles, less than 10 wt% of the gold particles are in physical contact with another gold particle. Preferably, based on the total weight of the gold particles, less than 7.5 wt% of the gold particles are in physical contact with another gold particle, and more preferably, based on the total weight of the gold particles, less than 5 wt% of the gold particles are in physical contact with another gold particle.

[0037] Preferably, at least 75 wt% of the gold particles are in the outer 50% of the catalyst volume (i.e., the volume of the average catalyst particle), more preferably in the outer 40% of the catalyst volume, even more preferably in the outer 30% of the catalyst volume, and still more preferably in the outer 25% of the catalyst volume. Preferably, for a volume having a constant distance from its inner surface to its outer surface (the surface of the catalyst particle) measured along a line perpendicular to the outer surface, the outer volume for any particle shape is calculated. For example, for a spherical particle, the outer x% of the volume is a spherical shell having the outer surface as the surface of the particle and a volume of x% of the entire spherical volume. Preferably, at least 95 wt%, preferably at least 97 wt%, preferably at least 99 wt% of the gold particles are in the outer volume of the catalyst. Preferably, at least 90 wt% (preferably at least 95 wt%, preferably at least 97 wt%, preferably at least 99 wt%) of the gold particles are at a distance from the surface not exceeding 30%, preferably not exceeding 25%, preferably not exceeding 20%, preferably not exceeding 15%, preferably not exceeding 10%, preferably not exceeding 8% of the catalyst diameter. The distance from the surface is measured along a line perpendicular to the surface. Preferably, the gold particles form an eggshell structure on the support particles. The eggshell layer may have a thickness of 500 microns or less, preferably 250 microns or less, more preferably 100 microns or less.

[0038] Preferably, at least 0.1% by weight of the total weight of the gold particles is exposed on the surface of the catalyst. As used herein, the term "exposed" means that at least a portion of the gold particles is not covered by another gold particle or metal oxide nanoparticle, i.e., the reactants can directly contact the gold particles. Thus, the gold particles can be disposed within the pores of the support material and still be exposed since the reactants can directly contact the gold particles within the pores. More preferably, at least 0.25% by weight of the total weight of the gold particles is exposed on the surface of the catalyst, even more preferably at least 0.5% by weight of the total weight of the gold particles is exposed on the surface of the catalyst, and still more preferably at least 1% by weight of the total weight of the gold particles is exposed on the surface of the catalyst.

[0039] Preferably, based on the percentages of gold and the support, the amount of gold is from 0.2% to 5% by weight, preferably at least 0.5% by weight, preferably at least 0.8% by weight, preferably at least 1% by weight, preferably at least 1.2% by weight; preferably not more than 4% by weight, preferably not more than 3% by weight, preferably not more than 2.5% by weight.

[0040] Preferably, the process for producing methyl methacrylate (MMA) is carried out in an oxidative esterification reactor (OER). The catalyst particles can be present in a slurry or a catalyst bed, preferably a catalyst bed. The catalyst particles in the catalyst bed are typically held in place by a solid wall and by a sieve or a catalyst support grid. In some configurations, the sieve or grid is at opposite ends of the catalyst bed and the solid wall is on the sides, although in some configurations, the catalyst bed can be completely surrounded by a sieve. Preferred shapes of the catalyst bed include a cylinder, a rectangular solid, and a cylindrical shell; preferably a cylinder. The OER also contains a liquid phase and a gas phase, the liquid phase containing methacrolein, methanol, and MMA, and the gas phase containing oxygen. The liquid phase can also contain by-products, e.g., methacrolein dimethyl acetal (MDA) and methyl isobutyrate (MIB). Preferably, the liquid phase is at a temperature of from 40 °C to 120 °C; preferably at least 50 °C, preferably at least 60 °C; preferably not more than 110 °C, preferably not more than 100 °C. Preferably, the catalyst bed is at a pressure of from 0 psig to 2000 psig (101 kPa to 14 MPa); preferably not more than 2000 kPa, preferably not more than 1500 kPa.

[0041] OER typically produces MMA, along with methacrylic acid and unreacted methanol. Preferably, methanol and methacrolein are fed to the reactor in a methanol:methacrolein molar ratio of from 1:10 to 100:1, preferably from 1:2 to 20:1, preferably from 1:1 to 10:1. Preferably, the catalyst bed also contains an inert material or an acidic material above and / or below the catalyst. Preferred inert materials or acidic materials include, for example, alumina, clay, glass, silicon carbide, and quartz. Preferably, the average diameter of the inert material or acidic material is equal to or greater than the average diameter of the catalyst, preferably not greater than 20 mm. Preferably, the reaction product is fed to a methanol recovery distillation column, which provides an overhead stream rich in methanol and methacrolein; preferably, this stream is recycled back to the OER. The bottoms stream from the methanol recovery distillation column contains MMA, MDA, methacrylic acid, salts, and water. In one embodiment of the present invention, MDA is hydrolyzed in a medium containing MMA, MDA, methacrylic acid, salts, and water. MDA can be hydrolyzed in the bottoms stream from the methanol recovery distillation column; the stream contains MMA, MDA, methacrylic acid, salts, and water. In another embodiment, MDA is hydrolyzed in the organic phase separated from the methanol recovery bottoms stream. It may be necessary to add water to the organic phase to ensure that there is sufficient water for MDA hydrolysis; these amounts can be readily determined from the composition of the organic phase. The product of the MDA hydrolysis reactor is phase separated, and the organic phase passes through one or more distillation columns to produce an MMA product and light and / or heavy by-products. In another embodiment, the hydrolysis can be carried out within the distillation column itself.

[0042] Preferably, based on the total volume of the gas stream leaving the reactor, the oxygen concentration at the reactor outlet is at least 1 mol%, more preferably at least 2 mol%, even more preferably at least 2.5 mol%, still more preferably at least 3 mol%, still more preferably at least 3.5 mol%, even still more preferably at least 4 mol%, and most preferably at least 4.5 mol%. Preferably, based on the total amount of the gas stream leaving the reactor, the oxygen concentration in the gas stream leaving the reactor does not exceed 7.5 mol%, preferably does not exceed 7.25 mol%, preferably does not exceed 7 mol%.

[0043] A preferred embodiment of the fixed-bed reactor for oxidative esterification is a trickle-bed reactor, which contains a fixed bed of catalyst and allows both gas and liquid feeds to pass through the reactor in a downward direction. In the trickle flow, the gas phase is continuous and the liquid phase is dispersed. Therefore, the region at the top of the reactor above the fixed bed will be filled with a gas-phase mixture of nitrogen, oxygen, and volatile liquid components at their respective vapor pressures. At typical operating temperatures and pressures (50 °C to 90 °C and 60 psig to 300 psig (400 kPa to 2000 kPa)), if the gas feed is air, this vapor mixture is within the flammable envelope. Therefore, only an ignition source is needed to initiate deflagration, which can lead to the loss of the primary containment and damage to nearby physical infrastructure and personnel. To address process safety concerns, a method of operating a trickle-bed reactor while avoiding a flammable overhead space atmosphere is to operate with a gas feed containing a low enough mole fraction of oxygen to ensure that the oxygen concentration in the vapor overhead space is below the limiting oxygen concentration (LOC).

[0044] Knowledge of the LOC is required for the relevant fuel mixtures, temperatures, and pressures. Since the LOC decreases with increasing temperature and pressure, and considering that methanol gives a lower LOC than the other two important fuels (methacrolein and methyl methacrylate), a conservative design choice is to select a feed oxygen-to-nitrogen ratio that ensures a composition below the LOC at the highest expected operating temperature and pressure. For example, for a reactor operating at up to 100 °C and 275 psig (2 MPa), the feed oxygen concentration in nitrogen should not exceed 7.4 mole%.

[0045] Examples

[0046] Examples 1 to 6 - Semi-batch slurry reactor operation :

[0047] Prepare a 10 wt% solution of methacrolein in methanol in advance. Place approximately 1 g of catalyst and 170 g of the methacrolein-methanol solution in a 300 mL stirred reactor equipped with baffles and a gas induction impeller. Seal the reactor while starting mixing, pressurization, and heating. Set the impeller to 1150 rpm and pressurize the reactor to 100 psig by introducing a continuous flow of 100 sccm of 8% O2 / N2 gas, which flows through the reactor to the condenser after pressurization is complete. The reactor reaches a reaction temperature of 80 °C in about 15 minutes, at which point the reaction is defined as started. Take aliquots from the reactor every half hour for 2.5 to 5 hours using a dip tube equipped with an on-line filter. Test the following Examples 1 to 6 in this reactor system.

[0048] Example #1

[0049] Preparation of Catalyst #1 :

[0050] First, a magnesium solution was prepared by adding 51.4 g of magnesium nitrate hexahydrate and 5.5 g of 60% nitric acid to 100 mL of deionized water. Then, approximately 100 g of Cariact Q50 silica was loaded into a 500 mL flask, and 200 mL of the magnesium solution was added while stirring. The slurry was stirred overnight at 50 °C, then filtered, and the separated material was dried in a vacuum oven at 80 °C for 1 hour, and then calcined overnight at 500 °C to produce magnesium-modified silica. Approximately 25 g of magnesium-modified silica was added to 85 mL of deionized water, and the resulting slurry was heated to 90 °C while stirring. A second solution containing 0.453 g of chloroauric(III) acid trihydrate, 1.255 g of cobalt(II) nitrate hexahydrate, and 85 mL of deionized water was prepared, and then the second solution was added to the slurry over 30 minutes while stirring, and then the resulting slurry was stirred for an additional 1 hour. The solid material was separated from the slurry by centrifugation. Then the solid was washed with a total of 300 mL of deionized water. In each wash, the sample was mixed with 100 mL of water for 5 minutes, and then the solid material was separated by centrifugation. Then the washed material was dried in air at 105 °C for 10 hours, and then calcined at 450 °C for 5 hours at a heating rate of 5 °C / min.

[0051] Example #2

[0052] Preparation of Catalyst #2 :

[0053] A slurry was prepared with 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.352 g of chloroauric(III) acid trihydrate, and 4.65 g of cerium(III) nitrate hexahydrate. Then the slurry was heated to 45 °C and stirred for 1 hour, and then the pH was adjusted to 8 by dropwise addition of 1 M sodium carbonate. The slurry was stirred at 45 °C for an additional 2 hours, and then filtered. During filtration, the resulting solid was washed with 500 mL of deionized water, and then vacuum dried overnight at ambient temperature. Then the dried solid was calcined in a box furnace in air with an air flow of 40 L / min, at a temperature of 400 °C, for 4 hours, with a heating rate of 5 °C / min.

[0054] Example #3

[0055] Preparation of Catalyst #3 :

[0056] Prepare a slurry using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.456 g of chloroauric acid(III) trihydrate, and 1.16 g of ammonium perrhenate. Heat the slurry to 60 °C and stir for 1 hour, then adjust the pH to 8 by dropwise addition of 1 M sodium carbonate. Stir the slurry at 60 °C for an additional 2 hours, then filter. While filtering, wash the resulting solid with 500 mL of deionized water, then vacuum dry overnight at ambient temperature. Then calcine the dried solid in a box furnace in air with an air flow of 40 L / min, at a temperature of 400 °C for 4 hours, with a heating rate of 5 °C / min.

[0057] Example #4

[0058] Preparation of Catalyst #4 :

[0059] Prepare a slurry using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.456 g of chloroauric acid(III) trihydrate, and 1.14 g of ammonium tungstate. Heat the slurry to 60 °C and stir for 1 hour, then adjust the pH to 8 by dropwise addition of 1 M sodium carbonate. Stir the slurry at 60 °C for an additional 2 hours, then filter. While filtering, wash the resulting solid with 500 mL of deionized water, then vacuum dry overnight at ambient temperature. Then calcine the dried solid in a box furnace in air with an air flow of 40 L / min, at a temperature of 400 °C for 4 hours, with a heating rate of 5 °C / min.

[0060] Example #5

[0061] Preparation of Catalyst #5 :

[0062] Prepare a slurry using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.456 g of chloroauric acid(III) trihydrate, and 0.737 g of cadmium chloride. Heat the slurry to 60 °C and stir for 1 hour, then adjust the pH to 8 by dropwise addition of 1 M sodium carbonate. Stir the slurry at 60 °C for an additional 2 hours, then filter. While filtering, wash the resulting solid with 500 mL of deionized water, then vacuum dry overnight at ambient temperature. Then calcine the dried solid in a box furnace in air with an air flow of 40 L / min, at a temperature of 400 °C for 4 hours, with a heating rate of 5 °C / min.

[0063] Example #6

[0064] Preparation of Catalyst #6 :

[0065] A slurry was prepared using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.456 g of chloroauric(III) acid trihydrate, and 0.87 g of zinc acetate dehydrate. The slurry was heated to 60 °C and stirred for 1 hour, then the pH was adjusted to 8 by dropwise addition of 1 M sodium carbonate. The slurry was stirred at 60 °C for an additional 2 hours and then filtered. While filtering, the resulting solid was washed with 500 mL of deionized water and then vacuum dried overnight at ambient temperature. The dried solid was then calcined in a box furnace in air with an air flow of 40 L / min at 400 °C for 4 hours with a heating rate of 5 °C / min.

[0066] Example 7 - Semi-batch recycle fixed bed reactor operation :

[0067] A 150 g feed solution containing 10 wt% methacrolein, 200 ppm inhibitor, and the balance methanol was prepared and placed in a 300 ml reaction vessel acting as a gas separation container. The vessel liquid was maintained at a temperature of about 20 °C. The liquid feed was pumped from the gas separation container into the bottom of a vertically oriented fixed bed reactor at a rate of 7 mL / min. Air and nitrogen were mixed to obtain 8 mol% oxygen, and this mixture was mixed with the liquid feed and then fed into the fixed bed reactor. The fixed bed reactor was a jacketed 1 / 4” stainless steel tube. The reactor itself was filled with 2 mm glass beads to fill approximately 18 inches (45.7 cm) of the tube, followed by the catalyst. The remaining void at the top of the reactor was filled with 3 mm glass beads. The liquid and gas leaving the top of the reactor were transferred to a condenser, and the non-condensable gas was vented while the liquid was recycled back to the gas separation container. Example 7 was tested in this reactor system.

[0068] Example #7

[0069] Preparation of Catalyst #7 :

[0070] The catalyst was prepared by incipient wetness impregnation of 10 g of Fuji Silysia Chemical, Ltd. CARiACT Q-10 support, which had been pre-modified by the supplier to add Ti in the form of 6.6 wt% titanium oxide. The solution consisted of 0.39 g of sodium thiosulfatoaurate, 0.4 g of mercaptosuccinic acid, and 0.12 g of citric acid monohydrate in 10 g of deionized water. The catalyst was then placed in a box furnace and purged with a constant air flow of 50 L / h at ambient temperature for 1 hour, then heated to 400 °C at 5 °C / min and calcined for 4 hours.

[0071] Example 8 - Single-pass fixed bed reactor operation :

[0072] A feed consisting of 20 wt% methacrolein, 200 ppm polymerization inhibitor, and the balance methanol is fed at a rate of 40 g / h into a 3 / 8” (9.5 mm) stainless steel tubular reactor containing short front-section borosilicate glass beads followed by 5 g of catalyst. A gas containing 8% oxygen in nitrogen is also fed into the reactor at a rate sufficient to obtain 4.5% O2 at the exhaust. The reactor is operated at 60 °C and 160 psig (1200 kPa). The product of the reactor is transferred to a liquid-gas separator, the vapor is transferred to a condenser, the liquid goes to the reactor outlet, and the non-condensable gas goes to the exhaust. Example 8 is tested in this reactor system.

[0073] Example #8

[0074] Preparation of Catalyst #8 :

[0075] The catalyst was prepared using 20 g of Fuji Silysia Chemical, Ltd. CARiACT Q-10 support as starting material by the incipient wetness technique, and 10.5 g of titanium isopropoxide and 3 g of glacial acetic acid were added in very small droplets in a rotary device to ensure uniform distribution of the solution onto the support material. The solution was at 40 °C when added. The modified support material was then dried in vacuo at 60 °C for 4 h and calcined in air at ambient pressure by the following steps: the temperature was raised from ambient temperature to 125 °C at 5 °C / min, held for 1 h, then raised to 250 °C at 5 °C / min and held for 1 h, then raised to 350 °C at 5 °C / min and held for 1 h, and finally raised to 450 °C at 5 °C / min and held for 4 h. Subsequently, gold was added to the support by the incipient wetness technique using 0.83 g of sodium thiosulfate gold in 10 g of deionized water at 40 °C. The resulting catalyst was dried and calcined in air using the same heating profile as above.

[0076] Examples 9 to 11 - Semi-batch slurry reactor operation :

[0077] Prepare a 10 wt% solution of methacrolein in methanol in advance. Place approximately 1 g of catalyst and 170 g of the methacrolein-methanol solution in a 300 mL stirred reactor equipped with a baffle and a gas induction propeller. Seal the reactor and simultaneously start mixing, pressurizing, and heating. Set the impeller to 1150 rpm and pressurize the reactor to 100 psig by introducing a continuous flow of 100 sccm of 8% O2 / N2 gas, which flows through the reactor to the condenser after the pressurization is completed. The reactor reaches a reaction temperature of 80 °C in about 15 minutes, at which point the reaction is defined as starting. Take aliquots from the reactor every half hour for 2.5 to 5 hours using a dip tube equipped with an on-line filter. Test the following Examples 9 to 11 in this reactor system.

[0078] Example #9

[0079] Preparation of Catalyst #9 :

[0080] As a first step, prepare a Zr-promoted SiC support. The support is prepared by impregnation-evaporation using a RotaVap. Place a portion of 10 g of SiC extrudates from SiCat into a round-bottom flask and add 22 ml of a solution of zirconyl(IV) nitrate hydrate 0.5 M in deionized water. Place the flask on a rotary evaporator. Remove the water by continuously rotating the flask under vacuum at 50 °C. Dry the material under vacuum at 50 °C for 30 minutes and then calcine the material in a box furnace in static air using the following procedure: heat the sample from ambient conditions at 3 °C / min and dry at 120 °C for 2 hours, then heat at 2 °C / min and calcine at 600 °C for 4 hours.

[0081] As a second step, add Au to the support material. Prepare a 1.5 wt% Au / Zr / SiC catalyst by incipient wetness impregnation followed by drying and calcining in air using a box furnace. Prepare a 0.1988 M solution by placing 3.877 g of sodium aurothiomalate(I) in a volumetric flask and filling to a volume of 50 ml with deionized water. Stir the flask gently until a clear yellow solution is formed. Then, prepare an impregnation solution by adding 1.7 ml of deionized water to 38.3 ml of the 0.1988 M sodium aurothiomalate(I) solution and impregnate 5 g of the Zr-SiC support dropwise with 2 ml of this impregnation solution until the incipient wetness point of the 1.5 wt% Au catalyst is reached. Dry the impregnated material and then calcine the impregnated material in a box furnace in static air using the following procedure: heat the sample from ambient conditions at 5 °C / min and dry at 120 °C for 1 hour, then heat at 5 °C / min and calcine at 300 °C for 4 hours.

[0082] Example #10

[0083] Preparation of Catalyst #10 :

[0084] As a first step, a Ti-promoted SiC support is prepared. The support is prepared by impregnation-evaporation using a RotaVap. A portion of 10 g of SiC extrudates from SiCat is loaded into a round-bottom flask, and 5.3 ml of a 50 wt% solution of bis(ammonium lactate) titanium(IV) dihydroxide is added. The flask is placed on a rotary evaporator. Water is removed by continuously rotating the flask under vacuum at 50 °C. The material is dried in vacuo at 50 °C for 30 minutes and then calcined in a box furnace in static air using the following procedure: The sample is heated from ambient conditions at 3 °C / min and dried at 120 °C for 2 hours, then heated at 2 °C / min and calcined at 600 °C for 4 hours.

[0085] As a second step, Au is added to the support material. A 1.5 wt% Au / Ti / SiC catalyst is prepared by incipient wetness impregnation followed by drying and calcination in air using a box furnace. A 0.1988 M solution is prepared by placing 3.877 g of sodium gold(I) thiomalate in a volumetric flask and filling to a volume of 50 ml with deionized water. The flask is gently stirred until a clear yellow solution is formed. Then, an impregnation solution is prepared by adding 1.7 ml of deionized water to 38.3 ml of the 0.1988 M sodium gold(I) thiomalate solution, and 5 g of the Ti-SiC support is impregnated dropwise with 2 ml of this impregnation solution until the incipient wetness point of the 1.5 wt% Au catalyst is reached. The impregnated material is dried and then calcined in a box furnace in static air using the following procedure: The sample is heated from ambient conditions at 5 °C / min and dried at 120 °C for 1 hour, then heated at 5 °C / min and calcined at 300 °C for 4 hours.

[0086] Example #11

[0087] Preparation of Catalyst #11 :

[0088] As a first step, a La-promoted SiC support was prepared. The support was prepared by incipient wetness impregnation using a RotaVap. A portion of 10 g of SiC extrudates from SiCat was loaded into a round-bottom flask, and 17.7 ml of a 0.623 M lanthanum(III) nitrate hexahydrate solution was added. The flask was placed on a rotary evaporator. Water was removed by continuously rotating the flask under vacuum at 50 °C. The material was dried under vacuum at 50 °C for 30 minutes and then calcined in a box furnace in static air using the following procedure: The sample was heated from ambient conditions at 3 °C / min and dried at 120 °C for 2 hours, then heated at 2 °C / min and calcined at 600 °C for 4 hours.

[0089] As a second step, Au was added to the support material. A 1.7 wt% Au / La / SiC catalyst was prepared by incipient wetness impregnation, followed by drying and calcination in air using a box furnace. A 0.1988 M solution was prepared by placing 3.877 g of sodium aurothiomalate(I) in a volumetric flask and filling it to a volume of 50 ml with deionized water. The flask was gently stirred until a clear yellow solution was formed. Then, an impregnation solution was prepared by adding 1.7 ml of deionized water to 38.3 ml of the 0.1988 M sodium aurothiomalate(I) solution, and 5 g of the La-SiC support was impregnated dropwise with 2 ml of this impregnation solution until the incipient wetness point of the 1.7 wt% Au catalyst was reached. The impregnated material was dried and then calcined in a box furnace in static air using the following procedure: The sample was heated from ambient conditions at 5 °C / min and dried at 120 °C for 1 hour, then heated at 5 °C / min and calcined at 300 °C for 4 hours.

[0090] Table 1 below shows the results of Examples 1 to 11.

[0091] Table 1

[0092]

[0093] * Preparation methods include: (1) immersion impregnation, (2) incipient wetness impregnation, and (3) spray or small droplet impregnation. ** Eggshell catalysts are defined as having at least 90 wt% gold content in the outer 40 vol% of the catalyst pellets.

[0094] NA indicates not applicable.

[0095] + Estimated by energy-dispersive spectroscopy (EDS) using scanning electron microscopy (SEM) or by comparison of the preparation method with other catalysts (when available).

[0096] ++The normalized MMA selectivity is the percentage of MMA in the products originating in the form of methacrolein reactants.

Claims

1. A method for preparing a catalyst for the oxidative esterification of methacrolein to methyl methacrylate, the method comprising: providing a support, wherein the support comprises a material selected from the group consisting of oxides of silicon, carbides of silicon, metal oxides, and metal carbides; providing particles of at least one oxide of a metal on the surface of the support, wherein the metal is selected from the group consisting of aluminum, titanium, lanthanides, zirconium, nickel, cobalt, zinc, tellurium, antimony, bismuth, rhenium, tungsten, alkali metals, and alkaline earth metals, contacting the support with a gold salt, heating the support at a temperature in the range of 50 °C to 600 °C for a time in the range of at least 0.1 hour to 48 hours to convert the gold salt into gold nanoparticles having an average diameter of less than 12 nm and a standard deviation of + / - 4 nm, wherein at least 75% of the gold nanoparticles by number are located within 20 nm of the particles of the oxide of the metal.

2. The method according to claim 1, wherein the support has an average diameter in the range of 50 nm to 500 μm, and the step of providing the support comprises producing the support by a method selected from: reaction forming the support and then drying, spray drying, filtration and / or centrifugation after precipitation, and comminution.

3. The method according to claim 1, wherein the support has an average diameter in the range of greater than 500 μm to 10 mm, and the step of providing the support comprises producing the support by extrusion or granulation.

4. The method according to any one of the preceding claims, wherein the step of heating the support comprises heating the support at a temperature in the range of 150 °C to 500 °C for a time in the range of at least 0.1 hour to 48 hours in the presence of an oxygen-containing gas.

5. The method according to any one of claims 1 to 3, wherein the step of heating the support comprises heating the support in the presence of a reducing gas comprising at least 0.1 vol% of a reducing agent.

6. The method according to any one of claims 1 to 3, wherein the step of heating the support comprises heating the support in an inert atmosphere.

7. The method according to any one of claims 1 to 3, wherein the step of heating the support comprises heating the support in the presence of a solvent and a reducing agent, wherein the ratio of the reducing agent to the solvent is at least 0.

01.

8. The method according to any one of the preceding claims, wherein contacting the support with the gold salt comprises a method selected from the group consisting of: - impregnating the support with a solution comprising the gold salt; - dip-coating the support with a solution comprising the gold salt; - spraying the support with a solution comprising the gold salt; and - sequentially impregnating the support by the steps of: impregnating the support with a first solution to fill at least 80% by volume of any pores in the support with a pore filler, and subsequently impregnating the support with a second solution comprising the gold salt.

9. The method according to any one of the preceding claims, wherein at least 75% by weight of the total weight of the gold particles is within the outer 50% of the volume of the catalyst.

10. The method according to any one of the preceding claims, wherein the oxide of the metal comprises an oxide of nickel or an oxide of titanium.

11. The catalyst according to any one of the preceding claims, wherein the support comprises an oxide of silicon and an oxide of titanium.

12. A method for preparing methyl methacrylate from methacrolein and methanol; the method comprising contacting a mixture comprising methacrolein, methanol and oxygen in a reactor in the presence of a catalyst according to any one of the preceding claims.

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