Process for preparing supported gold NP catalyst for the production of methyl methacrylate by oxidative esterification, the catalyst obtained thereby and the process of said OE

Abstract

A process for preparing a catalyst for the oxidative esterification of methacrolein to methyl methacrylate includes providing a support selected from an oxide of silicon, a carbide of silicon, a metal oxide, and a metal carbide. Particles of at least one oxide of a metal are provided on the support. The support is contacted with a gold salt and heated at a temperature ranging from 50°C to 600°C for a time ranging from 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, with at least 75% by number of the gold nanoparticles located within 20 nm of the metal oxide particle.

Description

[Technical Field]

[0001] The present invention relates to a process for making a catalyst for the preparation of methyl methacrylate from the oxidative esterification of methacrolein.

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

[0003] U.S. Patent No. 8,461,373 discloses a catalyst containing oxidized nickel and at least one element selected from nickel, palladium, platinum, ruthenium, gold, silver, and copper. The diameter of the catalyst is in the range of 10 to 200 μm.

[0004] WO 2016 / 113106 discloses a catalyst comprising gold, silicon oxide, aluminum oxide, and an oxide of at least one element selected from alkali metals, alkaline earth metals, lanthanides having atomic numbers 57 to 71, Y, Sc, Ti, Zr, Cu, Mn, Pb, and Bi. The average diameter of the catalyst is in the range of 10 to 200 μm.

[0005] However, there is a need for improved catalysts and processes for producing the catalysts that can improve selectivity and / or reduce the formation of by-products. Summary of the Invention

[0006] One aspect of the present invention relates to a process for preparing a catalyst for the oxidative esterification of methacrolein to methyl methacrylate. The process 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, lanthanides, 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 ranging from 50°C to 600°C for a time ranging from 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. At least 75% of the gold nanoparticles by number are located within 20 nm of the metal oxide particles. DETAILED DESCRIPTION OF THE INVENTION

[0007] Unless otherwise specified, all compositional percentages are in weight percent (wt%) and all temperatures are in °C. Unless otherwise specified, averages are arithmetic means. "Catalyst center" is the center of gravity of the catalyst particle, i.e., the average location of all points in all coordinate directions. Diameter is any linear dimension passing through the catalyst center, and average diameter is the arithmetic mean of all possible diameters. Aspect ratio is the ratio of the longest diameter to the shortest diameter. Unless otherwise specified, average particle size refers to the average particle size after the catalyst is prepared and before the catalyst is used. Aged catalyst is used catalyst.

[0008] The catalyst of the present invention comprises a support, with nickel oxide and gold particles disposed on the support.

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

[0010] The process includes providing a support, providing particles of at least one oxide of a metal on a 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 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% of the gold nanoparticles by number are located within 20 nm of the metal oxide particles.

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

[0012] In one embodiment, the support may have an average diameter ranging from 50 nm to 500 μm, preferably from 100 nm to 400 μm, and more preferably from 150 nm to 300 μm. In this embodiment, the catalyst may be suitable for reactors in which the catalyst is maintained in suspension, such as slurry reactors or continuous stirred tank reactors. When the support is less than 500 μm, the support may be formed directly as a reaction product followed by drying, spray drying the support, precipitation followed by filtration and / or centrifugation, or milling larger material to form the desired size. Alternatively, the support may be prepared by classifying particles to select the desired average particle size.

[0013] In another embodiment, the support may have an average diameter greater than 500 μm, e.g., from 500 μm to 10 mm. In embodiments in which the average diameter of the support is greater than 500 μm, the catalyst may be used in a reactor comprising a fixed bed, such as, for example, a fixed-bed reactor, a trickle-bed reactor, or a packed bubble column reactor. For supports having an average diameter greater than 500 μm, the support may be produced by extrusion or pelletization, or any other known method. When forming the support by extrusion or pelletization, the support may be formed with or without a binder.

[0014] Particles of at least one metal oxide are provided on the support, the metal being selected from aluminum, titanium, lanthanides, zirconium, alkali metals, alkaline earth metals, nickel, cobalt, zinc, magnesium, tellurium, antimony, rhenium, tungsten, and bismuth. The particles of the at least one metal oxide may be formed on the support by first contacting the support with a salt of the metal and then oxidizing the metal in an environment comprising an oxygen-containing gas, such as air or oxygen.

[0015] Preferably, the support comprises, consists of, or consists essentially of an oxide of silicon. More preferably, the support comprises, consists of, or consists essentially of an oxide of silicon modified with titanium oxide or nickel oxide particles. When used herein with respect to a support, the phrase "consisting essentially of" excludes the presence of materials that may reduce the mechanical strength of the support. Alternatively, "consisting essentially of" means that the support comprises at least 95 wt. % of the recited material, based on the total weight of the support.

[0016] Preferably, the carrier is 10 m 2 / g, preferably more than 30m 2 / g, preferably above 50m 2 / g, preferably more than 100m 2 / g, preferably above 120m 2 / g.

[0017] Preferably, the aspect ratio of the catalyst particles is 10:1 or less, preferably 5:1 or less, preferably 3:1 or less. Although the shape is not limited, preferred shapes of catalyst particles include spheres, cylinders, cuboids, rings, multi-lobed shapes (e.g., cloverleaf cross-sections), shapes with multiple holes and "wagon wheels," preferably spheres. Irregular shapes can also be used.

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

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

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

[0021] In another alternative embodiment, the step of heating the support to convert the gold salt to metallic gold may be carried out in the presence of an inert atmosphere, where 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 to metallic gold may be carried out in the liquid phase in the presence of a solvent and a reducing agent, the ratio of reducing agent to solvent being at least 0.01. In this embodiment, the support is heated at a temperature ranging from 50° C. to below the boiling point of the solvent.

[0023] Contacting the support with the gold salt can be carried out by several different methods. For example, contacting 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, spray-coating the support with a solution containing the gold salt, or sequentially impregnating the support by impregnating the support with a first solution, either aqueous or organic, to fill at least 80% by volume of any pores that may be present in the support, and then impregnating the support with a second solution containing the gold salt. When contacting the support with a solution or aqueous solution of a gold salt, the support may first be dried before heating the support to convert the gold salt to metallic gold particles.

[0024] Preferably, the catalyst is produced by precipitating gold and metal (i.e., metal of the metal oxide) from an aqueous solution of metal salts in the presence of a support. In a preferred embodiment, the catalyst is produced by contacting a porous inorganic oxide with an aqueous solution of suitable gold precursor salts and nickel salts so that the pores are filled with the solution, followed by removal of the water by drying. The resulting material is then converted to the final catalyst by calcination or reduction to decompose the gold and metal salts to gold and metal oxide. Preferably, the catalyst is a C2-C cation salt containing at least one hydroxyl or carboxylic acid substituent. 18 Thiols are present in solution. Preferably, C2-C thiols containing at least one hydroxyl or carboxylic acid substituent. 18 The thiol has 2 to 12, preferably 2 to 8, and preferably 3 to 6 carbon atoms. Preferably, the thiol compound contains a total of 4 or less, preferably 3 or less, and preferably 2 or less, hydroxyl and carboxylic acid groups. Preferably, the thiol compound has 2 or less, preferably 1 or less, thiol groups. When the thiol compound contains a carboxylic acid substituent, it can exist in the acid form, the conjugate base form, or a mixture thereof. Particularly preferred thiol compounds include thiomalic acid, 3-mercaptopropionic acid, thioglycolic acid, 2-mercaptoethanol, and 1-thioglycerol, including their conjugate bases.

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

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

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

[0028] More preferably, at least 75% of the gold particles, based on number, are within at least 20 nm of two metal oxide nanoparticles. That is, the edge of a gold particle is within at least 20 nm of the edges of the two metal oxide nanoparticles closest to it. 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, based on number, are within at least 20 nm of at least three metal oxide nanoparticles. That is, the edge of a gold particle is within at least 20 nm of the edges of the at least three metal oxide nanoparticles closest to it. 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, 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 formula:

[0031]

number

[0032]

number

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

[0034] The weight ratio of gold particles to the amount of metal oxide nanoparticles may be in the range of 1:1 to 1:20. Preferably, the weight ratio of gold particles to metal oxide nanoparticles is in the range of 1:2 to 1:15, more preferably 1:3 to 1:10, and even more preferably 1:3 to 1:6.

[0035] The amount by weight of metal oxide to the amount by weight of 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 even more preferably from 0.5:1 to 2:1.

[0036] Preferably, the gold particles are uniformly distributed among the metal oxide nanoparticles. As used herein, the term "uniformly distributed" means that the gold particles are randomly dispersed among the metal oxide nanoparticles and there is substantially no aggregation of the gold particles, e.g., less than 10 wt.% of the gold particles are in physical contact with other gold particles, based on the total weight of the gold particles. Preferably, less than 7.5 wt.% of the gold particles are in physical contact with other gold particles, based on the total weight of the gold particles, and more preferably, less than 5 wt.% of the gold particles are in physical contact with other gold particles, based on the total weight of the gold particles.

[0037] Preferably, at least 75% of the gold particles are in the outer 50% of the catalyst volume (i.e., the volume of an average catalyst particle), more preferably the outer 40% of the catalyst volume, even more preferably the outer 30%, and even more preferably the outer 25%. Preferably, the outer volume of any particle shape is calculated relative to the volume having a certain distance from its inner surface to its outer surface (the surface of the catalyst particle), measured along a line perpendicular to the outer surface. For example, for a spherical particle, the outer x% of the volume is the spherical shell, its outer surface is the surface of the particle, and its volume is x% of the volume of the entire sphere. Preferably, at least 95%, preferably at least 97%, preferably at least 99% by weight of the gold particles are in the outer volume of the catalyst. Preferably, at least 90% by weight (preferably at least 95%, preferably at least 97%, preferably at least 99%) of the gold particles are within a distance from the surface that is no more than 30%, preferably no more than 25%, preferably no more than 20%, preferably no more than 15%, preferably no more than 10%, preferably no more than 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 carrier particles. The eggshell layer may have a thickness of 500 microns or less, preferably 250 microns or less, and more preferably 100 microns or less.

[0038] Preferably, at least 0.1 wt.% 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 other gold particles or metal oxide nanoparticles, i.e., the gold particles can be directly contacted by reactants. Thus, the gold particles may be disposed within the pores of the support material and still be exposed to reactants that can directly contact the gold particles within the pores. More preferably, at least 0.25 wt.% of the total weight of the gold particles is exposed on the surface of the catalyst, even more preferably, at least 0.5 wt.% of the total weight of the gold particles is exposed on the surface of the catalyst, and even more preferably, at least 1 wt.% of the total weight of the gold particles is exposed on the surface of the catalyst.

[0039] Preferably the amount of gold as a percentage of gold and support is 0.2-5 wt.%, preferably at least 0.5 wt.%, preferably at least 0.8 wt.%, preferably at least 1 wt.%, preferably at least 1.2 wt.%, preferably no more than 4 wt.%, preferably no more than 3 wt.%, preferably no more than 2.5 wt.%.

[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 in a catalyst bed. The catalyst particles in the catalyst bed are typically held in place by solid walls and screens or catalyst support grids. In some configurations, screens or grids are at both ends of the catalyst bed and solid walls are at the sides, while in some configurations, the catalyst bed can be completely surrounded by screens. Preferred shapes of the catalyst bed include a cylinder, a rectangular parallelepiped, and a cylindrical shell, preferably a cylinder. The OER further contains a liquid phase containing methacrolein, methanol, and MMA, and a gas phase containing oxygen. The liquid phase may further contain by-products, such as methacrolein dimethyl acetal (MDA) and methyl isobutyrate (MIB). Preferably, the liquid phase is at a temperature of 40 to 120° C., preferably at a temperature of at least 50° C., preferably at least 60° C., and preferably at most 110° C., preferably at most 100° C. Preferably, the catalyst bed is at a pressure of 0 to 2000 psig (101 kPa to 14 MPa), preferably at most 2000 kPa, preferably at most 1500 kPa.

[0041] The 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 1:10 to 100:1, preferably 1:2 to 20:1, preferably 1:1 to 10:1. Preferably, the catalyst bed further comprises an inert or acidic material above and / or below the catalyst. Preferred inert or acidic materials include, for example, alumina, clay, glass, silica carbide, and quartz. Preferably, the inert or acidic material has an average diameter equal to or greater than the average diameter of the catalyst, preferably 20 mm or less. 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 bottom stream from the methanol recovery distillation column comprises 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 a methanol recovery distillation column, which stream contains MMA, MDA, methacrylic acid, salts, and water. In another embodiment, MDA is hydrolyzed in an organic phase separated from the methanol recovery bottoms stream. Water may need to be added to the organic phase to ensure sufficient water for MDA hydrolysis, the amount of which 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 is passed through one or more distillation columns to produce the MMA product and light and / or heavy by-products. In another embodiment, hydrolysis can be carried out in the distillation column itself.

[0042] Preferably, 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%, even more preferably at least 3 mol%, even more preferably at least 3.5 mol%, even more preferably at least 4 mol%, and most preferably at least 4.5 mol%, based on the total volume of the gas stream exiting the reactor. Preferably, the oxygen concentration in the gas stream exiting the reactor is 7.5 mol% or less, preferably 7.25 mol% or less, preferably 7 mol% or less, based on the total volume of the gas stream exiting the reactor.

[0043] One preferred embodiment of a fixed-bed reactor for oxidative esterification is a trickle-bed reactor, which contains a fixed bed of catalyst and passes both gas and liquid feed streams downward through the reactor. In the trickle-bed reactor, the gas phase is the continuous fluid phase. Thus, the zone at the top of the reactor above the fixed bed becomes filled with a vapor-phase mixture of nitrogen, oxygen, and volatile liquid components at their respective vapor pressures. At typical operating temperatures and pressures (50-90°C and 60-300 psig (400-2000 kPa)), when the gas feed is air, this vapor mixture is within a flammable envelope. Therefore, only an ignition source is required to initiate a deflagration, which could result in the loss of primary containment and damage to nearby physical infrastructure and personnel. To address process safety considerations, a means for operating a trickle bed reactor while avoiding a flammable headspace atmosphere is operation with a gas supply containing a sufficiently low oxygen mole fraction to ensure that the oxygen concentration in the vapor headspace is below a limiting oxygen concentration (LOC).

[0044] Knowledge of the LOC is required for the fuel mixture, temperature, and pressure of concern. Since LOC decreases with increasing temperature and pressure, and given that methanol provides a lower LOC than two other important fuels (methacrolein and methyl methacrylate), a conservative design would 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 up to 100°C and 275 psig (2 MPa), the feed oxygen concentration in nitrogen should not exceed 7.4 mole percent. [Example]

[0045] Examples 1-6 - Semi-batch slurry reactor operation: A 10 wt% methacrolein solution in methanol was prepared in advance. Approximately 1 gram of catalyst and 170 g of the methacrolein-methanol solution were placed in a 300 mL stirred reactor containing a baffle and a gas-inducing propeller. The reactor was sealed, and mixing, pressurization, and heating were initiated simultaneously. The impeller was set to 1150 rpm, and the reactor was pressurized to 100 psig by introducing a continuous flow of 100 sccm of 8% O in N gas, which flowed through the reactor and into the condenser after pressurization was complete. The reactor reached a reaction temperature of 80°C in approximately 15 minutes, at which point the reaction was defined as initiated. Reactor aliquots were sampled every half hour over a period of 2.5 to 5 hours using a dip tube equipped with an in-line filter. The following Examples 1 to 6 were tested with this reactor system.

[0046] Example No. 1 Preparation of catalyst No. 1: 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. Approximately 100 g of Cariact Q50 silica was then placed in a 500 mL flask and 200 mL of magnesium solution was added with stirring. The slurry was stirred overnight at 50°C, filtered, and the isolated material was dried in a vacuum oven at 80°C for 1 hour and then calcined at 500°C overnight to produce Mg-modified silica. Approximately 25 g of Mg-modified silica was added to 85 mL of deionized water, and the resulting slurry was heated to 90°C with stirring. A second solution containing 0.453 g of tetrachloroauric acid trihydrate, 1.255 g of cobalt nitrate hexahydrate, and 85 mL of deionized water was then prepared and added to the slurry with stirring over 30 minutes. The resulting slurry was then stirred for an additional hour. The solid material was isolated from the slurry by centrifugation. The solid was then washed with a total of 300 mL of deionized water. For each wash, the sample was mixed with 100 mL of water for 5 minutes, followed by centrifugation to isolate the solid material. The washed material was then 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.

[0047] Example No. 2 Preparation of catalyst No. 2: A slurry was prepared using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.352 g of tetrachloroauric acid trihydrate, and 4.65 g of cerium nitrate hexahydrate. The slurry was then heated to 45°C and stirred for 1 hour, after which the pH was adjusted to 8 by adding 1 M sodium carbonate dropwise. The slurry was stirred for an additional 2 hours at 45°C and then filtered. The resulting solid was washed with 500 mL of deionized water during filtration and then dried under vacuum at ambient temperature overnight. The dried solid was then calcined in air in a box oven at 400°C for 4 hours with a heating rate of 5°C / min, using an air flow of 40 L / min.

[0048] Example No. 3 Preparation of catalyst No. 3: A slurry was prepared using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.456 g of tetrachloroauric acid trihydrate, and 1.16 g of ammonium perrhenate. The slurry was heated to 60°C and stirred for 1 hour, after which the pH was adjusted to 8 by adding 1 M sodium carbonate dropwise. The slurry was stirred for an additional 2 hours at 60°C and then filtered. The resulting solid was washed with 500 mL of deionized water during filtration and then dried under vacuum at ambient temperature overnight. The dried solid was then calcined in air in a box oven at 400°C for 4 hours with a heating rate of 5°C / min, using an air flow of 40 L / min.

[0049] Example No. 4 Preparation of catalyst No. 4: A slurry was prepared using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.456 g of tetrachloroauric acid trihydrate, and 1.14 g of ammonium tungstate. The slurry was heated to 60°C and stirred for 1 hour, after which the pH was adjusted to 8 by adding 1 M sodium carbonate dropwise. The slurry was stirred for an additional 2 hours at 60°C and then filtered. The resulting solid was washed with 500 mL of deionized water during filtration and then dried under vacuum at ambient temperature overnight. The dried solid was then calcined in air in a box oven at 400°C for 4 hours with a heating rate of 5°C / min, using an air flow of 40 L / min.

[0050] Example No. 5 Preparation of catalyst No. 5: A slurry was prepared using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.456 g of tetrachloroaurate(III) trihydrate, and 0.737 g of cadmium chloride. The slurry was heated to 60°C and stirred for 1 hour, after which the pH was adjusted to 8 by adding 1 M sodium carbonate dropwise. The slurry was stirred for an additional 2 hours at 60°C and then filtered. The resulting solid was washed with 500 mL of deionized water during filtration and then dried under vacuum at ambient temperature overnight. The dried solid was then calcined in air in a box oven at 400°C for 4 hours with a heating rate of 5°C / min, using an air flow of 40 L / min.

[0051] Example No. 6 Preparation of catalyst No. 6: A slurry was prepared using 15 g of Siralox (Siralox 1.5 / 140), 200 mL of deionized water, 0.456 g of tetrachloroauric acid trihydrate, and 0.87 g of zinc acetate dehydrate. The slurry was heated to 60°C and stirred for 1 hour, after which the pH was adjusted to 8 by adding 1 M sodium carbonate dropwise. The slurry was stirred for an additional 2 hours at 60°C and then filtered. The resulting solid was washed with 500 mL of deionized water during filtration and then dried under vacuum at ambient temperature overnight. The dried solid was then calcined in air in a box oven at 400°C for 4 hours with a heating rate of 5°C / min, using an air flow of 40 L / min.

[0052] Example 7 - Operation of semi-batch recycle fixed bed reactor: A 150 g feed solution containing 10 wt. % methacrolein, 200 ppm inhibitor, and the remainder methanol was prepared and placed in a 300 mL reactor vessel, which served as a gas release vessel. The liquid in the vessel was maintained at a temperature of approximately 20 °C. The liquid feed was pumped from the gas release vessel at 7 mL / min into the bottom of a vertically oriented fixed-bed reactor. Air and nitrogen gas were mixed to provide 8 mol % oxygen and mixed with the liquid feed before entering the fixed-bed reactor. The fixed-bed reactor was a jacketed 1 / 4-inch stainless steel tube maintained at 60 °C using an external heater. The reactor itself was packed with 2 mm glass beads to fill approximately 18 inches (45.7 cm) of the tube, followed by the catalyst. The remaining void space at the top of the reactor was filled with 3 mm glass beads. The liquid and gas exiting the top of the reactor were sent to a condenser, where non-condensable gases were vented, while the liquid was recycled back to the gas release vessel. Example 7 was tested in this reactor system.

[0053] Example No. 7 Preparation of catalyst No. 7: The catalyst was prepared by incipient wetness impregnation of 10 g of Fuji Silysia Chemical, Ltd. CAriACT Q-10 support, previously modified by the supplier to add 6.6 wt. % Ti in the form of titanium dioxide. A solution consisting of 0.39 g of sodium gold thiosulfate, 0.4 g of mercaptosuccinic acid, and 0.12 g of citric acid monohydrate in 10 g of deionized water was then placed in a box oven with a constant air purge of 50 L / h at ambient temperature for 1 hour, then ramped to 400 °C at 5 °C / min and calcined for 4 hours.

[0054] Example 8 - Operation of a single pass fixed bed reactor: A feed consisting of 20 wt. % methacrolein, 200 ppm polymerization inhibitor, and the remainder methanol was fed at a rate of 40 g / hr to a 3 / 8-inch (9.5 mm) stainless steel tubular reactor containing a short front of borosilicate glass beads, followed by 5 g of catalyst. A gas containing 8% oxygen in nitrogen was also fed to the reactor at a rate sufficient to obtain 4.5% O in the vent. The reactor was operated at 60°C and 160 psig (1200 kPa). The reactor product was sent to a gas-liquid separator, the vapor to a condenser, the liquid to the reactor outlet, and the non-condensable gases to the vent. Example 8 was run with this reactor system.

[0055] Example No. 8 Preparation of catalyst No. 8: Catalysts were prepared using the incipient wetness technique, starting with 20 g of Fuji Silysia Chemical's CAriACT Q-10 support. 10.5 g of titanium isopropoxide was added dropwise to a rotating device with 3 g of glacial acetic acid to ensure uniform distribution of the solution on the support material. The solution was at 40°C at the time of addition. The modified support material was then dried under vacuum at 60°C for 4 hours and calcined in air at ambient pressure by increasing the temperature from ambient to 125°C at 5°C / min and holding for 1 hour, then increasing the temperature to 250°C at 5°C / min and holding for 1 hour, then increasing the temperature to 350°C at 5°C / min and holding for 1 hour, and finally increasing the temperature to 450°C at 5°C / min and holding for 4 hours. Gold was then added to the support at 40°C using the incipient wetness technique, utilizing 0.83 g of gold sodium thiosulfate in 10 g of deionized water. The resulting catalyst was dried and calcined in air using the same heating profile as above.

[0056] Examples 9-11 - Semi-batch slurry reactor operation: A 10 wt% solution of methacrolein in methanol was prepared in advance. Approximately 1 gram of catalyst and 170 g of the methacrolein-methanol solution were placed in a 300 mL stirred reactor containing a baffle and a gas-inducing propeller. The reactor was sealed, and mixing, pressurization, and heating were initiated simultaneously. The impeller was set to 1150 rpm, and the reactor was pressurized to 100 psig by introducing a continuous flow of 100 sccm of 8% O in N gas, which flowed through the reactor and into the condenser after pressurization was complete. The reactor reached a reaction temperature of 80°C in approximately 15 minutes, at which point the reaction was defined as initiated. Reactor aliquots were sampled every half hour over a period of 2.5 to 5 hours using a dip tube equipped with an in-line filter. The following Examples 9-11 were tested with this reactor system.

[0057] Example No. 9 Preparation of catalyst No. 9: As a first step, a Zr-promoted SiC support was prepared. The support was prepared by impregnation-evaporation using a RotaVap. A portion of 10 g of SiC extrudates supplied by SiCat was placed in a round-bottom flask, and 22 mL of 0.5 M zirconium(IV) oxynitrate hydrate in deionized water was added. The flask was placed in the RotaVap. Water was removed under vacuum with continuous flask rotation at 50°C. The material was dried under vacuum at 50°C for 30 minutes and then calcined in still air in a box oven using the following procedure: the sample was dried from ambient conditions at 120°C for 2 hours, ramped at 3°C / min, followed by calcination at 600°C for 4 hours, ramped at 2°C / min.

[0058] In the second step, gold was added to the support material. A 1.5 wt% Au / Zr / SiC catalyst was prepared by incipient wetness impregnation, followed by drying and calcination in air using a box oven. A 0.1988M solution was prepared by placing 3.877 g of sodium gold thiomalate (I) in a volumetric flask and filling it with deionized water to a volume of 50 mL. The flask was gently stirred until a clear yellow solution was formed. Next, an impregnation solution was prepared by adding 1.7 mL of deionized water to 38.3 mL of the 0.1988M sodium gold thiomalate (I) solution. 2 mL of this impregnation solution was added dropwise to 5 g of Zr-SiC support until the incipient wetness point of 1.5 wt% Au catalyst was reached. The impregnated material was dried and then calcined in still air in a box oven using the following procedure: the sample was dried from ambient conditions at 120°C at 5°C / min for 1 hour, followed by calcination at 300°C at 5°C / min for 4 hours.

[0059] Example No. 10 Preparation of catalyst No. 10: As a first step, a Ti-promoted SiC support was prepared. The support was prepared by impregnation-evaporation using a RotaVap. A portion of 10 g of SiC extrudates supplied by SiCat was placed in a round-bottom flask, and 5.3 mL of a 50 wt. % titanium(IV) bis(ammonium lactato) dihydroxide solution was added. The flask was placed in the RotaVap. Water was removed under vacuum with continuous flask rotation at 50°C. The material was dried under vacuum at 50°C for 30 minutes and then calcined in still air in a box oven using the following procedure: the sample was dried from ambient conditions at 120°C for 2 hours, ramped at 3°C / min, followed by calcination at 600°C for 4 hours, ramped at 2°C / min.

[0060] In the second step, gold was added to the support material. A 1.5 wt% Au / Ti / SiC catalyst was prepared by incipient wetness impregnation, followed by drying and calcination in air using a box oven. A 0.1988M solution was prepared by placing 3.877 g of sodium gold thiomalate (I) in a volumetric flask and filling it with deionized water to a volume of 50 mL. The flask was gently stirred until a clear yellow solution was formed. Next, an impregnation solution was prepared by adding 1.7 mL of deionized water to 38.3 mL of the 0.1988M sodium gold thiomalate (I) solution. 2 mL of this impregnation solution was added dropwise to 5 g of Ti-SiC support until the incipient wetness point of 1.5 wt% Au catalyst was reached. The impregnated material was dried and then calcined in still air in a box oven using the following procedure: the sample was dried from ambient conditions at 120°C at 5°C / min for 1 hour, followed by calcination at 300°C at 5°C / min for 4 hours.

[0061] Example No. 11 Preparation of catalyst No. 11: As a first step, a La-promoted SiC support was prepared. The support was prepared by impregnation-evaporation using a RotaVap. A portion of 10 g of SiC extrudates provided by SiCat was placed in a round-bottom flask, and 17.7 mL of 0.623 M lanthanum(III) nitrate hexahydrate solution was added. The flask was placed in the RotaVap. Water was removed under vacuum with continuous flask rotation at 50°C. The material was dried under vacuum at 50°C for 30 minutes and then calcined in still air in a box oven using the following procedure: the sample was dried from ambient conditions at 120°C for 2 hours, ramped at 3°C / min, followed by calcination at 600°C for 4 hours, ramped at 2°C / min.

[0062] In the second step, gold 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 oven. A 0.1988M solution was prepared by placing 3.877 g of sodium gold thiomalate (I) in a volumetric flask and filling it with deionized water to a volume of 50 mL. The flask was gently stirred until a clear yellow solution was formed. Next, an impregnation solution was prepared by adding 1.7 mL of deionized water to 38.3 mL of the 0.1988M sodium gold thiomalate (I) solution. 2 mL of this impregnation solution was added dropwise to 5 g of La-SiC support until the incipient wetness point of 1.7 wt% Au catalyst was reached. The impregnated material was dried and then calcined in still air in a box oven using the following procedure: the sample was dried from ambient conditions at 120°C at 5°C / min for 1 hour, followed by calcination at 300°C at 5°C / min for 4 hours.

[0063] The results of Examples 1 to 11 are shown in Table 1 below.

[0064] [Table 1] * Preparation methods include (1) dip impregnation, (2) incipient wetness impregnation, and (3) spray or droplet impregnation. ** Eggshell catalysts are defined as having at least 90% by weight of the gold content in the outer 40% by volume of the catalyst pellet. NA is not available. + It is estimated by energy-dispersive spectroscopy (EDS) using a scanning electron microscope (SEM) or from the preparation method combined with comparison with other catalysts, when available. ++ Normalized MMA selectivity is the percent MMA among products derived from the methacrolein reactant.

Claims

1. 1. A process for making a catalyst for the oxidative esterification of methacrolein to methyl methacrylate, comprising: providing a support, said support comprising 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 a surface of the support, the metal being 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 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% of the gold nanoparticles by number are located within 20 nm of a particle of the oxide of the metal.

2. 10. The process of claim 1, wherein the support has an average diameter in the range of 50 nm to 500 μm, and wherein the step of providing the support comprises reacting to form the support, followed by producing the support by a method selected from the group consisting of drying, spray drying, precipitation followed by filtration and / or centrifugation, and grinding.

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

4. 4. The process of any one of claims 1 to 3, wherein the step of heating the support comprises heating the support in the presence of an oxygen-containing gas at a temperature in the range of from 150°C to 500°C for a time in the range of from at least 0.1 hours to 48 hours.

5. 4. The process of claim 1, wherein the step of heating the support comprises heating the support in the presence of a reducing gas comprising at least 0.1% by volume of a reducing agent.

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

7. 4. The process of claim 1, 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 reducing agent to solvent is at least 0.

01.

8. contacting the support with a gold salt - impregnating the support with a solution containing the gold salt; - dip-coating the support with a solution containing the gold salt; - spray-coating the support with a solution containing the gold salt; - sequentially impregnating the support by impregnating the support with a first solution to fill at least 80% of the volume of any pore in the support with a pore filler, followed by impregnating the support with a second solution comprising the gold salt.

9. 9. The process of any one of claims 1 to 8, 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 process of any one of claims 1 to 9, wherein the oxide of the metal comprises an oxide of nickel or an oxide of titanium.

11. The process of any one of claims 1 to 10, wherein the support comprises an oxide of silicon and an oxide of titanium.

12. 12. A process for preparing methyl methacrylate from methacrolein and methanol, the process comprising contacting in a reactor a mixture comprising methacrolein, methanol, and oxygen in the presence of the catalyst of any one of claims 1 to 11.

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