Supported gold-NP and nickel oxide catalyst, and method for producing methyl methacrylate using the same

Abstract

The catalyst for the oxidative esterification of methacrolein to methyl methacrylate comprises a support having an average diameter of at least 0.8 mm. The support is selected from oxides of silicon, carbides of silicon, metal oxides, and metal carbides. The catalyst further comprises nickel oxide and gold particles disposed on the support. The gold particles have an average diameter of less than 12 nm and a standard deviation of + / - 4 nm. A process for preparing methyl methacrylate from methacrolein and methanol using the catalyst is also disclosed.

Description

[Technical Field]

[0001] The present invention relates to a catalyst and a process for preparing methyl methacrylate from methacrolein and methanol.

[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 ranges from 10 to 200 μm.

[0004] International Patent Application No. 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] Two types of reactors are most frequently used for producing carboxylic acid esters from aldehydes. Slurry or continuous stirred tank reactors use small catalysts (<200 μm) held in suspension, while fixed bed reactors use large catalysts (>200 μm) fixed in position within the reactor. Due to differences in reactor design, catalysts suitable for one type of reactor are not suitable for another. Each type of reactor subjects the catalyst to different conditions, including the forces to which the catalyst is exposed, and catalysts are designed differently based on their respective sizes, resulting in dramatically different ratios of catalyst active area to total catalyst volume.

[0006] However, there is a need for improved catalysts and processes for the production of methyl methacrylate that are effective and active over a longer life span. Summary of the Invention

[0007] One aspect of the present invention relates to a catalyst for the oxidative esterification of methacrolein to methyl methacrylate, comprising a support having an average diameter of at least 0.8 mm. The support is selected from silicon oxides, silicon carbides, metal oxides, and metal carbides. The catalyst further comprises gold particles and nickel oxide disposed on the support. The gold particles have an average diameter of less than 12 nm and a standard deviation of + / - 4 nm.

[0008] Another aspect of the present invention relates to a method for preparing methyl methacrylate from methacrolein and methanol, the method comprising contacting a mixture comprising methacrolein, methanol, and oxygen in a reactor with nickel oxide and gold particles disposed on a support in the presence of a catalyst comprising a support. The support has an average diameter of at least 0.8 mm and is selected from silicon oxides, silicon carbides, metal oxides, and metal carbides. The catalyst further comprises nickel oxide and gold particles disposed on the support. The gold particles have an average diameter of less than 12 nm and a standard deviation of + / - 4 nm. DETAILED DESCRIPTION OF THE INVENTION

[0009] All percentage compositions are weight percentages (wt%) and all temperatures are in °C unless otherwise indicated. Averages are arithmetic means unless otherwise stated. "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 stated, average particle size of particles refers to the average particle size of the particles after the catalyst is prepared and before the catalyst is used. Used catalyst is the catalyst as used.

[0010] The catalyst of the present invention comprises a support having gold particles and nickel oxide disposed thereon.

[0011] The carrier has an average diameter of at least 0.8 mm. More preferably, the carrier has an average diameter of at least 1.2 mm, even more preferably at least 1.5 mm, and even more preferably at least 2 mm.

[0012] 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 oxidation esterification reactor. A material that can withstand long-term use can avoid being crushed or pulverized during use.

[0013] The support material may further comprise at least one metal oxide, the metal being selected from aluminum, titanium, lanthanides, zirconium, alkali metals, alkaline earth metals, nickel, cobalt, zinc, magnesium, tellurium, antimony, and bismuth. The at least one metal oxide may be used to modify the support material.

[0014] 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. 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 listed materials, based on the total weight of the support.

[0015] 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.

[0016] 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.

[0017] The nickel 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.

[0018] The nickel oxide disposed on the support is preferably in the form of nanoparticles.

[0019] Preferably, at least 75% of the gold particles by number are within at least 20 nm of the nickel oxide, such as within at least 20 nm of the nickel oxide nanoparticles if the nickel oxide is in the form of nanoparticles. As used herein, the phrase "within at least X nm" means that the edge of a gold particle is within X nm of the nickel oxide, e.g., within X nm of the edge of the nickel oxide nanoparticle closest to the gold particle. Preferably, at least 75% of the gold particles are within at least 15 nm of the nickel oxide, more preferably within at least 12 nm of the nickel oxide, and even more preferably within at least 10 nm of the nickel oxide.

[0020] More preferably, the nickel oxide is in the form of nanoparticles, and at least 75% of the gold particles by number are within at least 20 nm of two nickel oxide nanoparticles, i.e., the edge of a gold particle is within at least 20 nm of the edge of the two nickel oxide nanoparticles closest to it. Preferably, at least 75% of the gold particles are within at least 15 nm of two nickel oxide nanoparticles, more preferably within at least 12 nm of two nickel oxide nanoparticles, and even more preferably within at least 10 nm of two nickel oxide nanoparticles.

[0021] Even more preferably, the nickel is in the form of nanoparticles, and at least 75% of the gold particles by number are within at least 20 nm of at least three nickel oxide nanoparticles, i.e., the edge of a gold particle is within at least 20 nm of the edge of the at least three nickel oxide nanoparticles nearest to it. Preferably, at least 75% of the gold particles are within at least 15 nm of at least three nickel oxide nanoparticles, more preferably within at least 12 nm of at least three nickel oxide nanoparticles, and even more preferably within at least 10 nm of at least three nickel oxide nanoparticles.

[0022] The gold particles have an average diameter of less than 12 nm, more preferably less than 10 nm, and even 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 using the following formula:

[0023]

number

[0024]

number

[0025] The average diameter of the nickel oxide nanoparticles is preferably 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 average diameter of the nickel oxide nanoparticles is at least half the average diameter of the gold particles, and more preferably at least the same as the average diameter of the gold particles.

[0026] The weight ratio of gold particles to the amount of nickel oxide can range from 1:1 to 1:20. Preferably, the weight ratio of gold particles to nickel oxide ranges from 1:2 to 1:15, more preferably from 1:3 to 1:10, and even more preferably from 1:3 to 1:6.

[0027] The weight ratio of nickel oxide to the weight of gold particles may be in the range of 0.1:1 to 10:1, preferably 0.2:1 to 5:1, more preferably 0.33:1 to 3:1, and even more preferably 0.5:1 to 2:1.

[0028] The gold particles are preferably uniformly distributed among the nickel oxide. As used herein, the term "uniformly distributed" means that the gold particles are randomly dispersed in the nickel oxide without substantial agglomeration, e.g., less than 10 wt.% of the gold particles, based on the total weight of the gold particles, are in physical contact with other gold particles. Preferably, less than 7.5 wt.% of the gold particles, based on the total weight of the gold particles, are in physical contact with other gold particles, and more preferably, less than 5 wt.% of the gold particles, based on the total weight of the gold particles, are in physical contact with other gold particles.

[0029] Preferably, at least 75% by weight of the gold particles are in the outer 50% of the catalyst volume (i.e., the volume of the average catalyst particle), more preferably the outer 40%, even more preferably the outer 30%, and even more preferably the outer 25% of the catalyst volume. 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% by weight of the gold particles are in the outer volume of the catalyst, preferably at least 97% by weight, preferably at least 99% by weight. Preferably, at least 90% by weight (preferably at least 95%, preferably at least 97%, preferably at least 99% by weight) of the gold particles are within a distance from the surface that is 30% or less, preferably 25% or less, preferably 20% or less, preferably 15% or less, preferably 10% or less, preferably 8% or less 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.

[0030] 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 nickel oxide, i.e., reactants can directly contact the gold particles. 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.

[0031] 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.%.

[0032] Preferably, the catalyst is prepared by precipitating gold and nickel from an aqueous solution of metal salts in the presence of a support. In a preferred embodiment, the catalyst is prepared by an incipient wetness technique in which an aqueous solution of the appropriate gold precursor salt and nickel salt is added to a porous inorganic oxide, thereby filling the pores with the solution, followed by drying to remove the water. The resulting material is then converted to the finished catalyst by calcination, reduction, or other pretreatment known to those skilled in the art to decompose the gold and nickel salts to the metal or 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.

[0033] In one embodiment of the present invention, the catalyst is prepared by deposition precipitation, in which a porous inorganic oxide is immersed in an aqueous solution containing suitable gold precursor salts and nickel salts, and then the pH of the solution is adjusted to allow the salts to interact with the surface of the inorganic oxide. The resulting treated solid is then recovered (e.g., by filtration) and then converted to the finished catalyst by calcination, reduction, or other pretreatment known to those skilled in the art to decompose the gold and nickel salts to the metals or metal oxides.

[0034] 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.

[0035] 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 a 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.

[0036] One preferred embodiment is a recirculating reactor with cooling capability within the recirculation loop. Another preferred embodiment is a series of reactors with cooling and mixing capabilities between the reactors.

[0037] 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.

[0038] 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 the limiting oxygen concentration (LOC).

[0039] 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]

[0040] Example #1 (approximately 1.25 mm, actual size varies from 0.85 to 1.70 mm, Au and Ni on Mg-modified SiO spheres) To prepare the catalyst, a Mg-modified SiO2 support was first prepared as follows: 100 g of Cariact Q-10SiO2 was placed in a container and treated with an aqueous solution of magnesium nitrate hexahydrate in water, prepared by dissolving 51 g of Mg(NO)3·6H2O in 100 mL of water and adding 5.5 g of 60% nitric acid. The silica suspension was stirred with the magnesium nitrate at 50 °C for 24 h. The mixture was filtered, dried in a vacuum oven at 80 °C for 1 h, and calcined at 500 °C overnight.

[0041] The catalyst was then prepared as follows: 50 g of Mg-modified SiO2 was suspended in 170 mL of deionized water. The slurry was heated to 90°C with stirring until well dispersed. Separately, a solution containing 0.883 g of tetrachloroauric acid and 2.73 g of nickel nitrate hexahydrate was prepared in 170 mL of deionized water. This solution was added to the hot slurry over 30 minutes with stirring. The mixture was stirred for an additional 30 minutes, and then the solid was filtered off. The separated solid was washed three times with 100 mL of water, mixing with the wash water for 5 minutes each time before filtering. The resulting solid was dried at 105°C for 10 hours and then calcined at 450°C (ramp 5°C / min) for 5 hours.

[0042] The resulting catalyst was primarily 0.38 wt % Au, 0.57 wt % Ni, and 1.49 wt % Mg on a SiO2 support.

[0043] Example #2 (3 mm catalyst of Au on Ni-coated SiC cylindrical pellet) The coated support was first prepared by the impregnation-evaporation method. 10 g of 3 mm cylindrical SiC extrudates were placed in a round-bottom flask, followed by 11 mL of 1 M nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O) solution in deionized water. The flask was placed in a RotaVap. Water was removed under vacuum with continuous flask rotation at 45-50 °C. The as-prepared support was dried under vacuum at 45-50 °C for 30 min and then calcined in air in a box oven using the following procedure: room temperature to 120 °C, 3 °C / min, hold for 2 h, 120-600 °C, 2 °C / min, hold for 4 h, cool to room temperature in 2 h. The as-promoted SiC support contained approximately 5.1 wt% Ni (in the form of oxide). The Ni-SiC support had a BET surface area of ​​28 m2 / g and an average pore width of 12.5 nm.

[0044] Gold (Au) was then deposited onto the catalyst support using gold sodium thiomalate (I) by first preparing a stock solution of 0.1988 M gold sodium thiomalate (I) in deionized water. The impregnation solution was prepared by mixing 38.3 mL of the 0.1988 M gold sodium thiomalate (I) stock solution with 1.7 mL of deionized water until a clear yellow solution was formed. The catalyst was prepared by incipient wetness impregnation, followed by drying and calcination in air using a box oven equipped with an air purge. 5 g of Ni-SiC support was impregnated with 2 mL of impregnation solution dropwise to the point of incipient wetness. The impregnated material was dried and calcined in air in a box oven using the following procedure: room temperature to 120 °C, 5 °C / min, hold for 1 hour, 120 to 300 °C, 5 °C / min, hold for 4 hours, and cool to room temperature over 2 hours.

[0045] The catalyst was shown to be active in reactor operation, and high yields were achieved: the catalyst was 1.4 wt. % Au and 5.1 wt. % Ni on a SiC support, achieving over 99% selectivity and a space-time yield of 21.8 mol MMA / kg catalyst-hour.

Claims

1. A catalyst for oxidative esterification of methacrolein to methyl methacrylate, comprising: a support having an average diameter of at least 0.8 mm, the support comprising a material selected from the group consisting of oxides of silicon, carbides of silicon, metal oxides, and metal carbides; nickel oxide disposed on the support; and gold particles disposed on the support, the gold particles having an average diameter of less than 12 nm and a standard deviation of + / - 4 nm.

2. 10. The catalyst of claim 1, wherein the nickel oxide is in the form of nanoparticles.

3. 3. The catalyst of claim 1 or 2, wherein at least 75% of the gold particles are located within 20 nm of the nickel oxide.

4. 4. The catalyst according to claim 1, wherein the gold particles are uniformly distributed among the nickel oxide particles.

5. 5. The catalyst of claim 1, wherein the support further comprises at least one metal oxide, and the metal is selected from the group consisting of aluminum, titanium, lanthanides, zirconium, alkali metals, alkaline earth metals, nickel, cobalt, zinc, magnesium, tellurium, antimony, and bismuth.

6. 6. The catalyst of any one of claims 1 to 5, wherein the gold particles have an average diameter of less than 10 nm and a standard deviation of + / - 2.5 nm.

7. 7. The catalyst of claim 1, wherein at least 0.1 wt. % of the total weight of the gold particles is exposed on the surface of the catalyst.

8. 8. The catalyst of claim 7, wherein at least 0.5 wt. % of the total weight of the gold particles is exposed on the surface of the catalyst.

9. 9. The catalyst of any one of claims 1 to 8, wherein at least 75 wt% of the total weight of the gold particles is within the outer 50% of the volume of the catalyst.

10. Catalyst according to any one of claims 1 to 9, wherein the support has an average diameter of at least 1.5 mm.

11. 11. The catalyst 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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