Catalyst supported with gold nanoparticles and nickel oxide, and method for producing methyl methacrylate using same

Abstract

A catalyst for the oxidative esterification of methacrolein to methyl methacrylate, the catalyst comprising a support having an average diameter of at least 0.8 mm. The support is selected from the group consisting of oxides of silicon, carbides of silicon, metal oxides, and metal carbides. The catalyst also includes 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. Also disclosed is a method for preparing methyl methacrylate from methylacrolein and methanol using the catalyst.

Description

Background Art

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

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

[0003] US Patent No. 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 catalyst has a diameter in the range of 10 μm 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 with 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 μm to 200 μm.

[0005] In the preparation of carboxylic acid esters from aldehydes, two types of reactors are most commonly used. Slurry or continuous stirred tank reactors use small catalysts (<200 μm) that are kept suspended, while fixed bed reactors use large catalysts (>200 μm) that are fixed in place within the reactor. Due to differences in reactor design, a catalyst suitable for one type of reactor is not suitable for another type of reactor. Each type of reactor subjects the catalyst to different conditions, including the forces to which the catalyst is exposed, and the catalysts are designed differently based on the respective sizes of the catalysts, wherein the ratio of the catalytically active area of ​​the catalyst to the total volume is significantly different.

[0006] However, there is a need for an improved catalyst and process for producing methyl methacrylate that is effective and active over a longer life cycle. 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 oxide, silicon carbide, metal oxide, and metal carbide. 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 producing methyl methacrylate from methacrolein and methanol. The method comprises contacting a mixture comprising methacrolein, methanol, and oxygen in a reactor in the presence of a catalyst comprising a support and nickel oxide and gold particles disposed on the support. The support has an average diameter of at least 0.8 mm and is selected from silicon oxide, silicon carbide, metal oxide, and metal carbide. 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

[0009] Unless otherwise indicated, all percentage compositions are weight percent (wt%) and all temperatures are in ° C. Unless otherwise indicated, average values ​​are arithmetic means. "Catalyst center" is the center of mass of the catalyst particle, that is, the average position of all points in all coordinate directions. The diameter is any linear dimension passing through the center of the catalyst, 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 indicated, 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. Aged catalyst is a catalyst that has been used.

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

[0011] The support has an average diameter of at least 0.8 mm. More preferably, the support has an average diameter of at least 1.2 mm, even more preferably at least 1.5 mm, and still 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 can be selected from, for example, aluminum, titanium, zirconium, zinc, and magnesium. Preferably, the support is capable of withstanding long-term use in the oxidative esterification reactor. Materials capable of long-term use are able to avoid being crushed or pulverized during use.

[0013] The support material may further comprise at least one metal oxide, wherein 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. 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 silicon oxide. More preferably, the support comprises, consists of, or consists essentially of silicon oxide modified with titanium oxide. As used herein with respect to a support, the phrase "consisting essentially of" excludes the presence of materials that would reduce the mechanical strength of the support. Alternatively, "consisting essentially of" means that the support comprises at least 95% by weight of the material in question, relative to the total weight of the support.

[0015] Preferably, the surface area of ​​the carrier is greater than 10 m 2 / g, preferably greater than 30m 2 / g, preferably greater than 50m 2 / g, preferably greater than 100m 2 / g, preferably greater than 120m 2 / g.

[0016] Preferably, the aspect ratio of the catalyst particles is no greater than 10:1, preferably no greater than 5:1, and preferably no greater than 3:1. Although the shape is not limited, preferred shapes of the catalyst particles include spheres, cylinders, rectangular solids, rings, multi-lobed shapes (e.g., cloverleaf cross-sections), shapes with multiple holes, and "wagon wheels," with spheres being preferred. Irregular shapes may 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 volume of the catalyst. 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 volume of the catalyst.

[0018] The nickel oxide provided 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 a nickel oxide nanoparticle when the nickel oxide is in nanoparticle form. As used herein, the phrase "within at least X nm" means that the edge of the gold particle is within X nm of the nickel oxide, for example, 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 nanoparticle form, and at least 75% of the gold particles, based on the number of gold particles, 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 the gold particle. 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 nanoparticle form and at least 75% of the gold particles, based on the number of gold particles, 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 closest to the gold particle. 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, 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:

[0023]

[0024] where x is the size of each particle, is the average value of n particles, and n is at least 500.

[0025] The nickel oxide nanoparticles preferably have an average diameter that is less than 5 times the average diameter of the gold particles, more preferably an average diameter that is less than 4 times the average diameter of the gold particles, even more preferably an average diameter that is less than 3 times the average diameter of the gold particles, still more preferably an average diameter that is less than 2 times the average diameter of the gold particles, and further more preferably an average diameter that is less than 1.5 times the average diameter of the gold particles. Preferably, the nickel oxide nanoparticles have an average diameter that 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 amount of gold particles by weight relative to the amount of nickel oxide may be in the range of 1:1 to 1:20. Preferably, the weight ratio of gold particles to nickel oxide 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.

[0027] The amount by weight of nickel oxide relative to the amount by weight of gold particles may range from 0.1:1 to 10:1, preferably 0.2:1 to 5:1, more preferably 0.33:1 to 3:1, and still more preferably 0.5:1 to 2:1.

[0028] Preferably, the gold particles are uniformly distributed in the nickel oxide. As used herein, the term "uniformly distributed" means that the gold particles are randomly dispersed in the nickel oxide, with substantially no agglomeration of the gold particles. For example, less than 10% by weight of the gold particles, based on the total weight of the gold particles, are in physical contact with one another. Preferably, less than 7.5% by weight of the gold particles, based on the total weight of the gold particles, are in physical contact with one another, and more preferably, less than 5% by weight of the gold particles, based on the total weight of the gold particles, are in physical contact with one another.

[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 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, the outer volume of any particle shape is calculated 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. For example, for a spherical particle, the outer x% of the volume is the spherical shell, whose outer surface is the surface of the particle and whose volume is x% of the total spherical volume. Preferably, at least 95% by weight, preferably at least 97% by weight, 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% by weight, preferably at least 97% by weight, preferably at least 99% by weight) of the gold particles are located no more than 30% of the catalyst diameter, preferably no more than 25% of the catalyst diameter, preferably no more than 20% of the catalyst diameter, preferably no more than 15% of the catalyst diameter, preferably no more than 10% of the catalyst diameter, preferably no more than 8% of the catalyst diameter from the surface. 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, 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 another gold particle or nickel oxide, 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 because the reactants 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 still 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, calculated as a percentage of gold and carrier, 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.

[0032] Preferably, the catalyst is produced by precipitating gold and nickel from aqueous solutions of metal salts in the presence of a support. In a preferred embodiment, the catalyst is produced by the incipient wetness technique, wherein aqueous solutions of suitable gold precursor salts and nickel salts are added to the porous inorganic oxide so that the pores are filled with solution, and the water is then removed by drying. The gold and nickel salts are then decomposed into metals or metal oxides by calcination, reduction, or other pretreatments known to those skilled in the art, thereby converting the resulting material into the finished catalyst. Preferably, the C2-C4-H2O2 containing at least one hydroxyl or carboxylic acid substituent is preferably a C2-C4-H2O2. 18 The thiol is present in the solution. Preferably, the C2-C 18 The thiol has 2 to 12, preferably 2 to 8, 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 one thiol group. If the thiol compound contains a carboxylic acid substituent, it may be present 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 produced by precipitation precipitation, wherein a porous inorganic oxide is immersed in an aqueous solution containing a suitable gold precursor salt and a nickel salt, and the salts are then allowed to interact with the surface of the inorganic oxide by adjusting the pH of the solution. The resulting treated solid is then recovered (e.g., by filtration) and then converted into a finished catalyst by calcination, reduction, or other pretreatment known to those skilled in the art to decompose the gold and nickel salts into 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 may 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 solid walls and by a screen or catalyst support mesh. In some configurations, the screen or mesh is on opposite ends of the catalyst bed and the solid walls are on the sides, although in some configurations, the catalyst bed may be completely surrounded by the screen. Preferred shapes for the catalyst bed include cylinders, rectangular solids, and cylindrical shells; preferably cylinders. The OER also comprises a liquid phase and a gas phase, the liquid phase comprising methacrolein, methanol, and MMA, and the gas phase comprising oxygen. The liquid phase may also comprise by-products, for example, methacrolein dimethyl acetal (MDA) and methyl isobutyrate (MIB). Preferably, the liquid phase is at a temperature of 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 0 psig to 2000 psig (101 kPa to 14 MPa); preferably no more than 2000 kPa, preferably no more than 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, silicon carbide, and quartz. Preferably, the average diameter of the inert 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 that 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 comprises MMA, MDA, methacrylic acid, salt, and water. In one embodiment of the present invention, MDA is hydrolyzed in a medium comprising MMA, MDA, methacrylic acid, salt, and water. MDA can be hydrolyzed in the bottoms stream from the methanol recovery distillation column; the stream comprises MMA, MDA, methacrylic acid, salts, and water. In another embodiment, MDA is hydrolyzed in an 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 enough water for MDA hydrolysis; these amounts can be readily determined by 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 an MMA product and light and / or heavy by-products. In another embodiment, the hydrolysis can be carried out within the distillation column itself.

[0036] One preferred embodiment is a recycle reactor with cooling capabilities in the recycle loop.Another preferred embodiment is a series of reactors with cooling and mixing capabilities between 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%, still more preferably at least 3 mol%, still 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 leaving the reactor. Preferably, 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%, based on the total amount of the gas stream leaving the reactor.

[0038] A 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 the gas and liquid feeds in a downward direction through the reactor. In trickle flow, the gas phase is a continuous liquid phase. Therefore, the area at the top of the reactor above the fixed bed will be filled with a gaseous mixture of nitrogen, oxygen, and the 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, the vapor mixture is within a flammable envelope. Therefore, only an ignition source is required to initiate a deflagration, which may result in the loss of 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 headspace atmosphere is to operate with a gas feed containing a sufficiently low mole fraction of oxygen to ensure that the oxygen concentration in the vapor headspace is below the limiting oxygen concentration (LOC).

[0039] The relevant fuel mixture, temperature, and pressure require knowledge of the LOC. Since LOC decreases with increasing temperature and pressure, and considering that methanol has a lower LOC than the other two important fuels (methacrolein and methyl methacrylate), a conservative design choice is to select a feed oxygen-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 mol%.

[0040] Example

[0041] Example #1 (approximately 1.25 mm, actual size varies from 0.85 mm to 1.70 mm, Mg-supported Au and Ni-modified SiO2 ball)

[0042] To prepare the catalyst, a Mg-modified SiO2 support was first prepared as follows. 100 g of Cariact Q-10 SiO2 was placed in a container and treated with an aqueous solution of magnesium nitrate hexahydrate 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 and magnesium nitrate were stirred at 50°C for 24 hours. The mixture was filtered, dried in a vacuum oven at 80°C for 1 hour, and calcined at 500°C overnight.

[0043] The catalyst was then prepared by the following procedure: 50 g of Mg-modified SiO2 was suspended in 170 mL of deionized water. The slurry was heated to 90°C while stirring until fully dispersed. Separately, a solution containing 0.883 g of tetrachloroauric acid and 2.73 g of nickel nitrate hexahydrate in 170 mL of deionized water was prepared. This solution was added to the hot slurry over 30 minutes with stirring. The mixture was stirred for an additional 30 minutes before the solid was filtered out. The separated solid was washed three times with 100 mL portions of water, each time mixing the solid with the wash water for 5 minutes before filtering. The resulting solid was dried in air at 105°C for 10 hours and then calcined at 450°C (5°C / min temperature ramp) for 5 hours.

[0044] The resulting catalyst was 0.38 wt% Au, 0.57 wt% Ni and 1.49 wt% Mg primarily on a SiO2 support.

[0045] Example #2 (3 mm catalyst of Ni-supported Au-coated SiC cylindrical pellets)

[0046] The coated support was first prepared by an impregnation-evaporation method. 10 g of SiC 3 mm cylindrical extrudates were placed in a round-bottom flask, followed by the addition of 11 ml of a 1 M solution of nickel (II) nitrate hexahydrate (Ni (NO 3 ) 2 * 6H 2 O) in deionized water. The flask was placed on a rotary evaporator. The flask was continuously rotated at 45 to 50 ° C and water was removed under vacuum. The prepared support was vacuum dried at 45 to 50 ° C for 30 minutes and then calcined in air in a box furnace using the following procedure: heating from room temperature to 120 ° C at 3 ° C / min, holding for 2 hours, heating from 120 ° C to 600 ° C at 2 ° C / min, holding for 4 hours, and cooling to room temperature within 2 hours. The SiC support as promoted contained approximately 5.1 wt % Ni (in the form of oxide). The Ni-SiC support had a BET surface area of ​​28 m 2 / g and an average pore width of 12.5 nm.

[0047] Gold (Au) was then placed on the catalyst support using sodium gold thiomalate (I) by first preparing a stock solution of 0.1988M sodium gold thiomalate (I) in deionized water. An impregnation solution was prepared by mixing 38.3 ml of the 0.1988M sodium gold thiomalate (I) stock solution with 1.7 ml of deionized water until a clear yellow solution was formed. The catalyst was prepared by initial wetness impregnation followed by drying and calcining in air using a box furnace equipped with an air purge. 5 g of the Ni-SiC support was impregnated dropwise with 2 ml of the impregnation solution until the initial wetness point. The impregnated material was dried and calcined in air in a box furnace using the following program: heating from room temperature to 120°C at 5°C / min, holding for 1 hour, heating from 120°C to 300°C at 5°C / min, holding for 4 hours, and cooling to room temperature within 2 hours.

[0048] The catalyst was shown to be active in the reactor to achieve high yields. The catalyst was 1.4 wt% Au and 5.1 wt% Ni on a SiC support and achieved a selectivity exceeding 99% and a space-time yield of 21.8 mol MMA / kg catalyst hour.

Claims

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

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. The catalyst according to any one of the preceding claims, wherein the gold particles are uniformly distributed in the nickel oxide.

5. The catalyst of any one of the preceding claims, wherein the support further comprises at least one metal oxide, wherein 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. The catalyst of any preceding claim, wherein the gold particles have an average diameter of less than 10 nm and a standard deviation of + / - 2.5 nm.

7. The catalyst of any one of the preceding claims, wherein at least 0.1 wt% of the total weight of the gold particles is exposed on the surface of the catalyst.

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. A catalyst according to any preceding claim, 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. The catalyst according to any one of the preceding claims, wherein the support has an average diameter of at least 1.5 mm.

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 process for preparing methyl methacrylate from methacrolein and methanol; the process 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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