Process and catalyst for oxidative esterification using long-life catalysts

Abstract

The catalyst comprises gold particles and titanium-containing particles. The catalyst comprises gold particles that are within at least 15 nm of at least one titanium-containing particle. The gold particles have an average diameter of less than 15 nm and a standard deviation of + / - 5 nm. A method 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 the preparation of methyl methacrylate from methacrolein and methanol. [Background technology]

[0002] Heterogeneous catalysts having precious metals concentrated in the outer regions of the catalyst are known (see, for example, US Pat. No. 6,228,800 for use in the production of methyl methacrylate).

[0003] WO 2019 / 057458 discloses a process for preparing carboxylic acid esters from aldehydes by heterogeneous catalysis in the liquid phase in the presence of catalyst particles. The catalyst particles consist of 0.1% to 3% by weight of gold, 25% to 99.8% by weight of TiO2, 0% to 50% by weight of silicon oxide, 0% to 25% by weight of Al2O3, 0% to 25% by weight of at least one oxide of an alkali metal, an alkaline earth metal, a rare earth metal and / or zirconium, 0% to 20% by weight of at least one oxide selected from the group consisting of iron oxide, zinc oxide and cobalt oxide, and 0% to 5% by weight of at least one other component. The catalyst is preferably composed mainly or exclusively of gold and TiO2.

[0004] 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

[0005] One aspect of the invention relates to a catalyst comprising gold particles and titanium-containing particles, the gold particles being within at least 15 nm of at least one titanium-containing particle, the gold particles having an average diameter of less than 15 nm and a standard deviation of ±5 nm.

[0006] Another aspect of the invention relates to a method for preparing methyl methacrylate from methacrolein and methanol, the method comprising contacting in a reactor a mixture comprising methacrolein, methanol and oxygen in the presence of a catalyst, the catalyst comprising gold particles within at least 15 nm of at least one titanium-containing particle, the gold particles having an average diameter of less than 15 nm and a standard deviation of + / - 5 nm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Unless otherwise stated, all compositional percentages are weight percent (wt%) and all temperatures are in °C. Unless otherwise stated, average is the arithmetic mean. "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 a particle refers to the average particle size of the particle after the catalyst is prepared and before the catalyst is used. Used catalyst is the catalyst that has been used.

[0008] The catalyst of the present invention comprises gold particles and titanium-containing particles.

[0009] The gold particles and titanium-containing particles are preferably disposed on the outer surface of the support material.

[0010] Preferably, the gold particles are within at least 15 nm of the titanium-containing particles. As used herein, the phrase "within at least X nm" means that the edge of the gold particle is within X nm of the edge of the titanium-containing particle closest to the gold particle. Preferably, each gold particle is within at least 10 nm of the titanium-containing particle, more preferably within at least 8 nm of the titanium-containing particle, and even more preferably within at least 6 nm of the titanium-containing particle.

[0011] More preferably, the catalyst comprises a gold particle that is within at least 15 nm of two titanium-containing particles, i.e., the edges of the gold particle are within at least 15 nm of the edges of the two titanium-containing particles closest to the gold particle. Preferably, the catalyst comprises a gold particle that is within at least 10 nm of two titanium-containing particles, more preferably within at least 8 nm of two titanium-containing particles, and even more preferably within at least 6 nm of two titanium-containing particles.

[0012] Even more preferably, the catalyst comprises a gold particle within at least 15 nm of the at least three titanium-containing particles, i.e., the edge of a gold particle is within at least 15 nm of the edge of the at least three titanium-containing particles nearest the gold particle. Preferably, the catalyst comprises a gold particle within at least 10 nm of the at least three titanium-containing particles, more preferably within at least 8 nm of the at least three titanium-containing particles, and even more preferably within at least 6 nm of the at least three titanium-containing particles.

[0013] The gold particles have an average diameter of less than 15 nm, preferably less than 12 nm, more preferably less than 10 nm, even more preferably less than 8 nm. The standard deviation of the average diameter of the gold particles is + / - 5 nm, preferably + / - 2.5 nm. As used herein, the standard deviation is calculated by the following formula:

number

number

[0014] The titanium-containing particles may be elemental titanium or titanium oxide (TiO). x Preferably, the titanium-containing particles comprise titanium oxide.

[0015] The titanium-containing particles 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.

[0016] The amount by weight of gold particles relative to the amount of titanium-containing particles may be in the range of 1:1 to 1:20. Preferably, the weight ratio of gold particles to titanium-containing particles is in the range of 1:2 to 1:15, more preferably 1:3 to 1:10, even more preferably 1:3 to 1:6.

[0017] Preferably, the gold particles are uniformly distributed among the titanium-containing particles. As used herein, the term "uniformly distributed" means that the gold particles are randomly dispersed among the titanium-containing particles, and there is substantially no aggregation of the gold particles, e.g., less than 10% by weight of the gold particles are in physical contact with another gold particle, based on the total weight of the gold particles. Preferably, less than 7.5% by weight of the gold particles are in physical contact with another gold particle, and more preferably less than 5% by weight of the gold particles are in physical contact with another gold particle, based on the total weight of the gold particles.

[0018] Preferably, the support is a particle of a refractory oxide that can withstand long-term use in the oxidative esterification reactor. A material that can withstand long-term use can avoid being crushed or pulverized during use. For example, titanium dioxide (TiO x ) is a support that is highly resistant to acids, but may be mechanically weak if it has a high surface area.

[0019] Preferably, the support is a particle of γ-, δ-, or θ-alumina, silica, magnesia, titania, zirconia, hafnia, vanadia, niobium oxide, tantalum oxide, ceria, yttria, lanthanum oxide, or a combination thereof. Preferably, the support comprises, consists of, or essentially consists of γ-, δ-, or θ-alumina, silica, and magnesia. More preferably, the support comprises, consists of, or essentially consists of silica. When used herein with respect to a support, the phrase "consists essentially of" excludes the presence of materials that may reduce the mechanical strength of the support. Alternatively, "consists essentially of" means that the support comprises at least 95% by weight of the listed material, based on the total weight of the support.

[0020] Preferably, the carrier is 10 m 2 / g, preferably 30m 2 / g, preferably 50m 2 / g, preferably 100m 2 / g, preferably 120m 2 / g.

[0021] 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.

[0022] Preferably, at least 90% by weight of the gold particles and titanium-containing particles are in the outer 70% of the catalyst volume (i.e. the volume of the average catalyst particle), preferably the outer 60% of the catalyst volume, preferably the outer 50% of the catalyst volume, preferably the outer 40% of the catalyst volume, preferably the outer 35% of the catalyst volume, preferably the outer 30% of the catalyst volume, preferably the outer 25% of the catalyst volume. Preferably, the outer volume of any particle shape is calculated for a 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, the outer surface is the surface of the particle, and the volume is x% of the volume of the entire sphere. Preferably, at least 95% by weight, preferably at least 97% by weight, preferably at least 99% by weight of the gold particles and titanium-containing 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 and titanium-containing particles are within a distance from the surface of 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 and titanium-containing particles form an eggshell structure on the support particle. The eggshell layer may have a thickness of 500 micrometers or less, preferably 250 micrometers or less, more preferably 100 micrometers or less.

[0023] Preferably, at least 0.1% by weight of the total weight of the gold particles is exposed on the surface of the catalyst. As used herein, the term "exposed" means that at least a portion of the gold particles is not covered by another gold particle or a titanium-containing particle, i.e., the reactants can directly contact the gold particles. Thus, the gold particles may be located in the pores of the support material and still be exposed by reactants that can directly contact the gold particles in the pores. More preferably, at least 0.25% by weight of the total weight of the gold particles is exposed on the surface of the catalyst, even more preferably, at least 0.5% by weight of the total weight of the gold particles is exposed on the surface of the catalyst, and even more preferably, at least 1% by weight of the total weight of the gold particles is exposed on the surface of the catalyst.

[0024] Preferably, the average diameter of the catalyst particles is at least 60 microns, preferably at least 100 microns, preferably at least 200 microns, preferably at least 300 microns, preferably at least 400 microns, preferably at least 500 microns, preferably at least 600 microns, preferably at least 700 microns, preferably at least 800 microns, and preferably no more than 30 mm, preferably no more than 20 mm, preferably no more than 10 mm, preferably no more than 5 mm, preferably no more than 4 mm. The average diameter of the support and the average diameter of the final catalyst particles do not differ significantly.

[0025] 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.%.

[0026] Preferably, the catalyst is produced by precipitating gold and titanium from an aqueous solution of metal salts in the presence of the support. In a preferred embodiment, the catalyst is produced by a solution drop impregnation technique, in which an aqueous solution of suitable gold precursor salts and titanium salts is added to a porous inorganic oxide to fill the pores with the solution, and the solvent and water are then removed by drying. The resulting material is then converted to the final catalyst by calcination, reduction, or other pretreatment known to those skilled in the art to decompose the gold and titanium salts to metals or metal oxides. Preferably, the catalyst is a C2-C cation salt containing at least one hydroxyl or carboxylic acid substituent. 18 Thiols are present in the solution. Preferably, they are C2-C thiols containing at least one hydroxyl or carboxylic acid substituent. 18 The thiol has 2 to 12, preferably 2 to 8, preferably 3 to 6 carbon atoms. Preferably, the thiol compound contains a total of 4 or less, preferably 3 or less, 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 compounds contain carboxylic acid substituents, they can 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.

[0027] In one embodiment of the present invention, the catalyst is produced by deposition-precipitation, where a porous inorganic oxide is immersed in an aqueous solution containing suitable gold precursor salts and titanium salts, which are then interacted 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 to the final catalyst by calcination, reduction, or other pretreatment known to those skilled in the art to decompose the gold and titanium salts to the metals or metal oxides.

[0028] Preferably, the process for producing methyl methacrylate (MMA) is carried out in an oxidative esterification reactor (OER). The catalyst particles may be 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, but in some configurations the catalyst bed may 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 comprises a liquid phase comprising methacrolein, methanol, and MMA, and a gas phase comprising oxygen. The liquid phase may further comprise by-products, such as methacrolein dimethyl acetal (MDA) and methyl isobutyrate (MIB). Preferably, the liquid phase is at a temperature of 40-120° C., preferably 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 0-2000 psig (101 kPa-14 MPa), preferably at most 2000 kPa, preferably at most 1500 kPa.

[0029] The OER typically produces MMA along with methacrylic acid and unreacted methanol. Preferably, methanol and methacrolein are fed to the reactor in a molar ratio of methanol:methacrolein 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 acid material above and / or below the catalyst. Preferred inert or acid materials include, for example, alumina, clay, glass, silicon carbide, and quartz. Preferably, the inert or acid material has an average diameter equal to or greater than the average diameter of the catalyst, preferably equal to or less than 20 mm. Preferably, the reaction product is fed to a methanol recovery distillation column providing an overhead stream rich in methanol and methacrolein, which is preferably recycled 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 comprising MMA, MDA, methacrylic acid, salts, and water. MDA can be hydrolyzed in a bottom stream from a methanol recovery distillation column, the stream comprising MMA, MDA, methacrylic acid, salts, and water. In another embodiment, MDA is hydrolyzed in an organic phase separated from the methanol recovery bottom stream. It may be necessary to add water to the organic phase to ensure that there is sufficient water present for the hydrolysis of MDA, and these amounts can be easily determined from the composition of the organic phase. The product of the MDA hydrolysis reactor is phase separated, and the organic phase passes through one or more distillation columns to produce the MMA product and light and / or heavy by-products. In another embodiment, the hydrolysis can be carried out in the distillation column itself.

[0030] One preferred embodiment is a recirculating reactor with cooling capability in the recirculation loop. Another preferred embodiment is a series of reactors with cooling and mixing capabilities between the reactors.

[0031] 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.

[0032] 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 gas and liquid feed streams in a downward direction through the reactor. In the trickle, 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)), this vapor mixture is inside a flammable envelope when the gas feed is air. Thus, only an ignition source is required to initiate a deflagration, which can result in 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 limit oxygen concentration (LOC).

[0033] Knowledge of the LOC is required for the fuel mixture, temperature and pressure of concern. Since the LOC decreases with increasing temperature and pressure, and given that methanol gives a lower LOC than the other two 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. EXAMPLES

[0034] Working Example Preparation of catalyst: The catalyst was prepared by solution dropwise impregnation on titanium modified, mostly spherical pellets, with titanium present in its oxide form in the final catalyst. 100 g of CARiACT Q-20 silica support material (Fuji Silysia Chemical) was treated with titanium salt to load Ti onto the support. 4.1 g of gold sodium thiosulfate was dissolved in 100 g of water to form an aqueous solution, which was then loaded onto the Ti-treated support. The sample was incubated at 120°C for 2 h at 37°C for 1 h at 37°C. o Dry at 400°C for 1 hour. o C for 4 h. The resulting catalyst contained 6.5 wt % Ti and 1.4 wt % Au, with a slightly higher gold loading near the outer surface of the catalyst.

[0035] The gold particle sizes measured by TEM for the unused catalyst, the catalyst after 2000 hours of pilot plant testing in a fixed bed bubble column reactor, and the catalyst after 15 months of additional laboratory aging in a fixed bed bubble column reactor are shown below in Table 1. The activity of the unused catalyst, the catalyst after 2000 hours of pilot plant testing, and the catalyst after additional laboratory aging showed little catalyst deactivation. [Table 1]

[0036] As can be seen in Table 1, the catalyst of the present invention exhibited excellent longevity, with measured particle sizes showing little to no agglomeration or change in average size of the gold particles after 2000 hours of pilot plant testing, and after 15 months of additional laboratory aging.

Claims

1. 1. A catalyst comprising gold particles and titanium-containing particles, the catalyst comprising gold particles within at least 15 nm of at least one titanium-containing particle, the gold particles having an average diameter of less than 15 nm and a standard deviation of ±5 nm.

2. 10. The catalyst of claim 1, wherein the gold particles and the titanium-containing particles are disposed on an outer surface of a support material.

3. The catalyst of claim 2 wherein the support material comprises silica.

4. The catalyst of claim 1 , wherein the titanium-containing particles comprise titanium oxide.

5. 10. The catalyst of claim 1, wherein the gold particles are uniformly distributed among the titanium-containing particles.

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

7. 10. 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. 14. 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 13.