Heterogeneous catalysts for the production of methyl methacrylate by oxidative esterification.

Abstract

To provide a catalyst especially useful in a process for preparing methyl methacrylate from methacrolein and methanol.SOLUTION: A heterogeneous catalyst comprises a support and a noble metal, wherein the support comprises silicon, and wherein the catalyst comprises from 0.1 to 40 mol% titanium and from 0.1 to 10 mol% of at least one noble metal based on total moles of silicon atoms and metal atoms. The noble metal can be, for instance, gold on silica.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heterogeneous catalyst that is particularly useful in a process for preparing methyl methacrylate from methacrolein and methanol.

[0002] Heterogeneous catalysts in which precious metals are supported on silica in combination with alumina and other elements are known, see, for example, U.S. Pat. No. 8,461,737 B2, however, there is a need for additional catalyst particles with improved properties. Summary of the Invention

[0003] The present invention is directed to a heterogeneous catalyst comprising a support and a noble metal, wherein the support comprises silicon, and the catalyst comprises 0.1 to 40 mol % titanium and 0.1 to 10 mol % of at least one noble metal, the mole percentages being based on the total moles of silicon atoms and metal atoms.

[0004] The present invention is further directed to a method for preparing a heterogeneous catalyst comprising a support and a noble metal, wherein the support comprises silicon and titanium, and the catalyst comprises 0.1 to 40 mole % titanium and 0.1 to 10 mole % of at least one noble metal, the mole percentages being based on the total moles of silicon atoms and metal atoms, the method comprising contacting a silicon-containing support with a titanium salt and a noble metal salt.

[0005] The present invention is further directed to a catalyst bed comprising the catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0006] Unless otherwise specified, all percent compositions are weight percent (wt%) and all temperatures are in °C. "Noble metal" means any of gold, platinum, iridium, osmium, silver, palladium, rhodium, and ruthenium. More than one noble metal may be present in the catalyst, in which case the limit applies to the sum of all noble metals. "Metal" means the elements of Groups 1-12 of the periodic table, excluding hydrogen, plus aluminum, gallium, indium, thallium, tin, lead, and bismuth. "Catalyst center" is the center of gravity of the catalyst particle, i.e., the average position of all points in all coordinate directions. Diameter is any linear dimension passing through the center of the catalyst, and average diameter is the arithmetic mean of all possible diameters. Aspect ratio is the ratio of the longest diameter to the shortest diameter.

[0007] Preferably, the support is a particle comprising a refractory oxide, preferably silica, titania, magnesia, or a combination thereof, and preferably the support is silica or silica modified with another refractory oxide. 2 / g, preferably more than 30m 2 / g, preferably above 50m 2 / g, preferably more than 100m 2 / g, preferably above 120m 2 The support has a surface area of ​​greater than 1 / g. Preferably, the support comprises silica particles containing 0.1 to 40 mol %, preferably at least 0.1 mol %, preferably at least 1 mol %, preferably 40 mol % or less, preferably 30 mol % or less of titanium, based on the total moles of silicon atoms and metal atoms (i.e., excluding oxygen and other non-metallic elements other than silicon). Preferably, the support comprises 10 mol % or less, preferably 5 mol % or less, preferably 2 mol % or less, preferably 1 mol % or less, preferably 0.5 mol % or less of aluminum, based on the total moles of silicon atoms and metal atoms.

[0008] Preferably, the aspect ratio of the catalyst particles is 10:1 or less, preferably 5:1 or less, preferably 3:1 or less, preferably 2:1 or less, preferably 1.5:1 or less, preferably 1.1:1 or less. Preferred particle shapes 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.

[0009] Preferably, the catalyst contains, based on the total moles of silicon atoms and metal atoms, 0.1 to 10 mol% of at least one noble metal, 50 to 95 mol% of Si, 0.1 to 40 mol% of Ti, and 0.1 to 40 mol% of an alkali metal or alkaline earth metal, or a combination thereof. Preferably, the catalyst contains at least 55 mol%, preferably at least 60 mol%, preferably at least 65 mol%, preferably at least 70 mol%, and preferably no more than 97 mol% of Si. Preferably, the catalyst contains at least 0.1 mol%, preferably at least 1 mol%, preferably at least 5 mol%, preferably no more than 30 mol%, preferably no more than 20 mol%, and preferably no more than 15 mol% of Ti. Preferably, the catalyst contains at least 0.1 mol%, preferably at least 0.2 mol%, preferably at least 0.3 mol%, preferably no more than 7 mol%, preferably no more than 5 mol%, and preferably no more than 3 mol% of the noble metal(s). Preferably, the catalyst comprises at least 0.1 mol%, preferably at least 1 mol%, preferably at least 2 mol%, preferably no more than 30 mol%, preferably no more than 20 mol%, preferably no more than 15 mol% of alkali or alkaline earth metal(s). In a preferred embodiment of the present invention, the catalyst comprises no more than 20 mol%, preferably no more than 10 mol%, preferably no more than 5 mol%, preferably no more than 2 mol%, preferably no more than 1 mol% of magnesium, based on the total moles of silicon atoms and metal atoms. In a preferred embodiment of the present invention, the catalyst comprises no more than 20 mol%, preferably no more than 10 mol%, preferably no more than 5 mol%, preferably no more than 2 mol%, preferably no more than 1 mol% of alkaline earth metal, based on the total moles of silicon atoms and metal atoms.

[0010] Preferably, at least 90% by weight of the precious metal(s) is located in the outer 80% of the catalyst volume (i.e., the average catalyst particle volume), preferably the outer 60%, preferably the outer 50%, preferably the outer 40%, preferably the outer 30%, preferably the outer 25%. Preferably, the external 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 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, preferably at least 97% by weight, preferably at least 99% by weight of the precious metal(s) is located 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 precious metal(s) is located within a distance from the surface of no more than 15% of the catalyst diameter, preferably no more than 10% by weight, preferably no more than 8% by weight, preferably no more than 6% by weight. Distance from the surface is measured along a line perpendicular to the surface.

[0011] Preferably, the noble metal is gold or palladium, preferably gold.

[0012] 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, preferably no greater than 30 mm, preferably no greater than 20 mm, preferably no greater than 10 mm, preferably no greater than 5 mm, preferably no greater than 3 mm. The average diameter of the support and the average diameter of the final catalyst particles do not differ significantly.

[0013] Preferably, the amount of precious metal as a percentage of precious metal 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 not more than 4 wt.%, preferably not more than 3 wt.%, preferably not more than 2.5 wt.%.

[0014] The catalyst of the present invention is useful in a process for producing methyl methacrylate (MMA) by treating methacrolein with methanol in an oxidative esterification reactor (OER) containing a catalyst bed. The catalyst bed includes catalyst particles and is located within the OER, and a fluid flow can pass through the catalyst bed. The catalyst particles within the catalyst bed are typically held in place by solid walls and screens. In some configurations, screens are located at both ends of the catalyst bed and solid walls are located on the side(s), 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 includes a liquid phase containing methacrolein, methanol, and MMA, and a gas phase containing oxygen. The liquid phase can further include 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, preferably no more than 110°C, preferably no more than 100°C. Preferably, the catalyst bed is at a pressure of 0-2000 psig (101.3-13890.8 kPa), preferably no more than 2000 kPa, preferably no more than 1500 kPa. Preferably, the catalyst bed has a pH of 4-10, preferably at least 4.5, preferably at least 5, preferably no more than 9, preferably no more than 8, preferably no more than 7.5, preferably no more than 7, preferably no more than 6.5. Preferably, the catalyst bed is in a tubular continuous reactor.

[0015] Preferably, the catalyst is produced by precipitating titanium from a titanium salt onto support particles (preferably silica) in the presence of a support, followed by precipitating the precious metal from an aqueous solution of the metal salt. Preferred titanium salts include titanium acetate, titanium sulfate, titanium(IV) oxysulfate, titanium chloride, titanium oxychloride, titanium(IV) bis(ammonium lactate) dihydroxide solution, titanium(IV) 2-ethylhexyl oxide, titanium(IV) butoxide, titanium(IV) isopropoxide, and titanium(IV) oxyacetylacetonate. Preferred precious metal salts include tetrachloroauric acid, gold sodium thiosulfate, gold sodium thiomalate, gold hydroxide, palladium nitrate, palladium chloride, and palladium acetate. In a preferred embodiment, the titanium-modified support is produced by the incipient wetness technique, in which an aqueous solution of a titanium precursor salt is added to a porous inorganic oxide to fill the pores with the solution, followed by removal of the water by drying. Preferably, the resulting material is then treated by calcination, reduction, or other treatment known to those skilled in the art to decompose the titanium salt into the metal or metal oxide. Preferably, the precious metal(s) are added to the calcined titanium modified support by incipient wetness followed by drying and preferably calcination.

[0016] Calcination is preferably carried out at a temperature of from 250° C. to 600° C., preferably at least 300° C., preferably up to 550° C. Preferably, the temperature is increased in a stepwise or continuous manner up to the final calcination temperature.

[0017] In another preferred embodiment, the catalyst is produced by deposition precipitation by immersing a porous inorganic oxide in an aqueous solution containing a suitable noble metal precursor salt, and then adjusting the pH of the solution to allow the salt 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 treatment known to those skilled in the art to decompose the noble metal salt to the metal or metal oxide. [Example]

[0018] Example 1 Single-pass fixed-bed bubble column reactor operation: A feed consisting of 20 wt. % methacrolein, 200 ppm 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. Catalyst 1 was utilized. Gas containing 8% oxygen in nitrogen was also fed to the reactor at a rate sufficient to obtain 4.5% O2 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 with liquid return, and noncondensable gases to the vent. The results are listed in the table below.

[0019] Preparation of catalyst 1: Catalyst 1 was prepared using 20 g of Fuji Silysia Chemical, Ltd. CAriACT Q-10 support as the starting material, and titanium was added to the support material by the incipient wetness technique. Specifically, 10.5 g of titanium isopropoxide was added to the catalyst in a rotator along with 3 g of glacial acetic acid to ensure uniform dispersion 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 at 60°C under a slight vacuum for 4 hours, and then calcined in air under ambient pressure by ramping from ambient temperature to 125°C at 5°C / min and holding for 1 hour, then ramping at 5°C / min up to 250°C and holding for 1 hour, then ramping at 5°C / min to 350°C and holding for 1 hour, and finally ramping at 5°C / min to 450°C and holding for 4 hours. Gold was then added to the support by the incipient wetness technique using 0.83 g of gold sodium thiosulfate in 10 g of deionized water at 40°C. The resulting catalyst was dried and calcined in air using the same heating profile as above. Analysis of the catalyst using a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) clearly shows the presence of eggshell deposits of both Ti and Au, with Au preferentially present only where Ti was deposited. The thickness of the Ti and Au eggshells was found to be approximately 50 microns or less. With an estimated loading of 10 mol% in the outer 50 microns of a 1 mm diameter catalyst, the localized loading of titanium is estimated to be up to 40 mol% as Ti / (Ti+Si).

[0020] Example 2 (Comparative) Batch recycle fixed bed bubble column reactor operation: A 150 g feed solution containing 10 wt. % methacrolein, 200 ppm inhibitor, and the remainder methanol was prepared and placed in a 300 mL PARR® reactor, 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 into the bottom of a vertically oriented fixed-bed reactor at 7 mL / min. Air and nitrogen gas were mixed to provide 7.8 mol % oxygen and mixed with the liquid feed before entering the fixed-bed reactor. The fixed-bed reactor was a jacketed 1 / 4 inch (6.4 mm) stainless steel tube maintained at 60°C using an external heater. The reactor itself was loaded with 2 mm glass beads to fill approximately 18 inches (46 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, and the non-condensable gases were vented while the liquid was recycled back to the gas release vessel. Catalyst 2, as well as the catalysts from Examples 3, 4, and 5 below, were run in this manner.

[0021] Preparation of catalyst 2: Catalyst 2 was prepared by incipient wetness of 4.1 g of gold sodium thiosulfate dissolved in 100 g of water to make an aqueous solution, which was then placed on 100 g of CAriACT Q-20 silica support material from Fuji Silysia Chemical, Ltd. The sample was dried at 120°C for 1 hour and then calcined at 400°C for 4 hours.

[0022] Example 3 Preparation of catalyst 3: Catalyst 3 was prepared by the following steps. First, a titanium precursor stock solution consisting of 51.7 g of titanium isopropoxide and 28.5 g of glacial acetic acid was mixed and stirred at ambient temperature. Then, a support material was prepared by impregnating 20 g of CAriACT Q-10 silica support material (Fuji Silysia Chemical, Ltd.) with 27.9 g of the titanium stock solution to its incipient wetness. The sample was then dried at 125°C for 1 hour, followed by calcination at 250°C for 1 hour, 350°C for 1 hour, and 450°C overnight, with a ramp rate of 5°C / min between the different temperature settings. Gold deposition was achieved by impregnating 10 g of the support material with a solution containing 0.4 g of gold sodium thiosulfate and 16 g of deionized water to its incipient wetness. The sample was then dried at 120°C for 1 hour and then calcined at 400°C for 4 hours. Analysis of the catalyst using a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) clearly shows the presence of both Ti and Au eggshell deposits, with Au preferentially present only where Ti has been deposited. The thickness of the Ti and Au eggshells was found to be approximately 300 microns or less.

[0023] Example 4 Preparation of catalyst 4: Catalyst 4 was prepared by the following steps. First, the support material was prepared by impregnating 10 g of Fuji Silysia Chemical, Ltd.'s CAriACT Q-10 silica support material with titanium isopropoxide to its incipient wetness point. The sample was then dried at 125°C for 1 hour, followed by calcination at 250°C for 1 hour, 350°C for 1 hour, 450°C for 1 hour, and 550°C for 12 hours, with a ramp rate of 5°C / min between different temperature settings. Gold deposition was achieved by impregnating 6 g of the above support material with a solution containing 0.25 g of gold sodium thiosulfate and 9 g of deionized water to its incipient wetness point. The sample was then dried at 120°C for 1 hour, followed by calcination at 400°C for 4 hours.

[0024] Example 5 Preparation of catalyst 5: Catalyst 5 was prepared by the following steps. First, the support material was prepared by impregnating 10 g of CAriACT Q-10 silica support material (Fuji Silysia Chemical, Ltd.) with magnesium nitrate hexahydrate to its incipient wetness point. The sample was then dried at 120 °C for 1 hour and then calcined at 450 °C for 4 hours, with a temperature ramp rate of 5 °C / min. 8.5 g of titanium isopropoxide and 1.5 g of acetic acid were mixed to obtain a titanium precursor solution, and then 3.1 g of the titanium precursor solution was impregnated into the calcined Mg-SiO2. The sample was then dried at 120 °C for 1 hour and then calcined at 550 °C for 6 hours, with a temperature ramp rate of 5 °C / min. Gold deposition was achieved by impregnating 8 g of the support material with a solution containing 0.3 g of gold sodium thiosulfate and 8 g of deionized water to its incipient wetness point. The sample was then dried at 120°C for 1 hour and then calcined at 400°C for 4 hours. The resulting sample contained a total of 4.7 wt% Mg and 4 wt% Ti in Si, with 1.5 wt% Au loaded into the material. This sample was not evaluated to determine if eggshell deposits were present. [Table 1]

[0025] Crushing Strength: The mechanical strength of catalyst or catalyst support particles was measured directly by crushing the particles to the point of mechanical failure. Crush strength tests were performed using a Mecmesin M100EC. A single particle was placed on a platform, and the upper plunger was pressed against the particle until the load reached a peak value and the material failed. The peak load was recorded using a Shimpo FGE-100X gauge. This test was repeated on 25 individual particles to obtain a statistical average of the crush strength of any material. The results are tabulated below. [Table 2]

Claims

1. 1. A heterogeneous catalyst comprising a support and a noble metal, the catalyst being used in a process for preparing methyl methacrylate from methacrolein and methanol, the support comprising silicon, the catalyst comprising 0.1 to 40 mol % titanium, 0.1 to 10 mol % of the noble metal, 50 to 95 mol % silicon, and 0.1 to 40 mol % of an alkali metal, alkaline earth metal, or combination thereof, the noble metal being gold, the mole percentages being based on the total moles of silicon atoms and metal atoms, the metal atoms being aluminum, gallium, indium, thallium, tin, lead, and bismuth, in addition to the elements of Groups 1 to 12 of the periodic table excluding hydrogen, with the proviso that the catalyst does not comprise nickel, and at least 90 wt % of the noble metal is within a distance from the surface of no more than 15% of the catalyst diameter.

2. 10. The catalyst of claim 1, wherein the catalyst has an average diameter of from 60 microns to 10 mm.

3. 3. The catalyst of claim 2, wherein the catalyst comprises 0.1 to 8 mole percent of the noble metal, 60 to 95 mole percent of silicon, 0.1 to 20 mole percent of titanium, and 0.1 to 20 mole percent of an alkali metal or alkaline earth metal.

4. 4. The catalyst of claim 3, wherein the support is a combination of silica, titania, and magnesia.

5. A catalyst bed comprising: (i) the heterogeneous catalyst of any one of claims 1 to 4; and (ii) a liquid phase comprising methacrolein, methanol, and methyl methacrylate.

6. 6. The catalyst bed of claim 5, wherein the catalyst has an average diameter of from 200 microns to 10 mm, and the catalyst bed further comprises a gas phase comprising oxygen.

7. 7. The catalyst bed of claim 6, wherein the catalyst comprises 0.1 to 8 mole percent of the noble metal, 60 to 95 mole percent of silicon, 0.1 to 20 mole percent of titanium, and 0.1 to 20 mole percent of an alkali metal or alkaline earth metal.

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