阅读说明：本技术 通过使用非均相催化剂进行氧化酯化来生产甲基丙烯酸甲酯的方法 (Method for producing methyl methacrylate by oxidative esterification using heterogeneous catalysts ) 是由 J·赫伦 D·J·阿里欧拉 D·W·布雷洛克 W-S·李 V·J·苏斯曼 D·A·希克曼 于 2018-09-12 设计创作，主要内容包括：一种从甲基丙烯醛和甲醇制备甲基丙烯酸甲酯的方法。所述方法包含使包含甲基丙烯醛、甲醇和氧气的混合物与包含载体和贵金属的非均相催化剂接触,其中反应器出口处的氧浓度为1至7.5mol％且其中反应器出口处的pH为不超过7.5。(A process for preparing methyl methacrylate from methacrolein and methanol. The process comprises contacting a mixture comprising methacrolein, methanol and oxygen with a heterogeneous catalyst comprising a support and a noble metal, wherein the oxygen concentration at the reactor outlet is from 1 to 7.5 mol% and wherein the pH at the reactor outlet is not more than 7.5.)

1. A process for producing methyl methacrylate from methacrolein and methanol; the process comprises contacting a mixture comprising methacrolein, methanol and oxygen with a heterogeneous catalyst comprising a support and a noble metal in a reactor, wherein the oxygen concentration at the outlet of the reactor is from 1 to 7.5 mol% and wherein the pH at the outlet of the reactor is not more than 7.5.

2. The process of claim 1, wherein the reactor is an axial flow reactor having a superficial velocity of the liquid phase of from 0.5 to 20mm/s and an average oxygen partial pressure of greater than 50 kPa.

3. The process of claim 2, wherein the catalyst has an average diameter of from 400 microns to 10 millimeters.

4. The process of claim 3, wherein the catalyst is contained in a catalyst bed at a temperature of 40 to 120 ℃.

5. The process of claim 4, wherein the pH in the reactor is from 3 to 7.2.

6. The process of claim 5, wherein the oxygen concentration at the reactor outlet is from 1.6 to 6 mol%.

7. The method of claim 6, wherein the noble metal is selected from the group consisting of gold and palladium.

8. The method of claim 7, wherein the vector is selected from the group consisting of: gamma-, -or theta-alumina, silica, magnesia, titania, zirconia, hafnia, vanadia, niobia, tantalum oxide, ceria, yttria, lanthana, and combinations thereof.

9. The process according to claim 8, wherein methanol and methacrolein are fed to the reactor containing the catalyst bed at a molar ratio of 1:1 to 10:1, respectively.

10. The process of claim 9 wherein at least 90 wt.% of the noble metal is in the outer 70% of the catalyst volume.

Background

The present invention relates to a method for preparing methyl methacrylate from methacrolein and methanol using a heterogeneous catalyst.

It is known to oxidatively esterify methacrolein at a relatively low pH to produce methyl methacrylate, see for example JP3408700 (B2). However, this reference uses palladium and lead catalysts and teaches that very low oxygen partial pressures are preferred. There is a need for a process that can provide improved selectivity in oxidative esterification reactions, particularly with respect to the level of by-product methyl isobutyrate.

Disclosure of Invention

The present invention relates to a method for producing methyl methacrylate from methacrolein and methanol; the process comprises contacting a mixture comprising methacrolein, methanol and oxygen with a heterogeneous catalyst comprising a support and a noble metal in a reactor, wherein the oxygen concentration at the outlet of the reactor is from 1 to 7.5 mol% and wherein the pH at the outlet of the reactor is not more than 7.5.

Detailed Description

Unless otherwise indicated, all percentage compositions are weight percent (wt%) and all temperatures are in units of ° c. The noble metal is any one 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 limits apply to the total amount of all noble metals. The "catalyst center" is the centroid of the catalyst particle, i.e., the average position of all points in all coordinate directions. The diameter is any linear dimension 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 to the shortest diameter.

Preferably, the support is a particle of an oxide material; preferably, gamma-, -or theta-alumina, silica, magnesia, titania, zirconia, hafnia, vanadia, niobia, tantala, ceria, yttria, lanthana, or combinations thereof; preferably gamma-, -or theta-alumina. Preferably, in the part of the catalyst comprising the noble metal, the surface area of the support is greater than 10m²G, preferably greater than 30m²G, preferably greater than 50m²G, preferably greater than 100m²G, preferably greater than 120m²(ii) in terms of/g. In the portion of the catalyst containing little or no noble metal, the surface area of the support may be less than 50m²G, preferably less than 20m²/g。

Preferably, the aspect ratio of the catalyst particles is not more than 10:1, preferably not more than 5:1, preferably not more than 3:1, preferably not more than 2:1, preferably not more than 1.5:1, preferably not more than 1.1: 1. Preferred shapes for the catalyst particles include spherical, cylindrical, rectangular solid, annular, multilobal (e.g., cloverleaf cross-section), shapes with multiple pores, and "carriage wheels"; preferably spherical. Irregular shapes may also be used.

Preferably, at least 90 wt.% of the noble metal is in the outer 70%, preferably the outer 60%, preferably the outer 50%, preferably the outer 40%, preferably the outer 35%, preferably the outer 30%, preferably the outer 25% of the catalyst volume (i.e. the volume of the average catalyst particle). 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 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 entire sphere volume. Preferably, at least 95 wt.%, preferably at least 97 wt.%, preferably at least 99 wt.% of the noble metal is in the outer volume of the catalyst. Preferably, at least 90 wt.% (preferably at least 95 wt.%, preferably at least 97 wt.%, preferably at least 99 wt.%) of the noble metal is within a distance of no more than 30%, preferably no more than 25%, preferably no more than 20%, preferably no more than 15%, preferably no more than 10%, preferably no more than 8% of the catalyst diameter from the surface. The distance to the surface is measured along a line perpendicular to the surface.

Preferably, the noble metal is gold or palladium, preferably gold. Preferably, the reaction mixture (including the catalyst) is substantially free of heavy metals that are not noble metals, such as lead, mercury, cadmium, chromium and manganese. Substantially free means having less than 500ppm, preferably less than 100ppm, preferably less than 50ppm, preferably less than 20ppm, preferably less than 10 ppm.

Preferably, the catalyst particles have an average diameter of 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 more than 30mm, preferably no more than 20mm, preferably no more than 10mm, preferably no more than 7mm, preferably no more than 5 mm. There was no significant difference between the average diameter of the support and the average diameter of the final catalyst particles.

Preferably, the amount of noble metal in percentage form of noble metal and support is 0.2 to 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%.

Preferably, the catalyst is produced by precipitating the noble metal from an aqueous solution of a noble metal salt in the presence of a support. In one embodiment of the invention, the catalyst is produced by incipient wetness,wherein an aqueous solution of a suitable noble metal precursor salt is added to the porous inorganic oxide such that the pores are filled with the solution and then the water is 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 noble metal salt to the metal or metal oxide. Preferably, C contains at least one hydroxy or carboxylic acid substituent₂-C₁₈The thiol is present in solution. Preferably, C contains at least one hydroxy or carboxylic acid substituent₂-C₁₈The thiols have 2 to 12, preferably 2 to 8, preferably 3 to 6 carbon atoms. Preferably, the thiol compound comprises 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 1 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 conjugate bases thereof.

In one embodiment of the invention, the catalyst is produced by precipitation, wherein a porous inorganic oxide is immersed in an aqueous solution containing a suitable salt of a noble metal precursor, and then the salt is 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 to the final catalyst by calcination, reduction, or other pretreatment known to those skilled in the art to decompose the noble metal salt to the metal or metal oxide.

A process for producing Methyl Methacrylate (MMA) comprises treating methacrolein with methanol and oxygen in an Oxidative Esterification Reactor (OER). Preferably, the catalyst particles are in the catalyst bed and are preferably held in place by solid walls and by screens or catalyst support grids. In some configurations, the screens or grids are 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 screens. Preferred shapes for the catalyst bed include cylinders, rectangular solids and cylindrical shells; preferably a cylinder. The liquid phase may further comprise by-products such as Methacrolein Dimethyl Acetal (MDA) and Methyl Isobutyrate (MIB). MIB is a particularly problematic by-product because it is difficult to remove and it produces off-flavors. Preferably, the temperature of the liquid phase is 40 to 120 ℃; preferably at least 50 ℃, preferably at least 60 ℃; preferably not more than 110 c, preferably not more than 100 c. Preferably, the pressure of the catalyst bed is from 0 to 2000psig (101.3 to 13890.8 kPa); preferably not more than 2000kPa, preferably not more than 1500 kPa. Preferably, the catalyst bed is in a tubular continuous reactor containing axial flow of liquid and gaseous reactants; preferably, the tubular reactor has a circular cross-section. Preferably, the catalyst bed further comprises oxygen.

OER typically produces MMA, along with methacrylic acid and unreacted methanol. Preferably, methanol and methacrolein are fed to the reactor containing the catalyst bed at a molar ratio of methanol to methacrolein of from 1:10 to 100:1, preferably from 1:2 to 20:1, preferably from 1:1 to 10: 1. Preferably, the catalyst bed further comprises an inert material located below and/or above the catalyst. Preferred inert materials include, for example, alumina, clay, glass, silicon carbide, and quartz. Preferably, the average diameter of the inert material is equal to or greater than the average diameter of the catalyst. 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 bottoms stream from the methanol recovery distillation column comprises MMA, MDA, methacrylic acid, salt and water. In one embodiment of the invention, the MDA is hydrolyzed in a medium comprising MMA, MDA, methacrylic acid and water. In another embodiment, the MDA is hydrolyzed in an organic phase separated from the bottoms stream of the methanol recovery distillation column. It may be necessary to add water to the organic phase to ensure that there is sufficient water for MDA hydrolysis; 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 is passed through one or more distillation columns to produce MMA product and light and/or heavy byproducts. In another embodiment, the hydrolysis may be performed within the distillation column itself.

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

Preferably, the oxygen concentration at the reactor outlet is at least 1.4 mol%, preferably at least 1.6 mol%, preferably at least 1.8 mol%, preferably at least 2.0 mol%, preferably at least 2.2 mol%; preferably not more than 7 mol%, preferably not more than 6.5 mol%, preferably not more than 6 mol%, preferably not more than 5.5 mol%. Preferably, the superficial velocity of the liquid through the reactor is from 1 to 50mm/s, preferably at least 2mm/s, preferably at least 3mm/s, preferably at least 4mm/s, preferably at least 5 mm/s; preferably not more than 40mm/s, preferably not more than 25 mm/s.

In a preferred embodiment of the invention, the pH at the reactor outlet is at least 3, preferably at least 3.5, preferably at least 4, preferably at least 4.5, preferably at least 5; preferably not more than 7.2, preferably not more than 7, preferably not more than 6.8, preferably not more than 6.7, preferably not more than 6.6, preferably not more than 6.5. Preferably, no base is added to the reactor or to the liquid stream entering the reactor. Preferably, the reactor is not connected to an external mixing tank where the base is introduced. The pH in the reactor may be higher near the inlet, may be higher than 7, and steadily decreases towards the outlet.

At typical operating temperatures and pressures (50-90 ℃ and 60-300psig), if the gas feed is air, this vapor mixture is within a flammable envelope.

The relevant fuel mixture, temperature and pressure requirements are to be understood that L OC., due to the lowering of L OC with increasing temperature and pressure, and considering that methanol gives L OC lower than the other two important fuels (methacrolein and methyl methacrylate), a conservative design selects a feed oxygen-to-nitrogen ratio that ensures a composition lower than L OC at the highest expected operating temperature and pressure.

Examples of the invention

The following provides the exhaust port O₂Examples of the effect of concentration and pH.

Example 1

A series of operations was carried out in which 20 wt% methacrolein, 200ppm inhibitor and the remainder methanol were fed to an 3/8"(9.5mm) stainless steel tubular reactor containing a short silicon carbide front stage, followed by feeding 10g catalyst. The catalyst consisted of 1.5 wt% Au on a NORPRO 1mm diameter high surface area alumina spherical support. In all cases, a gas containing 8% oxygen in nitrogen was also fed to the reactor, unless indicated otherwise (×), in which case air was fed to the reactor. The reactor was operated at 60 ℃ and 160psig (1205 kPa). The product of the reactor was sent to a liquid-vapor separator and the vapor was sent to a condenser with liquid reflux. In some cases, a portion of the product stream from this separator is recycled to the reactor inlet and combined with the feed entering the reactor. The results are described in the table below. MIB is reported in ppm based on 100% MMA product. In all runs, the% MMA in the product formed from methacrolein exceeded 95 wt%.

TABLE 1 influence of mol% oxygen and pH at the reactor outlet on MIB formation

Liquid velocity (L iq. vel.) is the superficial velocity and the average oxygen partial pressure (avg. p.)_O2) In absolute value in kPa. The mean partial pressure is the arithmetic mean of the inlet and outlet oxygen partial pressures.

In this case air was used instead of 8% O₂