DE102021128695A1 - Production of ketones from carboxylic acids - Google Patents

Abstract

Ketones are produced from carboxylic acids in the presence of a shaped catalyst body. The catalyst comprises zirconium dioxide and one or more metal oxides from the first or second main group of the periodic table. The shaped catalyst body has a through opening which is surrounded by a solid wall area with a wall thickness of less than 2 mm. The catalyst has increased mechanical stability without impairing the initial activity.

Description

The present invention relates to a process for preparing ketones from carboxylic acids.

Ketones are useful organic solvents for the paint, agricultural, and other industries. The production of ketones from carboxylic acids with metal oxide catalysts at high temperatures has been known for a long time.

In the procedure after EP0352674 a catalyst is used whose active material contains at least 50% by weight of titanium dioxide with a specific surface area of more than 10 m ² /g and one or more metal oxides from the first or second main group of the periodic table.

While the titania-based catalysts show a high initial activity, their mechanical stability decreases rapidly, leading to an increasing pressure drop in the reactor. Therefore, it is desirable to provide a catalyst with increased mechanical stability without sacrificing initial activity.

U.S. 2009/182173 relates to the production of mixed ketones from a mixture of carboxylic acids with high selectivity. The catalyst contains zirconia or zirconia and titania, and a Group 1 or 2 metal silicate or a phosphate salt. The catalyst is said to be more selective for the formation of the mixed ketone than for a symmetrical ketone.

The invention relates to a process for preparing ketones from carboxylic acids in the presence of a shaped catalyst body, the catalyst comprising zirconium dioxide and one or more metal oxides from the first or second main group of the periodic table, and the shaped catalyst body having a continuous opening which is covered by a solid Wall area is surrounded with a wall thickness of less than 2 mm, preferably less than 1.8 mm.

worin R¹ und R² unabhängig voneinander für Alkyl, Cycloalkyl, Aralkyl, Aryl oder Hetaryl stehen, und mindestens einer der Reste R¹ und R² ein oder mehrere, d.h. ein, zwei oder drei, Wasserstoffatome am α-Kohlenstoffatom trägt.In the process according to the invention, carboxylic acids are converted into ketones or mixtures of ketones with decarboxylation and dehydration. The reaction is illustrated by the following reaction scheme:

wherein R ¹ and R ² independently represent alkyl, cycloalkyl, aralkyl, aryl or hetaryl, and at least one of the radicals R ¹ and R ² carries one or more, ie one, two or three, hydrogen atoms on the α-carbon atom.

R ¹ and R ² are each preferably alkyl of 1 to 17 carbon atoms, cycloalkyl of 3 to 8 ring members, arylalkyl of 7 to 12 carbon atoms, aryl or hetaryl.

When R ¹ and R ² are identical, they are symmetrical ketones; in the case of asymmetric ketones, on the other hand, R ¹ and R ² are different. When R ¹ and R ² together form a divalent radical, it is the reaction of a dicarboxylic acid to form a cyclic ketone. However, it is also possible to react a dicarboxylic acid with two or more equivalents of a monocarboxylic acid to give a diketone.

When preparing asymmetric ketones, mixtures of symmetric ketones and asymmetric ketones are generally obtained, the ratio of which depends on the reactivities of the starting acids. The more reactive acid reacts preferentially with itself, and only a small portion of this acid is available to form the asymmetric ketone. If the starting mixture contains a carboxylic acid R ¹ -COOH without α-hydrogen atoms, eg a carboxylic acid with a tertiary α-carbon atom such as pivalic acid or an aromatic carboxylic acid, R ¹ -COOH is not autocondensed and only R ¹ -CO is formed ^-R2 and R2 ^-CO - ^R2 .

Examples of important ketones obtainable from the corresponding acids by the process are diethyl ketone, di-n-propyl ketone, diisopropyl ketone, methyl propyl ketone, methyl isopropyl ketone, ethyli sopropyl ketone, nonan-5-one, octane-2,7-dione, cyclopentanone, cycloheptanone, acetophenone, propiophenone, butyrophenone, isobutyrophenone, valerophenone, phenylacetone, 1,2-diphenylacetone, cyclohexyl methyl ketone, cyclohexyl phenyl ketone, cyclopropyl methyl ketone, pinacolone and even heterocyclic ketones, such as 3-acetylpyridine, 4-acetylpyrazole and 4-acetylimidazole.

In a preferred embodiment, diethyl ketone is produced from propionic acid.

Zirconia is more stable than titania under acidic conditions. Therefore, the new catalysts better maintain their mechanical properties and their stability as well as a low pressure drop over time.

The shaped catalyst body has a continuous opening which is surrounded by a solid wall area with a limited wall thickness. It is believed that this setup allows for shorter diffusion paths for reactants and/or products. The inventors have surprisingly found that catalysts with too great a wall thickness are quickly deactivated. In addition, the design reduces the pressure drop that occurs across a packed catalyst bed while also reducing catalyst loss through breakage, attrition, or crushing during handling or sorting.

The shaped catalyst body may have the shape of a hollow cylinder, a wagon wheel, or a multilobal shape. In general, the shape of a hollow cylinder (“annular shape”) is preferred. Preferably, the shaped catalyst body has a length to diameter aspect ratio of from 0.5 to 0.8, more preferably from 0.5 to 0.65.

Particularly preferred hollow cylinders are (external diameter×internal diameter×length): 5.5×3×3 mm or 5×2×3 mm.

The catalyst contains 0.05 to 50% by weight, preferably 1 to 10% by weight, of one or more metal oxides selected from the first or second main group of the periodic table, in particular from the elements lithium, sodium and potassium. Potassium is generally preferred.

In general, zirconia occurs in three allotropic forms: monoclinic, tetragonal, and cubic. During the phase transition from tetragonal to monoclinic, there is a strong volume expansion. While it is contemplated that both tetragonal zirconia and monoclinic zirconia may be used in the practice of the invention, zirconia having a high proportion of monoclinic phase is presently preferred. It is believed that zirconia with a large proportion of monoclinic phase enables the production of catalysts or catalyst supports with improved fracture toughness.

The zirconia is preferably at least 65% by weight, more preferably at least 75% by weight, monoclinic. The content of the monoclinic zirconia can be determined from the X-ray diffraction pattern of the product. The production of supports consisting essentially of monoclinic ZrO ₂ is, for example, in EP0716883 described.

A commercially available material that has been found useful is spray dried zirconia powder D9-89 available from BASF SE. D9-89 is approximately 20% tetragonal and 80% monoclinic.

It was found that the catalysts should have specific pore size characteristics. A high average pore diameter is generally preferred. Preferably, the shaped catalyst body has an average pore diameter of at least 0.013 µm, more preferably at least 0.019 µm. Tighter pore structure can promote by-product formation and rapid deactivation.

Preferably the total volume of intrusion is 0.15 to 0.40 mL/g.

Preferably the total pore surface area is 45 to 60 m ² /g.

It was found that there is a correlation between the porosity of the catalyst and its activity. It is known that more porous catalysts are more active catalysts and therefore over-compacting of the catalysts or catalyst supports to strengths greater than required for use in catalyst beds results in lower catalyst activity. a den The porosity of the catalyst corresponding to the above pore size characteristics can be controlled by varying the amount of powder fed into the cylinder of the die of a tableting machine for preparing the catalysts or catalyst supports, or by varying the compressive force applied to the punches of the tableting machine.

The catalysts can be provided in the form of impregnated or mixed catalysts.

Impregnated catalysts can be made as follows. A powdered zirconium dioxide starting material is brought into the desired shape by compression, e.g. by tabletting. Excipients such as graphite or magnesium stearate can be used during tableting. The porosity is determined, after which an impregnation solution is used, the volume of which corresponds to the pore capacity of the carrier.

The impregnation is carried out by adding the impregnation solution to the carrier located in a rotating drum, advantageously by spraying the solution onto the carrier. All soluble salts that decompose into oxides during calcination without leaving any residues can be used to prepare the impregnation solutions. Suitable salts are the hydroxides, carbonates or nitrates. Potassium carbonate is a preferred salt for impregnation.

Mixed catalysts are prepared in a manner similar to the supports of the impregnated catalysts. The appropriate salt solutions are added to the zirconia material in a kneader and thorough mixing is ensured. Shaping, drying and calcination are the same as in the manufacture of the carrier.

The decarboxylation reaction with dehydration is carried out in the gas phase. The reaction is preferably carried out at from 300 to 600° C., in particular at from 350 to 450° C., by passing the acid vapors preheated to this temperature through a fixed-bed furnace which is filled with the shaped catalyst body. In general, the reaction is carried out under atmospheric pressure. In the case of acids of low volatility, it may also be advisable to work at reduced pressure. In general, 200 to 500 g/h of ketones can be produced per liter of catalyst.

It is possible to use carboxylic acids containing up to 50% by weight of water. Since the water often has a beneficial effect on the active life of the catalyst, it is often even advantageous to add from 1 to 50% by weight of water to the carboxylic acids.

After passing through the catalyst zone, the vapors are cooled and worked up in a conventional manner.

The invention is illustrated by the following examples.

EXAMPLES

The following abbreviations have been used below: wt% weight percent cat catalyst DEC diethyl ketone PA priopionic acid (propionic acid ) TOS Catalyst runtime ( t ime o n s tream)

1. Measurement and determination methods used

i) Measurement of lateral crushing strength

Tablets, rings or spheres were subjected to increasing force on the convex side between two parallel plates until fracture occurred. The force registered at fracture is the lateral crushing strength (also called compressive strength for balls). The determination was carried out on Zwick model BZ2.5/TS1S and SotaxST50 model Smarttest50 test devices, with a rotary table fitted and a freely movable, vertical stamp which pressed the molded part against the rotary table fitted. The free moving one Stamp was connected to a pressure cell to absorb the force. The device was controlled by a computer, which registered and evaluated the measured values. From a well-mixed catalyst sample, 25 perfect (ie crack-free and without chipped corners) tablets, rings or spheres were taken, whose side crushing strength was determined and then averaged.

ii) measurement of porosity

The porosity of the catalyst was determined using the Hg intrusion method according to DIN 66133.

iii) measurement of conversion and selectivity

The conversion and the selectivity were determined by means of GC analysis (GC column: Stabilwax (30 m×0.25 mm×0.25 μm)).

2. Materials used to manufacture the catalysts

Catalyst support C1: Zirconia (20% tetragonal and 80% monoclinic), commercially available under the trade name D9-89 from BASF SE

Unless otherwise noted, the water used in the examples was deionized water.

3. General procedure for the preparation of the catalyst

3.1 Shape of the catalyst support

Ring tablets (7×3×3 mm, 5.5×3×3 mm and 5×2×3 mm) from the catalyst support C1 were pelleted on a Kilian LX18 tablet press machine with 3% by weight graphite.

3.2 Impregnation of the catalyst support

The ring tablets from the catalyst support C1 were impregnated with an aqueous potassium carbonate solution. The impregnated catalysts were dried at 120°C for 12 h and calcined at 500°C for 4 h. The potassium content, the mechanical stability and the pore properties are summarized in Table 1.

A K ₂ O comprehensive, TiO ₂ -based comparison catalyst was according EP 352674 produced. The potassium content, the mechanical stability and the pore properties are summarized in Table 1.

The comparative catalyst obtained was crushed to 2-3 mm. Table 1: catalyst K ₂ O content O [% by weight] carrier beam geometry [mm] Side crushing strength [N] catalyst 1 2 ZrO ₂ 5.5 × 3 × 3 ring tablets 10±1.8 Catalyst 2* 2 ZrO ₂ 7 × 3 × 3 ring tablets 31±4 Catalyst 3 2 ZrO ₂ 5 × 2 × 3 ring tablets 9±5.6 Catalyst 4 2 ZrO ₂ 5 × 2 × 3 ring tablets 10±1.5 Catalyst 5 2 ZrO ₂ 5 × 2 × 3 ring tablets 24±3.3 ^* not according to the invention Table 1 (continued) catalyst total intrusion volume [mL/g] total pore surface [m ² /g] average pore diameter [µm] catalyst 1 0.22 47.3 0.019 Catalyst 2* 0.19 49.9 0.015 Catalyst 3 0.36 55.9 0.026 Catalyst 4 0.25 57.5 0.017 Catalyst 5 0.16 54.3 0.012
* not according to the invention

Examples 1-5

• Propionsäure, gelöst in Wasser im Verhältnis 8:1, Temperatur: wie in den Beispielen angegeben, Druck: 0,1 barg, Katalysatormenge: 1 mL pro 1,6 g Propionsäure. Die Reaktionen wurden in einem Rohrofenreaktor durchgeführt. Die Umsetzungsrate der Propionsäure und die Selektivität bezogen auf Diethylketon wurden durch GC-Analyse bestimmt.

Various ZrO ₂ -based catalysts with different support geometry and a TiO ₂ -based catalyst were tested in the production of diethyl ketone from propionic acid and the conversion and selectivity were measured. The reaction conditions were:

• Propionic acid dissolved in water in a ratio of 8:1, temperature: as indicated in the examples, pressure: 0.1 barg, amount of catalyst: 1 mL per 1.6 g of propionic acid. The reactions were carried out in a tube furnace reactor. The conversion rate of propionic acid and the selectivity based on diethyl ketone were determined by GC analysis.

Example 1 (comparative example):

Catalyst based on a tetragonal modification of TiO ₂ ; 2% by weight K ₂ O; Temperature: 350℃

The TiO ₂ -based catalyst showed steady deactivation over time. DEK selectivity dropped from 99% to about 97% within 70 d TOS. At the same time, the propionic acid content increased from 0.2 to 2%. By-product formation: 0.5%.

Example 2:

Catalyst 1; Temperature: 350℃

DEK selectivity fell from 99.5% to 98.5% within 70 d TOS. At the same time, the propionic acid content increased from 0.06 to 1.25%. By-product formation: 0.4%. The spent catalyst had a compressive strength of 10N, which is comparable to that of the fresh catalyst.

The catalyst of the invention comprising potassium oxide on zirconia as a support showed better selectivity to the desired product and less by-product formation compared to a prior art catalyst comprising potassium on a titania support.

Example 3 (comparative example):

Catalyst 2; Temperature: 350℃

Catalyst 2 showed rapid deactivation after a short run time. DEK selectivity fell from 99.0% to 97.8% within 8 d TOS. At the same time, the propionic acid content increased from 0.5 to 1.8%.

Example 3 shows that the catalyst support geometry has an impact on the catalyst performance.

Example 4 (comparative example):

A crushed catalyst fraction (2-3 mm) from Catalyst 2 was used; Temperature: 315-305℃

Catalyst 2 is more active when crushed to 2-3 mm compared to the tests of the 7×3×3 mm ring tablets. Complete propionic acid conversion was observed even at an oven temperature of 320 °C.

A crushed catalyst fraction (2-3 mm) from Catalyst 1 was used; Temperature: 325-315℃ Complete propionic acid conversion was observed at 312°C.

Example 4 shows that the crushed catalyst from the small ring tablets was more active than the catalyst split from the larger ring tablets. Thus, characteristic length/wall thickness is a key parameter affecting catalyst performance. The wall thickness is 2 mm for the 7×3×3 mm comparison ring tablets and 1.25 mm for the 5.5×3×3 mm ring tablets according to the invention.

Example 5:

Catalysts 3, 4 and 5 according to the invention with different crush strengths and pore properties were used to investigate the influence of these parameters on the catalyst performance in the production of diethyl ketone from propionic acid. The temperature was 325 °C in each case.

The example shows that the larger the total intrusion volume and the larger the average pore diameter, the more active the catalyst and the lower the deactivation (see Fig 1, a ) Catalyst 4; b) Catalyst 5; c) Catalyst 6)).

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 0352674 [0003]
• US2009182173 [0005]
• EP 0716883 [0019]
• EP 352674 [0041]

Claims (8)

Process for the production of ketones from carboxylic acids in the presence of a shaped catalyst body, wherein the catalyst comprises zirconium dioxide and one or more metal oxides of the first or second main group of the periodic table, and the shaped catalyst body has a continuous opening which has a solid wall region with a wall thickness surrounded by less than 2 mm. procedure after claim 1 , wherein the solid wall portion has a wall thickness of preferably less than 1.8 mm. procedure after claim 1 or 2 wherein the shaped catalyst body has the shape of a hollow cylinder, a wagon wheel, or a multilobal shape. procedure after claim 1 or 2 , wherein the shaped catalyst body has an aspect ratio of 0.5 to 0.8. Process according to any one of the preceding claims, wherein the shaped catalyst body has an average pore diameter of at least 0.013 µm. A method according to any one of the preceding claims wherein the metal oxide is potassium oxide. A method according to any one of the preceding claims wherein the zirconia is at least 65% by weight monoclinic. Process according to any one of the preceding claims, in which propionic acid is converted to diethyl ketone.

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