EP1455933A1

EP1455933A1 - Supported metal oxides as catalysts for aldol condensations

Info

Publication number: EP1455933A1
Application number: EP02795106A
Authority: EP
Inventors: Marcus Sigl; Christian Miller; Walter Dobler; Mathias Haake
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2001-12-06
Filing date: 2002-12-05
Publication date: 2004-09-15
Also published as: BR0214603A; JP4112496B2; JP2005511274A; US20050070733A1; CN1599643A; MXPA04004917A; US7098366B2; AU2002361017A1; WO2003047748A1

Abstract

A supported catalyst comprising one or more metal oxides as active components on a catalyst support for carrying out an aldol condensation is disclosed. The catalyst support is gamma aluminium oxide, the active component is one or more oxides of the rare earth metals and the concentration of the active components, based on the weight of the catalyst support, lies in the range of 5 to 12 wt. %. The invention further relates to a method for the production of pseudoionone by aldolisation of citral and acetone by reactive distillation in a column in the presence of said catalyst and the regeneration of supported catalysts with an aqueous alkaline solution is also disclosed.

Description

Inert metal oxides as catalysts for aldol condensation

The invention relates to a supported catalyst containing one or more metal oxides as an active component for carrying out an aldol condensation, a column for carrying out an aldol condensation by reactive distillation using a supported catalyst and a process.

Aldol condensation is known in a known manner as the generally base-catalyzed reaction of a carbonyl component with a methylene component. The same compound can act as a carbonyl and methylene component at the same time. If different compounds are used as carbonyl or methylene components, it is often advantageous to use one of the components in excess, in particular in up to a hundredfold excess over the other component.

In addition to homogeneous catalysis in the presence of aqueous alkali metal or alkaline earth metal hydroxides, heterogeneous catalysis, for example by metal oxides of lanthanum or lanthanides, is known.

No. 3,578,702 describes the use of oxides of metals with atomic numbers 57 to 71 as an active component on a support made of an inert material, for example aluminum oxide, diatomaceous earth or preferably silica gel, the concentration of the active component being in the range from 0.5 to 10% by weight. -%, based on the total weight of the supported catalyst, is.

In contrast, it was an object of the invention to provide supported catalysts for carrying out an aldol condensation, which are distinguished from known supported catalysts by an increased catalyst activity or an improved space-time yield.

The object is achieved by a supported catalyst containing one or more metal oxides as an active component for carrying out an aldol condensation, the catalyst support being γ-aluminum oxide, the active component comprising one or more oxides of the elements having atomic numbers 39 or 57 to 71 and the concentration of Active component, based on the total weight of the supported catalyst, is in the range from 5 to 12% by weight.

As a result of extensive screening investigations, it was surprisingly found that a significant improvement in the catalyst activity is achieved if the conditions defined above are met.

The supported catalysts according to the invention are preferably suitable for carrying out the aldol condensation of citral and acetone to pseudo-ionone. Pseudojonon is an important intermediate for vitamin and fragrance production. Citral to acetone is advantageously used in a molar ratio of 1 to 2 to 50. Reaction temperatures between 30 and 100 ° C. and pressures between 1 and 10 bar absolute are particularly advantageous.

It was found that the suitable selection of the catalyst support significantly influences the catalyst activity. With γ-alumina as catalyst support, significantly improved space-time yields were obtained.

In a preferred embodiment, the geometry of the catalyst carrier is determined such that the ratio of the outer surface to the volume is in the range from 0.5 to 10 mm ^"1 , preferably in the range from 1 to 5 mm ^{" 1} , in particular that the catalyst carrier is in shape of solid or hollow cylinders, balls, honeycomb bodies, trilobes or gears.

Another condition that is decisive for the activity of the supported catalysts according to the invention is compliance with the concentration of the active component, which according to the invention must be in the range from 5 to 12% by weight, based on the total weight of the supported catalyst. It was found that good space-time yields are obtained if the concentration in the above range is maintained, and that concentrations outside the specified limit values lead to a decrease in the space-time yield.

Concentrations of the active component, based on the total weight of the supported catalyst, in the range from 7.5 to 10% by weight are particularly advantageous.

The supported catalysts according to the invention can in principle be used in any reactor suitable for heterogeneously catalyzed reactions. Without restriction The following may be mentioned by way of example to the general public: suspension reactor, stirred tank, stirred tank cascade, tube reactor, tray reactor, tube bundle reactor, fixed bed reactor, fluidized bed reactor, reactive distillation column. The reaction can be carried out at different temperatures and pressures, the optimum being determined by the starting materials used. As a rule, the reaction temperatures are between 20 and 200 ° C and the pressures between 0.1 and 100 bar absolute.

A particular advantage of the supported catalysts according to the invention is that simple regeneration by calcination or by washing with alkaline solutions is possible. It has been found that with a decrease in catalyst activity, which is reflected in a reduction in the space-time yield, it is possible to regenerate the catalyst and to restore the original activity. The regeneration can be carried out by treatment with aqueous alkaline solutions, in particular alkali, alkaline earth metal or ammonium hydroxide solutions or by calcinations in the presence of oxygen at temperatures between 150 and 700 ° C. In addition, it is also possible to increase the activity of the fresh catalyst by base treatment before use in the aldol condensation. Regeneration as well as pretreatment indicate a base-catalyzed mechanism of aldol condensation.

The invention also relates to a column for carrying out an aldol condensation by reactive distillation in the presence of a heterogeneous particulate catalyst with a packing or packing which form spaces in the interior of the column, the quotient of the hydraulic diameter for the gas flow through the packing or the packing and the equivalent diameter the catalyst particle is in the range from 2 to 20, preferably in the range from 5 to 10, in such a way that the catalyst particles are loosely introduced, distributed and discharged into the interspaces under the action of gravity, and supported catalysts are used as catalyst particles, as they are are described above.

The hydraulic diameter is defined in a known manner as the ratio between four times the area flowed through and the circumference thereof. The specific calculation of the same for a pack with straight folds is explained in the description of the figures in conjunction with FIG. 2. The hydraulic diameter of packing is determined via the porosity of the bed ψ, ie empty volume of the bed / total volume and the equivalent diameter of the packing,

where d _h y _drau ii _sch ⁼ hydraulic diameter, d _p = diameter of the packing and ψ = porosity. The equivalent diameter of the packing is defined by the ratio between six times the volume and the surface of the packing (cf. VDI Heat 0 meatlas, 5th edition, 1988, Lk 1).

The equivalent diameter of particles, in the present case catalyst particles, is defined by the ratio between six times the volume and the surface area of the particle (cf. VDI Wärmeatlas, 5th edition, 1988, Lk 1. 5

By maintaining a quotient of the hydraulic diameter for the gas flow through the packing or the packing and the equivalent diameter of the catalyst particles in the range defined above, it is ensured according to the invention that the catalyst particles loosely into the interstices of the packing under the influence of gravity kung or the packing can be introduced, distributed and discharged.

There are basically no restrictions with regard to the packings or packing that can be used: the column internals that are regularly used in distillation technology can be used to limit the phase interface between the phases moving in countercurrent through the column, the gaseous and the liquid phase enlarge. In this case, the packs or packing elements form spaces in the interior of the colomy, which in principle must be connected to one another in order to ensure the opposite flow of gaseous and liquid phases required for the distillative separating action. 0

The inventors have thus recognized that, in principle, it is possible to introduce catalyst particles loosely into the interspaces, which form the packing or the packing in the interior of the column, under the action of gravity, to distribute them and to discharge the used catalyst particles again , It is important to ensure that there are sufficient free spaces for the gas stream produced during the distillation so that there is no accumulation of the liquid stream flowing in countercurrent to the gas stream. This is ensured according to the invention in that the quotient of the hydraulic diameter for the gas flow through the packing or through the packing and the equivalent diameter of the catalyst particles is chosen to be very small, that is to say with values in the ranges defined above.

The invention is not restricted with regard to the shape and size of the catalyst particles which can be used; To improve the space-time yield, however, high specific surfaces and thus small catalyst particles are preferred. As is known, the pressure loss in catalyst particle beds increases with increasingly smaller catalyst particles and limits the liquid and vapor throughputs to uneconomically small values in the case of reactive distillation. Because of the generally pronounced formation of a stream of liquid in catalyst beds, only small distillation capacities can be achieved for large column diameters, which are required in production-scale plants. These disadvantages have hitherto prevented the use of catalyst beds as separating internals in reactive distillations, which is desirable per se. In contrast, according to the invention, small catalyst particles, which are also preferred with regard to the catalytic activity, are particularly suitable for combined use with a packing or with packing, since they are easier to insert and the smaller their dimensions compared to the dimensions of the spaces between the packing or the packing are.

Suitable dimensions of the catalyst particles are, for example, about 1 × 4 mm to about 4 × 40 mm for fully cylindrical catalyst particles.

Structured packings are preferably used as column internals, that is to say packings systematically constructed in regular geometry with defined passage areas for the countercurrent phases. Packs are generally constructed from metal sheets, expanded metal or Dralit fabric layers arranged essentially parallel to one another. Compared to other column internals, they are characterized by a higher load capacity, a better separation effect and a lower specific pressure loss. Packings are generally constructed from kinked metal sheets, expanded metal or fabric layers arranged essentially parallel to one another, with mostly straight folds which subdivide the packing sheet, the expanded metal or fabric layer into buckling surfaces, and the angle of inclination of the buckling surface to the vertical is usually 30 up to 45 ° amounts. For the present invention, packs with an angle of inclination of the kink surface to the vertical in the range from 10 to 45 °, preferably from 30 °, can be used. The arrangement of successive packing sheets at the same angle of inclination to the vertical, but with the opposite sign, creates the known cross-channel structures, such as those of the types Mellapak, CY or BX from Sulzer AG, CH-8404 Winterthur or the types A3, BSH , Bl or M from Montz GmbH, D-40723 Hilden.

For use in reactive distillation, special designs of structured packings are preferably used, which allow an increased gas flow.

A particularly preferred embodiment is characterized in that one or more packing sheets with a high specific surface are alternately arranged with one or more packing sheets with a low specific surface. This creates gaps with different hydraulic diameters. The specific surfaces of the packing sheets are particularly preferably selected such that, on the one hand, spaces are formed for which the quotient of the hydraulic diameter and the equivalent diameter of the catalyst particles is less than 1 and, on the other hand, spaces for which the quotient of the hydraulic diameter and the equivalent is The diameter of the catalyst particles is greater than 2, in particular in the range defined above between 2 and 20, in particular between 5 and 10. No catalyst particles are filled into the first-mentioned spaces, with a ratio of the hydraulic diameter to the equivalent diameter of the catalyst particles less than 1; according to the invention, they are only filled into the spaces in which the quotient is greater than 2. This special embodiment ensures an increased gas flow with low pressure losses.

Preferably, the starting material for the packs according to the invention is usually additionally provided with openings, for example with circular holes approximately 4 to 6 mm in diameter, in order to raise the flood limit of the pack and to enable a higher column load. The flood limit of a pack is understood to mean the gas or liquid volume per time and cross-sectional area at which the trickle liquid is dammed up in and above the pack until it is completely flooded or entrained by the gas flow. Exceeding this load results in a rapid decrease in the separating effect and a steep increase in pressure loss. Instead of packings, fillers can be used in the same way, although there are basically no restrictions with regard to the shape thereof. For example, all forms of fillers known in distillation technology, such as Raschig rings, Pal rings or saddles, can be used.

Packs or fillers which have horizontal areas are advantageous. The horizontal surface areas capture a part of the weight of the catalyst particles and lead it to the column wall. This reduces the mechanical load on the catalytic converter.

Packings which are formed from packing sheets for vertical installation in the column are preferred, with straight lines which subdivide the packing sheet into buckling surfaces, the angle of inclination of the buckling surfaces to the horizontal being in the range from 90 to 45 °, preferably 60 °.

The specific surface area of packages for distillation is approximately 250 to 750 m ² / m ³ . Packings with lower specific surface areas in the range from about 50 to 250 m ² / m ^{3 are} preferably used for columns for carrying out heterogeneously catalyzed reactive distillation.

In the case of distillation packs, wall thicknesses of the metal sheets of typically 0.07 to 0.1 mm are sufficient. In contrast, in the case of heterogeneously catalyzed reactive distillations, depending on the catalyst weight and mechanical stability of the catalyst grains, wall thicknesses of the metal sheets in the range from 0.1 to 5 mm, preferably from 0.15 to 0.3 mm, are used.

Packings or fillers are preferably used which have a reduced flow resistance on their surface, this reduced flow resistance being achieved in particular by perforations and / or roughening of the material of the pack or the fillers or by forming the pack as expanded metal. The number and dimensions of the perforations are preferably such that at least a proportion of 20%, preferably a proportion of 40 to 80%, of the liquid reaction mixture passes through these perforations and flows onto the catalyst particles underneath.

In a preferred embodiment variant, the packing material consists of expanded metal, the packing material being designed in such a way that the film is deposited on the packing material. running liquid can drain as completely as possible through the packing material, the draining being supported by drainage edges.

The perforations are preferably provided in the vicinity of the lower fold edges of the packing plates arranged vertically in the column, as described in DE-A 100 31 119. As a result, the fluid is preferably directed onto the top of the inclined kink surfaces and the liquid load on the critical bottom is reduced. For this purpose, packs of packing sheets are used for vertical installation in the column, with straight folds which subdivide the packing sheets into buckling areas and which have a width a to be measured from buckling edge to buckling edge and perforations, with a proportion X of at least 60% of the perforations has a distance b of at most 0.4 a to the lower fold edge of each fold surface. The proportion of the area occupied by the perforations of a buckling area is preferably 5 to 40%, in particular 10 to 20% of this buckling area.

Another preferred embodiment is characterized in that the pack is formed from corrugated or kinked layers and that a flat intermediate layer is arranged between two corrugated or kinked layers, the flat intermediate layers not extending to the edge of the pack or in the Edge zone of the pack have an increased gas permeability, in particular holes, according to DE-A 196 01 558.

It is also possible to provide layers which are less wavy or kinked instead of flat intermediate layers.

The edge zone of the packing is a concentric volume element which extends between an outer cylindrical surface and an inner cylindrical surface (the packages typically have a cylindrical shape), the outer cylindrical surface being defined by the outer ends of the corrugated or kinked layers and the inner cylindrical surface is defined by the outer ends of the flat layers. In this case, the horizontal connecting line of the inner to the outer cylinder surface, oriented parallel to the packing layers and running through the column axis, intersects one to twenty, preferably three to ten channels formed by layers arranged next to one another. In the case of flat layers not reaching into the edge zone, up to twenty channels in the edge zone are thus released side by side. Second layers reaching into the edge zone are preferably gas-permeable to 20 to 90%, particularly preferably 40 to 60% of their surface, that is to say provided with holes, for example. At the points where the channels formed by the sheets touch the column wall, the rising gas flow is blocked because the channels are closed off by the column wall. This leads to a significantly poorer separation performance of the pack. By opening the packing channels in the wall zone, this cause of reduced separation performance can be eliminated in a simple and effective manner. In this case, the gas can change from the channels ending on the column wall to other channels which carry it on in the opposite direction.

The invention also relates to a process for the preparation of pseudo-ions by aldolization of citral and acetone by reactive distillation in a column as described here. The column is preferably operated with regard to its gas and liquid load in such a way that a maximum of 50 to 95%, preferably 70 to 80% of the flood load is reached.

The invention is explained in more detail below with reference to a drawing and exemplary embodiments.

It show in detail

FIG. 1 shows a schematic representation of an embodiment of a pack according to the invention,

Figure 2 is a schematic representation of a packing sheet with straight bends and

Figure 3 is a schematic representation of a packing sheet with perforations and

Figure 4 is a schematic representation of an embodiment of a column according to the invention.

The schematic representation in FIG. 1 shows a packing 1 with packing sheets 2, which have rectilinear creases 5 with the formation of kink surfaces 6, an intermediate space 3 being formed between two successive packing sheets 2. According to the invention, catalyst particles 4 are filled into the same.

2 schematically shows a packing sheet 2 with straight folds 5, and fold surfaces 6. a represents the width of a fold surface 6, measured from fold edge 5 to fold edge 5, dar, c the distance between two adjacent fold edges 5 and h the height of a fold.

3 schematically shows a special embodiment of a packing sheet 2 with buckling edges 5, buckling surfaces 6 and a width a of the buckling surfaces 6 with perforations which are at a distance b from the bottom buckling edge 5 of each buckling surface 6.

The reactive distillation column 7 shown schematically in FIG. 4 has two pure separation zones 8, each in the upper and lower region of the reactive distillation column 7, which are equipped with structured fabric packs. A reaction zone 9 is arranged in the central column region and has a lower region 9a with a packing without introduced catalyst particles and an upper region 9b with a packing according to the invention with introduced catalyst particles. The reactive distillation column 7 is equipped with a bottom evaporator 10 and a condenser 11 at the top of the column. The starting materials are introduced as streams I or II in the upper region of the column, the reaction mixture is taken off as bottom stream III and a top stream IV is taken off at the top of the column. A pressure regulator PC is arranged on the column head.

embodiments

Example 1

A column section with a diameter of 0.3 m was equipped with two distillation packs of the type B1 from the Montz company, offset by 90 °, the height of each pack being 23 cm. Catalyst particles were poured into the distillation packs. The filling volume and the manageability of the introduction and removal of the catalyst particles were determined. Γ-Al O ₃ full cylinders coated with 5% praseodymium oxide were used as catalyst particles. The γ-Al ₂ O ₃ full cylinders with a diameter of 1.5 mm and a height of 1 to 4 mm have an equivalent particle diameter of 2 mm.

1A) Bulk tests with γ-Ai ₂ θ ₃ full cylinders, diameter 1.5 mm. Packs of type B1 from the Montz company were used, each with different specific surfaces and different angles of inclination of the buckling surfaces to the horizontal. lAi) A sheet metal packing of the type Bl-125.80 with a specific surface area of 125 m ² / m ³ and an angle of 80 ° to the horizontal was used. 90% of the empty tube volume could be filled with the above-mentioned catalyst particles. The pack had a hydraulic diameter of 19 mm. The catalyst was very easy to insert and, in the dry state, also trickled out completely. The ratio of the equivalent diameter of the catalyst particles to the hydraulic diameter of the packing was 9.

1A ₂ ) A package of the type Bl-250.80 with a specific surface area of 250 m Ina. and filled with the above-mentioned catalyst particles at an angle of 80 ° to the horizontal. Here, 80% of the empty tube volume could be filled with catalyst particles. The pack has a hydraulic diameter of 9.4 mm. The catalyst was very easy to insert and, in the dry state, also trickled out completely. The ratio of the equivalent diameter of the catalyst particles to the hydraulic diameter of the

Pack was 4.7.

1A ₃ ) A type Bl-250.60 pack was used, ie with a specific surface of 250 m / m and an angle of 60 ° to the horizontal. 80% of the empty tube volume of the same could be filled with the catalyst particles mentioned above. The pack has a hydraulic diameter of 9.4 mm. The catalyst was very easy to insert and, in the dry state, also trickled out completely. The ratio of the equivalent diameter of the catalyst particles to the hydraulic diameter of the packing was 4.7.

In contrast, in the case of commercially available catalyst packs in which the catalyst is placed in pockets, for example of the Katapack type from Sulzer or Multipack from Montz, only 20 to 30% in exceptional cases can be filled with a maximum of 50% of the empty tube volume with catalyst.

Example 2 Pressure loss measurements

In a column section with a diameter of 0.1 m, pressure loss measurements were made with the test mixture nitrogen / isopropanol. For this purpose, the catalyst bed was introduced into the column section and sprinkled with a defined amount of isopropanol

(a drip point). In counterflow to this, a defined amount of nitrogen of passed upwards through the packing / fill. In the tests, the specific pressure loss per packing or bed height was measured and the flood point was determined. Γ-Al ₂ O full cylinders coated with 5% praseodymium oxide were used as catalyst particles. The solid cylinders (d = 1.5 mm, h = 1 - 4 mm) had an equivalent particle diameter of 2 mm. The specific pressure drop and the flood point of a bed placed in a structured packing were then determined.

Example 2, comparison

At a dumping height of 45 cm, an F-factor of 0.038 Pa ^Λ ° ' ⁵ (corresponding to a gas flow of 1000 1 / h) and a sprinkling density of 0.178 m3 / m ² h (corresponding to a liquid flow of 1.4 1 / h ) a specific pressure drop of 3.33 mbar / m was measured. The pack began to flood at a constant liquid load of 0.178 m ³ / m ² h from an F factor of 0.0575 Pa ^A ° ' ⁵ (corresponding to a gas flow of 15001 / h).

Example 2 according to the invention:

Filling introduced into two layers of a structured packing of the type BS-250.60 from the company Montz.

At a bed height of 46 cm, an F-factor of 0.038 Pa ^Λ ° ' ⁵ (corresponding to a gas flow of 1000 1 / h) and a sprinkling density of 0.178 m ³ / m ² h (corresponding to a liquid flow of 1.4 1 / h) a specific pressure drop of 1.09 mbar / m was measured. The pack began to flood at a constant liquid load of 0.178 m ³ / m ² h from an F factor of 0.114 Pa ^Λ ° ' ⁵ (corresponding to a gas flow of 30001 / h). The maximum gas load could thus be increased by a factor of 2 compared to the bed, which was not placed in a pack.

In the following, the calculation of the hydraulic diameter for a pack with rectilinear bends is illustrated with reference to FIG. 2:

The packing sheet 2 shown by way of example in FIG. 2 has rectilinear bends 5 arranged parallel to one another, which subdivide the packing sheet 2 into buckling surfaces 6. The width of a folding surface 6, measured from folding edge 5 to folding edge 5, is designated by a, the distance between two successive folding edges 5 by c and the height of the Crease with h. The hydraulic diameter of the gas flow for a packing constructed from such packing sheets is then calculated using the formula

, _ 2 c ^• h hydraulic, gas ~, -. c + 2a

Example 3 Catalyst Screening

3.1 Catalyst preparation

As a standard, the supported catalysts to be tested were manufactured by impregnating the pore volume. For this purpose, the carrier was impregnated with the active component in the form of a metal salt solution, dried in a drying cabinet at 120 ° C. and then calcined in air. Unless otherwise stated, the calcination is carried out for 2 hours at 450 ° C. with a heating rate of 3.5 ° C./min.

For the production of catalysts with praseodymium oxide as the active component, a praseodrymnihate stock solution consisting of 1170 g of praseodymium oxide, 2276 g of 65% nitric acid and 1557 g of water was used. This solution contained 18.1% by weight of praseodymium oxide and was then used in accordance with the liquid absorption of the support diluted with fully deionized water.

3.2 Catalyst screening

The aim of the catalyst screening was to find catalysts with a high space-time yield and thus high catalyst activity.

The catalyst screening was carried out in an apparatus consisting of a reservoir, a pump and a temperature-controlled metal tube reactor. A mixture of 79% by weight of acetone and 21% by weight of citral, with a mass flow of 200 g / h, was passed from the storage container from bottom to top with the aid of a pump through the tube reactor filled with 50 g of catalyst and heated at the same time. The reaction was carried out at 90 ° C. and 2.5 bar _abs . Sampling was carried out after 2, 4 and 6 h, the values obtained were averaged. 3.3 Evaluation

The samples were analyzed by gas chromatography (GC). The concentrations of the individual components were determined using an internal standard (N-methyl-pyrrolidone, NMP). The data of the analysis method can be found in the following table:

GC separation method for analyzing the conversion of citral and acetone to pseudo-ionone

GC system: HP5890 and 6890 separation column: HP5-025 film 30 m x 0.32 mm

Detector: FID temperature program: 60 ° C 1 min

60 → 150 ° C 10 ° C / min

150 → 200 ° C 20 ° C / min

200 ° C 10 min

200 → 240 ° C 10 ° C / min

240 ° C 5 min

Internal standard: 0.1 g NMP on 0.7 g sample

Components considered Name retention times

(Min)

Acetone 2.9

Mesityl oxide (2-methyl-2-pentene -4-one) 4.5

Diacetone alcohol (4-hydroxy-4-methyl-2 - 5.3 pentanone)

Citral 11.9

PseudoJonon 15.9

3.4 Variation of the catalyst carrier composition

All tested carrier materials for the catalyst support were each coated with 5% praseodymium oxide as an active component. The results listed in the table below were achieved by varying the catalyst support composition: The abbreviation BET in the table header describes the catalyst surface in a known manner according to the method of determination by Stephen Brunauer, Paul Emmett and Edward Teller, according to DIN 66131. RZA denotes the space-time yield in gPSJ / gKat / h, ie in grams of pseudo-ionone per gram of catalyst and hour.

Table 1:

The results in the table show that among the tested carrier materials, γ-aluminum oxide has by far the best space-time yield.

3.5 Variation of the catalyst carrier geometry

The abbreviations in the table header have the same meaning as listed in section 3.4 above. The determination of the space-time yields was also carried out under the same conditions as in 3.4, that is, when the catalyst supports were coated with 5% praseodymium oxide. The test results are summarized in the table below:

Table 2:

The results in the table show that the use of catalyst supports with a large ratio of outer surface to volume leads to catalysts with good space-time yields. The catalyst supports marked as comparison in the geometry of 4 mm and 3 mm strands show space-time yields <0.5 g pseudo-ionone / g catalyst / h (comparison tests in the first two rows of the table).

In contrast, the examples according to the invention in rows 3 to 9 of the table show that thinner strands smaller spheres and special geometries (trilobes, gears and honeycomb bodies), that is to say catalyst carrier geometries with a larger outer surface in relation to volume, improved space-time yields in the range of 0, 5 to 0.6 g pseudo ion g catalyst / h ..

3.6 Variation in praseodymium oxide content

γ-alumina strands with a diameter of 1.5 mm were coated with different levels of praseodymium oxide in the manner described under 3.1 above. The test results are summarized in Table 3 below.

Table 3:

The results of the table show that a maximum of the space-time yields with a praseodymium oxide coating is between 7.5 and 10% by weight. Higher occupancies again lead to a decrease in the space-time yield. This decrease in activity with higher occupancies was also evident optically: the originally slightly greenish color of the supported catalyst changed to brownish. Agglomeration of the praseodymium oxide particles could be responsible for this.

3.7 Varying the composition of the active component

Γ-alumina strands with a diameter of 1.5 mm were used as supports and were coated with active components in the manner described under 3.1 above. The nitrate solution of the corresponding metals was assumed in all cases, with the exception of zinc, which was used as the zinc acetate solution. In all cases, 5% of the active component was assigned.

The abbreviation LnO-Mix means a commercially available rare earth mixture from Rhone-Poulenc with the composition: 13.87% CeO ₂ / 7.69% La ₂ O ₃ / 1.65% PrO _x / 5.69% Nd ₂ O _3rd

The results are shown in Table 4 below.

Table 4:

Example 4 Preparation of Pseudojonon by Aldolization of Citral and Acetone

The experimental arrangement corresponded to the schematic representation in FIG. 4. The reactive distillation column 7 was in the separation zones 8 each filled with a segment of a structured tissue pack of the A3-500 type from the Montz company, each with a total height of 23 cm. The reaction zone 9 was equipped in the lower region thereof with a layer of Montz-Pak type B 1-1000 with a special element height of 30 mm. This layer served as a catalyst barrier so that the catalyst particles could not trickle into the lower separation zone. Three layers of Montz-Pak type B 1-250.60 with an element height of 212 mm were installed on this layer, into which the catalyst was introduced by pouring. 3121 g of catalyst with a bulk density of 700 kg / m ^{3 were} poured in. Solid cylinders made of 5% praseodymium on γ-Al ₂ O ₃ with a particle diameter of 1.5 mm and a height of 1 to 4 mm were used as the catalyst, which were obtained by impregnating γ-Al ₂ O ₃ with an aqueous solution of praseodymium. Nitrate and subsequent calcination were produced. The column was equipped with thermocouples and sampling points in regular sections, so that the temperature profile and the concentration profile in the column could be determined.

The reactants citral and acetone (streams I and II in FIG. 4) were metered into the reactive distillation column with mass flow control from storage containers standing on scales.

The bottom evaporator 10, which was heated to 124 ° C. with the aid of a thermostat, had a hold-up between 50 and 150 ml during operation, depending on the dwell time. The bottom stream III was level-controlled from the bottom evaporator 10 with a pump into a scale standing container required.

The top stream of the reactive distillation column was condensed out in a condenser 11 which was operated with a cryostat. Part of the condensate was fed via a reflux divider as stream IV into a storage tank standing on a balance, while the other part was fed as reflux to the column. The apparatus was equipped with a pressure control PC and designed for a system pressure of 20 bar. All incoming and outgoing material flows were continuously recorded and registered with a process control system PLS during the entire test. The apparatus was operated continuously, 24 hours a day. A stream 1 of 220.0 g / h, corresponding to 1.4 mol / h of citral with a purity of 97% and a stream II of 840.0 g / h, corresponding to 14.32 mol / h, were continuously introduced into the reactive distillation column 7 described above. h acetone preheated to 80 ° C with a purity of 99%.

Experimental Procedure

Solid cylinders (d = 1.5 mm, h = 1-4 mm) made of 5% Pr on γ-Al ₂ O _{3 were} used as catalyst in reaction zone 9. A system pressure of 3 bar and a return ratio of 3 kg / kg were set. The bottom temperature was 92.5 °. The bottom stream III of the column was 735.6 g / h of crude product with 62.14% by weight of acetone, 0.71% by weight of water, 0.45% by weight of mesityl oxide, 0.95% by weight of diacetone alcohol, 9.14% by weight of citral, 24.43% by weight of pseudo-ionone and 2.18% by weight of high boilers. At the top of the column, 323.2 g / h of distillate (stream IV) consisting of 95.8% by weight of acetone and 4.2% by weight of water were taken off.

Pseudojonon with a selectivity of 97.3% based on citral and 84.4% based on acetone was obtained. The yield was 66.7% based on citral.

At F factors of 0.12 Pa ^Λ ° ' ⁵ and sprinkling densities of 0.3 m ³ / m ² h, a differential pressure across the column of approximately 1 mbar was measured.

In contrast, when a random catalyst bed without packing was used, the double pressure loss was measured.

The differential pressure is a measure of the load (gas and liquid) of the column, depending on the material properties and the type of internals used, the differential pressure rises with increasing load until it floods. In the state of flooding, the catalyst is whirled up and severe catalyst abrasion can occur. This condition should therefore be avoided.

When using a packing according to the invention, a higher throughput can therefore be achieved with the same column diameter.

Claims

claims

1. Supported catalyst, containing one or more metal oxides as active components on a catalyst support, for carrying out a heterogeneously catalyzed

Aldol condensation, characterized in that the catalyst support is γ-aluminum oxide, that the active component comprises one or more oxides of the elements with atomic numbers 39 or 57 to 71 and that the concentration of the active component, based on the weight of the catalyst support, is in the range from 5 to 12% by weight.

2. Supported catalyst according to claim 1, characterized in that the concentration of the active component, based on the weight of the catalyst support, is in the range from 7.5 to 10% by weight.

3. Supported catalyst according to claim 1 or 2, characterized in that the geometry of the catalyst carrier is determined such that the ratio of the outer surface to the volume in the range from 0.5 to 10 mm ^"1 , preferably from 1 to 5 mm ^{" 1} lies, preferably that the catalyst carrier is in the form of full or hollow cylinders, spheres and honeycomb bodies, trilobes or gears.

4. Supported catalyst according to one of claims 1 to 3, characterized in that the active component is yttrium oxide.

5. Supported catalyst according to one of claims 1 to 3, characterized in that the active component is praseodymium oxide.

6. Column for carrying out an aldol condensation by reactive distillation in the presence of a heterogeneous particulate catalyst with a packing or packing which form gaps in the interior of the column, characterized in that the quotient of the hydraulic diameter for the gas flow through the packing or the packing and the equivalent diameter the catalyst particles are in the range from 2 to 20, preferably in the range from 5 to 10, in such a way that the catalyst particles are loosely introduced, distributed and discharged into the interstices under the action of gravity, and that the catalyst particles are obtained from a supported catalyst according to one of the Claims 1 to 5 are formed.

7. Column according to claim 6, characterized in that the packing is a structured packing, preferably a cross-channel packing.

8. Column according to one of claims 6 or 7, characterized in that the packing or the Füllköφer have horizontal areas.

9. Column according to claim 8, wherein the packing is formed from packing sheets for vertical installation in the column, with rectilinear bends which subdivide the packing sheet into buckling areas, characterized in that the angle of inclination of the buckling faces to the horizontal in the range from 90 to 45 °, preferably at 60 °.

10. Column according to one of claims 6 to 9, characterized in that the packing or the Füllköφer have a reduced flow resistance on their surface, preferably by perforations and / or roughening of the material of the packing or the Füllköφer or by forming the packing as expanded metal.

11. Column according to one of claims 7 to 10, characterized in that the packing is formed from corrugated or kinked layers, and that a flat intermediate layer is arranged between two corrugated or kinked layers, the flat intermediate layers not extending up to extend the edge of the pack or have increased gas permeability, in particular holes, in the edge zone of the pack.

12. Column according to one of claims 7 to 11, wherein the packing is formed from packing sheets for vertical installation in the column, with rectilinear bends which subdivide the packing sheets into buckling areas and which have a width a to be measured from buckling edge to buckling edge and perforations, characterized in that a proportion X of at least 60% of the perforations has a distance b of at most 0.4 a to the lower fold edge of each fold surface.

13. Process for the production of pseudojonon by aldolization of citral and

Acetone by reactive distillation in a column according to one of claims 6 to

12, characterized in that the column is operated with regard to its gas and liquid loading in such a way that a maximum of 50 to 95%, preferably 70 to 80% of the flood loading is achieved.

4. A process for carrying out a heterogeneously catalyzed aldol condensation by reactive distillation in a column according to one of claims 6 to 12, characterized in that the supported catalyst when the initial catalyst activity has decreased by treatment with an aqueous alkaline solution, in particular with an alkali metal, alkaline earth metal or ammonium hydroxide solution.