DD292149A5 - TRAITERS FOR CATALYSTS TO CARRY OUT OXIDATIVE PARALLEL CONSECUTIVE REACTIONS - Google Patents

Abstract

Support for catalysts for carrying out oxidative parallel-consecutive reactions, in particular for silver-supported catalysts for the selective oxidation of ethene to ethene oxide with improved selectivity and activity, by carriers with a porosity of 30 to 80%, a surface area of 0.01 to 10 m2 g 1 and bimodal pore volume distribution with a proportion of invention less than 60% of the total pore volume in the range of pore diameters of 20 to 100 microns are used. The mean pore diameter of the carriers is in the range of 30 to 150 micrometers, preferably in the range of 70 to 120 micrometers. The partial volume of the pores with less than 20 micrometers pore diameter is negligible. {Katalysatorträger; Traegerkatalysator; Pore volume; Pore volume distribution; Pore diameter; oxidative parallel-consecutive reaction; Silver Traegerkatalysator; Selective oxidation; ethene oxide; Surface; Total pore volume}

Description

The invention relates to supports for catalysts for carrying out oxidative parallel-consecutive reactions, especially for supported silver catalysts for the selective oxidation of ethene to ethane oxide.

Characteristic of the known state of the art

The preparation of supports for silver-supported catalysts for carrying out oxidative parallel-consecutive reactions, especially the direct gas phase oxidation of ethene and oxygen to ethene oxide, depends in its approach on many factors, the requirements of the manufacturing technology itself, but above all the necessary properties of the catalyst support to be produced.

In order to significantly influence the properties of the carrier a significant contribution to increasing the

To achieve the performance of the catalyst prepared from the carrier, the requirements for the carrier material in Regarding mechanical and thermal loadability, but especially with regard to the design of the pore system of the

Support, to adapt the conditions of the reaction and the technology of the technical implementation of this reaction meaningful.

In the case of carrying out the above-mentioned reaction on supported silver catalysts, which are generally prepared by impregnating the catalyst support with silver salt solutions, it is known that carriers having a low internal surface area are advantageous for these catalysts, because thereby the residence time of the reactants and reaction products and thus the selectivity of the reaction is favorably influenced.

Furthermore, it is known that other texture data of the carrier, such as pore volume and distribution of the pore volume to different pore radius ranges, an important prerequisite for ensuring the effectiveness of the catalysts used (DE-OS 1542229, DE-OS 1542204, DE-AS 1260451, DE -OS 2359496).

A known method (DE-OS 2,729,918) describes for said carrier a bimodal pore volume distribution, as it is also known and desired for catalyst support with other uses, since the special type of pore volume distribution (more than 70% of the total pore volume accounts for the pores with smaller diameters up to a maximum of 20 microns) in many cases has a favorable effect on the reaction behavior of such catalysts.

However, the low surface area catalyst supports described therein have the disadvantage that this proportionate distribution of the total pore volume to the pore regions of different diameters does not correspond to the distribution which allows for the highest possible performance of the catalysts.

Generally, for the preparation of low surface area supports, inert, refractory materials (a-

Alumina, silica, silicon carbide, etc.) and mixtures thereof. These materials constitute the base substance of the carrier (hereinafter referred to as a scaffold former).

In order to ensure the mechanical strength of the shaped supports and to maintain the porous structure, binders are added to the skeleton former. For example, DE-OS 1936233 describes the use of temporary and permanent binders, the temporary binders constituting organic compounds of mostly polymeric structure which are easily, i. H. far below the melting temperature of the scaffold former and the other ceramic constituents, thermally decompose.

In addition, it is possible to use the temporary binders to improve the porosity of the carrier.

In contrast, the permanent binders are inorganic clay-like substances with melting temperatures close to the melting temperature of the skeleton former, which are not thermally destroyed by the carrier production and ensure the cohesion of the carrier components in the final state of the carrier production.

It is also known that the processing of the mixture of all constituents of the carrier mass with the addition of water as Means for producing a good mouldable, pasty mass takes place. This is followed by the shaping, the drying and the High temperature firing of preformed beams ... Influence on the texture of the support is generally determined by the selection of the grain size of the scaffold used

and the setting of the proportion of temporary binder limited possible. Also, the mixture to be processed may be added to a thermally decomposable pore builder. As a result, however, the mechanical strength of the end product is negatively affected, so that the use of this component is limited and requires accurate quantitative .Dosierung. Despite these possibilities of influencing the pore system in the carrier, it has hitherto not been possible to produce a bimodal pore volume distribution with great variability of the volume fractions in the range of pore diameters of 20 to 100 microns and larger in the carrier.

Object of the invention

The aim of the invention is to substantially improve the performance parameters of supported silver catalysts in the performance of oxidative parallel-consecutive reactions in terms of selectivity and activity through the texture of the catalyst support.

Explanation of the Wesans of the invention The invention is based on the object of providing a support for catalysts for carrying out oxidative para-consecutive Reactions, especially for supported silver catalysts for the selective oxidation of ethene to ethenoxide with a porosity of 30

to develop 80%, a surface of 0.01 to 10m ² g ~ 'and a bimodal pore volume distribution.

The object is achieved in that the carrier in the pore range vonf 20 to 100 microns Pore diameter has a share of the total pore volume of up to 60% and the average pore diameter in the Range of 30 to 150 microns, preferably in the range of 70 to 120 microns. In its manufacture, a temporary binder whose decomposition temperature is higher than 373 K and a pore-forming agent

added at a decomposition temperature less than 373K.

Furthermore, the starting mixture, hereinafter referred to as standard offset, water in amounts of 10 to 20%,

based on the mass of the standard offset added. The drying temperatures of the support material are chosen to be greater than 373K and below the decomposition temperature of the temporary binder. The prepared supports have a bimodal pore distribution in which the smaller pores have a diameter of 20 to 100 microns and a total pore volume fraction of less than 60%, preferably less than 50% and where the average pore diameters are in the range of 30 to 150 microns, preferably in the range of 70 to 120 microns.

The determination of the carrier surface by means of cryogenic nitrogen adsorption by the BET method, the Determination of the pore volume and the pore volume distribution by means of high pressure mercury and Quecksilberniederdruckporosimetrie.

The process of carrier preparation involves mixing the standard admixture with all other components of the mass to be molded (including water), shaping, drying the blanks and high temperature firing.

The drying may optionally follow a post-processing for shaping. For the preparation of the standard offset, a scaffold former is used which consists of a-alumina or other inert and

heat-resistant materials. The other component of the standard offset is the permanent binder which contains kaolin and / or finely divided a-alumina and / or finely divided silicurrent dioxide. The ratio of

Scaffolding agent to permanent binder is 5.58: 1.

This standard offset is contacted in the first step, the mixing, with a temporary binder (maximum 1% based on the mass standard offset) consisting of, for example, a 10% aqueous solution of polyvinyl alcohol. A further addition of water has to be made below taking into account the water concentration contained in this amount of solution, the total content of which may be between 10 and 20%, based on the mass standard offset. The further added pore former consists of foamable polystyrene granules in a grain size of 200 to 300 micrometers.

The mixture is followed by the shaping of the carrier, whose external shape is not important for the production, and the drying of the moldings. If this is carried out at room temperature, the supports baked at 1823 K, depending on the proportion of the pore former, show a proportion of the total pore volume of 20 to 28% in the range of pore diameters of 100 to 1000 micrometers. The pore volume fractions in the range of smaller than 20 microns in diameter were negligible as with all other prepared supports. As the proportion of pore-forming agent increases, the pore volume fraction in the area of the pore diameters greater than 100 microns increases, whereas in a carrier without pore-forming material, the vast majority of the total pore volume is located in the diameter range of 20 to 100 micrometers.

A further increase of the pore builder is above 9.85%, based on the mass standard offset, has a destruction of the bimodal ^D orenvolumenverteilung and an undesirable increase in the total pore volume result.

In contrast, the use of drying temperatures above 373K and below the decomposition temperature of the temporary binder results in a further increase in the pore volume fraction in the pore diameter greater than 100 microns diameter, while the proportion is reduced in the range of 20 to 100 microns without the content of

Pore former must be increased, with a bimodal pore distribution is maintained. A further enlargement of the pore volume fraction in the range of the diameter of the pores becomes larger 100 micrometers

possible in that a part of the skeleton former, with a constant total mass of the standard offset, is used with coarser grit. The increase in the proportion of coarse skeleton builder is also limited, since this leads to a reduction in the pressure and abrasion resistance.

If, on the other hand, a very finely divided scaffold former is used, a carrier is produced under the new production conditions

with bimodal pore volume distribution with a high pore volume fraction in the range of pore diameters smaller than 20 micrometers, while greater than 100 micrometers no significant pore volume fraction occurs. In contrast to used

Scaffolding agent and pore former has the temporary binder, due to the gegegen proportion of the total mass of

processed material, a negligible influence on the design of the pore system in the carrier.

The prevention of thermal decomposition of the temporary binder during drying by the use of Drying temperatures, which are below the decomposition temperature of this component, is after all for the

described support produced by the method described in the carrier produced texture is stabilized by the temporary binder and a high dry breaking strength of the carrier moldings is ensured in the drying subsequent transport and processing processes to high-temperature firing.

By this production method carriers are obtained, which have a bimodal pore volume distribution with great variability of the pore volume fractions in the range> pore diameter of 20 to 100 micrometers and in the range greater than 100 micrometers. Total pore volume and surface area of the new carriers are comparable to those of conventional carriers. The preparation of the catalysts from the said problems is carried out, for example, by the impregnation method by simultaneous application of the active component and a modifier to the support and subsequent activation under reductive conditions and / or temperature treatment.

The described setting of the pore volume fractions of different radii ranges in carrier materials according to the invention results in a significantly higher selectivity at higher or constant activity resulting from a favorable ratio of reaction and transport pores for the catalysts prepared therefrom.

An increase in the proportion of the total pore volume over 60% in the pore region of 20 to 100 microns pore diameter

the selectivity of the catalysts deteriorates considerably, while the activity is only slightly affected if a not significantly lower total pore volume is present.

Occur in the catalyst pores with diameters of less than 20 microns in non-negligible proportions Total pore volume and is a proportion of more than 70% of the total pore volume in the range of 20 to 100 microns Pore diameter localized, this leads to a further reduction despite preservation of the bimodal volume distribution

the selectivity.

This selectivity decrease continues when catalysts are used whose pore volumes are completely in the Pore range from 20 to 100 microns in diameter and thus have no bimodal pore volume distribution. From the relatively small proportions of the total pore volume in the pore range of 20 to 100 micrometers in diameter

result for the catalysts average pore diameter of preferably 70 to 120 microns.

embodiments

The following examples serve to further illustrate the invention. For the preparation of the supports A to F, a standard offset with constant mass ratio of scaffold to permanent binder of 5.58: 1 was used. The permanent binder was based on mass concentration of 65.8% kaolin, 24.6% a-alumina and 9.6% silica with particle sizes less than 10 microns. As a temporary binder, a 10% aqueous solution of polyvinyl alcohol was used. The scaffold former formed a-alumina. The mass fractions of the various grain sizes of the α-A'uminiumoxids are listed in the examples.

In all cases, 15% of water, based on the mass of standard offset, was added to the mixture of the components. The indication of the amounts of added pore former of foamable polystyrene granules also refer to the mass of the standard offset, this component was used with a grain size of 200 to 300 microns. The duration of drying was uniformly 120 minutes. The high temperature firing took place with a heating up period of 500 minutes at 1823K and a 180 minute hold time.

To prepare the described supported silver catalysts A to F, the carrier materials were impregnated with 15% silver, based on the total mass and 1% barium oxide, based on molar concentration of silver, according to a uniform method, wherein in Examples 1 and 2 inventive carrier (catalysts A and B) and in the comparative examples 1 to 4 non-inventive carrier (catalysts C to F) used νmden.

For this purpose, the corresponding amount of barium was dissolved as carbonate in 27.1 grams of lactic acid. After adding 5 Milliliters of 30% hydrogen peroxide solution 19.0 g of silver oxide were added so that the temperature of the mixture 363 K

not exceeded.

After complete dissolution of the silver oxide by heating on a boiling water bath, 100 g of the carrier with the

soaked in a yellow, clear solution. There remained no solution residue. The impregnated carrier was dried at 383K for 4 hours.

Activation was carried out by annealing the dried product for 4 hours at 573K and 673K, respectively. example 1 A carrier A was produced:

Scaffolding agent: 17.3% a-alumina 90 to 110 microns grain size 82.7% a-alumina 50 to 70 micron grain size Pore binder: 9.85% polystyrene granules, by mass Standard offset Drying temperature: 398K Texture analysis revealed: pore volume : 0.239 cm ³ g " ¹ Porosity: 61% Water absorption: 34.0% mean pore diameter: 109.9 microns

The pore distribution was bimodal. The smaller pores in the pore diameter range of 20 to 100 microns had a share in the total pore volume of 35.2%.

Example 2 The preparation of the carrier B was carried out with:

Scaffolding agent: 9.8% a-alumina aggregate of 90 to 110 microns 90.2% a-alumina of granules. 50 to 70 microns pore former: 9.85% polystyrene granules. based on mass standard offset Trocknungsstempelütur; 398K following texture data were determined: pore volume: 0 239cm ³ g "'Porosity: 61% Water absorption: 34.0% mean pore diameter: 110.0 microns

The proportion of the volume in the range of pore diameters of 20 to 100 microns was determined to be 48.8%. The pore distribution was bimodal. ''

Comparative Example 1 The preparation of the carrier C was carried out with: Scaffold Primer: 100% alumina of grain size 50 to 70 microns Pore former: 9.85% polystyrene granules, based on mass standard offset Drying temperature: 293K The following texture data was determined: Pore volume: 0,239cm ³ / g

Porosity: 61%

Water absorption: 34.0%

average pore diameter: 60.4 microns

The pore volume fraction in the region of the pores of 20 to 100 micrometers was 6.62%. The distribution was bimodal. Verglelchsbelspiel 2 The preparation of the carrier D was carried out with: Scaffolding agent: 100% a-alumina, grain size 60 to 70 microns Pore former: 5.70% polystyrene granules, based on mass standard offset Drying temperature · 293K The determination of the texture data showed: Pore volume: 0,299cm ³ g ~ '

Porosity: 58.4%

Water absorption: 32.5%

average pore diameter: 69.3 microns

The pore volume distribution was bimodal. In the range of pore diameters of 20 to 100 microns, the carrier D contained

79.9% of the total pore volume.

Comparative Example 3 A support E was prepared as follows without the addition of pore formers:

Scaffolding agent: 100% a-alumina, grain size 50 to 70 microns Drying temperature: 293K The texture data had the following values:

Pore volume: 0,199cm ³ g "'

Porosity: 51.0%

Water absorption: 28.0%

mean pore diameter: 50.2 micrometers The pore volume distribution was not bimodal, the carrier had no significant partial pore volume in the range of pore diameters smaller than 20 micrometers.

Comparative Example 4 Carrier F was prepared as follows: Scaffolding agent: 23.4% a-alumina, grain size 50 to 70 microns

76.6% a-alumina, grain size 10 to 20 microns

Pore former: 5.70% polystyrene granules, based on mass standard offset Drying temperature: 293 K The determination of the texture data showed: Pore volume: 0,232cm ³ g ^"1

Porosity: 59%

mean pore diameter: 2.52 microns

The pore volume distribution was bimodal. The total pore volume fraction in the range of the diameter of the pores from 20 to

100 microns was 29.1%. In the range above 100 microns pore diameter, the support had no significant

Partial pore volume on. 70.9% of the total volume was located in the range of pore diameters less than 20 microns.

The catalysts obtained from the described supports were tested in an oil-heated integral reactor with a tube of 0.5 m length and 21 mm inner diameter under the following conditions:

Catalyst 10 ~ ³ kg: 80 Total pressureMPa: 2,0 '· Gas load I · tr ¹ : 200

Test gas composition (volume concentration) Oxygen / o 7.0

Ethene% 15.0

Nitrogen / o 78.0

1,2-dichloroethane ppm 1.0

The calculation of conversion and selectivity was carried out from the gas chromatographically determined composition of the reaction gases.

To characterize the activity, the temperature of the heat transfer oil T _K at an ethene conversion of 10%, based on Mole Ethen, consulted. The ethene oxide - related selectivity S. pertains to the same ethene conversion Test results of these catalyst samples are given in Table 1 after 200 hours running time.

Table 1 Catalyst

A B c D E F

Kühlöltempe- selectivity Pore volume fraction MtUrT * Molar concentra the pore diameter K % in% from 20 to 100 micro meter at the total pore volume % 478 79 35.2 481 77 48.8 469 72 66.2 488 70 79.9 485 68 - 485 74 70.9

Claims (2)

1. Support for catalysts for performing oxidative parallel-consecutive reactions, especially for supported silver catalysts for the selective oxidation of ethene to ethene oxide with a porosity of 30 to 80%, a surface area of 0.01 to 10m ² g ~ ¹ and a bimodal pore distribution , characterized in that the carrier in the pore region of 20 to 100 micrometers pore diameter has a proportion of the total pore volume of not more than 60% and the average pore diameters in the range of 30 to 150 micrometers. 2. A carrier according to claim 1, characterized in that the average pore diameter in the range from 70 to 120 microns.
Application blot of the invention