DE102005023955A1 - Inert material for use in exothermic reactions - Google Patents

Abstract

The invention provides an inert material for use in exothermic reactions containing alpha-Al¶2¶O¶3¶ in the form of hollow cylinders or ring tablets. Objects of the invention are furthermore a process for the preparation of such inert materials and their use in exothermic gas phase reactions.

Description

The invention relates to the use of alpha-alumina (α-Al ₂ O ₃ ) in the form of hollow cylinders or ring tablets as inert material in exothermic reactions.

inert materials are used in exothermic reactions to remove heat to reduce the training of so-called hot spots. The use of inert materials in exothermic reactions in a fixed bed is necessary there when using a undiluted Catalyst at the beginning of the catalyst bed due to the high reaction rate a big heat becomes free. The formation of hot spots is to be avoided as they lead to one the selectivity the reaction unfavorable can influence and on the other to a faster deactivation of the catalysts to lead. Towards the end of the reaction, d. H. when most of the reactants are consumed is (at the end of the catalyst bed), will not be big heat more free. Therefore, in the fixed bed process according to the prior art a catalyst bed with graded activity profile used, with the activity the catalyst bed increases in the flow direction. This is usually achieved in that the catalysts with a graded content on active components and optionally with selectivity promoters be provided. additionally this is in the reactor sections in which the driving force of the Reaction is still very high, d. H. usually at the beginning of the bulk, with chemically inert materials, e.g. B. broken graphite, tabletted or extruded graphite powder, diluted (US-A-3184515, US-A-2866830). Also known as inert materials are silicon carbide, silicon dioxide, Aluminum oxides or glass, usually in tablet, strand or Ball shape can be used.

in the The range of fixed bed oxychlorination catalysts are commonly Graphite tablets used as "diluent".

Of the Use of inert diluent materials However, brings as a major disadvantage an increased pressure loss with him, in particular negative pressure loss catalyst shaped bodies negative affects as it substance and heat transport obstructed in the axial direction. The increased pressure loss also leads to a higher one required Compressor capacity, reducing the maximum load capacity of the catalyst bed, which ultimately leads to a lower productivity of the reactor and has a limiting effect on the capacity of the plant.

A too much dilution the active component on the carrier material is also not cheap because This severely affects the onset of the reaction.

The use of unimpregnated catalyst support material is not advantageous. So z. For example, the gamma-alumina (γ-Al ₂ O ₃ ) commonly used in oxychlorination has a high active surface area and is not inert. This negatively influences the selectivity of the reaction. The attenuation of the carrier activity by impregnation with alkali metals is z. As described in US-A-5202511, but leads to significantly higher cost of the inert material.

In order to avoid the selectivity disadvantages when using γ-Al ₂ O ₃ , according to the prior art it is also possible to use α-Al ₂ O ₃ which has only a small active surface area. α-Al ₂ O ₃ is usually used in the form of extruded strands or cylinders or in spherical form as a diluent material. However, these materials - in addition to the above-described problem of undesirable pressure drop - increased material abrasion, which requires only a short service life in the reactor.

The The object of the invention was thus to provide a alternative inert material that has a lower pressure drop caused, therefore, the capacity the system can be further increased. This is the material abrasion be kept low.

The object has been achieved according to the invention by using α-Al ₂ O ₃ in the form of hollow cylinders or ring tablets as the inert material.

The invention thus provides an inert material for use in exothermic reactions containing α-Al ₂ O ₃ in the form of hollow cylinders or ring tablets. Objects of the invention are still a Process for the preparation of such inert materials and their use in exothermic gas phase reactions.

It has now been found that by calcination of tableted γ-Al ₂ O ₃ rings at over 900 ° C rings of α-Al ₂ O ₃ can be obtained, in which the properties of low pressure drop of the ring geometry with a high mechanical strength combine. The pressure loss can be further reduced if γ-Al ₂ O ₃ rings with rounded, z. B. kalottierten, faces are used as a catalyst support material, which have already shown positive effects on the pressure loss.

The inert material according to the invention contains α-Al ₂ O ₃ in the form of hollow cylinders or ring tablets. Advantageously, the outer diameter (D _A ) of the molded body is 1 to 20 mm, preferably 2 to 10 mm and particularly preferably 3 to 7 mm, in particular 4 to 6 mm. The inner diameter (D _I ) of the moldings (diameter of the inner hole) advantageously has 0.1 to 0.7 times the outer diameter, preferably 0.3 to 0.7 times and more preferably 0.35 to 0.55 times the outside diameter. The height (H) of the shaped bodies is advantageously 0.2 to 2 times, preferably 0.3 to 1.8 times, more preferably 0.6 to 1.4 times the outer diameter.

In particularly advantageous embodiment have the hollow cylinder or ring tablets rounded, z. B. calved, faces on. The radius of curvature the faces (R) is while 0.01 to 0.5 times, preferably 0.05 to 0.4 times and more preferably 0.1 to 0.2 times the outer diameter.

The hollow cylinder according to the invention or ring tablets advantageously have a shape, in the cross-section of the outer wall surface (outer edge) and the inner wall surface (Edge of the inner hole) largely flat and arranged parallel to each other are. The faces can be flat or rounded. Preferably, the end faces are continuous so rounded that - along of the inner hole - itself the catalyst body both from the outer edge as well as tapered from the edge of the inner bore ago. It can be between the curvature the faces and the outside and the inner edge form a visible edge.

The inert material according to the invention advantageously has a content of α-Al ₂ O ₃ of at least 50 wt .-%, preferably greater than 80 wt .-%, more preferably greater than 90 wt .-% and particularly preferably greater than 95 wt .-%, on , Other types of alumina may also be included, such as delta-alumina (δ-Al ₂ O ₃ ), theta-alumina (θ-Al ₂ O ₃ ), γ-Al ₂ O ₃ or pseudo-boehmite, all in amounts of at most 50 wt .-%, preferably up to 20 wt .-%, particularly preferably up to 10 wt .-% and in particular not more than 5 wt .-%. In addition to the aluminum oxides, the inert material may also contain traces of other elements, such as Ti, Fe, Na and Si, which should then each lie at most in the 10 to 1000 ppm range.

The moldings according to the invention advantageously have a BET surface area of less than 50 m ² / g, preferably less than 20 m ² / g and particularly preferably less than 10 m ² / g.

The Side crushing strength of the inert materials according to the invention is advantageously at least 15 N, preferably 25 to 250 N, particularly preferably 50 up to 200 N, the mechanical abrasion resistance advantageously less than 20% by weight, preferably less than 5% by weight, and especially preferably less than 2% by weight.

The Determination of lateral compressive strength is carried out as follows: The moldings be with between two parallel plates on the shell side with Increasing force loads until breakage occurs. The at the break of the moldings registered force is the lateral crushing strength. Out of a good one mixed sample are measured 25 moldings in this way and the average value is determined.

Of the Abrasion test is performed according to ASTM D4058-81.

The inventively formed inert materials can be obtained by tableting a high surface area γ-Al ₂ O ₃ and / or δ-Al ₂ O ₃ and / or θ-Al ₂ O ₃ with subsequent calcination at high temperatures. In this case, there is a conversion of the alumina modifications used in α-Al ₂ O ₃ . The various forms of alumina can be used pure or in any mixtures with each other.

In the starting material used in the tabletting, the high surface area γ-Al ₂ O ₃ , δ-Al ₂ O ₃ and θ-Al ₂ O _{3 may} also be wholly or partly by further aluminum modifications, such as chi-alumina (χ-Al ₂ O ₃ ) or Compounds of the precursors of these aluminas, such as pseudoboehmite, are replaced, which also convert after calcination in the desired α-Al ₂ O ₃ .

Besides can also usual Tableting aids, such as graphite or magnesium stearate, be added to the starting material to be tabletted. Usually Be tabletting mixtures, the magnesium stearate in an amount from 0.5 to 7 wt .-%, preferably from 2 to 5 wt .-%, or graphite in an amount of from 0.5 to 3% by weight, preferably from 1 to 1.5% by weight, in each case based on the total mass of the mixture, used. The various Tablettierhilfsmittel can be pure or in any Mixtures are used with each other.

The Tablettierung to the above-described hollow cylinders or Ring tablets are used in a known manner the usual Press. The pressing force is preferably more than 9 kN, more preferably between 9 and 11 kN.

To the tablets are tableting at temperatures preferably above 900 ° C, in general between 1000 and 2000 ° C, more preferably between 1000 and 1500 ° C and especially at 1100 to 1400 ° C, calcined. The calcination process is usually over 0.5 to 10 h, preferably over 1 to 2 hours. The calcination can be carried out in an oxidizing or inert atmosphere are preferred, in an oxidizing atmosphere, generally in the air, worked. Calcination can be done dormant or agitated.

It is also possible to use α-Al ₂ O ₃ directly as starting material for producing the hollow cylinders or ring tablets according to the invention. The Tablettiermischung can optionally also - as described above - Tablettierhilfsmittel be added. In this case, after the tableting of the alpha-alumina Nachkalzinierung of the material can take place. This Nachkalzinierung is advantageously carried out between 400 and 1500 ° C, preferably between 500 and 1300 ° C for 0.5 to 10 hours, preferably for 1 to 2 hours.

By the preparation described become chemically inert diluent materials obtained when used in chemical reactions a small Create pressure loss and have a high mechanical stability.

The Inventive inert materials are particularly suitable as a diluent for catalysts in exothermic reactions. Advantageously, they are exothermic Oxidation reactions, particularly preferred in oxychlorination reactions of olefins and especially preferred for oxychlorination of ethylene to 1,2-dichloroethane used. You can but also, for example, in the production of acrylic acid, phthalic anhydride or maleic anhydride find advantageous use or even in the dehydration of Alkanes to alkenes, for example the reaction of propane to propene or butane to butene or butadiene.

The Invention will be explained in more detail with reference to the following examples, without However, this is to make a corresponding limitation.

Example B1

ine dry mixing of 6 kg γ-Al ₂ O ₃ (Puralox SCF a230, Fa. Sasol), 4 kg of pseudoboehmite (Pural SCF, Fa. Sasol), 324 g of magnesium stearate and 100 g of graphite were added to ring tablets with dimensions of 7 mm × 7 mm × 3 mm (height × outer diameter × diameter of the inner hole) and then calcined at 1300 ° C. for one hour. The physical properties of the material are given in Table 1.

Example B2

A dry mix as described in B1 was made into ring tablets of dimensions 5mm x 5mm x 2.5mm (height x outer diameter x diameter of the inner hole) and end surfaces rounded equally to the outer edge and rim of the inner bore, the radius of curvature of the End faces (R) 0.8 mm, tableted and then calcined for one hour at 1300 ° C. The physical properties of the material are given in Table 1.

Comparative Example C1

graphite was added to 5 mm × 5 mm tablets with sugar as tabletting aid shaped. Subsequently was by calcining at 500 ° C the tool burned out.

Comparative Example V2:

The Tablets of V1 were transferred to chippings of 1 to 3 mm in size.

Comparative Example C3:

Ring pellets were made according to B1, with the calcining step being carried out at only 700 ° C. Copper and potassium chloride (6% by weight Cu, 2% by weight K) were impregnated onto this support material after water absorption and dried at 120 ° C. This represents a typical oxychlorination catalyst on γ-Al ₂ O ₃ .

Comparative Example V4:

Ring pellets were made to B2, with the calcination step performed at only 700 ° C. Copper and potassium chloride (6% by weight Cu, 2% by weight K) were impregnated onto this support material after water absorption and dried at 120 ° C. This represents a typical oxychlorination catalyst on γ-Al ₂ O ₃ .

The following table summarizes some physical data of the moldings produced. Table 1: Physical data

The pressure drop measurements were determined in a glass tube with 2.5 cm diameter on a meter bulk length. An N ₂ stream at 2 bar was used. A diameter of 2.5 cm is typical of reactor tubes in industrial shell-and-tube reactors for highly exothermic, heterogeneously catalyzed gas phase reactions, such as the oxychlorination of ethylene to dichloroethane. The results are summarized in Table 2. In order to obtain very homogeneous beds in the test, the moldings were added slowly via a funnel so that the moldings successively and practically fell individually on each other. In the case of mixtures of inert material with shaped catalyst bodies in a ratio of 1: 3, the mixtures were homogenized in a slowly rotating drum. In this way, the mixtures V1 + V3, B1 + V3, V1 + V4, V2 + V4, B1 + V4 and B2 + V4 listed in Table 2 were prepared and measured. Table 2: Relative pressure drop Δp to 1 m bulk length at 2.5 cm pipe diameter in the N ₂ stream at 2 bar. The fields in which "not measurable" mean that at these flow velocities the bed already lifts, so that the pressure loss can not be determined.

Out From the table it can be seen that the pressure loss of the inventively prepared Inert materials is significantly lower than conventional Systems, such as the graphite tablets. Also in mixture with the actual catalysts are significantly lower Pressure losses than with other moldings.

Claims (9)

Inert material for use in exothermic Reactions containing alpha alumina in the form of hollow cylinders or ring tablets. Inert material according to claim 1, characterized in that the content of alpha-alumina at least 50 wt .-% is. Inert material according to claim 1 or 2, characterized in that the BET surface area is less than 50 m ² / g. Process for the preparation of inert material according to the claims 1 to 3, characterized in that gamma-alumina and / or delta-alumina and / or theta-alumina hollow cylinder or ring tablets Calcination in inert alpha-alumina hollow cylinder or -ring tablets are transferred. Method according to claim 4, characterized in that the calcining is carried out at over 900 ° C. Use of the inert material according to one of claims 1 to 3 for exothermic Gas phase reactions. Use of the inert material according to one of claims 1 to 3 for oxidation reactions. Use of the inert material according to one of claims 1 to 3 for oxychlorination reactions. Use of the inert material according to one of claims 1 to 3 for the oxychlorination of ethene to 1,2-dichloroethane.