DD248108B5 - PROCESS FOR PREPARING PRACTICALLY PURE RHO ALUMINUM OXIDE - Google Patents

Description

This object is achieved by aluminum trihydroxides according to the invention are transported with average secondary particle sizes between 0.1 and 45μπι in a conventional manner by means of a carrier gas stream through a tubular reactor, wherein

- Linear flow velocities of the carrier gas from 5 to 2OmVs

- Temperatures from 673 to 973 K and

- Mean residence times in the reaction zone of 0.1 to 10s can be adjusted.

It is particularly advantageous when working in the reaction zone at solids concentrations between 0.3 and 10kg / m ³ and moisture contents of 10 to 75Ma .-% water, or water vapor partial pressures between 10 and 75kPa. The inventive method can be carried out only in an apparatus that has no stationary heat carrier. The solution according to the invention leads to a virtually pure p-aluminum content or X-ray amorphous aluminum oxide with very high chemical reactivity of the aluminum oxide. The intermediate products of the catalyst preparation obtained in this way can be prepared well and further processed. They are comparable in their purity or chemical composition with those which are prepared by complex solution-precipitation process.

embodiments Example 1 (comparative example, not according to the invention)

An unground g hydrargillite having an average secondary particle size diameter of 50 to 80 μm , a 1063K firing residue of 65.3% by weight, a specific surface area of 0.5m ² .gamma. Porosity of 1.9% and a solubility in caustic soda (Chemical reactivity) of 14.7% by weight, is briefly thermoshock treated in a reactor with 5 separately heatable reticulated individual segments, wherein air was used as the carrier gas and a solids-gas ratio of 0.3 kg · Nm ^{-3 are} selected in order to be able to continuously transport the hydrargillite in finely dispersed form through the reactor. The process is carried out in an apparatus having a stationary solid heat carrier. The brief thermal shock treatment was carried out at a temperature in the reaction zone of 823 K and a mean residence time of the solid particles of 0.2 s, which is divided into a heating time of the particles of 0.135 s and a reaction zone of 0.065s. The degradation product obtained is characterized by the following properties:

- Glue residue 82.7Ma .-% at 1073 K.

- Surface area 275 m ² · g ' ¹

Porosity 28.6%

Solubility in NaOH 43Ma .-%.

The surface-rich aluminum oxide to be characterized by X-ray analysis as p or Y-Al ₂ O ₃ still contains small amounts of hydrargillite and traces of boehmite. It is characterized in particular by a pronounced "ink-bottle" pore shape.

Example 2 (according to the invention) A hydrargillite with a mean secondary particle size between 0.1 and 10μπη and a specific surface area of about

1 Omvg was subjected to a thermal shock treatment under the following conditions

- average residence time in the reaction zone 0.2 s

- average temperature in the reaction zone 923 K.

- mean linear flow velocity of the carrier gas 18.5m / s.

The reaction product obtained after this treatment is practically pure high reactivity p-alumina having the following characteristics

- Surface size 205 mVg

- Total pore volumeO, 41cmVg

Solubility in caustic soda 64Ma .-%.

Example 3 (according to the invention) A hydrargillite with an average secondary particle size between 10 and 35 μπ \ and a specific surface area of 5 m ² / g

was subjected to a brief thermal treatment under the following conditions

Average residence time in the reaction zone 8s

Average temperature in the reaction zone 693K

- Average linear flow velocity of the carrier gas 5.5 m / s.

The obtained thermally activated reaction product is a p-alumina with amorphous portions, which in addition to its high reactivity has the following characteristic characteristics

- Surface size 217 mVg

- Pore volume 0.42 cm '/ g

- Solubility in sodium hydroxide solution 62.5Ma .-%.

1. A process for the preparation of practically pure rho-alumina by brief shock heating of aluminum trihydroxides, characterized in that aluminum trihydroxide with average secondary particle sizes between 0.1 and 45 / um by means of a carrier gas stream at linear flow rates of 5 to 20m · s ~ ¹ shockingly to temperatures be heated from 673 to 973 K and the reaction zone of a reactor tube at these temperatures is continuously passed with a mean residence time of 0.1 to 10s.

2. The method according to item 1, characterized in that dry alpha-aluminum trihydroxide is used in which at least 70 wt .-% of the average secondary particles are smaller than 10μ.ηη.

3. The method according to item 1 and 2, characterized in that the used alpha-aluminum trihydroxide having a Sekundärteilchengrößenfraktion of 0.1 to 5μσ \ is heated at linear flow rates of 5 to 10m · s " ¹ and the reaction tube with a mean residence time of 0 , 2 to 2s, with air or oxygen and / or inert gas being used as the transport medium.

4. The method according to item 1 to 3, characterized in that in the reaction zone at solids concentrations between 0.3 and 10kg · m ~ ³ and moisture contents of 10 to 75 wt .-% water or Wasserdampfpartialdrücken worked between 10 and 75 kPa.

Field of application of the invention

The invention relates to a process for the preparation of virtually pure rho-alumina by short-term Schockerhitzen of aluminum trihydroxides, which can be used preferably as a catalyst component or intermediates of catalyst preparation due to its high reactivity and special pore structure.

Characteristic of the known technical solutions

The production of virtually phase-pure rho-alumina or X-ray-amorphous alumina is very difficult due to annealing of hydrargillite. By long-term heating of alpha-aluminum trihydroxide at temperatures between 470 and 620K and pressures between 0.13 and 5.3Pa, these products can indeed be synthesized (Naturwissenschaften 54 [1967] 164, J. Cat. 36 [1975] 99, 57 [1979]). 222), but for practical purposes have the distinct disadvantage that they are only accessible under the conditions of vacuum because of their high solid-state reactivity. Under atmospheric or hydrothermal conditions, only well-crystallized Al ₂ O ₃ transition forms are always formed, which have proven unsuitable for many applications.

For the production of rho- or X-ray amorphous alumina, therefore, methods for short-time heating of aluminum quaternaries have been proposed in which Al ₂ 0 ₃ transition forms of low crystallinity and remarkable reactivity arise as a result of partial dehydration of the solid. For such processes, in addition to tubular and fluidized bed reactors, cyclone and net bottom reactors are also cited as constructive solution variants (DD-PS 62821, DE-AS 1280231, DD-PS 137091, SU-PS 477113, DE-AS 1 028106, DD-PS 203625, 203038). Although the more or less pronounced formation of the desired products of the thermal short-term degradation, rho- or X-ray amorphous aluminum oxide, is generally found or achieved in the hitherto known process variants for the short-time thermal treatment of aluminum quaternaries, all these processes have the decisive disadvantage in that the accessible products are of heterogeneous composition and in some cases have too high crystallinity. Thus, in addition to still undecomposed hydrargillite, alpha-aluminum trihydroxide, and hydrothermally formed boehmite of high crystallinity also different amounts of different A ^ CVTief- or high-temperature forms, depending in particular on the method used or the set reaction conditions, in particular the inactive and compared to other treatments very Stable chi-alumina is detectable. Such a heterogeneous and in most cases poorly reproducible roentgenographically determined phase composition of the products produced by the known processes is a major disadvantage with respect to their use as an intermediate for the preparation of highly active or high surface area catalyst components or catalysts.

In addition, the crystallinity of the Al ₂ O ₃ transition forms prepared by the known routes is already relatively high, so that hydration of the partially destructured or dehydrated products necessary for catalyst preparation and resulting in brief thermal shock treatment does not lead to the formation of low-crystallinity or pseudoboehmite , which is necessary in order to process the obtained thermally treated and subsequently hydrated aluminum oxide to corresponding catalyst moldings.

The products of the short-term heating, which in particular contain proportionally chi- or gamma-alumina low solid-state reactivity and porosity, are insufficiently or not at all in the desired intermediate product for catalyst preparation (pseudoboehmite) to convict.

Object of the invention

The object of the invention is a cost-effective and environmentally friendly process for the production of practically pure crude aluminum oxide of particularly high solid-state reactivity.

Explanation of the essence of the invention

The object is to develop a process for the production of alumina by defined short-term thermal shock of aluminum trihydroxides, which provides virtually pure rho-alumina, which is suitable as a catalyst component or as intermediates in the catalyst preparation.

This object is achieved by the present invention aluminum trihydroxides with average secondary particle sizes between 0.1 and 45ju.m and surface sizes of at least 5 m ² / g by means of a carrier gas stream at linear flow rates of 5 to 20 m · s "'shock-like to temperatures of 673 to 973 K. are heated and the reaction zone of a reactor tube at these temperatures is continuously passed with a mean residence time of 0.1 to 10s.

It has proven particularly advantageous to use dry alpha-aluminum trihydroxide in which at least 70% by mass of the average secondary particles are less than 10 μm. It is favorable if the used alpha-aluminum trihydroxide with a secondary particle size fraction of 0.1 to 5 ^ m at linear flow rates of 5 to 10m - s ~ ^{1 is} shock-heated and the reaction tube passes with a mean residence time of 0.2 to 2 s , Where used as a transport medium air or oxygen and / or inert gas used.

It is particularly advantageous when working in the reaction zone at solids concentrations between 0.3 and 10 kg · ιτΓ ³ and moisture contents of 10 to 75Ma .-% water or Wasserdampfpartialdrücken between 10 and 75 kPa.

The inventive method can be carried out only in an apparatus that has no stationary heat carrier.

The solution according to the invention leads to a virtually pure rho aluminum content or X-ray amorphous aluminum oxide with very high chemical reactivity of the aluminum oxide. The intermediate products of the catalyst preparation obtained in this way can be prepared well and further processed. They are comparable in their purity or chemical composition with those that were prepared by complex solution-precipitation process.

embodiments

Example 1 (comparative example, not according to the invention)

A unground gibbsite having an average of 50 to Sekundärteilchengrößendurchmesser 80μηι, a residue on ignition at 1073 K of 65,3Ma .-%, a specific surface area of 0.5 m ² · g ~ \ a porosity of 1.9% and a solubility in sodium hydroxide solution (Dry Reactivity) of 14.7% by weight is briefly thermoshock treated in a reactor with 5 separately heatable net-like individual segments, wherein air was used as the carrier gas, and a solid-gas ratio of 0.3 kg · Nm " ³ had to be selected The process is carried out in an apparatus which has a stationary solid heat carrier The short-term thermal shock treatment was carried out at a temperature in the reaction zone of 55O ⁰ C and an average residence time of the solid particles of 0.2 s, resulting in a heating time of the particles of 0.135 s and a Reaktio nszeit of 0.065s divided. The degradation product obtained is characterized by the following properties:

Glue residue = 82.7Ma .-% at 073K

Surface area = 275m ² g ^-1

Porosity = 28.6%

Solubility in NaOH = 43Ma .-%

The surface-rich, by X-ray as rho- or gamma AI ₂ O ₃ to be characterized alumina still contains small amounts of hydrargillite and traces of boehmite. It is characterized in particular by a pronounced "ink-bottle" pore shape.

Example 2 (according to the invention)

According to the invention, a hydrargillite having a particle size distribution maximum between 0.1 and 10 μm at a maximum particle size of 45 μm is used for the thermal shock treatment (according to Example 1), which has the following characteristics:

Lucky residue at 1073 K = 65.3 Ma .-%

specific surface area = 10.3 m ² -g ~ '

Total pore volume = 0.04 cm ³ -g ~ '

Porosity = 36.4%

Solubility in caustic soda = 29Ma .-%

The short-term thermally treated product is, according to X-ray diffraction, a practically pure rho alumina (with X-ray amorphous portions) characterized by the following characteristics:

Glue residue at 1 073 K = 90.5 Ma .-%

specific surface = 201 m ² g "'

Total pore volume = 0.41 cm ³ g " ¹

Porosity = 56.1%

Solubility in caustic soda = 64Ma .-%

Claims (2)

1. A process for the preparation of practically pure p-alumina by shock-like heating of powdered aluminum trihydroxides with surface sizes above 5m ² / g, which are transported by a carrier gas through a tubular reactor, characterized in that aluminum trihydroxide used with average secondary particle sizes between 0.1 and 45μιτι and the procedure - Linear flow velocities of the carrier gas from 5 to 20 m / s - Temperatures from 673 to 973K and - Average residence times in the reaction zone of 0.1 to 10 s is performed. 2. The method according to claim 1, characterized in that in the reaction zone at solids concentrations between 0.3 and 10 kg / m ³ and moisture contents of 10 bis75Ma .-% water, or water vapor partial pressures between 10 and 75 kPa, is working. The invention relates to a process for the preparation of practically pure p-alumina by short-term Schockerhitzen of aluminum trihydroxides, which is preferred because of its high reactivity and special pore structure Use catalyst component or intermediate product of the catalyst preparation. The production of virtually phase-pure p-alumina or X-ray amorphous alumina is by annealing Hydrargillite only very difficult. By long-term heating of a-aluminum trihydroxide at temperatures between 470 and 620K and pressures between 0.13 and 5.3Pa, these products can indeed be synthesized (Naturwissenschaften 54 [1967] 164, J. Cat. 36 [1975] 99, 57 [1979] 222), but have for practical purposes the decisive disadvantage that they because of their high solid state reactivity are accessible only under the conditions of vacuum. Under atmospheric or hydrothermal conditions always formed only well crystallized Al ₂ O ₃ transition forms, which are suitable for many Use cases have proved to be unsuitable. For the production of p- or X-ray amorphous alumina, therefore, methods for short-term heating of Aluminiumaquoxiden been proposed in which due to partial dehydration of the solid Al ₂ O ₃ transition forms low crystallinity and remarkable reactivity arise. Such a method is known for example from DD 221160 There are low-crystalline solid powder, u. a. also pulverulent gibbsite having a surface area of more than 5 m ² / g, subjected to a thermal shock treatment, wherein the shock heating by means of radiant energy during the continuous transport of the powdery solid with Help a carrier gas flow through a tubular reactor. In addition to the tube reactors are for such methods also Fluidized bed reactors, cyclone and net bottom reactors listed as constructive solution variants (DD-PS 62821, DE-AS 1 280231, DD-PS 137091, SU-PS 477113, DE-AS 1028106, DD-PS 203625). In the previously known process variants for short-term thermal treatment of Aluminiumaquoxiden Although in general the more or less pronounced formation of the desired products of the thermal short-term degradation, p- or X-ray amorphous alumina, determined or achieved, but all these methods with the decisive Disadvantage that the accessible products are heterogeneous composition and z.T. have too high crystallinity. Thus, depending on the method used or the reaction conditions set aside undecomposed hydrargillite, a-aluminum trihydroxide, and hydrothermally formed boehmite high crystallinity, also different amounts of different AI ₂ O ₃ Tief- or high-temperature forms, in particular, the inactive and compared to other treatments very stable χ-alumina is detectable. In DD 203038 a process is described in which, in order to avoid the formation of χ-alumina, unground hydrargillite a Thermal shock treatment at temperatures between 725 and 850K on fixed, stationary heat carriers, with very short Residence times of 0.01 to 0.5s is subjected. For the most part, however, heterogeneous and in many cases poorly reproducible X-ray methods are used in these methods obtained phase compositions, with the significant disadvantage of their use as an intermediate for the preparation of highly active or high surface area catalyst components or catalysts. In addition, the crystallinity of the prepared on the known ways Al ₂ O ₃ transition forms is already relatively high, so that The hydration of the partially destructured products following the brief thermal shock treatment, necessary for catalyst preparation, does not result in the formation of the amount of low crystalline or pseudoboehmite necessary to provide the resulting thermally treated and subsequently hydrated aluminum oxide Further processing of catalyst moldings. The products of the Kurzzeiterhitzens, the particular proportionate χ- or γ-alumina low solid state reactivity and Contain porosity are insufficient extent or not at all in the desired intermediate Catalyst preparation (Pseudoböhmit) to convict. The object of the invention is a cost-effective and environmentally friendly process for the production of virtually pure p-alumina particularly high solid-state reactivity. The object is a method for alumina production by defined short-term thermal shock of To develop aluminum trihydroxides, which provides virtually pure p-alumina, which as a catalyst component or is suitable as an intermediate in the catalyst preparation.