DE2501056A1 - HIGH STRENGTH POROESE CLAY AGGLOMERATES - Google Patents

Description

High strength porous alumina agglomerates

The invention relates to porous alumina agglomerates starting from obtained from powders containing bayerite,

It is well known that porous ion earth agglomerates Find diverse applications, especially in adsorption and for catalysis purposes · These various applications especially in catalysis, require certain depending on the individual case defined properties in terms of specific. Surface and porosity, and in almost all cases a good one mechanical strength, especially crush resistance and mostly also good wear resistance.

Such porous ion earth agglomerates are used for certain applications desired, the microporosity, which has a certain specific surface area required for the activity corresponds, with a considerable macroporosity

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combine, which facilitates the gas exchange. Self-assurance the value for the total porosity in these Cases lead to an excessive deterioration in the mechanical strength properties of the used alumina agglomerates. This is particularly disadvantageous when the agglomerates for the catalytic cleaning or burning of the toxic Exhaust gases from motor vehicles are to be used and are subject to the strong vibrations that cause the wear and tear of the as Accelerate the agglomerates used.

In addition, most of the mechanical strength properties to the alumina agglomerates maintain sufficient levels during extended periods of time at fairly high temperatures which may be up to 100O ⁰ C.

Frequently, these porous alumina agglomerates are agglomerated obtained from powders and numerous processes for this have already been recommended in order to produce such agglomerates or to give bodies considerable macroporosity. The general procedures that apply to most agglomerates Substances can be used, for example, that the powders that are to be agglomerated v / ground, Adds substances of different properties which, after shaping into the desired agglomerated bodies, are removed and which, as a result of gas development, leave behind their own volume or an even larger volume than pores. There are also a number of processes that are more closely related to the special properties of alumina or aluminum oxide (hydrate) are bound, which, as is well known, in various amorphous or crystalline, optionally hydrated There are forms that have very different textures or structures can have.

Among the processes by agglomerating alumina too Leading porous materials includes the process described in FR-PS 1 077 163; it leads to particularly interesting ones

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Results and consists in being able to get partially and quickly Alumina hydrates are dehydrated in the form of particles, which are then severely disorganized and, if necessary, after grinding and agglomerated into different shapes after moistening and by a similar setting process as with hydraulic ones Binders can be hardened. This process is generally applied to alumina trihydrate, hydrargillite or gibbsite and is known to be obtained by the Bayer process, which is known to 'the aluminum industry supplies the required clay. Of course, the bodies obtained by agglomeration must activated by firing, so that they obtain the desired specific surface.

Is, however, is difficult to obtain by means of agglomeration of partially to give dehydrated hydrargillite particles a large-pore porosity. Certain procedures allow this Achieve this goal, primarily by controlling the amount of water required for moistening and applying a very narrow grain size distribution of these particles «. However, these processes are fraught with disadvantages: It is for example difficult to obtain a narrow grain size distribution on an industrial scale, and this problem can be solved as is well known, difficult to solve.

However, it is possible, to use porous alumina agglomerates To get macroporosity, if one as starting materials, which have to be partially dehydrated in hot gas strömeη, others Alumina hydrates used as hydrargillite. According to an older proposal (DT-OS 2 411 846), large-pored ones are obtained Alumina agglomerates based on precipitated gels, which not only have a considerable macroporosity but also already have good strength. But in the case of large-scale To obtain completely reproducible results, this procedure must be carried out in all phases or stages very much

* preserved bodies

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are well controlled because of the unstable nature of the precipitated gels, which are under the action of numerous factors can develop or change.

It has now been shown that another alumina trihydrate variety, bayerite, when dewatered in hot gas streams leads to highly disorganized alumina particles which can set through rehydration and, after activation, provide porous agglomerates which have a surprisingly high mechanical strength is also retained at fairly high temperatures in the region of 100O ^{0 C.} It has also now been shown that bayerite even gives these agglomerates only a low porosity, but that presumably as a result of the strength caused by it one can achieve the desired changes or modifications of the pore properties in the sense above all that a painterly porosity arises without that the mechanical properties of these agglomerates or bodies is considerably affected. These changes can be achieved by the various known processes mentioned above, as well as by other lesser known processes, for example the various hydrothermal treatments, and by using together with bayerite other alumina hydrate varieties which are suitable for contributing to the porosity «,

Because of the great strength brought about by the bayerite, other porous agglomerates can still be used as a starting point obtained from more complex starting mixtures to which further components have been added, especially the clays of the different crystalline varieties, possibly in Treated hot gas streams, as well as zeolites or molecular sieves. These additions can still be elements or compounds with catalytic effect of different kinds, especially oxides and metals, which the alumina before the hot gas treatment, after this, after the shaping or also the sodium aluminate solution or the aluminum salts are added, from the solutions of which the alumina is precipitated, which is then exposed to the action of hot gas is subject to "

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A wide variety of shaping processes are used in technical practice for agglomeration application, especially deforming into spheres in a rotary granulator, deforming into rings or cylinders by means of extrusion and compression deformation. Agglomerates are obtained with excellent reproducible properties, which is of great technical importance.

So that the best corresponding strong disorganized clays are obtained starting from bayerite, the starting material should preferably be dehydrated as completely as possible until the amount of residual water that can be removed by firing at a high temperature is a maximum of 10 wt .- ^. If complex mixtures of different alumina hydrate varieties are treated, the residual water content of these treated mixtures must of course be of the same order of magnitude in order to obtain sufficient disorganization of the bayerite present. Furthermore, the mixtures must contain a sufficient amount of dehydrated bayerite, because the strength of the agglomerates is due to this component; the other components contribute less to strength and more to porosity. The proportion of partially dehydrated bayerite should preferably make up at least $ 15 in the mixture.

The conditions under which alumina hydrates that more or

"Λ"

are less rich in bayerite, are well known. Usual procedures are, for example, that one at Temperatures a little above room temperature and at a relatively high pH of about 10 to 13 alkali aluminates or aluminum salts fails; preferably gels are allowed to develop or age at these same pH values, and those at less high pH values have been precipitated. The duration of this further development (maturation), the temperatures at which they takes place, as well as certain other conditions "such as condition and concentration of the reactants change the results in such a way that the products obtained are very different Compositions in terms of the existing

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Amount of bayerite and the nature of the other combined with it May have alumina hydrate varieties; the latter can be amorphous or crystallized, in the state of urstrandite, Hydrargillite or boehmite are present.

In the following examples, the precipitates were either starting from urodium aluminate or from aluminum sulfate, and the summary (general) information relates to the precipitation conditions and the composition this precipitation,

In a 1, example the properties of the balls are given, made from disorganized clays, which are treated in a stream of hot gas of clay containing different amounts of bayerite result. The following examples relate to balls whose Macropore volume has been increased by adding further compounds which can be removed by firing; further on spheres obtained from a mixture of alumina and from a mixture of alumina and molecular sieve have been. In a last example it is shown that the drainage of bayerite is preferably sufficiently far should be driven to get the best results.

example 1

This example mainly explains the relationships between the proportion of bayerite in the clays that are subsequently dewatered in the hot gas stream and the microporosity of the agglomerates that are produced from the dehydrated clays the special properties of bayerite is due, the microporosity of the original clays were also measured, which were simply dried by spraying and then ^{burned at 500 0} C as well as the microporosity of clays after dewatering but before agglomeration, the microporosity of the agglomerates obtained and the Total porosity.

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The different clays tested are designated below with A, B, C, D, E, E, G-; the method of their manufacture is indicated below:
Alumina A - i 15 ° bayerite

There was an alumina gel suspension containing 50 g / l AIpCU prepared by precipitating a Batriumaluminatlösung with nitric acid solution at 30 ⁰ C and at constant pH of 8.7. This suspension was kept at the precipitation temperature for 6 hours and then filtered; the filter cake was washed with demineralized water and resuspended in water and this suspension is atomized in hot gas from 30O ⁰ C.

Alumina B - $ 39 Bayerite

The manufacturing process was analogous; the precipitation was carried out at 43 ^° C. and at pH 10; the suspension obtained starting from the washed filter cake was 150 g / l AIPO, - and was prepared by sputtering in the hot gases of 45O ⁰ C

dried.

Alumina C - 50 fo bayerite

It was added in the course of 5 h hydrated alumina containing 80% bayerite, prepared separately and suspended in water to form a gel of amorphous alumina, which had been obtained by precipitating ITatriumaluminatlösung with nitric acid at 25 ⁰ C and at pH 7.5; the quantitative ratio was 30 $ alumina hydrate containing 80 % bayerite per 70 $> alumina gel, in each case calculated as Al ₂ O ^. The mixture was allowed to develop or age for 20 hours; it was then filtered and the cake obtained was washed. The cake was resuspended in water and the suspension is dried by sputtering at 45O ⁰ G.

Alumina D - $ 65> Bayerite

The same procedure was used as for Alumina C; only the time for allowing the mixture to age was different and was here 36 h.

Alumina E - 75 i » Bayerite

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At 45 ^° C. and at pH 9.5, an alumina gel was precipitated from water glass and nitric acid, filtered, washed and resuspended in water at room temperature. The suspension contained 150 g / l Al ₂ CU; after a port development (aging ^) of 2 days, the suspension was dried by spraying at 45O ⁰ C.

Alumina Έ - 80 i » Bayerite

The same procedure was used as for Alumina E with the modification that the development or aging time the suspension here was 3 days.

Alumina G- - $ 90 Bayerite

An aluminum sulfate ^{solution was precipitated continuously at 40 °} C. and pH 11 with a sodium aluminate solution. The concentrations of the solutions were such that the suspension obtained contained 50 g / l AlpO. The suspension was kept at room temperature for 12 h and then filtered and washed; the cake was resuspended in water and the suspension is dried by atomization in 30'O ⁰ C.

The various clays obtained in this way A, B, C, D, E,]? and G were partially dehydrated in hot gas streams in such a way that they still contained 3 to 8 ^σ / ο residual water which could be removed by burning at high temperature. Under these conditions, the bayerite could no longer be seen in the X-ray diffraction diagram.

These dehydrated clays were then moistened again and shaped in the rotary granulator into spheres with a diameter of 3 to 4 mm; the balls were left to mature in the oven at 105 ^{° C. for 24 hours.}

A part of the balls 2 h then was fired at 1000 h at 65O ⁰ C ⁰ C, the other part 24 for activation. To show the origin of the microporosity (VMP) in the fired at 65O ⁰ C agglomerates clear this microporosity was not only in these (fired) products gemessen.sondern on the

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in hot gas streams partially dehydrated aluminas and the clays after spray drying and then firing at 50O ⁰ C. These microporosity was determined by means of carbon tetrachloride. Furthermore, the total porosity of the fired at 65O ⁰ C was agglomerates with the aid of a mercury porosimeter determined as well as the specific surface of the partially dehydrated aluminas and of the agglomerated and calcined at 65O ⁰ C products. Finally, the crush strength was determined grain each grain of the baked at 65O ⁰ C and 'fired at 100O ⁰ C agglomerates.

The results are summarized in Table 1 below.

Table 1

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Table 1

Ϊonerde

After spray drying and firing at 500 ⁰ G

VmP cn? / G

After drainage

Agglomeration awake. And burning after burning

at 650 ^° C

at 1000 ^u C

V.m |

special surface 2 /

VmE in total porospecific top- crush- crushcnr / g ßi / bät surface strength cm3 / gm ² / g speed

kg

kg

15 5 A. 0.60 0.51 300 0.75 0.95 401 4th 2.5 50982 39 5
50 y B.
C. 0.55
0.48 0.40
0.33 310
310 0.70
0.65 0.90
0.80 220
205 5
6th 4th
5 9/0890 65:
75:
like this: D.
E.
1 0.42
0.39
0.35 0.31
0.28
0.26 250
230
. 210 0.60
0.56
0.50 0.78
0.75
0.70 215
220
210 6.5
¹ 7
15th 4.5 fe
4.5
7th 9o: G 0.18 0.13 185 0.47 0.57 196 18th 7.3 & Bayerite & Bayerite
fo bayerite fo. Bayerite
fo bayerite
$ Bayerite in bayerite

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The comparison of these test results clearly shows that the micropore volumes of the by agglomeration of the various The spheres obtained from clays change in the same way as the micropore volumes of the clays from which they were assumed is, in the same sense as with the dehydrated clays and in the opposite sense as the bayerite content of the clays. The micropore volumes of the spheres, however, are larger than those of the clays, probably because the tene disorganized clay rehydrates itself after agglomeration and thereby crystals in the form of highly porous Felting forms "

The increase in strength with the level of bayerite shows the importance of the agglomerates obtained from clays, which contain sufficient bayerite.

Which show by firing the balls at 100O ⁰ C for 24 h results obtained that the crushing strength is still sufficiently good,

Example 2

This example relates to balls made from a mixture from clays, one of which is based on a product rich in bayerite and the other from an alumina gel without bayerite has been made \

The gel which did not contain bayerite and was at a pH value of about 8 consisted mainly of pseudoboehmite and amorphous phases. It was washed, spray dried and then dewatered in a hot gas stream in such a way that the residual water content (removable only by burning at high temperature) was 8 wt .- ^. 68 kg of this dehydrated Gels were dehydrated with 103 kg (calculated as AIpO) Alumina D mixed according to the previous example, which contained 4 wt .-% residual water, da.s at high temperature could be removed. The mixture of the two clays became spheres with a diameter of 3 to 4 mm in the rotary granulator

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deformed; the balls were then allowed to ripen and then fired at 65O ⁰ O and at 100O ⁰ C. The specific surface, the microporosity (VmP), the total porosity and the crush strength were determined for these fired spheres; the results are summarized in the following table 2:

Table 2

! fold burning with laugh burning at 65O ⁰ O 100O ⁰ C

Specific surface m / g VmP cnr / g

Total porosity cnr / g crush strength kg

213 126 0.73 0.70 1.01 0.95 4.3 3.3

Example 3

This example concerns spheres whose total pore volume is through The addition of substances that can be removed by thermal decomposition has been increased.

The dehydrated alumina powder obtained starting from alumina G (Example 1) was used, which consists almost exclusively of Bayerite existed. A certain weight of this regrind powder was made with 10, 12 or 15 wt .- ^ wood cellulose fibers (Trade name "Solkafloc BW 40") decomposed.

The mixture was shaped in a rotary granulator into balls with a diameter of 3 to 4 mm; the Kugeln'wurden for 2 days in a moist atmosphere at 100 ⁰ C and ripened hours then dried and finally fired at 100 ° and at 200 ⁰ C 3 · 2 h at 65O ⁰ C.

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The properties of the balls obtained are summarized in Table 3 below:

Table 3

Addition of cellulose fibers

12 <fo

.15

Specific surface m / g 185 190 205 VmP cnr / g 0.47 0.49 0.50 Total porosity cnr / g 0.69 0.87 0.93 Crush strength kg 6th 5.2 2.1

This example shows that starting from bayerite ion earth Agglomerates can be obtained which have a large porosity, which consists to a considerable extent of large pores and which nevertheless have sufficient mechanical strength.

Example 4

This example concerns spheres based on molecular sieves *

dehydrated clay G (Example 1) and

Molecular sieve 4 A, dried _; was married and then im

A mixture of 30

Rotary granulator agglomerated into spheres. After ripening in a moist atmosphere at 100 ^° C., the balls were activated in a stream of hot air at 450 ^{° C.} The following were obtained

Characteristics:

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Specific surface area m / g 120

■ z

ymP cm / g 0.23

Total porosity cm / g 0.57 Crush strength kg 7

This example shows the importance of bayerite in the production of mixtures of active alumina and molecular sieve Agglomerates, which are characterized by special adsorption properties.

Example 5

There have been several portions alumina GSM Example 1 as far dewatered in accordance that each sample is not more than 8 and 10 or 15 wt -.!.% Of water, which could be removed at a high temperature ' It spheres were mm_hergestellt with diameter of 3 to 4 as shown in the previous examples, baked and then dried at 650 and at 1000 ^0C.

In the following Table 4, the values for the microporosity after firing at 65O ⁰ C and the values for the crushing strength after firing at 650 and at 1000 ⁰ C are listed.

Table 4 10 15th 0.39 0.35 8th 14th 10 0.42 5 2 16 7th

Residual water

YmP cnr / g after firing
65O ⁰ C

Crush strength according to
Baking at 65O ⁰ C

Crush strength according to
Burns at 100 ° C

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This example shows a clear decrease in the strength of the agglomerates when the alumina used has a residual water content of 15 G-evu%. As a result, it is beneficial to drive the dehydration of the alumina in the hot gas stream quite far.

Claims

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Claims (6)

Claims 1. High-strength porous alumina agglomerates, especially for adsorption and catalysis purposes, obtained by moistening and agglomeration of alumina powders, and subsequent activation by means of firing, characterized in that that at least some of the powder particles are caused by partial dewatering of alumina containing bayerite - hydrate has been obtained in a hot gas stream and that the proportion of partially dehydrated alumina based on bayerite " makes up at least 15% by weight of the total mass. 2. agglomerates according to claim 1, characterized in that the by partial dewatering of Alumina hydrate obtained in a stream of hot gas particles at most 10 wt .- ^ residual water that by burning at high Temperature can be eliminated included. 3. agglomerates according to one of claims 1 or 2, characterized in that the partially dehydrated Other components have been added to alumina particles, 4 · agglomerates according to claim 3, characterized in that the other components are fired can be removed, in particular to give the agglomerates macroporosity. 5c agglomerates according to claim 3, characterized in that the other components clays, Are zeolites, molecular sieves and / or metal oxides. 6th
ζ e Agglomerates according to claim 3, characterized in that g e k e η η - inet Have an effect. 7243 that the other components are catalytic ^ 509 8 29/0890