Highly reactive alumina and process for the preparation thereof

The invention relates to a new highly reactive alumina and the method of preparing it. The alumina is characterized by an amorphous structure and a specific surface of greater than 600 m.sup.2 /g. It is prepared by thermal decomposition of the double carbonate of aluminum and ammonium of the formula AlNH.sub.4 CO.sub.3 (OH).sub.2 at a temperature of between about 200.degree. and 500.degree. C. Aluminum hydroxychlorides of the formula Al.sub.2 (OH).sub.x Cl.sub.6-x can be prepared from it.

BACKGROUND OF THE INVENTION 
This invention relates to a new alumina and the method of preparing it. It 
also concerns the method for the preparation of aluminum hydroxychloride 
therefrom. More particularly, the alumina with which the present invention 
is concerned is a highly reactive alumina having a very high specific 
surface. 
French patent application No. 73.36846, published under No. 2,247,425, 
describes active aluminas having a specific surface of at least 200 to 250 
m.sup.2 /g. These active aluminas are prepared by partial dehydration of 
alumina hydrates (hydrargillite) in a stream of hot gases. This same 
French application describes the preparation of aluminum hydroxychlorides 
of the general formula Al.sub.2 (OH).sub.x Cl.sub.6-x which consists in 
reacting the above alumina with solutions of hydrochloric acid and/or 
aluminum chloride. 
French application for certificate of addition No. 74.22968, published 
under No. 2,277,039, describes active aluminas having a specific surface 
of between 250 and 600 m.sup.2 per gram. They are obtained by partial 
dehydration of alumina gels obtained by precipitation of aluminum salts or 
of sodium aluminate. This French application also describes the use of 
this active alumina for the preparation of aluminum hydroxychlorides. 
The active character of the aluminas used makes it possible to obtain 
aluminum hydroxychlorides in which "x" in the above formula may in the 
first case (active alumina obtained from hydrargillite) reach a value of 4 
and in the second case (active alumina obtained from amorphous gels), a 
value of 5. 
The interest which exists in being able to obtain aluminum hydroxychlorides 
of the general formula Al.sub.2 (OH).sub.x Cl.sub.6-x in which x=5 is 
known. It is from Al.sub.2 (OH).sub.5 Cl that alumina balls are prepared 
by the so-called "oil drop" or "salt gel" technique which is well known to 
those skilled in the art. 
However, the alumina described in the aforementioned French Application for 
Certificate of Addition, while it makes it possible to obtain an aluminum 
hydroxychloride of the formula Al.sub.2 (OH).sub.5 Cl, has a certain 
number of drawbacks, the main ones being due to the structure itself of 
this alumina. 
As a matter of fact, the activated alumina obtained by partial dehydration 
of amorphous gels contains a certain amount of gamma-alumina. This 
gamma-alumina reacts poorly in production of Al.sub.2 (OH).sub.5 Cl. Thus, 
the reaction of the alumina obtained from amorphous gels with solutions of 
hydrochloric acid and/or aluminum chloride is not quantitative, and the 
yield observed is only about 80 to 90%. Another drawback, which is related 
to the structure of the alumina used, resides in the rather long time of 
reaction required for the preparation of aluminum hydroxychloride. This 
reaction time is directly related to the specific surface of the alumina. 
As a matter of fact, the higher the specific surface, the greater the 
surface of contact and the faster the reaction velocity. 
On the other hand, it is known from U.S. Pat. No. 4,053,579 that the 
decomposition at about 223.degree. C. of a special double carbonate of 
aluminum and ammonium gives alumina of gamma-structure, the area of this 
gamma-alumina being between about 200 and 400 m.sup.2 /g. 
The foregoing clearly shows the interest which resides in being able to 
have alumina which has a specific surface and a crystallographic structure 
which are adapted to improve its reactivity. 
The present invention achieves this purpose while obviating the drawbacks 
of the prior art which have been pointed out above. 
It is, therefore, an object of the present invention to provide a new 
highly reactive alumina, especially adapted to produce aluminum 
hydroxychloride. 
It is also an object of the present invention to provide a process for the 
preparation of the new highly reactive alumina. 
It is a further object of the present invention to provide a process for 
producing aluminum hydroxychlorides from the new highly reactive aluminas.

GENERAL DESCRIPTION OF THE INVENTION 
By the present invention there has been discovered a new alumina having a 
specific surface of more than 600 m.sup.2 /g and an amorphous structure. 
Within the meaning of the present invention, there is understood by 
amorphous structure a structure such that X-ray analysis gives a diagram 
which no longer shows lines characteristic of a crystalline phase. 
Another important object of the invention is a process of preparing an 
alumina as described above, which process comprises thermally decomposing 
a double carbonate of aluminum and ammonium having the formula AlNH.sub.4 
CO.sub.3 (OH).sub.2 at a temperature of between about 200.degree. and 
500.degree. C. for approximately a period of time of between a fraction of 
a second and about 5 hours. 
The double carbonate of aluminum and ammonium of the formula AlNH.sub.4 
CO.sub.3 (OH).sub.2 which is decomposed in accordance with the process of 
the invention is substantially crystalline. It preferably has an X-ray 
diffraction pattern the interplanar distances and relative intensities of 
which have approximately the following values: 
______________________________________ 
d A 1/1.sub.1 
d A 1/1.sub.1 
d A 1/1.sub.1 
______________________________________ 
5.82 100 2.57 25 1.815 2 
4.07 21 2.25 5 1.729 12 
3.41 10 2.19 7 1.657 7 
3.32 44 2.038 20 1.465 3 
2.90 18 1.991 9 1.429 6 
2.63 2 1.879 2 1.410 3 
1.388 3 
______________________________________ 
The decomposition is preferably carried out at a temperature of between 
about 275.degree. C. and 325.degree. C., for a period of time of between 
about a fraction of a second and 3 hours. 
The decomposition in a fraction of a second is effected at a relatively 
high temperature, the specific surface of the alumina obtained having a 
tendency to decrease when the temperature and/or the time of decomposition 
increase. The decomposition between a fraction of a second (about 1/10 of 
a second) and about 10 seconds can advantageously be obtained in suitable 
devices by means of hot gases. 
A relatively low temperature requires a longer time of decomposition, the 
specific surface of the alumina thus obtained varying relatively little 
when the time of decomposition increases. 
Within the temperature and time ranges indicated above, the man skilled in 
the art can thus easily determine, by simple routine trials, the 
conditions to be employed in order to obtain the alumina of amorphous 
structure and specific surface greater than 600 m.sup.2 /g of the present 
invention. 
The operation is generally carried out at atmospheric pressure, but other 
pressures may be employed. 
Still another object of the invention is a process of preparing aluminum 
hydroxychlorides of the formula Al.sub.2 (OH).sub.x Cl.sub.6-x, in which x 
is equal to or greater than 5, which process comprises reacting alumina of 
the invention with a solution of hydrochloric acid and/or aluminum 
chloride. 
The hydrochloric acid solution used preferably has a concentration of 
between about 1 and 5 N. Values outside of this range are not excluded. 
When the concentration is less than about 1 N, the reaction times become 
very high. On the other hand, when the concentration increases, the 
concentration of alumina in the final aluminum hydroxychloride increases. 
This latter point is important since, for instance, if the aluminum 
hydroxychloride obtained is used to prepare alumina balls by the "oil 
drop" technique which has been mentioned above, the concentration of 
alumina in the aluminum hydroxychloride must be preferably between 200 and 
300 g/l. This value is obtained by using a hydrochloric acid solution of 
about 3 N. 
When an aluminum chloride solution is used, its concentration preferably 
varies between about 0.25 M/L and 1.7 M/L. When it is desired to obtain a 
hydroxychloride which can be used in the oil drop process, a concentration 
of 1 M/L is preferred. 
With respect to the reaction temperature, when operating with a 
hydrochloric acid solution, since the reaction is exothermal, no initial 
heating is necessary. The temperature increases spontaneously and is then 
maintained at a suitable value. The mixture is preferably maintained at 
the boiling point. When aluminum chloride is used, the reaction is not 
exothermal. It is, therefore, necessary to heat the reaction mixture, 
preferably up to its boiling point. 
The alumina and hydrochloric acid or aluminum chloride solution are 
generally used in a molar ratio of Al.sub.2 O.sub.3 to HCl of between 
about 0.95 and 1.05. 
Under the foregoing conditions of temperature and concentration, the 
reaction time is generally between about 3 hours and 5 hours. 
It is preferred to operate at atmospheric pressure, although higher or 
lower pressures may be employed. 
The advantages of such a process reside primarily, on the one hand, in the 
considerably slower reaction times than the processes of the prior art 
(this will become clearly evident from the examples) and, on the other 
hand, in the fact that it is not necessary to use an excess of alumina as 
was previously true in the prior art. These advantages are due to the very 
high reactivity of the amorphous alumina of very high specific surface in 
accordance with the invention. 
The double carbonate of aluminum and ammonium can be prepared by any 
technique known to the man skilled in the art. In particular, one can 
start from aluminum triisopropanolate and ammonium bicarbonate. 
The hydroxychlorides can be used, for instance, for the preparation of 
alumina balls by the "oil drop" technique as previously mentioned. They 
can also be used in other applications, among which particular reference 
may be had to the treatment of waters. 
SPECIFIC DESCRIPTION OF THE INVENTION 
In order to disclose more clearly the nature of the present invention, the 
following examples illustrating the invention are given. It should be 
understood, however, that this is done solely by way of example and is 
intended neither to delineate the scope of the invention nor limit the 
ambit of the appended claims. In the examples which follow, and throughout 
the specification, the quantities of material are expressed in terms of 
parts by weight, unless otherwise specified. 
EXAMPLE 1 
Preparation of double carbonate of aluminum and ammonium AlNH.sub.4 
CO.sub.3 (OH).sub.2. 
Into 300 cc. of absolute benzene at 25.degree. C., containing 1 mol of 
aluminum triisopropanolate, there is poured, with strong agitation, 1 mol 
of ammonium bicarbonate which is free of moisture. Agitation is continued 
for 5 hours, whereupon 100 cc. of water are added. The double carbonate of 
aluminum and ammonium AlNH.sub.4 (OH).sub.2 CO.sub.3, which has 
precipitated out, is removed by filtration and washed with water and then 
with alcohol. The double carbonate of aluminum and ammonium is then dried 
under vacuum at 40.degree. C. 
Analysis by X-ray diffraction gives the following interplanar spacings and 
relative intensities: 
______________________________________ 
d A 1/1.sub.1 
d A 1/1.sub.1 
d A 1/1.sub.1 
______________________________________ 
5.82 100 2.57 25 1.815 2 
4.07 21 2.25 5 1.729 12 
3.41 10 2.19 7 1.657 7 
3.32 44 2.038 20 1.465 3 
2.90 18 1.991 9 1.429 6 
2.63 2 1.879 2 1.410 3 
1.388 3 
______________________________________ 
EXAMPLE 2 
Preparation of amorphous alumina of very high specific surface of the 
invention from double carbonate of aluminum and ammonium. 
860 g. of double carbonate of aluminum and ammonium obtained in the manner 
described in Example 1, above, are introduced into a muffle-type furnace 
which is maintained at a temperature of 300.degree. C. The double 
carbonate is left in the furnace for 3 hours. 350 g. are obtained of a 
product comprising 90% Al.sub.2 O.sub.3 and 10% H.sub.2 O. 
The alumina obtained has a specific surface measured by the BET method of 
650 m.sup.2 /g. 
Analysis by X-ray diffraction shows an amorphous structure. The X-ray 
diffraction pattern diagram obtained is shown in FIG. 1 of the drawings. 
In order to be able to compare the structure of an alumina in accordance 
with the invention, produced by the foregoing example, with an active 
alumina of high-specific surface of the prior art, the following 
preparation was carried out: 
EXAMPLE 3 
Preparation of an active alumina of high specific surface from amorphous 
alumina gel (prior art). 
A dry amorphous alumina of 70% Al.sub.2 O.sub.3 is introduced into a flash 
dehydrator whose temperature gradient varies from 500.degree. to 
800.degree. C. 
After a residence time of a fraction of a second, there is removed a 
product which comprises about 95% Al.sub.2 O.sub.3 and 5% H.sub.2 O. 
A final product is obtained which has a specific surface of 375 m.sup.2 /g 
and whose X-ray diagram is shown in FIG. 2 of the drawings. 
A comparison of the X-ray diagrams (.lambda.Cu=1.5405 A) of FIGS. 1 and 2 
clearly illustrates the difference in structure between the two aluminas. 
It is noted that the characteristic peak of the gamma-alumina at 
67.03.degree. angle 2-theta is present in FIG. 2 while it does not appear 
in FIG. 1. 
EXAMPLE 4 
The same procedure is employed as in Example 2, but employing a temperature 
of 330.degree. C., for 3 hours. 
The alumina obtained has an amorphous structure comparable to that shown in 
FIG. 1 and a specific surface of 667 m.sup.2 /g. 
EXAMPLE 5 
The same procedure is used as in Example 2, but employing a temperature of 
370.degree. C. for 3 hours. 
The alumina obtained has an amorphous structure comparable to that shown in 
FIG. 1 and a specific surface of 625 m.sup.2 /g. 
EXAMPLE 6 
The same procedure is used as in Example 2, but employing a temperature of 
250.degree. C. for 5 hours. 
The alumina obtained has an amorphous structure comparable to that 
illustrated in FIG. 1 and a specific surface of 640 m.sup.2 /g. 
EXAMPLE 7 
The same procedure is used as in Example 2, but employing a temperature of 
400.degree. C. for 2 hours. 
The alumina obtained has an amorphous structure comparable to that shown in 
FIG. 1 and a specific surface of 605 m.sup.2 /g. 
EXAMPLE 8 
Preparation of aluminum hydroxychloride 
Into an agitated apparatus of Grignard type there are introduced 1 liter 
gas a 3 N hydrochloric acid solution and then 350 g. of alumina which has 
been prepared in accordance with Example 2. The temperature of the 
reaction medium rises to 103.degree. C. The mixture is maintained under 
reflux for 4 hours. After cooling to 20.degree. C., there is obtained 1 
liter of a solution of aluminum hydroxychloride of a density of 1.31, 
having the general formula Al.sub.2 (OH).sub.5.03 Cl.sub.0.97. 
EXAMPLE 9 
The same procedure is used as in Example 8, but employing 1 liter of a 1 M 
solution of aluminum chloride and 320 g. of alumina prepared in accordance 
with Example 2. The mixture is heated to reflux and maintained at this 
temperature for 4 hours. After cooling to 20.degree. C., there is obtained 
1 liter of a solution of aluminum hydroxychloride of a density of 1.31 and 
the general formula Al.sub.2 (OH).sub.5.01 Cl.sub.0.99. 
EXAMPLE 10 
The same procedure is used as in Example 8, but employing 1 liter of a 
solution consisting of 0.5 liters of 1 M aluminum chloride and 0.5 liters 
of 3 N hydrochloric acid, followed by 335 g. of alumina. The temperature 
of the reaction medium rises to 101.degree. C. 
The mixture is maintained at reflux for 4 hours. After cooling to 
20.degree. C., there is obtained 1 liter of a solution of aluminum 
hydroxychloride of a density of 1.31 and the general formula Al.sub.2 
(OH).sub.5.03 Cl.sub.0.97. 
The importance of the process of the invention which has been illustrated 
in Examples 8, 9 and 10 is very evident from a comparison of these 
examples with the examples of the two French patent applications referred 
to above. It is noted that in the application published under No. 
2,247,425, the reaction times are about 16 hours, the activated alumina 
being obtained from hydrargillite. In the application published under No. 
2,277,039, in which the alumina used is obtained from amorphous alumina 
gel, the reaction times are about 7 hours. Furthermore, as indicated 
previously, in these two published patent applications an excess of 
alumina is necessary in order to carry out the reaction while such an 
excess is not necessary in Examples 8, 9 and 10 above. 
The terms and expressions which have been employed are used as terms of 
description and not of limitation, and there is no intention in the use of 
such terms and expressions of excluding any equivalents of the features 
shown and described or portions thereof, but it is recognized that various 
modifications are possible within the scope of the invention claimed.