Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2~6833
The present invention relates to hydrous ~luminium
oxide containing substantially pseudobo~mite, a p~ocess for
producin~ same and the use thereo~.
Pseudobohmite is an aluminium oxide hydrate modifi-
cation which is frequently used as a catalyst, catalyst support,
filler and binder because of its large surface area, quality
of pores, dispersibility and its binding power.
The production of pseudob`ohmite from aluminium-sul-
phate solution is disclosed for example in US Patent ~o.
10 4,297,325, US Patent No. 4,154,812 and German Auslegeschrift
No. 2,24~,022. In these processes either long washing and
aging times are required or no gellable product is obtained,
i.e., the peptization index is >> 60 minutes.
The present invention provides a hydrous aluminium
oxide, containing substantially pseudobohmite which contains
less than 400 p.p.m. preferably less than 200 p.p.m. of
sodium oxide and less than 2% by weight, preferably 1~ by
weight of sulphate, computed as SO4, and has a peptization
index of less than 60 minutes, preferably less than 10 minutes
and a specific surface area of 200 to 400 sq m per gram.
The sodi~lm oxide content is determined by conven-
tional analytical methods, as for example, gravimetric deter-
mination via BaS~.
The degree of peptization i.e. the peptization
index is determined by means ofthe method according to US Patent
No 4,297,325.
The specific surface area is determined on the area
meter by the conventional method acc~rding to DIN 66132.
The present invention also provides a process for producing
the hydrous aluminium oxide containing substantiall~ pseudo-
bohmite, which contains less than 40Q p.p,m., preferably less
than 200 p.p.m. o~ sodium oxide ~nd less than 2% b~ weight,
- 1 -
~46~33
preferably less tllan 1~ by weight o~ sulphate, computed
as SO4, and has a peptization index of less than 60 minutes,
prefexably less than 10 minutes, and a specific surface area
of200 to 400 sq m per gram in which process an a~ueous
aluminium-sulphate solution having a pH value of 3.0 to 2.6,
preferably 2.8, and an A12O3 content of 70 to 105 g per litre
(5.8 to 8.0% by weight~ is heated to a temperature of 50 to
90C, preferably 60C and aqueous sodium aluminate solution
having a content of 120 to 265 g of Na2O per litre (10 to
18.8~ by weight) and 70 to 225 g of A12O3 per litre (5.9 to
15.9~ by weight), preferably 220 g of `.~a2O per litre (16.3%
by weight) and 160 g of A12O3 per litre (11.9% by weight),
is heated to a temperature of 50 to 90C, preferably 60C,
that thereafter the two solutions are allowed to flow simul-
taneously into a water receiver having a temperature of 50 to
90C, preferably 60C, such that during the precipitation the
reaction mixture has a constant pH value of less than 5,
preferably less than 4 and after the precipitation the pH
value of the reaction mixture is shifted into the alkaline
range, preferably higher than 8, by further addition of
sodium-aluminate liquor having the same concentration, the
- reaction mixture is subjected to aging 3.1 to 20 hours,
preferably for 5 to 18 hours at a temperature of 50 to 90C,
preferably 80C, alld the precipitate is filtered off, washed,
dried and, when required subjected to an ion exchange.
The aluminium-sulphate and sodium-aluminate solutions
can be produced b~- dissolving the corresponding salts.
The aluminium sulphate solution can also be produced
by reacting aluminium oxide with sulphuric acid and the
sodium-aluminate solution can be produced b~ reacting it with
a solution of caustic soda.
For example, light hydrate ~58 to 65~ b~ weight),
~2~6~
pseudoboh~ite and particularly moist h~drate (57 to 58% by
weight) can be used as aluminium oxide.
In a preferred embodiment of the present invention the
precipitation product is aged at a pH value of 8.5 to 9.
The aluminium oxide according to the present
invention has advantageously a low content of ~a~O. Despite
the relatively short aging time the gelling power is very
high.
The process according to the present invention will
be further illustrated by way of the following Exammples.
Examples
In the Examples 1 to 8 listed in Table 1 an aluminium-
sulphate solution having a pH value of 2.8 and a content of
75 to 97 g of A12O3 per litr~ is produced with aqueous sul-
phuric acid starting from a technical moist hydrate having a
content of 57.5% by weight of A12O3. The two solutions are
heated to the precipitation temperature and simultaneously
passed into a water receiver having the same temperature.
The desired pH value is kept constant during the precipitation.
The precipitation suspension obtained is subjected to
aging under constant conditions.
The product obtained is filtered off and washed with
water.
In the Examples 1 to 6 the filter cake is redispersed
with water to a suspension having a content of 11~ by weight
of A12O3 and the suspension is spray-dried.
In the Examples 7 and 8 the filter cake is dried
for 4 to 5 hours at 105C and then ground in a pinned disc mill.
The important parameters and the product data obtained
are listed in Table 1.
:~Z46~333
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~6~33
The rheological p~operties of pseudob~h~ite are
characterized by the peptiz~tion index (PI~, which is determined
according to the ~ollowing test directions:
A 10~ b~ weight suspension (relative to A1203) is
mixed with a 90% formic acid in the ratio of 100:1. The pep-
tization index is the time in minutes which the acidified sus-
pension requires to attain a viscosity of at least 5000 cps.
Because of its rheological properties pseudobo~nmite is
an excellent binder. It imparts the desired abrasion resistance
to the most varied end products such as FCC catalysts or endless
sanding belts. The peptization index (PI), which is determined
according to the standard directions described, serves as a
criterion of the binding strength. Accordingly a low index
means a rapidly peptizable product having good binding power.
When the componentS (sodium-aluminate liquid/aluninium-
sulphate) are passed simultaneously into a water receiver, then
the flow ratio determines the pH value of the product suspension.
A comparison of the examples shows the effect of this pre-
cipitation-pH value on the peptizability of the product: Under
otherwise identical conditions the pseudobohmite samples pre-
cipitated at pH 4 have the best peptizability (PI = 1 minute).
The higher tne pH value selected for the precipitation the more
will the peptizability decrease.
Since, as is well known, high temperatures accelerate
the formation of aluminium oxide trihydrates in strongly alkaline
media, care is taken during the precipitation that the pH
value of the suspension increasingly adjusts up to the desired
final value. Pure pseudobo~mite is thus obtained in all the
tests. Depending ~n the test conditions (p~, temperature,
aging time the samples diffex merely by the ae~ree of crystal-
linity, paxticularly by the crystal size, which can be deter-
mined by X-ray photo~raphy.
~L29L~33
Tile specif.ic surface areas are determined in the ~rea
meter after dr~ing the samples over ni~ht at 100C and then
rinsing them for 20 minutes at 150C with nitrogen (DIN 66 132).
After the precipitation the suspension is aged at
various pH ~7alues while adding sodium aluminate. A distinct
gradation could be determined:
-p~ = 8: Allthe tests resulted in nonpeptizable products.
-pH = 8.5-90: The peptizablity of the pseudobo~,lite is enforced
only by supporting factors (high temperatures,
strictly maintaining the precipitation conditions).
-pH = 9.5-lO.O:In this range pseudob'ohmite is obtained with
the desired rheological properties.
In pseudobo~mite sodium as an impurity causes unde-
sirable effects in many catalytic reactions. Therefore, as
support material the pseudobohmite must have a high degree of
purity. As is known the isoelectric point for pseudobohmite
lies at pH- 9.5. In more strongly alkaline ranges the material
adsorbs sodium ions from the solution to an ever increasing
extent.
The results of the chemical analysis confirm that
upon aging in strongly alkaline media (pH >9.5) the pseudobohmite
product always has a relatively high Na2O content.
The discussion of the rheological properties has shown
that even in the pH range of 8.5-9.0 peptizable products can
be produced under strictly controlled conditions. By selecting
the suitable boundary conditions we actually succeeded in produc-
ing pseudoboShmites which are low in sodium and at the same time
easily dispersible.
Comparision_Example 1
The example according to US Patent No. 4,154,812,
columns 2~, 30 and 31 is adjusted. The concentration of the
A12lSO4)3 solution is approximatel~ 8% by weight (as A12O3).
t:~3
The concentration of the sodium aluminate li~uor
~d = 1.46 g per cu ~) is 336 g of Na2O per litre and 236 g of
A12O3 per litre, in other words 23% by weight of Na2O and
16.2% by weight of A12O3.
1.6 litres of water are put into a round-necked flask
at 70C and 2.5 ml of the aluminium sulphate solution are added.
The pH value of this mixture is thus reduced to 3.1.
Fi~e minutes after this seeding the aluminium-sul-
phate and sodium-aluminate solutions, which had been preneated
to 65C, are simultaneously dosed in such that the pH value
of the suspension remains constant at 7.4.
During the entire reaction the temperature of the mix-
ture is maintained at 75C. After a consumption of 0.9 litre
the flow of aluminium sulphate is interrupted and the final
pH value is adjusted to 10 by adding further 50 ml of aluminate
liquor within one minute. The total consumption of aluminate
liquor is 600 ml.
On reaching the final pH value the suspension is
further stirred for 30 minutes at the same temperature (75C),
then filtered with suction while hot and washed until it is
free from sulphate.
The results are evident from Table 2.
Comparis~n Example 2
The procedure according to the claims of the German
Auslegeschrift 2,249,022 is followed. The concentration of
the A12(SO4) solution is 97~0 g of A12O3 per litre. The con-
centration of the sodium-aluminate liquor is 166.6 g of A12O3
per litre and 241.7 g of Na2O per litre.
81Q litres o~ water (8Q~C~ are put into ~ 2 cu m
3~ precipitating vat and 600 litres of the aluminiu~-sulphate
solution~, preheated to 8QQC, are dosed in. The p~ value o
the Suspens~on is adjusted to lQ with 5Q0 litres of NaAlO2
~Zg~6~33
(80C). After an a~ing time of 2 hours at the same temperature
(80C~ the suspension IS fil~ered and washed until it is free
from sulphate. The product is further processed in the usual
manner and teste~. The xesults have been listed in Table 2.
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