Note: Descriptions are shown in the official language in which they were submitted.
1ZS~5977
PROCESS FOR THE PREPARATION OF ALUMINA
11 1
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Background of the Invention
This invention relates ~enerally to a process for the
preparation of alumina. More specifically, the present invention
is concerned with a process for the preparation of alumina having
desirable pore diameter and surface area suitable for use as a
¦ catalyst carrier.
Alumina is widely used as a catalyst carrier because of its
higher mechanical strength and larger surface area as compared
with other inorganic oxides, a large surface area being long
considered to be advantageous since the ~eactivity of a catalyst
depends on its surface area. In recent years, however, the pore
diameter and pore distribution of a catalyst carrier have been
recognized as being also of importance. In fac~, the pore
diameter ~nd the pore volume of a catalyst have a greater
influence on the catalytic reaction than the surface area when the
; I molecular size of the reactant has an effect on the catalytic
reaction. In addition, the mechanical strength of a catalyst
l generally depends upon its pore diameter and pore volume. There-
¦ fore, many attempts have been made to provide an effective method
¦ which can control the pore distribution of alumina and which can
¦produce an alumina carrier having an improved mechanical strength.
¦ In many catalytic reactions, the pore diameter of the catalyst
has an important effect on the catalytlc activlty and selectivity.
l The smaller the pore diameter, the lower becomes the rate of
¦ diffusion of the reactant molecules into the catalyst pores,
i resulting in a decrease of the catalytic effectiveness factor and, ¦
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thus, the catalytic activity. When the pore dia~eter i= increased,l
the catalytic effectiveness factor i5 also increased, but the
increase of the effectiveness factor stops after the pore diameter
reaches a certain value. When the pore diameter is increased
beyond the specific value, the apparent catalytic activity is
decreased as a result of a decrease in the surface area. If the
pore diameter is increased while maintaining the surface area
jwithin a certain level, then the pore volume becomes so large
¦that the mechanical strength of the catalyst is considerably
!deteriorated. Therefore, in order to provide a catalyst exhibiting
¦excellent cataly~ic activity, it is necessary tc provide a catalyst
¦carrier which has both an optimum pore diameter and large surface
¦larea while controlling the pore volume to a value so that the
¦deterioration of the mechanical strength is prevented.
I Among many types of alumina, y-alumina is known to have a
¦high thermal stability and a high mechanical strength. It is also
I ; known that y-alumina can be produced by calcining boehmite gel
and that y-alumina can be converted into alumina of other
crystalline forms such as ~-alumina~ Boehmite gel is a hydrated
gel of fibrous boehmite cxystallites, generally called "pseudo-
boehmite". The boehmite gel can be generally produced by aging
non-crystalline aluminum hydroxide at a temperature of at least
50C and a pH of 6 - 11. To produce alumina carriers (not only
y-alumina but also other forms of alumina) having suitably
controlled pore diameter distribution and pore volume, the crystal
size of the pseudo-boehmite must be adjusted to a suitable size.
¦When the pseudo-boehmite has an excessively large crystal size,
¦ the resultant alumina formed by calcination of the pseudo-boehmite ¦
will have a~large pore diameter. On the other hand, when the
pseudo-boehnite has an excessively small crystal size, the
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resulting alumina will have a small pore diameter and, further,
the pore volume will be reduced as a result of the excessive
sintering of the crystallites during calcination. Furthermore, if
the pseudo-boehmite crystallites have not uniform sizes, the
resultant alumina obtained by calcination will have non-uniform
crystal sizes so that the pore diameter will he also non-uniform
and the pore volume will become very small. Additionally, when
the boehmite gel contains a large amount of non-fibrous fine
crystals or amorphous ~omponents, the gel will densely aggromerate
and the alumina product obtained therefrom by calcination will
have a small pore volume. Therefore, in order to obtain alumina
carriers having desirably controlled pore diameter distribution
and pore volume, it is necessary to prepare a boehmite hydrogel
¦ containing alumina crystallltes of a uniform and suitable size.
Conventionally, the control of the pore diameter and pore
vol~ne of a catalyst carrier has resorted to a method in which
¦ the particle size of each of the primary particles constituting
the carrier and the packing of the primary particles are controlled
l so as to control the size and the volume of the space de-fined
¦ between the primary particles. However, from the standpoint of
!j mechanical strength, the manner of packing cannot be freely
¦ varied but is limitad according to the particle size. In other
¦~ words, the pore diameter cannot be varied independent of the pore
1I volume. This also applies to`alumina carriers. Thus, though
¦I the pore diameter can be increased by increasing the particle
¦ size of the primary particles, the pore volume~cannot be increased¦
¦ and the specific surface area lS reduced thereby.
Various methods have thus far been proposed for preparing
alwnina, especially y-alumina, having a large pore volume and a
large pore d a~eter while mainta nlng the specific surface area
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;at a high level. One such method includes controlling the
shrinkage of the gel structure during drying and calcining of
boehmite hydrogel. Since, accordin~ to this metho~, the specific
surface area is maintained unchanged, the control of the pore
¦ volume can be made by the control of the pore diameter. An example
of the above method is disclosed in Journal of Polymer Science,
Vol. 34, p. 129, in which the drying speed of the boehmite hydrogel
is controlled. This method, however, suffers f.rom a drawback
¦because the control of the pore volume must be limited to a very
I!narrow range in order to maintain the mechanical strength of the
¦¦alu~ina product in an appropriate range. Some methods are
proposed which are capable of controlling the pore volume in a
l¦wide range, such as (1) a method in which a water-soluble polymeric
!I material such as a polyethylene glycol is adde~ ~o the boehmite
: ~ 15 ¦¦ hydrogel (Japanese.Published Unexamined Patent Applications Nos.
52-104498 & 52-77891); and (2) a method in which an alcohol is
¦substituted for a part of, or a greater part of, the water in the
boehmite hydrogel tJapanese Published Une~amined Patent Application
No. 52-1235B8), In both methods, the pore volume is controlled
by use of an amount of the water-soluble polymeric material ~in
the former case) or the alcohol (in the latter case~ which may
inhibit the dense aggregation of the boehmite crystallites that
would occur during the drying step as a result of the surface
¦ tension of the water contained in the gel. The alumina carrier
1 obtained by these methods, however, fails to exhibit satisfactory
: I mechanical strength and stability to water because the binding
¦ forces between boehmite crystallites are weak due to the
i deterioration of the surface tension of water.
Japanese Examined Patent Publication No. 49-37517 proposes
a method in which a part of the boehmlte gel is first changed to
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xerogel and the xerogel is then incorporated into a hydrogel of
boehmite to increase the pore volume. The alumina thus obtained
has a so-called "double-peak" pore distribution having small pores
defined between boehmite fine crystallites and large pores defined
between the xerogels. Therefore, this method cannot produce an
alumina carrier having a large pore volume in pores having a
, desirable pore diameter and a large surface area.
I ¦ In order to control the particle size of the primary particles¦
I forming an alumina carrier, it is necessary to control the
l particle size of the primary particles forming the boehmite
hydrogel which is a precursor material for the carrier. As
¦describ~d previously, the conventional method of preparing a
¦hoehmite hydrogel includes aging seed aluminum hydroxide at a pH
¦of 6 - 11 which range is suited for the formation of boehmite.
IIHowever, in suoh a p~ range, the rate of dissolution of fine
crystallites is extremely low so that the so-called Ostwald's
¦ rate (rate at which crystals grow with accompanying dissolution
of fine crystallites) becomes very low. There~ore, the conventio-
l nal method requires a long period of time ~or the growth of
¦ boehmite particles.
United States patent No. 4,248,852 discloses a method for
the preparation of an alumina carrier~ especially ~-alumina,
having a large surface area and a controlled pore volume. This
~ethod includes alternately adding to a slurry containing aluminum
hydroxide which serves as seed crystals, while maintaining the
temperature of the slurry at 50C or more, an aluminum compound
and a neutralizing agent with stirring so as to form active
aluminum hydroxide which is occluded into the seed aluminum
hydroxide, thereby to accelerate ~hè growth of the crystals. The ¦
thus grown boehmite particles combine with each other to form a
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sparse aggreg~te. ~y controlling the st~te of the aggregate, the
shrinkage o~ boehmite gel during dr~ing can be prevented and an
alumina carrier having a controlled pore charac~eristics and a
large surface area can be obtained. This method, however, has
a problem in practice because the operation of the process is
complicated.
Summary of tle Invention
l With the foregoing situation in view, the present invention
Ijhas as its prime object the provision of a simple process by
~which an alumina carrier having a high mechani~al strength and a
large pore volume in pores of a desired diameter can be easily
l obtained.
i The present invention pro~ides an improved process for the
~reparation of alumina, including the steps of forming an alumina
lS ¦hydrogel from aluminum hydroxide, and processing the hydrogel for
iconversion into alumina. The improvement involves the alumina
hydrogel forming step which is performed in the presence of sulfate
ion and which comprises providing, in a reaction zone, an aqueous
slurry containing seed aluminum hydroxide and havin~ a pH of
6 - 11, and foeding an aluminum compound and a pH controlling
agent to the reaction zone for mixing with the aqueous slurry,
¦while maintaining the squeous slurry at a temperature of at least
about 50C, at feed rates so that the pH of the aqueous slurry is
ll maintained within the range of 6 - 11 and that 0.2 - 5 mols/hour
! of aluminum components, in terms of elemental aluminum, are fed
to the reaction zone per mol of the aluminum hydroxide originally
contained in the a~ueous slurry, whereby the seed aluminum
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IZ~59~7
hydroxide s caused to grow to the alumina hydrogel.
The feature of the present invention resides in the specified
feed rates of the aluminum compound and the pH controlling agent. I
When the aluminum compound and the pH controlllng agent are added
to the aqueous slurry, the aluminum compound is converted into
active aluminum hydroxide having a high reactivity. In the
presence of the seed aluMinum hydroxide, the thus formed active
¦¦aluminum hydroxide is occluded thereinto to effect the growth
¦¦thereof. However, when the active aluminum hydroxide exists in
lla large amount, a part of the active aluminum hydroxide tends to
¦¦form, without being occluded into the seed aluminum hydroxide
originally present in the slurry, new seed aluminum hydroxide by
coalescence o~ the excess active aluminum hydroxide, similar to
~- the generatlon of secondary crystal nuclei in crystal growth. As
a consequence of the formation of the new seed aluminum hydroxide,
the resultant boehmite slurry contains boehmite of various sizes,
rendering it difficult to control the pore structure of the
alumina carrier produced therefrom. It has been found that when
tne ~eed rates of the aluminum compound and the pH controlling
agent is controlled so that the feed rate of their aluminum
¦components does not exceed 500 molar ~ per hour, interms of
elemental metal, based on the seed aluminum hydroxide originally
¦ present in the slurry, the seed aluminum hydroxide can grow to
l boehmite nydrogel without involving the above problem. On the
other hand, when the feed rate of the aluminum compound and the
pH controlling agent is insufficient to provide at least 20 molar
% per hour of aluminum components, in terms of elemPntal aluminum,
¦,based on the seed aluminum hydroxide, the growth of the seed
¦ aluminum hydroxide requires a considerably long time and is
disadvantageous from an economic point o~ view.
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I
Another feature of the present invention is that the alumina
hydrogel forming step is conducted in the presence of sulfate ion.
The advantages accruing from performing the alumina hydrogel
forming step in the presence of sulfate ion are as follows.
~irstly, sulfate ion can prevent the coalescence of the active
aluminum hydroxide. Even if the relative amount of the active
aluminum hydroxide to the seed aluminum hydroxide is maintained
at a proper range, coalescence of the active aluminum hydroxide
will take place unless the active aluminum hydroxide is swiftly
occluded into the seed aluminum hydroxide. Si~ce sulfate ion is
easily adsorbed on the surface of the seed aluminum hydroxide and
since the sulfate ion thus adsorbed serves to accelerate khe
occlusion of the active aluminum hydroxide into the seed aluminum
hydroxide, the occurrence of the coalescence of the active aluminum
1 15 hydroxide may be minimi~ed when the alumina hydrogel forming step
is performed in the presence of sul~ate. Secondly, the growth
of the alumina hydrogel proceeds faster in the presence of sulfate
ion than that in the presence of other ion such as halide ion and
¦nitrate ion. Thirdly, the sulfate ion is easily removed from the
1 alumina hydrogal. Whils~ the formation of precipitates proceeds
much faster in the presence of phosphate ion as compared with
sulfate ion, the rate of the precipitation is so fast that the
¦¦boehmite crystallites hardly form in the presence of phosphate
¦ion. Further, it is very difficult to remove the phosphate ion
I from the precipitates. Such precipitates containing phosphate ion ¦
cannot give alumina having a large pore volume and a large surface
area. In contrast, the sulfate ion in the alumina hydrogel
prepared in accordance with the process of the present invention
may be easily removed therefrom by, for example, washing and
¦ filtration, enabling to produce alumina having ~oth a large pore
.: I lZ!~15~77
volume and a large surface area. Fourthly, sulfate ion serves
to accelerate the formation of a stable aggregate of grown boehmite
particles with the active aluminum hydroxide acting as a binding
agent. The aggregate is not destroyed when subjected to subsequent
treatments for the conversion into an alumina carrier. As a result
the alumina carrier may have a high mechanical strength, a large
pore volume and a large surface area.
The present invention i5 also characterized in that the
¦alumina hydrogel forming step is performed at a pH of 6 - 11.
In an alumina hydrogel forming system containing sulfate ion,
there is established, at a pH of below 6, a condition wherein
amorphous aluminum hydrate is precipitated. In the pll region of
abov~ 11, on the other hand, there is established a condition in
l!which bayerite crystals are formed. Since the alumina hydrogel
iiforming step of thç present invention is carried out at a pH of
6 - 11, there is little possibility that the alumina hydrogel be
licontaminated with other crystallites than boehmite. For the above ¦
¦Ireason, it i5 preferred that the aluminum compound and the pH
¦ controlling agent be added continuously and simultaneously into
!I the seed aluminum hydroxide-containing slurry with stirring. The
,¦maintenance of the pH within the range of 6 - 11 has an additional j
merit that th~ rate of growth of boehmite crystals is faster as
compared with the case in which the pH is alternately swung
¦between the region of below 5 and the region of above 11, because
~5 at a pH within the range of 6 - 11 no dissolution of boehmite
crystallites occurs.
Other objects, features and advantages of the present
invention will become apparent from the detailed description of
the invention to follow.
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ILZl~159~7
Detailed Description of the Invention
The aluminum hydroxide contained in the aqueous slurry which
is used as the starting material in the process of the present
invention serves as a seed for the formation of boehmite hydrogel.
The aqueous slurry may be produced by any conventional methods
used in this field. For example, the seed aluminum hydroxide may
be produced by (1) adding an al~ali to an aqueous solution of an
aluminum salt of a strong acid such as aluminum nitrate, aluminum
l chloride or aluminum sulfate at a pH of 6 - 11, and ~2) adding
¦ an acid or the above aluminum salt to an aqueous solution of
sodium aluminate, potassium aluminate or the like aluminate at a
l pH of 6 - llo
¦ As described hereinafter, the aluminum compound and the pH
controlling agent which are added to the slurry for the formation
¦ of alumina hydrogel can be the same substances as used in the
slurry forming step. Therefoxe, the formation of the seed
aluminum hydroxide and the growth thereof to the alumina hydrogel
may be continuously performed in accordance with the process of
~ the present invention without a need of separation, washing and
1 other operations after -the formation of th~ seed aluminum
i hydroxide.
The seed aluminum hydroxide prepared by the above~described
neutralization reaction is found to have a fibrous form having a
! length of 100 A and a diameter of 10 - 20 A by a microscopic
j examination. The ibrous material is considered to have a boehmite
structure. However, because of its smallness in particle size,
an X-ray diffraction analysls indicates that the fibrous material
is amorphous. Such seed aluminum hydroxide, when calcined at
a temperature of 400~, gives amorphous alumina having a pore
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lZ~S977
~volume of as small as 0.4 cc/g. Even when such a seed aluminum
hydroxide-containing slurry is allowed to stand at a temperature
of 50C and a pH of 6 - 11 for over 24 hours, no crystal growth
takes place and the alumina produced from the aged seed aluminum
¦ hydroxide has a pore volume of as small as 0.4 cc/g.
According to the present invention, the slurry having a pH
of 6 - 11 is provided in a reaction zone, to which are added the
aluminum compound and the pH controlling agent while maintaining
¦the pH and the temperature at 6 - 11 and at least about 50C,
¦respectively, for the growth of the seed aluminum hydroxide and
¦¦for the formation of an alumina hydrogel. When the hydrogel
forming step is performed at a low temperature, the pore volume
of y-alumina derived from the resultant alumina hydrogel becomes
distributed in a broad range of pore diameters. Under a
¦pressurized condition, thelhydrogel forminy step may be carried
out at a temperature of 100C or more. In this case, too, the
pore volume distribution tends to slightly broaden. Generally,
however, the influence of the temperature on pore distribution
lof the alumina product does not cause any essential problems so
¦¦long as the alumina hydrogel forming step is performed at least
¦labout 50C. Preferably, the hydrogel forming step is carrled out
at a temperature of above 70C but below the bo.iling point of the
¦Islurry.
! Any water-soluble aluminum salt or aluminate is suitably
¦ used as the aluminum compound. Examples of the aluminum salts
l include aluminum sulf ate, aluminum chloride and aluminum nitrate.
¦ Examples of the aluminates include sodium aluminate and potassium
aluminate. When aluminum sulfate is used as the aluminum compound,
¦¦an alkaline substance such as sodium aluminate, potassium
30 1l aluminate, ammonia, sodium hydroxide or potassium hydroxide is
` I ~LZ~9~7
¦lused as the pH controlling agent. Such an alkaline substance is
also used in combination with aluminum salts other than aluminum
sulfate. In such a case, the aluminum salts are generally used
together with sulfuric acid. When an aluminate is used as the
¦ aluminum compound, sulfuric acid is suitably used as the pH
!¦controlling agent. Illustrative of suitable combinations of the
¦laluminum compound and the pH contxolling agent are aluminum
¦¦sulfate-sodium aluminate~ sodium aluminate-sulfuxic acid and
l¦aluminum sulfate-sodium hydxoxide. Above all, the combination of
I aluminum sulfate and sodium aluminate is especially preferred
since the conbination can n.inimize the local increase or decrease
of the pH of the aqueous slurry out of the pH range of 6 - ll
during the alumina hydrogel forming step. It is essential that
the reaction system contain sulfate ion. The amount of the sulfatel
ion is preferably 0.12 - 3 mols, more preferably 0.2 - l mol per
mol of the total aluminum components contained in the reaction
system in terms of elemental aluminum, throughout the ~rowth of
l the seed aluminum hydroxide. Sulfate ion may be provided in the
I reaction system in various manners. The seed aluminum hydroxide- t
~ containing slurry can contain the necessary amount of sulfate ion
¦ so that the alumina hydrogel forming step may be performed in
, the presence of sulfate ion. When the aluminum compound and~or
I the pH controlling agent are of a type which is capable of
providing sulfate ion, such as sulfuric acid or aluminum sulfate,
1 the alumina hydrogel forming step can be performed in the presence
o~ sulfate ion. The use of a combination of an aluminum salt,
such as aluminum chloride, and sulfuric acid can also provide
the react system with sulfate ion.
~ ~s described prPviously, the feed rates of the aluminum
¦ compound and the pH controlling agent should be controlled so that
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aluminum components are hourly supplied to the reaction zone in
an amount of 0.2 - 5 mols, in terms of elemental aluminum, per
¦~mol of the seed aluminum hydroxide originally contained in the
aqueous slurry, the aluminum components being derived not only
from the aluminum compound but also from the pH controlling agent
if it contains aluminum.
; When the feed rates of the aluminum compound and the pH
controlling agent are too low to provide the 0.2 mol/hour lower
limit, the growth of the seed aluminum hydroxide fails to proceed
at a des.irable high velocity and, moreover, the selective growth
of fine particles of seed aluminum hydroxide cannot occur. In
general, the smaller the particle size of seed aluminum hydroxide,
the higher is the rate at which the seed aluminum hydroxide grows.
Therefore, even when both fine and relatively large particles of
seed aluminum hydroxide coexist, the particle size of the resultant
hydrogel becomes uniform if active aluminum hydroxide is present
in a proper amount.
! On the other hand, too high a feed rate of aluminum
ll components resulting from the addition of the aluminum compound
1 and the pH controlling agent causes the formation o~ new seed
aluminum hydroxide by coalescence of excess active aluminum
hydroxide, which in turn results in the non-uniformlty of particle
size of the resultant boehmite gel. Since the ability of seed
l aluminum hydroxide to occlude active aluminum hydroxide is high
1 at the initial stage of the hydrogel forming step, new seed
aluminum hydroxide will not form even when the initial feed rate
is the maximum (5 mols). However, such an ability becomes
lowered with th~ growth of boehmite gel particles. Therefore,
it is desired to lower the feed rates of aluminum components after ¦
boehmite gel l~artlcles grow to ha.e a certain degree so that the
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formation of new seed aluminum hydroxide is pre~ented.
The total amount of the aluminum components to be added to
¦the seed aluminum hydroxide-containing slurry by the supply of
the aluminum compound and the p~ controlling agent may vary
depending upon the intended pore volume and pore diameter of the
¦ alumina carrier to be prepared. For example, in order for seed
¦ aluminum hydroxide having a particle size of 10 - 20 A to grow,
l~by occlusion of active aluminum hydroxide, to boehmite gel
¦Iparticles having a particle size of 30 - 40 A, the feed rate of
¦¦aluminum components should be at least several times the amount
l of the seed aluminum hydroxide. Preferably, the total amount of
¦ the aluminum components is at least a value so that the formation
of boehmite crystallites may be clearly observed by an X-ray
l diffraction analysis. Generally, the Lotal amount is about 3 - 30
1 times the amount, in terms of alumina, of the seed aluminum
i hydroxide.
The aluminum compound and the pH controlling agent are
preferably added to the slurry each in the fvrm of an aqueous
solution. The concentrations of the aluminum compound and of the
p~l controlling agent in respective solutions are not critical.
However, too high concentrations are undesirable because the pH
control becomes difficult to perform smoothly. Too low concent-
l rations are also undesirable because the rate of the growth of
! boehmite gel becomes slow~ Further, the concentration of the
1 solid matters in the reaction mixture within the reactor is
desired to be controlled throughout the hydrogel forming step
so that the agitation may be effected thoroughly without bringing
about local denseness or sparseness of active aluminum hydroxide
l or local increase or decrease in pH of the reaction mixture.
¦ Therefore, it is advisable to adjust the concentrations of the
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starting aqueous slurry and the solutions of the aluminum compound
and the pH controlling agent so that the reaction mixture can be
agitated uniformly and completely throughout the hydrogel forming
stage. When the concentration of solid matters in the reaction
mlxture is below about 5 weight % in terms of ~12O3, agitation
¦ with customarily employed rotary blade-type agitator may be
satisfactorily performed.
, The resultant slurry containing boehmite hydrogel particles
!which have thus grown and aggregated are then processed to obtain
io ~j alumina in any known manner, for example, in the following manner:
¦The hydrogel is filtered to obtain a cake. After being washed
¦Iwith water for the removal of sulfate ion, sodium ion, etc., the
cake is dehydrated to control its solids content, thereky to
facilitate the subsequent molding operation. The solids content,
for the purpose of extrusion molding, is generally adjusted to
I ¦ 20 - 35 %. The cake of which the water content has thus been
adjusted is molded into any desired shape by way of, for example,
extrusion, oil dropping and wet granulation method. A spray dry
method may also be adopted for the formation o~ a powdery alumina
~0 ¦ carrier. The extrudates or other shaped boehmite thus obtained
~are then dried, generally at a temperature of 100 - 200C, and
calcined to obtain alumina. If ~--alumina is intended, the
calcination is generally performed at a temperature of 4Q0 - 700C.
The following examples will further illustrate the present
invention.
Comparatlve Example 1
0.224 Liter of an aqueous solution of alwninum sulfate
(concentration: 80 g/Q in terms of A12O3) and 10 liters of
¦ deionized water were placed in an enamel-coated vessel and heated
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to 90C. Then, 1.5 liters of an aqueous solution o~ sodium
aluminate (concentration: 69 g/Q in -terms of A12O3) were poured
into the vessel all at once, with vigorous agitation, to ~orm a
slurry having a pH of 10. A portion of the slurry was aged at
90C for 3 hours and the remainder portion was for 6 hours. Each
of the aged slurries was filtered and washed with deionized water
to remove a greater part of the sulfate ion and sodium ion
contained therein. The each of the resultant cakes was extruded
: to obtain an extrudate having a diameter of 1.6 mm. Each
extrudate was dried at 120C for 6 hours and calcined for three
hours to form Alumina Sample Rl (aged for 3 hours) and Alumina
Sample R2 (aged for 6 hours), the physical properties of which
are shown in Table 1.
l Comparative Example 2
1 0.10 Liter of an aqueous solution of aluminum nitrate
¦ (concentration 40 g/Q in terms of A12O3) and 10 liters of a
deionized water were placed in an enamel-coated vessel and heated
to 90C. Then 0.35 liter of an aqùeous solution of sodium alumi-
l nate (concentration: 69 g/Q in terms of ~12O3~ ~as poured into
1 the vessel all at once, with vigorous agitation, to form an
! aluminum hydroxide-containing slurry having a pH of 9.5. Then an
aqueous solution of aluminum nitrate (concentration: 8 g/Q in
terms of A12O3) and an aqueous solution of sodium aluminate
(concentration: 69 g/Q in terms of A12O3) were continuously fed
to the reactor at constant rates of 0.29 Q/hour and 0.20 Q/hour,
respectively, from separate f~ed ports for mixing with the
aluminum hydroxide in the reactor, which served as a seed, while
maintaining the temperature at 90C. During the addition of the
solutions, the pH of the mixture in the reactor was found to be
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maintained within the range of ~ - 10. A portion of the reaction
¦mixture was sampled after 3 hours from the commencement of the
¦feed of the two aqueous solutions. Another portion of the
l reaction mixture was also sampled 3 hours after the first sampling.
¦ Each sample was filtered and washed with deionized water to obtain
; j a cake which was subsequently extruded through a die, whereb~ an
extrudate having a diameter of 1.6 mrn was obtai~ed. Each
extrudate was dried and calcined in the same manner as described
lin Comparative Example 1 to obtain Alumina Sample R3 (Feed of the
¦solutions continued for 3 hours) and Alumina Sample R4 (Feed of
the solutions continued for 6 hours) whose physical properties
are summarized in Table 1.
Example 1
0.05 Liter o,f an aqueous solutlon o aluminum sulfate
l (concentration: 80 g/Q in terms of ~12O3) and iO liters of
deionized water were placed in an enamel-coated vessel and
heated to 90C. Then, 0.35 liter of an aqueous solution of sodium
aluminate (concentration: 69 g/Q in terms of A12O3) ~as poured
into the vessel all at once, with vigorous agitation, to form an
~ aluminum hydroxide-containing slurry having a pH of 10. Then an
aqueous solution of aluminum sulfate (concentration: 8 g/Q in
terms of A12O3) and an aqueous solution of sodium a,luminate
(concentration: 69 g/Q in terms of A12O3) were continuously fed
to the reactor at constant rates of 0.29 Q/hour and 0.20 Q/hour,
¦ respectivel~, from separate feed ports for mixing with the
aluminum hydroxide in the reactor, which served as a seed, while
maintaining the temperature at 90C. During the addition of the
solutions, the p~ of the mixture in the reactor was found to be
maintained within the range of 9 - 10. 0.3 Liter of the reaction
11 lZ1~5977
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I
mixture was sampled after 3 hours from the commencement of the
feed of the two aqueous solutions. Further three portions of the
reaction mixture, each in an amount of 0.3 liter, were also sampled
hourly after the first sampling. Each sample was filtered and
~dispersed into 2 liters of deionized water and again filtered.
Such dispersion and filtration operation was repeated thrice in
total to obtain a cake which was subsequently extruded through a
die, whereby an extrudate having a diameter of 1.6 mm was
¦obtained. The resultant 4 types of extrudates were dried and
¦calcined in the same manner as described in Comparative Example 1,
¦whereby obtaining Alumina Samples A - D (Feed of the solutions
continued for 3, 4, 5 and 6 hours, r~spectively) whose physical
properties are summarized in Table 1.
. Table 1
1 _ Rl R2 R3 R4 _ B C D
Specific surface area 162 159 203 146 234 205 185 173
(m2/g)
Pore volume ~cc/g~
75 ~ 100 0.30 0.29 0.06 0.03 0.07 0.05 0.04 0.05
100 - 200 A 0.02 0.02 0.30 0.19 0,28 0.25 0.19 0.17
200 - 400 A 0,00 0.00 0.38 0.27 0.63 0.75 0.56 0.39 l
400 A - 0.00 0~00 0.51 1.32 0.03 0.04 0.34 0.65 I
Total 0.32 0.31 1.26 1.81 1.01 1.09 1.13 1.26
Average pore diameter
11 (~) 79 78 248 499 lgO 212 244 292
Pellet diameter(mm)1.0 1.0 1.4 1.4 1.1 1.1 1.3 1.3
Side crushing strength
(Xg)2.5 2.6 1.0 0.9 2.9 2.~ 2.6 ~.3
I _ I I I
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05977
¦ From the res~lts shown in Table 1, it will be noted that
~Samples Rl and R2 have a very small pore volume. Though Samples
R3 and R4 have a large pore volume, the pore volume is distributed
in pores having broad range of pore diameters. Further, Samples
R3 and R4 have their large pore volume in pores of a diameter of
above 400 A, in which pores the surface area is small.
Additionally, Samples R3 and R4 are low in mechanical strength.
In contrast, Samples A-D prepared in accordance with the process
of the present invention have a remarkably high mechanical
strength and a large pore volume. The average pore diameter
increases in the order from A to D, i.e. with the increase of the
l hydrogel forming reaction time. The pore volume of any of
¦ Samples A-D is concentrated in pores havin~ a diameter of 200 -
1¦400 A.
~1 .
¦I Example 2
0.1 Liter of an aqueous solution of aluminum nitrate
(concentrationo 40 g/Q in terms of A12O3) and 10 liters of
deionized water were placed in an enamel-coated vessel and
heated to 90C. Then, 0~35 ]iter of an aqueous solution of
I sodium aluminate Iconcentration~ 69 g/Q in terms of A12O3) was
poured into the vessel all at once, with vigorous agitation, to
form an aluminum hydroxide-containing slurry having a pH of 9. 5.
The thus obtained slurry was then subjected to an alumina hydrogel-
l forming txeatment in the same manner as described in Example 1.
IITwo portions of the reaction mixture were sampled 3 and 6 hours
¦ after the commencement of the treatment, respectively. Each
Isample was then processed in the same manner as describPd in
¦Exam~le 1 to obtain Alumina Samples E and F (Feed of the solutions
continued for 3 and 6 hours, respectively) whose physical
lZI~15977
l properties were as shown in Table 2.
I
: ¦ Table 2
~ ec~flc ~ ~lace area (m /g) ~ 235 ~ 161
: 5 ~l Pore volume (cc/g)
75 - 100 A 0.23 0.03
ll 100 - 200 A . 0.35 0.15
: : 200 400 A 0.02 0.54
: 400 A - 0.01 0.34
Total 0.60 1.06
Average pore diameter (A) 101 265
l Pellet diameter (mm) 1.1 1.2
: ~ Side crushing stFength (Kg) 2.8 2.5
l Example 3
1 To the same aqueous solution containing seed aluminum hydro-
xide as used in Example 1 were added an a~ueous solution of
aluminum sulfate (First Solution, ~oncentration: 8 g/Q in terms
of A1203) and an aqueous solution of sodium aluminate (Second
: Solution, Concentration: 69 g/Q in terms of A12O3~ at various feed
rates indicated in Table 3 for 3 hours while maintaining the
temperature at 90C to form alumina hydrogel. The pH of each
reaction mixture during the hydrogel forming stage was also shown
¦in Table 3. The hydrogel was then processed in the same manner
las described in Example 1 whereby there were obtained seven types
¦of alumina (Alumina Samples G-M) whose physical properties are
shown in Table 4. For convenience of comparison, the data for
- :~0-
~z~77
Alumina Sample A (Example 1) are also shown in Tables 3 and 4.
Table 3 Feed Rates (Q/hr~
1 2 1 3 4 5 6 7 E~le 1
_ _ _
First solution 0.07 0.58 2.9 1.16 0.29 2.20 0.07 0.29
: 5 1 Second solution O.05 O.40 2.0 O.05 0.15 O.30 0.80 0.20
I pH 9-10 9-10 8-11 4-10 8-10 10-11 10-12 9-10
;l ¦Alu~Da ~ H ¦ I ¦ J ¦ K ¦ L ¦ M ¦ A
Table 4
G 3 I J j K L M A
~ _ .. l
Specific surface area ~m2/g) 198 222 173 154 233 217 178 234
: Pore volume (cc/gj .
75 - 100 A 0~41 0.11 0.05 0.07 0.07 0.07 0.35 0.07
100 - 200 A 0.03 0.59 0.23 0.43 0.70 0.40 0.02 0.28
200 - 400 A 0.01 0.02 0.33 0.01 0.06 0.45 0.01 0.63
400 ~ - 0 0.01 0.67 0.01 0.03 0.03 0.01 0.03
Total 0.45 0.73 1.29 0.52 0.85 0.96 0.38 1.01
Average pore diameter tA) 90 132 299 135 145 177 86 180
Pellet diameter (mm) 1.0 1.1 1.3 1.1 1.2 1.4 0.9 1.1
¦Sidb ~n~hlng :~ _ngth (K~) ¦ 1.5 ~3.1 ¦1.5 ¦1.8 3
20 l As seen from the data summarized in Tables 3 and 4, Alumina
¦ Sample ~ obtained with a very low feed ratè oE aluminum components¦
j (0.14 mol/hour in terms of elemental aluminum per mol of the
, aluminum hydroxide in the starting material slurry) has a very
Il I
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1:
jl ~
1 12a~977
small pore volume and a low mechanical strength. On the other
¦ hand, Alumina Sample I obtained with a very high feed rate ~5.7
mol/hour) has a large pore volume. However, Alumina Sample I is
broad in pore distribution and .is low in mechanical strength. The
Ismallness in pore diameter and pore volume and the lowerness in
mechanical strength of Alumina SampIes J and M are attributed to
improper pH control during the hydrogel forming stage. In
contrast, Alumina Samples H, K, L and A prepared in accordance
with the process of this invention have excellent physical
1~ properties suitable for use as catalyst carriers.
Example 4
~.15 Liter of 11.6 wt % sulfuric acid and 10 liters of
deionized water were placed in an enamel-coated vessel and heated
:~ to 90C. Then, 0.4 liter of an aqueous solution of sodium
aluminate (concentration: 69 g/Q in terms of A12O3) was poured
into the vessel all at once, with vigorous agitation, to form an
aluminum hydroxide-containing slurry having a pH of 10. Then
11.6 wt % sulfuric a¢id and an aqueous solution of sodium aluminat~
¦l (concentration: 69 g/Q in terms of ~12O3) were continuously fed
l to the reactor at constant rates of 0.13 Q/hour and 0.27 Q/hour,
respectively from separate feed ports for mixing with the aluminum
hydroxide in the reactor, which served as a seed, while maintain-
ing the temperature at 80C. During the ~ddition of the solutions
~ the pH of the mixture in the reactor was found to be maintained
¦ within the range of 9.5 - 10. 0.3 Liter of the reaction mixture
¦ was sampled after 6 hours from the commencement of the feed of
the two aqueous solutions. Another 0.3 liter of the reaction
mixture was also sampled after 3 hours from the first sampling.
Each sample, which contained alumina hydrogel, was processed in
11 ~
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~ ~z~
the same manner as described in E~ample 1 to obtain Alumina
Sample N and O (Reaction time: 6 and 9 hours, respectively) whose
physical properties are sho~n in Table 5.
I
¦ Example 5
0.25 Liter of an aqueous solution of aluminum sulfate
(concentration: 80 g/Q in terms of A1203) and 10 liters of
deionized ~ater were placed in an enamel-coated vessel and heated
to 70C. Then, 0.34 liter of 5~ NaOH solution was poured into
the vessel all at once, with vigorous agitation, to form an
aluminum hydroxide-containing slurry having a pH of 10.5. Then
an a~ueous solution of aluminum sulfate (concentration: 80 g/Q in
terms of A1~03) and ~N NaOH solution were continuously fed to the
reactor for 3 hours at constant rates of 0.25 ~/hour and 0.31
j Q/hour, respectivel~ from separate feed ports for mixing with the
laluminum hydroxide in the reactor, which served as a seed, while
maintaining the temperature at 70C. During the addition of the
solutions, the pH of the mixture in the reactor was found to be
maintained within the range of 9.5 - 10.5. The thus obtained
l alumina hydrogel was processed in the same manner as described in
¦ Example 1 to obtain Alumina Sample P whose physical properties
are shown in Table 5.
i Example 6
l 0.05 Liter of an aqueous solution of aluminum sulfate (First
: Solution, Concentration: 80 ~/Q in terms of A12~3) and 10 liters
of deioni.zed water were placed in an enamel-coated vessel and then,
after being heated to 95C, 0.45 liter of an aqueous solution of
sodium aluminate (Second solution, Concentration: 69 g/Q in terms
of A1203) was poured into the vessel all at once, with vigorous
20S~77~
agitation, to form an aluminum hydroxide-containing slurry having
a pH of 11. After being allowed to stand at 95C for 1 hour with
agitation, the reaction mixture was further added with 0.05 liter
of the first solution and 0.3 liter of the second solution
5simultaneously and at once whereby the pH of the mixture became
10.5. After being allowed to stand at 95C for 1 hour with
agitation, the mixture was again added with 0.05 liter of the
~first solution and 0.3 liter of the second solution so that the
¦pH of the mixture became 11. After being aged at 95C for 3.5
¦hours with agitation, the mixture was hourly added thrice with the
: Ifirst and second solutions in amount, in each time, of 0.06 and
0.28 liter, respectively, thereby obtaining alumina hydrogel. The
l¦hydrogel was processed in the same manner as described in Example
¦ll to obtain alumina Sample Q whose physical properties are shown
'lin Table 5.
Table 5
= ¦ N ¦ 0 ¦ P ¦ Q
Specific surface area (m2/g) 239 189 194 200
Pore volume (cc/g)
¦ 75 - lon A 0.11 0.04 0.06 0~07
¦ 100 - 200 A 0.57 0.20 0.26 0.34
200 - 400 A 0.02 0.75 0.61 0.52
400 A - 0.02 0.14 0~07 0.03
; Total 0.71 1.12 1.00 0.95
1 Average poxe diameter (A) 119 238 206 189
Pellet diameter (mm) 1.1 1.4 1.2 1.2
Side crushing strength (~g) 3.5 2.7 3.0 2.3
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