CA1205977A - Process for the preparation of alumina - Google Patents
Process for the preparation of aluminaInfo
- Publication number
- CA1205977A CA1205977A CA000455478A CA455478A CA1205977A CA 1205977 A CA1205977 A CA 1205977A CA 000455478 A CA000455478 A CA 000455478A CA 455478 A CA455478 A CA 455478A CA 1205977 A CA1205977 A CA 1205977A
- Authority
- CA
- Canada
- Prior art keywords
- aluminum
- alumina
- aluminum hydroxide
- controlling agent
- seed
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/34—Preparation of aluminium hydroxide by precipitation from solutions containing aluminium salts
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Catalysts (AREA)
Abstract
Abstract of the Disclosure An improved process for the preparation of alumina, including forming an alumina hydrogel from aluminum hydroxide, and processing the alumina hydrogel into alumina. The improvement involves the alumina hydrogel forming step which is conducted in the presence of sulfate ion and which comprises providing, in a reaction zone, an aqueous slurry containing seed aluminum hydroxide and having a pH of 6 - 11, and feeding to the reaction zone an aluminum compound and a pH controlling agent for mixing with the aqueous slurry while maintaining the aqueous slurry at a temperature of at least about 50°C at feed rates so that the pH of the aqueous slurry is 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 mole of the seed aluminum hydroxide originally contained in the aqueous slurry, whereby the seed aluminum hydroxide is caused to grow to the aluminum hydrogel.
Description
1ZS~5977 PROCESS FOR THE PREPARATION OF ALUMINA
il I
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, ¦
~1 5977~ I
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 I
' ~ :120S977 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 lZ/~S977 ;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 Z~S977 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
il I
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, ¦
~1 5977~ I
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 I
' ~ :120S977 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 lZ/~S977 ;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 Z~S977 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
2~5~77 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 Il 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.
Il 11 ~2~;977 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.
_ g_ Il 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 ~1 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 ; 1l iz~s~7 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 1~ 1 5~77 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 ~ - 14 -lZ0597~
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 Il I ~z~5~7~
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 97~
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 I
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
ll - 18 -¦ 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
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 ~
~ ~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 ll .
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 Il 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.
Il 11 ~2~;977 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.
_ g_ Il 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 ~1 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 ; 1l iz~s~7 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 1~ 1 5~77 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 ~ - 14 -lZ0597~
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 Il I ~z~5~7~
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 97~
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 I
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
ll - 18 -¦ 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
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 ~
~ ~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 ll .
Claims (10)
1. In a process for the preparation of alumina, including forming an alumina hydrogel from aluminum hydroxide, and processing the alumina hydrogel into alumina, the improvement comprising the alumina hydrogel forming step which is conducted in the presence of sulfate ion and which comprises feeding an aluminum compound and a pH controlling agent to a reaction zone, in which an aqueous slurry containing seed aluminum hydroxide is contained, for mixing with said aqueous slurry while maintaining said aqueous slurry at a temperature of at least about 50°C at feed rates so that the pH
of said aqueous slurry is 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 said reaction zone per mole of the seed aluminum hydroxide originally contained in said aqueous slurry, whereby the seed aluminum hydroxide is caused to grow to the alumina hydrogel.
of said aqueous slurry is 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 said reaction zone per mole of the seed aluminum hydroxide originally contained in said aqueous slurry, whereby the seed aluminum hydroxide is caused to grow to the alumina hydrogel.
2. A process according to claim 1, wherein said feeding of the aluminum compound and the pH controlling agent is conducted continuously and simultaneously.
3. A process according to claim 1, wherein said aqueous slurry contained in said reaction zone contains sulfate ion so that the alumina hydrogel forming step is conducted in the presence of sulfate ion.
4. A process according to claim 1, wherein at least one of the aluminum compound and the pH controlling agent is capable of generating sulfate ion so that the alumina hydrogel forming step is conducted in the presence of sulfate ion.
5. A process according to claim 1, wherein the aluminum compound and the pH controlling agent are each fed to said reaction zone in the form of an aqueous solution, at least one of the aqueous solutions of aluminum compound and of the pH controlling agent containing sulfate ion so that the alumina hydrogel forming step is conducted in the presence of sulfate ion.
6. A process according to claim 1, wherein the aluminum compound is aluminum sulfate and the pH controlling agent is selected from the group consisting of sodium aluminate, sodium hydroxide, potassium hydroxide and ammonia.
7. A process according to claim 6, wherein the pH controlling agent is sodium aluminate.
8. A process according to claim 6, wherein the pH controlling agent is sodium hydroxide.
9. A process according to claim 1, wherein the aluminum compound is an aluminate and the pH controlling agent is sulfuric acid.
10. A process according to claim 9, wherein the aluminum compound is sodium aluminate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000455478A CA1205977A (en) | 1984-05-30 | 1984-05-30 | Process for the preparation of alumina |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000455478A CA1205977A (en) | 1984-05-30 | 1984-05-30 | Process for the preparation of alumina |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1205977A true CA1205977A (en) | 1986-06-17 |
Family
ID=4127970
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000455478A Expired CA1205977A (en) | 1984-05-30 | 1984-05-30 | Process for the preparation of alumina |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1205977A (en) |
-
1984
- 1984-05-30 CA CA000455478A patent/CA1205977A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4555394A (en) | Process for the preparation of alumina | |
| US4248852A (en) | Process for the production of alumina suitable for use as a catalyst carrier | |
| US4514511A (en) | Preparation of spheroidal alumina particulates | |
| US4562059A (en) | Method of preparing alumina | |
| US4315839A (en) | Spheroidal alumina particulates having bifold porosity and process for their preparation | |
| EP0722422B1 (en) | Preparation of spheroidal aggregates of platy synthetic hydrotalcite | |
| US6171573B1 (en) | Alumina sol, process for preparing the same, process for preparing alumina molding using the same, and alumina-based catalyst prepared thereby | |
| US6429172B1 (en) | Method of manufacturing pseudo-boehmite | |
| US3120426A (en) | Process for the production of aragonite crystals | |
| US9045349B2 (en) | Method for preparing porous alumina | |
| US4211667A (en) | Process for producing alumina sols | |
| US5800797A (en) | Process for producing alumina and apparatus therefor | |
| WO2001026805A1 (en) | Catalyst for hydrorefining distillate oil, its carrier and preparation thereof | |
| JP2002519297A (en) | Novel dispersible hydrated aluminum, its preparation method and its use in the preparation of catalysts | |
| GB2146633A (en) | Process of preparing alumina for use as a catalyst carrier | |
| CN113735150A (en) | 4N high-purity pseudo-boehmite and preparation method thereof | |
| Ono et al. | Control of the pore structure of porous alumina | |
| JP3469285B2 (en) | Method for producing granular alumina and spherical alumina particles | |
| HU187981B (en) | Process for producing of medium granulated aluminium-hydroxide free choosable between 2 and 100 micron | |
| US4849190A (en) | Process for the production of hydrated alumina and process for the treatment of acid wastes | |
| US3352636A (en) | Process for producing alumina gel | |
| CA1205977A (en) | Process for the preparation of alumina | |
| JPH0116772B2 (en) | ||
| US2973245A (en) | Method of preparing alumina hydrate compositions containing trihydrate | |
| CN115124056A (en) | Pseudo-boehmite, preparation method and application thereof |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |