Title of Invention	"AN IMPROVED PROCESS FOR THE PREPARATION OF PURE STOICHIOMETRIC ALUMINIUM ORTHOPHOSPHATE"
Abstract	This invention relates to an improved process for the preparation of pure stoichiometric aluminum orthophosphate useful as catalyst. The product is also used as catalyst support and as an ingredient for the preparation of Radiation sensitive phosphate glasses.The process is simpler and easier than the existing process. The process is less expensive, and raw material is easily available. Process steps are: preparing a homogenous mixture of water soluble aluminium salt and water soluble orthophosphate salt, precipitating the aluminium phosphate gel out of the mixture by adding buffer, washing gel with deionised water and miscible organic solvent, removing the water and drying the material.

Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF PURE STOICHIOMETRIC ALUMINIUM ORTHOPHOSPHATE"

Abstract

This invention relates to an improved process for the preparation of pure stoichiometric aluminum orthophosphate useful as catalyst. The product is also used as catalyst support and as an ingredient for the preparation of Radiation sensitive phosphate glasses.The process is simpler and easier than the existing process. The process is less expensive, and raw material is easily available. Process steps are: preparing a homogenous mixture of water soluble aluminium salt and water soluble orthophosphate salt, precipitating the aluminium phosphate gel out of the mixture by adding buffer, washing gel with deionised water and miscible organic solvent, removing the water and drying the material.

Full Text	This invention relates to an improved process for the prepa¬ration of pure stoichioroetric aluminium Orthophosphate useful as catalyst, catalyst support and as an ingredient for the prepara¬tion of Radiation sensitive phosphate glasses. In the case of heterogeneous catalysis of chemical reaction aluminium Orthophosphate (A1PO4 ) refered here in after as alumini- um phosphate, is well known through its acid-base properties either as a catalyst or a catalyst support. However its acidic or base character varies with the variation of its A1:P:0 = 1:1:4 stoichiometry. In fact, stoichiometric aluminium phosphate where A1:P:0 = 1:1:4, is more an acidic catalyst than a basic catalyst and can be used to prepare nitrided aluminium phosphate (A1PON) which is a strongly basic catalyst. In ceramic field on the other hand, pure aluminium phosphate is used in making various radiation sensitive glasses like Radio photoluminescence glasses, laser glasses etc. The sensitivity to radiation of such glasses is also found to be dependent on the purity as well as A1:P stoichiometry of the aluminium phosphate used. So pure stoichiometric aluminium phosphate is a widely demad-ing material all over the world. Unfortunately, most of the com¬mercially available aluminium phosphates are not stoichiometric even in respect of A1:P ratio and are frequently found to contain aluminium metaphosphate [AlfPO3 )3 ], free aluminum (Al2 O3 ) etc. as impurities. The methods which are presently used for the preparation of stoichiometric aluminium phosphate are (1) a method due to Stephen T. Wilson etal disclosed in an U.S. Patent No 4310440 and (2) a controlled reaction method using alkene oxide, recently reported in a paper in the Journal "High Temp Chem Processes" I (1992) P-157. In the first method aluminium phosphate crystals stuffed o with organic amines are hydrothermally grown at 100-300 C from a gel formed by adding an organic templating agents like organic amines or quarternary ammonium salts to a mixture of an active form of alumina (Al2 O3 ), Orthophosphoric acid (H3 PO4 ) and water. The 'pH' of the mixture is kept in between 5-8. Pure aluminium phosphate (microporous) are then obtained by calcining the stuffed crystals at 400-600o C. In the second method amorphous and highly dispersed aluminium phosphate is prepared by slowly adding suitable amount of propyl- ene oxide to a vigorously stirred A1C1 ,6H O/H PO (M) mixture cooled to 0o C. After standing several hours, the transperent gel is thoroughly washed with propanol-2, dried and calcined in the temperature range 500-800oC. However, the major disadvantages of the existing methods described above are (1) they are very expensive and (2) tedious. Therefore, the main objective of the present invention is to provide an improved process for the preparation of stoichiometric aluminium phosphate which is simpler and less expensive compared to the existing methods. Accordingly, the present invention provides an improved process for the preparation of stoichiometric aluminum orthophosphate (AlPO4) useful as acid-base catalyst, which comprises: a) preparing a homogeneous solution of a water soluble aluminum salt as herein described in the concentration range of 0.2 - 0.5 M in deionised water, b) preparing a homogeneous solution of a water soluble phosphate salt as herein described in the concentration range of 0.2 - 0.5 M in deionised water, c) preparing a homogeneous mixture of the above two solution keeping aluminum cation and phosphate anion concentration ratio 1:1 in the total mixture, d) precipitating the aluminum phosphate gel out of the mixture by controlling the pH of the mixture at pH ~ 6 by adding a buffer such as herein described, e) washing the gel repeatedly first with deionized water and then with a water miscible organic solvent as herein described, f) removing the absorbed water out of the gel as far as practicable by washing with a dry water-miscible organic solvent as herein described, g) drying the material to obtain the product. Aluminum salt used may be chosen out of aluminum trichloride (AlCl3), aluminum sulphate A l2(SO4)3, aluminum nitrate Al (NO3)3 and the like. The water soluble phosphate salt used may be selected from sodium dihydrogen phosphate NaH2PO4 disodium hydrogen phosphate Na2HPO4, potassium dihydrogen phosphate KH2PO4, ammonium dihydrogen phosphate NH4H2PO4 and the like. The buffer solution used may be chosen from known buffers like sodium dihydrogen phosphate ± citric acid, sodium acetate + acetic acid, potassium dihydrogen phosphate + sodium hydroxide and the like. The organic solvent used for washing and dehydrating aluminum phosphate gel may be selected from dry methanol, ethanol, acetone, glycerol and the like. The drying may be affected by keeping the product in a desicator. The yield of the stoichiometric aluminum phosphate was found to be in between 60-70% depending on the ingredients used. The product is an amorphous powder and can be converted into its various crystalline variety by heat treatment. The details of the invention is described in the examples given below which are provided by way of illustration only and should not be construed to limit the scope of the invention. Example - 1 Stoichiometric aluminum phosphate can be prepared by making a homogeneous mixture of 0.3 (M) aqueous deionised solution of aluminum trichloride and 0.3 (M) aqueous deionised solution of potassium dihydrogen phosphate in a ratio such that the Al (+3) cation and PO4 (-3) anion content in the mixture becomes 1:1, then precipitating out the aluminium phosphate gel through controlling the pH of the mixture around pH ≈ 6 using a buffer of potassium dihydrogen phosphate and sodium hydroxide. The precipitate is repeatedly washed with deionised water and then with methanol and finally filtered off. The gel may be further dehydrated by washing with pure dry acetone and keeping in desiccator. The product is highly dispersed and stoichiomet¬ric, yield 65%. Example -2 Stoichiometric aluminium phosphate can also be prepared by using a 2:1 mixture respectively of 0.2(M) aqueous (deionised) solution of disodium hydrogen posphate and 0.2 (M) aqueous solu¬tion of aluminium sulphate and precipitating the aluminium phos¬phate gel by controlling the pH of the mixture around pH^e with the help of a buffer of sodium acetate and acetic acid. The precipitated gel is repeatedly washed with deionised water and the analytical grade acetone and finally filtered off. The material is then further dehydrated by repeatedly washing with dry acetone and keeping in desiccator. The product is perfectly stoichiometric and shows all desired properties, yield 60%. Example - 3 Stoichiometric aluminium phosphate may be prepared also by using a 1:1 homogeneous mixture of 0.5(M) acqueous (deionised) solution of ammonium dihydrogen phosphate and 0.5(M) aqueous (deionised) solution of aluminium nitrate and precipitating out the aluminium phosphate gel by controlling the pH at around pH 6 with the help of a buffer of sodium dihydrogen phosphate and citric acid. The precipitated gel similar to the previuos methods is washed repeatedly with deionised water and then with pure acetone and filtered under suction and finally dehydrated by washing with dry acetone and keeping in a desiccator. The product in this case is also found to be highly dispersed and stoichiometric yield 71%. Advantages of the invention 1. The process is simpler and easier than the existing processes. 2. The process is less expensive than the existing ones. 3. The process can be easily adopted by the industries for large scale production with a minimum installation cost. 4. All raw materials required for the process are easily available. We Claim: 1. An improved process for the preparation of stoichiometric aluminum orthophosphate (A1PO4) useful as acid-base catalyst, which comprises: a) preparing a homogeneous solution of a water soluble aluminum salt as herein described in the concentration range of 0.2 - 0.5 M in deionised water, b) preparing a homogeneous solution of a water soluble phosphate salt as herein described in the concentration range of 0.2 - 0.5 M in deionised water, c) preparing a homogeneous mixture of the above two solution keeping aluminum cation and phosphate anion concentration ratio 1:1 in the total mixture, d) precipitating the aluminum phosphate gel out of the mixture by controlling the pH of the mixture at pH ~ 6 by adding a buffer such as herein described, e) washing the gel repeatedly first with deionized water and then with a water miscible organic solvent as herein described, f) removing the absorbed water out of the gel as far as practicable by washing with a dry water-miscible organic solvent as herein described, g) drying the material to obtain the product. 2. An improved process as claimed in claim 1 - wherein the aluminum salt used is selected from aluminum sulphateAl2 (SO4)3, aluminum chloride A1C13, aluminum nitrate A1(NO3)3. 3. An improved process as claimed in claim 1 and 2 wherein the water soluble phosphate salt used is selected from ammonium dihydrogen phosphate (NH4H2PO4), disodium hydrogen phosphate (Na2HPO4), potassium dihydrogen phosphate (KH2PO4) 4. An improved process as claimed in claims l-3,wherein the buffer solution used is selected from sodium acetate and acetic acid buffer, potassium dihydrogen phosphate + sodium hydroxide buffer, sodium dihydrogen phosphate + citric acid buffer. 5. An improved process as claimed in claims 1-4, wherein the organic solvent used for washing and drying the gel is selected from methanol, acetone, ethanol, glycerol. 6. An improved process as claimed in claims 1-5, wherein the drying is effected by keeping the washed gelin a desiccator. 7. An improved process for the preparation of a stoichiometirc aluminum orthophosphate useful as acid base catalyst, substantially as herein described with reference to the examples.

Full Text

This invention relates to an improved process for the prepa¬ration of pure stoichioroetric aluminium Orthophosphate useful as catalyst, catalyst support and as an ingredient for the prepara¬tion of Radiation sensitive phosphate glasses.
In the case of heterogeneous catalysis of chemical reaction
aluminium Orthophosphate (A1PO4 ) refered here in after as alumini-
um phosphate, is well known through its acid-base properties either as a catalyst or a catalyst support. However its acidic or base character varies with the variation of its A1:P:0 = 1:1:4 stoichiometry. In fact, stoichiometric aluminium phosphate where A1:P:0 = 1:1:4, is more an acidic catalyst than a basic catalyst and can be used to prepare nitrided aluminium phosphate (A1PON) which is a strongly basic catalyst.
In ceramic field on the other hand, pure aluminium phosphate is used in making various radiation sensitive glasses like Radio photoluminescence glasses, laser glasses etc. The sensitivity to radiation of such glasses is also found to be dependent on the purity as well as A1:P stoichiometry of the aluminium phosphate used.
So pure stoichiometric aluminium phosphate is a widely demad-ing material all over the world. Unfortunately, most of the com¬mercially available aluminium phosphates are not stoichiometric even in respect of A1:P ratio and are frequently found to contain
aluminium metaphosphate [AlfPO3 )3 ], free aluminum (Al2 O3 ) etc. as

impurities.

The methods which are presently used for the preparation of stoichiometric aluminium phosphate are (1) a method due to Stephen T. Wilson etal disclosed in an U.S. Patent No 4310440 and (2) a controlled reaction method using alkene oxide, recently reported in a paper in the Journal "High Temp Chem Processes" I (1992) P-157.
In the first method aluminium phosphate crystals stuffed
o with organic amines are hydrothermally grown at 100-300 C from a
gel formed by adding an organic templating agents like organic amines or quarternary ammonium salts to a mixture of an active
form of alumina (Al2 O3 ), Orthophosphoric acid (H3 PO4 ) and water.

The 'pH' of the mixture is kept in between 5-8. Pure aluminium
phosphate (microporous) are then obtained by calcining the
stuffed crystals at 400-600o C.
In the second method amorphous and highly dispersed aluminium phosphate is prepared by slowly adding suitable amount of propyl-
ene oxide to a vigorously stirred A1C1 ,6H O/H PO (M) mixture

cooled to 0o C. After standing several hours, the transperent gel
is thoroughly washed with propanol-2, dried and calcined in the
temperature range 500-800oC.
However, the major disadvantages of the existing methods described above are (1) they are very expensive and (2) tedious.
Therefore, the main objective of the present invention is to provide an improved process for the preparation of stoichiometric aluminium phosphate which is simpler and less expensive compared

to the existing methods.
Accordingly, the present invention provides an improved process for the preparation of stoichiometric aluminum orthophosphate (AlPO4) useful as acid-base catalyst, which comprises:
a) preparing a homogeneous solution of a water soluble aluminum salt as herein
described in the concentration range of 0.2 - 0.5 M in deionised water,
b) preparing a homogeneous solution of a water soluble phosphate salt as herein
described in the concentration range of 0.2 - 0.5 M in deionised water,
c) preparing a homogeneous mixture of the above two solution keeping aluminum
cation and phosphate anion concentration ratio 1:1 in the total mixture,
d) precipitating the aluminum phosphate gel out of the mixture by controlling the pH
of the mixture at pH ~ 6 by adding a buffer such as herein described,
e) washing the gel repeatedly first with deionized water and then with a water
miscible organic solvent as herein described,
f) removing the absorbed water out of the gel as far as practicable by washing with a
dry water-miscible organic solvent as herein described,
g) drying the material to obtain the product.
Aluminum salt used may be chosen out of aluminum trichloride (AlCl3), aluminum sulphate A l2(SO4)3, aluminum nitrate Al (NO3)3 and the like.
The water soluble phosphate salt used may be selected from sodium dihydrogen phosphate NaH2PO4 disodium hydrogen phosphate Na2HPO4, potassium dihydrogen phosphate KH2PO4, ammonium dihydrogen phosphate NH4H2PO4 and the like. The buffer solution used may be chosen from known buffers like sodium dihydrogen phosphate ± citric acid, sodium acetate + acetic acid, potassium dihydrogen phosphate + sodium hydroxide and the like. The organic solvent used for washing and dehydrating aluminum phosphate gel may be selected from dry methanol, ethanol, acetone, glycerol and the like.
The drying may be affected by keeping the product in a desicator. The yield of the stoichiometric aluminum phosphate was found to be in between 60-70% depending on the ingredients used.
The product is an amorphous powder and can be converted into its various crystalline variety by heat treatment.
The details of the invention is described in the examples given below which are provided by way of illustration only and should not be construed to limit the scope of the invention.
Example - 1
Stoichiometric aluminum phosphate can be prepared by making a homogeneous mixture of 0.3 (M) aqueous deionised solution of aluminum trichloride and 0.3 (M) aqueous deionised solution of potassium dihydrogen phosphate in a ratio such that the Al (+3) cation and PO4 (-3) anion content in the mixture becomes 1:1,
then precipitating out the aluminium phosphate gel through controlling the pH of the mixture around pH ≈ 6 using a buffer of potassium dihydrogen phosphate and sodium hydroxide.
The precipitate is repeatedly washed with deionised water and then with methanol and finally filtered off. The gel may be further dehydrated by washing with pure dry acetone and keeping in desiccator. The product is highly dispersed and stoichiomet¬ric, yield 65%.
Example -2
Stoichiometric aluminium phosphate can also be prepared by using a 2:1 mixture respectively of 0.2(M) aqueous (deionised) solution of disodium hydrogen posphate and 0.2 (M) aqueous solu¬tion of aluminium sulphate and precipitating the aluminium phos¬phate gel by controlling the pH of the mixture around pH^e with the help of a buffer of sodium acetate and acetic acid.
The precipitated gel is repeatedly washed with deionised water and the analytical grade acetone and finally filtered off. The material is then further dehydrated by repeatedly washing with dry acetone and keeping in desiccator. The product is perfectly stoichiometric and shows all desired properties, yield 60%.
Example - 3
Stoichiometric aluminium phosphate may be prepared also by using a 1:1 homogeneous mixture of 0.5(M) acqueous (deionised) solution of ammonium dihydrogen phosphate and 0.5(M) aqueous (deionised) solution of aluminium nitrate and precipitating out the aluminium phosphate gel by controlling the pH at around pH 6
with the help of a buffer of sodium dihydrogen phosphate and citric acid.
The precipitated gel similar to the previuos methods is washed repeatedly with deionised water and then with pure acetone and filtered under suction and finally dehydrated by washing with dry acetone and keeping in a desiccator. The product in this case is also found to be highly dispersed and stoichiometric yield 71%.
Advantages of the invention
1. The process is simpler and easier than the existing
processes.
2. The process is less expensive than the existing ones.
3. The process can be easily adopted by the industries for large
scale production with a minimum installation cost.
4. All raw materials required for the process are easily
available.

We Claim:
1. An improved process for the preparation of stoichiometric aluminum
orthophosphate (A1PO4) useful as acid-base catalyst, which comprises:
a) preparing a homogeneous solution of a water soluble aluminum salt as herein
described in the concentration range of 0.2 - 0.5 M in deionised water,
b) preparing a homogeneous solution of a water soluble phosphate salt as herein
described in the concentration range of 0.2 - 0.5 M in deionised water,
c) preparing a homogeneous mixture of the above two solution keeping aluminum
cation and phosphate anion concentration ratio 1:1 in the total mixture,
d) precipitating the aluminum phosphate gel out of the mixture by controlling the pH
of the mixture at pH ~ 6 by adding a buffer such as herein described,
e) washing the gel repeatedly first with deionized water and then with a water
miscible organic solvent as herein described,
f) removing the absorbed water out of the gel as far as practicable by washing with a
dry water-miscible organic solvent as herein described,
g) drying the material to obtain the product.

2. An improved process as claimed in claim 1 - wherein the aluminum salt used is
selected from aluminum sulphateAl2 (SO4)3, aluminum chloride A1C13,
aluminum nitrate A1(NO3)3.
3. An improved process as claimed in claim 1 and 2 wherein the water soluble
phosphate salt used is selected from ammonium dihydrogen phosphate
(NH4H2PO4), disodium hydrogen phosphate (Na2HPO4), potassium dihydrogen
phosphate (KH2PO4)
4. An improved process as claimed in claims l-3,wherein the buffer solution used is
selected from sodium acetate and acetic acid buffer, potassium dihydrogen
phosphate + sodium hydroxide buffer, sodium dihydrogen phosphate + citric acid
buffer.
5. An improved process as claimed in claims 1-4, wherein the organic solvent used
for washing and drying the gel is selected from methanol, acetone, ethanol,
glycerol.
6. An improved process as claimed in claims 1-5, wherein the drying is effected by
keeping the washed gelin a desiccator.
7. An improved process for the preparation of a stoichiometirc aluminum
orthophosphate useful as acid base catalyst, substantially as herein described with
reference to the examples.

Documents:

1802-del-1996-abstract.pdf

1802-del-1996-claims.pdf

1802-del-1996-correspondence-others.pdf

1802-del-1996-correspondence-po.pdf

1802-del-1996-description (complete).pdf

1802-del-1996-form-1.pdf

1802-del-1996-form-2.pdf

1802-del-1996-form-4.pdf

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Patent Number

214899

Indian Patent Application Number

1802/DEL/1996

PG Journal Number

10/2008

Publication Date

07-Mar-2008

Grant Date

18-Feb-2008

Date of Filing

14-Aug-1996

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI, 110001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	RADHA BHALLABH DEBNATH	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA - 700032, INDIA

PCT International Classification Number

C01B 25/36

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA