Zirconium hydroxide
This invention relates to an improved amorphous zirconium hydroxide and a method for its production. The hydroxide has a surface area of at least 300 m 2 /g, a total pore volume of at least 0.70 cm 3 /g and an average pore size of between 5 nm and 15 nm, and is prepared by a process which comprises the steps of: a) preparing an aqueous solution comprising sulphate anions and a zirconium salt such that the ZrO 2 :SO 3 ratio is 1:0.40 to 1:0.52, (b) chilling the solution to below 25° C., (c) adding an alkali in order to precipitate the amorphous zirconium hydroxide, (d) filtering and washing the precipitated zirconium hydroxide with water or an alkali to remove residual sulphate and chloride, (e) hydrothermally treating the zirconium hydroxide at a pressure of less than 3 barg, and (f) drying the zirconium hydroxide. The zirconium hydroxide of the present invention, which can be doped, is particularly useful in catalytic applications.
1. An amorphous zirconium hydroxide having a surface area of at least 300 m 2 /g, a total pore volume of at least 0.70 cm 3 /g and an average pore size of between 5 nm and 15 nm.
2. An amorphous zirconium hydroxide as claimed in claim 1 which when calcined at 450° C. for 2 hours has a surface area of at least 80 m 2 /g, a total pore volume of at least 0.35 cm 3 /g and an average pore size of between 10 nm and 30 nm.
3. An amorphous zirconium hydroxide as claimed in claim 1 which when calcined at 650° C. for 2 hours has a surface area of at least 30 m 2 /g, a total pore volume of at least 0.20 cm 3 /g and an average pore size of between 20 nm and 40 nm.
4. An amorphous zirconium hydroxide as claimed in claim 1 which when calcined at 700° C. for 2 hours has a surface area of at least 20 m 2 /g, a total pore volume of at least 0.15 cm 3 /g and an average pore size of between 25 nm and 60 nm.
5. An amorphous zirconium hydroxide as claimed in claim 1 doped with an alkaline earth oxide, a rare earth oxide, a first row transition metal oxide, silica, alumina, tin oxide or lead oxide, or a mixture thereof.
6. An amorphous zirconium hydroxide as claimed in claim 5 doped with silica in an amount of from 0.1% to 10% by weight.
7. A process for preparing said amorphous zirconium hydroxide of claim 1 which comprises the steps of:
(a) preparing an aqueous solution comprising sulfate anions and a zirconium salt such that the ZrO 2 :SO 3 ratio is 1:0.40 to 1:0.52,
(b) chilling the solution to below 25° C.,
(c) adding an alkali in order to precipitate the amorphous zirconium hydroxide,
(d) filtering and washing the precipitated zirconium hydroxide with water or an alkali to remove residual sulfate and chloride,
(e) hydrothermally treating the zirconium hydroxide at a pressure of less than 3 barg, and
(f) drying the zirconium hydroxide.
8. A process as claimed in claim 7 , wherein the sulfate anions are added as sulfuric acid.
9. A process as claimed in claim 7 , wherein the ZrO 2 :SO 3 ratio is 1:0.45.
10. A process as claimed in claim 7 , wherein the zirconium salt is zirconium oxychloride.
11. A process as claimed in claim 7 , wherein the solution is chilled to less than 10° C.
12. A process as claimed in claim 11 , wherein the solution is chilled to less than 2° C.
13. A process as claimed in claim 12 , wherein the solution is chilled to −2° C.
14. A process as claimed in claim 7 , wherein the alkali is chilled to less than 25° C.
15. A process as claimed in claim 7 , wherein the alkali is sodium hydroxide.
16. A process as claimed in claim 15 , wherein 10% sodium hydroxide is added over 2 hours until the solution reaches a pH greater than or equal to 6, followed by the addition of room temperature 28% sodium hydroxide until the solution reaches a pH greater than or equal to 11.
17. A process as claimed in claim 16 , wherein the 10% sodium hydroxide is added over 2 hours until the solution reaches pH 8.
18. A process as claimed in claim 16 , wherein the room temperature 28% sodium hydroxide is added until the solution reaches pH 13.
19. A process as claimed in claim 7 , wherein the hydrothermal treatment is carried out at 1 barg for 5 hours.
20. A process as claimed in claim 7 additionally comprising after step (d) and before step (e) the steps of:
(i) reslurrying the washed precipitate in water and adjusting the pH to between 4 and 9 with nitric acid, and
(ii) filtering and washing the slurry with water or an acid to remove residual sodium.
21. A process as claimed in claim 20 , wherein the pH is adjusted to pH 8 in step (i).
22. A process as claimed in claim 20 , wherein the washing and reslurrying are carried out with deionized water.
23. A process as claimed in claim 7 , wherein the amorphous zirconium hydroxide is milled.
24. A process for forming a zirconia comprising preparing an amorphous zirconium hydroxide in accordance with a process as claimed in claim 7 , wherein the process additionally comprises the step of calcining the amorphous zirconium hydroxide after step (f).
25. A process as claimed in claim 24 , wherein the amorphous zirconium hydroxide is calcined at 450° C. to 900° C. for between 1 and 24 hours.
26. A process as claimed in claim 25 , wherein the amorphous zirconium hydroxide is calcined at 450° C. to 750° C.