Alumina support, a process for preparing the support, a silver catalyst prepared from the support, and use thereof
An alumina support comprises alpha-alumina as the main crystal phase of its backbone, and having a specific surface area of no higher than 3.0 m 2 /g, a pore volume ranging from 0.3 ml/g to 0.8 ml/g, an alkaline earth metal content ranging from 0.05% to 2.0% by weight of the support, wherein the support has such properties that treating the support with an aqueous oxalic acid solution having a concentration ranging from 0.4% to 2.0% by weight and having twice the weight of the support for 30 minutes can produce a leach liquor having an aluminum content of no higher than 60 μg/mL, a sodium content of no higher than 20 μg/mL, and a silicon content of no higher than 40 μg/mL. Processes for preparing the alumina support, silver catalysts comprising the alumina support, and methods of preparing ethylene oxide by ethylene oxidation using the silver catalyst are also disclosed herein.
1. A process for preparing an alumina support, comprising:
(a) mixing at least one alumina starting material, at least one alkaline earth metal salt, optionally at least one carbonaceous burnout material, optionally at least one fluoride, at least one binder and water to produce a mixture,
wherein the alumina starting material comprises alpha-alumina trihydrate and pseudo-boehmite in a weight ratio of alpha-alumina trihydrate to pseudo-boehmite ranging from 0,5:1 to 5:1, and
wherein based on the total weight of the alumina starting material,
the alkaline earth metal salt is in an amount ranging from 0.05% to 3.0% by weight, calculated based on the alkaline earth metal,
the carbonaceous burnout material is in an amount ranging from 0% to 30% by weight,
the fluoride is in an amount ranging from 0% to 3% by weight, and
the binder and water are in a total amount ranging from 10% to 40% by weight;
(b) extruding the mixture obtained in step (a) to form shaped entities;
(c) drying the shaped entities obtained in step (b) at a temperature ranging from 60° C. to 200° C.;
(d) calcining the shaped entities obtained in step (c) at a temperature ranging from 1100° C. to 1600° C. to convert to a semi-finished alpha-alumina support;
(e) treating the semi-finished alpha-alumina support obtained in step (d) with a thermally decomposable organic acid solution having a pH of no more than 2.5;
(f) washing the treated support obtained in step (e) with water to produce a leach liquor having a pH of more than 5 and a water-washed product: and
(g) heat-treating the water-washed product obtained in step (f) at a temperature ranging from 80° C. to 1200° C.
2. The process according to claim 1 , wherein the thermally decomposable organic acid solution having a pH of no more than 2.5 used in step (e) is substantially free of fluorine.
3. The process according to claim 1 , wherein in step (e), the thermally-decomposable organic acid solution having a pH of no more than 2.5 is used in such an amount that the semi-finished alpha-alumina support can be fully immersed therein.
4. The process according to claim 1 , wherein the at least one carbonaceous burnout material is chosen from petroleum coke, carbon powder, graphite, polyethylene, polypropylene, rosin, and vaseline.
5. The process according to claim 1 , wherein the at least one alkaline earth metal salt is chosen from salts of barium, magnesium, calcium and/or strontium.
6. The process according to claim 1 , wherein the at least one fluoride is chosen from aluminum fluoride and ammonium fluoride.
7. The process according to claim 1 , wherein the at least one binder is chosen from nitric acid and acetic acid.
8. The process according to claim 1 , wherein a portion or all of the alpha-alumina trihydrate is replaced by a substituting alumina powder, which has been pre-calcined into alpha-alumina or a transition alumina; a portion or all of the pseudo-boehmite is replaced by an alumina sol; the ratio of the total weight of alpha-alumina trihydrate and its substitute if present to the total weight of pseudo-boehmite and its substitute if present ranges from 0.5:1 to 5:1.
9. The process according to claim 8 , wherein the ratio of the total weight of alpha-alumina trihydrate and its substitute if present to the total weight of pseudo-boehmite and its substitute if present ranges from 1:1 to 4:1.
10. The process according to claim 1 , wherein the thermally decomposable organic acid solution comprises at least one thermally decomposable organic acid chosen from formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, benzoic acid, and phenol.
11. The process according to claim 10 , wherein the at least one thermally decomposable organic acid is chosen from formic acid, acetic acid, and oxalic acid.
12. The process according to claim 1 , wherein in step (g), the water-washed product obtained in step (f) is heat-treated at a temperature ranging from 260° C. to 1200° C.
13. The process according to claim 1 , wherein in step (g), the water-washed product obtained in step (f) is heat-treated at a temperature ranging from 1000° C. to 1200° C.