Method for synthesizing silicoaluminophosphate-34 molecular sieves using monoisopropanolamine
A method for synthesizing small crystals of silicoaluminophosphate-34 (SAPO-34) molecular sieves with high structural purity. The method includes first forming a slurry comprising monoisopropanolamine. Then, the slurry is aged to form an aged slurry. Finally, crystallization of silicoaluminophosphate molecular sieves comprising the SAPO-34 molecular sieves is induced from the aged slurry.
1. A method for synthesizing silicoaluminophosphate-34 (SAPO-34) molecular sieves, comprising:
forming a slurry comprising monoisopropanolamine, a source of phosphorus, a source of aluminium, and a source of silicon;
aging the slurry to form an aged slurry; and
inducing crystallization of silicoaluminophosphate molecular sieves comprising the SAPO-34 molecular sieves from the aged slurry.
2. The method of claim 1 , wherein the molar ratio of monoisopropanolamine to Al 2 O 3 ranges from about 0.1 to about 3.
3. The method of claim 1 , wherein the slurry further comprises one or more other structure directing agents.
4. The method of claim 3 , wherein the other structure directing agents are selected from the group consisting of tetraethylammonium hydroxide, morpholine, diethylamine, and triethylamine.
5. The method of claim 3 , wherein the other organic structure directing agents comprise tetraethylammonium hydroxide.
6. The method of claim 3 , wherein forming the slurry comprises:
combining the source of phosphorus and water to form a phosphoric solution;
introducing the source of aluminium into the phosphoric solution;
introducing the source of silicon into the phosphoric solution after the introduction of the source of aluminium; and
introducing monoisopropanolamine and one or more other structure directing agents into the phosphoric solution after the introduction of the source of silicon.
7. The method of claim 1 , wherein forming the slurry comprises:
combining the source of phosphorus and water to form a phosphoric solution;
introducing the source of aluminium into the phosphoric solution;
introducing the source of silicon into the phosphoric solution after the introduction of the source of aluminium; and
introducing monoisopropanolamine into the phosphoric solution after the introduction of the source of silicon.
8. The method of claim 1 , wherein aging the slurry is performed by aging the slurry at a temperature within the range from about 10° C. to about 170° C. for a time within the range from about 0.5 to 72 hours.
9. The method of claim 1 , wherein aging the slurry is performed by aging the slurry at a temperature within the range from about 20° C. to about 150° C. for a time within the range from about 1 hour to about 30 hours.
10. The method of claim 1 , wherein the inducing crystallization step comprises:
initially heating the aged slurry to a first temperature within the range from about 50° C. to about 170° C. and then holding the slurry at the first temperature for a time within the range from about 0.5 hour to about 24 hours; and
further heating the aged slurry to a second temperature within the range from about 150° C. to about 250° C. and then holding the slurry at the second temperature for a time within the range from about 1 hour to about 100 hours.
11. The method of claim 1 , wherein the inducing crystallization step comprises:
initially heating the aged slurry to a first temperature within the range from about 80° C. to about 150° C. and then holding the mixture at the first temperature for a time within the range from about 1 hour to about 10 hours; and
further heating the aged slurry to a second temperature within the range from about 170° C. to about 220° C. and then holding the slurry at the second temperature for a time within the range from about 5 hour to about 72 hours.
12. The method of claim 1 , wherein the inducing crystallization step comprises:
heating the aged slurry to a temperature within the range from about 150° C. to about 250° C. and then holding the slurry at the temperature for a time within the range from about 1 hour to about 100 hours.
13. The method of claim 1 , wherein the inducing crystallization step comprises:
heating the aged slurry to a temperature within the range from about 170° C. to about 220° C. and then holding the slurry at the temperature for a time within the range from about 5 hour to about 72 hours.
14. The method of claim 1 , wherein the silicoaluminophosphate molecular sieves have a silicon ratio of about 0.01 to about 0.3.
15. The method of claim 1 , wherein the silicoaluminophosphate molecular sieves have a silicon ration of about 0.03 to about 0.2.
16. The method of claim 1 , wherein the average diameter of the SAPO-34 molecular sieves is smaller than 10 μm.