Synthesis of high silica zeolite via interzeolite transformation without OSDAs
Provided is a method for preparing a zeolite having a Si/Al ratio of at least 10 by interzeolite transformation in the absence of an organic structure directing agent. The method is more cost effective and less equipment intensive as it eliminates the costly organic structure directing agent and the waste treatment at the plant.
1. A method of preparing a zeolite having a silica to alumina ratio of at least 10, which comprises:
a. providing a first zeolite comprising BEA or FAU, and
b. converting the first zeolite to a second zeolite having a higher framework density than the first zeolite and with the second zeolite having a silica to alumina ratio of at least 10 and comprising a MFI, CHA, STF or MTW zeolite; with the conversion conducted in the absence of an organic structure directing agent (OSDA), with the time for the conversion ranging from about 10 to about 80 hours; the conversion conducted in a solution having a H 2 O/SiO 2 ratio greater than 50 and a NaOH/SiO 2 ratio that ranges from 0.25-1.00, and with seed crystals of the second zeolite added to the first zeolite prior to or during the conversion.
2. The method of claim 1 , wherein the conversion is achieved by hydrothermal synthesis.
3. The method of claim 1 , wherein the conversion is achieved in a basic solution.
4. The method of claim 3 , wherein the pH of the basic solution is in the range of from greater than 7 up to 13.
5. The method of claim 4 , wherein the pH of the basic solution is in the range of from greater than 7 up to 11.
6. The method of claim 2 , wherein the temperature of the conversion is above the crystallization temperature of the first zeolite.
7. The method of claim 1 , wherein the temperature of the conversion is in the range of about 130 to about 160° C.
8. The method of claim 1 , wherein the silica to alumina ratio of the second zeolite is in the range of from 11 to 25.
9. The method of claim 1 , wherein the silica to alumina ratio of the second zeolite is at least 40.
10. The method of claim 1 , wherein the second zeolite comprises ZSM-5, SSZ-35, ZSM-12 or chabazite.
11. The method of claim 1 , wherein the first zeolite comprises FAU having a silica to alumina ratio of at least 10.