Silicon substituted zeolite compositions and process for preparing same
AssigneeUnion Carbide Corporation
InventorsDonald W. Breck, deceased, by Harold Blass, executor, Gary W. Skeels
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Abstract
Aluminum from AlO.sub.4 -tetrahedra of as-synthesized zeolites is extracted and substituted with silicon to form zeolite compositions having higher SiO.sub.2 /Al.sub.2 O.sub.3 molar ratios and exhibiting distinctive chemical and physical properties. The preparative procedure involves contact of the starting zeolite with an aqueous solution of a fluorosilicate salt using controlled proportions and temperature and pH conditions which avoid aluminum extraction without silicon substitution.
Claims20
Method for inserting silicon atoms as SiO.sub.4 tetrahedra into the crystal lattice of an aluminosilicate zeolite which comprises contacting a crystalline zeolitic aluminosilicate having a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of at least 3 and pore diameters of at least 3 Angstroms with a fluorosilicate salt in an amount of at least 0.0075 moles per 100 grams of the zeolitic aluminosilicate on an anhydrous basis, said fluorosilicate salt being in the form of an aqueous solution having a pH value within the range of 3 to about 7 and brought into contact with the zeolitic aluminosilicate at a rate sufficiently slow to preserve at least 60 percent of the crystallinity of the starting zeolitic aluminosilicate.
Zeolitic aluminosilicate composition having in the dehydrated state, a chemical composition expessed in terms of mole ratios of oxides
- 0.9.+-.0.1M.sub.2/n O:Al.sub.2 O.sub.3 :XSiO.sub.2
- wherein "M" is a cation having the valence "n" and "x" is a value greater than 8, an X-ray powder diffraction pattern having at least the d-spacings set forth in Table E, and having extraneous silicon atoms in its crystal lattice in the form of framework SiO.sub.4 tetrahedra.
A crystalline aluminosilicate having an X-ray powder diffraction pattern having at least the d-spacings set forth in Table E, and having at least some of its original framework aluminum atoms replaced by extraneous silicon atoms and having the chemical composition
- [Al.sub.(a-N) Si.sub.b+(N-.DELTA.z) .quadrature..sub.z ]O.sub.2
- wherein Al.sub.(a-N) represents the mole fraction of aluminum tetrahedra in the product zeolite;
- "a" represents the mole fraction of aluminum tetrahedra in the original zeolite;
- "N" represents the mole fraction of aluminum tetrahedra removed from the original zeolite, and has a value of at least 0.3a;
- Si.sub.b+(N.DELTA.z) represents the mole fraction of silicon tetrahedra in the product zeolite;
- "b" represents the mole fraction of silicon tetrahedra in the original zeolite;
- (N-.DELTA.z) represents the mole fraction of silicon tetrahedra resulting from the substitution of extraneous silicon into the crystal lattice;
- ".quadrature." represents framework defect sites;
- "z" represents the mole fraction of framework defect sites;
- ".DELTA.z" represents the difference between the mole fraction of framework defect sites of the original zeolite and the zeolite containing the extraneous silicon atoms and has a value of less than 0.08;
- (N-.DELTA.z)/N has a value at least as great as 0.5;
- and [b+(N-.DELTA.z)]/(a-N) has a value of at least 4.0.
Dependencies are inferred from the claim text.