Process for synthesizing a zeolite catalyst on a pH controlled basis to improve catalyst life

Claim 2

A process for producing a crystalline alumino-silicate zeolite which comprises: (1) admixing to form a reaction mixture in the absence of a buffer: (a) at least one tetraalkyl ammonium hydroxide in an amount sufficient to impart a pH to the reaction mixture in the initial absence of said acid of (f) of not less than 13 when measured at room temperature; (b) at lest one sodium cation source; (c) at least one silica source; (d) at lest one alumina source; (e) water; and (f) at least one organic acid in a manner and under such conditions that the reaction mixture prior to acid addition has a composition within the following molar ratio ranges: ______________________________________ (TAA).sub.2 O/SiO.sub.2 0.01 to 5 SiO.sub.2 /Al.sub.2 O.sub.3 80 to 2200 H.sub.2 O/SiO.sub.2 10 to 200 Na.sub.2 O/SiO.sub.2 0.05 to 5 ______________________________________ wherein TAA is the sum of the tetraalkyl ammonium cations; the initial pH of the reaction mixture, when measured at room temperature, being adjusted with said acid to be from about 11.3 to about 11.7; (2) heating the reaction mixture until crystals of said zeolite form; and (3) separating said crystals from the reaction mixture.

Claim 3

The process of claim 1 wherein said tetraalkylammonium hydroxide is tetrapropylammonium hydroxide.

Claim 4

The process of claim 2 wherein the silica source and sodium cation source is sodium silicate.

Claim 5

The process of claim 3 wherein the alumina source is aluminum nitrate.

Claim 6

The process of claim 2 wherein the initial pH of the reaction mixture is adjusted with acid to between about 11.4 and about 11.6.

Claim 7

The process of claim 2 wherein the acid is HNO 3 .

Claim 8

The process of claim 1 wherein the pH of the initial reaction mixture in the absence of said acid is 14, and sufficient acid is added to reduce the initial pH of the reaction mixture to 11.5.

Claim 9

The process of claim 1 wherein the SiO 2 /Al 2 O 3 mole ratio in the resulting zeolite is from about 100 to about 1000.

Claim 10

The process of claim 1 wherein the separated zeolite crystals are converted to the hydrogen form by cation exchange and calcination.

Claim 11

The process of claim 1 wherein said reaction mixture is heated to a temperature of from about 100° to about 220° C. for a period of from about 3 to 8 days.

Claim 12

A process for producing a crystalline aluminosilicate ZSM-5 zeolite which comprises: (A) providing in the absence of a buffer, a reaction mixture comprising tetrapropylammonium hydroxide, a silica source, an alumina source, a sodium cation source, and water, said reaction mixture components being present in amounts sufficient to impart: (i) an initial pH to the reaction mixture of not less than about 13; and (ii) a composition to the reaction mixture expressed in terms of mole ratios comprising: ______________________________________ (TPA).sub.2 O/SiO.sub.2 0.05 to 1 SiO.sub.2 /Al.sub.2 O.sub.3 220 to 800 H.sub.2 O/SiO.sub.2 20 to 140 OH.sup.- /SiO.sub.2 0.2 to 5 H.sub.2 O/OH.sup.- 10 to 200 Na.sub.2 O/SiO.sub.2 0.1 to 4 ______________________________________ wherein TPA signifies tetrapropylammonium; (B) adjusting the initial pH of the reaction mixture to between about 11.3 and about 11.7 when measured at room temperature, by the addition of nitric acid; (C) heating the pH adjusted reaction mixture in a manner and under conditions sufficient to cause crystals of said zeolite to form; and (D) separating said crystals from the reaction mixture.

Claim 13

A process for producing a crystalline aluminosilicate ZSM-5 zeolite which comprises: (A) providing in the absence of a buffer, a reaction mixture comprising tetrapropylammonium hydroxide, a silica source, an alumina source, a sodium cation source, and water, said reaction mixture components being present in amounts sufficient to impart: (i) an initial pH to the reaction mixture of not less than about 13; and (ii) a composition to the reaction mixture expressed in terms of mole ratios comprising: ______________________________________ (TPA).sub.2 O/SiO.sub.2 0.05 to 1 SiO.sub.2 /Al.sub.2 O.sub.3 220 to 800 H.sub.2 O/SiO.sub.2 20 to 140 OH.sup.- /SiO.sub.2 0.2 to 5 H.sub.2 O/OH.sup.- 10 to 200 Na.sub.2 O/SiO.sub.2 0.1 to 4 ______________________________________ wherein TPA signifies tetrapropylammonium; (B) adjusting the initial pH of the reaction mixture to between about 11.3 and about 11.7 when measured at room temperature, by the addition of nitric acid; (C) heating the pH adjusted reaction mixture in a manner and under conditions sufficient to cause crystals of said zeolite to form; and (D) separating said crystals from the reaction mixture.

Claim 14

The process of claim 11 wherein said crystals are exchanged with an ammonium cation to replace sodium cations present therein and calcined at a temperature of from about 400° to about 900° C. in a manner sufficient to convert the zeolite to the hydrogen form.

Claim 15

The process of claim 11 wherein in said reaction mixture the Na 2 O/SiO 2 mole ratio is from about 0.3 to about 3.

Claim 16

The process of claim 11 wherein the alumina source is aluminum nitrate, and the silica and sodium cation source is sodium silicate.

Claim 17

The process of claim 11 wherein the composition of the reaction mixture is sufficient to impart a SiO 2 /Al 2 O 3 mole ratio to the crystalline zeolite of from about 200 to about 650.

Claim 18

The process of claim 11 wherein the pH adjusted reaction mixture is heated to a temperature of from about 120° to about 190° C. for a period of from about 3 to about 8 days.

Claim 19

The process of claim 16 wherein the reaction mixture is agitated for at least 24 hours during said heating.

Claim 20

The process of claim 16 wherein said heating is conducted under an inert atmosphere at a pressure of from about 5 to about 100 psi.