Method of synthesizing a molecular sieve of MWW framework type
Disclosed is a method of synthesizing a molecular sieve of MWW framework type, and molecular sieves so synthesized. The method comprises preparing a synthesis mixture for forming a molecular sieve of MWW framework type, said synthesis mixture comprising water, a silicon source, a source of a trivalent element X, a potassium cation source, a structure directing agent R, and a source of another alkali metal cation M.
1 . A method of synthesizing a molecular sieve of MWW framework type, the method comprising the steps of:
a) preparing a synthesis mixture capable of forming a molecular sieve of MWW framework type, said synthesis mixture comprising water, a silicon source, a source of a trivalent element X, a potassium cation source, a structure directing agent R, a source of another alkali metal cation M, optionally a source of a pentavalent element Z, optionally a source of hydroxide ions, and optionally seed crystals, the synthesis mixture having the following molar ratio composition:
Si:X 2 =8 to 18
H 2 O:Si=5 to 100
(M+K + ):Si=0.1 to 0.5
M:K + =1 to 10
R:Si=0.1 to 1;
b) heating said synthesis mixture under crystallization conditions for a time sufficient to form crystals of said molecular sieve of MWW framework type, said crystallization conditions including a temperature of from 100° C. to 220° C.; and
c) recovering said crystals of the molecular sieve of MWW framework type from the synthesis mixture.
2 . The method according to claim 1 , wherein the potassium source comprises potassium hydroxide, potassium aluminate, potassium silicate, a potassium salt such as KCl or KBr or potassium nitrate, or a combination thereof.
3 . The method according to claim 1 , wherein the synthesis mixture has a molar ratio (M+K + ):Si=0.15 to 0.25.
4 . The method according to claim 1 , wherein the synthesis mixture has a molar ratio K + :Si=0.01 to 0.1.
5 . The method according to claim 1 , wherein the structure directing agent R is selected from the group consisting of cyclopentylamine, cyclohexylamine, cycloheptylamine, hexamethyleneimine (HMI), heptamethyleneimine, homopiperazine, pentamethonium bromide or hydroxide, hexamethonium bromide or hydroxide, heptamethonium bromide or hydroxide, and combinations thereof.
6 . The method according to claim 1 , wherein X is selected from the group consisting of aluminum, boron, gallium, and mixtures thereof.
7 . The method according to claim 1 , wherein the source of a trivalent element X comprises Al 2 O 3 .
8 . The method according to claim 1 , wherein the silicon source comprises SiO 2 .
9 . The method according to claim 1 , wherein the synthesis mixture has a molar ratio M:K + =2 to 8, wherein M is sodium, lithium and/or rubidium.
10 . The method according to claim 1 , wherein the synthesis mixture comprises the alkali metal cation M source in a molar ratio of M:Si of from 0.1 to 0.25.
11 . The method according to claim 1 , wherein the synthesis mixture comprises a source of hydroxide ions, wherein the OH source is an alkali metal hydroxide.
12 . The method according to claim 1 , wherein the synthesis mixture comprises seed crystals in an amount of from 0.05 to 2 g seed /g (silicon source+source of trivalent element X).
13 . The method according to claim 1 , wherein the crystallization conditions in step (b) include a temperature of from 100° C. to 200° C.
14 . The method according to claim 1 , wherein the crystallization conditions in step (b) include heating for a period of from 1 to 800 hours.
15 . The method according to claim 1 , wherein the recovered crystals of molecular sieve of MWW framework type has a Si/X 2 molar ratio of from 8 to 16.
16 . A molecular sieve of MWW framework type obtainable by the method of claim 1 .
17 . The molecular sieve of claim 16 , having, in its as-synthesized and dried form, a density, as measured by a pycnometer, higher than 2.0 g/cm 3 .
18 . The method according to claim 1 , further comprising forming the molecular sieve and using the molecular sieve in a hydrocarbon chemical conversion process.
19 . The method according to claim 1 , wherein X is aluminum.
20 . The method according to claim 1 , wherein the synthesis mixture does not contain any pentavalent element Z.
21 . The method according to claim 1 , wherein the synthesis mixture comprises a source of hydroxide ions in a OH/Si molar ratio of from 0.1 to 0.5.
22 . The method according to claim 12 , wherein the seed crystals comprise a molecular sieve of framework type MWW.
23 . The molecular sieve of claim 16 , wherein the molecular sieve has, in its calcined and anhydrous form, a composition with a Si/X 2 molar ratio of from 8 to 18.
24 . The method of claim 18 , wherein the hydrocarbon chemical conversion process is aromatic alkylation.