Process for preparing ammonium zeolites of low alkali metal content

Ammonium zeolites of extremely low alkali metal content are prepared by a process of potassium ion exchange followed by ammonium ion exchange. Zeolite X or zeolite Y that contain a significant amount of sodium are contacted with a potassium salt solution under conditions that provide a substantial exchange of potassium for sodium. The potassium enriched zeolite is then contacted with an ammonium salt solution so that the ammonium ion replaces the sodium and potassium ions. The resulting ammonium zeolite X or Y contains considerably less than 1% alkali metal calculated as Na.sub.2 O.

BACKGROUND OF THE INVENTION 
This invention relates to the ion exchange of zeolites and provides a 
process for preparing ammonium zeolites of extremely low alkali metal 
content. In particular, the process involves ion exchange of a zeolite 
usually containing a significant amount of sodium to a potassium enriched 
form of the zeolite. Contact with an ammonium salt solution then provides 
the ammonium form zeolite with low alkali metal content. 
Most zeolites (crystalline aluminosilicates) contain significant amounts of 
alkali metals, usually sodium. Many applications of said zeolites require 
the removal of nearly all the sodium and its replacement with ammonium 
ions. Many zeolite modifications such as stabilization also require 
removal of nearly all the sodium. Some zeolites including the faujasites 
have structures that impede the exchange of ammonium ion for sodium, 
especially when more than 70 to 80% of the sodium they contain is to be 
exchanged. Prior art methods include exhaustive ion exchange processes 
with solutions of high concentrations of ammonium salts. See Example IX of 
U.S. Pat. No. 3,449,020. An alternative process involves the steam 
calcination of an ammonium zeolite Y that still contains 2.5 to 5% 
Na.sub.2 O followed by an additional exchange with an ammonium salt 
solution. See U.S. Pat. No. 3,929,672 among others. This process is not 
always desirable, as some of the properties of the zeolite are changed and 
the hydrogen form of the zeolite is formed upon steam calcination. Not all 
zeolites of the faujasite structure are stable in the hydrogen form. U.S. 
Pat. No. 4,058,484 discloses a method for providing an ammonium zeolite 
which involves ion exchange with at least 20 equivalents of ammonium ions 
for each equivalent of sodium in the zeolite. The temperatures required 
for the exchange are very high, being in excess of 300.degree. F. 
It is an object of this invention to provide ammonium zeolite X or ammonium 
zeolite Y by a method that does not involve temperatures above boiling, 
the use of ammonium salt solutions of high concentrations, and/or high 
ammonium ion to zeolite contact ratios. 
SUMMARY OF THE INVENTION 
I have found that ammonium zeolites of faujasite structure such as zeolite 
X, Y, ZSM-20, ZSM-3 and CSZ-1 with very low alkali metal content can be 
prepared by a process that includes an initial potassium ion exchange 
followed by an ammonium ion exchange. The starting zeolite X or Y which 
can contain sodium (about 11% Na.sub.2 O or more) is contacted with a 
potassium salt solution at a temperature less than boiling. The contact is 
such that a significant portion of the zeolitic sodium is replaced by 
potassium. This exchange need not be exhaustive, as only 80 to 90% of the 
sodium needs to be exchanged. The nearly complete ion exchange of the 
zeolitic potassium and sodium for ammonium is now attained relatively 
easily. The extremely low level of alkali metal in the ammonium zeolite is 
attained at temperatures less than boiling and without numerous exchange 
steps. Ion exchange solutions of very high concentrations of ammonium salt 
and high ammonium ion to zeolite contact ratios are not required. 
In contrast to the prior art methods that require high temperatures, high 
contact ratios of NH.sub.4.sup.+ /zeolite, highly concentrated ammonium 
salt solutions, numerous contacts, and steam calcinations to remove the 
most difficult-to-exchange sodium ions, my process's initial potassium 
exchange surprisingly renders all of the alkali metal ions (sodium and 
potassium) easily exchanged for ammonium ions, as will be shown in the 
examples. 
THE INVENTION 
The zeolites treated by the process of my invention are faujasite-type 
materials, the most common of which are designated as zeolite X or Y. Such 
materials are prepared by the hydrothermal treatment of sources of 
SiO.sub.2, Al.sub.2 O.sub.3 and Na.sub.2 O as described in numerous U.S. 
Patents including U.S. Pat. Nos. 2,882,244 and 3,130,007. 
The zeolites produced by the processes disclosed in these patents are 
represented by the following formula: 
EQU 0.9.+-.0.2 Na.sub.2 O:Al.sub.2 O.sub.3 :X SiO.sub.2 :Y H.sub.2 O 
wherein X can be about 2 to 6, and Y can be 0 to 9 and have a faujasite 
structure. The amount of sodium these materials contain depends upon the 
SiO.sub.2 /Al.sub.2 O.sub.3 ratio. A zeolite Y with a SiO.sub.2 /Al.sub.2 
O.sub.3 ratio of 6 contains about 11% Na.sub.2 O. Faujasites of lower 
SiO.sub.2 /Al.sub.2 O.sub.3 ratio contain more Na.sub.2 O. These materials 
are articles of commerce and are available as powders and agglomerates. 
The zeolite is contacted with a potassium salt solution using conditions 
that produce zeolites wherein at least about 80% of the sodium for zeolite 
X and at least about 90% of the sodium for zeolite Y is replaced with 
potassium. The contacting solution can contain one or more potassium salts 
of strong acids. These can include among others KCl, K.sub.2 SO.sub.4, 
KNO.sub.3. The concentration can be 1 to 10 normal. The contact time can 
be 0.5 to 5 hours. The temperature is below boiling, but is usually above 
room temperature. The number of contacts can be varied, but not more than 
5 are needed. Usually 1, 2 or 3 contacts are all that are required. After 
contact or between contacts the zeolite is filtered and washed. 
The potassium exchanged zeolite contains sufficient potassium to facilitate 
the nearly complete exchange of ammonium ion for the sodium and potassium 
in the zeolite. For zeolite X which has 2.0 to 2.5 moles of SiO.sub.2 for 
each mole of Al.sub.2 O.sub.3 about 84% of the sodium must be exchanged 
for potassium. For zeolite Y, which has about 3 to 6 moles of SiO.sub.2 
for each mole of Al.sub.2 O.sub.3, about 90% of the sodium must be 
exchanged for potassium. To obtain the potassium content required, the 
starting zeolite should be contacted with up to 10 moles of potassium ion 
for each mole of sodium to be exchanged. The potassium level can be more 
than the minimum required to facilitate the ammonium exchange but no 
additional process advantages are realized. 
The predominately potassium substituted zeolite X or Y is now contacted 
with a solution of one or more ammonium salts. The salts of strong mineral 
or organic acids are all useful, and examples include NH.sub.4 Cl, 
(NH.sub.4).sub.2 SO.sub.4 and NH.sub.4 NO.sub.3. The concentration of the 
solution can be 1 to 10 normal and is usually considerably less than about 
10 normal. The contact time can vary considerably but is usually 0.5 to 24 
hours. The temperature of the exchange is 100.degree. C. or less. Several 
contacts can be used, but we prefer 2 or 3 contacts. For example, using 
zeolite Y a 3 stage counter-current contact of a total of 7 moles of 
NH.sub.4.sup.+ ion for each mole of M.sup.+ would provide a 97% 
replacement of M.sup.+, where M=[Na.sup.+ +K.sup.+ ]. 
An alternative method of carrying out the process of my invention involves 
the contact of a zeolite such as zeolite X, zeolite Y, zeolite ZSM-20, or 
zeolite CSZ-1 to a solution containing both ammonium and potassium salts 
under conditions to produce the desired replacement of sodium by either 
potassium or ammonium ions. Then the ammonium, potassium exchanged zeolite 
is contacted with a solution containing an ammonium salt. This alternative 
method results in saving potassium salt values. 
The products of this ion exchange process are faujasite-type zeolites 
wherein the properties of the zeolites are not changed very much except 
that the alkali metal content is well below about 0.8% calculated as 
Na.sub.2 O, and usually well below about 0.5%. I prefer materials that 
contain less than 0.15% alkali metal calculated as Na.sub.2 O. These 
products can be used in various sorption and catalyst applications. They 
are also useful as starting materials for stabilization and dealumination 
processes.