Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~1~16 ~CTIVITY ENHANCEi/i~lT OF ~I~H SILICA Z~OLITES
Backgroun~ of The Invention
This invention relates to a method of
enhanclng the acid activity of certain hiyh
silica-containing crystalline materials by a process
which involves contacting them with aluminum chloride
(AlC13) vapors, followed by hydrolysis and
calcination.
~iyh silica-containing zeolites are well
known in the art, and it is yenerally accepted that
the ion exchange capacity of a crystalline alumino-
silicate is directly dependent upon its aluTninum
content. Thus, for example, th~ more aluminum there
is in a crystalline structure, the rnore cations are
required to balance the electronegativity thereof,
and when such cations are of the acidic type such as
hydrogen, they impart tremendous catalytic activity
to the crystalline material. On the other hand, hi~h
silica-containing zeolites havin~ little or
substantially no aluminum have many important
properties and characteristics and a high degree of
structural stability such that they have become
candidates for use in various processes including
catalytic processes. Materials of this type are
known in the art and include hiyh silica-containing
aluminosilicates such as ZSM-5 (U.S. Patent
3,702,886), ZSM-ll (U.S. Patent 3,709,979), and
zeolite ZSM-12 (U.S. Patent 3,832,449) to rnention a
few.
The silica-to-alumina ratio of a yiven
zeolite is often variable; for example, zeolite X can
be synthesized with silica-to-alumina ratio of ~rom 2
to 3; zeolite Y from 3 to about 6. In some zeolites,
the upper limit of silica-to-alur,lina ratio was
virtually unboun~ed. ZSM-5 is one such exarnple
~2~Z~
wherein the silica-to-alumina ratio is at least 5.
U. S. Patent 3,941,~71 discloses a crystalline Inetal
or~anosilicate essentially free of aluminum and
exhibiting an x-ray diffraction pattern
characteristlc of ZSM-5 type aluminosilicates. U.S.
Patents 4,061,724; 4,073,865; and 4,104,294 describe
microporous crystalline silicas or oryanosilicates
wherein the alur,linum content present is at impurity
levels.
Because of tlle extremely low aluminum
content of these silica-containing zeolites, their
ion exchange capacity is not as great as materials
with a higher aluminurm content. Therefore, w~en
these rnaterials are contacted with an acidic solution
and thereafter are processed in a conventional
manner, they are not as catalytically actlve as their
higher aluminum-containing counterparts.
The novel process of this invention yermits
the preparation o~ certain high silica-containing
materials which have all the desirable yroperties
inherently possessed by such high silica materials
and, yet, have an acid activity which heretofore has
only been possible to be achieved by r.laterials having
a higher aluminum content ln thelr "as synthesized~
form.
Description of The Prior Art
It is to be immediately understood that
there are yatents relating to contactin~ crystalline
aluminosilicate zeolites with alumlnum chloride
followed by hydrolysis, i.e. United States 3,354,07
and United States 3,644,220. However, neither of
these two yatents is in any way concerned with
treatment of crystalline materials having a silica to
~z~
alumina ratio of at least 100 and even more desirably of
at least 500 which have been synthesized from a forming
solution containing quarternary ammonium cations. The
novel process of this invention results in introducing
the aluminum within the intracrystalline structure such
that its constraint index is substantially unaltered.
Description of the Invention
As has heretofore been stated, the novel pro-
cess of this invention is concerned with the treatment
of high silica-containing crystalline material. The
expression "high silica-containing crystalline material'
is intended to define a crystalline structure which has
a silica-to-alumina ratio greater than 100 and more
preferably greater than 500, up to and including those
highly siliceous materials where the silica-to-alumina
ratio is infinity or as reasonably close to infinity
as practically possible. This latter group of highly
siliceous materials is exemplified by U.S. Patents
3,941,871; 4,061,724; 4,073,865; 4,104,294 wherein the
materials are prepared from reaction solutions which
involve no deliberate addition of aluminum. However,
trace quantities of aluminum are usually present due
to the impurity of the reaction solutions. It is to be
understood that the expression "high silica-containing
crystalline material" also specifically includes those
materials which have other metals besides silica and/or
alumina associated therewith, such as boron, iron and
chromium, etc. Thus, the only requirements with regard
to the starting materials utilized in the novel process
of this invention is that they have a silica to alumina
ratio greater than about 100 (irrespective of what other
materials or metals are present in the crystal structure)
and that they be synthesized from a reaction miXtlJre con-
taining tetraalkylammonium ions. It has been found that
the novel process of this invention is not applicable to
high silica-containing crystalline materials which have
been synthesized with diamines.
The novel process of this invention is simple
in nature and easy to carry out, although the results
therefrom are dramatic. The novel process of this in-
vention is carried out simply by ca]cining a high silica
crystalline material having a silica to alumina ratio of
at least 100 and preferably of at least 500 which has
been prepared from a reaction mixture containing tetra-
alkylammonium ions by heating the same at a temperaturewithin the range of about 200-600C in an atmosphere
such as air, nitrogen, etc. and at atmospheric, super-
atmospheric, or subatmospheric pressures for between 1
and about 4~ hours. The calcined zeolite is thereafter
treated with aluminum chloride vapors at elevated tem-
peratures, preferably admixed with an inert gas such as
nitrogen at a temperature ranging from 100 to 600C.
The amount of aluminum chloride vapor which is utilized
is not narrowly critical but usually 0 01 to 1 gram and
preferably about 0.5 of aluminum chloride is used per
gram of high silica crystalline material. Following
the treatment with aluminum chloride, the crystalline
material is then hydrolyæed in water, preferably at a
temperature ranging from 20 to 100C, followed by a
final calcination preferably at a temperature ranging
from 200 to 600C, more preferably from 450 to 550C.
~2~
--5--
The activity enhanced high silica-containing
crystalline materials prepared by the present process are
useful as catalyst components for acld catalyzed hydro-
carbon conversion reactions. Such reactions include, as a
non-limiting example, cracking of hydrocarbon compounds
under reaction conditions including a temperature of from
about 300C to about 650C, a pressure of from about atmos-
pheric to about 200 psig and a weight hourly space velocity
of from about 0.5 to about 50 hr 1.
In practicing a particularly desired chemical con-
version process, it may be useful to incorporate the above-
described activity enhanced crystalline zeolite with a
matrix comprising another material resistant to the temperature
and other conditions employed in the process. Such matrix
material is useful as a binder and imparts greater
resistance to the catalyst for the se~ere temperature,
pressure and reactant feed stream velocity conditions en-
countered in many cracking processes.
Useful matrix materials include both synthetic and
naturally occurring substances, as well as inorganic materials
such as clay, silica and/or metal oxides. The latter may
be either naturally occurring or in the form of gelatinous
precipitates or gels including mixtures of silica and metal
oxides. Naturally occurring clays which can be composited
with the zeolite include those of the montmorillonite and
kaolin families, which families include the sub-bentonites
and the kaolins commonly known as Dixie, McNamee, Georgia
and Florida clays or others in which the main mineral con-
stituent is halloysite, kaolinite, dickite, nacrite or
anauxite. Such clays can be used in the raw state as
originally mined or initially subjected to calcination,
acid treatment or chemical modification.
In addition to the foregoing materials, the
zeolites employed herein may be composited with a porous
matrix material, such as alumina, silica-alumina, silica-
magnesia, silica-zirconia, silica-thoria, silica-beryllia,
and silica-titania, as well as ternary compositions, such
as silica-alumina-tharia, silica-alumina-zirconia, silica-
alumina-magnesia and silica-magnesia-zirconia. The matrix
may be in the form of a cogel. The relative proportions
of activity enhanced zeolite component and inorganic oxide
gel matrix, on an anhydrous basis, may vary widely with
the zeolite content ranging from between about 1 to about
99 percent by weight and more usually in the range of
about 5 to about 80 percent by weight of the dry composite.
~2~2,6~
~ 7
EXAMPL~
Four differen~ high silica containiny
zeolites were used in this example -- all of which
were syntIlesized from reaction rnixtures containing
tetraalkylammonium ions. These included three
crystalline materials havlny the x-ray diffraction
uattern of ZSM-5, having silica-to-alurnina ratios of
600, 2900 and greater than 50,U00 respectively. one
sa~ple of a crystalline material having the x-ray
diffraction pattern of ZSM-ll and having a silica-
to-alumina ratio of about l,056 was also utilized.
The above as synthesized zeolites were
calcined in either air or nitrogen at 1C per minute
to about 540C where the temperature was maintained
for about 10 hours. Two ~rams of each of the
calcined zeolites were ~laced in a horizontal tube on
one side of a fritted disc and one grarn of aluminum
chloride was placed on the other side. Dry nitrogen
at 50-100 cc per minute was introduced from the
direction of the zeolite while heating at 100C for
one hour. The direction of the nitroyen flow was
then reversed and the temperature raised to 500C at
2C per minute and maintained at 500C for 1/2 hour.
After cooliny, the zeolite was transferred to another
reactor and again heated to 500C in nitrogen to
remove any residual unreacted alurninum chloride.
Each of the four zeolites was then
hydrolyzed at lO0 ml of water at roonl telnperature for
at least two hours. The hydrolyzed samples were
filtered, washed well with water, air-dried, and then
finally calcined at 540C for ten hours.
The results obtained, as well as the
properties o the aluminum enhanced zeolites are
shown in the following table:
TAE3LE
Properties of Aluminum-Enhanced Zeolites
zeolite Type ZSM-5 ZSM-5 ZSM-5 ZSM-ll
Si/Alz 6U0 2900 -- 5U,UU0 1056
% Al (oriy.) 0.15% 0.03% ~ U.01% - 0.1%
% Al (after treatment) 2.55% 1.63% 1.55% 1.93%
% Crystallinity
(after treatment) n.d. n.d. 74%
Alpha (orig. in E~-form) 17 ~est.) 4 (est.) O.OU4 lU (est.)
Alpha ~after treatment) 102 75 70 101 g~
Increase in Alpha 85 71 70 91
Constraint Index
(after treatlnent) n.d. n.d. 4.1 4.8
- 9
As can be seen, the alpha value of each of
the four zeolites was considerably raised in
accordance with the novel process of this invention.
Furtherlnore, this enhanced acid activity was clearly
intrazeolitic as evidenced by the shape selective
constraint index values.
As is well known in the aet, the alpha
activity yives an approximate indication of the
catalytic cracking activity of the catalyst compared
to a standard catalyst and it gives the relative ra~e
constant (rate of normal hexane conversion per volume
of oxide composition per unit time). It is based on
the activity of the highly active silica alunlina
crackin~ catalyst taken as an alpha of 1. This test
is described in U. S. 3,354,078 an~ in The Journal of
Catalysis, Vol. 4, pp. S22-529, August 1965.
The constraint index is a measure of the
selectivity of a ~articular catalyst and it involves
conversion of normal hexane and 3-methylpentane.
This test is described in many issued United States
patents, including U. S. 4,231,899.
