Zeolites and processes for their manufacture

Colloidal Offretite, a process for its manufacture, and zeolite manufacture using it.

This invention relates to the zeolite Offretite, to processes for its 
manufacture, and to the use of the zeolite as catalyst. 
A traditional synthesis of Offretite obtains the zeolite from synthesis 
mixtures relatively rich in potassium and containing the 
tetramethylammonium cation as template or structure directing agent. The 
resulting product has a relatively large particle size. 
EP-A-400961 describes a synthesis of Offretite using a synthesis mixture 
containing metakaolin obtained by calcination at a temperature of at least 
550.degree. C., the resulting product having an average particle size in 
the range of 0.1 to 10 .mu.m. 
WO 92/14680 describes the use of additional, divalent, cations to 
facilitate manufacture of Offretite of small particle size. U.S. Pat. No. 
3,578,398 describes a procedure for producing "sub-micron" Offretite. 
WO 93/08125 describes the preparation of MFI, MEL and Beta zeolites of 
particle size sufficiently small to enable a colloidal suspension to be 
formed; in general for this purpose the largest dimension of the particles 
is required to be at most 100 nm. 
Products of small particle size have advantages over larger particle size 
products, for example, when used as a catalyst, e.g., in hydrocarbon 
conversions, they have an enhanced ratio of surface area to mass, high 
diffusion rates, reactivities and resistance to deactivation by pore 
plugging and surface contamination. Similarly, they have advantages in 
organic separations, and are also valuable in the manufacture of supported 
layers, especially membranes, as described in WO 94/25151. In certain of 
the procedures described in that patent application, the disclosure of 
which is incorporated herein by reference, the zeolite layer is deposited 
from a colloidal suspension onto a support; instability in the suspension 
is deleterious. Accordingly, it would be desirable to be able to 
manufacture Offretite capable of forming a stable suspension, and for this 
purpose a particle size of at most 100 nm, and advantageously at most 75 
nm, is desirable. A stable suspension is one in which no settlement takes 
place at all, or one in which settlement takes place so slowly as to be 
insignificant over the time scale concerned. Such a suspension is referred 
to herein as colloidal and particles capable of forming such a suspension 
may be referred to as colloidal size particles. 
The present invention is based on the observation that if the concentration 
of inorganic cations, especially potassium, in the synthesis mixture is 
reduced from that typically previously used a colloidal suspension of 
Offretite may be obtained. It has surprisingly been found also that it is 
not in fact essential for the synthesis mixture to be clear and 
homogeneous as previously suggested, e.g., in WO 93/08125, as necessary 
for colloidal zeolite production. Similarly WO 94/05597 indicates that 
though a clear synthesis mixture is a necessary condition for the 
manufacture of colloidal zeolites, it is not a sufficient one. 
Surprisingly, mixture in which, for example, the source of silicon is 
incompletely dissolved, is capable of yielding uniform colloidal-size 
Offretite crystals. 
The present invention accordingly provides a process for the manufacture of 
a colloidal suspension of Offretite, wherein a synthesis mixture having a 
molar composition, when calculated in terms of oxides, in the following 
ranges: 
______________________________________ 
K.sub.2 O:Al.sub.2 O.sub.3 
0.25 to 0.5:1 
(TMA).sub.2 O:Al.sub.2 O.sub.3 at least 2.0:1 
SiO.sub.2 :Al.sub.2 O.sub.3 8 to 10:1 
H.sub.2 O:Al.sub.2 O.sub.3 80 to 100:1 
______________________________________ 
wherein TMA represents the tetramethylammonium cation, is subjected to 
thermal treatment at a temperature and for a tine sufficient to form a 
colloidal suspension of Offretite. 
Advantageously, the molar ratio of (TMA).sub.2 O:Al.sub.2 O.sub.3 is 2.0 to 
3.5:1. 
The process according to this aspect of the invention has the advantage of 
being capable of providing a stable suspension free from unreacted solid 
starting material. 
The invention further provides a process for the manufacture of the zeolite 
Offretite of particle size at most 100 nm, wherein a colloidal suspension 
prepared as described above is washed with water, advantageously to a pH 
within the range of from 9 to 12, if desired cation exchanged, dried and, 
if desired, calcined. 
The process of the invention provides individual crystals, rather than 
agglomerates, and the suspension produced directly, or by washing, is a 
stable one. 
The invention also provides a colloidal suspension of zeolite Offretite. 
The invention further provides Offretite of a particle size of at most 100 
nm. The invention also provides the use, in a process for the thermal 
treatment of a synthesis mixture to form Offretite, of a synthesis mixture 
having a molar ratio of K.sub.2 O:Al.sub.2 O.sub.3 of from 0.25 to 0.5:1 
and of (TMA).sub.2 O:Al.sub.2 O.sub.3 of at least 2.0:1. 
As described above, the zeolite of the invention is primarily an 
aluminosilicate, and will be described herein as such. It is, however, 
within the scope of the invention to replace aluminium wholly or partly 
with gallium, and partly with boron, iron or other trivalent elements, and 
silicon may similarly be replaced by germanium or phosphorus. It is also 
within the scope of the invention to include inorganic cations other than 
potassium, e.g., sodium, in the synthesis mixture. 
The sources of the various elements required in the final product may be 
any of those in commercial use or described in the literature, as may the 
preparation of the synthesis mixture. 
For example, the source of silicon may be a silicate, e.g., an alkali metal 
silicate, a tetraalkyl orthosilicate, or an aqueous colloidal suspension 
of silica, for example one sold by E.I. du Pont de Nemours under the trade 
name Ludox. Ludox HS-40 is a sodium-containing product, while AS-40 
contains very little sodium. Preferably, however, the source is silica 
powder. 
The source of aluminium is preferably aluminium metal, e.g., in the form of 
chips, dissolved in the alkaline solution of structure-directing agent. 
Other aluminium sources include, for example, hydrated alumina, a 
water-soluble aluminium salt, e.g., aluminium sulphate, or an alkoxide, 
e.g., aluminium isopropoxide. 
The potassium source is advantageously potassium hydroxide. 
The TMA cation may be introduced in the hydroxide form, which is 
commercially available as a powder as the pentahydrate, or as an aqueous 
solution, which is preferred. The cation may also be introduced in the 
form of a mixture of hydroxide and salt, e.g. a halide; preferably a major 
proportion of the cation is introduced in the form of hydroxide. 
The synthesis mixture is conveniently prepared by dissolving the aluminium 
source and potassium source in a solution of the TMA source, adding the 
silica source, heating to boiling, cooling, and correcting for water loss 
such that the required molar proportions result. 
Crystallization is effected, either under static conditions or with 
moderate stirring, and, if desired, under reflux. 
Thermal treatment (otherwise known as ageing at elevated temperatures) at a 
temperature in the range of from 40, more especially 60, to 100.degree. C. 
is convenient; advantageously from 75 to 95.degree. C. and preferably at 
about 85.degree. C. Suitable crystallization times are within the range of 
from 48 to 500 hours, preferably from 120 to 240 hours. A lower 
temperature in general gives a smaller particle size zeolite, if other 
conditions remain constant. By appropriate choice of temperature, crystals 
of greatest dimensions in the range of 25 nm to 100 nm may be obtained. A 
period of ageing at a temperature below that at which crystallization 
takes place may precede thermal treatment; smaller particle size material 
then results. 
The colloidal suspension, or the crystals obtainable from the suspension, 
produced by the processes described above may be used in a number of 
applications including in the manufacture of thin films on substrates, in 
which application the crystals may provide a growth-enhancing layer, or as 
the base of the film itself, for example by multiple in-situ 
crystallization. More especially, however, according to the present 
invention, the nanometric sized crystals may be used as seeds in the 
manufacture of Offretite. 
The present invention accordingly also provides, in a second aspect of the 
invention, a process for the manufacture of Offretite which comprises 
forming an Offretite-forming synthesis mixture, advantageously having a 
molar composition, calculated in terms of oxides, in the following ranges: 
______________________________________ 
M.sub.2 O:Al.sub.2 O.sub.3 
1.3 to 4.0:1 
(TMA).sub.2 O:Al.sub.2 O.sub.3 0.2 to 0.6:1 
SiO.sub.2 :Al.sub.2 O.sub.3 7 to 13:1 
H.sub.2 O:Al.sub.2 O.sub.3 50 to 540:1 
______________________________________ 
wherein M represents potassium, of which up to 30 molar per cent may be 
replaced by sodium, and also containing seed crystals of Offretite of 
maximum dimension at most 100 nm, and subjecting the seed-containing 
synthesis mixture to hydrothermal treatment at a temperature and for a 
time sufficient to form Offretite. 
As indicated above, it is possible to replace aluminium by gallium; the 
invention accordingly also provides a process in which the synthesis 
mixture is as defined above, in which Al.sub.2 O.sub.3 is replaced by 
Ga.sub.2 O.sub.3. 
The lower the proportion of potassium, the lower the preferred water 
content of the synthesis mixture. 
It has been found that the presence of the nanometric-sized seed crystals 
significantly accelerates the formation of Offretite from the synthesis 
mixture. Further, it has been found that very small proportions of the 
colloidal seed crystals are effective to promote crystallization of 
Offretite. The process may employ very small proportions of colloidal 
seeds, e.g., from 0.0002 to 0.1%, by weight of the total synthesis 
mixture, adantageously from 0.01 to 0.05%, and conveniently about 0.025%, 
although it will be understood that it is within the scope of the 
invention to use a higher proportion. Since the proportion of seeds may be 
so low, it is possible to employ alumina-derived seeds in Ga-Offretite 
manufacture without affecting the essential gallium-based nature of the 
product. The gallium product may present advantages over the aluminium 
product because of its lower acidity (at a given molar composition). 
Hydrothermal treatment of the seeded synthesis mixture is advantageously 
carried out at a temperature within the range of from 100.degree. C. to 
200.degree. C., preferably from 125.degree. to 175.degree. C. and 
conveniently at about 150.degree. C., advantageously for a time within the 
range of from 2 to 10 hours, preferably within the range of from 3 to 6 
hours. This compares with a time within the range of from 16 to 48 hours 
for a synthesis mixture of the same composition but without seeds. 
Treatment may be carried out with gentle stirring or, preferably, 
statically. 
The source of the various components of the synthesis mixture, other than 
the seeds, may be as described above for the first embodiment of the 
invention, except that colloidal silica is preferred as the silica source, 
a TMA halide as the structure-directing agent, and hydrated alumina as the 
alumina source. The seeds are advantageously the product of the first 
embodiment of the invention. 
The invention further provides the use, in the hydrothermal treatment of an 
Offretite-forming synthesis mixture, of a colloidal suspension of 
Offretite seeds, i.e., a suspension of seeds of Offretite having a 
greatest dimension of at most about 100 nm, to promote or accelerate he 
formation of zeolite Offretite. 
The use of colloidal seed crystals in the synthesis mixture results in a 
product of more uniform size and shape than an unseeded synthesis mixture. 
As indicated above, only very small proportions of colloidal seed crystals 
are needed to accelerate Offretite formation. It has, however, 
surprisingly been found that, under given synthesis conditions, variation 
of the proportion of seed crystals effects a change in the particle size 
of the resulting Offretite product, a greater numerical concentration of 
seeds resulting in a smaller product, thereby providing accurate control 
of product particle size. 
The present invention accordingly further provides, in a third aspect, the 
use, in a process for the manufacture of Offretite by hydrothermal 
treatment of an Offretite-forming synthesis mixture, of the concentration 
of colloidal Offretite seeds in the mixture to control the particle size 
of the product. 
It has also been found that lowering the alkalinity of a seeded synthesis 
solution reduces the particle size of the resulting Offretite product. 
In a particular synthesis mixture, described in an example below, by 
increasing the concentration of colloidal seed crystals from 2 ppm 
(0.0002%) to 1000 ppm (0.1%) the particle size (greatest dimension) of the 
resulting product was decreased from about 1.5 .mu.m to about 0.20 .mu.m, 
with intermediate concentrations resulting in intermediate product 
particle sizes. Further the particle size distribution was in each case 
narrow, and the crystals uniform in shape. 
In contrast, a synthesis mixture, unseeded but otherwise identical, gave 
generally larger particle size product, as might be expected, but also one 
of a wide particle size distribution. A mixture seeded with 5 .mu.m size 
crystals gave a product of multilayer particle size and poor size 
uniformity. 
The invention accordingly also provides the use, in a process for the 
manufacture of Offretite by hydrothermal treatment of an Offretite-forming 
synthesis mixture, or colloidal Offretite seeds to enhance the uniformity 
of particle size of the resulting product. 
Preferred reaction conditions, except for choice of concentration of seeds, 
are as described with reference to the second aspect of the invention. 
As indicated above, the traditional Offretite synthesis employs a mixture 
containing the TMA cation. Since disposal of organic residues from 
manufacturing processes is becoming increasingly difficult or expensing, 
it would be desirable to have a process for Offretite manufacture in which 
the need for an organic template or structure directing agent was 
obviated. Such a procedure would also have advantages in ease of handling 
the synthesis mixture, and could avoid the need for calcining to remove 
the template. 
It has now surprisingly been found that the presence of colloidal Offretite 
seeds in the synthesis mixture makes the presence of an organic template 
unnecessary. 
The present invention, in a fourth aspect, accordingly further provides a 
process for the manufacture of Offretite which comprises forming a 
synthesis mixture, substantially, and preferably completely, free from a 
free organic structure directing agent, and having a molar composition, 
calculated in terms of oxides, in the following ranges: 
______________________________________ 
M.sub.2 O:Al.sub.2 O.sub.3 
1.9 to 2.1:1 
SiO.sub.2 :Al.sub.2 O.sub.3 9 to 11:1 
H.sub.2 O:Al.sub.2 O.sub.3 140 to 180:1 
______________________________________ 
wherein M represents potassium, of which up to 30 molar per cent may be 
replaced by sodium, and also containing seed crystals of Offretite of 
maximum dimension at most 100 nm, and subjecting the seed-containing 
synthesis mixture to hydrothermal treatment for a time and at a 
temperature sufficient to form Offretite. 
The preferred reaction conditions, except for the absence of organic 
reagent (other than that possibly introduced within the channels of the 
seeds), are as described above with reference to the second aspect of the 
invention, although a longer time may be needed. 
The Offretite produced by the second, third and fourth aspects of the 
invention, if required after washing, cation exchange and/or calcining, is 
suitable for use as a catalyst in numerous hydrocarbon conversions and is 
effective in hydrocarbon separations or adsorptions. The Offretite 
material may be used alone, or in admixture with other zeolites, in 
particulate form or in the form of a layer on a support, especially in the 
form of a membrane. Hydrocarbon conversions include, for example, 
cracking, reforming, hydrofining, aromatization, alkylation, isomerization 
and hydrocracking.

The following examples illustrate the invention. 
EXAMPLE 1 
This example illustrates the production of Offretite of particle size as 
low as 70 nm by the use of a synthesis mixture having higher template and 
lower potassium content than traditionally used. The synthesis mixture 
contained the following components. 
______________________________________ 
Parts by Weight 
______________________________________ 
KOH pellets, 87.4% wt purity (Baker) 
3.4 
TMAOH, 25% by weight in water (Fluka) 108.52 
Al chips, 99.99% wt purity (Fluka) 2.8924 
SiO.sub.2 powder, 89.8% wt, 10.2% water (Baker) 35.52 
______________________________________ 
(The TMAOH was contaminated with potassium.) 
The KOH pellets were dissolved in the TMAOH solution in a glass beaker at 
room temperature, and the Al chips then dissolved in the resulting 
solution with stirring and gentle heat. After addition of the silica 
powder, the mixture was heated to boiling with stirring and kept at 
boiling point for 5 minutes. It was apparent that not all the silica had 
dissolved, some settling on the base of the glass beaker. The molar 
composition of the synthesis mixture, taking into account the potassium 
present in the TMAOH, was: 
EQU 2.78 (TMA).sub.2 O:0.98 K.sub.2 O:Al.sub.2 O.sub.3 :9.90 SiO.sub.2 
:91H.sub.2 O 
The synthesis mixture was homogenized by vigorous stirring for several 
minutes, then immediately poured into a plastic bottle which was then 
placed in an oil bath, the open end of the bottle being connected to a 
reflux condenser. The oil bath was heated to 85.degree. C., and maintained 
at that temperature over a period. The appearance of the mixture gradually 
changed, with the quantity of deposited silica reducing, while the mixture 
developed a whitish appearance. Heating was terminated after 160 hours, 
with the contents of the bottle whitish and more viscous than the starting 
mixture. 
The product was washed several times, using a high speed centrifuge to 
decant the wash water, and dried overnight at 110.degree. C. X-ray 
diffraction (XRD) showed an excellently crystalline pure Offretite, while 
scanning electron microscopy (SEM) showed particles uniform in shape and 
size, with dimensions about 200.times.70 nm. 
This example illustrates the synthesis of material on the borderline of 
colloidal particle size. 
FIGS. 1 and 2 show X-ray diffractogram and peak values and SE micrographs 
of the products of Example 1. 
EXAMPLE 2 
In this example, the procedure of Example 1 was repeated, the sole 
difference being the replacement of the potassium hydroxide by 
substantially the same molar proportion of sodium hydroxide, to provide a 
synthesis mixture of molar composition: 
EQU 2.78 (TMA).sub.2 O:0.47 K.sub.2 O:0.50 Na.sub.2 O:Al.sub.2 O.sub.3 :9.90 
SiO.sub.2 :91 H.sub.2 O 
(The K.sub.2 O originated as contamination in the TMAOH.) 
The synthesis mixture again developed a homogeneous whitish appearance. XRD 
and SEM analysis showed an Offretite product, consisting of spherulitic 
particles with a size of about 60 nm. 
FIGS. 3 and 4 show X-ray diffractogram and peak values and SE micrographs 
of the product of Example 2. 
EXAMPLE 3 
A synthesis mixture was prepared as in Examples 1 and 2 but omitting any 
deliberate additional of alkali metal hydroxide. Subsequent analysis 
showed, however, that the TMAOH was contaminated with K.sub.2 O to an 
extent of 1.83 wt. percent; it is believed that this small proportion of 
alkali metal suffices to ensure nanocrystalline product, by providing a 
synthesis mixture of the molar composition: 
EQU 2.78 (TMA).sub.2 O:0.47 K.sub.2 O:Al.sub.2 O.sub.3 :9.90 SiO.sub.2 :91 
H.sub.2 O 
The synthesis mixture was thermally treated as in Example 1. After 160 
hours heating at 85.degree. C., the crystallization was stopped. The 
originally inhomogeneous mixture changed during heating to a jelly; this, 
however, was transparent. 
After washing using a 17500 rpm centrifuge, the product was suspended in 
the last wash water, a stable, colloidal, suspension resulting. A portion 
was evaporated to dryness and characterized by XRD and SEM. Although the 
diffractogram showed weak and broad peaks, the pattern was still 
recognizable as pure Offretite. The SEM showed that the product consisted 
of uniformly sized and shaped particles, about 45 nm.times.20 nm. XRD 
analysis of a portion of product calcined in air at 475.degree. C. for 20 
hours showed essentially no change in crystallinity, evidence of thermal 
stability. 
FIGS. 5, 6 and 7 show XRD diffractograms of the dried and calcined products 
and an SE micrograph of the dried product. 
EXAMPLE 4 
When the technical grade TMAOH used in Example 3 was replaced by a material 
of greater than 99% purity, no Offretite was produced. To show that the 
production of colloidal Offretite depends on the presence of potassium, a 
synthesis mixture was prepared using KOH and high purity TMAOH. The molar 
composition of the mixture was: 
EQU 2.49 (TMA).sub.2 O:0.47 K.sub.2 O:Al.sub.2 O.sub.3 :9.9 SiO.sub.2 :91 
H.sub.2 O 
The synthesis mixture was thermally treated at 85.degree. C. for 6 days, 
and product recovered as described in Example 3. XRD showed the product to 
be pure Offretite, while SEM indicated a particle size of about 
70.times.25 nm. 
By way of comparison, a synthesis mixture of molar composition 
EQU 2.49 (TMA).sub.2 O:0.24 K.sub.2 O:9.9 SiO.sub.2 :91 H.sub.2 O 
was prepared using pure TMAOH and half the above proportion of KOH. XRD 
showed an Offretite product contaminated with sodalite. 
EXAMPLE 5 
This example illustrates the acceleration of Offretite formation by 
seeding. A synthesis mixture was prepared using the following components. 
______________________________________ 
Parts by Weight 
______________________________________ 
KOH pellets, 87.4% wt purity (Baker) 
39.40 
Al(OH).sub.3 powder, 98.5% wt purity (Alcoa) 24.29 
H.sub.2 O, deionized 286.55 
Ludox HS-40, 40% SiO.sub.2 by weight 230.38 
in water (Du Pont) 
TMACl, &gt; 99% wt purity (Fluka) 16.81 
Colloidal seed suspension, 5.36% wt % 2.81 
in water (From Ex. 3) 
______________________________________ 
The potassium hydroxide and hydrated alumina were dissolved in 115 parts 
water with boiling until a clear aluminate solution resulted. The TMA 
chloride was dissolved in 171.55 parts water, the solution added to the 
colloidal silica, the colloidal seeds were added to the resulting 
solution, and stirred for 3 minutes. The aluminate solution was then added 
and the resulting mixture stirred for 5 further minutes. Its molar 
composition was 
EQU 2.00 K.sub.2 O:1.00 TMACl:Al.sub.2 O.sub.3 :10 SiO.sub.2 :160 H.sub.2 O 
and it contained 0.025 wt % colloidal Offretite. 
For comparison purposes, a second synthesis mixture of identical molar 
proportions was prepared without seeds. 
The seeded synthesis mixture was divided between four stainless steel 
autoclaves which were placed in an oven at room temperature. The oven was 
heated to 150.degree. C. over the course of 2 hours. One autoclave was 
removed from the oven after 1 hour at 150.degree. C. and rapidly cooled to 
room temperature with running water. The other three autoclaves were 
removed after 2, 3 and 4 hours at 150.degree. C. and similarly cooled. 
The autoclave contents were washed with water to a pH about 10. After 
separation from the wash water by centrifuging, the products were dried in 
an oven for 16 hours at 110.degree. C. From XRD and SEM analysis it 
appeared that crystallization had already started by 1 hour and the 
product was fully crystalline after 4 hours. FIG. 8 shows the 
XR-diffractograms of each product, and FIGS. 9 and 10 show the SE 
micrographs of the products after 1 and 4 hours respectively. 
The unseeded mixture was divided between 5 autoclaves and treated 
identically to the seeded samples, except that one autoclave was withdrawn 
at each of 4, 8, 16, 48 and 72 hours at 150.degree. C. XRD analysis shows 
that crystallization did not start until about 16 hours, and was not 
complete until about 48 hours. 
EXAMPLE 6 
This example demonstrates the control of crystallite size by concentration 
of seed crystals. 
A synthesis mixture was prepared using the following components. 
______________________________________ 
Parts by Weight 
______________________________________ 
KOH pellets, 87.4% wt purity (Baker) 
25.67 
Al(OH).sub.3 powder, 98.5% wt purity (Alcoa) 15.84 
H.sub.2 O, deionized 189.19 
Ludox HS-40, 40% SiO.sub.2 by weight 150.23 
in water (Du Pont) 
TMACl, &gt; 99% wt purity (Fluka) 10.95 
______________________________________ 
The potassium hydroxide and hydrated alumina were dissolved in 75.20 parts 
water with boiling until a clear aluminate solution resulted. The TMA 
chloride was dissolved in 133.99 parts water, the solution added to the 
colloidal silica, and stirred for 3 minutes. The aluminate solution was 
then added and the resulting synthesis mixture stirred for 5 further 
minutes. Its molar composition was 
EQU 2.00 K.sub.2 O:1.00 TMACl:Al.sub.2 O.sub.3 :10 SiO.sub.2 :160 H.sub.2 O 
Eleven identical synthesis solutions were prepared, one of which was left 
unseeded for comparison purposes. The other ten samples were seeded with 
colloidal Offretite crystals at 2, 4, 8, 16, 31, 62, 128, 251, 501, and 
1002 ppm by weight, based on the weight of the synthesis mixture. To avoid 
any unwanted seeding effects, the autoclaves used for hydrothermal 
treatment were each treated twice with 4 molar KOH solution for 16 hours 
at 110.degree. C., thereby dissolving any zeolite crystals adhering to the 
autoclave interior from any previous synthesis. The autoclaves were heated 
to 150.degree. C. as described in Example 5, the seeded samples being 
maintained at that temperature for 48 hours, and the unseeded comparison 
for 72 hours, in each case without stirring. The products of the seeded 
synthesis were washed to a pH of 10.4, and that of the unseeded synthesis 
to pH 9.8, and dried at 120.degree. C. and 110.degree. C. respectively. 
XRD showed that all products were excellently crystalline and pure 
Offretite. Analysis of the SEM micrographs showed that the crystallites of 
each seeded sample were remarkably uniform in size and shape, while the 
crystallites of the comparison unseeded sample had a wide particle size 
distribution; the average size of the rod-like crystals was 6.5 .mu.m in 
length, 3.5 .mu.m in diameter, but the smallest particle size was about 
2.4 .mu.m long, while the largest was about 9.2 .mu.m. The table below 
shows the average length and diameter, and the length:diameter ratio, of 
each of the samples. 
______________________________________ 
Seeds 
added, Particle size, .mu.m, by SEM 
ppm length diameter l/d ratio 
______________________________________ 
none 6.5 3.5 1.9 
2 1.55 1.03 1.5 
4 1.30 0.78 1.7 
8 1.08 0.71 1.5 
16 0.81 0.52 1.6 
31 0.68 0.45 1.5 
62 0.51 0.33 1.5 
128 0.41 0.21 1.9 
251 0.33 0.19 1.7 
501 0.25 0.13 1.9 
1002 0.20 0.09 2.2 
______________________________________ 
FIG. 11 shows the SEM of the comparison sample, FIG. 12 that of the sample 
with 2 ppm seeds. 
EXAMPLE 7 
This example demonstrates the use of seeds to avoid the need for an organic 
template in Offretite manufacture. 
A synthesis mixture was prepared using the following components. 
______________________________________ 
Parts by Weight 
______________________________________ 
KOH pellets, 87.4% wt purity (Baker) 
25.70 
Al(OH).sub.3 powder, 98.5% wt purity (Alcoa) 15.84 
H.sub.2 O, deionized 185.67 
Ludox HS-40, 40% SiO.sub.2 by weight 150.23 
in water (Du Pont) 
Colloidal seed suspension, 5.36 wt % 3.56 
in water (from Ex. 3) 
______________________________________ 
The potassium hydroxide and hydrated alumina were boiled in 75.02 parts 
water until clear. The colloidal silica was diluted with 110.65 parts of 
water, the colloidal seeds added to the resulting solution, and stirred 
for 3 minutes. The aluminate solution was then added and the resulting 
synthesis mixture stirred for 3 further minutes. Its molar composition was 
EQU 2.00 K.sub.2 O:Al.sub.2 O.sub.3 :10 SiO.sub.2 :160 H.sub.2 O 
and it contained 0.050 wt % colloidal Offretite. 
For comparison purposes, a second synthesis mixture of identical molar 
proportions was prepared without seeds. 
The synthesis mixtures were placed in separate autoclaves, heated to 
150.degree. C. as described in Example 5, and maintained at that 
temperature for 96 hours. The resulting products were washed with water to 
a pH of 10.5 and dried at 110.degree. C. The yield of the process 
according to the invention was about 17%, based on the total weight of 
synthesis mixture. 
X-ray diffraction analysis of the product of the seeded process showed the 
characteristic pattern of Offretite, slightly contaminated with zeolite W, 
SEM showing rod-like particles of about 2 .mu.m length and 0.1 .mu.m 
diameter. Thermographic analysis showed a micropore capacity for toluene 
of 2.86%. The comparison process yielded a mixture of zeolite W and 
amorphous material. 
EXAMPLE 8 
To reduce the contamination by zeolite W resulting from the process of 
Example 7, the alkalinity of the synthesis mixture was increased, to give 
a molar composition of 
EQU 2.20 K.sub.2 O:Al.sub.2 O.sub.3 :10 SiO.sub.2 :160 H.sub.2 O 
seeding with 0.0502% colloidal Offretite crystals, other components and 
reaction conditions being as in Example 7. XRD analysis showed an 
Offretite product free from zeolite W but now slightly contaminated with 
zeolite KL. Thermographic analysis showed a micropore capacity for toluene 
of 3.69%, which confirms the absence of zeolite W. 
EXAMPLE 9 
EXAMPLE 7 was repeated with a synthesis mixture of the following molar 
composition: 
EQU 2.10 K.sub.2 O:Al.sub.2 O.sub.3 :10 SiO.sub.2 :160 H.sub.2 O 
XRD analysis shows an Offretite product free from both zeolites KL and W. 
FIGS. 13 and 14 show XRD and SEM of the product of this example. 
EXAMPLE 10 
The procedure of Example 9 was repeated, but using 0.075% by weight 
Offretite seeds. In a comparison example, a similar synthesis mixture, but 
with no seeds, was used. 
The synthesis mixture seeded with Offretite gave an Offretite product, with 
no KL or W contamination. 
The unseeded mixture gave a largely amorphous product with small 
proportions of W and KL. 
EXAMPLE 11 
This example illustrate the preparation of Gallium Offretite. A synthesis 
mixture was prepared using the following components: 
______________________________________ 
Solution A Parts by Weight 
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KOH pellets, 87.4 wt % purity (Baker) 
28.15 
Ga.sub.2 O.sub.3, 99.999 wt % purity (Ingal) 17.86 
H.sub.2 O, deionized (of which 39 parts are 74.03 
used to transfer the solution 
quantitatively to Solution B) 
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The potassium hydroxide and gallium oxide were dissolved in water with 
boiling, and the solution allowed to cool to room temperature. 
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Solution B Parts by Weight 
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Ludox HS-40 143.13 
TMACl, &gt; 99% wt purity (Fluka) 10.44 
H.sub.2 O, deionized 107.13 
Colloidal Offretite Seed Suspension, 1.80 
5.36 wt % in water (Ex. 3) 
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The TMACl was dissolved in 54.41 parts water. The silica gel was weighed 
into a blender, and the colloidal suspension and the TMACl solution added; 
52.72 parts of water were used as rinse water to effect quantitative 
transfer of the TMACl solution. After 2 minutes stirring of solution B, 
solution A was added, and stirring continued for a further 4 minutes. A 
slightly blueish, clear, non-gelling mixture resulted, of molar 
composition: 
2.3 K.sub.2 O:1.00 TMACl:1.00 Ga.sub.2 O.sub.3 :10 SiO.sub.2 :159 H.sub.2 O 
and containing 0.025 wt % colloidal Offretite. 324.85 parts of synthesis 
mixture were transferred to a stainless steel autoclave which was placed 
in a room temperature oven. The oven was heated over 2 hours to 
150.degree. C. and maintained at that temperature for 8 hours. 
The product was washed several times until the pH of the washwater was 9.7, 
and dried at 120.degree. C. 61.8 parts of product were recovered. 
XRD (FIG. 15) showed that the product was fully crystalline Offretite, SEM 
(FIG. 16) showed that it was formed of extremely uniform ovate particles 
with a size of 0.25 .mu.m. 
Four comparison experiments were carried out. In the first, a synthesis 
mixture of the same molar composition but omitting seeds was subjected to 
the same hydrothermal treatment for 8 hours. The product was completely 
amorphous. In the second, the same synthesis mixture was seeded with 0.22% 
by weight of micron size aluminium-based Offretite seeds, the seeds being 
dispersed in the synthesis mixture by vigorous mixing with a magnetic 
stirrer for 5 minutes, and then subjected to the same hydrothermal 
treatment for 8 hours. XRD showed the product to be largely amorphous. In 
the third and fourth comparisons, the unseeded and micron-seeded mixtures 
were subjected to hydrothermal treatment at 150.degree. C. for 70 hours. 
XRD of the unseeded and seeded products showed a crystalline Offretite 
product, but contaminated with other dense, crystalline phases. SEM of the 
unseeded product showed further contamination by unreacted gel particles. 
The results show that the use of colloidal Offretite is necessary to obtain 
pure Ga-Offretite, and also speeds reaction rate significantly. 
EXAMPLE 12 
A gallium-based synthesis mixture with a lower potassium content and 
containing colloidal seeds was formed in the same way as described in 
Example 11; its molar position was: 
EQU 2.00 K.sub.2 O:1.00 TMACl:1.00 Ga.sub.2 O.sub.3 :10 SiO.sub.2 :159 H.sub.2 
O 
and it contained 0.025% colloidal Offretite. 
324 parts of synthesis mixture were hydrothermally treated for 8 hours as 
described in Example 11. 64 parts of product were recovered. XRD showed 
that the product was pure Offretite, while SEM (FIG. 17) showed it was 
formed of extremely uniform ovate particles of size 0.20 .mu.m. This 
indicates the control of particle size by variation of alkalinity.