Process for preparing LTL nano-crystalline zeolite compositions

The reaction of premade gels with KOH in aqueous ammonia solvents yields highly crystalline but ultrasmall particulate, colloidal, products having major advantages in catalytic and sorption process.

BACKGROUND OF THE INVENTION 
This invention relates to a novel process for the preparation of 
nano-crystallite forms of LTL, having crystal sizes less than 30 
nano-meters. In particular, the zeolite has a structure of zeolite LTL and 
is prepared using stoichiometric quantities such that the ratio of product 
to reactants approaches unity, and the product crystals are less than 
about 30 nanometers diameter. The use of ammonia as a solvent or 
co-solvent in the process is essential to achievement of the desired 
product. 
Ammonia is similar to water in that it is a dipolar, protonic solvent 
capable of acid-base chemistry. It has a dipole moment of 
3.4.times.10.sup.-30 C.multidot.m compared to 4.9.times.10.sup.-30 
C.multidot.m for the more polar water molecule. This results in ammonia 
being a poorer solvent than water for ionic substances, but a better 
solvent for more covalent compounds. At a pH greater than about 9, the 
equilibrium NH.sub.4 +OH.sup.- .fwdarw.NH.sub.3 +H.sub.2 O totally favors 
gaseous ammonia dissolved in the base solution. Pure ammonia has a vapor 
pressure of over 60 atm at 100.degree. C. compared to 1 atm for pure 
water. In this invention ammonia either promotes the "flood" nucleation of 
LTL or poisons the surface of crystals at the nucleus stage of between 100 
.ANG. and 200 .ANG.. 
A zeolite designated as zeolite L is known to exhibit good catalytic 
properties, particularly for hydrocarbon conversion, and advantageous 
sorbent properties as described, for example, by Barrer et al., Surface 
Science, 12, 341 (1968). The chemical composition of zeolite L is 
disclosed in U.S. Pat. No. 3,216,789 to be: 
EQU 0.9-1.3(M.sub.2 /n):Al.sub.2 O.sub.3 :5.2 to 6.9SiO.sub.2 :xH.sub.2 O 
where M is an exchangeable cation of valence n and x is from 0 to 9. 
Zeolite L also has a characteristic x-ray diffraction pattern, and its 
structure has been determined by Barrer et al., Zeit. Krist., 128, 352 
(1969). The structure code LTL has been assigned to this structure type 
(Atlas of Zeolite Structure Types, 3rd Edn., W. M. Meier and D. H. Olson, 
Intl. Zeolite Assoc./Butterworths Press (1992)). The x-ray diffraction 
pattern of zeolite L has the following more significant d(.ANG.) values: 
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16.1 .+-. 0.3 
7.52 .+-. 0.04 
6.00 .+-. 0.04 
4.57 .+-. 0.04 
4.35 .+-. 0.04 
3.91 .+-. 0.02 
3.47 .+-. 0.02 
3.28 .+-. 0.02 
3.17 .+-. 0.01 
3.07 .+-. 0.01 
2.91 .+-. 0.01 
2.65 .+-. 0.01 
2.46 .+-. 0.01 
2.42 .+-. 0.01 
2.19 .+-. 0.01 
______________________________________ 
A typical preparation of Zeolite L as disclosed by Breck, Zeolite Molecular 
Sieves, New York: J. Wiley, 283 (1974) employs an excess of SiO.sub.2 and 
a greater excess of K.sub.2 O. Isostructural compositions include ECR-2 
(U.S. Pat. No. 4,552,731) and BaG-L (Baerlocher & Barrer, Zeit. Krist., v. 
36, p. 245, (1972)). 
The preparation of zeolite L described in U.S. Pat. No. 3,216,789 involves 
crystallizing the zeolite from a reaction mixture having a mole ratio of 
silica to alumina which is significantly higher than the ratio in the 
formed zeolite. Specifically, the reaction mixture comprises mole ratios: 
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K.sub.2 O/(K.sub.2 O + Na.sub.2 O) 
0.33-1 
(K.sub.2 O + Na.sub.2 O)/SiO.sub.2 
0.35-0.5 
SiO.sub.2 /Al.sub.2 O.sub.3 
10-28 
H.sub.2 O/(K.sub.2 O + Na.sub.2 O) 
15-41 
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Zeolite L and zeolites having related structures belong to the "L" family 
of zeolites. This family is characterized by having a 12-ring hexagonal 
structure with pore dimensions of about 5.5 to 7.2 .ANG.. In addition to 
zeolite L there are also barium zeolites Ba-G and Ba-G,L described by 
Barrer et al in J. Chem. Soc., 2296 (1964), J. Chem. Soc., 1254 (1972) and 
J. Chem. Soc., 934 (1974); ZSM-10 (U.S. Pat. No. 3,692,470) may be a DABCO 
containing member of this group of zeolites. Similarly, zeolite UJ (U.S. 
Pat. No. 3,298,780) may also be of the zeolite L type. Numerous syntheses 
of zeolite L have been reviewed in U.S. Pat. No. 4,973,461. 
Structures have been proposed for zeolite L (Barrer et al, Zeit. Krist., 
128, 352 (1969)) and GL (Baerlocher et al, ibid). If all cation positions 
in L are filled by monovalent cations, L will have a minimum Si/Al ratio 
of 1.8 according to Baerlocher et al (Zeit. Krist., v. 136, p. 253 
(1972)). ECR-2 has an Si/Al composition in this range (U.S. Pat. No. 
4,552,731). 
Subsequently, several patents have claimed specific morphology LTL 
products, such as discs (EP 0096479), large cylindrical crystals (U.S. 
Pat. No. 4,544,539), and microcrystals (U.S. Pat. No. 5,064,630), and the 
subject of morphology variation and control has been discussed generally 
by Fajula (NATO ASI Series, v. 221B, p. 53 (1990)). 
It has been found that zeolite L may be used as a catalyst base in 
aromatization reactions. U.S. Pat. No. 4,104,320 discloses 
dehydrocyclization of aliphatic compounds in the presence of hydrogen 
using a catalyst comprising zeolite L and a group VIII metal, in which the 
zeolite L is of the formula: 
EQU M.sub.2/n (AlO.sub.2).sub.9 (SiO.sub.2).sub.27 
(where M is a cation of valence n), but the silica to alumina ratio may 
vary from 5 to 7. 
East German Patent 88,789 discloses dehydrocyclization using a catalyst 
formed from a zeolite precursor with a silica to alumina ratio of 5 or 
greater which is dealuminized to give a silica to alumina ratio of up to 
70. Zeolite L is mentioned as a precursor. 
European Patent Application Publication 40119 discloses a 
dehydrocyclization process operating at low pressure (1 to 7 bars) or low 
H.sub.2 /hydrocarbon ratio using a catalyst comprising platinum on a 
potassium zeolite L. Belg. Patent 888,365 describes dehydrocyclization 
using a catalyst comprising platinum, rhenium (incorporated in the form of 
its carbonyl) and sulphur to give an atomic ratio of sulphur to platinum 
of 0.05 to 0.6 on a zeolitic crystalline aluminosilicate base such as 
zeolite L. Belg. Patent 792,608 discloses the treatment of zeolite L for 
use as a catalyst in isomerization by exchange with ammonium and chromium 
ions. 
SUMMARY OF THE INVENTION 
The present invention is a process to make synthetic nano-sized crystalline 
zeolites isostructural with LTL, having desirable property advantages 
because of small crystal sizes, and having the composition, in terms of 
mole ratios of oxides, in the range: 
EQU 0.9 to 1.1M.sub.2/n O:(Al,Ga,Fe).sub.2 O.sub.3 :2.5 to 7.0SiO.sub.2 
:xH.sub.2 O 
wherein m represents at least one exchangeable cation of a metal selected 
from Group I through VIII of the Periodic Table (Kirk-Othmer Encyclopedia 
of Chemical Tech., 2nd Edn., V. 8, (1965)), n represents the valence of M, 
and x may be 0 or a number from 1 to about 6. 
The steps of the process include: 
(a) preparing a reaction mixture comprising water, a source of silica, a 
source of alumina, KOH and up to about 30 mole percent of NaOH based on 
total moles of KOH and NaOH, ammonia, the reaction mixture having a 
composition, in terms of mole ratios of oxides, within the following 
ranges: 
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M.sub.2.sup.' O:Al.sub.2 O.sub.3 
2.5 to 8 
SiO.sub.2 :Al.sub.2 O.sub.3 
4 to 20 
H.sub.2 O:Al.sub.2 O.sub.3 
80 to 400 
NH.sub.3 :Al.sub.2 O.sub.3 
30 to 150 
______________________________________ 
where M' is either K or a mixture of K and Na; and Al may be partly or 
wholly replaced by Ga; and Fe may replace up to about 30% Al or Ga. 
(b) maintaining the reaction mixture at between about 70.degree. C. and 
160.degree. C. under autogenous pressure for a sufficient period of time 
to form a crystalline product in which the crystals have a diameter less 
than about 30 nanometers.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention is a new way to synthesize LTL in ammonia solvent and 
co-solvent systems which results in colloid sized crystallites less than 
300 .ANG., and in some cases less than 200 .ANG. in diameter. In 
hydrocarbon processes such small crystals give high diffusion rates, high 
reactivities, and exceptional resistance to deactivation by pore plugging 
and surface contamination. The characteristic X-ray diffraction patterns 
show very broad peaks, and in some cases near--amorphous spectra. However, 
their IR spectra are fully characteristic of LTL. Such materials may be 
expected to have superior performance characteristics in such catalytic 
reactions as aromatization of normal paraffins, reforming, dewaxing, 
isomerization and oligomerization, as a result of their enhanced 
accessibility to the micropores. These products show exceptionally high 
micropore capacity for hydrocarbons, together with unusual mesopore 
capacity characteristic of agglomerated colloidal particles. Nano-crystals 
of this type are particularly useful for the preparation of inorganic 
membranes; the micro crystals filling the pores of the ceramic, usually, 
alumina, titania or silica, supports, so providing a resilient microporous 
membrane useful for hydrocarbon, catalytic and separation applications. 
At this time the preferred way to make these products is to react a premade 
silica-alumina gel--typically an amorphous fluid cracking catalyst--having 
an Si/Al ratio between about 4 and 12 in a potassic ammonia or aqueous 
ammonia solution. In the absence of ammonia entirely different zeolite 
products such as chabazite and phillipsite crystallize. The preferred 
reaction composition is: 
EQU 3 to 6K.sub.2 O:(Al,Ga,Fe).sub.2 O.sub.3 :4 to 15SiO.sub.2 :50 to 
150NH.sub.3 :150 to 400H.sub.2 O 
Materials of this invention may be difficult to filter in a conventional 
way from the mother liquor of waste products, in which case centrifuge 
separation and washing is a preferred mode of product separation and 
purification. 
EXAMPLE 1 
A composition: 
EQU 3.0K.sub.2 O:Al.sub.2 O.sub.3 :11.4SiO.sub.2 :100NH.sub.3 :240H.sub.2 O 
was made by mixing 5 gms high alumina fluid cracking catalyst gel (Davison 
Chemical Co., Hi-Alumina FCC, having a chemical composition of about 12.5 
wt % Al.sub.2 O.sub.3, 87.5 wt % SiO.sub.2) in a solution of 2.40 gms 
KOH.1/2H.sub.2 O in 40 mls aqueous ammonium hydroxide (29% NH.sub.3), and 
reacting in an autoclave at 100.degree. C. After 12 days reaction the 
autoclave was cooled, the product filtered, washed and dried at 
100.degree. C. X-ray diffraction analysis gave the spectrum shown in FIG. 
1 which is similar to that for a typical LTL material except that the 
peaks are very broad, indicating very small crystals. The n-hexane 
sorption capacity of this sample was 11.2 wt % (25.degree. C., 51 torr) 
and the sorption isotherm is shown in FIG. 2. Transmission Electron 
microscopy (TEM) showed that the crystallites were less than about 150 
.ANG. by 200 .ANG., as shown in FIG. 3, and clearly showing the 12-ring 
channels. 
Thermogravimetric analysis (FIG. 4) showed a H.sub.2 O+NH.sub.3 capacity of 
about 15 wt %. 
EXAMPLE 2 
A composition: 
EQU 3.5K.sub.2 O:Al.sub.2 O.sub.3 :11.4SiO.sub.2:100 NH.sub.3 :240H.sub.2 O 
was made and reacted as for Example 1, except that 2.8 KOH.1/2H.sub.2 O was 
used in the reaction. The X-ray diffraction pattern after 12 days is shown 
in FIG. 1, and is now showing increased line broadening, almost amorphous 
like characteristics. The 5 day reaction sample showed a similar spectrum. 
Thermogravimetric analysis showed a H.sub.2 O+NH.sub.3 capacity of 19 wt % 
(FIG. 4), and TEM showed crystallites having dimensions 50 .ANG. by 80 
.ANG.. Infrared analyses gave spectra characteristic of zeolite L. 
EXAMPLE 3 
A composition: 
EQU 4.0K.sub.2 O:Al.sub.2 O.sub.3 :11.4SiO.sub.2 :100NH.sub.3 :240H.sub.2 O 
was made and reacted as described in Example 1 except that 3.2 gm 
KOH.1/2H.sub.2 O were used in the reaction. 
The product X-ray diffraction pattern is shown in FIG. 1, and may be 
described as characteristic of a near amorphous material. However, the TEM 
examination shows the material to be highly crystalline, but with crystals 
having very small dimensions (100 .ANG. by 150 .ANG.). Thermogravimetric 
analysis showed a H.sub.2 O+NH.sub.3 capacity of about 23 wt % (FIG. 3), 
and a hexane sorption capacity at 22.degree. C. (50 torr) gave 20 wt % 
sorption. A 25.degree. C. n-hexane isotherm showed a distinctive micropore 
capacity of 8-9 wt %, plus a larger meso-pore sorption, characteristic of 
small pores between colloidal particles. 
EXAMPLE 4 
A composition: 
EQU 5K.sub.2 O:Al.sub.2 O.sub.3 :11.4SiO.sub.2 :100NH.sub.3 :240H.sub.2 O 
was made and reacted in the manner described in Example 1, except that 4 
gms of KOH.1/2H.sub.2 O were used. The product was essentially similar to 
that made and described in Example 3 (FIG. 1). 
EXAMPLE 5 
A composition: 
EQU 6K.sub.2 O:Al.sub.2 O.sub.3 :11.4SiO.sub.2 :100NH.sub.3 :240H.sub.2 O 
was made and reacted as described in Example 1 except that 4.8 gms 
KOH.1/2H.sub.2 O were used. The product was essentially identical to that 
described in Example 3 (FIG. 1).