FIELD OF THE INVENTION
The present invention relates to synthesis of ZSM-5 type of molecular sieve
material importantly in the absence of using any organic template/s and also
with reduced time for crystallization with avoidance of calcination (heat
treatment) step at the end. More particularly, the present invention relates to an
Improved Hydrothermal Process to Synthesize ZSM-5 type Molecular Sieve
Materials without using any Templates.
BACKGROUND OF THE INVENTION
Materials belonging to alumino silicate series with high silica content having
unique catalytic activity, defined structural pores and shape selectivity, which are
the characteristics of ZSM-5 zeolite based material as a molecular sieve.
ZSM-5 molecular sieve having high silica content was developed for the first time
by Mobil Corporation in the early 1970. Extensive research on synthesizing such
material/s has been carried out and also its catalytic activity and properties
related to molecular sieving have been exploited in a number of industrial
applications.
Unlike conventional alumino silicate materials, ZSM-5 is normally prepared by
using various types of template of materials. These template materials make the
synthesis process very easy for synthesizing ZSM-5. Among the template
materials, tetrapropylammonium cation has excellent template effects and hence
has been widely used to synthesize ZSM-5 materials and several research
papers arid patents have been reported using the said template material.

Despite all the advantages of using template materials for synthesizing ZSM-5
molecular sieves, one major reason why the template material is not preferred to
be used is that the material is very expensive. The material is also very toxic and
when ZSM-5 is synthesized using the said template, additional cost for treating
the toxic chemical that still contained in the reactor is involved, which is also
regarded as a concern of contamination by various means in the environment. In
addition, ZSM-5 prepared by using the said template material are subjected to a
calcination reaction at a temperature about 550°C (heat treatment) in order to
remove the organic material present in channel structure of the ZSM-5, before it
is used for any other applications.
With a view to overcome the above problems, research for preparation of ZSM-5
without using such organic template material/s has also been carried out, as a
result, some preparation processes were developed in the meantime.
US Patent No.4257885 (1981) describes a method for synthesizing ZSM-5 in the
absence of an organic template material and with or without the use of a
crystallization seed. However the above mentioned process has a disadvantage
of having reaction duration in the range of 68 - 120 hours that makes the
process relatively lengthy.
Further, US Patent No. 4565681 (1986) discloses a method of synthesizing ZSM-
5 in absence of an organic template material by mixing a silica source with an
acid- treated alumina source having a reaction period of 8 - 48 hours at a
temperature range of 150 - 180°C.

US Patent No. 5240892 (1993) discloses another method for synthesizing ZSM-5
in absence organic template/s by using a silica precursor that is neutralized with
sulfuric acid.
However, in the known methods, the products thus obtained have only 75%
crystalline structure, in spite of the reaction occurring at a temperature of 180°C
by using crystallization seed acting to promote the crystallization.
Prior art teaches several methods to manufacture ZSM-5 molecular sieve material
using organic template structure.
French Patent No. 1,587,860 describes a process for synthesis of ZSM-5 by
mixing a source of silicon and an inorganic base namely sodium hydroxide in
presence of organic template compound, tetrapropylammonium ion in the form
of amines or amino alcohols, after which crystallization is carried out at a
temperature of about 150°C.
US Patent No. 4257885 teaches the introduction of Zeolite seeds in an aqueous
reaction medium so as to yield material.
U.K. Patent No. 1567948 describes a process which disallows using ZSM-5 seeds
in the reaction medium, however in that case, the synthesis is carried out in an
alcoholic medium. These prior art, process however suffer from the disadvantage
of being lengthy, because of very slow kinetics of the reaction.
There is continuing research work to invent convenient and economical route for
synthesizing ZSM-5 molecular sieve materials using common raw materials.

The invention describes an improved hydrothermal process for synthesizing
crystalline ZSM-5 material, importantly without using any organic template
material in the process and also avoiding any calcination reaction (heat
treatment) in the process besides achieving lower duration of chemical reaction.
OBJECTS OF THE INVENTION:
An object of this invention is to propose an improved hydrothermal process for
preparation of ZSM-5 type of zeolitic-based molecular sieve material by using
common raw materials under pre-defined experimental conditions and
parameters.
Another object of this invention is to propose a process to synthesize ZSM-5 type
of zeolitic-based molecular sieve material without employing any organic
template compound/s in the process, which is usual for synthesizing such
materials in other processes described elsewhere.
Other object of the invention is also to avoid calcination reaction (heat
treatment) in the process besides achieving shorter crystallization time in the
reaction for synthesizing ZSM-5 type of zeolitic-based molecular sieve material.
Further objects are to propose experimental parameters with pre-defined sources
of Si02 and AI2O3 materials with pre-defined molar ratio in the process for
synthesizing ZSM-5 molecular sieve material in a reproducible manner.

SUMMARY OF THE INVENTION
Accordingly, there is provided an improved hydrothermal method to synthesize
ZSM-5 type of molecular sieves by using the common raw materials, i.e., sodium
aluminate, aqueous colloidal silica and sodium hydroxide respectively and
importantly without using any template structure material/s in the process, which
is associated with reduced crystallization time that has also avoided the
calcination steps at the end. As per the invention, an aqueous solution of sodium
aluminate is mixed with aqueous solution of sodium hydroxide first and then
aqueous colloidal silica (10 - 50 wt% colloidal silica, preferably with about 30
w% colloidal silica) was added to the reaction mixture by maintaining the
Si02/Al203 molar ratio in the range of 30 -100, preferably within the range of 40
- 70, in order to obtain a homogeneous primary gel upon constant stirring the
mixed solution at ambient temperature. The resultant homogeneous primary gel
is then agitated for a period of 12 - 24 hours at ambient temperature by
continuous stirring, wherein an aged homogeneous gel resulted. The aged
homogeneous gel is then transferred to a Teflon reactor and allowed to undergo
a hydrothermal reaction with autogenously pressure level of the Teflon reactor
for a period of 18 - 24 hours and by maintaining a reaction temperature in the
range of 150°C - 180°C, wherein ZSM-5 type of zeolite molecular sieve material
resulted as-precipitates. The resultant precipitates of ZSM-5 material is filtered
off, washed with de-ionized water and the resultant washed precipitate was
dried in an oven in air for a period of 4 - 8 hours maintaining a temperature in
the range of 120 - 150°C, wherein crystalline ZSM-5 molecular sieve materials
yielded. The resultant ZSM-5 material has a specific surface area in the range of
350 - 400 m2/g and showed crystalline structure in the X-ray powder diffraction
analysis, similar to XRD pattern of JCPDS No. 44-0003.

DETAIL DESCRIPTION OF THE INVENTION
As per the invention, ZSM-5 type of zeolitic-based molecular sieve material is
synthesized first by mixing desired amounts of aqueous solution of sodium
aluminate and aqueous solution of sodium hydroxide in which a clear solution is
obtained. In this clear solution, aqueous colloidal silica (10 - 50 wt% colloidal
silica, preferably with about 30 w% colloidal silica) is added slowly under
constant stirring at ambient temperature and agitated under stirring for a period
of 12 - 24 hours in order to get a homogeneous gel of all the reactants.
The resultant gel is then transferred into a Teflon reactor in a way that internal
volume of the reactor remains empty by volume of l/4th' The Teflon reactor is
then placed in an oven for nucleation for a period of 18 - 24 hours thereby
maintaining a temperature in the range of 150 - 180°C for carrying out an
autogenously pressurized hydrothermal reaction in which a white precipitate
results at the end of the reaction.
The resultant white precipitate is filtered, washed with de-ionized water and
dried in an oven in presence of air at a temperature in the range of 120 - 150°C
for a period of 4 - 8 hours in which a dry powder is obtained.
The resultant dry powder shows a crystalline structure in the X-ray powder
diffraction analysis and a specific surface area in the range of 350 - 400m2/g in
the BET analysis. This material is called ZSM-5 type of zeolitic-based molecular
sieve material.

As per the process, the following are the steps for synthesizing ZSM-5 materials
without using any template materials with reduced crystallization time and
avoiding the calcination step in the process:
• In the first step, all the solutions, i.e., i) aqueous sodium aluminate (A), ii)
aqueous solution of sodium hydroxide (B) and iii) aqueous colloidal silica
10 - 50 wt% colloidal silica, preferably with about 30 w% colloidal silica
(C) are prepared;
• Mixing desired volumes of solutions of "A" and "B" first to get a clear
solution and then to it "C" is added to form a homogeneous primary gel
by maintaining a molar ratio of Si02/AI203 in the range of 30-100,
preferably in the range of 40-70;
• The resultant homogeneous primary gel is agitated for a period of 12 - 24
hours by continuous stirring at ambient temperature to form an aged gel;
• The aged homogeneous gel is crystallized by heating the gel at the
temperature range of 150°C - 180°C under hydrothermal pressure for the
period of 18 - 24 hours; and
• Filtering, washing with de-ionized water until pH of the filtrate becomes
~ 7 and drying in presence of air in the temperature range of 120 -
150 °C to form the desired ZSM-5 molecular sieve material.

The process could be more realized by citing more examples under variable
experimental parameters and conditions so as to get the ZSM-5 material under
different conditions.
Example 1
In this example, 1.63 g of sodium aluminate and 4 gm of sodium hydroxide is
dissolved in 135 gm de-ionized water, in which a clear solution was obtained. To
this clear solution, 100 gm aqueous colloidal silica slowly added with continuous
stirring using a mechanical stirrer, in which a primary homogeneous gel formed
that had Si02/AI203 molar ratio of 50.
The so-obtained homogeneous primary gel is then agitated by continuous stirring
at ambient temperature for a period in the range of 12 - 24 hours to get an aged
gel. The resultant aged gel was then transferred in a Teflon reactor by keeping
the reactor volume about 1/4th empty and then carrying out a hydrothermal
reaction for a period of 24 hours by placing the reactor in an oven at a
temperature of 150°C ± 5°C and by applying autogenously pressure in the
reactor.
After this hydrothermal reaction, a white colored precipitate resulted, which was
then filtered off and washed with distilled water till the filtrate reaches a pH ~ 7.
The washed precipitate was dried in an oven in air at a temperature of 120°C for
a period of 4 hours, in which a dry powder was resulted.
The dry powder is zeolitic-based ZSM-5 molecular sieve material that has the
nominal composition as [(Na20)i2 (Si02)100 (Al203)2 (H20)2278] corresponding to
the above silica and alumina molar ratio in the ZSM - 5 compounds.

The material showed a crystalline structure in the X-ray Powder Diffraction
pattern (XRD) corresponding to 44-0003. The dry powder had a specific surface
area of 390 m2/g in the BET analysis.
The batch composition can be scaled-up by following the Table 1 composition.
Table 1: Batch Composition

Example 2:
In this example, all the procedure remains the same to that of the Example 1,
except the molar ratio of Si02/AI203 is changed at 40 for the synthesis of ZSM-5
compound. The nominal composition corresponding to the above Si02/AI203
molar ratio becomes, [(Na20) io(SiO2)8o(Al2O3)2 (H20 ) 2233].
As per this example, 1.63 gm sodium aluminate and 3.2 gm sodium hydroxide
are dissolved in 145 gm de-ionized water to get a clear solution. 80 gm aqueous
colloidal silica was slowly added to this solution with continuous stirring using a

mechanical stirrer, in which the resultant primary gel is aged for a period of 24
hours at a room temperature and then heated at a temperature of 150°C in a
Teflon reactor for a period of 24 hours.
The resultant precipitate was filtered off and washed with distilled water till the
filtrate reaches pH ~ 7 and dried at 100°C for 4 hours to get the crystalline ZSM-
5 powder.
The crystallized zeolitic ZSM-5 was had a crystalline structure in XRD and a
counter specific surface area of 390 m2/g in the BET.
The batch composition can be scaled-up by following the Table 2 composition.
Table 2: Batch Composition


Example 3:
In this example, all the procedure remains the same to that of the Example 1,
except the molar ratio of Si02/Al203 is changed at 60 for the synthesis of ZSM-5
compound. The nominal composition corresponding to the above Si02/AI203
molar ratio becomes, [(Na20)14 (Si02)120 (Al2O3)2 (H20)2322],
As per this example, 1.63 gm sodium aluminate and 4.8 gm sodium hydroxide
are dissolved in 125 gm de-ionized water to get a clear solution. 80 gm aqueous
colloidal silica was slowly added to this solution with continuous stirring using a
mechanical stirrer, in which the resultant primary gel is aged for a period of 22
hours at a room temperature and then heated at a temperature of 140°C in a
Teflon reactor for a period of 20 hours.
The resultant precipitate was filtered off and washed with distilled water till the
filtrate reaches pH ~ 7 and dried at 110°C for 4 hours to get the crystalline
ZSM-5 powder.
The crystallized zeolitic ZSM-5 was had a crystalline structure in XRD and a
counter specific surface area of 380 m2/g in the BET.
The batch composition can be scaled-up by following the Table 3 composition.


Example 4:
In this example, all the procedure remains the same to that of the Example 1,
except the molar ratio of Si02/AI203 is changed at 70 for the synthesis of ZSM-5
compound. The nominal composition corresponding to the above Si02/AI203
molar ratio becomes, [(Na20)16(SiO2)140(Al203)2(H20 )2662],
As per this example, 1.63 gm sodium aluminate and 5.6 gm sodium hydroxide
are dissolved in 115 gm de-ionized water to get a clear solution. 140 gm
aqueous colloidal silica was slowly added to this solution with continuous stirring
using a mechanical stirrer, in which the resultant primary gel is aged for a period
of 20 hours at a room temperature and then heated at a temperature of 150°C
in a Teflon reactor for a period of 18 hours.
The resultant precipitate was filtered off and washed with distilled water till the
filtrate reaches pH ~ 7 and dried at 100°C for 4 hours to get the crystalline ZSM-
5 powder.

The crystallized zeolitic ZSM-5 was had a crystalline structure in XRD and a
counter specific surface area of 360 m2/g in the BET.
The batch composition can be scaled-up by following the Table 4 composition.
Table 4: Batch Composition

References:
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WE CLAIM:
1. An improved hydrothermal process for synthesis of zeolitic-based ZSM-5 type
of molecular sieve material/s without using a template structure material with
reduced crystallization time and avoiding calcination step (heat treatment) in
order to obtain a well crystalline ZSM-5 type of material, the process
comprising the steps of:
- preparing aqueous solutions of all the starting reactants i) sodium aluminate
solution (A), ii) sodium hydroxide solution (B) and iii) aqueous colloidal silica
(C),
- Mixing desired volumes of solutions of "A" and "B" first to get a clear solution
and then to it "C" is added to form a homogeneous primary gel by
maintaining a molar ratio of Si02/AI203 in the range of 30-100, preferably in
the range of 40-70;
- agitating the primary gel at ambient temperature for a predefined period of
time to obtain an aged gel;
- transferring the aged gel into a reactor for nucleation/crystallization;
- conducting a hydrothermal reaction by keeping the reactor in an oven for a
selected period of time by maintaining a pre-determined temperature and by
applying autogenously pressure to the reactor, to generate a white
precipitate;

- filtering the resultant white precipitate and washing the precipitate by de-
ionized water; and
- drying the washed precipitates in an oven in air at a pre-determined
temperature in order to obtain the zeolitic-based ZSM-5 type of molecular
sieve material.
2. The process as claimed in Claim 1, wherein said aqueous solutions of the
starting reactants are prepared by dissolving the required raw materials in
de-ionized/distilled water respectively having Si02/AI203 ratio in the range
of 30 -100, preferably in the range of 40-70.
3. The process as claimed in claim 1, wherein a homogeneous primary gel
was obtained by mixing the aqueous solutions of sodium aluminate and
sodium hydroxide first in which a clear solution was obtained and then
aqueous colloidal silica was added to the clear solution by maintaining
SiO2/Al2O3 ratio in the range of 30 - 100, preferably in the range of 40 -
70 in the solution under constant stirring using a magnetic stirrer
4. The process as claimed in claim 1, wherein the aged homogeneous gel is
obtained by agitating the homogeneous primary gel under constant
stirring using a magnetic stirrer for a period of 12 - 24 hours.
5. The process as claimed in claim 1, wherein the hydrothermal reaction is
carried out by transferring the aged "gel into a Teflon reactor maintaining
the internal volume empty by 1/4th.

6. The process as claimed in claim 1, wherein said hydrothermal reaction is
carried out by keeping the reactor in an oven for a period of 18 - 24 hours
and by maintaining a temperature in the range of 120 - 180°C and further
by applying the pressure autogenously to the Teflon reactor.
7. The process as claimed in claim 1, wherein the dried precipitate is
obtained by filtering the white precipitate and washing with de-
ionized/distilled water until pH of the filtrate becomes ~7.
8. The process as claimed in claim 1, wherein a dried crystalline zeolitic-
based ZSM-5 type of molecular sieve material is obtained by drying the
washed precipitate in an oven at a temperature range of 120 - 150°C for
a period of 4 - 8 hours in air.
9. The process as claimed in claim 1, wherein the produced zeolitic-based
crystalline ZSM-5 type of molecular sieve material, showed similar
crystalline structure in the X-ray Powder Diffraction analysis (XRD) to that
of JCPDS No. 44-0003 and having specific surface area in the range of
350-400 m2/g .

ABSTRACT

The invention describes an improved hydrothermal process for synthesizing
crystalline ZSM-5 material, importantly without using any organic template
material in the process and also avoiding any calcination reaction (heat
treatment) in the process besides achieving lower duration of chemical reaction.