Description:FIELD OF THE INVENTION
The present invention relates to the field of catalyst used in refineries. More specifically, the present invention relates to a process for the preparation of a protruded ZSM-5 zeolite having enhanced mesopores, nano-sized crystal and reduced internal diffusion limitation and a protruded ZSM-5 zeolite for catalytic cracking reaction.

BACKGROUND OF THE INVENTION
ZSM-5 zeolite mostly consists of micropores, and pore size is 5.4 angstrom. Microporous surface area of conventional ZSM-5 zeolite is in range of 300-350 m2/g and external surface area is in range of 100-150 m2/g. It is known that zeolite crystal size can impact the mass transport properties of zeolites for catalytic reaction. In the case of zeolite catalysis, it is well established that smaller crystal size can improve catalyst lifetime and can also influence product selectivity. Smaller dimensions lead to a reduction in the average residence time of reactants and products within the pores of the zeolite. This reduction in internal diffusion path length, for example, reduces the rate of coke formation (i.e. carbon deposits that block pores), thereby increasing the catalyst lifetime and potentially altering the number of secondary reactions taking place in the pores, which impacts selectivity.

Available methods to reduce diffusion limitations in ZSM-5 zeolite include the preparation of nano-sized (with sizes 10-100 nm) zeolites, 2-dimensional zeolites (with sizes of 2-10 nm) and mesoporous ZSM-5 zeolite. Achieving such small sizes and mesopores is often nontrivial and can involve multi-step processes that often involve the use of organic structure-directing agents.

CN107640777A discloses a seed-induced method for preparing large/mesoporous zeolite molecular sieves, to overcome the problem of large diffusion resistance in the pores of existing microporous zeolite molecular sieve.

CN114804141A discloses the preparation method for nanocluster mesoporous ZSM-5 molecular sieve wherein the steps include mixing the template agent (TPAOH), deionized water, silica source, alkali metal hydroxide in water, alumina source (sodium aluminate) and uniformly stirring at room temperature; forming a precursor solution; crystallizing, filtering, washing, drying and roasting. The reference also discloses decreasing the diffusion resistance to increase the yield of the target product.

NL8603170A discloses a method for preparation of zeolite of the ZSM-5 type from a reaction mixture containing a source of SiO2, a source of Al2O3, a source of alkali metal, ethanol, water, and previously synthesised ZSM-5 zeolite crystals. This process takes place in the presence of extremely small amounts of pre-synthesized ZSM-5 type zeolite inoculum.

CN106829998A discloses a method for preparing zeolite molecular sieves wherein steps include mixing sodium aluminate in water and adjusting the pH with sodium hydroxide, adding the sodium aluminate solution and the silica sol to the stirred water to obtain the mixed material, and then adding a ZSM-5 seed crystal to the mixed material, sealing and heating to 70 to 90? for 10 to 14 hours, and then raising the temperature to 170 to 190? for 20 to 30 hours to obtain a molecular sieve slurry, which is filtered, washed and dried to obtain powdered zeolite molecular sieves.

US8840864B2 discloses a method for preparing ZSM-5 zeolite wherein steps include directly adding prepared nanocrystalline ZSM-5 seed to a stock solution containing glass as a silica source, an alumina source which could be sodium aluminate, a neutralizer and water to form a reaction mixture; and maintaining the reaction mixture at 150-200 ? to crystallize the reaction mixture a molecular sieve slurry, which is then filtered, washed, and dried to obtain powdered zeolite molecular sieves.

However, the solution to overcome the problem of diffusion resistance in the pores of microporous zeolite molecular sieve has been addressed in few of the prior art such as by reducing the crystal size of ZSM-5 zeolite to less than 100 nm. But synthesis of nano-sized ZSM-5 zeolite suffer from low yield. All of these factors pose problems for mass production of zeolites.
OBJECTIVES OF THE INVENTION
The main objective of the present invention is to provide a process for the preparation of a protruded ZSM-5 zeolite having enhanced mesopores, reduced crystal size and reduced internal diffusion limitation.

Another objective of the present invention is to utilize the protruded ZSM-5 zeolite in catalytic cracking reactions.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.

The present invention provides a process for preparation of a protruded ZSM-5 zeolite using two stage crystallization approach, wherein the process comprises steps of preparing a first reaction mixture by mixing a silica source, an alumina source, sodium hydroxide, a template, an alcohol and water and crystallizing first reaction mixture; filtering the first reaction mixture after crystallization followed by washing to obtain a ZSM-5 zeolite nucleating agent; preparing a second reaction mixture by mixing the silica source, the alumina source, the template, and water; adding the ZSM-5 zeolite nucleating agent to the second reaction mixture and crystallizing the second reaction mixture; and filtering the second reaction mixture after crystallization, exchanging with ammonium sulphate solution and calcining at 550 ? for 5 hour to obtain the protruded ZSM-5 zeolite.

The first reaction mixture crystallizes at 100 to 200 ? for 20 to 50 hours and second reaction mixture crystallizes at 70 to110 ? for 12 to 50 hours. Preferably, the first reaction mixture crystallizes at 150 to 180 ? for 40 to 50 hours and second reaction mixture crystallizes at 90 to 105 ? for 12 to 24 hours.

The template is selected from a group comprising tetrapropyl ammonium hydroxide, tetrapropyl ammonium bromide, tetrabutyl ammonium hydroxide and tetrabutyl ammonium bromide. The alcohol used in first reaction mixture is selected from a group consisting of ethanol, propanol, butanol and pentanol. The silica source is colloidal silica, and the alumina source is sodium aluminate.

The ZSM-5 zeolite nucleating agent is obtained as a wet cake having a water content in a range of 20 to 90%, preferably in a range of 30 to 60%. The second reaction mixture and the ZSM-5 nucleating agent has a weight ratio in a range of 1:1 to 25:1, preferably in a range of 5:1 to 10:1.

The protruded ZSM-5 zeolite consists of protrusions/crystals of size 5 to 20 nm and mesopore to micropore surface area ratio in a range of 0.6 to 1.

BRIEF DESCRIPTION OF THE DRAWINGS:
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 depicts SEM image of protruded ZSM-5 zeolite.

DETAILED DESCRIPTION OF THE INVENTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated process, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.

The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The term “some” as used herein is defined as “none, or one, or more than one, or all”. Accordingly, the terms “none”, “one”, “more than one”, “more than one, but not all” or “all” would all fall under the definition of “some”. The term “some embodiments” may refer to no embodiments or to one embodiment or to several embodiments or to all embodiments. Accordingly, the term “some embodiments” is defined as meaning “no embodiment, or one embodiment, or more than one embodiment, or all embodiments”.

More specifically, any terms used herein such as but not limited to “includes”, “comprises”, “has”, “consists” and grammatical variants thereof is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. The specification will be understood to also include embodiments which have the transitional phrase “consisting of” or “consisting essentially of” in place of the transitional phrase “comprising”. The transitional phrase “consisting of” excludes any element, step, or ingredient not specified in the claim, except for impurities associated therewith. The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.

Whether or not a certain feature or element was limited to being used only once, either way it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element”. Furthermore, the use of the terms “one or more” or “at least one” feature or element do NOT preclude there being none of that feature or element, unless otherwise specified by limiting language such as “there NEEDS to be one or more” or “one or more element is REQUIRED”.

Use of the phrases and/or terms such as but not limited to “a first embodiment”, “a further embodiment”, “an alternate embodiment”, “one embodiment”, “an embodiment”, “multiple embodiments”, “some embodiments”, “other embodiments”, “further embodiment”, “furthermore embodiment”, “additional embodiment” or variants thereof do NOT necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

To overcome the problem of diffusion resistance in the pores of existing microporous ZSM-5 zeolite, the present invention discloses a method for preparing ZSM-5 zeolite with small protrudes, these protrudes reduces diffusion path length and hence reduces diffusion resistance which in turn reduces secondary reaction such as coke formation in hydrocarbon cracking reactions.

For reducing crystal size, increasing mesopores, increasing pore volume and for reducing internal diffusion limitation, protrusions are grown on ZSM-5 zeolite crystals in two stage crystallization. These protrusions helps in reducing internal diffusion limitation which in turn reduces secondary reactions such as coke formation in light cracked naphtha cracking.

The present invention provides a process for preparation of protruded ZSM-5 zeolite using two stage crystallization approach, wherein the process comprises steps of:
i. preparing a first reaction mixture by mixing a silica source, an alumina source, sodium hydroxide, a template, an alcohol and water and crystallizing the first reaction mixture;
ii. filtering the first reaction mixture after crystallization followed by washing to obtain a ZSM-5 zeolite nucleating agent;
iii. preparing a second reaction mixture by mixing the silica source, the alumina source, the template, and water;
iv. adding the ZSM-5 zeolite nucleating agent to the second reaction mixture and crystallizing the second reaction mixture; and
v. filtering the second reaction mixture after crystallization, exchanging with ammonium sulphate solution and calcining at 550 ? for 5 hour to obtain the protruded ZSM-5 zeolite.

In an embodiment of the present invention, the first reaction mixture crystallizes at 100 to 200 ? for 20 to 50 hours and second reaction mixture crystallizes at 70 to110 ? for 12 to 50 hours.

In a preferred embodiment, the first reaction mixture crystallizes at 150 to180 ? for 40 to 50 hours and second reaction mixture crystallizes at 90 to 105 ? for 12 to 24 hours.

The template is selected from a group comprising tetrapropyl ammonium hydroxide, tetrapropyl ammonium bromide, tetrabutyl ammonium hydroxide and tetrabutyl ammonium bromide.

The alcohol used in first reaction mixture is selected from a group consisting of ethanol, propanol, butanol and pentanol. The silica source is colloidal silica. The alumina source is sodium aluminate.

The ZSM-5 zeolite nucleating agent is obtained as a wet cake. In an embodiment, the wet cake has a water content in a range of 20 to 90%.

In a preferred embodiment, the wet cake has the water content in a range of 30 to 60%.

In an embodiment of the present embodiment, the second reaction mixture and the ZSM-5 nucleating agent has a weight ratio in a range of 1:1 to 25:1.

In a preferred embodiment, the second reaction mixture and ZSM-5 nucleating agent has a weight ratio in a range of 5:1 to 10:1.

The protruded ZSM-5 zeolite consists of protrusions/crystals of size 5 to 20 nm.

The protruded ZSM-5 zeolite consists of mesopore to micropore surface area ratio in a range of 0.6 to 1.

EXAMPLES:
The present disclosure with reference to the accompanying examples describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.

Example 1: Preparation of protruded ZSM-5 zeolite
1.2 g of sodium aluminate was added in 18 g of water to prepare sodium aluminate solution. 0.47 g of sodium hydroxide is added in 12 g of water to prepare sodium hydroxide solution. Above prepared sodium aluminate solution, sodium hydroxide solution and 75 g of tetrapropyl ammonium hydroxide are mixed together and solution was stirred for 30 minutes. In above prepared solution, 45.7 g of ethanol was added and then 37 g of colloidal silica was added and prepared solution is stirred for 1 hour. The above prepared solution was transferred in autoclave and crystallized at 170 ? for 40 h. After crystallization, the obtained wet cake was filtered and washed with de-mineralized water for 3 times to obtain a ZSM-5 zeolite nucleating agent.

1.5 g of sodium aluminate was added in 80 g of water to obtain sodium aluminate solution. In sodium aluminate solution, 22.4 g of tetra propyl ammonium hydroxide was added and solution was stirred for 30 minutes. Then 52 g of colloidal silica was added in above solution and solution was stirred for 1 hour. In this solution, ZSM-5 zeolite nucleating agent (as obtained hereinabove) was added and final solution was stirred for 1 hour. This solution was transferred in autoclave and crystallization was carried out at 100 oC for 48 hours. After crystallization, obtained zeolite was filtered, washed with water, and dried. Dried zeolite is 3 times ammonium exchanged with 5 % ammonium sulphate solution. After ammonia exchange, protruded ZSM-5 zeolite was calcined in muffle furnace at 550 ? for 5 hours to obtain H form of protruded ZSM-5 zeolite. Physical properties of ZSM-5 zeolite are mentioned in table 1.

Table 1: Physical properties of ZSM-5 zeolite

Properties Example 1 Comparative example 1
Total Surface area, m2/g 507 425
Microporous surface area, m2/g 302 295
External surface area, m2/g 205 130
Pore Volume, cc/g 0.45 0.19

Example 2: Hydrothermal deactivation of protruded ZSM-5 zeolite
For catalytic cracking experiment, the protruded ZSM-5 zeolite as obtained from example 1 was hydrothermally deactivated in presence of 100% steam at 815 ? for 10 hours.

Comparative example 1: Preparation of ZSM-5 zeolite
2 g of sodium aluminate, 0.6 g of NaOH and 90 g of water was mixed together, 220 g of tetrapropyl ammonium hydroxide solution and 62 g of colloidal silica was added, and solution was stirred for 1 hour. This solution was transferred in autoclave and crystallization was carried out at 100 ? for 24 hours. After crystallization, obtained zeolite was filtered, washed and dried at 120 ? for 5 hours. Dried zeolite is 3 times ammonium exchanged with 5% ammonium sulphate solution. After ammonia exchange, ZSM-5 zeolite was calcined in muffle furnace at 550 ? for 5 hours to obtain H form of ZSM-5 zeolite. Physical properties of ZSM-5 zeolite obtained are mentioned in table 1.

Comparative example 2: Hydrothermal deactivation of ZSM-5 zeolite
For catalytic cracking experiment, the ZSM-5 zeolite obtained in comparative example 1 was hydrothermally deactivated in presence of 100 % steam at 815 ? for 10 hours.

Catalytic Cracking performance evaluation:
Catalytic cracking evaluation of ZSM-5 zeolites obtained from example 2 and comparative example 2 was carried out in fixed bed reactor at reaction temperature of 600 ?, cat/oil of 8 with light cracked naphtha feedstock. Results are given in table 2.

Experiments & Results

Table 2: Catalytic Cracking evaluation of ZSM-5 zeolites
Catalyst Name Example 2 Comparative example 2
Feed Name Light cracked naphtha Light cracked naphtha
Reactor Temperature (ºC) 600 600
Cat/oil 8 8
Yields (wt %)
Coke 4.73 6.70
Hydrogen 1.42 0.80
Methane 5.46 4.55
Ethane 0.39 0.20
Ethylene 9.54 8.45
Propylene 22.48 20.75
Propane 1.40 1.03
i-Butane 3.34 5.93
n-Butane 2.44 4.80
C4 Olefins 9.93 8.34
Unconverted LCN 38.87 38.45

Protruded ZSM-5 zeolite gives low coke and high propylene, ethylene and C4 olefins.

ADVANTAGES OF THE INVENTION:
The protruded ZSM-5 zeolite is used for catalytic cracking of light cracked naphtha and straight run naphtha. Due to reduced crystal size of protruded ZSM-5 zeolite, light olefin yield has increased by 3 to 4 wt%.
, Claims:1. A process for preparation of a protruded ZSM-5 zeolite using two stage crystallization approach, wherein the process comprises steps of:
i. preparing a first reaction mixture by mixing a silica source, an alumina source, sodium hydroxide, a template, an alcohol and water and crystallizing the first reaction mixture;
ii. filtering the first reaction mixture after crystallization followed by washing to obtain a ZSM-5 zeolite nucleating agent;
iii. preparing a second reaction mixture by mixing the silica source, the alumina source, the template, and water;
iv. adding the ZSM-5 zeolite nucleating agent to the second reaction mixture and crystallizing the second reaction mixture; and
v. filtering the second reaction mixture after crystallization, exchanging with ammonium sulphate solution and calcining at 550 ? for 5 hour to obtain the protruded ZSM-5 zeolite.

2. The process as claimed in claim 1, wherein the first reaction mixture crystallizes at 100 to 200 ? for 20 to 50 hours and second reaction mixture crystallizes at 70 to110 ? for 12 to 50 hours.

3. The process as claimed in claim 2, wherein the first reaction mixture crystallizes at 150 to180 ? for 40 to 50 hours and second reaction mixture crystallizes at 90 to 105 ? for 12 to 24 hours.

4. The process as claimed in claim 1, wherein the template is selected from a group comprising tetrapropyl ammonium hydroxide, tetrapropyl ammonium bromide, tetrabutyl ammonium hydroxide and tetrabutyl ammonium bromide.

5. The process as claimed in claim 1, wherein the alcohol used in first reaction mixture is selected from a group comprising ethanol, propanol, butanol and pentanol; the silica source is colloidal silica; and the alumina source is sodium aluminate.

6. The process as claimed in claim 1, wherein the ZSM-5 zeolite nucleating agent is obtained as a wet cake; wherein the wet cake has a water content in a range of 20 to 90 %.

7. The process as claimed in claim 6, wherein the wet cake has the water content in a range of 30 to 60 %.

8. The process as claimed in claim 1, wherein the second reaction mixture and the ZSM-5 nucleating agent has a weight ratio in a range of 1:1 to 25:1.

9. The process as claimed in claim 8, wherein the second reaction mixture and ZSM-5 nucleating agent has a weight ratio in a range of 5:1 to 10:1.

10. The process as claimed in claim 1, wherein the protruded ZSM-5 zeolite consists of protrusions of size 5 to 20 nm.

11. The process as claimed in claim 1, wherein the protruded ZSM-5 zeolite consists of a mesopore to micropore surface area ratio in a range of 0.6 to 1.