DESC:FIELD
The present disclosure relates to a supported metallocene catalyst and a process for preparation thereof.
DEFINITION
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
The term “Phillips type catalyst” refers to a heterogeneous catalyst consisting of a chromium oxide supported on silica gel.
The term “Metallocene catalyst” refers to organometallic coordination compounds in which one or two cyclopentadienyl rings or substituted cyclopentadienyl rings are bonded to a central transition metal atom.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Polyolefins are commercially produced using free-radical initiators, Phillips type catalysts, Ziegler-Natta catalysts and metallocene catalysts. Metallocene catalysts are organometallic coordination compounds in which one or two cyclopentadienyl rings or substituted cyclopentadienyl rings are bonded to a central transition metal atom. Metallocene complexes have revolutionized the world of polyolefins and offer various process advantages over conventional thermoplastics and elastomers. Owing to their homogeneous nature, every molecule has an active site and thus metallocene catalysts can be many more times as active as established Ziegler–Natta catalysts. Conventionally, the metallocene catalysts are supported on solid carriers for maximum benefit to the polyolefin industry to reduce the amount of the catalyst required for the polymerization and also to improve the morphology of the resulting polymer product.
However, known supported metallocene catalysts has lower resistance towards moisture and air. Further, these metallocene catalysts cannot be applied in the conventional gas phase or slurry reactors because they cause “fouling” in the reactors.
Therefore, there is felt a need to provide a metallocene catalyst that overcomes the drawbacks mentioned herein above.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a supported metallocene catalyst.
Another object of the present disclosure is to provide a supported metallocene catalyst, which is capable of reducing fouling in the reactor.
Still another object of the present disclosure is to provide a supported metallocene catalyst, which is resistant towards moisture and air.
Yet another object of the present disclosure is to provide a process for preparation of a supported metallocene catalyst.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure relates to a supported metallocene catalyst. The catalyst comprises an inorganic oxide support, an organo-aluminium compound, a metallocene complex and an antistatic agent, wherein the amount of aluminium in the organo-aluminium compound is in the range of 6 to 18 mmol per gram of the inorganic oxide support; and the amount of the metal in the metallocene complex is in the range of 0.1 to 0.3 mmol per gram of the inorganic oxide support.
The present disclosure further relates to a process for preparation of a supported metallocene catalyst. Initially, a mixture of an inorganic oxide support and organo-aluminium compound in a first fluid medium is heated at a temperature in the range of 80 to 100 °C for a time period in the range of 1 to 4 hours under stirring to obtain a first slurry. The first slurry is dried at a temperature in the range of 80 to 100 °C under nitrogen flow to obtain a solid support. Separately, a metallocene complex is dissolved in a second fluid medium to obtain a metallocene solution. The so obtained metallocene solution is added to the solid support in a dropwise manner at a temperature in the range of 20 to 40 °C, followed by stirring for a time period in the range of 0.5 to 3 hours to obtain a second slurry. To the second slurry, an anti-static agent is added, followed by stirring for a time period in the range of 10 to 50 min to obtain a third slurry. The third slurry is dried to a free flowing powder at a temperature in the range of 50 to 90 °C under nitrogen flow to obtain the supported metallocene catalyst.
DETAILED DESCRIPTION
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Metallocene complexes are actively used for the preparation of polyolefins. Owing to their homogeneous nature, every molecule has an active site and thus metallocene catalysts can be many more times as active as established Ziegler–Natta catalysts. However, these metallocene catalysts are associated with drawbacks such as fouling of the reactors. Conventionally, the metallocene catalysts are supported on the solid carriers for maximum benefit to the polyolefin industry. However, the conventional supported metallocene catalysts has lower resistance towards moisture and air.
To overcome the drawbacks of the conventional catalysts, the present disclosure provides a supported metallocene catalyst, which is resistant towards moisture and air; and which is capable of reducing fouling in the reactor.
In an aspect, the present disclosure provides a supported metallocene catalyst comprising an inorganic oxide support, an organo-aluminium compound, a metallocene complex and an antistatic agent.
The supported metallocene catalyst of the present disclosure is characterized in that the amount of aluminium in the organo-aluminium compound is in the range of 6 to 18 mmol per gram of the inorganic oxide support; and the amount of the metal in the metallocene complex is in the range of 0.1 to 0.3 mmol per gram of the inorganic oxide support.
The inorganic oxide support is selected from silica, alumina and zeolite. In an exemplary embodiment, the inorganic oxide support is silica, preferably dehydroxylated silica.
The organo-aluminium compound is selected from methyl aluminoxane and ethyl aluminoxane. In an exemplary embodiment, the organo-aluminium compound is methyl aluminoxane.
The metallocene complex is selected from zircocene, titanocene, and hafnocene. In an exemplary embodiment, the metallocene complex is zircocene.
The antistatic agent is selected from alkyl benzene sulphonic acid, salts of alkyl benzene sulphonic acid, fatty acid and ester of fatty acid. Typically, the antistatic agent is at least one selected from aluminium distearate, dodecyl benzenesulfonic acid and combination thereof. In an exemplary embodiment, the antistatic agent is aluminium distearate. In another exemplary embodiment, the antistatic agent is dodecyl benzenesulfonic acid. In still another exemplary embodiment, the antistatic agent is a combination of aluminium distearate and dodecyl benzenesulfonic acid.
In another aspect, the present disclosure provides a process for preparation of the supported metallocene catalyst. The process of the present disclosure is described in detail herein below:
In the first step, a mixture of an inorganic oxide support and organo-aluminium compound in a first fluid medium is heated at a temperature in the range of 80 to 100 °C for a time period in the range of 1 to 4 hours under stirring to obtain a first slurry. The so obtained first slurry is dried at a temperature in the range of 80 to 100 °C under nitrogen flow to obtain a solid support.
The fixation of organo-aluminium compound on the silica support at high temperature (80-100 °C) resulted in homogenous distribution of aluminum and/ or aluminium compound on the inorganic oxide support.
Separately, a metallocene complex is dissolved in a second fluid medium to obtain a metallocene solution. The metallocene solution is added to the solid support in a dropwise manner at a temperature in the range of 20 to 40 °C, followed by stirring for a time period in the range of 0.5 to 3 hours to obtain a second slurry.
To the second slurry, an antistatic agent is added under stirring, and stirring is continued for a time period in the range of 10 to 50 min to obtain a third slurry.
Preferably, the antistatic agent is added in the solution form. Typically, antistatic agent is dissolved in toluene to form a solution.
The third slurry is dried to a free flowing powder at a temperature in the range of 50 to 90 °C under nitrogen flow to obtain the supported metallocene catalyst.

The first fluid medium and the second fluid medium is independently selected from toluene and dichloromethane. In an exemplary embodiment, the first fluid medium and the second fluid medium is same, which is toluene.
The mole ratio of aluminium in organo-aluminium compound to the metal in the metallocene complex is in the range of 20: 1 to 80: 1. In an exemplary embodiment, the ratio of aluminium of organo-aluminium compound to the metal of the metallocene complex is 40: 1.
The supported metallocene catalyst of the present disclosure is stable towards moisture and air. Further, the incorporation of antistatic agent in accordance with the present disclosure obviates lump formation and layer formation, thereby avoiding fouling of the reactors.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
EXPERIMENTAL DETAILS
Experiment 1: Preparation of the metallocene catalyst
General procedure:
To a three litre glass reactor fitted with Teflon stirrer and condenser, anhydrous toluene was added, followed by addition of 10 wt% solution of methylaluminoxane (MAO) at 30 °C and silica 2408D (US, Grace Company) to obtain a mixture. The mixture was heated at 90 °C for 3 hours to obtain a first slurry. The so obtained first slurry was dried at the same temperature under flow of nitrogen to obtain solid support.
In a separate round bottom flask (bis(1-butyl-3-methyl-cyclopentadienyl)zirconium dichloride) was dissolved anhydrous toluene to obtain a metallocene solution. The metallocene solution was transferred to a dropping funnel and added slowly into the dried solid support at 30 °C and stirred at 30 °C for 60 minutes to obtain a second slurry.
A solution of the antistatic agent in toluene is added to the second slurry and the resultant slurry is stirred for a time period in the range of 10 to 40 min to obtain a third slurry.
The so obtained third slurry was dried at 70 °C under flow of nitrogen to obtain the supported metallocene catalyst of the present disclosure.
Examples 1-5: Preparation of the supported metallocene catalyst in accordance with the present disclosure
Examples 1-5 were carried out by following the general procedure described herein above by varying the amounts of reactants.
Examples 6-11: Preparation of the supported metallocene catalyst (Comparative examples)
Examples 6-11 were carried out by following the general procedure described herein above, except the addition of an antistatic agent and amounts of reactants.
The summary of amounts of the reactants in example 1-11 is given below in table 1:
Table 1: Summary of amounts of the reactants in examples 1-11
Ex. No. Silica
gm Toluene
ml Methyl aluminoxane
(10 wt% sol)
ml Bis(1-butyl-3-methyl-cyclopentadienyl) zirconium dichloride
gm Statsafe 6000
mg Aluminium distearate
mg
1 2 8 12 0.14 - 50
2 2 8 12 0.14 - 100
3 2 8 12 0.14 - 150
4 4 100 30 0.28 180 -
5 4 100 16 0.28 200 120
6 100 400 750 7.0 - -
7 4 100 30 0.3 - -
8 4 40 40 0.45 - -
9 4 40 30 0.3 - -
10 100 400 600 7.0 - -
11
100 400 400 3.0 - -
Experiment 2: Polymerization performance study of the metallocene catalyst
The polymerization was conducted in a bench scale gas phase stirred seed bed reactor. The seed bed was made up of linear low density polyethylene pellets. Tri isobutyl aluminium (TIBAL) was used as a scavenger. The ethylene feed was purified by passing through adsorbent beds before injection into the reactor. 1-hexene was used as co-monomer.
The solid metallocene catalysts prepared in examples 1-11 were injected into reactor using nitrogen as carrier.
The polymerization was carried out at 80 °C temperature and 14.0 bar pressure (partial pressure of ethylene-10 bar).
The results obtained are summarized in Tables 2 and 3 given below.

Table-2: Catalyst composition of examples 1-11 and polymerization performance study

Catalyst MAO
loading
(Al mmol/g silica) Zircocene loading
(Zr mmol/g silica) Zr wt% Al wt% Aluminium distearate loading (mg) Statsafe 6000 loading
(mg) Productivity (g.PE/g.cat) Fouling indicator
Example- 1 10.3 0.162 1.0 14.5 50 - 315 0
Example- 2 10.3 0.162 1.0 14.5 100 - 580 0
Example- 3 10.3 0.162 1.0 14.5 150 70 0
Example- 4 13.1 0.169 1.0 17 - 180 900 0
(20% lumps and
No layer formation)
Example- 5 6.8 0.16 0.9 12.5 120 200 530 0
Example- 6 12.9 0.162 0.91 17 - - 850 1
Example- 7 12.9 0.175 0.97 19 - - 700 1
(30% lumps and Layer formation)
Example- 8 17.2 0.25 0.95 18.4 - - 720 1
Example- 9 12.9 0.17 0.8 17 - - 650 1
Example- 10 10.3 0.162 1.0 14.5 - - 800 1
Example- 11
6.0 0.07 0.45 12.0 - - 470 1
*The Al wt% and Zr wt% in the final catalysts were determined from ICP-OES method.
Fouling indicator which is a measure of lumps, aggregates in polymer or layer formation in wall of reactor is provided in the Table 1. The higher the value, the greater the fouling observed. A Fouling indicator of zero indicate no layer formation on walls of reactor and no lump formation. A Fouling indicator of one indicate layer formation on walls of reactor and lumps formation.
From table-2, it is evident that the incorporation of antistatic agent obviates lump formation and layer formation, thereby avoiding fouling of the reactor.

Table-3: Characterization of polymer resin
Catalyst MFI
(@ 2.16 kg, 190 °C) Molecular weight
(Mw) MWD Melting Point (°C) Hexene wt%
Example-1 0.2 1.8 × 105 2.6 122 -
Example-2 0.2 1.6 × 105 2.5 123 -
Example-3 0.3 1.6 × 105 2.7 121 -
Example-6 0.3 1.7 × 105 2.7 122 7.0
Example-8 0.21 1.7 × 105 2.7 122 5.5
Example-9 0.24 1.8 × 105 2.9 125 6.0
Example-10 0.2 1.9 × 105 2.8 124 5.0
Example-11
0.3 1.6 × 105 2.6 6.0

From table-3, it is evident that the supported metallocene catalyst obtained by the process of the present disclosure is suitable for production of high and linear low density polyethylene with narrow molecular weight distribution in the range of 2.5 to 2.7.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing supported metallocene catalyst:
• having a high loading of metallocene and aluminoxane;
• which obviates fouling of the reactors; and
• which is capable of providing polymer with narrow molecular weight distribution.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM:
1. A supported metallocene catalyst comprising:
a. an inorganic oxide support;
b. an organo-aluminium compound;
c. a metallocene complex; and
d. an antistatic agent,
wherein the amount of aluminum in the organo-aluminium compound is in the range of 6 to 18 mmol per gram of the inorganic oxide support; and
wherein the amount of the metal in the metallocene complex is in the range of 0.1 to 0.3 mmol of per gram of the inorganic oxide support.
2. The catalyst as claimed in claim 1, wherein the inorganic oxide support is selected from silica, alumina and zeolite.
3. The catalyst as claimed in claim 1, wherein the organo-aluminium compound is selected from methyl aluminoxane and ethyl aluminoxane.
4. The catalyst as claimed in claim 1, wherein the metallocene complex is selected from zircocene, titanocene, and hafnocene.
5. The catalyst as claimed in claim 1, wherein the antistatic agent is at least ome selected from alkyl benzene sulphonic acid, salts of alkyl benzene sulphonic acid, fatty acid and ester of fatty acid.
6. The catalyst as claimed in claim 5, wherein the antistatic agent is selected from aluminium distearate, dodecyl benzenesulfonic acid and combination thereof.
7. A process for preparation of a supported metallocene catalyst, the process comprising the following steps:
a) heating a mixture of an inorganic oxide support and an organo-aluminium compound in a first fluid medium at a temperature in the range of 80 to 100 °C for a time period in the range of 1 to 4 hours under stirring to obtain a first slurry;
b) drying the first slurry at a temperature in the range of 80 to 100 °C under nitrogen flow to obtain a solid support;
c) separately, dissolving a metallocene complex in a second fluid medium to obtain a metallocene solution;
d) adding the metallocene solution to the support in a dropwise manner at a temperature in the range of 20 to 40 °C, followed by stirring for a time period in the range of 0.5 to 3 hours to obtain a second slurry;
e) adding an antistatic agent to the second slurry and stirring for a time period in the range of 10 to 50 min to obtain a third slurry; and
f) drying the third slurry to a free flowing powder at a temperature in the range of 50 to 90 °C under nitrogen flow to obtain the supported metallocene catalyst,
wherein the mole ratio of aluminium in organo-aluminium compound to the metal in the metallocene complex is in the range of 20: 1 to 80: 1.
8. The process as claimed in claim 7, wherein the antistatic agent is added in the solution form.
9. The process as claimed in claim 7, wherein the first fluid medium, and the second fluid medium is independently selected from toluene and dichloromethane.
Dated this 3rd Day of October, 2019

_______________________________
MOHAN DEWAN, IN/PA - 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI