Claims:1. A process for preparing a bimetallic heterogeneous catalyst system, said process comprising the following steps:
a. forming a first catalyst component by depositing soluble magnesium chloride onto the surface of a support selected from the group consisting of silica, calcined silica, zeolite, polyethylene resin and combinations thereof; and
b. adding a second catalyst component, selected from the group consisting of triethyl aluminium (TEAL), diisobutylaluminum (TIBAL), diethylaluminium chloride (DEAC), tri-n-octyl aluminum (TnOAL), tri – hexyl aluminum (TnHAL) and isobutylaluminum dichloride (IBADIC) to the first catalyst component, to obtain the bimetallic heterogeneous catalyst system.

2. The process as claimed in claim 1, wherein the first catalyst component is formed by:
a. treating magnesium chloride with at least two metal halides in a fluid medium in the temperature of 50 °C to 80 °C for a time period ranging from 30 minutes to 120 minutes to obtain a reaction mixture,
b. adding a support to said reaction mixture and heating said reaction mixture containing said support to a temperature in the range of 50 °C to 80 °C for a time period ranging from 30 minutes to 120 minutes to obtain a first reaction mass;
c. adding an alkylating agent to said first reaction mass and heating said first reaction mass containing said alkylating agent to a temperature in the range of 80 °C to 110 °C for a time period ranging from 60 minutes to 180 minutes to obtain a second reaction mass; and
d. cooling said second reaction mass to a temperature in the range of 25 °C to 35 °C and further allowing the second reaction mass to settle, to obtain a precipitate of the first catalyst component.

3. The process as claimed in claim 2 wherein the step (a) comprises a first metal halide and a second metal halide, and both the metal halides are heated together with the magnesium chloride in said step.

4. The process as claimed in claim 2 wherein the step (a) includes a first metal halide and a second metal halide, and step (a) is performed in two sub-steps, wherein in a first sub-step, the first metal halide is heated with magnesium chloride to obtain a pre-reaction mixture and in a second sub-step, the second metal halide is added to the pre-reaction mixture and heated therewith to obtain the reaction mixture.

5. The process as claimed in claim 2, wherein said metal halide is at least one selected from the group consisting of halides of and stereorigid complexes of titanium, hafnium, zirconium, iron, nickel, cobalt and palladium; and said fluid medium is tetrahydrofuran.

6. The process as claimed in claim 2, wherein said support is selected from the group consisting of silica, calcined silica, zeolite, polyethylene resin and combinations thereof.

7. The process as claimed in claim 2, wherein the process step (a) optionally comprises heating in the presence of an inorganic modifier, such as tetraethyl orthosilicate.

8. The process as claimed in claim 2, wherein said alkylating agent is at least one selected from the group consisting of diethyl aluminum chloride, isobutyl aluminum dichloride (IBADIC), triethyl aluminum, triisobutyl aluminum, trioctyl aluminum and boron containing alkylating agents, and is diluted in a fluid medium, such as decane, before adding to the first reaction mass.

9. The process as claimed in claim 2, wherein said precipitate is further subjected to washing and drying to obtain the dried first component of the bimetallic heterogeneous catalyst system.

10. A process for polymerizing a-olefins and dienes; said process comprising subjecting olefins and dienes to at least one of slurry, solution and gas phase polymerization, in the presence of a bimetallic heterogeneous catalyst system, as claimed in claim 1. , Description:
FIELD
The present disclosure relates to a process for preparing a bimetallic heterogeneous catalyst system.
DEFINITIONS
As used in the present disclosure, the following words and phrases are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.
Co-catalyst: A Co-catalyst is a compound of a catalyst system which cooperates with at least one more co-catalyst to perform a catalytic reaction.
Steriorigid Complex: Steriorigid complexes are metal complexes having sites that can be converted into highly efficient catalysts for the stereoselective polymerization of olefins.
BACKGROUND
Polymerization of ethylene for the preparation of polyethylene is commercially carried out in the presence of a homogeneous catalyst system consisting of titanium tetrachloride and vanadium oxytrichloride. However, the product obtained using the homogeneous catalyst system has a dull color due to the presence of vanadium. Further, the alumina bed used for the removal of the residual catalyst from the polymer has to be changed frequently.
Recently, the homogeneous catalyst system has been replaced by magnesium dichloride supported bimetallic catalyst system, with titanium/zirconium/hafnium replacing vanadium in the homogeneous catalyst system.
US6723809 suggests a bimetallic catalyst for the production of high molecular weight polyethylene by solution polymerization process. The solid component of the catalyst consists of 95 wt% of titanium, magnesium, hafnium, aluminum, chorine and carboxylate group, which makes the catalyst suitable for the solution polymerization process.
US20090264282 suggests a process for the synthesis of a magnesium-titanium-hafnium olefin polymerization pro-catalyst by a) incomplete chlorination of di-organo magnesium compound with a source of active chlorine, b) removing unreacted di-organo magnesium from the reaction mixture, c) adding tetrabenzyl hafnium, and d) adding tetravalent titanium to obtain the pro-catalyst.
US7666810 suggests a process for the synthesis of a magnesium titanium olefin polymerization pro-catalyst by: a) reacting a di-organo magnesium compound with a source of active chlorine, b) removing unreacted di-organo magnesium from the reaction product followed by washing of the reaction product, and c) adding tetravalent titanium chloride to obtain the pro-catalyst.
However, the magnesium dichloride supported bimetallic catalyst system, requires filtering of the un-dissolved magnesium dichloride obtained during the catalyst synthesis and uses an organic acid for the solubilization of the magnesium dichloride, hafnium/ zirconium tetravalent halides, which adds to the process costs.
The present disclosure therefore, envisages a process for preparing a catalyst system that mitigates the drawbacks associated with conventional processes.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure 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 process for preparing a bimetallic heterogeneous catalyst system.
Another object of the present disclosure is to provide a bimetallic heterogeneous catalyst system for the polymerization process.
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
In accordance with one aspect of the present disclosure there is provided a process for preparing a bimetallic heterogeneous catalyst system. The process comprises forming a first catalyst component by depositing soluble magnesium chloride onto the surface of a support. The support is selected from the group consisting of silica, calcined silica, zeolite, polyethylene resin and combinations thereof. A second catalyst component is added to the first catalyst component to obtain the bimetallic heterogeneous catalyst system. The second catalyst component is selected from the group consisting of triethyl aluminium (TEAL), diisobutylaluminum (TIBAL), diethylaluminium chloride (DEAC), tri-n-octyl aluminum (TnOAL), tri – hexyl aluminum (TnHAL) and isobutylaluminum dichloride (IBADIC).
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1 illustrates a schematic representation of the process for preparing the first catalyst component of a bimetallic heterogeneous catalyst system in accordance with the present disclosure.
DETAILED DESCRIPTION
Conventionally, the magnesium dichloride supported bimetallic catalyst system is synthesized using titanium/zirconium/hafnium halides. However, these catalysts require filtration of un-dissolved magnesium dichloride. Further, the processes require an organic acid for the solublization of magnesium dichloride and the metal halides. These additional steps result in increased process costs.
Accordingly, the present disclosure provides a process for preparing a bimetallic heterogeneous catalyst system, wherein magnesium chloride in soluble form is deposited on the surface of a support such as silica, zeolite and polyethylene resin to obtain a first catalyst component. Also, an inorganic modifier is incorporated in the bimetallic heterogeneous catalyst system of the present disclosure, which further improves the performance of the catalyst.
A second catalyst component is added to the first catalyst component to obtain the bimetallic heterogeneous catalyst system of the present disclosure.
Figure 1 illustrates a schematic process for preparing the first catalyst component of a bimetallic heterogeneous catalyst system in accordance with the present disclosure: magnesium chloride A is heated in the presence of metal halides B and B’ and then a support D is added, followed by heating. The reaction mixture obtained is cooled E and then an alkylating agent F is added and again heated, followed by cooling and allowing to settle to obtain the first catalyst component of the bimetallic heterogeneous catalyst system G. Optionally, an inorganic modifier C is used along with the metal halide.
The process is described now, in detail. In an aspect of the present disclosure, the process for preparing a bimetallic heterogeneous catalyst system includes the following steps.
In the first step, magnesium chloride is heated with a first metal halide in a fluid medium to generate a magnesium-metal complex. The heating is carried out in the temperature range of 50 °C to 80 °C for a time period ranging from 30 minutes to 120 minutes.
The first metal halide is at least one selected from the group consisting of the halides of and stereorigid complexes of titanium, hafnium, zirconium, iron, nickel, cobalt and palladium.
In an embodiment of the present disclosure, the fluid medium is tetrahydrofuran. Tetrahydrofuran forms a soluble complex and hence, the process of the present disclosure does not require the use of an additional solubilizing agent.
In the second step, the magnesium-metal complex obtained in the first step is cooled to a temperature in the range of 25 °C to 35 °C. A second metal halide is then added to the magnesium-metal complex of the first process step and heated to a temperature in the range of 50 °C to 80 °C for a time period ranging from 60 minutes to 180 minutes to obtain a reaction mixture. The second metal halide is at least one selected from the group consisting of the halides of and stereorigid complexes of titanium, hafnium, zirconium, iron, nickel, cobalt and palladium.
In accordance with an embodiment of the present disclosure, magnesium chloride is heated with the first and the second metal halides together to generate the magnesium-metal complex.
Optionally, the reaction mixture is treated with an inorganic modifier before heating. In an exemplary embodiment of the present disclosure, the inorganic modifier is tetraethyl orthosilicate. An improvement in the catalyst performance is observed when the inorganic modifier is used in the preparation of the bimetallic heterogeneous catalyst system of the present disclosure.
In the third step, a support is added to the reaction mixture obtained in the second step and the reaction mixture containing the support is heated to a temperature in the range of 50 °C to 80 °C for a time period ranging from 30 minutes to 120 minutes to obtain a first reaction mass.
The support is selected from the group consisting of calcined silica, zeolite and polyethylene resin.
In the fourth step, the first reaction mass obtained in the third step is cooled to a temperature in the range of 25 °C to 35 °C and an alkylating agent diluted in decane, is added drop wise to the first reaction mass and the reaction mass containing the alkylating agent is further heated to a temperature in the range from 80 °C to 110 °C for a time period ranging from 60 minutes to 180 minutes to obtain a second reaction mass.
The alkylating agent is at least one selected from the group consisting of diethyl aluminum chloride, isobutyl aluminum dichloride (IBADIC), triethyl aluminum, triisobutyl aluminum, trioctyl aluminum and boron containing alkylating agents.
In the fifth step, the second reaction mass obtained in the fourth step is cooled to a temperature in the range of 25 °C to 35 °C and then allowed to settle to obtain a precipitate containing the first catalyst component of the bimetallic heterogeneous catalyst system.
Next, the precipitate is washed at least once, using an organic washing medium and then dried. In a preferred embodiment of the present disclosure, washing is carried out five times using dry hexane (organic washing medium).
A second catalyst component, is added to the first catalyst component to obtain the bimetallic heterogeneous catalyst system of the present disclosure. In accordance with the embodiments of the present disclosure, the second catalyst component is selected from the group consisting of triethyl aluminium (TEAL), diisobutylaluminum (TIBAL), diethylaluminium chloride (DEAC), tri-n-octyl aluminum (TnOAL), tri – hexyl aluminum (TnHAL) and isobutylaluminum dichloride (IBADIC).
The bimetallic heterogeneous catalyst system prepared in accordance with the present disclosure is used for homo and co-polymerization of a-olefins and dienes. The polymerization process can be carried out in a slurry, a solution or a gas phase mode. It is observed that incorporating a second support (silica/ zeolite/ PE resin) to the bimetallic heterogeneous catalyst system enhances its polymerization performance. Also, the addition of the inorganic modifier results in a further improvement in the catalyst activity. The sequence of addition of the reactants also influences the physical property and the activity of the obtained catalyst.
The present disclosure is further described in light of the following laboratory experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale.
Experiment 1: Preparation of the first catalyst component of the bimetallic heterogeneous catalyst system
Nine mmoles of magnesium chloride was reacted with 1.1 mmoles of HfCl4 in 100 ml dried tetrahydrofuran and heated to 65 °C for 1 hour. Then, 3.0 mmoles of TiCl4 was added at 30 °C and again heated to 65 °C for 2 hours. One gram of Calcined silica (support) was added and further heated for 1 hour. After cooling to 30 °C, 100 mmoles of diethyl aluminum chloride (DEAC), diluted in decane, was added drop wise to obtain a reaction mixture. The reaction mixture was further heated at 90 °C for 2 hours. The reaction mixture was cooled to 30 °C and allowed to settle to obtain a reaction mass. The reaction mass was then washed with dry hexane. The washing was conducted 5 times to obtain the catalyst. Finally, the catalyst was dried under the flow of dry nitrogen to obtain the first catalyst component of the catalyst system.
Different reactants in varying proportions were used to prepare the bimetallic heterogeneous catalyst system of the present disclosure as summarized in Table-1.
Experiment 2: Polymerization performance of the catalysts
The set up consisted of a preheated moisture free, jacketed 1 liter glass reactor fitted with a stirrer. Dry hexane was charged in to the glass reactor. The first catalyst component obtained in the experiment 1, along with the second catalyst component (triethyl aluminium) was added such that the second catalyst component/first catalyst component molar ratio of 100 was maintained. The reactor temperature was maintained at 80 °C by heating/cooling system. The reactor pressure was maintained at 2 kg/cm2. Polymerization reaction was carried out for 30 minutes and then the polymer was collected and dried.
The polymerization performances of the different catalysts obtained are summarized in Table-2.

Table-1: Composition and Reactant Amount of the Catalysts
Catalyst Examples
Precursor/ TiCl4
(mole ratio) Precursor/ HfCl4
(mole ratio) Second Support Precursor/ TEOS
(mole ratio) Alkyl aluminum halide/ precursor (mole ratio) Catalyst composition, wt% Remarks
Mg Ti Cl Hf
CAT-1 0.97 8.19 - - 2.32 15.5 4.2 31.8 5.5 Only MgCl2 as support

CAT-2 1.14 9.64 Silica - 3.79 13.3 1.6 24.3 2.2 Silica, along with MgCl2 as support

CAT-3 3.23 8.19 Zeolite - 11.16 17.2 2.9 21.9 3.7 Zeolite along with MgCl2 as support

CAT-4 4.57 7.71 PE Resin - 9.49 13.2 1.1 32.7 2.1 PE resin along with MgCl2 as support

CAT-5 3.23 8.19 - 4.97 11.15 17.7 2.2 33.1 6.4 Only MgCl2 as support & use of inorganic modifier

CAT-6 3.23 8.19 Zeolite 4.97 11.15 19.8 0.9 21.6 1.8 Zeolite along with MgCl2 as support & use of inorganic modifier

Inorganic modifier is found to replace titanium of the catalyst (as reflected by the composition of CAT-5 and CAT-6), without hampering rest of the catalyst composition.

Table-2: Comparison of slurry phase polymerization and product properties of the polymer obtained

Catalyst Triethyl aluminum/ Ti
(Molar ratio) Productivity, kg PE/g.Ti Peak Melting Temp., °C Crystallinity, % Molecular Wt. (By RSV) Bulk density, g/cc
CAT-1 150 3.1 133.4 63.4 7.8 0.197
CAT-2 152 39.7 134.4 65.0 6.1 0.190
CAT-3 156 6.9 134.4 59.1 7.6 0.165
CAT-4 155 4.1 134.4 62.9 6.0 0.162
CAT-5 157 9.8 134.1 63.0 7.5 0.179
CAT-6 152 74.9 135.0 62.5 7.8 0.241
Polymerization conditions – Fluid medium: Hexane (350ml), Temperature: 80 °C, Pressure: 2Kg/cm2, RPM: 450, second catalyst component: Triethyl aluminum, Reaction time: 30 minutes.
Differential Scanning Calorimetry (DSC) conditions: Heating to 250 °C at 10 °C /min.

It is seen from the Table-2 that using only magnesium chloride (CAT-1) as the support results in low productivity. Using silica (CAT-2) as a second support results in high productivity as compared to the zeolite (CAT-3) and the dry PE resin powder (CAT-4) as the support. Also, the use of an inorganic modifier (TEOS) along with the support (zeolite) gives a very high productivity as seen in CAT-6.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The process of the present disclosure described herein above has several technical advantages including, but not limited to, the realization of a bimetallic heterogeneous catalyst system:
? having improved ethylene polymerization activity; and
? a simple and economic process for preparing the bimetallic heterogeneous catalyst system.

The foregoing description of the specific embodiments will 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.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
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 ten percent 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.