DESC:FIELD
The present disclosure relates to a modified Ziegler catalyst composition and a method for preparing the same.
BACKGROUND
Polyolefins are polymers produced from simple olefins as the monomers. Polyethylene is a polyolefin produced by polymerizing the olefin ethylene. Polypropylene is another common polyolefin which is made from the olefin propylene. Industrially produced polyolefin are made via polymerization, using a catalyst, such as, the Ziegler catalyst composition. Ziegler catalyst composition consists of a pro-catalyst, an electron donor system and a co-catalyst.
The electron donor system of the Ziegler catalyst composition plays a vital role in olefin polymerization as a selectivity control agent. The electron donor system also influences the porosity and the specific surface areas of the Ziegler catalyst. Further, the electron donor system of the Ziegler catalyst composition can influence the catalytic activity of the Ziegler catalyst composition and the properties of the polyolefin obtained. The electron donor system may be present internally in the Ziegler catalyst composition or can be added externally.
Different internal electron donor systems are reported as a catalyst component of the Ziegler catalyst composition for the polymerization of olefin. Different supported Ziegler catalysts have been developed having high activity in olefin polymerization reactions. However, with the increasing worldwide demand for polymers, there exists a scope to improve the internal electron donor system to enhance the performance of the Ziegler catalyst composition by proper selection of the electron donor system.

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 Ziegler catalyst composition.
Another object of the present disclosure is to provide an improved electron donor system for the Ziegler catalyst composition.
Still another object of the present disclosure is to provide a Ziegler catalyst composition for olefin polymerization.
Yet another object of the present disclosure is to provide a method for preparing a Ziegler catalyst composition.
Still another object of the present disclosure is to provide a method for preparing polyolefin in presence of a Ziegler catalyst composition with improved productivity of polyolefin.
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 provides a modified Ziegler catalyst composition for olefin polymerization. The catalyst composition comprises a pro-catalyst, an organo-aluminium co-catalyst; and a hydrocarbon fluid medium. The pro-catalyst comprises a magnesium compound; a titanium component; and an internal electron donor system consisting of a mixture of at least one substituted succinate compound and at least one alkyl silicate of Formula (I);

wherein, R1, R2, R3 and R4 are independently selected from the group consisting of C1-C20 linear or branched alkyl and arylalkyl groups. The substituted succinate compound is selected from a group consisting of Formula (II);

wherein, R1, R2, R3, R4, R5 and R6 are independently selected from a group consisting of C1-C20 linear or branched alkyl and alkylaryl groups. The substituted succinate compound is selected from a group consisting of diisopropyl succinate, diethyl 2,2-dimethylsuccinate, diethyl 2-ethyl-2-methylsuccinate, diethyl 2-benzyl-2 isopropylsuccinate, diethyl 2-(cyclohexylmethyl)-2 isobutylsuccinate, diethyl 2-cyclopentyl-2-n propylsuccinate, diethyl 2,2-diisobutylsuccinate, diethyl 2-cyclohexyl-2-ethylsuccinate, diethyl 2-isopropyl-2 methylsuccinate, diethyl 2,2-diisopropyl diethyl 2-isobutyl 2-ethylsuccinate, diethyl 2-(1,1,1-trifluoro-2-propyl)2 methylsuccinate, diethyl 2-isopentyl-2-isobutylsuccinate, diethyl 2-phenyl-2-n-butylsuccinate, diisobutyl 2,2 dimethylsuccinate, diisobutyl 2-ethyl-2-methylsuccinate, diisobutyl 2-benzyl-2-isopropylsuccinate, diisobutyl2-(cyclohexylmethyl)2-isobutylsuccinate, diisobutyl 2-cyclopentyl-2-n-propylsuccinate, diisobutyl 2,2 diisobutylsuccinate, diisobutyl 2-cyclohexyl-2 ethylsuccinate, diisobutyl 2-isopropyl-2-methylsuccinate, diisobutyl 2-isobutyl-2-ethylsuccinate, diisobutyl 2-(1,1,1trifluoro-2-propyl)-2-methylsuccinate, diisobutyl 2-isopentyl-2-isobutylsuccinate, diisobutyl 2,2 diisopropylsuccinate, diisobutyl 2-phenyl-2-n propylsuccinate, dineopentyl 2,2-dimethylsuccinate, dineopentyl 2-ethyl-2-methylsuccinate, dineopentyl 2-benzyl-2isopropylsuccinate, dineopentyl 2-(cyclohexylmethyl)-2isobutylsuccinate, dineopentyl 2cyclopentyl-2-npropylsuccinate, dineopentyl 2,2-diisobutylsuccinate, dineopentyl 2-cyclohexyl-2-ethylsuccinate, dineopentyl 2-isopropyl-2-methylsuccinate, dineopentyl 2-isobutyl-2 ethylsuccinate, dineopentyl 2-(1,1,1-trifluoro-2-propyl)-2 methylsuccinate, dineopentyl 2,2-diisopropylsuccinate, dineopentyl 2-isopentyl-2-isobutylsuccinate, and dineopentyl 2-phenyl-2-n-butylsuccinate. The alkyl silicate is at least one selected from the group consisting of tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, and diethyldimethyl orthosilicate. The molar ratio of the substituted succinate compound and the alkyl silicate is in the range of 1:2 to 2:1. The magnesium compound is at least one selected from the group consisting of magnesium dichloride, magnesium methoxide, magnesium ethoxide, magnesium isopropoxide and mixtures thereof. The titanium component is at least one selected from the group consisting of TiCl4, Ti(OC2H5)3Cl, Ti(OC3H7)3Cl and Ti(OC4H9)Cl3. The organo-aluminium co-catalyst is at least one selected from the group consisting of triethylaluminium, tridecylaluminium, tri-n-butylaluminium, tri-isopropylaluminium, tri-isoprenylaluminium, tri-isobutylaluminium, ethyl aluminium sesquichloride, diethylaluminium chloride, di-isobutyl aluminium chloride, triphenylaluminium, tri-n-octylaluminium and tri-n-decylaluminium. The molar ratio of the amount of the organo-aluminium co-catalyst and the amount of the pro-catalyst is in the range of 50 to 300. The hydrocarbon fluid medium is at least one selected from the group consisting of hexane, decane, toluene, cyclohexane, chlorobenzene and heptane. The molar ratio of the amount of the substituted succinate compound and the amount of the magnesium compound is in the range of 0.01 to 0.5.
Further, the present disclosure provides a method for preparing the Ziegler catalyst composition. The method comprises the following steps: mixing a pre-determined amount of a magnesium alkoxide, a pre-determined amount of an internal electron donor system consisting of a mixture of at least one substituted succinate compound and at least one alkyl silicate, a pre-determined amount of titanium halide and a hydrocarbon fluid medium to obtain a slurry and heating the slurry to a temperature in the range of 80 °C to 100 °C; separating solid from the slurry and adding fresh hydrocarbon fluid medium to the solid and reacting the solid with titanium halide to obtain a complex of the pro-catalyst and the internal electron donor system; drying the complex at a temperature in the range of 30 °C to 80 °C to obtain a solid complex; and mixing the solid complex with an organo-aluminium co-catalyst and the hydrocarbon fluid medium to obtain the Ziegler catalyst composition. The hydrocarbon fluid medium is at least one selected from the group consisting of hexane, decane, heptane, chlorobenzene, toluene and cyclohexane. The magnesium alkoxide is at least one selected from the group consisting of magnesium methoxide, magnesium ethoxide and magnesium isopropoxide. The titanium halide is at least one selected from the group consisting of TiCl4, Ti(OC2H5)3Cl, Ti(OC3H7)3Cl and Ti(OC4H9)Cl3.
Still further, the present disclosure provides a method for preparing a polyolefin in the presence of the Ziegler catalyst composition. The method comprises the following steps: introducing the Ziegler catalyst composition into a reactor; introducing an olefin to the reactor containing the Ziegler catalyst composition; and subjecting the olefin to polymerization at a temperature in the range of 60 °C to 100 °C and pressure of the olefin in the range of 1 bar to 3 bar to obtain the polyolefin. The polyolefin is at least one selected from the group consisting of polyethylene and polypropylene. The amount of polyethylene produced per gram of Ziegler catalyst composition is in the range of 0.2 Kg to 1.5 Kg.
DETAILED DESCRIPTION
The present disclosure envisages a Ziegler catalyst composition comprising a pro-catalyst, and an organo-aluminium co-catalyst. The pro-catalyst comprises a magnesium compound, a titanium component, and an electron donor system. The electron donor system consists of at least one substituted succinate compound and at least one alkyl silicate. The use of alkyl silicate along with the substituted succinate compound as an internal electron donor system in the Ziegler catalyst composition of the present disclosure significantly improves the productivity of the polyolefin.
In accordance with one aspect of the present disclosure, there is provided a Ziegler catalyst composition for olefin polymerization comprising a pro-catalyst, an organo-aluminium co-catalyst and a hydrocarbon fluid medium.
In accordance with one embodiment of the present disclosure, the pro-catalyst comprises a magnesium compound, a titanium component, and an internal electron donor system. The internal donor system of the present disclosure consists of a mixture of at least one substituted succinate compound and at least one alkyl silicate.
In accordance with the embodiments of the present disclosure, the magnesium compound is at least one selected from the group consisting of magnesium dichloride, magnesium methoxide, magnesium ethoxide, magnesium isopropoxide and mixtures thereof. The magnesium compound acts as a support in the Ziegler catalyst composition. In an embodiment of the present disclosure, magnesium dichloride in the form of the support is obtained by contacting a titanium component comprising at least one titanium-halogen bond with magnesium alkoxide.
The titanium component is at least one selected from the group consisting of TiCl4, Ti(OC2H5)3Cl, Ti(OC3H7)3Cl and Ti(OC4H9)Cl3.
The internal electron donor system consists of a mixture of at least one substituted succinate compound and at least one alkyl silicate of formula (I):

wherein, R1, R2, R3 and R4 are independently selected from a group consisting of C1-C20 linear or branched alkyl and arylalkyl groups.
The alkyl silicate is selected from the group consisting of tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, Tetrabutyl orthosilicate, and diethyldimethyl orthosilicate. In accordance with one embodiment of the present disclosure, the alkyl silicate is tetraethyl orthosilicate (TEOS).
The substituted succinate compound is selected from a group consisting of formula (II):

wherein, R1, R2, R3 R4, R5 and R6 are independently selected from a group consisting of C1-C20 linear or branched alkyl and alkylaryl groups.
The substituted succinate compound is selected from a group consisting of diisopropyl succinate, diethyl 2,2-dimethylsuccinate, diethyl 2-ethyl-2-methylsuccinate, diethyl 2-benzyl-2 isopropylsuccinate, diethyl 2-(cyclohexylmethyl)-2 isobutylsuccinate, diethyl 2-cyclopentyl-2-n propylsuccinate, diethyl 2,2-diisobutylsuccinate, diethyl 2-cyclohexyl-2-ethylsuccinate, diethyl 2-isopropyl-2 methylsuccinate, diethyl 2,2-diisopropyl diethyl 2-isobutyl 2-ethylsuccinate, diethyl 2-(1,1,1-trifluoro-2-propyl)2 methylsuccinate, diethyl 2-isopentyl-2-isobutylsuccinate, diethyl 2-phenyl-2-n-butylsuccinate, diisobutyl 2,2 dimethylsuccinate, diisobutyl 2-ethyl-2-methylsuccinate, diisobutyl 2-benzyl-2-isopropylsuccinate, diisobutyl2-(cyclohexylmethyl)2-isobutylsuccinate, diisobutyl 2-cyclopentyl-2-n-propylsuccinate, diisobutyl 2,2 diisobutylsuccinate, diisobutyl 2-cyclohexyl-2 ethylsuccinate, diisobutyl 2-isopropyl-2-methylsuccinate, diisobutyl 2-isobutyl-2-ethylsuccinate, diisobutyl 2-(1,1,1trifluoro-2-propyl)-2-methylsuccinate, diisobutyl 2-isopentyl-2-isobutylsuccinate, diisobutyl 2,2 diisopropylsuccinate, diisobutyl 2-phenyl-2-n propylsuccinate, dineopentyl 2,2-dimethylsuccinate, dineopentyl 2-ethyl-2-methylsuccinate, dineopentyl 2-benzyl-2isopropylsuccinate, dineopentyl 2-(cyclohexylmethyl)-2isobutylsuccinate, dineopentyl 2cyclopentyl-2-npropylsuccinate, dineopentyl 2,2-diisobutylsuccinate, dineopentyl 2-cyclohexyl-2-ethylsuccinate, dineopentyl 2-isopropyl-2-methylsuccinate, dineopentyl 2-isobutyl-2 ethylsuccinate, dineopentyl 2-(1,1,1-trifluoro-2-propyl)-2 methylsuccinate, dineopentyl 2,2-diisopropylsuccinate, dineopentyl 2-isopentyl-2-isobutylsuccinate, and dineopentyl 2-phenyl-2-n-butylsuccinate. In accordance with one embodiment of the present disclosure, the substituted succinate compound is diisopropyl succinate.
In accordance with the embodiments of the present disclosure, the molar ratio of the amount of the substituted succinate compound and the amount of the alkyl silicate is in the range of 1:2 to 2:1
In accordance with a preferred embodiment of the present disclosure, the molar ratio of the amount of the substituted succinate compound and the amount of the magnesium compound is in the range of 0.01 to 0.5.
Typically, the molar ratio of the amount of the organo-aluminium co-catalyst and the amount of the pro-catalyst is in the range of 50 to 300.
In accordance with another aspect of the present disclosure, there is provided a method for preparing a Ziegler catalyst composition. The method is described hereinafter in detail.
Initially, a pre-determined amount of a magnesium alkoxide, a pre-determined amount of an internal electron donor system, a pre-determined amount of titanium halide and a hydrocarbon fluid medium are mixed to obtain a slurry.
Magnesium alkoxide is at least one selected from the group consisting of magnesium methoxide, magnesium ethoxide, magnesium isopropoxide and mixtures thereof.
Titanium halide is at least one selected from the group consisting of TiCl4, Ti(OC2H5)3Cl, Ti(OC3H7)3Cl and Ti(OC4H9)Cl3.
Typically, the organo-aluminium is at least one selected from the group consisting of triethylaluminium, tridecylaluminium, tri-n-butylaluminium, tri-isopropylaluminium, tri-isoprenylaluminium, tri-isobutylaluminium, ethyl aluminium sesquichloride, diethylaluminium chloride, di-isobutyl aluminium chloride, triphenylaluminium, tri-n-octylaluminium and tri-n-decylaluminium.
In accordance with one embodiment of the present disclosure, the organo-aluminium co-catalyst is triethylaluminium.
The hydrocarbon fluid medium is at least one selected from the group consisting of hexane, decane, heptane, chlorobenzene, toluene, and cyclohexane.
In accordance with an exemplary embodiment of the present disclosure, the hydrocarbon fluid medium is chlorobenzene.
The slurry is then heated to a temperature in the range of 80 °C to 100 °C. Once the slurry temperature in the range of 80 °C to 100 °C is achieved, the slurry is maintained at this temperature for a time period in the range of 40 minutes to 80 minutes with stirring. The slurry is then allowed to stand, to settle down.
The solid part is separated from the slurry and fresh hydrocarbon fluid medium is added to the solid and is further reacted with titanium halide to obtain a complex of the pro-catalyst and the internal electron donor system.
The so obtained complex is dried at a temperature in the range of 30 °C to 80 °C to obtain a solid complex. The complex is then mixed with an organo-aluminium co-catalyst and the hydrocarbon fluid medium to obtain the Ziegler catalyst composition.
In accordance with still another aspect of the present disclosure, there is provided a method for the preparation of a polyolefin in presence of the Ziegler catalyst composition. The method comprises the following steps:
The Ziegler catalyst composition of the present disclosure is introduced into a reactor.
In one embodiment of the present disclosure, an organo-aluminium compound is mixed with a fluid medium to obtain co-catalyst solution. Next, the pro-catalyst is added to the co-catalyst solution, mixed thoroughly with stirring at ambient temperature to obtain the solution of the Ziegler catalyst composition of the present disclosure.
Thereafter, olefin is charged to the reactor containing the Ziegler catalyst composition and is subjected to polymerization at a temperature in the range of 60 °C to 100 °C and pressure of olefin in the range of 1 bar to 3 bar to obtain a slurry comprising polyolefin.
Typically, the polymerization is carried out for a time period ranging from 0.5 hour to 5 hours.
At the end of the reaction time, the reactor is depressurized and cooled to a temperature in the range of 20 °C to 40 °C. The polyolefin is recovered from the slurry and is dried at a temperature in the range of 30 °C to 50 °C. In one embodiment of the present disclosure, the recovered polyolefin is dried in a vacuum oven at 40 °C.
Typically, the olefin is at least one selected from the group consisting of ethylene and propylene.
In accordance with one embodiment of the present disclosure, the olefin is ethylene.
In accordance with the present disclosure, the polyolefin is one of polyethylene and polypropylene.
In accordance with one embodiment of the present disclosure, the polyolefin is polyethylene.
The amount of polyethylene produced per gram of the Ziegler catalyst composition is in the range of 0.2 Kg to 1.5 Kg.
The present disclosure is further described in light of the following laboratory scale experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The experiments 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. These laboratory experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
Experimental Details:
Experiment 1: Synthesis of a pro-catalyst
A 500 ml glass reactor, provided with a stirrer was charged with 100 mL of chlorobenzene and 7.3 g of magnesium alkoxide (21 % Mg, 8 % methoxy and 71 % ethoxy) under nitrogen atmosphere to obtain a mixture. Calculated amount of internal electron donor (0.79 g diisopropyl succinate and 0.81 g tetraethyl orthosilicate) was added to the mixture to obtain a solution of magnesium alkoxide and the internal electron donor in chlorobenzene. 15 mL of TiCl4 was added slowly to the solution of magnesium alkoxide and the internal electron donor, in chlorobenzene and the temperature of the mixture was raised to 90 °C. The resulting solution was stirred for 60 minutes. After 60 minutes, stirring was stopped and the solution was allowed to settle down. The liquid phase was separated at 30 °C to obtain a residue. 5 mL of TiCl4 was added to the residue and the temperature was raised to 90 °C. The solution was stirred for another 60 minutes. After 60 minutes of stirring, the solution was allowed to cool down and liquid phase was removed from the solution. The residue was washed thrice with 300 mL of anhydrous hexane to obtain a complex of the pro-catalyst and the internal electron donor system. The complex was dried at 50 °C.
The internal electron donor systems used for preparation of the complex of pro-catalyst and internal electron donor system are given in Table 1. Experiment 1a and Experiment 1b represent the Ziegler catalyst compositions prepared with the electron donor systems (mixture of substituted succinate compound and alkyl silicate) of the present disclosure. Whereas, Test-1 and Test-2 represent comparative Ziegler catalyst compositions prepared with only di-isopropyl succinate as the electron donor system.
Table 1: Compositional data of single electron donor and mixed electron donor catalyst system
Catalyst system Di-isopropyl succinate: magnesium (mol) Tetraethyl
orthosilicate: magnesium (mol) Ti (wt%) Mg (wt%)
Test-1 0.25 -- 30 9
Test-2 0.125 -- 13 10
Experiment 1a 0.2 0.2 9.7 11.2
Experiment 1b 0.06 0.06 8.9 13.5
The complex of the pro-catalyst and the internal electron donor system with calculated amount of an organo-aluminium co-catalyst constitute the Ziegler catalyst composition.

Experiment 2: Polymerization of ethylene using the pro-catalyst prepared in experiment 1
Ethylene polymerization was performed in a 1000 mL glass reactor equipped with a stirrer, a temperature indicator, a pressure indicator and feeding lines for catalyst, ethylene gas and nitrogen.
A 100 mL three necked glass reactor was charged with 50 mL of anhydrous decane. Calculated amount of triethylaluminium (TEA/Ti=250) was added to decane to form a co-catalyst solution. 20 mg of the pro-catalyst synthesized in experiment 1 was added to the co-catalyst solution to obtain the solution of Ziegler catalyst composition. The solution was mixed together and stirred at room temperature for 5 minutes. The solution of Ziegler catalyst composition was transferred to the 1000 mL glass reactor. The reactor with the Ziegler catalyst composition was charged with ethylene gas, so that the pressure of the reactor increased upto 2 bar. The reaction mixture was stirred at a speed of 400 rpm and heated to 80 °C. At the end of the reaction time, the reactor was depressurized and the temperature was dropped to 30 °C. The polymer was recovered from the reaction mixture and dried under vacuum at 40 °C.
Similar polymerization was also carried out using the Ziegler catalyst comprising only diisopropyl succinate as the internal electron donor (Test-1 and Test-2). The ethylene polymerization results obtained using the Ziegler catalyst composition of the present disclosure (internal electron donor comprising mixture of substituted succinate compound and alkyl silicate) and Ziegler catalyst composition comprising single internal electron donor are summarized in the following Table 2 below.

Table 2: Ethylene polymerization catalyzed by different catalyst systems
Catalyst
System Temperature (°C) Ethylene pressure (bar) Time (hour) Productivity (Kg of polyethylene per g of catalyst) BD (U) BD (T)
Test-1 80 2 1 0.3 0.09 0.1
80 3 1 0.4 0.1 0.12
Test-2 80 2 1 0.3 0.1 0.1
80 3 1 0.35 0.11 0.12
Experiment 1a 80 2 1 1 0.1 0.12
80 3 1 1.3 0.15 0.17
Experiment 1b 80 2 1 0.9 0.1 0.12
80 3 1 1.2 0.16 0.18

The catalytic activities of the catalyst systems Test-1 and Test-2 containing only diisopropyl succinate as internal electron donor are similar. Also, the bulk density of the synthesized polyethylene is same for Test-1 and Test-2. Whereas, the Ziegler catalyst composition of the present disclosure, Experiment 1a and Experiment 1b, having internal electron donor as a mixture of diisopropyl succinate and tetraethyl orthosilicate, showed three fold increased productivity as compared to the single donor catalyst system (Test-1 and Test-2).The higher productivity of the Ziegler catalyst composition of the present disclosure may be due to the synchronizing effect of mixed electron donor. Further, it is also seen from Table- 2, that an improvement in the productivity can be achieved by increasing the reactor ethylene pressure during polymerization. The bulk density of the resulting polyethylene is similar to the single donor catalyst system.
TECHNICAL ADVANCEMENT
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
• a modified Ziegler catalyst composition;
• an internal electron donor system comprising a mixture of substituted succinate compound and the alkyl silicate; and
• a method for polymerization that employs an internal electron donor system, which influences the catalytic activity and product properties of the polyolefin.
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 invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of experiment only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment 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:1. A modified Ziegler catalyst composition for olefin polymerization, said catalyst composition comprising:
? a pro-catalyst comprising:
i. a magnesium compound;
ii. a titanium component; and
iii. an internal electron donor system consisting of a mixture of at least one substituted succinate compound and at least one alkyl silicate of Formula (I);

wherein, R1, R2, R3 and R4 are independently selected from the group consisting of C1-C20 linear or branched alkyl and arylalkyl groups; and
wherein, the molar ratio of the substituted succinate compound and the alkyl silicate is in the range of 1:2 to 2:1;
? an organo-aluminium co-catalyst; and
? a hydrocarbon fluid medium.

2. The Ziegler catalyst composition as claimed in claim 1, wherein said substituted succinate compound is selected from a group consisting of Formula (II);

wherein, R1, R2, R3, R4, R5 and R6 are independently selected from a group consisting of C1-C20 linear or branched alkyl and alkylaryl groups.

3. The Ziegler catalyst composition as claimed in claim 1, wherein said substituted succinate compound is selected from a group consisting of diisopropyl succinate, diethyl 2,2-dimethylsuccinate, diethyl 2-ethyl-2-methylsuccinate, diethyl 2-benzyl-2 isopropylsuccinate, diethyl 2-(cyclohexylmethyl)-2 isobutylsuccinate, diethyl 2-cyclopentyl-2-n propylsuccinate, diethyl 2,2-diisobutylsuccinate, diethyl 2-cyclohexyl-2-ethylsuccinate, diethyl 2-isopropyl-2 methylsuccinate, diethyl 2,2-diisopropyl diethyl 2-isobutyl 2-ethylsuccinate, diethyl 2-(1,1,1-trifluoro-2-propyl)2 methylsuccinate, diethyl 2-isopentyl-2-isobutylsuccinate, diethyl 2-phenyl-2-n-butylsuccinate, diisobutyl 2,2 dimethylsuccinate, diisobutyl 2-ethyl-2-methylsuccinate, diisobutyl 2-benzyl-2-isopropylsuccinate, diisobutyl2-(cyclohexylmethyl)2-isobutylsuccinate, diisobutyl 2-cyclopentyl-2-n-propylsuccinate, diisobutyl 2,2 diisobutylsuccinate, diisobutyl 2-cyclohexyl-2 ethylsuccinate, diisobutyl 2-isopropyl-2-methylsuccinate, diisobutyl 2-isobutyl-2-ethylsuccinate, diisobutyl 2-(1,1,1trifluoro-2-propyl)-2-methylsuccinate, diisobutyl 2-isopentyl-2-isobutylsuccinate, diisobutyl 2,2 diisopropylsuccinate, diisobutyl 2-phenyl-2-n propylsuccinate, dineopentyl 2,2-dimethylsuccinate, dineopentyl 2-ethyl-2-methylsuccinate, dineopentyl 2-benzyl-2isopropylsuccinate, dineopentyl 2-(cyclohexylmethyl)-2isobutylsuccinate, dineopentyl 2cyclopentyl-2-npropylsuccinate, dineopentyl 2,2-diisobutylsuccinate, dineopentyl 2-cyclohexyl-2-ethylsuccinate, dineopentyl 2-isopropyl-2-methylsuccinate, dineopentyl 2-isobutyl-2 ethylsuccinate, dineopentyl 2-(1,1,1-trifluoro-2-propyl)-2 methylsuccinate, dineopentyl 2,2-diisopropylsuccinate, dineopentyl 2-isopentyl-2-isobutylsuccinate, and dineopentyl 2-phenyl-2-n-butylsuccinate.

4. The Ziegler catalyst composition as claimed in claim 1 or claim 2, wherein said substituted succinate compound is diisopropyl succinate.

5. The Ziegler catalyst composition as claimed in claim 1, wherein said alkyl silicate is at least one selected from the group consisting of tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, and diethyldimethyl orthosilicate.

6. The Ziegler catalyst composition as claimed in claim 1, wherein said alkyl silicate is tetraethyl orthosilicate.

7. The Ziegler catalyst composition as claimed in claim 1, wherein said magnesium compound is at least one selected from the group consisting of magnesium dichloride, magnesium methoxide, magnesium ethoxide, magnesium isopropoxide and mixtures thereof.

8. The Ziegler catalyst composition as claimed in claim 1, wherein said titanium component is at least one selected from the group consisting of TiCl4, Ti(OC2H5)3Cl, Ti(OC3H7)3Cl and Ti(OC4H9)Cl3.
9. The Ziegler catalyst composition as claimed in claim 1, wherein said organo-aluminium co-catalyst is at least one selected from the group consisting of triethylaluminium, tridecylaluminium, tri-n-butylaluminium, tri-isopropylaluminium, tri-isoprenylaluminium, tri-isobutylaluminium, ethyl aluminium sesquichloride, diethylaluminium chloride, di-isobutyl aluminium chloride, triphenylaluminium, tri-n-octylaluminium and tri-n-decylaluminium.

10. The Ziegler catalyst composition as claimed in claim 1, wherein the molar ratio of the amount of said organo-aluminium co-catalyst and the amount of said pro-catalyst is in the range of 50 to 300.

11. The Ziegler catalyst composition as claimed in claim 1, wherein said hydrocarbon fluid medium is at least one selected from the group consisting of hexane, decane, toluene, cyclohexane, chlorobenzene and heptane.

12. The Ziegler catalyst composition as claimed in claim 1, wherein the molar ratio of the amount of said substituted succinate compound and the amount of said magnesium compound is in the range of 0.01 to 0.5.

13. A method for preparing the Ziegler catalyst composition as claimed in claim 1, said method comprises the following steps:
? mixing a pre-determined amount of a magnesium alkoxide, a pre-determined amount of an internal electron donor system consisting of a mixture of at least one substituted succinate compound and at least one alkyl silicate, a pre-determined amount of titanium halide and a hydrocarbon fluid medium to obtain a slurry and heating said slurry to a temperature in the range of 80 °C to 100 °C;
? separating solid from said slurry and adding fresh hydrocarbon fluid medium to said solid and reacting said solid with titanium halide to obtain a complex of the pro-catalyst and the internal electron donor system;
? drying said complex at a temperature in the range of 30 °C to 80 °C to obtain a solid complex; and
? mixing said solid complex with an organo-aluminium co-catalyst and said hydrocarbon fluid medium to obtain said Ziegler catalyst composition.

14. The method as claimed in claim 13, wherein said hydrocarbon fluid medium is at least one selected from the group consisting of hexane, decane, heptane, chlorobenzene, toluene and cyclohexane.

15. The method as claimed in claim 13, wherein said magnesium alkoxide is at least one selected from the group consisting of magnesium methoxide, magnesium ethoxide and magnesium isopropoxide.

16. The method as claimed in claim 13, wherein said titanium halide is at least one selected from the group consisting of TiCl4, Ti(OC2H5)3Cl, Ti(OC3H7)3Cl and Ti(OC4H9)Cl3.

17. A method for preparing a polyolefin in the presence of the Ziegler catalyst composition as claimed in claim 1, wherein said method comprises the following steps:
? introducing said Ziegler catalyst composition into a reactor;
? introducing an olefin to said reactor containing said Ziegler catalyst composition; and
? subjecting said olefin to polymerization at a temperature in the range of 60 °C to 100 °C and a pressure of the olefin in the range of 1 bar to 3 bar to obtain said polyolefin.

18. The method as claimed in claim 17, wherein said polyolefin is at least one selected from the group consisting of polyethylene and polypropylene.

19. The method as claimed in claim 17, wherein the amount of polyethylene produced per gram of Ziegler catalyst composition is in the range of 0.2 Kg to 1.5 Kg.