FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
A CATALYST SYSTEM FOR PREPARATION OF POLYETHYLENE AND A METHOD OF ITS PREPARATION
Inventors: Kaur Sukhdeep, Patil Harshad Ramdas and Gupta Virendra Kumar
Applicant:
RELIANCE INDUSTRIES LTD.,
i
an Indian Company
of 3rd Floor, Maker Chamber-IV, 222, Nariman Point,
Mumbai 400 021, Maharashtra, India.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE DISCLOSURE:
The present disclosure relates to a catalyst system for polymerization of ethylene and a method for preparing the same.
BACKGROUND:
It is well known in the literature that Ziegler-Natta catalyst is used for the polymerization of olefins. Ziegler-Natta catalyst consists of pro-catalyst and a co-catalyst. The pro-catalyst is based on a transition metal compound belonging to any of groups IVb to Vllb, VIII of the periodic table; usually it is a titanium compound. The co-catalyst is based on organo-metallic compounds of metals belonging to any of groups IA to IIIA of the periodic table; usually it is an organo-aluminum compound. The catalyst system frequently comprises a solid support and an electron donor that alters the catalytic properties of the system with or without a solvent. The following patent documents disclose various catalyst systems.
US Patent No. 5330949 discloses a method of producing catalyst using a solid catalyst carrier having a surface hydroxyl group concentration up to 3 u mole/m which is useful for preparing a catalyst containing solid catalyst component, an organoaluminum compound and an electron donating compound.
European Patent No. 1016676 discloses a catalyst system comprising i) magnesium halide, ii) titanium compound containing at least one bidentate ligand wherein the titanium is in the tetravalent state, iii) an electron donor, iv) an inert filler and v) an alkyl

aluminum compound as co-catalysts. It also discloses the use of aliphatic alcohol, alkyl or cycloalkyl ether or ketone as an electron donor.
European Patent No. 186322 discloses a method of preparing the catalyst for polymerization of olefins. The process involves contacting silicon dioxide with organomagnesium compound to obtain mixture which is further contacted with carbon dioxide followed by halogen containing compound and titanium compound.
Further, US Patent No. 7504464 discloses a process for preparing a catalyst which comprises preparing a solution of magnesium compound, titanium compound, an electron donor and a solvent followed by adding catalyst support to the solution to form slurry, spray drying the slurry at 100 °C to 140 °C resulting into spray dried precursor. The precursor is then slurried again in mineral oil and then finally activated by Lewis acid to give a catalyst to be used for polymerization. The process of preparing the catalyst as disclosed in US Patent No. 7504464 is complex and involves many steps, which results in time consuming. Further, it involves the use of Lewis acid which enhances the complexity of the procedure. Thus the process is not cost effective.
European Patent No. 1539834 discloses a method of making a composition of spray-dried particles which comprises following steps- a preparation of solution of magnesium halide, solvent, transition metal compound selected from Group 3-10 and lanthanides of periodic table and an electron donor such as alcohol, b. contacting the solution with an inert filler to form slurry and c. spray drying the slurry. It further discloses the use of triethylaluminum as moisture remover from the fillers being used.

European Patent No. 604850 discloses preparation of catalyst by using a chlorinating agent in the initial stage. It first includes contacting the inorganic support and chlorinating agent i.e alkyl aluminum chloride and then impregnating it with a solution based on magnesium halide, magnesium alkoxy compound, titanium tetravalent compound and an electron donor.
European Patent No. 184347 provides a method of preparing a catalyst system of metal oxide, magnesium dihydro-carbyloxide, halogen containing compound and titanium compound with inert solvent.
US Patent No. 4427573 specifically discloses the order of addition of components present in the catalyst. The orders of addition consist of adding the magnesium compound to a mixture of an electron donor and activator compounds, followed by solid support and titanium compound.
Another US Patent No. 7211535 discloses a process of preparing a catalyst for gas phase polymerization of olefins, wherein the properties and productivity of polymer can be altered depending on the sequence of addition of the catalyst components. The catalyst components consist of titanium, magnesium, aluminum and optionally an electron donor on a support.
The preparation of catalyst system without using an electron donor is disclosed in US Patent No. 6046126.

The catalyst system disclosed in European Patent No. 91135 is activated by organo-aluminum compounds before the polymerization reaction.
US Patent No. 5290745 discloses a catalyst system comprising organoaluminum component and, TiCl3, MgCl2 prepared by reacting TiCl4 with Mg metal in presence of electron donor solvent being free of radicals containing active hydrogen. The resultant catalyst system contains Mg/Ti in a ratio of 1:1 to 56:1 which was then either mixed with silica or spray dried to obtain particles of catalyst.
US 2002/0065378 disclose preparation of a catalyst in which initially silica gel support is calcined at 600 °C for 4 hours and then treated with triethyl aluminum along with a halide promoter. The mother liquor consisting of TiCl4, MgCl2 and THF is prepared and mixed with treated silica gel followed by drying. This solid mixture is again pretreated with diethylchloroaluminum. The obtained catalyst is dried under nitrogen.
Another method of preparation of a catalyst useful for polymerization of ethylene is disclosed in Journal of Applied Polymer science 1990, 39, 837-854. The external electron donor used in the preparation of catalyst is THF.
The use of organo-aluminum compounds, specifically lower chain length alkyl aluminum, as an activator of the catalyst is associated with several drawbacks which include the facts that organo-aluminum compounds are moisture sensitive, they react violently with water, are corrosive and hence require great care while handling. Use of

organo-aluminum compounds further leads to the corrosion of the molding equipment, thus resulting into fouling of the reactors and peripheral equipment.
The catalyst systems disclosed in the prior art suffer from several shortcomings which include low molecular weight of the resultant polyethylene. Generally, the catalyst system containing an electron donor used for polymerization of ethylene leads to narrowing of the molecular weight distribution of the polyethylene. It is desirable to have a broad molecular weight distribution for polyethylene for some important applications. It is also advantageous to have self extinguishing characteristics of the polyethylene, specifically for gas phase polyethylene production.
Further, it is observed that the catalyst system containing only tetrahydrofuran as an electron donor results in a polymerized product having- molecular weight not more than 200000 g/mol.
Furthermore, the electron donor in the Ziegler-Natta catalyst does not effectively provide a control on the polymerization kinetics at a higher temperature in gas phase.
Accordingly, it is desirable to develop an effective catalyst system which can be useful for producing high molecular weight polyethylene.
OBJECTS OF THE DISCLOSURE:
Some of the non-limiting objects which at least one embodiment of this disclosure may achieve are:

It is an object of the present disclosure to provide a catalyst system comprising a combination of donors for polymerization of lower olefins.
It is another object of the present disclosure to provide a catalyst system which is useful for producing a polyethylene of higher molecular weight and broad molecular weight distribution.
It is yet another object of the present disclosure to provide a simple process for preparing a catalyst system for polymerization reactions.
SUMMARY OF THE DISCLOSURE:
These and other objects of the present disclosure are to a great extent dealt in the disclosure.
In accordance with the present disclosure there is provided a catalyst system for
polymerization of ethylene; said catalyst system comprising:
(A) a procatalyst comprising
i) electron donor comprising Tetrahydrofuran (THF) and N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA);
ii) titanium tetrachloride and magnesium dichloride; and
iii) a silica support,
and
(B) a cocatalyst

Typically, the electron donor comprises N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA) ranging between 30 and 50 weight % of the total mass of the electron donor and tetrahydrofuran (THF) ranging between 50 and 70 weight % of the total mass of the electron donor.
Typically, the amount of electron donor is in the range of about 8 to 14 % of the total mass of the catalyst system.
Typically, the cocatalyst is tri alkyl aluminum.
Preferably, the cocatalyst is tri-n-octyl aluminum.
Typically, the mole ratio of cocatalyst to procatalyst is 1 to 5.
Preferably, the mole ratio of cocatalyst to procatalyst is 1 to 1.25.
Typically, the amount of titanium is in the range of about 1.0 to 2.0 % of the total mass of the catalyst system.
Typically, the amount of magnesium is in the range of about 1.5 to 2.5 % of the total mass of the catalyst system.
Typically, the amount of chlorine is in the range of about 10.0 to 13.0 % of the total mass of the catalyst system.
In another aspect of the present disclosure there is provided a method for preparing a catalyst system for polymerization of ethylene; said method comprising the following steps:

a) subjecting silica to calcination to obtain a calcined silica;
b) preparing a homogenous mother liquor comprising MgCl2, TiCl4, tetrahydrofuran (THF) and N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA);
c) adding the calcined silica to the homogenous mother liquor to obtain a catalyst system; and
d) drying the catalyst system to obtain desired amount of electron donor in the catalyst system.
Typically, the calcination is carried out at a temperature in the range of about 300 °C to 700 °C for a period of about 3hours to 7hours to obtain calcined silica.
Typically, the calcination is preferably carried out at a temperature 600°C for 6 hours.
Typically, the method step of preparing homogeneous mother liquor is carried out at a temperature in the range of about 20 °C to a reflux temperature for a period of about 3 hours to 6 hours.
Typically, the method step of preparing homogeneous mother liquor is preferably carried out at a reflux temperature for 5 hours
Typically, the method step (c) is carried out under stirring.
Typically, the method step of drying is carried out under nitrogen gas.

Typically, the polymer prepared in accordance with the present disclosure has molecular weight distribution in the range of 10 to 16.
DETAIL DESCRIPTION OF THE DISCLOSURE:
In accordance with the present disclosure there is provided a catalyst system which is useful for preparing high molecular weight polyethylene.
The inventors of the present disclosure focused on the problem associated with the use of known donor. After conducting several trials with various combinations of donor it was found that when THF is used in combination with N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA) in a particular proportion, it is useful for producing high molecular weight polyethylene and broad MWD.
The present disclosure is directed to a catalyst system for polymerization of ethylene; said catalyst system comprising:
(A) a procatalyst comprising
i) electron donor comprising Tetrahydrofuran (THF) and N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA);
ii) titanium tetrachloride and magnesium dichlortde; and
iii) a silica support,
and
(B) a cocatalyst

In accordance with the present disclosure a particular proportion of N,N',N',N",N" pentamethyldiethylenetriamine (PMDETA) and tetrahydrofuran (THF) is maintained for regulating the molecular weight of the resultant polyethylene. The electron donor comprises N,N',N,,N",N"-pentamethyldiethylenetriamine (PMDETA) ranging between 30 and 50 weight % of the total mass of the electron donor and tetrahydrofuran (THF) ranging between 50 and 70 weight % of the total mass of the electron donor.
The amount of electron donor system of the present disclosure is in the range of about 8 to 14 % of the total mass of the catalyst system.
The cocatalyst selected is tri-alkyl aluminum and the mole ratio of cocatalyst to procatalyst is lto 5. Tri-n-octyl aluminum is the preferred cocatalyst. The preferred mole ratio of cocatalyst to procatalyst is 1 to 2.5.
The amounts of titanium, magnesium and chlorine in the catalyst system of the present disclosure is in the range of about 1.0 to 2.0 % of the total mass of the catalyst system, 1.5 to 2.5 % of the total mass of the catalyst system and 10.0 to 13.0 % of the total mass of the catalyst system respectively.
The polymer obtained by using the catalyst system of the present disclosure has a molecular weight distribution in the range of 10 to 16.
In another aspect of the present disclosure there is provided a simple method for preparing a catalyst system for polymerization of ethylene.
The method involves the following steps;

In first step silica support is calcined at a temperature in the range of about 300 °C to 700 °C for a period of about 3 hours to 7 hours.
The calcination process is preferably carried out at 600 °c for 6 hours.
Separately a homogenous mother liquor comprising MgCl2, TiCl4, tetrahydrofuran (THF) and N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA) is prepared at a temperature in the range of about 20 °C to a reflux temperature for a period of about 3 hours to 6 hours.
The process of preparing the homogenous mother liquor is preferably carried out at reflux temperature for a period of 5 hours.
The calcined silica obtained is then added to a homogenous mother.
The desired amount of an electron donor is achieved by drying the catalyst system under nitrogen.
The catalyst of the present disclosure is morphologically controlled. It exhibits enhanced activity for polymerizing ethylene as a result of combination of N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA) and tetrahydrofuran(THF) as external donor.
The present disclosure is further illustrated by non limiting examples.
Example 1A: Synthesis of mixed electron donor catalyst system
Synthetic amorphous silica having surface area of 300 m7g, pore volume of 1.6 mL/g and average particle size of 50 u was calcined at 600°C for 6 hours for removing

moisture and activating both free and bonded hydroxyl groups. In 250 mL round bottom flask (attached with a condenser having fluid circulated at -10°C), 1.2 g of anhydrous MgCl2 was added followed by 100 mL of dried THF addition with stirring at 30°C for 5 min. To this, 0.9 mL of PMDETA was added followed by 0.5 mL of TiCl4 addition to obtain mother liquor. The temperature was set at 70°C with continues stirring. After initiation of reflux, the mother liquor was heated for 5 hours. Then 10 g of calcined silica was added to the mother liquor and again refluxed for 1 hour after which the solvent was dried under nitrogen till free flowing catalyst was obtained. Further, drying of catalyst was continued till the desired THF content was obtained.
Example 1 B: Synthesis of single electron donor catalyst system
Single electron donor containing silica catalyst was prepared following procedure of
example 1A wherein only THF was used as solvent as well as an electron donor.
The compositional and physical characteristics of both the catalysts are shown in Table -
1.
Table - 1: Chemical and physical characteristics of mixed and single electron donor
catalyst system

Catalyst characteristics Unit Mixed Electron Donor catalyst system Single electron donor catalyst system
Composition
Ti, wt% Wt% 1.4 1.5

Mg, wt%
Wt% 2.1 2.2
CI, wt% Wt% 11.1 11.3
THF, wt% Wt% 6.0 6.0
PMDETA Wt% 5.1 Nil
Physical characteristics
Surface area M2/g 178 180
Porosity mL/g 0.9 0.9
Mean PS Micron 48 47
The study indicated that PMDETA can be used in addition to THF without affecting other compositional elements of the catalyst system. The obtained mixed electron donor catalyst system shows comparable physical characteristics such as surface area, porosity and mean particle size with respect to single electron donor catalyst system.
Example 2 A: Polymerization performance of mixed electron donor catalyst system
A stainless steel autoclave (450 ml) equipped with mechanically stirrer was heated at 120 °C for 1 hour and cooled to 40 °C under nitrogen steam venting to remove moisture and impurities. An autoclave was rinsed with n-hexane with tri-n-octyl aluminum to remove solvent impurities. To the rinsed autoclave a solution of 150 ml of n-hexane and tri-n-octyl aluminum was added. The solution was saturated with ethylene. Later, mixed electron donor catalyst system (as prepared in example 1 A) and tri-n-octyl aluminum in n-hexane was added into the autoclave. The co-catalyst (tri-n-octyl aluminum) was added

to maintain Al/Ti molar ratio of 200 + 10 followed by raising reactor temperature to 80 °C. Polymerization reaction was carried out for 1 hr. At the end of the polymerization, the un-reacted ethylene was vented and the reaction was quenched with acidic methanol and filtered. After filtration, polymer was washed with methanol (70 ml) and then dried at 60 °C under vacuum to till constant weight was obtained. Productivity was calculated based on amount of polymer synthesized and catalyst added for polymerization. Bulk density was calculated by standard methodology. Polymer molecular weight was determined by gel permeation chromatography (GPC) using Polymer Laboratory's PL-GPC220 High Temperature Chromatograph instrument (columns: 3 PL gel Mixed-BlO mm) with two detectors (viscometer and refractometer) in 1,2,4- trichlorobenzene at flow rate of 1 mL/ min at 160 °C. The system was calibrated with polystyrene standards using universal 80 calibration.
Example 2 B: Polymerization performance of single electron donor catalyst system
Polymerization performance of single electron donor catalyst system was studied as per example 2 A using the single electron catalyst of example IB.
The compositional and physical characteristics of polyethylene prepared by using both the catalyst systems are shown in Table -2
Table - 2: Chemical and physical characteristics of polyethylene prepared by using mixed and single electron donor catalyst system

Catalyst characteristics Unit PE prepared by Mixed
Electron Donor catalyst
system PE prepared by Single electron donor PE catalyst
Productivity gPE/gcat 150 340
Resin Bulk Density g/cc 0.34 0.37
Mnx 10"4 g/gmol 2.6 1.8
Mwx 10° g/gmol 3.7 1.9
MWD Mw/Mn 14.1 10.8
Results indicated broad molecular weight distribution of polyethylene with increase of number average molecular weight (Mw) for mixed electron donor catalyst system compared to single electron donor catalyst system. Productivity of electron donor catalyst system was lower compared to single electron donor catalyst system. Bulk density remained unchanged in both the cases.
Example 3: Effect of temperature on polymerization and product performance of mixed electron donor catalyst system.
Polymerization procedure as described in example-2A was followed for mixed electron donor catalyst system at reaction temperatures 80 °C, 90 °C and 110 °C. Molecular weight study and bulk density was also determined. Results are described in Table-3.
Table - 3: Polymerization and product performance of mixed electron donor catalyst system at 80, 90 and 110 °C.

Temp Activity (gPE/gcat) GPC BD
(g/cc)
(°Q
Mn x 10-4 Mw x 10-5 MWD

80 150 2.6 3.7 14.1 0.34
90 51 1.3 2.2 16.9 0.34
110 32 0.9 2.0 22.9 0.12
Reduction in polymerization activity was observed with increase in reaction temperature. This is desirable in gas phase polymerization. Such characteristics - also called self extinguishing characteristics - will help to reduce reactor fouling due to run away reaction. Polydispersity also indicated broadening trend with increase in reaction temperature. From the result it was also observed that at 110 °C there is a formation of amorphous type polymer which is reflected by reduction in bulk density.
Example 4: Effect of change of proportion of THF/PMDETA on polymerization performance
Effect of change of proportion of THF/PMDETA on polymerization performance was studied and the results are provided in Table-4.
Table - 4: Polymerization performance of two different mixed electron donor catalyst

Cat
THF
(gm) PMDETA (gm) Activity (gPE/gcat) GPC BD
(g/cc)

Mn x 104 Mw xlO-
5 MWD

1 6.0 5.1 150 2.6 3.7 14.1 0.34
2 7.5 2.9 210 2.1 2.6 12.0 0.32
Results indicated that polymerization activity increases with reduction of PMDETA content. Further, it was found that the polydispersity decreases with reduction of PMDETA content. It is probably due to different steric and electronic environment exerted by PMDETA around active titanium sites leading to change of polymerization performance and product properties.
Technical Advancement:
The molecular weight of polyethylene produced by the catalyst of present disclosure i.e a
catalyst system comprising a combination of THF and PMDETA as electron donor is 370000 g/mol as against 190000 g/mol when only THF is used as an electron donor.
The catalyst prepared by the method of the present disclosure provides choice on performance and properties of the resulting polymer.
The catalyst of the present disclosure broadens the molecular weight distribution of polyethylene as compared to the polyethylene produced by the catalyst of prior art.
The catalyst of the present disclosure also provides a control on polymerization kinetics at higher temperature which can avoid reactor fouling in gas phase process.

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 example only, and are not intended to limit the scope of the inventions. Variations or modifications to the design and construction 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 accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the 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 and the claims unless there is a statement in the specification to the contrary.

We Claim:
1. A catalyst system for polymerization of ethylene; said catalyst system comprising:
(A) a procatalyst comprising
i) electron donor comprising Tetrahydrofuran (THF) and N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA); ii) titanium tetrachloride and magnesium dichloride; and iii) a silica support, and
(B) a cocatalyst
2. The catalyst system as claimed in claim 1, wherein the said electron donor comprises N,N',N',N",N"-pentamethyldiethylenetriamine (PMDETA) ranging between 30 and 50 weight % of the total mass of the electron donor and tetrahydrofuran (THF) ranging between 50 and 70 weight % of the total mass of the electron donor.
3. The catalyst system as claimed in claim 1, wherein the amount of electron donor is in the range of about 8 to 14 % of the total mass of the catalyst system
4. The catalyst system as claimed in claim 1, wherein the cocatalyst is tri alkyl aluminum, preferably tri-n-octyl aluminum
5. The catalyst system as claimed in claim 1, wherein the mole ratio of cocatalyst to procatalyst is 1 to 5, preferably 1 to 1.25

6. The catalyst system as claimed in claim 1, wherein the amount of titanium is in the
range of about 1.0 to 2.0 % of the total mass of the catalyst system.
7. The catalyst system as claimed in claim 1, wherein the amount of magnesium is in the
range of about 1.5 to 2.5 % of the total mass of the catalyst system.
8 The catalyst system as claimed in claim 1, wherein the amount of chlorine is in the range of about 10.0 to 13.0 % of the total mass of the catalyst system.
9. A method for preparing a catalyst system for polymerization of ethylene; said method
comprising the following steps:
a) subjecting silica to calcination to obtain a calcined silica;
b) preparing a homogenous mother liquor comprising MgCl2, TiCl4, tetrahydrofuran (THF) and N,N,,N',N",N"-pentamethyldiethylenetriamine (PMDETA);
c) adding the calcined silica to the homogenous mother liquor to obtain the catalyst system; and
d) drying the catalyst system to obtain desired amount of electron donor in the catalyst system.
10. The method for preparing the catalyst system as claimed in claim 9, wherein
calcination is carried out at a temperature in the range of about 300 °C to 700 °C,
preferably at 600 °C, for a period of about 3 hours to 7 hours.

11. The method for preparing the catalyst system as claimed in claim 9, wherein the method step of preparing homogeneous mother liquor is carried out at a temperature in the range of about 20 °C to a reflux temperature, preferably at reflux temperature for a period of about 3 hours to 6 hours.
12. The method for preparing the catalyst system as claimed in claim 9, wherein the
method step (c) is carried out under stirring.
13. The method for preparing the catalyst system as claimed in claim 9, wherein the
method step of drying is carried out under nitrogen gas.
14. A polymer obtained using the catalyst system as claimed in claims 1 to 8, wherein
said polymer has molecular weight distribution in the range of 13 to 16.