DESC:FIELD
The present disclosure relates to a Ziegler-Natta catalyst composition and a process for preparing the same.
DEFINITIONS
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 “pre-polymerization” as used in the context of the present disclosure refers to a process wherein a monomer or a system of monomers are reacted to an intermediate molecular mass state. The intermediate state is further capable of being polymerized by reactive groups to a fully cured high molecular weight state.
The term “degree of pre-polymerization” as used in the context of the present disclosure refers to the number of monomeric units present in the pre-polymerized olefin.
The term “polymer-fines” or “polyolefin fines” as used in the context of the present discourse, refers to polymer/ polyolefins having an average particle size below 100 µm.
BACKGROUND
Ziegler-Natta catalyst systems are known for catalyzing the polymerization of olefins. Conventional Ziegler-Natta catalyst systems contain a pro-catalyst and co-catalyst and additionally may comprise other agents such as a selectivity control agent (SCA) and an internal electron donor.
When polymerization takes place on the active sites of the catalyst, localized heat is generated due to an exothermic polymerization reaction which break the catalyst particles and generate fine particles. However, the degree of the breakage or attrition is a function of the inherent strength of the catalyst itself depending primarily on its chemistry, manufacturing process, and precursor used. The resin fines thus generated causes reactor continuity issues leading to the process upsets and operational issues in the fluidized bed reactor.
To overcome the above difficulties, the option of pre-polymerization has been proposed as it imparts additional strength to the catalyst to withstand the thermal effect of reaction, thereby arresting fragmentation of particles, generates less resin fines, leads to reduced resin carry-over and avoids the formation of agglomerates or lumps.
However, the conventional catalyst systems comprising pre-polymerized olefins are expensive, provide unsatisfactory performance for preparing impact grade polymers and do not address polymer fines generation issue. Some of the suggested catalysts are not capable of carrying stable polymerization and are not suitable for the preparation of various grades of polypropylene having uniform property and high quality.
Therefore, there is a need felt for a Ziegler-Natta catalyst composition which overcomes the afore stated drawbacks.
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.
Another object of the present disclosure is to provide a Ziegler-Natta catalyst composition.
Yet another object of the present disclosure is to provide a simple and economical process for preparing a Ziegler-Natta catalyst composition.
Still another object of the present disclosure is to provide a Ziegler-Natta catalyst composition which generates a reduced amount of polyolefin fines.
Other objects of the present invention will be more apparent to a person skilled in the art from the description provided hereinafter.
SUMMARY
The present disclosure relates to Ziegler-Natta catalyst composition capable of polymerizing an olefin and a process for preparing the same.
The Ziegler-Natta catalyst composition comprises at least one transition metal catalyst, at least one pre-polymerized olefin component, and at least one co-catalyst. The Ziegler-Natta catalyst composition optionally comprises at least one selectivity control agent. The degree of pre-polymerization of the component is in the range of 25% to 50%.
The present disclosure further provides the process for the preparation of the Ziegler-Natta catalyst composition. The process comprises admixing the transition metal catalyst in a mineral oil to form a slurry. The co-catalyst and optionally the selectivity control agent are added to the slurry to form a first mixture. Further, the olefin monomer is pre-polymerized in presence of the first mixture to obtain a Ziegler-Natta catalyst composition.
The Ziegler-Natta catalyst composition obtained by the process of the present disclosure is further employed for polymerization of olefin, wherein it is observed that the polyolefin fines generation is reduced. The amount of polyolefin fines generated in the polymerization process of the present disclosure is in the range of 1% to 8%.
DETAILED DESCRIPTION
The Ziegler-Natta catalyst systems are known for catalyzing the polymerization of olefins. When polymerization reaction takes place on the active sites of the catalyst composition, localized heat is generated due to the exothermic polymerization reaction, which results in breakage or fragmentation of the catalyst particles, which further leads to the generation of the polyolefin fines in the reactor.
The present disclosure provides a Ziegler-Natta catalyst composition for polymerization of olefin with reduced generation of polyolefin fines and the process for the preparation of the same.
In accordance with the present disclosure, it is found that the pre-polymerization of at least one olefin monomer in presence of the mixture of the trnsition metal catalyst and co-catalyst results in formation of a catalyst composition comprising Ziegler-Natta catalyst and pre-polymerized olefin component. The pre-polymerized olefin component present in the catalyst composition imparts additional strength to the catalyst to withstand the thermal effect of the exothermic polymerization reactions, thereby arresting fragmentation of the catalyst particles which results in reduced generation of the polyolefin fines.
In one aspect, the present disclosure provides a Ziegler-Natta catalyst composition comprising at least one transition metal catalyst, at least one pre-polymerized olefin component, at least one co-catalyst and optionally at least one selectivity control agent. Typically, the degree of pre-polymerization of the component is in the range of 25% to 50%.
The transition metal catalyst comprises at least one transition metal compound supported on a magnesium precursor. The transition metal compound can be a halide, oxide or alkoxide of the transition metal element. The transition metal element can be selected from the group consisting of scandium, titanium, vanadium, chromium, iron, cobalt, nickel, copper, zirconium, chromium, and palladium. Typically, the transition metal is titanium.
The magnesium compound can be at least one selected from the group consisting of magnesium halides, magnesium dialkoxides, and magnesium diaryloxides. Typically, the magnesium compound is selected from the group consisting of magnesium methoxide, magnesium ethoxide, magnesium iso-propoxide, magnesium n-butoxide, magnesium phenoxide, and combinations thereof.
The pre-polymerized olefin component can be at least one selected from the group consisting of polyethylene and polypropylene.
The co-catalyst can be at least one organo-aluminum compound. Typically, the organo-aluminum compound is at least one selected from the group consisting of triethyl aluminum, tridecyaluminum, tri-n-butyl aluminum, tri-isopropyl aluminum, tri-isoprenyl aluminum, tri-isobutyl aluminum hydride, ethyl aluminumsesquichloride, diethyl aluminum chloride, di-isobutyl aluminum chloride, triphenyl aluminum, tri-n-octyl aluminium, and tri-n-decyl aluminum.
The selectivity control agent can be at least one selected from the group consisting of alkyl benzoate, aryl benzoate, and alkoxy silane.
In another aspect, the present disclosure provides a process for preparing the Ziegler-Natta catalyst composition. The process comprises the steps described below in details:
At least one transition metal catalyst is mixed with a mineral oil in an inert atmosphere under agitation at a speed in the range of 200 rpm to 300 rpm to form slurry. At least one co-catalyst is then added to the slurry to obtain a first mixture. Optionally, at least one selectivity control agent is added to the slurry along with the co-catalyst.
At least one olefin monomer is then introduced in the first mixture and subjected to pre-polymerization in presence of the first mixture under pressure in the range of 0.1 kg/cm2 to 5.0 kg/cm2, and at a temperature in the range of 10 °C to 40 °C, while continuously stirring the resultant mixture at a speed in the range of 200 rpm to 450 rpm to obtain the Ziegler-Natta catalyst composition.
The molar ratio of the co-catalyst to the transition metal catalyst is in the range of 1.5 to 2.0.
The process for the pre-polymerization is carried out at low temperature and low pressure conditions, for controlling reaction kinetics. The controlled reaction kinetics further helps in controlling the initial heat of polymerization which in turn helps in reducing the catalyst attrition or generation of fines.
The conventional processes use organic solvents for pre-polymerization of olefin monomer in presence of Ziegler-Natta catalyst. However, the organic solvents are not downstream process friendly and therefore need to be removed and recovered. On the other hand, the process of the present disclosure does not use any organic solvents and therefore does not involve the solvent removal or the solvent recovery step. The process of the present disclosure has less number of steps, thereby making the process simple and economical.
It is observed that the catalyst composition obtained in accordance with the present disclosure has improved average particle size, improved donor response and catalyst productivity as compared to a non pre-polymerized catalyst.
In still another aspect of the present disclosure, the catalyst composition of the present disclosure is employed for the polymerization of olefins. The polymerization is carried out using gas-phase fluidized bed reactor. The process for the polymerization of olefin comprises contacting at least one olefin monomer with Ziegler-Natta catalyst composition at a temperature in the range of 65 °C to 75 °C and under pressure in the range of 20 kg/ cm2g to 30 kg/ cm2g to obtain polyolefin.
The so obtained polyolefin has an average particle size in the range of 450 to 550 micron and bulk density is in the range of 0.3 to 0.6 gm/ cc.
The generation of the polyolefin fines in the fluidized bed reactor during the polymerization process of the present disclosure is monitored and found to be less than 8%. The percentage of the polyolefin fine produced during the polymerization process is found to be related to the catalyst attrition due to exothermic polymerization reactions. The pre-polymerization of olefin in accordance with the present disclosure provides additional strength to catalyst particles to withstand thermal effects, thereby arresting the fragmentation of the catalyst particles and leading to reduced generation of the polyolefin fines.
The reduced generation of polyolefin fines helps in stable reactor operatability which leads to improved bulk density and overall improved morphology of polyolefin obtained.
The present disclosure is further described in light of the following experiment which is set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following laboratory scale experiment can be scaled up to industrial/commercial scale.
Experiments
Experiment-1: Preparation of the Ziegler-Natta catalyst composition.
The titanium supported on magnesium dichloride (90 Kg) was mixed with mineral oil (510 kg having 10 to 70 cSt at 40°C) under inert atmosphere to form a slurry. Triisobutyl aluminium (15.2 Kg) was added to the slurry to obtain a first mixture. Ethylene monomer was subjected to pre-polymerization in the presence of the first mixture under pressure of 3 bar and at a temperature of 35 °C to obtain Ziegler Natta catalyst composition.
Experiment-2: Polymerization of ethylene monomer
This experiment describes the process of the polymerization of ethylene monomer in the presence of the Ziegler-Natta catalyst composition prepared in accordance with the process described in Experiment-1.
Similar experiment of the polymerization of ethylene monomer was carried out in the presence of the conventional Ziegler-Natta catalyst not containing the pre-polymerised olefin component.
The polymerization was carried out in the gas-phase fluidized bed reactor at a temperature of 68 °C and under pressure of 23.4 kg/ cm2g to obtain polyethylene.
Table 1: The evaluation of the gas phase polymerization using the Ziegler-Natta catalyst composition prepared in accordance with the present disclosure and its comparison with the conventional Ziegler Natta catalyst not containing the pre-polymerised olefin component.
Description Unit Ziegler Natta catalyst composition of the present disclosure Conventional Ziegler Natta Catalyst
Reactor # 1 Reactor # 2 Reactor #1 Reactor #2
Production rate
Productivity
Reactor pressure
C3 partial pressure
C2 partial pressure
Reactor control temperature
H2/C3
C2/C3
TEAL/Ti kg/hr
kg PP/gcat
kg/cm2
kg/cm2
kg/cm2
°C
molar ratio
molar ratio
molar ratio
10-13
9-10
32
23.4
-
68
0.03
-
75
10-13
9-10
21
-
2.5
68
-
0.25
- 10-13
8-9
32
23.4
-
68
0.03
-
75
10-13
8-9
21
-
2.5
68
-
0.25
-

Resin - MFI
Resin -XS
Resin - Fines g/10min
wt%
wt% 23-24
1.4-2.0
6-8 11-12
-
- 23-24
1.4-2.0
14-18 11-12
-
-
*TEAL- Triethyl Aluminum;
The generation of polyolefin fines is reduced by 50 wt% with Ziegler-Natta catalyst composition of the present disclosure as compared to the conventional Ziegler Natta catalyst.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several advantages including, but not limited to, the realization of a process for the preparation of pre-polymerized Ziegler-Natta catalyst for polymerization of olefins, that:
• is simple and economical;
• provides improved catalyst particle size and it’s distribution;
• provides improved polyolefin particle size and it’s distribution;
• reduces generation of polyolefin fines; and
• provides improved plant operability and throughput.
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 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:WE CLAIM:
1. A Ziegler-Natta catalyst composition comprising:
(i) at least one transition metal catalyst;
(ii) at least one pre-polymerized olefin component; and
(iii) at least one co-catalyst;
wherein, the degree of pre-polymerization of said component is in the range of 25% to 50%.
2. The catalyst composition as claimed in claim 1, wherein said transition metal catalyst comprises at least one transition metal compound supported on a magnesium precursor.
3. The catalyst composition as claimed in claim 2, wherein said transition metal compound is a halide, oxide, or alkoxide of the transition metal element.
4. The catalyst composition as claimed in claim 3, wherein said transition metal element is selected from the group consisting of scandium, titanium, vanadium, chromium, iron, cobalt, nickel, copper, zirconium, chromium, and palladium.
5. The catalyst composition as claimed in claim 3 or claim 4, wherein said transition metal is titanium.
6. The catalyst composition as claimed in claim 2, wherein said magnesium precursor is selected from the group consisting of magnesium halides, magnesium dialkoxides, and magnesium diaryloxides.
7. The catalyst composition as claimed in claim 2 or claim 6, wherein said magnesium precursor is selected from the group consisting of magnesium methoxide, magnesium ethoxide, magnesium iso-propoxide, magnesium n-butoxide, magnesium phenoxide, and combinations thereof.
8. The catalyst composition as claimed in claim 1, wherein said pre-polymerized olefin component is at least one selected from the group consisting of polyethylene, and polypropylene.
9. The catalyst composition as claimed in claim 1, wherein said co-catalyst is at least one organo-aluminum compound.
10. The catalyst composition as claimed in claim 9, wherein said organo-aluminum compound is at least one selected from the group consisting of triethyl aluminum, tridecyaluminum, tri-n-butyl aluminum, tri-isopropyl aluminum, tri-isoprenyl aluminum, tri-isobutyl aluminum hydride, ethyl aluminumsesquichloride, diethyl aluminum chloride, di-isobutyl aluminum chloride, triphenyl aluminum, tri-n-octyl aluminium, and tri-n-decyl aluminum.
11. The catalyst composition as claimed in claim 1 further comprises at least one selectivity control agent.
12. The catalyst composition as claimed in claim 11, wherein said selectivity control agent is at least one selected from the group consisting of alkyl benzoate, aryl benzoate, and alkoxy silane.
13. A process for preparing a Ziegler-Natta catalyst composition, wherein said process comprising:
i. admixing at least one transition metal catalyst, and a mineral oil in an inert atmosphere under agitation at a speed in the range of 200 rpm to 300 rpm to form a slurry;
ii. adding at least one co-catalyst, and optionally at least one selectivity control agent to said slurry to obtain a first mixture;
iii. pre-polymerizing at least one olefin monomer in the presence of said first mixture under pressure in the range of 0.1 kg/cm2 to 5.0 kg/cm2, at a temperature in the range of 10 °C to 40 °C., and under continuous stirring at a speed in the range of 200 rpm to 450 rpm to obtain the Ziegler-Natta catalyst composition.
14. The process as claimed in claim 13, wherein the molar ratio of said co-catalyst to said transition metal catalyst is in the range of 1.5 to 2.0.
15. A process for polymerizing olefin in the presence of said Ziegler-Natta catalyst composition as claimed in claim 1, said process comprising contacting at least one olefin monomer with said Ziegler-Natta catalyst composition, in a gas-phase fluidized bed reactor, at a temperature in the range of 65 °C to 75 °C, and pressure in the range of 20 kg/ cm2g to 30 kg/ cm2g to obtain polyolefin,
wherein the amount of the polyolefin fines generated is in the range of 1% to 8%.
16. The polyolefin obtained by the process as claimed in claim 15, said polyolefin being characterized by having an average particle size in the range of 450 to 550 micron and bulk density in the range of 0.3 and 0.6 gm/ cc.