Heterogeneous Ziegler-Natta Catalyst Composition, A Process For Its Preparation And A Process For Polymerizing Olefin Using The Same (Reliance industries)

CATEGORY: OLEFINS
Heterogeneous Ziegler-Natta Catalyst Composition, A Process For Its Preparation And A Process For Polymerizing Olefin Using The Same (Reliance industries)
United States Patent Application 20160347881
Patil; Yogesh Popatrao ;   et al.   December 1, 2016
Applicant: Reliance industries (India)
Abstract
The present disclosure provides a Ziegler-Natta catalyst composition for preparing polymers of ethylene monomers having ultrahigh molecular weight, said composition comprises (i) a pro-catalyst component containing a reaction product of a magnesium containing compound and a titanium containing compound, characterized in that said pro-catalyst component comprises magnesium, titanium and chlorine in an amount ranging between 15 and 18 mole %; 20 and 23 mole %; and 60 and 64 mole %, respectively, all proportions being with respect to the total weight of the Ziegler-Natta catalyst composition; (ii) a co-catalyst component; and (iii) at least one external electron donor compound selected from the group of organosilane compounds having the general formula (I), wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are all the same or all are different, or some are the same, and are individually selected from the group consisting of linear or branched alkyl groups, cycloalkyl groups, aryl groups, alkoxy and aryloxy groups. ##STR00001##
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates to a Ziegler-Natta catalyst composition and a process for its preparation. The present disclosure further relates to a process for preparing polyolefins having Ultrahigh Molecular Weight by using the Ziegler-Natta catalyst composition of the present disclosure.
BACKGROUND
[0002] Polyolefins with molecular weight higher than 1.times.10.sup.6 g/mol are generally termed as Ultrahigh Molecular Weight (UHMW) polyolefins. Ultrahigh Molecular Weight Polyethylene (UHMWPE) is known to demonstrate excellent toughness and high impact strength. This is mainly due to the presence of long and linear polymeric chains, as longer chains serve to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions.
[0003] UHMWPE with porous morphology and enhanced crystallinity complimented with reduced chain entanglement property is an example of another commercially desired polymer. Conventionally, it is prepared by ethylene polymerization catalyzed by metallocene or non-metallocene type homogeneous catalyst compositions, also known as single site catalyst compositions. The homogenous catalyst compositions mainly contain transition metal complexes such as complexes of Titanium (Ti), Zirconium (Zr), Hafnium (Hf) metals and the like. For activation of these homogenous single site catalyst compositions, relatively larger quantities of costly co-catalyst components such as methylaluminoxane are required. The use of relatively larger quantities of co-catalyst components results in less kinetic control and consequently reactor fouling by generation and deposition of polymer lumps on the reactor unit walls and stirrer shaft/paddle assembly. The use of a homogeneous catalyst composition, therefore, leads to increased polymerization cost.
[0004] Conventionally, heterogeneous Ziegler-Natta catalyst compositions based on titanium, magnesium and organo-aluminum co-catalyst have been developed. Since their inception till date, several modifications in the Ziegler-Natta catalyst compositions have been proposed in order to obtain specific properties in polymers, which are desired for specific applications.
[0005] The activity of these catalyst compositions to a great extent depends on the stability of Titanium (Ti.sup.+3)/(Ti.sup.+2) ion geometry, which is responsible for the growth of the polymer chain during the polymerization process. To improve the stability of Titanium (Ti.sup.+3)/(Ti.sup.+2) ion in the catalyst composition, electron donors are preferably added, either before the activation of the pro-catalyst component (internal electron donors) or after the activation of the pro-catalyst component (external electron donor). A variety of compounds have therefore been explored as internal and external electron donors for modification of heterogeneous Ziegler-Natta catalyst compositions.
Existing Knowledge:
[0006] U.S. Pat. No. 4,962,167 suggests a process for preparing an ultrahigh molecular weight polyethylene having narrow particle size distribution by polymerizing ethylene monomers in the presence of a catalyst composition comprising a solid catalyst component and an organometallic compound. The solid catalyst component as disclosed in the aforementioned US patent is obtained by contacting component A and component B, wherein component A is a reaction product of a magnesium dihalide and a titanium alkoxide and component B is a reaction product of an aluminum trihalide and a silicon alkoxide compound.
[0007] U.S. Pat. No. 6,559,249 suggests a process for preparing an ultrahigh molecular weight polyethylene with large bulk density and narrow particle size distribution by using an organometallic compound and a catalyst component. The catalyst component is prepared by reacting (i) a mixture of halogenated magnesium compound and an aluminum or a boron compound with alcohol to produce a magnesium compound, (ii) reacting the magnesium compound with an ester compound having at least one hydroxyl group and a silicon compound having an alkoxy group; and (iii) reacting the obtained reaction mixture with a titanium compound and a silicon compound. In the aforementioned US patent, esters and silane compounds are used as electron donors.
[0008] United States Patent Publication No. 2011159287 suggests a process for preparing ultrahigh molecular weight polyethylene by using a Ziegler-Natta catalyst composition that comprises a solid catalyst component obtained by reacting a magnesium compound, a titanium compound and an organo aluminum halogen compound, and a co-catalyst component. The use of external electron donors such as alcohols, ethers, esters, silanes and amines is also mentioned. However, the aforementioned United States Patent documents and patent application disclose the preparation of relatively dense ultrahigh molecular weight polyethylene with remarkably less porosity.
[0009] European Patent No. 0159110 suggests ultrahigh molecular weight polyolefin fine powders by using a specified Ziegler catalyst composition. The Ziegler catalyst used in the process of the aforementioned EP patent is prepared according to the teachings of Japanese Laid-open patent application 811/81 by reacting magnesium chloride and titanium chloride at low temperature and thereafter adding a small amount of monocarboxylate such as benzoate at high temperature. The aforesaid European patent document talks about the ultrahigh molecular weight polyethylene having a specified particle diameter and a specified particle size distribution and which is easily processable. However, the aforesaid European patent document is silent on the manufacturing of ultrahigh molecular polyethylene with improved porosity and crystallinity, and with flaky morphology.
[0010] Korean Patent No. 101161752 suggests a method for preparing an ultrahigh molecular weight polyethylene having high productivity and high apparent density (bulk density) by using a Ziegler-Natta catalyst composition. Though, the aforesaid Korean patent discloses the use of a heterogeneous Ziegler-Natta catalyst composition for the production of ultrahigh molecular weight polyethylene, it is silent on the production of ultrahigh molecular weight polyethylene having improved porosity and crystallinity, and flaky morphology.
[0011] Another Korean Patent No. 101144513 suggests an ultrahigh molecular weight polyethylene attributed with narrow molecular weight distribution which is prepared by polymerizing ethylene monomers in the presence of a heterogeneous Ziegler-Natta catalyst composition comprising a reaction product of a magnesium alcoholate, a titanium halide, an organoaluminum compound and an organo-silane compound. However, the aforesaid Korean patent document is also silent on the manufacturing of ultrahigh molecular weight polyethylene having improved porosity, crystallinity, and flaky morphology.
[0012] PCT Publication No. 2013087185 suggests a process for preparing ultrahigh molecular weight polyethylene with high powder bulk density by using a Ti--Mg based heterogeneous Ziegler-Natta catalyst composition. The ultrahigh molecular weight polyethylene as suggested in the aforesaid PCT document is dense in nature and characterized with poor crystallinity and porosity.
[0013] From the forgoing description, it is evident that though a number of records pertaining the production of ultrahigh molecular weight polyethylene using heterogeneous Ziegler-Natta catalyst compositions have been suggested, but none of these documents disclose the use of heterogeneous Ziegler-Natta catalyst compositions which when used in the production of polyolefins gives kinetically controlled polymerization reaction to provide polyolefins with significantly improved molecular weight along with flaky morphology, enhanced porosity and crystallinity, and lower to moderate bulk density, which are otherwise obtained by the use of expensive single-site homogeneous catalyst compositions.
[0014] Therefore, there is felt a need to provide a heterogeneous Ziegler-Natta catalyst composition which is an economic alternative to the existing expensive single site homogeneous catalyst system for the production of polyethylene having ultrahigh molecular weight and with porous and flaky morphology.
Objects:
[0015] Some of the objects of the present disclosure are described herein below:
[0016] 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.
[0017] Another object of the present disclosure is to provide a heterogeneous Ziegler-Natta catalyst composition with modified properties for producing polymers of ethylene monomers having ultrahigh molecular weight, increased intrinsic viscosity, enhanced porosity and crystallinity, lower to moderate bulk density and reduced chain entanglement.
[0018] Still another object of the present disclosure is to provide a heterogeneous Ziegler-Natta catalyst composition with better control on the polymerization process thereby obtaining a polymer of ethylene monomers with the desired bulk density and without reactor fouling.
[0019] Yet another object of the present disclosure is to provide a process for the preparation of heterogeneous Ziegler-Natta catalyst composition.
[0020] A further object of the present disclosure is to provide polymers of ethylene monomers having ultrahigh molecular weight, increased intrinsic viscosity, lower to moderate bulk density and having a unique flaky morphology with enhanced porosity, and reduced chain entanglement.
[0021] A still further object of the present disclosure is to provide a process for preparing polymers of ethylene monomers having ultrahigh molecular weight by using a heterogeneous Ziegler-Natta catalyst composition of the present disclosure.
[0022] A yet further object of the present disclosure is to provide a process for preparing polymers of ethylene monomers having ultrahigh molecular weight by using a heterogeneous Ziegler-Natta catalyst composition of the present disclosure that employs relatively lesser amounts of a co-catalyst component as compared to the conventional polymerization processes that employ single site catalyst compositions.
[0023] Another object of the present disclosure is to provide a process for preparing polymers of ethylene monomers having ultrahigh molecular weight, wherein the process is simple, cost-efficient and that eliminates the risk of polymerization unit fouling.
[0024] 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.
DEFINITIONS
[0025] 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.
[0026] The term "American Society for Testing and Materials (ASTM)" in the context of the present disclosure refers to a standard used to calculate molecular weight of polyolefins from measured intrinsic viscosity.
[0027] The term "intrinsic viscosity" in the context of the present disclosure refers to the intrinsic viscosity of the polymer of ethylene monomers having ultrahigh molecular weight, as measured by a standard method ASTM-D 4020-01a. The measured intrinsic viscosity of the polymer of ethylene monomers having ultrahigh molecular weight is used to calculate the molecular weight of the polymer of ethylene monomers having ultrahigh molecular weight, based on the intrinsic viscosity of a 0.02% solution in decalin at 135.degree. C. and using the equation M=K[{acute over (.eta.)}].sup..alpha.; where {acute over (.eta.)} is the intrinsic viscosity, K=53700 and .alpha.=1.37.
[0028] The term "crystallinity" in the context of the present disclosure refers to the degree of structural order in the polymers of ethylene monomers having ultrahigh molecular weight. The crystallinity of the polymer of ethylene monomers having ultrahigh molecular weight is represented by a fraction or percentage as a measure of how effectively and systematically the polymer chains are aligned or stacked. The crystallinity of the polymer of ethylene monomers having ultrahigh molecular weight is measured by using Differential Scanning calorimetry (DSC). A standard value of 290 J/g for highly crystalline polyethylene (as reported in literature) is used to compute the % crystallinity of the polymer of ethylene monomer having ultrahigh molecular weight. The results are also validated through XRD techniques.
[0029] The term "bulk density" in the context of the present disclosure refers to the "apparent density" and is measured as per ASTM D-1895-96. Apparent density is a measure of the fluffiness of a material. It is the weight per unit volume of a material, including voids inherent in the material as tested.
SUMMARY
[0030] In accordance with one aspect of the present disclosure there is provided a Ziegler-Natta catalyst composition for preparing polymers of ethylene monomers having ultrahigh molecular weight, said composition comprising: [0031] i. a pro-catalyst component containing a reaction product of a magnesium containing compound and a titanium containing compound, characterized in that said pro-catalyst component comprises magnesium, titanium and chlorine in an amount ranging between 15 and 18 mole %; 20 and 23 mole %; and 60 and 64 mole %, respectively, all proportions being with respect to the total weight of the Ziegler-Natta catalyst composition; [0032] ii. a co-catalyst component comprising at least one organoaluminum compound; and [0033] iii. at least one external electron donor compound selected from the group of organosilane compounds having the general formula (I),
[0033] ##STR00002## [0034] wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are all the same, or all are different, or some are the same, and are individually selected from the group consisting of linear or branched alkyl groups, cycloalkyl groups, aryl groups, alkoxy and aryloxy groups.
[0035] In one embodiment of the disclosure, the molar ratio of magnesium, titanium and chlorine is 1:1.3:3.7.
[0036] In one embodiment of the present disclosure, the magnesium containing compound can be selected from a magnesium alkoxide and a magnesium halide.
[0037] The magnesium containing compound can be selected from magnesium ethoxide and magnesium chloride.
[0038] The titanium containing compound can be a titanium halide.
[0039] In one embodiment the titanium containing compound is titanium tetrachloride. The aluminum to titanium molar ratio can range from 50:1 to 100:1.
[0040] The silicon to titanium molar ratio can range from 1:1 to 4:1.
[0041] In accordance with another aspect of the present disclosure there is provided a process for preparing a Ziegler-Natta catalyst composition of the present disclosure, said process comprising the following steps: [0042] i. reacting a pre-determined weight proportion of at least one magnesium containing compound and at least one titanium containing compound at elevated temperature and pressure for a pre-determined period of time to obtain a pro-catalyst component, wherein at least one of the titanium containing compound and the magnesium containing compound is also a chloride compound; [0043] ii. isolating said pro-catalyst component; [0044] iii. adding a pre-determined weight proportion of an organoaluminum compound to an inert hydrocarbon liquid medium to obtain a mixture; [0045] iv. adding to said mixture, said pro-catalyst component and agitating the obtained mass for a pre-determined period of time to obtain a mass containing an activated pro-catalyst component; and [0046] v. adding a pre-determined weight proportion of at least one external electron donor compound to the mass and agitating further for a pre-determined period of time to obtain a Ziegler-Natta catalyst composition.
[0047] The magnesium and titanium containing compounds can be in amounts sufficient for obtaining the Ziegler-Natta catalyst composition having 15 to 18 mole % of magnesium, 20 to 23 mole % of titanium, and 62 to 64 mole % of chlorine, based on the total weight of the Ziegler-Natta catalyst composition.
[0048] The orgaoaluminum compound can be added in an amount sufficient for obtaining the Ziegler-Natta catalyst composition having aluminum to titanium molar ratio in the range of 50:1 to 100:1.
[0049] The external electron donor compound can be an organosilane compound of the general formula (I),
##STR00003##
wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are all the same, or all are different, or some are the same, and are individual selected from the group consisting of linear or branched alkyl groups, cycloalkyl groups, aryl groups, alkoxy and aryloxy groups.
[0050] The organosilane compound can be added in an amount sufficient for obtaining the Ziegler-Natta catalyst composition having silicon to titanium molar ratio in the range of 1:1 and 4:1.
[0051] In accordance with another aspect of the present disclosure, there is provided a process for polymerization of ethylene monomers in the presence of the Ziegler-Natta catalyst composition of the present disclosure, said process comprising the following steps:
[0052] contacting ethylene monomers with a Ziegler-Natta catalyst composition of the present disclosure under polymerization reaction conditions of temperature ranging from 50 to 80.degree. C., ethylene pressure ranging from 1 to 15 bars for a time period ranging from 1 to 5 hours and with agitation speed ranging from 300 to 1000 revolutions per minutes (rpm) to obtain a polymer of ethylene having ultrahigh molecular weight.
[0053] In accordance with yet another aspect of the present disclosure, there is provided a polymer of ethylene monomers having ultrahigh molecular weight prepared in accordance with the polymerization process of the present disclosure, said polymer of ethylene monomers is characterized with a molecular weight ranging from 2 to 13 million g/mole; an intrinsic viscosity ranging from 18 to 54 dl/g; a bulk density ranging from 0.1 to 0.3 g/cc; crystallinity ranging from 50 to 70%; and a porous and flaky morphology.
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