DESC:FIELD
The present disclosure relates to a process for preparing a bimetallic catalyst.
BACKGROUND
Homogeneous catalyst systems are commercially used in ethylene polymerization which mainly consists of titanium tetrachloride and vanadium oxytrichloride. It has been observed that, the presence of vanadium in the catalyst system produces a dull colored polymerization product.
Recently, the commercial homogeneous catalyst system has been replaced by magnesium dichloride supported bimetallic catalyst system. In magnesium dichloride supported bimetallic catalyst, vanadium is replaced by zirconium/hafnium.
Conventionally known processes for the preparation of magnesium dichloride (MgCl2) based bimetallic catalyst system requires a step of filtration of undissolved magnesium dichloride produced during the catalyst synthesis. The undissolved magnesium dichloride support creates mass transfer as well as chemical limitation during the polymerization process by blocking some of the polymerization centers and leads to approximately 1-10% lower production of polymer.
Therefore, there is felt a need for a simple and cost effective process for preparing a bimetallic catalyst, which obviates the filtration step.
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.
Another object of the present disclosure is to provide a simple and cost effective process for preparing a bimetallic catalyst.
Still another object of the present disclosure is to provide a process for the polymerization of olefin using the bimetallic catalyst.
Yet another object of the present disclosure is to provide a bimetallic catalyst for polymerization of olefin with comparatively high yield.
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 relates to a process for preparing a bimetallic catalyst comprising the step of reacting at least one magnesium alkoxide, at least one first metal halide, and optionally at least one organic acid in a first fluid medium to obtain a first reaction mixture. The so obtained first reaction mixture is treated with at least one second metal halide other than the first metal halide and optionally with at least one organic acid to obtain a second reaction mixture containing a pro-catalyst. The so obtained second mixture containing the pro-catalyst is homogenous and transparent and hence does not require filtration. The pro-catalyst from said second reaction mixture is alkylated with at least one alkylating agent in a second fluid medium to obtain the bimetallic catalyst. The bimetallic catalyst has comparatively higher activity during the polymerization of olefin.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A process for the preparation of a bimetallic catalyst will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates an X-ray diffraction pattern of a commercially available MgCl2 as a support (A) and in-situ generated MgCl2 as a support (B) in accordance with the present disclosure.
DETAILED DESCRIPTION
Bimetallic catalyst systems can be prepared by two methods depending on the method of introduction of MgCl2. In one of the methods, commercially available MgCl2 is used as a support for preparing the bimetallic catalyst. The main drawback of using commercially available MgCl2 support is that, it does not completely dissolve in the organic solvent (which is a necessary step for impregnation of metal species onto the support) and needs to be filtered out. Further, commercial magnesium dichloride is very hygroscopic in nature and hence, difficult to obtain in a totally dehydrated form. The presence of even traces of moisture in magnesium dichloride leads to precipitation and formation of magnesium oxide.
Whereas, in the second method MgCl2 is generated in-situ by reacting magnesium alkoxide (dialkyl Magnesium,Mg(OR)2/Grignard reagent) and a chlorinating agent (TiCl4, HfCl4, alkyl chloride or HCl) during the catalyst preparation. In the second method, a magnesium source is heated with a chlorine source to give MgCl2 support. However, this method necessarily requires filtration of the undissolved MgCl2.
Therefore, the present disclosure envisages a simple and cost effective process for the preparation of bimetallic catalyst which does not require the step of filtration of MgCl2. The process is described in detail:
In the first step, at least one magnesium alkoxide, at least one first metal halide, and optionally at least one organic acid is reacted in a first fluid medium. The reaction mixture is stirred at a speed ranging from 200 rpm to 500 rpm, at a first predetermined temperature greater than 40 oC to obtain a first reaction mixture.
In one embodiment, the magnesium alkoxide can be at least one selected from the group consisting of magnesium methoxide, magnesium ethoxide, magnesium propoxide, magnesium butaoxide and the like. Magnesium alkoxide can be referred to as a precursor. An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. Alkoxide is represented by the general formula RO-, where R is the organic substituent.
The alkoxide used in the present disclosure can be at least one selected from the group consisting of C1-C5 carbon containing alcohols. In an exemplary embodiment the alcohol is ethanol and methanol.
The first metal halide can be at least one selected from the group consisting of halides of titanium, hafnium, zirconium, iron, nickel, cobalt, and palladium. In accordance with the embodiments, the first metal halide can be at least one selected from the group consisting of titanium tetrachloride, hafnium tetrachloride and zirconium tetrachloride and the like.
The first fluid medium in accordance with the present disclosure can be at least one selected from the group consisting of chlorobenzene, bromobenzene, iodobenzene, dichlorobenzene, trichlorobenzene, dibromobenzene, tribromobenzene, hexane, heptane, decane, and the like. In an exemplary embodiment, dry chlorobenzene is used as the first fluid medium.
The first predetermined temperature can be in the range of 70 oC to 100 oC.
In one embodiment the metal halide is dissolved in the first fluid medium and added into magnesium alkoxide to obtain the first reaction mixture.
During the reaction of magnesium alkoxide with metal halide in the first fluid medium, metal-halide-alkoxy species are generated as a side product which helps in the solubilization of in-situ generated magnesium dichloride. Generally, solubilization of commercial magnesium dichloride is achieved by using magnesium dichloride-alcoholate product.
In-situ generation of magnesium dichloride from magnesium alkoxide, as disclosed in the process of the present disclosure leads to distorted d- MgCl2 structure which results in better active site incorporation. Figure 1 illustrates the X-ray diffraction pattern of a commercially available MgCl2 as a support (A) and in-situ generated MgCl2 as a support (B) in accordance with the present disclosure.
The distorted d-MgCl2 structure is achieved by reaction of magnesium alkoxide (MgCl2.xEtOH) with metal tetra chroride and dialkyl aluminum chloride. d-MgCl2 has a comparatively higher degree of crystallographic disordered structure, which is required for higher performance of the catalyst.
The ratio of the amount of magnesium alkoxide to the amount of the metal halide can be in the range of 0.3 to 6.0.
The organic acid used in the process of the present disclosure can be selected from the group consisting of pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, decanoic acid dodecanoic acid, and derivatives thereof. Typically, hexanoic acid is used for the solublization of solid components
The mole ratio of the amount of organic acid to magnesium alkoxide used in the process of the present disclosure can be in the range of 1 to 10.
In the second step of the process of the present disclosure, the first reaction mixture obtained in the first step is cooled to a temperature in the range of 25 to 40 oC to obtain a cooled mixture. The cooled mixture is then reacted with at least one second metal halide other than said first metal halide and optionally with at least one organic acid at a second predetermined temperature greater than 40 oC, followed by cooling to a temperature to obtain a second reaction mixture containing a pro-catalyst.
The second predetermined temperature can be in the range of 70 oC to 100 oC. The so obtained pro-catalyst in the said second reaction mixture is homogeneous and transparent and hence the filtration step can be omitted, which results in saving the process time and the operational cost. Further, the completely soluble pro-catalyst allows proper distribution of the active metal species on the pro-catalyst.
The so obtained second reaction mixture containing the pro-catalyst is cooled to a temperature in the range of 25-40 oC.
The organic acid used in the process of the present disclosure can be selected from the group consisting of pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, decanoic acid dodecanoic acid and derivatives thereof. Typically, hexanoic acid is used for the solublization of solid components.
In one embodiment of the present disclosure organic acid is not used when TiCl4 is used as the metal halide. In one embodiment the organic acid is used only in the first step of the process of the present disclosure. In another embodiment the organic acid is used only in the second step of the process of the present disclosure.
The mole ratio of the amount of magnesium alkoxide to the metal halide used in the process of the present disclosure can be in the range of 0.01 to 1.0.
In the third step of the process of the present disclosure, the cooled second mixture containing the transparent pro-catalyst is reacted with at least one alkylating agent in a second fluid medium at a third predetermined temperature greater than 40 oC to obtain the bimetallic catalyst. In one embodiment the pro-catalyst is precipitated out by adding an alkylating agent. The precipitation method usually produces a uniform distribution of metal species on the catalyst support. The higher activity achieved is the result of better utilization of the active species in forming the polymerization centers.
The process of alkyalation is required for reducing the oxidation state of the active catalyst from M4+ to M3+, where ‘M’ can be Titanium, Hafnium or Zirconium. The third predetermined temperature can be in the range of 70 oC to 100 oC.
The alkylating agent can be at least one selected from the group consisting of alkyl aluminum halide and alkyl aluminum. The alkyl aluminum halide can be selected from the group consisting of diethyl aluminum chloride (DEAC) and isobutyl aluminum dichloride (IBADIC). The alkyl aluminum can be selected from the group consisting of triethyl aluminum, triisobutyl aluminum and trioctyl aluminum. The amount of alkylating agent cn be in the range of 1wt% to 30 wt%.
The second fluid medium used for dissolving the alkylating agent can be selected from the group consisting of decane, pentane, hexane, heptane, and chlorobenzene.
In an exemplary embodiment, the alkylating agent is alkyl aluminum halide or alkyl aluminum.
In one of the embodiments, the alkylating agent is dissolved in a dry fluid medium and added dropwise into the reaction mixture.
After 2 hours, the reaction in the third step can be stopped and the reaction mixture can be allowed to cool and settle. After 2 hours of reaction, the color of the reaction mixture changes which is an indication of the change in the transition state of the metal and also the completion of the reaction. The cooled reaction mixture is decanted and washed with dry hexane 4-5 times. The dry hexane is removed by decantation. The solid mass left is dried under inert atmosphere (nitrogen gas) to obtain a dry solid catalyst (PESOL).
In another aspect of the present disclosure, a process for the polymerization of olefin is provided. The process involves polymerization of olefin in the presence of a bimetallic catalyst. The polymerization process in the presence of the bimetallic catalyst of the present disclosure has higher productivity.
In the present process, in-situ magnesium dihalide (MgCl2) is generated as a homogeneous mixture as a result of the reaction between magnesium alkoxide and metal halide. In-situ generated magnesium dichloride does not have the problem of precipitation associated with the commercial magnesium chloride.
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 provided herein below can be scaled up to industrial/ commercial scale.
Experimental Details:
Experiments:
Experiment 1 below describes a process for the preparation of the bimetallic catalyst of the present disclosure. A comparative study was carried out with respect to TiCl4/VOCl3 homogenous catalyst and the present catalyst; and
Experiment 2 below describes the polymerization performance of the bimetallic catalyst system in accordance with the present disclosure.

Experiment 1: Preparation of bimetallic catalyst in accordance with the present disclosure
In the first step, 9.0 mmoles of magnesium alkoxide (referred as precursor - containing 21.2 wt% magnesium, 71.7 wt% ethoxy and 6.6 wt% methoxy content) was reacted with 18.4 mmoles of TiCl4 which was dissolved in 60 ml of dry chlorobenzene. The reaction mixture containing magnesium alkoxide and TiCl4 was heated to 90 oC for 1 hour to obtain a first reaction mixture.
In the second step, 1.1 mmoles of HfCl4 and 30.0 mmoles of hexanoic acid were directly added in the first mixture obtained in the first step. The addition of hexanoic acid to HfCl4 was carried out at 30 oC. After addition of HfCl4, the reaction mixture was again heated at 90 oC for 1 hour and cooled to a temperature of 30 oC to obtain a second reaction mixture.
In the third step, 129 mmoles (16.2 ml) of diethyl aluminum chloride (DEAC) were dissolved in decane. Dissolved DEAC was added dropwise to the reaction mixture obtained in the second step. After addition of DEAC, the reaction mixture was heated at 90 oC for 2 hours, followed by cooling at 30 oC and allowed to settle. The solvent was removed by decantation and the solid was washed with dry hexane for 4 times. Hexane was removed by decantation and the solid was dried to obtain powdered catalyst PESOL-1.
Similarly, PESOL-2 & 3 were synthesized by varying the quantity of the reactants and sequence of addition of the reactants. A comparative catalyst was synthesized using commercially available MgCl2 support in decane.
Various catalysts were prepared by the process of the present disclosure by varying the reactant quantities and the sequence of addition as summarized in Table 1.
Table-1: composition and reactant ratios of pro-catalyst, commercial TiCl4/VOCl3 homogenous catalyst and the catalyst of the present disclosure (PESOL)

Catalyst Examples TiCl4/ precursor (mole ratio) HfCl4/ precursor (mole ratio) Hexanoic acid/ precursor (mole ratio) Alkyl aluminium halide/ precursor (mole ratio) Catalyst Remark
Mg Ti Cl Hf
Commercial catalyst: TiCl4 +VOCl3 Catalyst - - - - - 5 64.1 - Commercial catalyst
Comparative catalyst 0.09 0.12 3.3 14.4 11.9 2.4 45.1 8.0 HfCl4 is added in First step
PESOL-1 2 0.12 3.3 14.4 7.9 8.1 46 6.3 TiCl4 is added in First step
PESOL-2 2 0.12 3.3 14.4 4.9 14.7 48.2 1.4 HfCl4 is added in First step
PESOL-3 0.09 0.12 3.3 14.4 11 2.9 54.9 7.9 HfCl4 is added in First step and reduced quantity TiCl4

From table 1, it is observed that PESOL-1 and PESOL-2 was prepared using excess amounts of titanium tetrachloride as compared to PESOL-3. In the preparation of PESOL-1 and PESOl-2, the same molar ratio of all the reactants was used. The metal tetrachlorides (HFCl4 and TiCl4) were added in two different steps. The addition sequence of metal tetrachloride’s (HFCl4 and TiCl4) was altered to study the effect of the catalyst composition. In PESOL-1, TiCl4 was added in the first step and HFCl4 was added in the second step. In PESOL-2, HfCl4 was added in the first step and TiCl4 was added in the second step. The preparation of PESOL-3 was optimized with reduced quantity of titanium tetrachloride in the composition and the addition sequence of the metal tetrachlorides was maintained similar to PESOL-2.
The inventors surprisingly found that when HfCl4 is added in the first step along with organic acid (hexanoic acid) and TiCl4 is added in the second step (with reduced quantity) as in the case of PESOL 3, the activity of the catalyst increases due to more active sites being available.
Further, when TiCl4 is added in the first step along with hexanoic acid and HfCl4 is added in the second step as in the case of PESOL 1, the support is crowded with active sites, and mass transfer limitation is observed. PESOL 1 does not allow the chain to grow as compared to the addition of HfCl4 in the first step.
Still further, when HfCl4 is added in the first step along with organic acid (hexanoic acid) and TiCl4 is added in the second step (with more quantity) as in the case of PESOL 2, the activity of the catalyst is similar to the activity of PESOL 1.
Experiment 2: Polymerization performance of the catalyst:
The process for synthesis of a polymer using the above bimetallic catalyst is given below.
Dry hexane was taken in a preheated moisture free jacketed 1 liter glass reactor fitted with a stirrer. The pro-catalyst along with triethyl aluminium (TEAl) co-catalyst were added such that co-catalyst/catalyst molar ratio of ~100 was maintained. Reaction temperature was maintained at 80 °C by heating/cooling the system. Reactor pressure was maintained at 2±0.2 kg/cm2. Polymerization reaction was carried out for 30 minutes and then hexane was removed and the polymer was collected and dried.
The slurry phase polymerization productivity, melting temperature and bulk density of the polymer produced using the pro-catalysts as compared to commercial TiCl4/VOCl3 homogenous catalyst and the catalyst (PESOL) of the present disclosure is summarized in Table 2.
Table-2: Composition of slurry phase polymerization productivity and product properties of the polymer produced using pro-catalyst, commercial TiCl4/VOCl3 homogenous catalyst and the catalyst of the present disclosure (PESOL)
Catalyst TEAl/Ti
(Molar ratio) Catalyst quantity mg Polymer weight gm Productivity, KgPE/gm TI Peak melting point based on DSC*, Deg C Bulk Density gm/cc Remarks
Commercial Catalyst TiCl4 +VOCl3 catalyst 100 35 21 12 133.2 0.116 Commercial homogeneous catalyst
Comparative catalyst
Commercial available MgCl2 100 20.4 16.5 34.4 134.6 0.144 Commercially available MgCl2 (without in-situ)
PESOL-1 100 28.4 30 13.2 134.7 0.248 Activity higher than commercial homogeneous catalyst
PESOL-2 100 26.8 56.8 14.2 134.2 0.196 Activity higher than commercial homogeneous catalyst
PESOL-3 100 20 21 36.4 134.6 0.164 Activity higher than commercial homogeneous catalyst
DSC* (Differential Scanning Calorimetry): condition means heating from 30°C to 250°C, at 10°C/min rate, holding for 1 min there, then cooling at the same rate to 30°C, again heating at the same rate.
From the above Table 2, it is observed that an increased productivity and comparatively better bulk density of the polymer is obtained when PESOL-3, the bimetallic catalyst of the present disclosure is used in the polymerization reaction with respect to the comparative catalyst. The productivity values for PESOL-1 and PESOL-2 are considerably lower than the productivity value of PESOL-3. This may be attributed to the different compositions of the catalysts (as given in table 1) and the sequence of addition of metal tetrachlorides (TiCl4 and HfCl4) to the in-situ generated magnesium dichloride.
TECHNICAL ADVANCEMENTS AND ECONOMIC SIGNIFICANCE
The process of preparation of a bimetallic catalyst as disclosed in the present disclosure has several technical advancements that include, but are not limited to, the realization of:
- simple and cost effective;
- comparatively higher activity; and
- devoid of filtration step.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:1. A process for preparing a bimetallic catalyst, said process comprising the following steps:
a) reacting at least one magnesium alkoxide, at least one first metal halide and optionally at least one organic acid in a first fluid medium at a first predetermined temperature greater than 40 oC, to obtain a first reaction mixture;
b) cooling said first reaction mixture to a temperature in the range of 25 oC to 40 oC to obtain a cooled first mixture and reacting said cooled first mixture with at least one second metal halide other than said first metal halide and optionally with at least one organic acid followed by heating at a second predetermined temperature greater than 40 oC, to obtain a second reaction mixture containing a pro-catalyst;
c) cooling said second reaction mixture containing said pro-catalyst to a temperature in the range of 25 oC to 40 oC to obtain a cooled second mixture and adding at least one alkylating agent and at least one second fluid medium to said cooled second mixture for alkylating the pro-catalyst at a third predetermined temperature greater than 40 oC, to obtain the bimetallic catalyst in a third reaction mixture; and
d) separating said bimetallic catalyst from said third reaction mixture.

2. The process as claimed in claim 1, wherein said alkoxide is at least one selected from the group consisting of C1-C5 alcohols.
3. The process as claimed in claim 1, wherein said magnesium alkoxide is at least one selected from the group consisting of magnesium ethoxide, magnesium methoxide, magnesium propoxide, magnesium butaoxide and mixtures thereof.
4. The process as claimed in claim 1, wherein said first metal halide and second metal halide is at least one independently selected from the group consisting of halides of titanium, hafnium, zirconium, iron, nickel, cobalt and palladium.
5. The process as claimed in claim 1, wherein the mole ratio of the amount of said magnesium alkoxide to said metal halide is in the range of 0.01 to 1.
6. The process as claimed in claim 1, wherein said first fluid medium and, second fluid medium is at least one independently selected from the group consisting of chlorobenzene, bromobenzene, iodobenzene, dichlorobenzene, trichlorobenzene, dibromobenzene, tribromobenzene hexane, heptane and decane.
7. The process as claimed in claim 1, wherein said organic acid is hexanoic acid and derivatives thereof.
8. The process as claimed in claim 1, wherein the mole ratio of the amount of said organic acid to said magnesium alkoxide is in the range of 1 to 10.
9. The process as claimed in claim 1, wherein said alkylating agent is at least one selected from the group consisting of diethyl aluminum chloride (DEAC), isobutyl aluminum dichloride (IBADIC), triethyl aluminum, triisobutyl aluminum, trioctyl aluminum and boron containing alkylating agents.
10. The process as claimed in claim 1, wherein the amount of said alkylating agent is in the range of 1 wt% to 30 wt%.
11. The process as claimed in claim 1, wherein said first predetermined temperature, second predetermined temperature and third predetermined temperature is in the range of 70 oC to 100 oC.
12. A process for polymerizing a-olefin and dienes; said process comprises subjecting an olefin or a diene to polymerization in the presence of the bimetallic catalyst as claimed in claim 1, wherein said polymerization is carried out in at least one of slurry, solution and gas phase.