A Detailed Report on Polymerization Process and Ziegler-Natta Catalyst

This report provides a comprehensive analysis of the polymerization process, focusing on the application of Ziegler-Natta catalysts in the production of polymers, particularly polypropylene. It begins by outlining the fundamental principles of polymerization, emphasizing the role of Ziegler-Natta catalysts in forming long-chain polymers from short-chain monomers. The report then delves into the catalyst's mechanism, including the Cossee-Arlman mechanism, and the preparation of both heterogeneous and homogeneous Ziegler-Natta catalysts, detailing the specific raw materials and procedures involved. The report also covers the reactions involved in the process, the different reactors used, and the storage requirements for the raw materials. The report provides insights into various catalyst compositions and their impact on catalyst productivity. Ultimately, the report provides a detailed overview of the production process, including the preparation of the catalyst and the polymerization process, which is crucial for understanding the industrial application of Ziegler-Natta catalysts.

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Polymerization process
Polymerization is the process by which very long chain polymers are formed from short chain
monomers in the production of polypropylene (KEII, 2015, p. 272). Ziegler Natta catalyst is used
in this process since it makes it possible for both unbranched and isotactic polymers to be
formed. The catalyst, TiCl4 together with aluminum based co-catalyst is placed in the propene
monomer and left overnight under appropriate conditions such as room temperature and a
constant flow of nitrogen gas. These centers of the Ziegler Natta catalyst acts as the active sites
through which polymer molecules grow through an insertion of C=C bonds into the ion’s Zr-C
bond (Magni & Somorjai, 2015, p. 826). Very long chains of polymer are formed from thousands
and thousands of these insertions at the active center. The chains are attached to the center of the
active centers. Ziegler-Natta catalyst forms stereospecific polymers. The growth of these
polymer chains is made possible through a mechanism called Cossee-Arlman, in which polymers
grow through alkene coordination at the active sites. Insertion, into the active centers’ Ti-C bond,
of the C=C bond then ensues (Novokshonova & Zakharov, 2013, p. 115).
Preparation of Ziegler-Natta catalyst
Ziegler-Natta catalyst is product of two scientist, Karl Ziegler and Giulio Natta, its majorly used
in industries for the polymerization of polymers .They are of two types in the industry; the
heterogeneous and homogenous catalyst ,heterogeneous being the most employed in
the ,industries. In both different composition of raw materials are needed. For the heterogeneous
type of the catalyst TiCl4 ,MgCl2 and triethylaluminium is used .where triethylaluminium acting
as a coacatalyst while on the other hand for the homogenous catalyst TiCl4, MgCl2 and
methylaluminoxane is used, methylaluminoxane acting as the catalyst. The structure below is an
example of a type of homogeneous catalyst which is metallocene together with the cocatalyst.

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Fig 1.1: Homogenous Catalyst
To prepare Ziegler-Natta catalyst, about 508g of anhydrous magnesium chloride followed by
800ml of anhydrous ethanol are first added to a reactor containing 1270ml of mineral oil kept at
room temperature to form an alcoholic adduct of mole ratio 1:3.The resulting alcoholic solution
is then dealcoholized by addition of TiCl4 at a mole ratio of ½:1. TiCl4 is added at a temperature
of 00C but then raised to 600C. 1500ml of isoparaffin together with internal electron donor is also
added at temperatures of 600C and mole ratio of 8:1. The temperature is then raised through
heating and maintained for about 2 hours. Thereafter, TiCl4 is added resulting to a catalytic solid
then washed with dry hexane and dried to a constant mass. Polymerization is then carried out in
the Buchi reactor as stirring during the process is done by a mechanical stirrer (TAIT, 2014,
p. 161). A glass reactor is thermally dried and then attached to a metal support under constant
flowing nitrogen. The mixer is then cooled and about 880ml of hexane added followed by a
cocatalyst triethylaluminium. Polypropylene monomer is then added and pressure raised by 5bar
with the temperatures maintained at 70oC.The polymer produced is washed and kept in oven at a
constant mass .These measurements of the raw material used ensures production adequate
Ziegler-Natta catalyst that can daily yield about 681,820kg of polypropylene(Novokshonova &
Zakharov, 2013, p. 117). In the preparation process, different catalyst compositions can be
chosen where each composition gives a different productivity of the catalyst. When a
composition of MgCl2,TiCl4, benzoate and AlR3( used as a cocatalyst) and a stirrer rate of 120
RPM 15-30 kgpp/g of the catalyst is produced, different composition for production of Ziegler
–Natta catalyst can be used as shown in table below

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Fig 1.2: Various compositions for production of Ziegler –Natta catalyst
Mechanism of reactions involved
The Ziegler- Natta catalyst used combines with Al(C2H5)3 to produce the polymer polypropylene
as shown below. The catalyst speeds up the polymerization process. AlCl3 is used as a cocatalyst.
Fig 1.3: Mechanism of reactions involved in production of polymer polypropylene

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Fig 1.4: Ziegler Natta production process
The figure above show step by step how the catalyst Ziegler Natta prepared, the series of
reactions involved and how it aids in the polymerization process by combining with monomer
propene gas to form a polymer polypropylene
The mixture reactor used
Both the Buchi reactor and glass reactor are used to mix the raw materials in the mixer reactor. A
glass reactor is attached to a metal support under a constant flowing Nitrogen.

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Fig 1.5: Flow sheet showing the preparation process
The flow sheet above show every process stepwise from the start to the final extraction of the
gas, raw materials needed and the conditions for the raw materials
Storage for the raw materials
Magnesium chloride is deliquesce substance and thus it should be stored in its anhydrous form.
Magnesium diethoxide is used without any purification since it’s obtained commercially from
Titanium. Tetrabutoxide used to make titanium tetrachloride -used as a raw material in the
preparation of the catalyst- is first purified before use. Hexane is kept dry, dried over molecular
sieves(Novokshonova & Zakharov, 2013, p. 130). All the raw materials are then kept in a solvent
tank bubbled with nitrogen gas .The solvent tank helps to minimize the level of oxygen
concentration hence ensures that magnesium chloride remains in a stable condition. Water level
is checked and maintained. This is because magnesium absorbs water in its anhydrous form(Boor,
2014, p. 28).

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REFERENCES
Boor, J. (2014). Genesis of Ziegler–Natta Catalysts. Ziegler–Natta Catalysts Polymerizations,
19-31.
Fan, Z., & Yu, Y. (2018). Ziegler-Natta Catalysts. Encyclopedia of Polymer Science and
Technology, 1-24.
KEII, T. (2015). A Kinetic Approach to Elucidate the Mechanism of Ziegler-Natta
Polymerization. Coordination Polymerization, 263-289.
Magni, E., & Somorjai, G. (2015). Surface science study of model Ziegler-Natta catalysts.
Surface Science, 377-379, 824-827.
Novokshonova, L. A., & Zakharov, V. A. (2013). Kinetics of Olefin Polymerization and Active
Sites of Heterogeneous Ziegler–Natta Catalysts. Polyolefins: 50 years after Ziegler and
Natta I, 99-134.
TAIT, P. J. (2014). A Kinetic Model for Heterogeneous Ziegler-Natta Polymerization.
Coordination Polymerization, 155-197.