2.  Polypropylene production  

Isotactic isomers of polypropylene are most useful. It is stronger and harder than polyethylene and frequently used in block copolymer production. Various catalysts are used for this process.

 

1. Using Zeigler – Natta catalyst : The process is carried out at 70°C and ~13 atm using slurry reactors. Catalyst are prepared by reducing TiCl 4 with Al (C₂H₅)₃ in a cold hydrocarbon liquid to produce stereo-unselective form of TiCl₃. On heating to 100-200°C, TiCl₃ form convert to the stereo-selective form. Isotactic yield of propylene is about 92 %. The final active catalysts contain TiCl 3 and AlCl 3 .
   
   
2. Using MgCl₂ supported TiCl 3 catalyst : The process is carried out at 70°C and 13-20 atm pressure. It gives around ~ 95 % isotactic polypropylene yield. The catalyst is prepared by first milling MgCl₂ with ethy bezanoate extensively to produce a highly active disordered state. Then it is treated with TiCl₄ at 100°C .
   
   
3. Metallocene catalysts are m ore active with higher stereo selectivity. 100 % yield of isotactic or syndiotactic is possible.

Deactivation: CO, O₂ and S compounds act as poison for the catalysts. Reactants are passed through molecular sieve adsorbent column before treating with catalysts.

Text References

• H. Bartholomew and R. J. Farrauto, Fundamentals of Industrial catalytic Processes, Wiley, VCH, 2006
• Piet W.N.M. van Leeuwen, Homogeneous catalysis: Understanding the Art, Springer, 2004
• George Odian, Principles of polymerization, Wiley India, 2008.

 

Journal Reference

1. M. Abboud, P. Denifl, K.-H. Reichert, Macromol. Mater. Eng. 290 (2005) 1220.
2. H. L.Ronkko, T. Korpela, H. Knuuttila, T.T. Pakkanena, P. Denifl, T. Leinonen, M. Kemell, M. Leskela, Journal of Molecular Catalysis A: Chemical 309 (2009) 40–49