(373ae) Propylene Polymerization Process Modelling and Simulation

Polypropene has demonstrated certain advantages in improved strength, stiffness and higher temperature capability over polyethylene and other terminal polyolefins.¹ Polypropene (PP) is a translucent commodity thermoplastic material with excellent physical and mechanical properties. PP is produced by polymerizing propene with suitable catalysts.

In the face of existing enormous market for polypropene the global polypropene market is expected to reach $126.89 billion by 2026 growing at a CAGR of 6.4%, continuing holding a significant portion of the market share of the commodity thermoplastics globally.² Due to the predictable growth of consumption, there's a yearning to intensify the productivity and yield in existing processes to mollify its demand.

Catalysts for use in Ziegler Natta polymerization have been widely researched. They are generally categorized into two groups on the basis of solubility.³ Heterogeneous catalysts: Titanium or vanadium-based compounds used in conjunction with organoaluminum complexes, and; Homogeneous catalysts: Complexes are based on Titanium, Zirconium, or Hafnium and include metallocenes and/or multidentate oxygen and nitrogen-based ligands.

There are three categories of processes generally employed to produce isotactic polypropene (iPP), homo- and co-polymers, namely, liquid slurry processes, bulk or liquid pool processes, and gas-phase processes.

Aspen Plus is a market-leading process modeling tool used for conceptual design, optimization, and performance monitoring for the chemical, polymer, specialty chemical, metals and minerals, and coal power industries.

Aspen Polymers is the market-leading technology for accurate and reliable design and optimization of polymer processes. It is fully integrated with industry-standard simulators including Aspen Plus®, Aspen Plus® Dynamics and Aspen Custom Modeler®.⁴

The propene gas-phase polymerization process model illustrates the use of Aspen Polymers Plus to model a gas-phase UNIPOL process for propylene homo-polymerization using a multi-site Ziegler-Natta kinetic model.

In the present simulation study, an Aspen Polymers Plus model is developed to simulate a polypropene gas-phase UNIPOL flow sheet. The flow sheet includes the fluidized bed reactor, the gas recycle/cooling loop, discharge, and purge units. The fluidized bed reactor is modeled using the CSTR reactor in Aspen Plus with two phases: a gas phase and a polymer phase.

The focal segments in the application of simulation software’s to polymerization processes, specially polymer component characterization, polymerization kinetics, and thermodynamic property requirements, are pronounced in this work.

In present study, POLYPCSF, Perturbed-Chain Statistical Associating Fluid Theory (PCSAFT) thermodynamic model is used to relate the gas phase monomer, hydrogen, etc. composition to their concentrations in the polymer phase. The multisite Ziegler-Natta kinetic model is used to describe the polymerization reactions in the polymer phase. The kinetic model calculates the reaction rates for the components and polymer attributes at each site type.

Further, parametric analysis is carried out to investigate the effects of temperature, pressure, catalyst amount, and catalyst/co-catalyst ratio on polypropene properties.

References

• Prakash, N. (2013). Commodity Thermoplastics with Bespoken Properties using Metallocene Catalyst Systems. Responsive Materials and Methods. Ashutosh Tiwari and Hisatoshi Kobayashi (eds.), WILEY-Scrivener Publishing LLC, USA , 379-398.
• https://www.businesswire.com/news/home/20180615005461/en/Global-Polyprop....
• Shamiri, A.; Mohammed H.; Jahan, Shah; Hussain, M. A.; Kaminsky, W.; Aravind, P. V.; Yehye, W. A. (2014). The Influence of Ziegler-Natta and Metallocene Catalysts on Polyolefin Structure, Properties, and Processing Ability. Materials 7(7) 5069–5108.
• Aspen Polymers: Conceptual design and optimization of polymerization processes, 2017 Aspen Technology, Inc. AT-03150-0417.