Process Economics Program Report 128C
Polypropylene Update 128C
Published: November 2002
This report continues our evaluation of polypropylene processes. Isotactic polypropylene produced with metallocene catalyst represents less than 0.5% of the total global polypropylene capacity. The vast majority of polypropylene is produced with Ziegler-Natta catalyst. However, growth rate for metallocene polypropylene (mPP) is expected to be good, approximately 8% annual from 2001-2006. ExxonMobil Chemical and Basell are the leading producers of mPP.
ExxonMobil Chemical produces the resin in the Sumitomo stirred reactor bulk process and Basell produces it in the Novolen. vertical stirred-bed process. With ExxonMobil and Basell recent mPP research and development agreement, it should soon be introduced into the Spheripol process.
In this report, we compare the operating economics for Ziegler-Natta and metallocene catalysts for the production of polypropylene impact copolymer. The three leading process technologies are chosen for the analysis. They are the Spheripol., Unipol., and Novolen. processes. The Spheripol. process uses two bulk slurry loop reactors in series with a fluidized bed gas-phase reactor. The Unipol. process uses two fluidized bed gas-phase reactors in series. Lastly, the Novolen. process uses two vertical stirred-bed gas-phase reactors in series.
We have selected a design capacity of 441-million lb/yr (200,000 t/yr). Both metallocene catalyst and Ziegler-Natta catalyst are evaluated. In addition, a speculative second-generation metallocene catalyst is evaluated. For the Unipol. and Novolen. processes, SHAC. and PTK.
Ziegler-Natta catalysts are used, respectively. For the Spheripol. process, Basell "fifthgeneration" Ziegler-Natta system is used. The first-generation metallocene catalyst system, a silica supported metallocene catalyst with methyl aluminoxane (MAO) co-catalyst that was developed jointly by Exxon and Hoechst, is used for the case studies. The speculative secondgeneration metallocene catalyst is a silica supported metallocene catalyst with a non-coordinating anion, e.g., tri(n-butyl)ammonium tetrakis(pentafluorophenyl)boron and tris(pentafluorophenyl)borane, as a co-catalyst.
We conclude that the operating economics for a first-generation metallocene catalyst is 1.3-2.2 cent/lb higher than for the Ziegler-Natta systems. A speculative second-generation metallocene catalyst can reduce the margin to 0.3-1.2 cent/lb but these systems are known to be difficult to commercialize because of their sensitivity to poisons. Although Basell "fifth generation" Ziegler-Natta catalyst has a much higher catalyst activity, nearly four times, than either SHAC. or PTK. catalysts, the operating economics are slightly higher for the Spheripol. process.