Technology

Technical and Commercial Overview

Historical Process Development

ExxonMobil’s polypropylene technology is the result of decades of innovation, combining and refining elements from leading industry processes. The technology draws on the Mitsui Hypol (loop reactor) and Montell (now LyodellBasell) Spheripol (gas-phase) systems, integrating them into a proprietary hybrid process. The company focused on:

• Expanding reactor size and heat transfer efficiency (moving from 4-leg to 6–8-leg loop reactors).
• Developing a unique monomer recovery system that avoids steam-hydrocarbon mixing, improving energy efficiency and product purity.
• Decoupling catalyst supply from process technology, allowing users to select from third-party Ziegler-Natta or metallocene catalysts
  
  Figure 1 - 6-Leg Loop Reactor
  
  Legend: 3. Series reactor, 9. First loop, 11. Second loop, 13. Pump, 15: Pump, 5. Individual reactor leg, 7. Reactor jacket.

Technology Summary

The ExxonMobil PP process features:

• Series bulk-liquid loop reactors for homopolymer and random copolymer production.
• Gas-phase reactor for impact copolymer production.
• Advanced monomer recovery using indirect heating, reducing steam and electricity consumption.
• Catalyst flexibility: Users can select from a range of commercial Ziegler-Natta or metallocene catalysts.

Step-by-Step Process Description (Based on Patents and Technical Documentation)

1. First Loop Reactor (Homopolymer/Random Copolymer)
   • Feed: Propylene, catalyst, optional hydrogen/comonomer.
   • Operating parameters:
     • Temperature: 60–75°C
     • Pressure: 500–550 psig
   • Reactor: 6–8 jacketed legs for enhanced heat removal and capacity.
   • Output: Slurry containing polypropylene and unreacted monomer.
      
2. Second Loop Reactor (for Bimodal or Random Copolymer)
   • Feed: Slurry from first reactor, additional propylene, comonomers, hydrogen as needed.
   • Operating parameters: Similar to first reactor, with independent hydrogen/comonomer control.
   • Key feature: Recycle system can route unreacted monomers/hydrogen only to the second reactor, allowing for independent molecular weight control and bimodal polymer production.
      
3. Gas-Phase Reactor (Impact Copolymer)
   • Feed: Output from loop reactors, ethylene for rubber phase.
   • Operating parameters:
     • Temperature: 65–80°C
     • Pressure: 20–30 bar
   • Function: Incorporates ethylene-propylene rubber into the PP matrix for impact copolymers.
      
4. Monomer Recovery and Finishing
   • Monomer Recovery: Indirect heating separates unreacted monomer without steam contact, reducing energy use and simplifying purification.
   • Finishing: Polymer is pelletized and additivated using twin-screw extrusion, with optional controlled rheology steps for tailored properties.

Products

ExxonMobil’s PP technology enables production of:

• Homopolymers: High stiffness, heat resistance (injection molding, fibers).
• Random Copolymers: Enhanced clarity, flexibility (packaging films, containers).
• Impact Copolymers: Superior impact/stiffness balance (automotive, appliances).
• Bimodal PP: Custom molecular weight distributions for specialty applications

Process Efficiency and Yields

• Energy Efficiency: Monomer recovery system reduces steam and electricity consumption versus conventional processes.
• Yield: High catalyst productivity (≥40 kg PP/g catalyst typical).
• Capacity: Each train designed for 400–500 kTA; up to 600–800 kTA possible with 8-leg reactors.
• Product Flexibility: Rapid transition between product grades with minimal off-spec material.

Commercial Experience

Singapore Integrated Complex:

• The ExxonMobil Singapore site operates two polypropylene trains, with a capacity of respectively 480 kTA and 450 KTA for a combined PP capacity of 930 kTA.
• Both trains use the described proprietary slurry-gas phase hybrid technology.
• The Singapore PP units are fully integrated with the site's refinery and chemical operations, supporting a broad product slate and efficient logistics.

Baton Rouge, Louisiana:

• In 2023, ExxonMobil commissioned a 450 kTA polypropylene unit in Baton Rouge, doubling the site’s PP capacity and demonstrating the scalability of the technology.
  
  Figure 2 - ExxonMobil Polypropylene Plant in Bâton Rouge
  

Licensing Experience:

• ExxonMobil offered this technology for licensing starting in the mid-2000s, emphasizing its flexibility, energy efficiency, and catalyst neutrality and it was still mentioned in a May 2018 document that "ExxonMobil also licenses this proprietary innovation, which is a pioneering integration of polypropylene slurry and gas phase technologies".
• No evidence exists of successful third-party licensing or external commercial adoption. The technology does not appear in current lists of licensed PP technologies, and ExxonMobil’s PP technology remains primarily deployed at its own integrated sites.

References

1. Dr. Balaji B. Singh et al., Chemical Market Resources Inc., PR723 ExxonMobil PP, 7^th Nov 2005, ExxonMobil Enters the Global Polypropylene Technology Licensing.
2. Lawrence C. Smith, US Patent N° US 2009/0023872 A1, Polypropylene Series Reactor, Filed: 19^th Jul 2007, Assignee: ExxonMobil Chemical Company.
3. Kevin W. Lawson, Rodney S. Smith, US Patent N° US 2013/0296506 A1, Copolymer Production System and Process, Filed: 18^th Mar 2018, Assignee: ExxonMobil Chemical Patent Inc.
4. exxonmobil.com, 15^th May 2018, ExxonMobil Singapore Integrated Manufacturing Complex brochure.
5. Jack, Oil & Gas Processing Technology, 18^th June 2018, Polypropylene Process by ExxonMobil.
6. Opportunity Louisiana, 19^th Jan 2023, ExxonMobil’s Polypropylene Growth Project Begins Operations in Baton Rouge.
7. exxonmobil.com, Technology Licensing. (accessed 25^th Jun 2025)