Technology

Lummus Technology’s Comonomer Production Technology (CPT) – 1-Butene is a process for producing polymer-grade 1-butene from raffinate-2. It is a response to demand for high-purity linear alpha-olefins as comonomers for LLDPE and HDPE resins. The technology combines butene skeletal isomerization with advanced heat-pump assisted distillation to achieve efficient conversion and separation without external heat input. The technology is deployed in standalone or integrated configurations across multiple geographies.

Figure 1 - Steam cracker C4 processing^[1]

Feedstock and Pretreatment

• Feed: 
  • Primary feed: The normal feed to the CPT process is raffinate-2 (RAF-2), a C₄ stream in which reactive butadiene and isobutylene have already been removed (commonly by selective hydrogenation and etherification of isoolefins, respectively).
  • Alternative feed: The process is adaptable to alternative feeds including steam cracker crude C₄'s or raffinate-1, provided that upstream treatment assures low isobutylene and butadiene content.
     
• Typical Feed (RAF-2) Composition:
  • 1-butene: 10-25%
  • 2-butene: (cis/trans): 50-60%
  • n-Butane: 15-25%
  • Minimal isobutene and butadiene content

Main Process Steps

1. Butene Isomerization
   • Process: RAF-2 feed, blended with recycle from butene separation, is vaporized, preheated, and passed over a proprietary fixed-bed catalyst.
   • Reaction: The isomerization reactor promotes equilibrium between 2-butenes (cis and trans) and 1-butene, favoring an increased amount of 1-butene relative to the feed.
   • Catalyst: Skeletal isomerization only—no metathesis or skeletal rearrangement, ensuring purity and preventing byproduct formation.
      
2. Butene Fractionation / Superfractionation
   • Separation: Reactor effluent is cooled, condensed, and fed to a fractionation (superfractionation) section for product separation.
   • Configuration: The core separation uses a high-efficiency, heat pump-integrated butene splitter to separate overhead 1-butene from bottoms (recycle 2-butenes and n-butane).
   • Recycling: The bulk of 2-butenes are recycled to the isomerization reactor, maintaining high overall conversion and stable process efficiency.
   • Purge: A controlled portion of the bottoms is purged to remove n-butane and prevent buildup in the recycle loop.
      
3. Product Recovery
   • 1-Butene: High-purity, comonomer-grade 1-butene is recovered overhead. The system consistently meets or exceeds market specification (typically >99wt%, with very low isobutylene and butadiene).
   • Integration: CPT can be operated alone or integrated with metathesis units (OCT process), further expanding comonomer portfolio to include 1-hexene where desired.

Key Technical Features and Innovations

• Equilibrium Isomerization: CPT achieves above-equilibrium yield of 1-butene due to continuous recycle and efficient fractionation.
• Heat-Pump Fractionation: The butene splitter employs heat integration for energy efficiency (no external reboiler heat input), minimizing operating costs.
• Flexible Operation: CPT is suitable for both large-scale merchant plants and captive on-site comonomer demand. 
• Integrated Purge Management: Selective purge strategy keeps butane from accumulating, ensuring robust process control and optimal recycle economics.

References

1. Stacia M Edwards et al. | Q1 1998. Relative economics of mixed C₄ stream from ethylene plants to improve operating economics. Digital Refining PTQ.
2. Robert J Gartside | Apr 2018. Integrating CPT with existing OCT Units. Digital Refining.
3. Apr 26, 2018. Comonomer Production Technology — 1-Butene. McDermott Technology.
4. Jack. June 5, 2018. Butene-1 Process by Lummus Technology. Oil & Gas Process Engineering.
5. Rene Gonzalez | Jun 26, 2018. Overcoming butylene deficits. CatCracking.