Technology

Overview

AlphaButol^® is Axens’ proprietary process for the on-purpose production of high-purity 1-butene via the dimerization of ethylene. Developed in collaboration with SABIC, the process produces high purity 1-butene via ethylene dimerization with a yield higher than 90%. The process operates in the liquid phase using a soluble catalyst system, which avoids isomerization of 1-butene to 2-butene; thus superfractionation of the product stream is not needed. Polymer-grade ethylene is dissolved in the reaction medium. The dimerization reaction takes place in the liquid phase while the heat of reaction is removed by external cooling. Reactor effluent is routed to catalyst separation section. The hydrocarbon portion is vaporized and fractionated in the distillation section and spent catalyst is recovered. The first distillation column separates unconverted ethylene, which is recycled directly to the reactor. The second column recovers high purity 1-butene.

Figure 1 - Selective ethylene dimerization mechanism M: metal / L: Ligand

Key Process Features

• Homogeneous Catalysis:
  AlphaButol^® process utilizes a soluble, homogeneous catalyst system—most traditionally a titanium-based complex—along with an organoaluminum activator (such as triethylaluminum, TEAl). This chemistry is foundational to AlphaButol^®’s selectivity and operational reliability. The reaction mechanism is highly tuned to produce 1-butene specifically, avoiding unwanted isomerization (to 2-butene) or formation of isobutene under the employed mild conditions.

• Operating Conditions:
  • Temperature: Typically 50–60°C
  • Pressure: 20–25 kg/cm²
  • These moderate conditions ensure high catalyst activity without promoting side reactions or catalyst degradation.
     
• Liquid-Phase Reaction:
  Ethylene is dissolved in the reaction medium, allowing dimerization to occur in the liquid phase. No solvent is required, and no heat input is needed in the reaction section. This liquid-phase design underpins the process’s operational simplicity and safety.
   
• Process Flow Summary:
  1. Ethylene Dimerization: Ethylene reacts with the catalyst/activator in a reactor, forming 1-butene with a yield above 90%. The reaction is exothermic, and heat is removed by external cooling.
  2. Product/Catalyst Separation: The reactor effluent is directed to a catalyst separation section. Spent catalyst is treated for safe disposal, minimizing hydrocarbon loss.
  3. Distillation: Two sequential distillation steps are used:
     1. First column: Removes and recycles unreacted ethylene
     2. Second column: Recovers high-purity 1-butene. The heavy by-product “C₆⁺ cut” is drawn off as a secondary stream.
  4. No Superfractionation Required: The selectivity of the chemistry obviates the need for superfractionation—simplifying plant design and operation.
      
• Purity and Quality:
  The 1-butene produced is of exceptional purity (>99.5wt%), with undetectable butadiene, extremely low levels of other C₄s, and extremely low traces of additional potential impurities. This quality is important for polymerization processes, where contaminants (e.g., butadiene or isobutene) can poison downstream catalysts or affect polymer properties.

  Typical 1-Butene Product Specification (AlphaButol^®)

  1-Butene content	>99.5wt%
  Other C4s (butenes/butanes)	<0.30wt%
  Ethane	<0.15wt%
  Ethylene	<0.05wt%
  C6 olefins	<100wt ppm
  Ethers (as DME)	<2wt ppm
  Sulfur, Cl	<1wt ppm
  Acetylenes	<5wt ppm
  Dienes	<10wt ppm
  CO, CO₂, O₂, etc.	<5wt ppm each

Technology Advantages

• Process Efficiency:
  • High conversion and selectivity for 1-butene yield (>90%).
  • Low capital expenditure (CAPEX) and operating costs due to simple plant design—no compressors, no superfractionation columns, carbon steel equipment can be used for most parts.
  • Energy-efficient (no need for heating the reaction section).
     
• Product Flexibility:
  • The exceptionally pure 1-butene obtained can go directly to polyethylene plants without further purification.
  • The process exhibits steady, reliable operation even with fluctuating feedstock qualities.
     
• Environmental and Safety Benefits:
  Operating in mild conditions and in the liquid phase reduces risks associated with pressurized gas-phase processes.

Process Scale and Commercial Adoption

• Industry Share:
  AlphaButol^® is responsible for roughly a third of the global butene-1 production capacity.
   
• Operability:
  Over 20 commercial units worldwide, with several recent startups and references in the ME and Asia.
   
• Design Flexibility:
  Units can be modular/skid-mounted or stick-built, catering to diverse business cases and project requirements.

References

1. Axens. Oligomerization - AlphaButol^® - Dimerization of Ethylene to 1-Butene
2. Nov 2018. Axens. Commercial Bulletin - Alphabutol^®
3. Jeet Kacha. Apr 14, 2024. AlphaButol® Process by Axens SA: An Overview. Linkedin.
4. Hamoud Alenezi et al.. Recent Developments on Ethylene Dimerization with Focus on Alphabutol Optimization. IJITEE, Vol. 8, Issue 10, August 2019. DOI: 10.35940/ijitee.J9936.0881019. ISSN: 2278-3075.
5. Zhuoran Xu et al.. Ethylene Dimerization and Oligomerization to 1-Butene and Higher Olefins with Chromium-Promoted Cobalt on Carbon Catalyst. ACS Catal., DOI: 10.1021/acscatal.7b03205, 05 Feb 2018. U.S. DoE, Office of Scientific and Technical Information (OSTI)
6. Axens Blog. Mar 28, 2017. The Story of On-Purpose Production of Alpha-Olefins.