Technology

Overview

AlphaHexol™ is a process developed by Axens for the on-purpose production of high-purity 1-hexene through the selective trimerization of ethylene. The technology operates in the liquid phase using a proprietary homogeneous catalyst system and a solvent under mild temperature and pressure. Polymer-grade ethylene is converted to 1-hexene with 85 to 90% selectivity; unconverted ethylene is recycled, and the product is recovered via distillation after catalyst separation. The process produces 1-hexene with a typical purity above 99wt%, meeting specifications for use as a comonomer in HDPE and LLDPE production. AlphaHexol™ minimizes by-products and avoids the need for complex product fractionation, offering efficient ethylene utilization and operational simplicity.

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

Key Process Features

• Homogeneous Catalysis and Chemistry
  • Utilizes a proprietary soluble metal-ligand catalyst system, activated by TEA (triethylaluminum) alkyl aluminum compounds.
  • Employs a mechanism grounded in hybrid transfer principles, resulting in high selectivity towards 1-hexene while minimizing by-products and internal or branched olefins.
  • Catalyst composition and activation are carefully tuned to suppress chain growth and oligomerization beyond C_6, making it highly selective for the C₆ alpha-olefin.
     
• Operating Conditions
  • The reaction occurs in the liquid phase and requires a solvent, ensuring excellent mass transfer and temperature control.
  • The process is conducted under mild operating temperature and pressure, thus minimizing the risks of thermal degradation and impurity formation.
     
• Process Flow Summary
  1. Ethylene Trimerization: Polymer-grade ethylene is dissolved in the reaction medium containing the catalyst and solvent. Trimerization in the reactor yields 1-hexene.
  2. Product/Catalyst Separation: Reactor effluent proceeds to a catalyst separation step. Volatile hydrocarbons are removed from the spent catalyst before safe disposal.
  3. Distillation and Purification:
     1. The first distillation column recycles unconverted ethylene directly to the reactor.
     2. A separation section then removes the solvent for recycling, and isolates high-purity 1-hexene as the product.
     3. Heavy by-products (“C₈⁺ cut,” typically <0.25wt%) and spent catalyst are safely withdrawn.
• Product Purity
  • The 1-hexene produced via AlphaHexol™ typically exceeds 99wt% purity, with internal olefins and other C₆ impurities each below 0.5wt%.
  • n-hexane and lower/higher carbon impurities are very limited due to stringent operating conditions and excellent catalyst control.

    Typical 1-Hexene Product Specification (AlphaHexol™)

    Parameter	Typical Value
    1-Hexene	>99wt%
    Internal Olefins	<0.5wt%
    n-Hexane	<0.2wt%
    Carbon < C₆	<0.25wt%
    Carbon > C₆ (C₈+ cut)	<0.25wt%

Technology Performance

• High Selectivity & Purity
• Typically achieves a selectivity toward linear 1-hexene in the range of 85% to 90% under commercial operating conditions with minimal production of internal olefins, cyclics, or aromatics.
• No C₄ by-products; no aromatics are formed, eliminating the need for additional separation and purification.
   
• Operational Simplicity & Economy
  • Mild temperature and pressure requirements.
  • Liquid-phase reaction for ease of heat management and system safety.
  • Carbon steel can be used for the majority of process equipment, reducing CAPEX.
  • High efficiency in ethylene use, delivering excellent raw material and energy economy.
  • Full recovery and recycling of unconverted ethylene and solvent, minimizing losses and emissions.
• Flexibility and Modularity
  • Designer-friendly: Simple process flow can be tailored for different plant scales or integrated into existing olefin complexes.
  • Suitable for both grassroots installations and retrofits.
• Commercial Track Record
  • AlphaHexol™ leverages Axens’ industrial track record, with the foundational AlphaButol^® process accounting for more than 30 references and over 710,000t/y of global capacity for 1-butene (2018). AlphaHexol™ has been commercially licensed and demonstrates reliable performance.

References

1. Axens Blog. Mar 28, 2017. The Story of On-Purpose Production of Alpha-Olefins.
2. Xavier Liege. Feb 2018. Axens Technologies to Support Polyethylene Business. Ethylene Middle East Technology Conference (EMET). 
3. Axens. 2018. Commercial Bulletin - AlphaHexol™.
4. Axens. Oligomerization - AlphaHexol™ - Trimerization of Ethylene to 1-Hexene