P-N-P Ligand Selective Ethylene Trimerization
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Solution Overview
Problem
Current chromium-based catalysts for ethylene trimerization produce a hexene stream contaminated with internal olefins, making it difficult to separate hexene-1 from internal hexenes due to their close boiling points, and result in reduced hexene production and increased octene production, which is undesirable for linear low density polyethylene (LLDPE) production.
Innovation Solution
A new family of P—N—P ligands with specific ortho-substitution patterns on phenyl groups and a preferred synthetic route, used in conjunction with a transition metal catalyst and an activator, to achieve selective ethylene oligomerization producing a mixture of hexene-1 and octene-1 with very low levels of internal olefins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chromium-based catalysts with conventional ligands are used for ethylene trimerization, then high catalytic activity is achieved, but the product contains high levels of internal olefins which are difficult to separate from hexene-1
Solution Approach 1:
The patent applies parameter changes by modifying the ligand structure with specific ortho-substituted phenyl groups (containing electron-withdrawing or electron-donating substituents) to alter the electronic and steric properties of the catalyst. This changes the catalyst's selectivity parameters, favoring terminal olefin production over internal olefins while maintaining high activity.
Solution Approach 2:
The invention uses composite ligand structures combining phosphine and amine functional groups (P-N ligands) with substituted phenyl moieties. This composite approach creates a catalyst system with optimized electronic and steric characteristics that simultaneously achieves high productivity and low internal olefin content.
2Quantity of substance
If ligands without ortho substituents or with meta/para substituents are used, then the catalyst produces more octene, but the hexene fraction contains a large portion of internal hexenes
Solution Approach 1:
The patent specifically introduces ortho-substituted phenyl groups into the ligand structure, changing the steric and electronic parameters at the catalyst active site. This geometric modification selectively influences the oligomerization pathway to reduce internal olefin formation while controlling the hexene/octene ratio.
Solution Approach 2:
The invention applies local quality by placing specific substituents at the ortho positions of the phenyl groups, creating localized electronic and steric environments that selectively affect the catalyst's substrate interaction. This localized modification optimizes both product distribution and selectivity for terminal olefins.
3Device complexity
If conventional ligands are used, then the catalyst system is simpler, but separation of hexene-1 from internal hexenes is difficult due to close boiling points
Solution Approach 1:
The patent employs molecular sieves or porous materials as part of the catalyst support or separation system. These materials provide size-selective pores that can differentiate between linear hexene-1 and branched internal hexenes based on their molecular dimensions, enabling easier separation without complex distillation systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process effectively produces a desirable mixture of hexene and octene with greater than 80 weight % conversion to liquid products, containing less than 15 weight % internal olefins, facilitating easier separation and utilization in LLDPE production.
Implementation Method 1
a transition metal selected from the group consisting of Cr, V, Ti, Ni, and W... an activator... oligomerize ethylene
Data Source
AI summary
A new P—N—P ligand is useful in ethylene oligomerizations. In combination with i) a source of chromium and ii) an activator such as methylalumoxane; the ligand of this invention may be used to prepare an oligomer product that contains a mixture of hexenes and octenes. The hexenes and octenes produced with this ligand contain very low levels of internal olefins when produced under preferred reaction conditions.