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A Process for the Trimerisation and Tetramerisation of ethylene to 1-hexene and 1-Octene Disclosure Number: IPCOM000031729D
Publication Date: 2004-Oct-07

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Trimerisation and tetramerisation systems generally share the common requirement of a co-catalyst to be employed. The most favourable results are achieved with an aluminoxane. In particular, the most active systems result when an aluminoxane based on hydrolysed trimethylaluminium is used (methylaluminoxane, MAO). However, the high cost of trimethylaluminium, and as a result MAO, have a significant detrimental impact on the economics of ethylene trimerisation and tetramerisation with these systems. An alternative means of activation which does not rely on aluminoxanes would be advantageous. A process is discussed that utilises the Sasol trimerisation/tetramerisation systems either as preformed complexes or as in-situ systems, for the selective oligomerisation of ethylene to 1-hexene and/or 1-octene. As an activator, a mixture of metal-alkylating agent (for example AlEt3) and an alkyl abstracting reagent (a Lewis acid, for example B(C6F5)3) is used.

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A Process for the Trimerisation and Tetramerisation of ethylene to 1-hexene and 1-Octene

David S. McGuinness, Sasol Technology (


) Ltd



, North



KY16 9ST


United Kingdom

1. Introduction

There is a great demand within the chemical industry for linear alpha olefins (


) as intermediates in the production of detergents, synthetic lubricants, plasticizer alcohols, and as comonomers for the production of polymers. By far the majority of LAO production involves ethylene oligomerisation via so called full range processes. Examples of such full range ethylene oligomerisation processes are those practiced by Shell, BP Amoco, and Chevron Phillips. These processes are characterised by production of a geometric distribution (Schulz-Flory or Poisson) of alpha olefins. While the LAO distribution of these processes can be controlled to some extent, very often such a range of olefins does not match market demand.

In this regard, demand for the comonomer range alpha olefins, 1-hexene and 1-octene, is expected to increase steadily. Importantly, the growth in demand for 1-hexene and 1-octene is expected to be greater than that for other alpha olefins. As such, there is considerable interest within the chemical industry for alternatives to the full range processes, which are able to selectively oligomerise ethylene to 1-hexene (Trimerisation) and 1-octene (Tetramerisation).

The trimerisation of ethylene to 1-hexene has received considerable research attention, as documented in a recent review article.[1] Sasol Technology have disclosed a number of trimerisation catalysts based on chromium complexes in combination with multidentate ligands. In particular, three highly active ligand systems are as shown in I-III, below.[2],[3],[4]

In such systems, the R group is a hydrocarbyl group, such as a phenyl group or an alkyl group, whereas R’ is a phenyl group with non-polar ortho substitution, such as ortho-Me, Et or iPr. A fuller description of the ligand structure of each system is as found in the patents listed in references 2-4. The catalysts are prepared either by making preformed  chromium complexes of these ligands, or by introducing the ligand and a chromium source to the reactor (in-situ system). A final component required to produce an active trimerisation system is a hydrolysed alkyl aluminium reagent (an aluminoxane), which is know as the co-catalyst or activator.

Furthermore, Sasol Technology have discosed a system for the tetramerisation of ethylene to produce 1-octene.[5] Like the above systems, this is composed of a ligand (IV, below), a Cr source, and an aluminoxane activator. Both preformed complexes or an in-situ system can be employed. The R groups in this system are hydrocarbyl groups, such as phenyl or alkyl, as further expanded upon in the patent listed in reference 5.

Trimerisation and tetramerisation systems based on ligands I-IV all share the common requirement for a co-catalyst to be employed. The most favourable resul...