Research progress of ligands in chromium-based catalysts for ethylene trimerization/tetramerization
The research progress of PNP-type ligands and other types of ligands such as PNS type,NNN type,PN-(CH2)n-NP type,PCCP type used in chromium catalysts for ethylene trimerization/tetramerization in recent years is reviewed.The selectivity of PNP-type ligands to 1-octene is 72.52%,and whose activity is up to 9.46×106 g/(mol·h).The selectivity of other ligands for 1-octene is up to 76.00%,and whose activity is up to 1.71×107 g/(mol·h).The effects of N and P substituents in ligand skeleton,space volume,electron donor and electron attractor on the activity and selectivity of ethylene trimerization/tetramerization were analyzed.The increase of space volume or electron donor atom on the ligands can improve the activity and selectivity of ethylene trimerization/tetramerization.The problems such as pipeline clogging due to more by-products and higher cost of cocatalyst need be solved in the industrialization of ethylene tetramerization.
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