Synthesis And Performance Study Of New Structure PNP Chromium Ethylene Oligomerization Catalyst

In this paper,a series of 1.0G hyperbranched macromolecules with different end-group core alkyl chain lengths are used as ligand frameworks,followed by substitution and complexation reactions with chlorodiphenylphosphine and Cr Cl₃（THF）₃in sequence.And synthesized a series of homogeneous hyperbranched PNP chromium catalysts with different core alkyl chain lengths.Then,using FT-IR,UV,¹H-NMR,³¹P-NMR and ESI-MS and other test methods,the structure of the synthesized hyperbranched PNP ligand and its chromium-based catalyst were characterized.On the basis of synthesis and characterization,the oligomerization performance of hyperbranched PNP chromium catalysts was studied.The types of solvents,types of cocatalysts,reaction temperature,Al/Cr molar ratio,reaction pressure and the amount of catalyst were used to catalyze influence of ethylene oligomerization performance;In addition,hyperbranched the effect of alkyl chain length at the core of PNP chromium catalyst on catalytic performance.The results show that when R₆-C₂-P-Cr is the main catalyst,toluene is the solvent,MAO is the cocatalyst,the reaction temperature is 35℃,the ethylene pressure is 0.5MPa,the catalyst dosage is 2μmol,and the Al/Cr molar ratio is 500,the reaction time is 30min,the catalytic activity can reach up to1.92×10⁴g/（mol Cr·h）,and the total selectivity to hexene and octene reaches 39.11%.In addition,as the length of the alkyl chain at the core of the hyperbranched PNP chromium catalyst increases,the catalytic activity continues to decrease,while the selectivity to hexene and octene also decreases.Based on the above research on homogeneous hyperbranched PNP chromium catalysts,this paper takes the mixed organometallic（MixMOFs）structure as the framework,and introduces the PNP ligand into the MixMOF containing amino groups for the first time through the post-synthesis modification method.The amino group is converted into a functional group,and finally through a complex reaction with Cr Cl₃（THF）₃,a heterogeneous MixMOFs grafted PNP chromium catalyst（MixMOFs-PNP-Cr）is synthesized,and FT-IR,XRD,SEM and other test methods are used structural characterization of the synthesized MixMOFs,MixMOFs-PNP ligand and MixMOFs-PNP-Cr catalyst;Then,the effects of solvent type,cocatalyst type,reaction temperature,Al/Cr molar ratio,and reaction pressure on the ethylene oligomerization performance of MixMOFs-PNP-Cr catalyst were investigated in detail.The results show that when cyclohexane is used as the solvent,dichloroaluminum monochloride is used as a cocatalyst,the reaction temperature is 25℃,the ethylene pressure is 0.5MPa,the catalyst dosage is 2μmol,the Al/Cr molar ratio is 600,and the reaction time is30min,the catalytic activity can reach up to 2.57×10⁴g/（mol Cr·h）.In addition,the study also found that MixMOFs-PNP-Cr catalyst catalyzes the oligomerization of ethylene with butene as the main product,and also has certain selectivity to hexene and octene（hexene and octene selectivity up to 35.78%）,With lower selectivity to higher carbon olefins(≥C₁₀).