Synthesis And Catalytic Performance Of Hyperbranched Metal Catalysts In Ethylene Oligomerization

α-Olefin is one of the important chemical raw materials,which is widely used in the fields of pipes,lubricating oils,cars,surfactants,additives of oil and food packaging etc.The ethylene oligomerization technology is main method to prepare α-olefin production in industry.The core technology of ethylene oligomerization is the research of catalyst.In this work,according to the research focus of catalysts for ethylene oligomerization and the characteristic of functionalized modification for functional groups of hyperbranched macromolecules,a series of transition metal complexes were creatively designed and synthesized with low generation hyperbranched macromolecules as skeleton.The complexes were used as catalysts for ethylene oligomerization to synthesize olefins and the structure-property relationship was analysed.Based on the research of ethylene oligomerization mechanism,the dynamic model was builted.The main research contents and results are listed below.1.A series of hyperbranched salicylaldimine ligands and hyperbranched iminopyridyl ligands with different length of alkyl chain in terminal groups were synthesized with 1.0G hyperbranched macromolecules as ligand skeletons.Then a series of hyperbranched salicylaldimine iron,cobalt and nickel catalysts as well as hyperbranched iminopyridyl iron,cobalt and nickel catalysts with different length of alkyl chain in molecular cavity were synthesized by the complexation reaction between hyperbranched ligands and MCl2·x H₂O（FeCl₂·4H₂O,CoCl₂·6H₂O,NiCl₂·6H₂O）.The hyperbranched ligands and the corresponding metal complexes were characterized by Fourier transform infrared（FT-IR）spectroscopy,nuclear magnetic resonance hydrogen（1H NMR）spectroscopy,ultraviolet（UV）visible spectroscopy and electrospray ionization mass spectrometry（ESI-MS）.2.Activated with alkyl aluminium,the effects of oligomerization system on catalytic performance of hyperbranched salicylaldimine iron,cobalt and nickel catalysts were investigated,and the research results showed that the hyperbranched salicylaldimine metal catalysts showed better catalytic properties when toluene was used as solvent and MAO was used as co-catalyst.Furthermore,the study results of process parameters showed that the optimum reaction conditions of hyperbranched salicylaldimine iron and nickel catalysts were the reaction temperature of 25 ℃,ethylene pressure of 0.5 MPa and Al/M molar ratio of 500.However,the optimum reaction conditions of hyperbranched salicylaldimine cobaltcatalyst were the reaction temperature of 25 ℃,ethylene pressure of 0.5 MPa and Al/M molar ratio of 1000.Under the optimum reaction conditions,the selectivity of high carbon olefins（≥C8）of hyperbranched salicylaldimine cobalt catalyst with dodecylamine as core and ethylenediamine in molecular cavity（R12-C2-S-Co）was the best,reaching up to 61.58%.3.In order to investigate the effect of the structure of ligand complexing groups on the catalytic performances in ethylene oligomerization,the catalytic performances of hyperbranched iminopyridyl metal catalysts were researched based on the study for the catalytic properties of hyperbranched salicylaldimine metal catalysts,and the researched results showed that with the increase of reaction temperature and Al/M molar ratio,the catalytic activity firstly increased and then decreased,and the selectivity of high carbon olefins（≥C8）decreased,however,the catalytic activity and selectivity of high carbon olefins（≥C8）increased with increasing of ethylene pressure.The catalytic properties of hyperbranched iminopyridyl nickel catalyst with dodecylamine as core and ethylenediamine in molecular cavity（R12-C2-I-Ni）were better when toluene was used as solvent and MAO was used as co-catalyst under the optimum reaction conditions,and catalytic activity of1.56×106 g/mol Ni·h and selectivity of 29.45% for high carbon olefins（≥C8）was obtained.4.Based on the study of catalytic performances of hyperbranched metal catalysts,the structure-property relationships were researched,and the results indicated that the catalytic activity was higher when the alkyl chain of skeleton was shorter,the steric hindrance was smaller and the amount of metal active species was larger.However,the selectivity of high carbon olefins（≥C8）was greater when the amount of metal active species and the steric hindrance of ligand were smaller.Under the same reaction conditions,the tendency of the catalytic activity for the hyperbranched metal catalysts which had the same ligand structure and different metal active species in sequence from high to low was: the nickel catalysts,the cobalt catalysts and the iron catalysts.In addition,under the same catalytic system and process parameters,the catalytic activities of hyperbranched iminopyridyl metal catalysts were higher,but the selectivity of high carbon olefin（≥C8）were lower when compared with hyperbranched salicylaldimine metal catalysts.5.The mechanisms of ethylene oligomerization for the hyperbranched salicylaldimine metal catalysts and hyperbranched iminopyridyl metal catalysts were assumed according to Cossee-Arlaman reaction mechanism.The reaction rate equations of catalystic ethylene oligomerization of R12-C2-S-Ni and R12-C2-I-Ni were derived combining four elementary reactions of active species activation,chain initiation and chain propagation,chain transfer as well as catalyst deactivation,and the corresponding kinetic parameters were obtained at the same time.According to the dynamic model,the calculated values of reaction rate for the hyperbranched salicylaldimine nickel catalyst R12-C2-S-Ni and hyperbranched iminopyridylnickel catalyst R12-C2-I-Ni were basically the same as the experimental values.