The Construction Of Supported Metallocene Catalysis System And Its Application In Copolymerization Of 1-octene And Ethylene

1-octene/ethylene copolymer is a class of high-performance polyethylene with a density range of 0.860-0.960 g/cm~3,covering elastomers,plasticities and conventional polyethylene resins.It is widely used in many fields such as wires and cables,packaging films,pipes,and so on.Due to the large steric hindrance of 1-octene,the copolymerization performance of catalysts is highly required.Conventional catalysts can not meet the requirements.It is extremely urgent to develop an autonomous metallocene polyethylene catalyst system suitable for 1-octene/ethylene copolymerization.1-octene/ethylene copolymer is mainly produced in solution process and fluidized-bed process.Compared to solution process,fluidized-bed process has more advantages,mainly reflected in relatively mild reaction operating conditions(polymerization temperature of solution process is 150～300℃,pressure is 10～16 MPa;fluidized bed process temperature is75～110℃,pressure is 1.8～2.5 MPa),no solvent recovery,and lower production costs.Because of traditional fluidized-bed processes can only use in gas-solid two-phase polymerization operations,the high boiling point of 1-octene and its difficulty in gasification and dispersion in fluidized-bed reactor have led to unstable fluidization and complex operation.The key scientific issue of 1-octene/ethylene fluidized bed copolymerization is to innovate and realize the new stable construction of gas-solid liquid multiphase fluidization and achieve continuous and stable operation.In response to the urgent demand for 1-octene copolymerized polyethylene in China,the specific research content and results are as follows:1.Two rigid bridged metallocene complexes[(2-methylbenzoindene)(N-phenyl-5,10-dihydroindeno[1,2-b]indole)dimethylsilyl]zirconium dichloride and[(2-methylbenzoindene)(N-phenylindene[2,1-b]indole)dimethylsilyl]zirconium dichloride were designed and synthesized using common 1,1-diphenylhydrazine hydrochloric acid solution and 2-indene raw materials.[(2-methylbenzoindene)(N-phenyl-5,10-dihydroindeno[1,2-b]indole)dimethylsilyl]zirconium dichloride was chosed for 1-octene/ethylene copolymerization by homogeneous polymerization method.2.A combination of MAO treatment and thermal activation was used to modify the surface of the silica carrier,and the suitable silica supports were selected.The optimal activation process for the support was determined.Under the conditions of 10 wt%methylaluminoxane concentration,6 m L/g silica gel dosage,and activation time of 6 hours,the number of hydroxyl groups on the surface of 955 silica treated decreased from 2.38 per square nanometer to 1.72.A supported metallocene catalyst was prepared using[(2-methylbenzindene)(N-phenyl-5,10-dihydroindeno[1,2-b]indole)dimethylsilyl]zirconium dichloride.The catalyst particles have a regular morphology and uniform particle size.3.The influence of 1-octene/ethylene copolymerization parameter on the performance of supported metallocene catalysts and their resulted polymer was studied in a 5L autoclave reactor.Under the conditions of Al/Zr molar ratio=300,polymerization time 2 hours,polymerization pressure 1.0 MPa,and 1-octene addition of 8 m L,the polymerization activity of supported metallocene Cat-1 can reach 1823 g PE/g Cat.The bulk density of the polymerization products was higher than 0.30 g/cm~3,the polymerization particle size is concentrated in 35-60 mesh,and the fine powder content is 0.59%.By adjusting the polymerization process parameters,the performance of the catalyst and structure of polymerization products can be regulated.4.Based on self-developed supported metallocene catalyst,a fluidized bed reactor model was studied after introducing 1-octene.The fluidization state in a 50 kg/h gas-phase fluidized bed pilot plant was simulated.When 1-octene was introduced into the fluidized bed reactor,the ratio of heat absorption and release based on unit particle mass per unit time in the fluidized bed layer was between 1.15 and 1.34.Under this condition,the steady-state of the gas-liquid-solid three-phase zone can be achieved.By studying the formation and fracture mechanisms of1-octene liquid film and liquid bridge,the optimal size of 1-octene droplets introduced into the fluidized bed reactor was determined to be≤0.6 mm.The copolymerization of 1-octene and ethylene was achieved in a 50 kg/h gas-phase polyethylene pilot plant,which validated the gas-solid-liquid three phase fluidized bed reactor model mentioned afore.Then the operating status of the pilot plant after the introduction of 1-octene was systematically investigated.The boundary conditions of the plant were confirmed,and a long-term stable operation of 880 hours was achieved.A series of 1-octene copolymer products were developed.5.The"melt memory effect"and tensile properties of typical 1-octene copolymer were studied.It was found that at different melt temperatures,the introduction of a small amount of1-octene could make the polymer melt temperature appear four regions:incomplete melting(zone I),crystal residue or chain segment orientation residue(zone II),phase separation melt structure gradually disappearing(zone III),and uniform melt structure(zone IV).The pilot product of 1-octene/ethylene exhibits high yield stress and large strain hardening during the tensile process,exhibiting higher amorphous network modulus.