Design Of Key Components For Gas Phase Fluidized Bed Reactor And Research On Polymerization Process Of 1-hexene/ethylene

At present,the general polyethylene is mainly modified by copolymerization ofα-olefin and ethylene.Numerous high-performance polyethylene new products are developed to meet the new requirements in various fields.The preparation of high-performance polyethylene products in a gas phase fluidized bed reactor（FBR）with metallocene catalyst by copolymerization of 1-hexene and ethylene is a research hotspot.As to the high 1-hexene content of polyethylene products,a large number of liquid phase monomers is need to introduce into the FBR.The excessive monomer is easy to congregate in the bottom of FBR and form into liquid-bridge,which lead to agglomeration of polymer particles and breaking the fluidization state of the fluidized bed reactor.Therefore,the continuous operation of the polymerization reaction is deteriorated.In this paper,the key components of the fluidized bed reactor were innovatively designed by simulating the structure and polymerization state of the 50 kg/h gas phase full density polyethylene pilot plant.Based on the study of supporting metallocene catalyst and the morphology replication mechanism of catalyst particle,a novel catalyst system for polyethylene polymerization in gas phase process was constructed.Using the optimized pilot FBR and developed catalyst system,the polymerization characteristics of1-hexene/ethylene in gas-phase polyethylene process were studied,and the pilot products of medium density polyethylene rotary molding and polyethylene elastomer（POE）were prepared.This study is of great significance to the development of new technology and new products of polyethylene.In order to construction a versatile fluidized bed reactor for the1-hexene/ethylene copolymerization,the liquid monomer was introduced into reactor through an atomizing nozzle in the form of micro-droplets to ensure the uniform distribution of 1-hexene monomer.The atomizing nozzle was developed and designed through simulation.The influencing factors such as droplet diameter,droplet injection velocity,nozzle injection direction,nozzle diameter and nozzle form（hollow/solid cone）were systemly investigated.After optimization,the optimal position for introduction of 1-hexene was axial Z=1.6～1.75 m in the fluidized bed reactor.In addition,an innovative design was carried out on the internal component distribution plate of the fluidized bed reactor.Three kinds of distribution plate,which are the opposite side hole wind cap distribution plate,triangular cap distribution plate and umbrella-shaped distribution plate,are calculated and simulated.The results show that the side hole hood distribution plate was most fit for fluidized reactor.Under this structure,the solid phase is more likely to fluidize,the fluidization time required to reach the stable fluidization state is the shortest,and the fluidization under the distribution plate structure is more sufficient.A metallocene supporting technology was developed and a proprietary catalyst MPC-8 was also obtained.[t-Bu NC（Me）₂（η₅-C₅H₄）]Zr Cl₂ was used as main metallocene.The evaluation polymerization of supported metallocene catalyst MPC-8 are studied.The influence of reaction conditions such as reaction temperature,pressure,reaction time,amount of alkyl aluminum,dosage of comonomer on supported metalloceme catalyst and polymerization reaction kinetics were investigated.Compared with imported catalyst,the particle shape of MPC-8 is better,the particle size distribution is more uniform,and the replication function is better.The catalyst center distribution of the MPC-8 is homogeneous with the activity of 1.15×10⁷ g PE/mol Zr.In order to test the internals and atomizing nozzles of fluidized reactor,a medium density polyethylene rotary molding product,MPER3405,was produced in a pilot plant.The melt flow rate and density of resulted product were 5.1 g/10 min and 0.9334 g/cm³.When used in rotary molding,MPER3405 has better toughness.In the end,1-hexene copolymerized POE product was prepared by using MPC-8catalyst.The calibrated catalyst activity reached 14330 g PE/gcat.The product density range is 0.890～0.910 g/cm³.The basic properties,auxiliary system and toughening application of the pilot product were studied.The results showed that the content of higher-olefin copolymer monomer was 10.74 wt%and the weight average molecular weight was 1.5×10⁶～3×10⁶.The brittle-ductile transition point of PP/POE blends was 10 wt%POE and the toughening effect of PP at-20°C was obvious when the POE content was 15%.