Study On Performance Of High Activity And High Directionality Propylene Polymerization Catalyst And Deash Process Of Polypropylene

The development of polyolefin technology is one of the important symbols of the development of petrochemical industry in a country.High purity polypropylene is widely used because of its low impurity content,good mechanical properties and corrosion resistance.Propylene polymerization catalyst and processing technology are the key to the synthesis of high performance polypropylene.Ziegler-natta catalyst has been developed to the sixth generation due to its good hydrogen modulation sensitivity and high activity,but the interaction between the components in the preparation process of the catalyst is not very clear.The residual catalyst affects the conductive properties,processing properties and serviceability of polypropylene resin during propylene polymerization.To solve these problems,interaction between components in the preparation process of Ziegler-Natta catalyst without external donor was studied,at the same time,the washing and deash process in the preparation and post-treatment process of polypropylene was also researched by the method of experimental and molecular simulation.The Ziegler-Natta catalyst was prepared by Ti Cl₄Ti-loaded reaction with Mg Cl₂/isoctanol/phthalic anhydride/n-decane as mother liquor and the interaction between the components and the effect on the properties of the catalyst were studied.The results showed that Mg Cl₂could inhibit the esterification reaction between iso-octanol and phthalic anhydride,while Ti Cl₄could promote the esterification reaction to diiso-octanyl phthalate（DOP）.Adjusting the amount of Mg Cl₂and Ti Cl₄could control the amount of hydroxyl group involved in the esterification reaction,controlling the amount of electron donated.The amount of iso-octanol in the mother liquor had a great influence on the particle size and particle size distribution.When the amount of iso-octanol increased,magnesium alcohol adduct formed,which was easy to cause the catalyst to break and produce fine powder.The complex formed by Ti Cl₄and internal electron donor 9,9-dimethoxymethyl fluorene（BMMF）might adsorb on the catalyst surface by chlorine bridge chemisorption,which affected the particle size of the catalyst.Reducing the amount of 9,9-dimethoxymethyl fluorene could inhibit the formation of the complex.On the basis of the above experiments,molecular simulation was used to reveal the interaction between components in the titanium-carrying reaction from the molecular level.Ti Cl₄could not spontaneously adsorb on the Mg Cl₂（110）crystal surface,but could spontaneously adsorb on the Mg Cl₂（100）crystal surface,and adsorb on the defects of Mg Cl₂support.The inner donor 9,9-dimethoxymethyl fluorene could be stably adsorbed on various types of crystal surfaces of Mg Cl₂（110）and Mg Cl₂（100）.When the internal electron donor,Mg Cl₂and Ti Cl₄were co-adsorbed,Ti Cl₄could be adsorbed on the surface of Mg Cl₂support preferentially than the internal electron donor,and the defects on the crystal plane were more conducive to the adsorption of Ti Cl₄.On the basis of the above studies,FTIR,SEM,BET,etc were used to characterize the synthesized propylene polymerization catalyst.The researched results showed that compared with the commercial Ref catalyst,the synthesized propylene polymerization catalyst had the advantages of concentrated particle distribution,less large particles and fine powder content,better regularity,no obvious fragmentation phenomenon,larger specific surface area,pore volume and pore size.The performance of propylene polymerization catalyzed by the synthesized propylene polymerization catalyst showed that the catalyst had excellent hydrogen conditioning performance.In the process of polymerization,the polypropylene isotacticity could reach 97%when the external electron donor such as cyclohexyl methyldimethoxysilane was added,while the isotacticity could still reach more than95%when the electron donor was not added.Using the catalyst to catalyze propylene polymerization could reduce the introduction of silicon extraneous electron donors,leading to the increase of ash content of polypropylene products.The washing and deashing technology of the polymeric products was studied.The solubility parameters of the washing solvent were calculated according to the formula of cohesive energy density and the molar attraction constant of the structural groups,so as to determine the better solvent.Hexane was determined as the deash solvent,and its solubility parameter was 14.9,which was close to that of polypropylene（PP）16.4.After washing with n-hexane,the volume expansion rate of polypropylene reached 33%,and the weight increased by 14.0%,which proved that n-hexane had obvious swelling effect on polypropylene,and n-hexane as the main detergent could improve the efficiency of ash washing removal.The ash content of polypropylene prepared by the propylene polymerization catalyst was 221.71μg/g,which was reduced to 33.39μg/g after washing in and out of the kettle,and the total ash removal reached 84.9%.The deash effect was obvious,which met the requirements of low ash polypropylene.The Results showed that the technical solution for preparation of high purity polypropylene was feasible with the technology of high activity no external electron donor propylene polymerization catalyst and washing deash.Compared with the imported Nordic chemical HC300resin,the synthesized polypropylene had high gauge,high weight average molecular weight,narrow molecular weight distribution and excellent heat resistance,meeting the foreign standards of high purity polypropylene.