Studies On The Activity And Supports Of Ti-Mg Catalyst

Ziegler-Natta catalysts for polyethylene is the most widely-used catalyst for itsmerits in easy preparation and low sensitivity on O₂ and H₂O, but the existingquestions about low catalytic activity and low bulk density still puzzle the operatorsand managers. Therefore, the impovement on the catalytic activity and bulk densityis indispensable and significative.The study on Ziegler-Natta catalyst focuses on the MgCl₂ support and electrondonor. In this paper, the factors that affect the catalytic activity were studied, and theoptimal polymerization condition were determined. Second, the factors that affectthe bulk density were investigated. Thirdly, based on the recrystallization techniques,several ethanols, diols and electron donors were studied and the methods about howto get supports with smaller particle size and greater surface area were obtained. Themain results in this theis can be summarized as follows:1. The factors that affect of the activity of the catalyst were studied. Theexperimental results showed that the catalyst got its best activity at 80-85℃andAl/Ti molar ratio 120-140. The electron donor ethyl benzoate(EB) can improvethe activity by 50% to 70%, and ethyl acetate can improve the activity by 30%. ButDibutyl o-phthalate(DNBP) and 1,4-dioxane reduce the activity.2. The factors that affect of the bulk density of the polyethylene were studied. Theexperimental results showed that the bulk density increase as the polymerizationtime decrease, as the catalytic activity decrease. the reason is that as the catalyticincreases and the polymerization time increases, the polymer chain get longer, andthe polymer particles get bigger, so the void fraction between different particlesincrease. As a result, the bulk density decrease.3. Based on the recrystallization techniques, several ethanols, diols and electrondonors were studied and the methods about how to get supports with smaller particlesize and greater surface area were obtained. (1) The effects of ethanol, n-propanol, n-butanol, n-pentanol and n-hexanol onMgCl₂ supports were studied. The result showed that as the C-chain of the ethanolincrease, the surface area of the obtained supports increase and the particle sizedecrease. The surface area and particle size of the support obtained from ethanolsolvent was 101.5m²/g and 19.816μm, and the surface area and particle size of thesupport obtained from ethanol solvent was 160.8m²/g and 11.014μm.(2) The effects of THF/ethanol hybrid solvents on MgCl₂ supports were studied.The result showed that the surface area and particle size of the support weredetermined by the part of the hybrid solvent which have bigger solubility on MgCl₂.The solubility on MgCl₂ varies in this order: n-hexanol≈n-pentanol≈n-butanol≈n-propanol>THF>ethanol.(3) The effects of electron donors on MgCl₂ supports were studied. EB and DNBPcan improve the support well. The addtion of EB makes a support with surface area137.2m²/g and particle size 13.991μm, while the addtion of DNBP makes a supportwith surface area 180.6m²/g and particle size 13.855μm. But 1,4-dioxane makes thesupport agglomerate, the particle size grows to 69.179μm.(4) The effects of diols on MgCl₂ supports were studied. The analytical resultsshow that after treated by diols, the surave area and the particle size improve a lot.The surface area and particle size of the support obtained from ethanediol was187.4m²/g and 10.986μm, and the surface area and particle size of the supportobtained from 1,4-butanediol was 197.9m²/g and 9.454μm. After TiCl₄ treatment, thesurface area of the support obtained from 1,4-butanediol increase to 251.4m²/g. Theactivity of the catalysts based on the MgCl₂ treated by n-hexanol and1,4-butanediol can reach 3029gPE/gcat/2h and 3374gPE/gcat/2h, improved by 39% and 54%compared with the catalyst with MgCl₂/silical support.