Catalyst composition for ethylene gas-phase polymerization or co-polymerization, preparation and applications thereof

Abstract

The invention relates to a catalyst composition for ethylene gas-phase polymerization or co-polymerization, preparation and applications thereof. The preparation method comprises the following steps: dissolving a titanium compound, an iron compound, and a magnesium compound in tetrahydrofuran so as to obtain a mother liquid; adding a modified silica carrier, which has been subjected to a thermal treatment and a chemical treatment, into the mother liquid, carrying out refluxing for 1 hour under stirring, blow-drying the mother liquid with high-purity nitrogen gas to remove the excess tetrahydrofuran, controlling the residual tetrahydrofuran content to be in a range of 10 to 15 wt% of the total weight of the product, floating the obtain solid in a low-carbon alkane solvent, carrying out a reduction treatment for 30 minutes on the solid at a room temperature by using one or more alkyl aluminum compounds, and then blow-drying the product with high-purity nitrogen gas so as to obtain the catalyst composition. The catalyst has a high catalytic activity when the catalyst is used to catalyze ethylene polymerization especially the gas-phase fluidized bed polymerization; and can prepare polyethylene products with a wide molecular weight distribution or double-peak distribution. The prepared polyethylene product has a high bulk density and little fine powder.

Description

technical field [0001] The invention relates to a catalyst suitable for producing bimodal or broad-modal distribution polyethylene in a single reactor and a preparation method thereof, in particular to a bimetallic silica gel carrier catalyst composition suitable for ethylene polymerization or copolymerization and its preparation method. Background technique [0002] Polyethylene resin is one of the four major synthetic resins. High-performance polyethylene resin must have high toughness, high strength and high environmental stress cracking resistance. Increasing the molecular weight of polyethylene can lead to a corresponding improvement in these properties. However, as the molecular weight of the polymer increases, the processability of the resin generally decreases. By preparing polymers with a broad or bimodal molecular weight distribution, not only can the characteristic properties of high molecular weight resins be maintained, but the processability of the resins can...

AI Technical Summary

Problems solved by technology

That is to mix resins with different molecular weights in a molten state. This method is not only costly, but also difficult to achieve complete and uniform blending of the resins, which affects the final properties of the resins;

[0004] (2) By performing staged polymerization in multi-stage reactors, a relatively uniform resin can be obtained, and the operation and adjustment flexibility is relatively large, but there are problems affecting efficiency and high cost;

[0008] Chinese patent CN101225129A discloses that a composite catalyst composed of two late transition metals iron and nickel is used to prepare bimodal polyethylene, but the required cocatalyst is generally methyl aluminoxane, resulting in higher production costs of bimodal polyethylene

[0010] As can be seen from the catalysts disclosed in the above-mentioned patents, although the multi-active center catalysts formed by two or more Ziegler-Natta type catalyst components can be used to prepare broad distribution or bimodal distribution polyethylene resins, there is still activity. The low problem is generally below 100,000 g / g metal; and for the Ti / V catalyst system disclosed in Chinese patent CN88101779, the molecular weight distribution of the obtained polyethylene resin is also relatively narrow, and its melt flow ratio (MFR) is 40 ~70

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