Preparation method of propylene random copolymer

Abstract

The invention relates to a preparation method of a propylene random copolymer. The method comprises the steps of continuously carrying out liquid phase copolymerization of propylene and ethylene and gas phase copolymerization of propylene and ethylene in multiple reactors in sequence in the presence of catalysts and hydrogen, wherein the liquid phase copolymerization temperature and pressure are respectively 60-85 DEG C and 2-5MPa; the gas phase copolymerization temperature and pressure are respectively 70-90 DEG C and 1-3MPa; the catalysts are reaction products of a main catalyst, a cocatalyst and an external electron donor compound; the mass ratio of the addition of the catalysts to the addition of propylene is 0.00001-0.0001; the mass ratio of the addition of hydrogen to the addition of propylene is 0-0.0005; and the mass ratio of the addition of ethylene to the addition of propylene is 0.03-0.045. The preparation method has the following beneficial effects: the propylene random copolymer with a lower melting point is obtained under the condition of lower content of comonomer ethylene, and the propylene random copolymer has wider molecular weight distribution (PI(polyimide)), therefore the polymer has good mechanical properties and excellent processing properties, and the obtained product has good surface properties and can be widely applied to pipe production.

Description

technical field [0001] The invention relates to a method for preparing a propylene random copolymer, in particular to a method for preparing a propylene-ethylene random copolymer on a kettle-type continuous polymerization process device. Background technique [0002] At present, the propylene polymers used in the industry to prepare hot water pipes are all produced by conventional Ziegler-Natta catalysts, and the impact resistance of the prepared propylene homopolymer is not good. In order to improve its impact resistance, people pass Propylene is copolymerized with a small amount of comonomers such as ethylene to obtain random copolymers. But the copolymerization performance of conventional Ziegler-Natta catalyst is not good, the distribution of the comonomer in the polymer molecule in its obtained copolymer is not uniform enough, when its comonomer content is low, the melting point of the obtained copolymer is not low enough, resistance The impact performance is not high ...

AI Technical Summary

Problems solved by technology

But the copolymerization performance of conventional Ziegler-Natta catalyst is not good, the distribution of the comonomer in the polymer molecule in its obtained copolymer is not uniform enough, when its comonomer content is low, the melting point of the obtained copolymer is not low enough, resistance The impact performance is not high enough; when the comonomer content is further increased, the xylene soluble matter of the polymer will increase, which will easily cause the stickiness of the polymer powder, which is not conducive to industrial production

In addition, the molecular weight distribution of polymers produced by conventional Ziegler-Natta catalysts is not wide enough, and the PI value measured by rheology is relatively low, especially when producing polymers with low melt index, the PI value is even lower, which makes the polymer processability not good. Well, the production load is reduced, and the surface of the pipe products obtained with this polymer is not smooth enough

In response to the above problems, industrially adopt multi-tank or multi-loop polymerization process to make the concentration of hydrogen in each kettle or loop different, so that the polymers with different molecular weight distribution produced by each kettle or loop can make the final product The polymer has a wide molecular weight distribution, but this method also has certain limitations. When producing low melt index polymers, it is difficult to widen the hydrogen concentration in multiple reactors, so it is difficult to obtain the desired molecular weight Distributed polymer, but also possible to reduce the load on the polymerization plant

The industry also improves the processing performance of polymers by adding plasticizers such as fluororesins to polymers, but the processing performance of such plasticizers is limited and expensive

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