Online switching method of metallocene catalyst and Ziegler-Natta catalyst

Abstract

The invention discloses an on-line switching method of a metallocene catalyst and a Ziegler-Natta catalyst, and the switching method does not need thorough reaction shutdown, does not need to open a reactor, does not need to replace a seed bed, and realizes switching in an original bed layer, so that the switching difficulty is greatly reduced, and the risk that a reaction system is exposed in air is avoided; the operation risk is also reduced, the consumed time is short and is only about 48 hours, and the cost is effectively reduced. In addition, CO2 and O2 are used as terminators of the Ziegler-Natta catalyst, the two terminators are easy to obtain and low in use cost, the terminating effect of the two terminators on the Ziegler-Natta catalyst is irreversible, the subsequent catalytic reaction of the metallocene catalyst is better facilitated, and the smooth proceeding of the switching process is also facilitated. By using the switching method provided by the invention, large-scale transformation of an existing raw material refining system, a catalyst filling system, a raw material feeding control system, an electrostatic control system and the like is not needed, so that the transformation investment cost is greatly reduced, and the operation state of the reactor before and after switching is stable.

Description

technical field [0001] The invention belongs to the technical field of on-line switching of polymerization catalysts, in particular to an on-line switching method of a metallocene catalyst and a Ziegler-Natta catalyst. Background technique [0002] Metallocene catalysts are single-site catalysts with high activity and can precisely customize the molecular structure of polyethylene resins, including relative molecular mass distribution, comonomer content, and distribution of comonomers on the molecular chain. direction of development. [0003] During the production and operation of the gas-phase polyethylene plant, it is necessary to switch between the Ziegler-Natta (titanium or chromium) catalyst and the metallocene catalyst. In the prior art, the off-line bed changing method is generally used to switch Ziegler-Natta catalysts and metallocene catalysts, that is, the reaction needs to be shut down first, the existing seed bed is emptied, and then the seed bed of the type to ...

AI Technical Summary

Problems solved by technology

If the Ziegler-Natta catalyst is operated under low hydrogen conditions, it will produce very high molecular weight polymers, and the combination of Ziegler-Natta catalysts and metallocene catalysis at 500 ppm hydrogen will lead to reaction products containing ultra-high molecular weight polymers and hard particles, handling of this polymer will be difficult

In addition, the catalyst killing agent used in the above method is a special organic terminator, which is not easy to obtain, and the cost of use is relatively high