Method for synthesizing polyethylene

Abstract

The invention discloses a method for synthesizing polyethylene, which comprises the following steps: (1) before a catalyst is injected, setting the temperature of a system to be 20-30% lower than the reaction temperature; (2) the catalyst is conveyed in a nitrogen flow mode, the feeding rate of the catalyst is 0.5-2.0 g / h, and the heating rate is 0.5-1.5 DEG C / h; (3) when the inlet temperature of the reactor reaches 90%-95% of the reaction temperature and the bed pressure difference of the reactor reaches 0.1 KPa to 0.6 KPa in the first section, 0.4 KPa to 0.7 KPa in the second section, 0.8 KPa to 2.0 KPa in the third section, 1.0 KPa to 1.8 KPa in the fourth section and 8.0 KPa to 12.4 KPa in the fifth section, the feeding rate of the catalyst is set to be 1.0-2.5 g / h, and the heating rate is set to be 1.0-5.0 DEG C / h; and (4) after the activity of the catalyst meets the design requirement and the polymerization system enters steady-state operation, the feeding rate of the catalyst is related to the change of the vicat softening point of a polymerization reaction product.

Description

technical field [0001] The invention belongs to the field of olefin polymerization, in particular to a method for synthesizing polyethylene, which is especially suitable for gas-phase fluidized bed reactors. Background technique [0002] Polyolefin production processes include slurry process, solution process, and gas phase process. With the advancement and development of technology, the advantages and disadvantages of each major production process are gradually emerging. Slurry method polyethylene, dispersed in a solvent to form a slurry, this production method solves the viscosity problem of the polymer solution, there is no limit to the MFR of the product, but there is a strict limit on the lower limit of the product density, generally at 0.935g / cm 3 About; the solution method is restricted by the viscosity of the solution, and has a certain limit on the lower limit of the product MFR, but there is no limit on the density; the gas phase method polymerizes ethylene in a ...

AI Technical Summary

Problems solved by technology

However, the production process control of high-end brands by major domestic production companies is not yet very mature, especially for the active release technology of emerging high-activity catalyst systems, they still lack experience, and most of them use the traditional pulsed continuous feeding method, which is no longer suitable for new-type catalysts. The high-activity catalyst’s polymerization characteristics require that it is very easy to cause the catalyst’s activity to be released too quickly, causing implosion or local hot spots, causing the device to flake, blocking each operation unit, and causing the device to stop production; at the same time, frequent switching of grades is important for the stability of resin performance. Sexuality also has a certain impact, leading to an increase in the complaint rate of downstream users

Therefore, in the development of high-end new products in China, there are shortcomings such as short device operation period and unstable performance of special materials, resulting in frequent shutdown of devices and excessive transition materials, which greatly affects the benefits of enterprises and restricts the process of domestic new product development.

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