FIELD: chemistry.
SUBSTANCE: invention relates to a procatalyst composition, methods of preparing such compositions and to methods of using such compositions to produce polymers. The Ziegler-Natta procatalyst composition which is in form of solid particles and is meant for polymerisation of olefins, contains magnesium, a halide and a transition metal as components, where the said particles have average size (D50) which ranges from 10 to 70 mcm. The composition is distinguished by that, at least 5% of the particles are empty inside and are essentially or completely surrounded by a monolithic surface layer (shell), where the said layer is distinguished by average ratio of thickness of the shell to particle size (thickness ratio), which is determined through scanning electron microscopy (SEM), which exceeds 0.2 for particles with size over 30 mcm. The method of obtaining the above mentioned procatalyst composition involves the following steps: a) preparing a liquid composition which contains i) a magnesium halide, ii) a solvent or diluent, iii) a transition metal compound, where the transition metal is selected from group 3-10 metals and lanthanides, iv) an optional internal electron donor and v) as well as optional filler; b) spray drying the composition so as to obtain spray-dried particles; and c) collecting the obtained solid particles. The method is distinguished by that, the magnesium halide forms an essentially saturated solution in the solvent or diluent, and that, in order to obtain spray-dried particles at step b) with particle size defined in paragraph 1, the said spray drying is carried out by passing the liquid composition obtained at step a) through a suitable spraying device together with an inert drying gas, where bulk flow of the drying gas is considerably greater than bulk flow of the said liquid composition, and the said suitable spraying device is an atomiser or a centrifugal high-speed disc, where i) when the said spraying device is an atomiser, size of the obtained particles is controlled by selecting pressure of the drying gas such that, a suitable droplet size is provided, and pressure of the drying gas in the atomiser essentially varies from 100 to 1500 kPa; or ii) when the said spraying device is a centrifugal high-speed disc, size of the obtained particles is controlled by selecting diametre and speed of rotation of the centrifugal high-speed disc, and when basically using a centrifugal disc with diametre ranging from 90 mm to 180 mm, speed of rotation of the disc ranging from 8000 to 24000 rpm is chosen.
EFFECT: obtaining catalyst with high mechanical strength, which leads to reduced content of fine polymer particles, but has high efficiency and activity during polymerisation at the same time.
15 cl, 2 tbl, 3 dwg
