GB1071305A - Polymerization process - Google Patents

Abstract

Polyethylene resins having a broad polymodal molecular weight distribution are prepared by a process which comprises passing a first ethylene gas stream at 700 to 2700 atmospheres and 150 DEG to 260 DEG C. through a first reaction region, adding thereto a first catalyst effective at 190 DEG to 245 DEG C., passing a second ethylene gas stream at 650 to 1200 atmospheres, but at least 70 atmospheres less than the pressure in the first reaction region, and 230 DEG to 275 DEG C. through a second reaction region, adding thereto a second catalyst effective at 245 DEG to 290 DEG C., removing reaction mixture from the end of said first reaction region and feeding it into said second reaction region at a point intermediate its ends, the reaction product from said first region commingling with the reaction mixture in said second region in a proportion of 3.3 to 20/1 by weight, and removing the resulting composite reaction product and separating the polyethylene therefrom. The first reactor may be divided by partitions into more than one zone. The second reactor may also be divided and the product of the first reactor introduced into the first or "reaction" zone when further polymerization occurs in the presence of said product or into the second or "mixing" zone. Specified first catalysts are methyl ethyl ketone peroxide, t.-butyl hydroperoxide, di-t.-butyl peroxide, t.-butyl perbenzoate and t.-butyl peracetate. Specified second catalysts are methyl ethyl ketone peroxide, p-menthane hydroperoxide, t.-butyl hydroperoxide and di-t.-butyl peroxide. Catalysts may be introduced in an inert hydrocarbon diluent, e.g. kerosene, at one or more points in the reactors. Modifiers, e.g. isobutylene, propylene, n-butane and propane, may also be added. Apparatus suitable for carrying out the process of the invention is described and illustrated and in examples ethylene is polymerized using as catalyst (I, II, IV and V) t.-butyl perbenzoate in the first reactor and di-t.-butyl peroxide in the second, and (III) diisopropyl peroxydicarbonate, t.-butyl perisobutyrate and di-t.-butyl peroxide successively in each reactor.