ES353811A1 - Polymerisation of ethylene - Google Patents

Abstract

The continuous polymerization of ethylene in two or more zones comprises passing ethylene through a first polymerization zone at a pressure of not less than 1600 atmospheres and a temperature of not less than 125 C. in the presence of a Ziegler type initiator and passing the mixture of polymer and unreacted monomer to a second zone at a pressure of at least 1600 atmospheres and a temperature higher than the lowest temperature in the first zone in the presence of a free-radical forming initiator, the combined conditions of temperature and pressure being such that the polymerization reaction takes place in a single fluid phase and the reaction mixture remains as a single fluid phase until removal from said zone. In the first zone the temperature is preferably from 145 to 220 C., and the residence time is not more than 6 minutes. A suitable Ziegler type initiator is one which causes at least 3,000 moles of ethylene to be polymerized per mole of Group 4A, 5A or 6A metal compound component of the initiator. The Ziegler type initiator which may have a particle size not exceeding 5 microns, may be protracted by polymerizing it in contact with an unbranched [alpha]-olefin containing at least 6 carbon atoms. A free radical forming initiator active at the temperature of the first zone, may be introduced into the first zone. Chain transfer agents, such as hydrogen, paraffins or [alpha]-olefins, may be present in the zones. In the example, ethylene containing hydrogen as a modifier, is polymerized in a two zone reaction. The Ziegler initiator was formed by mixing in pentamethyl heptane, aluminium diethyl chloride and titanium trichloride, and exposing this mixture to hexene-1, resulting in the formation on the catalyst of polyhexene. The free radical forming catalyst was tertiary butyl perbenzoate.