Continuous process for the preparation of polyolefins having widely distributed molecular weights

Claim 1

In a process for preparing polyolefins by polymerizing olefins in the presence of a solvent, hydrogen and a highly active Ziegler-type catalyst comprising a transition metal compound supported on a solid carrier and an organometallic compound, in a plurality of reactors, to prepare polyolefins having widely distributed molecular weights, the improvement comprising: (a) polymerizing olefins in a first stage reactor at a temperature of from 30° to 100° C. and a pressure of from 2 to 100 kg/cm 2 , in the presence of a gas phase containing an inert gas in the upper portion of the reactor to form a polymerization reaction mixture comprising a dispersion of relatively high molecular weight polymer particles in the solvent, the concentration of said inert gas in said gas phase being from 40 to 99 mol %; (b) continuously effecting the flow of the polymerization reaction mixture from the first stage reactor to a second stage reactor, the second stage reactor maintained at a pressure lower than that of the first stage reactor, whereby the flow of polymerization reaction mixture is driven by the pressure difference; (c) subsequently polymerizing olefins in the second stage reactor, with agitation and beneath a gas phase containing hydrogen and olefins to form polymers having a relatively lower molecular weight, the olefin polymerization in said second stage reactor being effected by supplying hydrogen and additional olefin monomers; and (d) continuously removing from the second stage reactor a polymerization reaction mixture containing polyolefins having widely distributed molecular weights, dispersed in the solvent.