Direct conversion of a polymerization reaction catalyzed by a Ziegler-type catalyst into one catalyzed by a chromium-based catalyst

Claim 1

A process for converting a continuous olefin polymerization reaction catalyzed by a Ziegler-type catalyst comprises of (1) a transition metal halide, and (2) an organometallic compound of a metal of Groups I to III of the Mendelyveev Periodic Table, into one catalyzed by a chromium-based catalyst which comprises (a) discontinuing the introduction of the components of the Ziegler catalyst system into the polymerization reactor; (b) maintaining polymerization conditions in the reactor and permitting polymerization to continue for a time in order to allow the components of the Ziegler catalyst system present in the reactor to consume themselves in the production of additional polymer; (c) introducing a hydroxyl-containing compound into the reactor, said hydroxyl-containing compound having carbon-hydroxyl or metal-hydroxyl linkages which are capable of reacting with the organometallic component of the Ziegler catalyst system to form a Lewis acid, and circulating said hydroxyl-containing compound in the reactor, while continuing to maintain polymerization conditions, for a time sufficient to allow said hydroxyl-containing compound to interact with the components of the Ziegler catalyst system; and then (d) introducing a chromium-based catalyst into the reactor under polymerization conditions suitable for said catalyst at a rate of from 25 percent to 100 percent of the rate employed during polymerization to maintain a catalytically effective amount of such catalyst in the reactor, and maintaining said conditions until polymerization with said catalyst has initiated.