Stabilising high-pressure (co)polyethylene - with one-phase antioxidant system added to reaction mixt. after leaving reactor but before separation

摘要

High pressure, i.e. low density (co)polyethylene is stabilised by adding the anti-oxidants to the reaction mixt. after leaving the reactor but before separation in standard separation equipment. The anti-oxidants consist of one-phase stabiliser systems stable under high pressure. The stabiliser systems can be mixts. of a high mol.wt. sterically hindered phenol, a phosphite stabiliser or a thio cpd. either of which dissolves with difficulty under a high pressure, or a mixt. of these cpds. with a low mol.wt. sterically hindered phenol. The anti-oxidants are added to the reaction mixt. in the pressure-release zone after leaving the autoclave reactor. The anti-oxidants can be added to the reaction compartment or to the mixt. in the reactor pressure relaxation valve zone. The anti- oxidants are pref. added at a distance which is at least 10 times the nominal dia. of the relevant pipe cross-section in front of the reactor pressure relaxation valve and no more than 20 times the nominal width of the relevant pipe cross-section after the reactor pressure relaxation valve in the high pressure zone of 800-2000 bar. The prods. have improved properties, esp. improved drawability.