Various activation procedures of Phillips catalyst for ethylene polymerization

Abstract

Nowadays, the Phillips CrOx/SiO2 catalyst is still attracting interest from both industrial and academic fields owing to its unique characteristics for HDPE production. Compared with other industrial catalysts for ethylene polymerization, the Phillips catalyst can be activated by ethylene monomer, CO or Al-alkyl cocatalyst after a simple calcination process (thermal activation). In this work, a brief review of our recent new understanding on various activation procedures, including thermal activation, monomer activation, and CO activation, on industrial Phillips catalyst was presented. A new initiation mechanism, ethylene metathesis mechanism, was proposed according to some experimental evidence during the induction period when ethylene monomer was used to activate the catalyst. Such an ethylene metathesis mechanism was also indirectly confirmed in CO-prereduced Phillips catalyst. The formation of short chain branches in polymer can be rationalized well by this newly proposed unique mechanism during ethylene homo-and copolymerization with hexene-1 using CO-prereduced Phillips catalyst in the presence of triethylaluminum cocatalyst.