Kinetic and microstructural studies of Cp2ZrCl2 and Cp2HfCl2-catalyzed oligomerization of higher α-olefins in mPAO oil base stocks production

• Main Authors: Ahad Hanifpour, Mahdi Hashemzadeh Gargari, Mohammad Reza Rostami Darounkola, Zahra Kalantari, Naeimeh Bahri-Laleh
• Format: Article
• Language: English
• Published: Iran Polymer and Petrochemical Institute 2021-01-01
• Series: Polyolefins Journal
• Subjects: olefin; oligomerization; metallocene; microstructure; oil
• Online Access: http://poj.ippi.ac.ir/article_1755_a54ba3e64d3a81a3dbd5ff1205cd9e3e.pdf
• ISSN: 2322-2212; 2345-6868

Herein a quenched-flow kinetic technique was applied to calculate the rate constants of 1-hexene and 1-octene oligomerization catalyzed by the Cp₂ZrCl₂ and Cp₂HfCl₂/MAO catalyst systems, and subsequently a mechanism for the higher α-olefin oligomerization reaction was proposed. The oligomerization results showed that Zr-based catalyst in the oligomerization of 1-octene had the highest activity of 17 in comparison to Hfbased one with an activity value of 15 g oligomer/(mmolCat.h)). According to the obtained results, increasing monomer length led to a shift in molecular weight and polydispersity index value (M_w/M_n) to lower values. Furthermore, the microstructure-viscosity relationship was followed by the calculation of branching ratio and short-chain branching percentage. The obtained results revealed that, the oligomers synthesized by the Cp₂HfCl₂ catalyst had lower short chain branching ratio value and short-chain branching percentages. According to the kinetic results, the initiation rate constant (k_i) of Zr-based catalyst was higher than that of Hf-based catalyst, and the order of calculated propagation rate constants was Zr>Hf for both the 1-hexene and 1-octene-based oligomerizations.