Ethene oligomerization on Ni-SiO2-Al2O3: Experimental investigation and Single-Event MicroKinetic modeling

An experimental investigation of the intrinsic ethene oligomerization kinetics on an amorphous 1.8 wt.% Ni-SiO2-Al2O3 was performed. The temperature ranged from 443 to 503 K, the total pressure from 1.5 to 3.5 MPa, the inlet ethene partial pressure from 0.15 to 0.35 MPa and the space time was between 4.8 and 14.4 kg(cat) s mol(C2)(-1). Due to the absence of strong acid sites, the catalytic activity toward oligomerization originated solely from the nickel ion sites at the investigated conditions and resulted in an Anderson Schulz Flory product distribution. The oligomerization rate amounted from 0.007 to 0.027 mol s(-1) kg(cat)(-1) with butene selectivities of 80-90%. A Single-Event MicroKinetic (SEMK) model for ethene oligomerization, based upon an insertion-termination mechanism, was constructed. The kinetic parameter estimates were all statistically significant with a precise physical meaning. The model was found to be globally significant and adequate, that is, it was able to describe all experimental data without any systematic deviation. Using the model, it was determined that mainly ethene, because of its abundance, and octene, because of its higher carbon number, were physisorbed. The corresponding catalyst occupancy by physisorbed species typically ranged between 10% and 50%. Coordination of the alkenes at the active nickel ions resulted in about 90% of these ions being present under the form of a nickel-ethene species. (C) 2014 Elsevier B.V. All rights reserved.