Ethylene Oligomerization over Ni–Hβ Heterogeneous Catalysts

We report results for the oligomerization of ethylene in a continuous packed bed reactor loaded with Ni–Hβ. We performed a parametrized study of the effects of temperature (50–190 °C), ethylene partial pressure (8.5–25.6 bar), and weight hourly space velocity (WHSV, 2.0–5.5 h –1 ) on the ethylene conversion and product selectivity. The steady-state ethylene conversion increased from 38 to 57% as the pressure increased from 8.5 to 25.6 bar, due to increased concentration of the reactant ethylene and lower linear velocities at higher pressures. Higher temperatures led to the formation of larger oligomers and coke, but the effect of temperature on the ethylene conversion was small. The WHSV played an important role on ethylene conversion and product selectivity. An increase in the WHSV from 2.0 to 5.5 h –1 resulted in a 13% decrease in conversion. At a low space velocity (2.00 h –1 ), we observed 57% conversion, whereas a high space velocity (5.50 h –1 ) resulted in 44% conversion and higher selectivities to butene (74.9 wt %). The parametric analysis provided the basis for a 78 h on-stream study to examine the deactivation of Ni–Hβ. We conducted this study at 19.0 bar partial pressure of ethylene, 120 °C, and 3.1 h –1 WHSV. Catalyst deactivation took place only during the initial startup period largely due to coke formation. However, negligible coke formation occurred after the initial 8 h, and the conversion remained steady at 47% for the duration of the experiment. Our results indicate that Ni–Hβ is a viable catalyst for ethylene oligomerization.