The oligomerization of butenes with partially alkali exchanged NiNaY zeolite catalysts

A number of catalysts were prepared by exchanging NaY zeolite with various amounts of nickel (NiNaY) as well as partially exchanging NaY zeolite with alkali and alkaline-earth cations (M) followed by nickel promotion (NiMNaY). These catalysts were used to oligomerize butenes in the liquid phase. For the NiMNaY catalysts prepared from similar concentrations of nickel chloride, the nickel loading decreased with increase in the cationic size of M. The acidity of catalysts was measured using temperature programmed desorption of ammonia. The NiNaY catalysts showed an increase in acid concentration with nickel loading. For the NiMNaY catalysts, a linear correlation between the acid concentration and the Sanderson electronegativity of M was found. The oligomerization activity of NiNaY and NiMNaY catalysts increased with nickel loading and acidity. It was observed that the increase in activity also led to an increase in the deactivation rate. This is attributed to the increased adsorption of olefins on the more acidic catalysts leading to the formation of long chain oligomers that foul the catalysts. For the catalysts with similar activities, the dimer selectivity was found to increase with cationic size of M, but decreased with increase in Sanderson's electronegativity of M. This improvement in catalyst stability imparted by M is probably due to the partial blocking of windows for the hexagonal prisms and/or sodalite cages of the nickel exchanged catalysts. The NiCsNaY catalyst was found to be an almost exclusive dimer selective catalyst and has the lowest deactivation rate.