Abstract
Oligomerization of ethylene and propylene on a nickel oxide-silica-alumina catalyst (NiO-SA) was studied in the presence of benzene homologues.
In a series of experiments, benzene homologues were used as solvent. The reaction conditions were as follows: catalyst: Ni content of NiO-SA 7.5wt%, amount used for a run 3.0g, feed: ethylene or propylene 1.0 mole; solvent volume: 30ml, reaction temp. for ethylene 30°C, for propylene 80∼120°C, reaction time: for ethylene 30min, for propylene 2∼3hr, stirring: 70k.p.m..
In the presence of benzene homologue solvent, the activity of both olefins decreased rapidly in the following order:
Cl-B>B>T>p-X>o-X>m-X.
On the other hand, the dimer selectivity increased with the decrease of olefin reactivity.
In another series of experiments, small amount of xylenes (0.5∼5.0g) was added to a mixture of the catalyst and solvent iso-octane in order to observe the poisoning effect of xylenes. In these cases, high dimer selectivity was maintained without losing high olefin activity. For example, when 0.5g of p-X was added to 3.0g of NiO-SA and 30ml of iso-octane, 75wt% of propylene conversion and 83wt% of dimer yield (based on oligomer) were obtained.
Olefin oligomerization on NiO-SA was also observed to be poisoned by a small amount of ethanol. In this case, however, it was impossible to obtain a high yield of oligomers of high dimer selectivity.
It is suggested that the different poisoning behaviors of ethanol and xylenes are due to the difference in their electron donor strength. According to the experimental results shown in this paper, the weak acid sites produced by the addition of NiO to SA are considered to selectively promote the dimerization of olefins. These weak acid sites may not be so strongly poisoned by weak electron donors as xylenes. But they may be fatally poisoned by strong electron donors such as ethanol.
