Effects of acid properties of Y zeolites on the liquid-phase alkylation of benzene with 1-octene: A reaction path analysis

The liquid-phase alkylation of benzene with 1-octene was investigated over three USY zeolites with bulk Si/Al ratios of 6, 13 and 30, at temperatures ranging from 343 K to 373 K, benzene/1-octene feed molar ratios ranging from 1 to 10 and 1-octene conversions between 10% and 99%. 2-, 3- and 4-octene isomers are formed consecutively from double bond isomerization of 1-octene; 2-, 3- and 4-phenyloctanes are obtained as alkylated products. Catalyst deactivation is less important at 1-octene conversions higher than 90%. Reaction path analysis reveals that on the fresh catalyst double bond isomerization and benzene alkylation occur on comparable time scales necessitating the simultaneous consideration of all elementary steps involved in the formation of linear alkylbenzenes. Only 2-octene and 2-phenyloctane are identified as primary products. The higher initial selectivity to 2-octene as compared to 2-phenyloctane is related to differences in entropy of activation associated with deprotonation and alkylation steps. The catalytic activity increases with increasing Si/Al ratio while the selectivities are not affected. The higher rates observed for the catalyst with the higher average acid strength can be traced back to a decrease in the activation energy for the protonation step leading to an increased concentration of carbenium ions on the catalyst surface that compensates for the higher activation energies for the deprotonation and alkylation steps. The constant selectivities are explained by a similar dependency of the different elementary steps on the acid site strength.

The liquid phase alkylation of benzene with 1-octene was investigated over three USY zeolites with bulk Si/Al ratios of 6, 13 and 30, at temperatures ranging from 343 K to 373 K, benzene/1-octene feed molar ratios ranging from 1 to 10 and 1-octene conversions between 10 and 99%. The catalytic activity increases with increasing Si/Al ratio while the selectivities are not affected. The higher rates observed for the catalyst with the higher average acid strength can be traced back to a decrease in the activation energy for the protonation step leading to an increased concentration of carbenium ions on the catalyst surface that compensates for the higher activation energies for the deprotonation and alkylation steps. The constant selectivities are explained by a similar dependency of the different elementary steps on the acid site strength.Figure optionsDownload as PowerPoint slide