Skeletal isomerization of 1-butene on ferrierite: deactivation and regeneration conditions

Abstract

The skeletal isomerization of 1-butene on ferrierite at 350°C and 400°C, atmospheric pressure and 0.14 atm 1-butene partial pressure is studied. The rapid decrease in activity with an increase in the isobutene selectivity is related to coke deposition. The carbon content is similar for both reaction temperatures. Temperature-programmed oxidation profiles of the used catalysts show two peaks for coke combustion, one each at low and high temperatures. The low-temperature peak is higher when reaction takes place at 350°C while the one at high temperatures is larger for reaction at 400°C. The carbonaceous deposits corresponding to the low-temperature combustion peak can be eliminated after stripping with a helium stream, suggesting that these deposits are rich in hydrogen. Diffuse-reflectance infrared spectroscopy measurements indicate that coke presents olefinic and aromatic character for all samples, being more olefinic after reaction at 350°C and more aromatic after reaction at 400°C. The presence of water during the treatment before the reaction changes the proportion of olefinic and aromatic coke formed. Regeneration under a nitrogen plus air stream at 660°C for 15 h allows almost complete elimination of the coke and full restoration of the catalytic activity to that of the fresh sample. However, the presence of a residual carbonaceous deposit (i.e. 0.9 wt.%) when starting the reaction, improves catalytic activity, isobutene yield and catalyst stability after some minutes on stream, as compared to the fresh sample. Therefore, we propose that the optimum regeneration procedure for ferrierite catalyst for n-butene isomerization consists of an oxidative treatment at high temperatures, but without the complete coke removal.