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

The skeletal isomerization of 1-butene on ferrierite at 350 degrees C and 4 00 degrees C, atmospheric pressure and 0.14 atm 1-butene partial pressure i s studied. The rapid decrease in activity with an increase in the isobutene selectivity is related to coke deposition. The carbon content is similar f or 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 degrees C while the one at high temperatures is larger for rea ction at 400 degrees 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-refle ctance infrared spectroscopy measurements indicate that coke presents olefi nic and aromatic character for all samples, being more olefinic after react ion at 350 degrees C and more aromatic after reaction at 400 degrees C. The presence of water during the treatment before the reaction changes the pro portion of olefinic and aromatic coke formed. Regeneration under a nitrogen plus air stream at 660 degrees C for 15 h allows almost complete eliminati on of the coke and full restoration of the catalytic activity to that of th e fresh sample. However, the presence of a residual carbonaceous deposit (i .e. 0.9 wt.%) when starting the reaction, improves catalytic activity, isob utene yield and catalyst stability after some minutes on stream, as compare d 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 re moval. (C) 1999 Elsevier Science B.V. All rights reserved.