Selective production of olefins from bioethanol on HZSM-5 zeolite catalysts treated with NaOH

The behaviour of a HZSM-5 zeolite (SiO2/Al2O3 = 30) in several time treatments with 0.2 M NaOH solution has been studied for the transformation of bioethanol into hydrocarbons in an isothermal fixed bed reactor and in the 225–425 °C range. A short treatment (for 10 min) decreases the acid strength of the sites from 135 kJ (mol of NH3)−1 to 125 kJ (mol of NH3)−1, which is effective for increasing the selectivity of propene and butenes and for attenuating the deactivation by coke. This catalyst allows obtaining a yield of 30 wt% of propene + butanes at 400 °C with 136 (g of catalyst) h (g ethanol)−1 and a feed of ethanol/water with 5 wt% water. The operation in reaction–regeneration cycles can be carried out continuously without irreversible deactivation of the catalyst, which means not exceeding extreme conditions in the reaction step: 375 °C and 400 °C for water contents in the feed of 75 wt% and 5 wt%, respectively. More severe treatments decrease the hydrothermal stability of the zeolite.