Kinetic Model for the Transformation of Bioethanol into Olefins over a HZSM-5 Zeolite Treated with Alkali

A kinetic model for the transformation of bioethanol (aqueous ethanol into hydrocarbons) has been established for a catalyst with slow deactivation by coke (prepared from a HZSM-5 zeolite treated with alkali in order to moderate its acid strength and generate mesopores in the zeolite structure). The kinetic model allows quantifying the distribution of the lumps of products (ethylene, C 3 −C 4 olefins, gasoline or C 5 −C 10, and C 1 −C 3 paraffins) and is particularly interesting for quantifying the production of C 3 −C 4 olefin lump, which is the one of greater commercial interest. The experimental data have been obtained in an isothermal fixed-bed reactor in a wide range of operating conditions (temperature of 300−400 °C, space time and water content in the feed). The remarkable features of the kinetic model are (i) consideration of the autocatalytic formation of C 3 −C 4 olefin lump following their reaction with ethylene, (ii) consideration of the combined involvement of ethylene and the light olefin lump in the formation of heavier hydrocarbons; and (i) quantification of the effect of water in the reaction medium, which attenuates the rate of each one of the steps in the kinetic scheme, except the dehydration of ethanol which is instantaneous under these conditions.