BIOETHANOL CONVERSION INTO HIGH-OCTANE COMPONENTS OF MOTOR FUEL IN THE PRESENCE OF COBALT-CONTAINING HZSM-5 TYPE ZEOLITES

The influence of the concentration of cobalt introduced into HZSM-5 on its acidic and catalytic properties in the transformation of ethanol into high-octane components of motor fuels has been studied in the plug-flow unit within the temperature range of 300-450 °С. The unmodified НZSM-5 zeolite is shown to be highly selective to aromatization products (27.5-47.6 %) and С1-С3 alkanes (25.8-37.1 %). A significant increase in selectivity to isomerisation products (from 17.2-19.8 to 34.0-42.7 %) is established for cobalt-modified (1.0-3.0 wt. %) zeolite catalysts within the temperature range 300-350 °C. The highest increase in the selectivity of modified catalysts to aromatisation products (32.7-40.7 %) is observed within the temperature interval of 400-450 °С. The effect of modification on the acid properties of HZSM-5 zeolite has been studied using the temperature-programmed desorption of ammonia. It is shown that the changes of the catalytic properties of HZSM-5 zeolite are connected with a considerable decrease in the concentration of strong Brønsted acid centres (from 538 to 317 μmol/g), with the formation of new stronger Lewis acid centres (37-80 μmol/g) including cobalt ions and acid-base Coδ+-Oδ- type pairs capable of strong polarization and activation of C-H bonds in the intermediates. Selectivity to the products of isomerisation and aromatization on the modified catalysts is regulated by cobalt concentration and process temperature. The highest selectivity to isomerisation products (42.7 %) is achieved over the 2 % Co/HZSM-5 catalyst at a temperature of 300 °C. The catalysate obtained over the 2 % Co/HZSM-5 catalyst at 300 °С corresponds to Euro-5 standard in the content of isoparaffin (56.4 %) and aromatic (29.8 %) hydrocarbons, benzene (0.6 %) and olefins (1.1 %).