Effect of temperature in the conversion of methanol to olefins (MTO) using an extruded SAPO-34 catalyst

The methanol-to-olefin (MTO) reaction was investigated in a bench-scale, fixed-bed reactor using an extruded catalyst composed of a commercial SAPO-34 (65 weight percentage, wt-%) embedded in an amorphous SiO2 matrix (35 wt-%). The texture properties, acidity and crystal structure of the pure SAPO-34 and its extruded form (E-SAPO-34) were analyzed and the results indicated that the extrusion step did not affect the properties of the catalyst. Subsequently, E-SAPO-34 was tested in a temperature range between 300 and 500 degrees C, using an aqueous methanol mixture (80 wt-% water content) fed at a weight hour space velocity (WHSV) of 1.21 h(_1). At 300 degrees C, a low conversion was observed combined with the catalyst deactivation, which was ascribed to oligomerization and condensation reactions. The coke analysis showed the presence of diamandoid hydrocarbons, which are known to be inactive molecules in the MTO process. At higher temperatures, a quasi-steady state was reached during a 6 h reaction where the optimal temperature was identified at 450 degrees C, which incidentally led to the lowest coke deposition combined with the highest H/C ratio. Above 450 degrees C, surges of ethylene and methane were associated to a combination of H-transfer and protolytic cracking reactions. Finally, the present work underscored the convenience of the extrusion technique for testing catalysts at simulated scale-up conditions.