Highly selective synthesis of light olefins from methanol on a novel Fe-silicate

Abstract

Methanol to hydrocarbon conversion on a number of metallosilicates having the pentasil pore-opening structure were investigated to develop a highly selective catalyst for the olefin synthesis from methanol. The metallosilicates were prepared by replacing the Al ingredient with various metal salts at the stage of gel formation in a modified preparation method (the rapid crystallization method) of ZSM-5. The catalysts were active for the methanol to hydrocarbon conversion, and the selectivity to lower olefins, gasoline, or aromatics changed greatly with the kind of metal incorporated. As for the conversion to lower olefins, silicates of Fe, Co, and Pt exhibited the best selectivity. Among them, the Fe-silicate was least active for the formation of aromatics—undesirable products caused by a consecutive reaction of olefins. Further investigations were then made for the preparation, characterization, and methanol to hydrocarbon conversion on Fe-silicates. It was found that various amounts of Fe up to 10 wt% as Fe 2O 3 are incorporated in the crystal having pentasil pore-opening structure by the rapid crystallization method. The incorporated Fe was highly dispersed in the crystal and a considerable part of Fe was suggested to be in its framework. The incorporated Fe produced both strong and weak acid sites, and their amounts were controlled by changing Fe content in the catalyst. It was also suggested that a part of the Fe ingredient plays a role as nuclei of crystal growth of the high-silica crystal. The selectivity to C 2C 4 olefins was greatly increased by the incorporation of Fe in the crystal. The total selectivity to C 2-C 4 olefins was achieved as high as 97.6 C-mol%, and the space-time yield attained 11.9 C-mol/liter · h at 295 °C.