Abstract
A series of SAPO-34/SAPO-18 intergrowth materials were prepared with a range of silicon content from 0.5 to 7.0%, where low levels of silicon resulted in SAPO-18 and higher levels resulted in CHA/AEI intergrowths. These materials were tested for their performance in the Methanol-to-Olefins reaction. The acidity of the catalysts was related to their silicon content, where a higher level of silicon gave a greater acid site density. The catalytic activity increased with increasing acid site density. There was consequently a higher level of heavy hydrocarbons in the catalysts at the end of the reaction in the materials with higher silicon content. The selectivity as a function of overall time on stream was similar for all catalysts, but at a given level of conversion, the C2/C3 ratio was lower for the materials with higher AEI content. Catalysts with a higher ratio of AEI cages had a higher selectivity to C3 and C4 products than the other catalysts, due to the larger size of the internal AEI cage. The C2/C3 ratio showed a strong correlation to the cage shape, making catalysts with high AEI content suitable where higher propylene ratios are desired.
