Synthesis of SAPO-34 by utilizing spent industrial MTO catalyst and their catalytic applications

Abstract

The methanol-to-olefins (MTO) process has realized its large-scale industrialization over the past decade. The corresponding consumption of MTO catalyst is currently more than 10,000 tons per year. To convert the spent industrial MTO catalyst into valuable materials would be significant for environment protection and for the development of MTO industry. Here, the spent industrial MTO catalyst was utilized as raw material to explore the synthesis of SAPO-34 and their catalytic applications. Two amines with different sizes including diethylamine (DEA) and tetraethylammonium hydroxide (TEAOH) were employed as the synthesis templates. It was found that the Si/Al/P sources in spent MTO catalyst have high reactivity and SAPO-34 with varied Si contents can be synthesized in high crystallinity. Low-silica SAPO-34 exhibits good catalytic performance in the MTO reaction. More importantly, compared with SAPO-34-TEAOH, SAPO-34-DEA shows excellent catalytic performance in the methanol ammoniation reaction with high selectivity to methylamine (MMA) and dimethylamine (DMA) due to its higher acid concentration and larger crystal size. After hydrothermal treatment of SAPO-34-DEA at 800 °C, although the methanol conversion shows a decrease (∼25% drop), the MMA plus DMA selectivity in three methylamines increases to as high as 94%.