Kinetics of steam regeneration of SAPO-34 zeolite catalyst in methanol-to-olefins (MTO) process

Abstract

• With the increase of regeneration temperature, the compositions of residual coke on the catalyst change from pyrene and phenanthrene to naphthalene; • The appearance of nitrogen oxide compounds during steam regeneration makes the regeneration temperature not too high. • We derive the kinetics of steam regeneration and obtain an activation energy of about 177.8 kJ/mol during the steam regeneration process. • Compared with the air combustion process, the steam regeneration process is more difficult to occur. Methanol-to-olefins (MTO) is industrially applied to produce ethylene and propylene using methanol converted from coal, synthetic gas, and biomass. SAPO-34 zeolites, as the most efficient catalyst in MTO process, are subject to the rapid deactivation due to coke deposition. Recent work shows that steam regeneration can provide advantages such as low carbon dioxide emission and enhanced light olefins yield in MTO process, compared to that by air regeneration. A kinetic study on the steam regeneration of spent SAPO-34 catalyst has been carried out in this work. In doing so, we first investigated the effect of temperature on the regeneration performance by monitoring the crystal structure, acidity, residual coke properties and other structural parameters. The results show that with the increase of regeneration temperature, the compositions of residual coke on the catalyst change from pyrene and phenanthrene to naphthalene, which are normally considered as active hydrocarbon pool species in MTO reaction. However, when the regeneration temperature is too high, nitrogen oxides can be found in the residual coke. Meanwhile, as the regeneration temperature increases, the quantity of residual coke reduces and the acidity, BET surface area and pore structure of the regenerated samples can be better recovered, resulting in prolonging catalyst lifetime. We have further derived the kinetics of steam regeneration, and obtained an activation energy of about 177.8 kJ·mol −1 . Compared that with air regeneration, the activation energy of steam regeneration is higher, indicating that the steam regeneration process is more difficult to occur.