Deactivation by coke of a catalyst based on a SAPO-34 in the transformation of methanol into olefins

Abstract

When methanol is converted to olefins on a SAPO‐34 catalyst between 350 and 425°C, there is a rapid initial formation of coke, followed by a slower rate of coke deposition. The rate of coke formation decreases with increasing temperature, and with progression through the catalyst bed. The coke completely blocks the internal channels of the SAPO‐34 crystals and subsequently blocks the mesopores (intercrystalline and those of the bentonite). Coke deposition mainly blocks sites of acidic strength above 175 kJ mol−1. The presence of water in the feed lessens coke formation, either by converting Lewis to Brønsted sites or by competing for surface sites with coke precursors. © 1999 Society of Chemical Industry

Steam-dealuminated, OSDA-free RHO and KFI-type zeolites as catalysts for the methanol-to-olefins reaction

“…For small-pore zeolites such as CHA, it has been established that deactivation occurs via the formation of polycyclic aromatic compounds inside the cavities that hinders diffusion through the crystal and leads to blockage of the pore structure [5,29,30]. In the steamed zeolites studied here, coke may also adsorb onto the acid sites located in the mesopores, contributing to pore blockage.…”

A methanol to olefins review: Diffusion, coke formation and deactivation on SAPO type catalysts

“…SAPO-34 has a high catalytic activity for the MTO reaction, but suffers fast deactivation due to coke formation [24,25,34,35,48,49,[52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67]. The rate of deactivation is so high that it is difficult to decouple it from the kinetics of the main reactions.…”

“…Coke deposition is often studied as a function of time on stream [52,68]. Marchi and Froment [61] studied deactivation during MTO over SAPO-34 as a function of the cumulative amount of methanol fed to the catalyst.…”

“…Higher temperatures favoured the reactions leading to coke formation more than the reactions leading to olefins, hence a faster deactivation, in good agreement with the observation on H-ZSM-5 [70]. However, the coking rate was found to decrease with increasing temperature in the low temperature range of 613 to 693 K on SAPO-34 [52], which was explained by increased cracking of coke precursors.…”

Effect of nickel incorporation on the acidity and stability of HZSM-5 zeolite in the MTO process

“…Due to this circumstance, the catalyst used in the commercial MTO process is SAPO-34 [10], which shows higher selectivity to light olefins than the several modifications carried out in the HZSM-5 (due to its high shape selectivity, with micropores of 3.8 Å , compared to those of around 5.5 Å in the HZSM-5) and it also shows higher hydrothermal stability. SAPO-34 undergoes very rapid deactivation by coke deposition [11][12][13], although activity is completely recovered subsequent to combustion of coke with air [14,15]. Consequently, the MTO process is based on two units (reactor and regenerator), which are interconnected fluidised beds with catalyst circulation from one to the other.…”