Directed transforming of coke to active intermediates in methanol-to-olefins catalyst to boost light olefins selectivity

Abstract

Methanol-to-olefins (MTO), the most important catalytic process producing ethylene and propylene from non-oil feedstocks (coal, natural gas, biomass, CO2, etc.), is hindered by rapid catalyst deactivation due to coke deposition. Common practice to recover catalyst activity, i.e. removing coke via air combustion or steam gasification, unavoidably eliminates the active hydrocarbon pool species (HCPs) favoring light olefins formation. Density functional theory calculations and structured illumination microscopy reveal that naphthalenic cations, active HCPs enhancing ethylene production, are highly stable within SAPO-34 zeolites at high temperature. Here, we demonstrate a strategy of directly transforming coke to naphthalenic species in SAPO-34 zeolites via steam cracking. Fluidized bed reactor-regenerator pilot experiments show that an unexpectedly high light olefins selectivity of 85% is achieved in MTO reaction with 88% valuable CO and H2 and negligible CO2 as byproducts from regeneration under industrial-alike continuous operations. This strategy significantly boosts the economics and sustainability of MTO process.

Stabilizing the framework of SAPO-34 zeolite toward long-term methanol-to-olefins conversion

“…To further investigate the spatiotemporal evolution of organic compounds formed during the MTO conversion, the high-resolution structured illumination microscopy (SIM) was also employed. Following the previous research results 17 , 47 – 51 , the characteristic UV-vis signals of benzene- (B + ) and naphthalene-based (N + ) carbenium ions should appear at about 390 and 480 nm, respectively, and those of phenanthrene- (PH + ) and pyrene-based (PYR + ) carbenium ions appear at ~560 and ~640 nm, respectively. Thereupon, distinguishable emission wavelengths in the range of 480–490, 500–520, 620–630, and 670–700 nm are expected for the aforementioned carbenium ions, respectively.…”

Methanol-to-olefins catalysis on ERI-type molecular sieves: towards enhancing ethylene selectivity

“…It has been shown previously, too, both experimentally and theoretically, that 4MB undergoes dealkylation via the side-chain route of the aromatic cycle to yield ethylene whereas 5MB and 6MB undergo dealkylation via the pairing route of the aromatic cycle to give propylene [3,40,44,85]. The presence of naphthalenes has also been associated with improved ethylene formation [86]. However, none of these conditions (concentration of naphthalenes or 4MB/(5MB+6MB)) alone explained the differences observed in product distributions.…”

Transforming inactive coke molecules into active intermediates in zeolites

“…This process can be performed in different ways, e.g., air combustion (e.g., oxidation with air) and steam gasification (e.g., with H 2 O). 7 In their recently published paper, Zhou and co-workers 8 show that regeneration processes can be used to enhance the catalytic selectivity toward ethylene by transforming coke molecules into active naphthalenic cations. With density functional theory (DFT) calculations, it was shown that these naphthalenic cations are stable in the CHA cages at high temperatures because of spatial confinement.…”

“…Further research on the evident differences between the two regeneration methods could Figure 1. Schematic representation of the developed catalyst regeneration approach to transform coke-like molecules into active HCP intermediates in a SAPO-34 molecular sieve This method, as described by Zhou et al 8 in Nature Communications, is visualized by the blue figures. Proposed catalyst regeneration approaches for further studies could aim for the transformation of coke deposits into aromatic intermediates by using gentler conditions (air combustion) or CO 2 to limit environmental contributions.…”