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

Jibin Zhou,Wenjuan Liu,Mao Ye,Mingbin Gao,Jinling Zhang,Zhongmin Liu,Zhaochao Xu,Hua Li,Tao Zhang

doi:10.1038/s41467-020-20193-1

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.

Highlights

Methanol-to-olefins (MTO), the most important catalytic process producing ethylene and propylene from non-oil feedstocks, is hindered by rapid catalyst deactivation due to coke deposition
In catalytic processes accompanying with catalyst deactivation by coke deposition, e.g., MTO and fluid catalytic cracking (FCC), air combustion or steam gasification[21,22] has been used as common practices to eliminate coke for catalytic activity recovering
We sweep coked SAPO-34 catalyst with nitrogen under high temperature and obtain naphthalenic species-rich SAPO-34 zeolite (Fig. 1a), which exhibits high light olefins selectivity but poor methanol conversion

Summary

Introduction

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. 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. Laboratory experimental results demonstrate that directionally transforming coke confined in SAPO-34 zeolites to naphthalenic species by steam cracking, restores the catalytic activity and promotes light olefins selectivity in MTO reaction. Steam cracking of coke releases only a small amount of byproducts in the form of flue gas, which is dominantly composed of valuable syngas (H2 and CO) with negligible greenhouse gas CO2 (Fig. 1b) By verifying it in a fluidized bed reactor-regenerator pilot plant, we show this strategy can significantly boost the economics and sustainability of industrial MTO process

Methods

Results

Conclusion