High Propylene Selectivity in Methanol Conversion over a Small-Pore SAPO Molecular Sieve with Ultra-Small Cage

Abstract

Conversion of methanol to olefins (MTO) is an important non-oil alternative route for ethylene and propylene production, which has been industrialized based on a fluidized-bed process with a small-pore SAPO-34 (CHA topology) molecular sieve as the active catalyst component. However, it remains a challenge to effectively regulate the selectivity toward single ethylene or propylene due to the limited catalyst selection and insufficient understanding of the selectivity control principle. Herein, we report the synthesis of a small-pore SAPO-14 molecular sieve (AFN topology) with an ultra-small cage structure and a narrow 8-membered ring (8-MR) channel system, over which the propylene selectivity can rise to as high as 77.3%, representing the highest record of one-pass propylene selectivity in the MTO reaction. The influence of reaction conditions on the catalytic performance was investigated, and the olefin formation mechanism was revealed by combining the analyses of 12C/13C-methanol isotopic switch experiments, confined organics analysis, and reaction-diffusion simulations. This work provides a possibility to subtly control the MTO product distribution by the design and synthesis of the molecular sieve catalyst.

Control of zeolite microenvironment for propene synthesis from methanol

“…Current top-performing MTO catalysts include: M–ZSM-5 (M = Mg, Ca, Sr) affording propene selectivities of 38–51%, P/E ratios of 3.3–6.8 and catalyst lifetime of 24–95 h 6 ; high-silica Beta zeolite exhibiting a high propene selectivity of 58%, a P/E ratio of 9.8 and catalyst lifetime of 23 h 11 ; RUB-13 zeolite with precise cage cavity showing propene selectivity of 45%, P/E ratio of 3.0 and lifetime of 11 h at 95% conversion of methanol 8 ; CON-type zeolite giving high propene selectivity of 60% and lifetime of 25 h, but a low P/E ratio of 2.7 21 ; SAPO-14 zeolites with small pores exhibiting high propene selectivity of 66% and P/E ratio of 4.1 at full conversion of methanol, but having a short lifetime of ~0.3 h 9 . Small pore catalysts generally suffer from severe deactivation due to the rapid blockage of pores by coke.…”

Zeolitic Octahedral Metal Oxides with Ultra‐Small Micropores for C2 Hydrocarbon Separation

“…Na‐CM was a high‐performance adsorbent for isolating the ternary C 2 hydrocarbon. To compare the gas separation performance of Na‐CM with other adsorbents, the materials including UTSA‐280 , [7c] SSZ‐13 , [22] Co‐gallate , [17] SAPO‐14 , [23] and MUF‐15 , [7a] were synthesized, and the XRD patterns of the materials demonstrated that the synthese were successful (Figure S21). The breakthrough experiments showed the best performance of Na‐CM compared with other adsorbents (Figure S22).…”

Selective conversion of methanol to propylene over highly dealuminated mordenite: Al location and crystal morphology effects

“…Another possible reason responsible for the excellent performance of dealuminated MOR could be related to the low acid density and strength. According to the hydrocarbon pool mechanism, the low acid density and strength may change the reaction mechanism from aromatic-based cycle to olefin-based cycle [16,[54][55][56][57][58]. This change is also beneficial to longer lifetime, the production of higher alkenes and higher P/E ratio.…”

“…The size of cages and 8-member ring (MR) pores in SAPO catalysts play an essential role in determining the product distribution. Recently, SAPO-14, with AFN topology and consisted of narrower 8-MR pores and ultra-small cages, has been reported to show propylene selectivity as high as 77.3% in spite of fast deactivation [16]. However, numerous reports revealed that the MTP process takes place more readily on zeolites with larger pores, such as 10-or 12-MR pore channels [17][18][19][20][21][22][23][24][25][26].…”