Further Studies on How the Nature of Zeolite Cavities That Are Bounded by Small Pores Influences the Conversion of Methanol to Light Olefins

Abstract

A series of small-pore zeolites are synthesized and investigated as catalysts for the methanol-to-olefins (MTO) reaction. Small-pore zeolites SSZ-13, SSZ-16, SSZ-27, SSZ-28, SSZ-52, SSZ-98, SSZ-99, SSZ-104, SSZ-105 and an ITQ-3-type material are synthesized, and the results from their use as catalytic materials in the MTO reaction compared to those obtained from SAPO-34. The production of propane that tends to correlate with catalytic material lifetime (higher initial propane yields lead to shorter lifetimes) declines with increasing Si/Al (as has been observed previously for SSZ-13), and a larger cage dimension leads to higher propane yields at a fixed Si/Al. Data from these materials and others reported previously, for example, SSZ-39 and Rho, that were tested at the same reaction conditions, revealed four different patterns of light olefin selectivities: 1) ethylene greater than propylene with low butene, for example, SSZ-17, SSZ-98, SSZ-105, 2) ethylene equal to propylene and low butene, for example, SAPO-34, SSZ-13, SSZ-16, SSZ-27, SSZ-52, SSZ-99, SSZ-104, 3) propylene greater than ethylene with butene similar to ethylene, for example, SSZ-28, SSZ-39, and 4) ethylene equal to propylene equal to butene, for example, Rho. No clear relationships between zeolite cage architecture and light olefin selectivity emerged from this investigation, although several trends are presented as suggestions for further study.

Recent trends and fundamental insights in the methanol-to-hydrocarbons process

“…77 Similarly, the more spacious cage of ERI delivers higher selectivity to ethylene in comparison to CHA, which might be due to narrower window openings of ERI (3.6 x 5.1 Å) in comparison to CHA (3.8 x 3.8 Å). 80 Medium pore 10-ring zeolites, on the other hand, are composed of straight and/or curved channels (Fig. 5c-f).…”

Chemical and Structural Parameter Connecting Cavity Architecture, Confined Hydrocarbon Pool Species, and MTO Product Selectivity in Small-Pore Cage-Based Zeolites

“…It has also been reported that the contribution of each of the two pathways to the global conversion of methanol, and therefore to the final light olefin product distribution, depends on the topology of the zeolite cage. 3,19,[21][22][23] Very recently, the concept of cage-defining ring size has been introduced to classify small-pore cage-based zeolites into four structural categories that differ in their light olefin product distribution. 24 However, the chemical origin of this behavior has not been clearly explained yet.…”

Synthesis of reaction‐adapted zeolites as methanol-to-olefins catalysts with mimics of reaction intermediates as organic structure‐directing agents

“…It has been described in the literature that when small pore zeolites containing cavities in their structure are used in the MTO reaction, the product selectivity towards different light olefins as well as the catalyst lifetime are influenced by the framework structure. 15,26,27 That observation could be explained by the ability of the cavities present in the zeolite to favor the formation of different polyalkylated aromatics depending on their size/shape. In general, small pore zeolites with very large cavities [i.e.…”

“…26 On the other hand, different small pore zeolite structures containing cavities with intermediate sizes, though prepared with similar crystal sizes and chemical compositions, present different selectivities towards ethylene and propylene. [28][29][30][31][32] For instance, the high-silica SSZ-39 (AEI, cage dimensions: 12.6x11.2 Å, C3 = /C2 = 2.4) and RUB-13 (RTH, cage dimensions: 11.6x10.0 Å, C3 = /C2 = 3.4) zeolites tend to give higher propylene/ethylene ratio compared to high-silica CHA (cage dimensions: 11.7x10.2 Å, C3 = /C2 = 1.0) zeolite (see Supplementary Figure 1), 27,28,30 though the size of the pores and cavities, especially in the case of RTH and CHA, are very close. According to these results, it could be envisioned that even small differences in the zeolite cages may stabilize in a different manner the formation of the HP aromatic intermediates shown in Figure 1, favoring the side chain or the paring mechanism, and changing in that way the selectivity within the olefins obtained.…”