Propene Production by Butene Cracking. Descriptors for Zeolite Catalysts

Abstract

Among the possible on-purpose technologies for propene production, direct conversion of butene-rich fractions to propene represents an attractive alternative to conventional routes such as steam cracking or fluid catalytic cracking (FCC). Here we present an approach for designing an efficient ZSM-5 based catalyst for the selective cracking of butenes to propene by properly balancing diffusional and compositional effects. Instead of the large coffin-shaped ZSM-5 crystallites with very high Si/Al ratios generally reported, the optimal catalyst in terms of propene selectivity and catalyst life was found to be a ZSM-5 zeolite with squared morphology, sub-micron sized crystals (0.8 x 0.3 x 1.0 μm), and Si/Al molar ratio around 300. For this crystal conformation, the short dimensions of both, sinusoidal and straight channels, facilitate propene diffusion and reduce its consumption in consecutive reactions, limiting the formation of C5+ oligomers and aromatics and maximizing propene selectivity. Coffin-type ZSM-5 crystals, with higher diffusional restrictions than square-shaped crystals, show faster catalyst deactivation than the latter, independently of crystal size and Al content. However, among the ZSM-5 zeolite crystallites with coffin morphology, the one presenting intergrowths on the (010) face, with larger proportion of sinusoidal channels, shows lower aromatics selectivity and deactivation rate, whereas the other two, with straight channels open to the clean (010) faces, favour the formation of aromatics by direct cyclisationdehydrogenation of oligomeric intermediates.

Theoretical investigation of the side-chain mechanism of the MTO process over H-SSZ-13 using DFT and ab initio calculations

“…[37][38][39] Within the olefin cycle of the HCP, olefins convert methanol to olefins autocatalytically, where olefins are repeatedly methylated to higher olefins that are subsequently cracked to lighter olefins. 28,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] In the dual cycle concept (see Scheme 1) aromatic species also play a role in the production of light olefins, and ethene and propene in particular. 6,[8][9][10][11][12][13][14]30 This is highly interesting both from a conceptual but also practical point of view, as the selectivity towards lighter olefins might significantly differ for these two cycles.…”

Diffusion anisotropy descriptor revealing morphology effect of H-ZSM-5 zeolite for olefin catalytic cracking

“…Therefore, differentiating diffusivities in straight and sinusoidal channels for these anisotropic molecules over H-ZSM-5 zeolites are benefit to the understanding of activity, stability or product distribution in catalysis and the guidance of catalyst design with designated morphology. The catalytic cracking of low-value C4+ olefins fractions (OCC), deriving from fluid catalytic cracking (FCC) and methanol to olefins (MTO) processes 7,[20][21][22] , represents a meaningful route to improve the ethylene and propylene production (important to the polymer industry) using H-ZSM-5 catalysts in industrial application [23][24][25][26][27] . Herein, the olefin catalytic cracking process was employed to clarify the descriptor of morphology effect in catalysis process by revealing the diffusion anisotropy in straight and sinusoidal channels of H-ZSM-5 zeolite.…”

“…It was reported that regulating the preferred orientations of the pore systems to crystal planes will cause the variety of the H-ZSM-5 morphologies, thus correspondingly affecting the diffusion resistances 5,6 . Morphology adjustment by reducing the particle size and shape with a controllable a/b or a/c "aspect ratios" is considered as an efficient route to reduce the diffusion path lengths, increase the accessibility of active sites, and finally promote catalytic activities of H-ZSM-5 samples [7][8][9][10][11][12] . In particular, constructing H-ZSM-5 catalysts with intergrowths on well-defined crystal facet opening 7,12 or nanosheet morphology with extremely short thickness along b-axis 8,9,11 , showing remarkably longer lifetime in catalytic reactions.…”

Analysis of n-hexane, 1-hexene, cyclohexane and cyclohexene catalytic cracking over HZSM-5 zeolites: effects of molecular structure

“…Hydrocarbon catalytic cracking is a traditional topic that has been researched for almost a century. Detailed information about hydrocarbon behavior over zeolites is of significant importance to the production of light olefins, [1][2][3][4][5] the petroleum process, [6][7][8] solid waste resources, [9][10][11][12] etc.…”