Abstract
Solid acid catalyzed cracking of waste oil-derived fatty acids is an attractive route to hydrocarbon fuels. HZSM-5 is an effective acid catalyst for fatty acid cracking; however, its microporous nature is susceptible to rapid deactivation by coking. We report the synthesis and application of hierarchical HZSM-5 (h-HZSM-5) in which silanization of pre-crystallized zeolite seeds is employed to introduce mesoporosity during the aggregation of growing crystallites. The resulting h-HZSM-5 comprises a disordered array of fused 10–20 nm crystallites and mesopores with a mean diameter of 13 nm, which maintain the high surface area and acidity of a conventional HZSM-5. Mesopores increase the yield of diesel range hydrocarbons obtained from oleic acid deoxygenation from ~20% to 65%, attributed to improved acid site accessibility within the hierarchical network.
Highlights
The synthesis of renewable fuels from triglycerides and fatty acids, derived from non-food plant oils, low grade waste cooking oils [1], or algal oils [2], is an attractive means to replace fossil energy resources [3,4,5,6]
Shape selective zeolite catalysts have been widely used for catalytic cracking, with HZSM-5 the most efficient for fatty acid conversion to paraffins, olefins, and aromatic compounds in the range of gasoline and kerosene fractions [7]
Assembly of zeolite nanocrystals into hierarchically porous aggregates is reported for Mordenite Framework Inverted (MFI) [16,17,18], Beta polymorph A (BEA) [17,19], and Mordenite (MOR) [20] via surface passivation by silanizing agents which hinder aggregation of zeolitic seeds during their hydrothermal aging and serve as soft mesopore templates
Summary
The synthesis of renewable fuels from triglycerides and fatty acids, derived from non-food plant oils, low grade waste cooking oils [1], or algal oils [2], is an attractive means to replace fossil energy resources [3,4,5,6]. Top-down or bottom-up methods to introduce pore hierarchy involve the introduction of mesopores by respective post dealumination/desilication of pre-formed zeolites or incorporation of structure directing agents during zeolite nanocrystal assembly [15] Regarding the latter, assembly of zeolite nanocrystals into hierarchically porous aggregates is reported for Mordenite Framework Inverted (MFI) [16,17,18], Beta polymorph A (BEA) [17,19], and Mordenite (MOR) [20] via surface passivation by silanizing agents which hinder aggregation of zeolitic seeds during their hydrothermal aging and serve as soft mesopore templates. Hierarchical nanozeolite assemblies of 200–400 nm diameter are formed
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