Catalytic Cracking of Fatty Acid Methyl Esters for the Production of Green Aromatics Using Zn-Modified HZSM-5 Catalysts

Catalytic cracking of fatty acid methyl esters (biodiesel) is an attractive alternative to petroleum processing to produce valuable and versatile aromatics over the Zn-modified HZSM-5(25) catalysts. The catalysts with a Zn loading amount of 0–2.6 wt % were prepared and characterized. The introduction of Zn species presented great effects on the textural property and acidity of the parent HZSM-5(25) zeolite, and the chemical state of Zn species was heavily dependent on the amount of Zn loading. The strong Brönsted acid sites on the 0.5% Zn/HZSM-5(25) catalyst were exchanged by Zn species and formed new Zn-Lewis acid sites, which were identified as [ZnOH]+ and Zn2+ species. These Zn species greatly enhanced the dehydrogenation activation of alkanes to form more alkenes. Besides, they also promoted the further dehydrogenation reactions during aromatization of alkenes, thus improving the formation of H2 (>4 wt %) and increasing the production of aromatics (>40 wt %). The dominant components in the organic liquid product were monocyclic aromatics including benzene, toluene, and xylenes. Moreover, the 0.5% Zn/HZSM-5(25) catalyst exhibited an excellent stability, adaptability, and regeneration.