Quantitative conversion of triglycerides to hydrocarbons over hierarchical ZSM-5 catalyst

• The B/L acid distributions of desilicated ZSM-5 were tailored by controlling NH4+ exchange degree.
• Lewis acid sites favored the Diels–Alder cyclization during the formation of Aromatics.
• Aromatics were formed by dehydrogenation–aromatization on Brønsted acid sites.
• Quantitative conversion to paraffins and aromatics were tuned by support modification.

Hierarchical ZSM-5 was prepared by desilication with 0.5 M NaOH and ion-exchanged in NH4NO3 aqueous solution with different NH4+ concentrations. The quantitative selectivity for paraffins and aromatics in the conversion of triglycerides was investigated by tailoring the Lewis and Brønsted sites distribution of these hierarchical catalysts through the ion exchange process. The amount of Brønsted acidity in ZSM-5 increased with the NH4+ exchange degree, meanwhile the textural properties and Lewis acidity changed little. The untreated NiMo/ZSM-5 sample exhibited the small extent of cracking and high selectivity of C16–C18 hydrocarbons (79.47%) because of low Brønsted acidity. The C4–C8 hydrocarbons with few aromatics became the dominant products for the samples treated by low NH4NO3 concentration (less than 0.01 M). As the concentration of NH4+ further increased, the aromatics began to be detected and became the major products due to the high Brønsted acidity density. The mechanism of aromatic formation was presumed. The olefins obtained by cracking and dehydrogenation were converted into cycloalkanes by Diels–Alder cyclization on Lewis acid sites. And then the cycloalkanes were transferred to Brønsted acid sites to form the aromatics by dehydrogenation–aromatization. These results showed that the desirable products could be obtained by modifying the acid distribution of the support.

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