Shape Selectivity of AEL Channels for Anomalously Facilitating Biojet Fuel Production from Long-Chain n-Alkane Hydrocracking

Hydrocracking of long-chain n-alkanes from hydrotreating of vegetable oil is critical for biojet fuel production and requires selective C–C cleavage near the long-chain alkane end. Due to preferential cracking near the carbon chain end in AEL channels, SAPO-11 optionally produces heavy jet fuel fractions in hydrocracking of the model reactant n-C16. Also, the weak acidity of SAPO-11 promotes olefin desorption and markedly reduces the second cracking of jet fuel fractions formed. Compared to 10-MR Si–Al ZSM-22, ZSM-23, ZSM-5, and ZSM-35 zeolites, SAPO-11 significantly improves the jet fuel production performance. Surprisingly,10-membered rings (10-MR) SAPO-11 exhibits higher jet fuel yields than 12-membered rings (12-MR) HUSY (FAU topology), contrary to the general belief that larger pores are more conducive to heavy cracking product production. Further, theoretical molar cracking product distributions of C15–C18 fractions are proposed, highlighting the superior performance of SAPO-11 over that of HUSY and delineating the yield limits for jet fuel production. Higher than those of commercial biojet fuels, the isomer content of jet fuel fractions exceeds 89% at cracking yield above 70%. It indicates that weakly acidic SAPO-11 has potential for specific cracking reactions near the long-chain alkane end, which enriches the understanding of selective C–C cleavage by zeolites for high-value cracking products.