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

Abstract

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.