Monolithic HZSM-5/SS-fiber catalysts with high coke-resistance and selectivity for catalytic cracking of castor oil to produce biofuel

Monolithic HZSM-5/SS-fiber catalysts with hierarchical porous structure from micro-to macro-size for catalytic cracking of castor oil to produce biofuel were fabricated by seed coating and subsequent hydrothermal synthesis of ZSM-5 zeolite crystals onto the thin-sheet stainless steel fiber (SS-fiber). Compared with the powdered HZSM-5, the HZSM-5/SS-fiber catalyst exhibited high hydrocarbon selectivity (78% in gasoline and 57% in diesel) with enhanced physical properties of liquid products, as well as excellent coke-resistance with coking rate of 0.47 mg gzeolite−1 h−1 (one-eighth of the powdered HZSM-5), indicating a significant intensification on cracking process due to a unique combination of high heat/mass transfer and hierarchical pore structure. SiO2/Al2O3 ratio exerts a pivotal influence on HZSM-5 loading and acid strength/amount of the HZSM-5/SS-fiber, which thereby strongly relates to the degree of cracking, aromatization, and deoxygenation. The HZSM-5/SS-fiber (200) with moderate acid amount and strength permitted mild secondary cracking and sufficient deoxygenation reactions, resulting in a low coke yield, a high liquid product yield and a high hydrocarbon/aromatic selectivity along with reduced acid values (7.4 mg KOH g−1 in gasoline and 83.2 mg KOH g−1 in diesel). The physical properties including kinematic viscosity, density, oxygen content and heating value, were optimal at SiO2/Al2O3 ratio of 200.