Producing gasoline-like hydrocarbons by cracking crude soybean oil: tuning the NaZSM-5 zeolite's acidity for increasing the catalyst lifetime

This work investigates the effect of NaZSM-5 zeolite's acid properties on the catalytic cracking of crude soybean to produce gasoline-like hydrocarbons. We modified both the acid concentration and the acid strength of the NaZSM-5(60) zeolite (where 60 denotes the SiO₂/Al₂O₃ molar ratio) either by varying the SiO₂/Al₂O₃ ratio (i.e., 30, and 90) or by exchanging the compensation cation (i.e., from Na⁺ to H⁺). Given the ammonia temperature-programmed desorption and temperature-programmed oxidation tests, we observed that the acid strength of the catalyst is associated not only with the distribution of the cracking products, but also with the nature of the carbonaceous deposits formed during the reaction. Weak, medium, and strong acidity were associated with the formation of heavy hydrocarbon species, soft, and hard coke, respectively. The NaZSM-5 zeolites exhibited weak and medium acidity, while the HZSM-5(60) zeolite exhibited weak and strong acidity. Although both NaZSM-5(30) and HZSM-5(60) zeolites delivered higher gasoline yield than the NaZSM-5(60) zeolite due to its higher acid concentration, the HZSM-5(60) zeolite formed carbonaceous deposits with lower reactivity (i.e., hard coke). Therefore, low values of SiO₂/Al₂O₃ ratio in the NaZSM-5 zeolite drive the reaction products towards gasoline-like hydrocarbons and favor the catalyst reactivation through the formation of more reactive carbonaceous deposits. (author)