Effects Of Supercritical Conditions On Coke Formation During Catalytic Cracking Of Toluene And N-dodecane

Endothermic fuel serves as a"heat sink"to remove waste heat from aircraft subsystems in modern aircraft, especially at higher March numbers. Catalytic cracking is a primary approach for the endothermic reaction, however, coke formation during cracking is a primary obstacle. It is a significance to research the coke formation during the catalytic cracking.Effects of pressure and temperature on cracking of toluene over USY catalyst were studied. The coke deposited on the catalyst is mainly composed of polyaromatic hydrocarbons. It reveals that the total amount of coke decreases and the number of the ring of PAHs and yields of PAHs in the liquid increase with increasing cracking pressure. It concludes that the supercritical liquid can extract coke precursors during cracking. However, the total amount of coke, the ring of PAHs and yields of PAHs in the liquid all increase with increasing temperature. It indicates that high temperature is bad for coke inhibition.Effects of pressure and temperature on coke formation were also studied during catalytic cracking of n-dodecane over HY, Hβand HZSM-5, respectively. The yields of aromatic hydrocarbons in the liquid and the amount of coke increase with increasing pressure while those decrease with increasing temperature. Compared with that the catalyst is HY, when the catalyst is Hβ, the cracking ratio of n-dodecane, the yields of aromatic hydrocarbons and the amount of coke deposited on catalyst are higher, but coke on inner surface of the reactor and ceramic ring is lower. However, when the catalyst is HZSM-5, the cracking ratio of n-dodecane and the yields of monocyclic aromatic hydrocarbons are highest while yields of polycyclic aromatic hydrocarbons and the totle amount of coke are lowest. It concludes that HZSM-5 is the perfect catalyst duing cracking of n-dodecane.The coke formation follows the mechanism of carbocation. The olefin of small molecule forming through cracking oligomerizes into naphtene, dehydrogenates into aromatic hydrocarbons, or olefin of big molecule directly cyclizes and dehydrogenates into aromatic hydrocarbons. The aromatic hydrocarbons furtherly cyclize , dehydrogenate and condensate into coke.The main reason for coke formation during cracking is different under supercritical conditions because of the different structure of reagent. Extraction of supercritical liquid and effect of temperature on speed of reaction is important for coke formation during cracking of toluene. However, effect of pressure and temperature on cracking ratio is the most important during cracking of n-dodecane...