Abstract: Several mechanisms about coke formation from hydrocarbon molecules' cracking are reviewed, and polycyclic aromatic hydrocarbons are reaction intermediates of coke formation during petroleum processing.Three mechanisms contribute to the coke formation:heterogeneous catalytic mechanism, heterogeneous noncatalytic mechanism and homogeneous noncatalytic mechanism. Researches on molecular model compounds show that during alkanes catalytic cracking process at higher temperature, coke composition is not related to the molecular structure, but the cracking depth;during thermal cracking process, coke formation rate of iso-paraffin is faster than normal paraffin, and olefins, aromatics lead to coke formation easily, the basicity of aromatics related to the coke yield.Depending on the optical microstructure, coke can be divided into three categories, point structure, mosaic structure and fibrous structure.Researches show that the intermediate phase morphology would affect coke structure;carbonaceous mesophase of good plasticity can easily aggregate to form anisotropy fibrous coke.In technical process, many factors will influence the coke formation, such as the nature of feedstock, the type of catalyst and addictives, operating conditions, and so on.

Key words: coking, multiphase reaction, microstructure, second liquid phase

摘要： 回顾了多种烃类分子裂解生焦的机理,指出多环芳烃是石油加工过程中焦炭形成的反应中间体。从分子化学反应水平上综述了3种生焦机理:多相催化结焦、多相非催化结焦、均相非催化结焦,研究表明:较高温度下烷烃催化裂解过程中,焦炭的组成与裂解反应深度有关,但不受烷烃分子结构的影响;热裂解过程中,异构烷烃的生焦速率大于正构烷烃,烯烃、芳烃具有较大的生焦趋势,且芳烃裂化的生焦量与物质的碱性对数线性相关。依据显微结构的不同,焦炭可以分为3类:点状焦炭、镶嵌状焦炭和纤维状焦炭,相关研究表明:焦的结构特性与中间相形态有关,可塑性好的碳质中间相易聚合、溶并形成各向异性的纤维状焦炭。工艺过程中,原料的性质、催化剂及添加剂种类、工艺操作条件等因素都会影响焦炭的生成。

关键词: 焦化, 多相反应, 显微结构, 第二液相