催化裂解中甲烷选择性的影响因素

Influencing Factors of Methane Selectivity in Catalytic Cracking

针对催化裂解反应中甲烷的生成机理及其选择性的影响因素,以C8烷烃为模型化合物,研究了反应温度、辛烷异构体及ZSM-5、MPZ和拟薄水铝石3种催化材料对催化裂解过程甲烷选择性的影响。结果表明:随着反应温度升高,烷烃分子发生质子化裂化过程中能够生成甲烷的路径发生概率提高;原料的分子结构是决定其催化裂解甲烷选择性的本质因素,甲烷选择性随原料分子烷基侧链数目的增加而增大,弱化正碳离子的异构化反应可抑制甲烷过度生成;催化材料的结构特征和酸性是影响甲烷选择性的关键因素,较大的孔径和比表面积在促进内扩散的同时提供了更多的活性位点,能有效提高反应物分子的转化率,但对甲烷选择性影响不显著,而Lewis酸则对甲烷的生成起到重要的催化作用。

Aiming at the generation mechanism and influencing factors of methane in catalytic cracking process,C 8 alkanes were used as model compounds to study the effects of reaction temperature,octane isomers and three kinds of catalytic materials including ZSM-5,MPZ and pseudo-boehmite on methane selectivity in the catalytic cracking process.The results reveal that the occurrence probability of paths for forming methane in the protonation cracking process of alkane molecules grows with the increase of reaction temperature;the molecular structure of raw materials is an essential factor for determining the methane selectivity during catalytic cracking;the methane selectivity increases with the increase of the number of alkyl side chains in raw material molecules;the isomerization reaction,in which the carbonium ions are decreased,can inhibit the excessive methane formation.The structural characteristics and acidity of catalytic materials are key influencing factors of methane selectivity;the larger bore diameter and specific surface area provide more active sites while promoting in-diffusion,which can effectively increase the conversion rate of reactant molecules,and its influence on methane selectivity is not significant,whereas Lewis acid plays an important catalytic role in the formation of methane.