催化裂化生成干气的反应机理研究

STUDY ON THE CATALYTIC MECHANISM OF DRY GAS FORMATION IN CATALYTIC CRACKING REACTIONS

以4-甲基辛烷、4-乙基辛烷为模型化合物,采用分子模拟技术,研究了催化裂化过程生成干气的反应化学。结果表明,烷烃分子首先在催化剂酸性中心作用下发生质子化反应,烷烃分子链上易受到氢质子进攻的位置一般在其叔碳原子或碳链中心碳原子附近的C—H键或C—C键处,形成两种反应过渡态物种——五配位正碳离子H-Carbonium和C-Carbonium。上述反应过渡态主要以桥式结构存在,随后共价键的异裂主要发生在烷烃分子链上桥式活化结构α位的C—H键或C—C键处,前者异裂生成氢气,当后者相连的是小于C3的小分子基团时,异裂就会生成甲烷、乙烷、乙烯等干气分子。

The reaction molecular simulation chemistry of the dry gas formation in FCC process was studied by technique and using 4-methyloctane and 4-ethyloctane as model compounds. The results show that the formation of dry gas is abided by reaction mechanism involving the cleavage of pentacoordinated Carbonium ion which is formed by the protonation of alkanes over acidic catalyst. The protonation occurres at the C-H bond or C-C bond adjacent to tertiary or central carbon atom. Two reaction intermediates having various structures are firstly proposed and defined as C Carbonium ion and H-Carbonium ion,which are formed by the protonation of C-C bond and C-H bond, respectively. These intermediates exist as bridged structure mainly. The heterolytic cleavage of covalent bond takes place via the rupture of C-H bond or C-C bond located at a position, H2 will be formed by the former and dry gas components, such as CH4, C2 He and C2 H4, will be formed by the latter when said C-C bond is linked to an alkyl with a carbon number of less than 3.