Acid Strength Controlled Reaction Pathways for the Catalytic Cracking of 1-Pentene to Propene over ZSM-5

The influence of acid strength was evaluated toward the selectivity to propene on conversion of 1-pentene. For the catalytic cracking of 1-pentene, the main reaction pathways and the molar ratio of propene to ethene (P/E ratio) were controlled by acid strength with the appropriate amount of total acid sites. The results showed that the P/E ratio increased with decreasing amounts of strong acid sites, since the activation energies of individual reaction pathways were influenced by acid strength to a different extent. Strong acid sites could promote pathway 1' (C-5(2-) -> C-2(2-) + C-3(2-)) and pathway II'-1 (C-6(2-) -> C-2(2-) + C-4(2-)), while weak acid sites preferred pathway II' (2C(5)(2-) -> C-10(+) -> C-4(2-) + C-6(2-)) and pathway II'-2 (C-6(2-) -> 2C(3)(2-)), since pathways II' and II'-2 underwent some energetically favorable routes (tertiary-secondary, secondary-secondary) of carbenium ion intermediates. By manipulation of the acid strength distribution on ZSM-5, the P/E ratio and selectivity of propene could be significantly improved, suggesting that this can provide an important guideline for improving such a process. In addition, we also designed a coupled process combing butene and pentene coconversion, as pentene and butene could be produced during C-4(2-) and C-5(2-) catalytic cracking. The coupled process could offer a promising solution to gain high selectivity of propene from C-4 and C-5 olefin cracking.