Acid Strength Controlled Reaction Pathways For The Catalytic Cracking Of C₄⁼/C₅⁼Over ZSM-5

Catalytic cracking of C4=/C5=is one of the most effective methods to produce propene. With the demand of propene growing rapidly, the world may suffer a great shortage of propene. On the other hand, it is urgent to improve the utilization efficiency of C4and C5resources. Therefore, it is of great significant to investigate catalytic cracking of C4=/C5=. In the present, numerous studies focus on investigating how to improve the selectivity of propene. Usually, researchers selected suitable zeolite structures and acid amounts to suppress side reactions. Meanwhile, researchers studied how to control main reaction pathways by zeolite structures to improve propene selectivity. In this paper, we attempted to control the main reaction pathways to improve the P/E ratio and the selectivity of propene by means of designing acid strength distribution on ZSM-5.1. Under the appropriate amount of total acid sites, the reaction pathways of dimerization-cracking of1-butene, which involve the mole ratio of propene to ethene (P/E ratio) and conversion of butenes, could be controlled by acid strength distribution. Strong acid sites could promote the pathway â…  (2C4=â†'C8â… â†'2C4=) and pathway â…¡ (2C4=C8â…¡â†'C2+C6=) favorably, while weak acid sites preferred the pathway â…¢ (2C4=â†'C8â…¢â†'C3=C5=) since pathway â…¢ underwent some energetically favorable forms (tertiary-secondary, secondary-secondary) of craking (C8â… , C8â…¡, C8â…¢, represent octyl carbenium ions). According to designing acid strength distribution on ZSM-5, P/E ratio and selectivity of propene could be significantly improved.2. About catalytic cracking of pentene, the main reaction pathways also could be controlled by acid strength distribution. Strong acid sites could promote the pathway Ⅰ’(C5H10â†'C2H4+C3H6) favorably, while weak acid sites preferred the pathway Ⅱ’-2(C5H10â†'C10H20â†'C4H8+C6Hi2â†'2C3H6). Thus, P/E ratio could be improved by decreasing the amount of weak acid sites. 3. In the reaction systems of the C4catalytic cracking or the C5=catalytic cracking, P/E ratio could be significantly adjusted through designing acid strength distribution on ZSM-5. As pentenes could be produced during C4=catalytic cracking, while butenes could be produced during C5=catalytic cracking, in order to using C4=and C5=efficiently, we designed a technological process which coupled the two systems of butenes and pentenes conversion. The coupled technological process is a promising solution for cracking light olefins to propene with high selectivity.