Insight into the Co-Cracking of C6 Hydrocarbons (n-Hexane, Cyclohexane and 1-Hexene) Over HZSM-5 Zeolites

C6 hydrocarbon (n-hexane, cyclohexane and 1-hexene) co-cracking over HZSM-5 zeolites at 320-550 degrees C were studied in this work to get an insight into the catalytic cracking process, which played an important role in the petrochemical industry. The total conversion was in an order of 1-hexene > n-hexane/1-hexene > n-hexane > n-hexane/cyclohexane > cyclohexane, and the conversion reduction with the prolonged reaction time was in an order of 1-hexene < n-hexane/1-hexene, n-hexane < n-hexane/cyclohexane < cyclohexane. It was deduced that the presence of 1-hexene promoted the total conversion and alleviated the conversion reduction in the co-cracking, while the presence of cyclohexane reduced the total conversion and accelerated the conversion reduction with the prolonged reaction time. In addition, increasing reaction temperature and 1-hexene content promoted ethene and propene selectivity in the co-cracking. The conversion and product distribution in the co-cracking can be attributed to the unique interaction of C6 molecular structure. The six-member ring of cyclohexane hindered the diffusion process, and thus inhibited n-hexane decomposition in the co-cracking. The C = C bond of 1-hexene was easy to interact with and occupied the acid site and carbenium ions, which inhibited n-hexane decomposition while promoted the durability of n-hexane decomposition against high coke content.