Abstract: The feasibility study of catalytic pyrolysis of mix C4 fraction to maximize propylene yield was carried out on a small-scale riser unit and the effect of recycling C4 fraction blended with various heavy feeds on the dry gas yield was investigated. Results showed that reaction temperature and reaction time had significant influence. Optimum high temperature and short contact time were in favor of cracking C4 fraction to form propylene and suppressing hydrogen transfer reactions, thus the yields of dry gas and coke reduced and propylene yield increased. Using C4 fraction as feed, at a reaction temperature of 600 ℃ and a reaction time of 0.3 s, the yields of propylene and dry gas were 18.25％ and 5.76％, respectively; when using C4 fraction blended heavy oil as feed, at 600 ℃ the yields of propylene and dry gas were in the range of 13.05％~17.41％ and 3.81％~5.28％, respectively.

Key words: C4, catalytic pyrolysis, propylene, recycling