Abstract: Under various reaction temperatures and reaction time, the behaviors of isoprene (IP), 1,3-pentadiene (PD) and cyclopentadiene (CPD) during thermal dimerization of steam cracking C5 were studied by seal-tube method. The produced codimers (CPD with IP and CPD with PD) and self-dimers were analyzed to investigate the causes of IP loss during thermal dimerization. Results showed that the co-dimerization between CPD and IP was the main cause of IP loss, besides, the self-dimerization of IP at high temperature range (110-130 ℃) was another cause for the increase of IP conversion under high temperature. Therefore, in the design of process and thermal dimerization reactor, to eliminate the contact of CPD and IP is essential, as well as processing under lower temperature (below 110 ℃) and relatively short resident time.

Key words: C5 fractions, thermal dimerization, isoprene, co-dimers, cyclopentadiene