Cyclopentadiene Dimerization Kinetics in the Presence of C₅ Alkenes and Alkadienes

This work describes an experimental kinetic study and the development of a kinetic model for the dimerization of cyclopentadiene (CPD) to dicyclopentadiene (DCPD) in multicomponent reaction mixtures at temperatures ranging from 80 to 160 °C. The reaction mixtures consist of CPD and other reactive C₅ compounds, including isoprene, trans-1,3-pentadiene, 1-pentene, cis-2-pentene, and trans-2-pentene, which are normally present in the CPD stream derived from steam cracking of naphtha. Reaction rate constants for (a) dimerization of CPD to form exo- and endo-DCPD, (b) the codimerization of CPD with the other reactive components, and the homodimerization of each of the reactive components are presented along with the corresponding activation energies and pre-exponential factors. By including the retro Diels–Alder reaction of endo-DCPD and the formation of CPD trimers, our kinetic model accurately predicts concentrations of CPD, endo-DCPD, exo-DCPD, and codimers with respect to time. The model identifies CPD self-dimerization as the dominant reaction occurring in the multicomponent mixture, followed by the codimerization between cyclopentadiene and isoprene. At 120 °C, codimerization reactivity with CPD was found in the following order: 1-pentene > cis-2-pentene > 2-methyl-1-butene > cyclopentene > 2-methyl-2-butene > trans-2-pentene, with reaction rate constants 1 to 2 orders of magnitude lower than that of exo-DCPD formation. Overall, the model established herein allows an accurate prediction of the DCPD purity that can be obtained from a petroleum pyrolysis stream no matter what the impurity concentrations may be.