Dominant reaction pathway for methanol conversion to propene over high silicon H-ZSM-5

The reaction pathway for propene formation in methanol to propene (MTP) process over a high silica H-ZSM-5 catalyst has been investigated in a fixed bed reactor by comparing the experimental results from three kinds of feeding: alkene only, methanol only and mixed alkene and methanol. The results show that alkene methylation with methanol is dominant for the case of methanol and individual C 3–C 6 alkenes co-feeding, C 2 = is almost un-reactive. C 7 = cracks to propene and butene immediately whether co-fed with methanol or not, and C 6 = cracks to propene readily when reacted alone. Oligomerization occurs but is suppressed by the co-fed methanol for light alkenes of C 2–C 5. Methylation-cracking has been verified as the main reaction mechanism of a typical MTP process in which recycling of C 2 = and C 4 =–C 6 = to the reactor inlet is required. Based on the relative reactivities of alkenes towards methylation and inter-conversion, a reaction scheme has been presented including a cycle composed of a consecutive methylation from C 4 = through C 5 = to C 6 = and further to C 7 =, the β-scission of hexene and heptene for propene, and the α-scission of hexene for ethene as well. ► Methylation-cracking is the dominant reaction pathway in a typical MTP process. ► The rank of reactivities of C 2-C 6 alkenes towards methylation is C 5=>C 4=>C 6=>C 3=>C 2=. ► Propene is formed mainly from cracking of C 6=and C 7=via methylation of C 4=∼C 6=. ► Ethene is formed mainly from C 6=cracking.